WorldWideScience

Sample records for asian monsoon climate

  1. Thrusts and Prospects on Understanding and Predicting Asian Monsoon Climate

    Institute of Scientific and Technical Information of China (English)

    WANG Bin

    2008-01-01

    Development of monsoon climate prediction through integrated research efforts to improve our understanding of monsoon variability and predictability is a primary goal of the Asian Monsoon Years (2007-2011) and International Monsoon Study under the leadership of the World Climate Research Programme.The present paper reviews recent progress in Asian monsoon research focusing on (1) understanding and modeling of the monsoon variability, (2) determining the sources and limits of predictability, and (3) assessing the current status of climate prediction, with emphasis on the weekly to interannual time scales. Particular attention is paid to identify scientific issues and thrust areas, as well as potential directions to move forward in an attempt to stimulate future research to advance our understanding of monsoon climate dynamics and improve our capability to forecast Asian monsoon climate variation.

  2. EVIDENCE FOR ABRUPT CLIMATIC CHANGES ON NORTHWESTERN MARGIN OF EAST ASIAN MONSOON REGION DURING LAST DEGLACIATION

    Institute of Scientific and Technical Information of China (English)

    QIANG Ming-rui; LI Sen; GAO Shang-yu

    2004-01-01

    Based on investigations of the Zhongwei Nanshan aeolian section situated in the southeastern margin of Tcngger Desert, carbon-14 and TL (thermoluminescence) dating results and paleoclimatic proxies such as magnetic susceptibility and grain size, we inferred that the northwestern margin of East Asian monsoon region experienced abrupt climatic changes during the last deglaciation. Six oscillation events were identified: Oldest Dryas, B¢lling, Older Dryas, Aller¢d, Intra-Aller¢d Cold Period (IACP) and Younger Dryas (YD). The summer monsoon was weaker during Oldest Dryas and Younger Dryas when the winter monsoon was stronger. However, during the B/A (B¢lling/Aller¢d)period, the summer monsoon strengthened, reflected by magnetic susceptibility, when the winter monsoon also became strong, which is different from the paleoclimatic pattern established in the East Asian monsoon region. Furthermore,the summer monsoon was nearly in phase with the climate changes inferred from the oxygen isotopic records of Greenland ice cores. It could be speculated that the variations of the sea ice cover in the high latitudes of the North Hemisphere affected the high pressure of Asian continent and the changes of the winter monsoon inland. On the other hand,the sea ice cover variations might have indirectly caused the occurrence of ENSO events that has tightly been related to the summer monsoon in northwest margin of East Asian monsoon region.

  3. History and variability of East Asian monsoon climate since the late Miocene

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    @@ The variability and dynamic mechanism of the East Asian monsoon climate is a major scientific puzzle in the exploration of global change.As early as in the late 1990s,a research team led by Prof.AN Zhisheng from the CAS Institute of Earth Environment started their work in this topic,with an objective of improving the hypothesis of monsoon-controlled East Asian environment and advancing the basic studies of past global changes in eastern Asia.

  4. Mid-Pliocene East Asian monsoon climate simulated in the PlioMIP

    Directory of Open Access Journals (Sweden)

    R. Zhang

    2013-09-01

    Full Text Available Based on simulations with 15 climate models in the Pliocene Model Intercomparison Project (PlioMIP, the regional climate of East Asia (focusing on China during the mid-Pliocene is investigated in this study. Compared to the pre-industrial, the multi-model ensemble mean (MMM of all models shows the East Asian summer winds (EASWs largely strengthen in monsoon China, and the East Asian winter winds (EAWWs strengthen in south monsoon China but slightly weaken in north monsoon China in the mid-Pliocene. The MMM of all models also illustrates a warmer and wetter mid-Pliocene climate in China. The simulated weakened mid-Pliocene EAWWs in north monsoon China and intensified EASWs in monsoon China agree well with geological reconstructions. However, there is a large model–model discrepancy in simulating mid-Pliocene EAWW, which should be further addressed in the future work of PlioMIP.

  5. Subseasonal features of the Asian summer monsoon in the NCEP climate forecast system

    Institute of Scientific and Technical Information of China (English)

    Song YANG; WEN Min; R Wayne HIGGINS

    2008-01-01

    The operational climate forecast system (CFS) of the US National Centers for Environmental Prediction provides climate predic-tions over the world, and CFS products are becoming an important source of information for regional climate predictions in many Asian countries where monsoon climate dominates. Recent studies have shown that, on monthly-to-seasonal time-scales, the CFS is highly skillful in simulating and predicting the variability of the Asian monsoon. The higher-frequency variability of the Asian summer monsoon in the CFS is analyzed, using output from a version with a spectral triangular truncation of 126 waves in horizon-tal and 64 sigma layers in vertical, focusing on synoptic, quasi-biweekly, and intraseasonal time-scales. The onset processes of different regional monsoon components were investigated within Asia. Although the CFS generally overestimates variability of mon-soon on these time-scales, it successfully captures many major features of the variance patterns, especially for the synoptic time-scale. The CFS also captures the timing of summer monsoon onsets over India and the Indo-China Peninsula. However, it encoun-ters difficulties in simulating the onset of the South China Sea monsoon. The success and failure of the CFS in simulating the onset of monsoon precipitation can also be seen from the associated features of simulated atmospheric circulation processes. Overall, the CFS is capable of simulating the synoptic-to-intraseasonal variability of the Asian summer monsoon with skills. As for seasonal-to-interannual time-scales shown previously, the model is expected to possess a potential for skillful predictions of the high-frequencyvariability of the Asian monsoon.

  6. Interconnections between the Asian monsoon, ENSO, and high northern latitude climate during the Holocene

    Institute of Scientific and Technical Information of China (English)

    HONG Bing; LIN Qinghua; HONG Yetang

    2006-01-01

    The article emphatically reviews the research progress in interconnections between the East Asian and Indian Ocean summer monsoons, between the Asian monsoon and the El Nino-Southern Oscillation (ENSO) activity, and between the monsoon, ENSO and the changing of the North Atlantic climate during the Holocene. According to the studies of recent years, it is found that the intensity variations of the East Asian and Indian Ocean summer monsoons show an opposite relationship, which may be closely related to the phenomena of ENSO in the equatorial Pacific Ocean and the variation of the deep-water formation of the North Atlantic Ocean on the interannual to orbital time scales. The 4k and 8k events occurring at around 4200 and 8200 a BP, respectively, might be the two in a series of severe paleo-El Nino events during the Holocene, strongly reflecting the interactions and influences of the monsoons, ENSO and the North Atlantic climate. In order to better understand the relationships between these paleoclimatic phenomena, scientists need to strengthen the research work on the Asian monsoon division and the comparison between monsoon proxy records, and the study on the proxy record of sea surface temperature with high time-resolution in the equatorial Pacific Ocean and the simulation research of paleoclimate condition.

  7. Winter climate changes over East Asian region under RCP scenarios using East Asian winter monsoon indices

    Science.gov (United States)

    Hong, Ja-Young; Ahn, Joong-Bae; Jhun, Jong-Ghap

    2016-03-01

    The changes in the winter climatology and variability of the East Asian winter monsoon (EAWM) for the late 21st century (2070-2099) under the Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios are projected in terms of EAWM indices (EAWMIs). Firstly, the capability of the climate models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5) in simulating the boreal winter climatology and the interannual variability of the EAWM for the late 20th century (1971-2000) is examined. Nine of twenty-three climate models are selected based on the pattern correlations with observation and a multi-model ensemble is applied to the nine model data. Three of twelve EAWMIs that show the most significant temporal correlations between the observation and CMIP5 surface air temperatures are utilized. The ensemble CMIP5 is capable of reproducing the overall features of the EAWM in spite of some biases in the region. The negative correlations between the EAWMIs and boreal winter temperature are well reproduced and 3-5 years of the major interannual variation observed in this region are also well simulated according to power spectral analyses of the simulated indices. The fields regressed onto the indices that resemble the composite strong winter monsoon pattern are simulated more or less weakly in CMIP5 compared to the observation. However, the regressed fields of sea level pressure, surface air temperature, 500-hPa geopotential height, and 300-hPa zonal wind are well established with pattern correlations above 0.83 between CMIP5 and observation data. The differences between RCPs and Historical indicate strong warming, which increases with latitude, ranging from 1 to 5 °C under RCP4.5 and from 3 to 7 °C under RCP8.5 in the East Asian region. The anomalous southerly winds generally become stronger, implying weaker EAWMs in both scenarios. These features are also identified with fields regressed onto the indices in RCPs. The future projections reveal

  8. Regional climate model experiments to investigate the Asian monsoon in the Late Miocene

    Directory of Open Access Journals (Sweden)

    H. Tang

    2011-03-01

    Full Text Available The Late Miocene (11.6–5.3 Ma is a crucial period for the Asian monsoon evolution. However, the spatiotemporal changes of the Asian monsoon system in the Late Miocene are still ambiguous, and the mechanisms responsible for these changes are debated. Here, we present a simulation of the Asian monsoon climate (0 to 60° N and 50 to 140° E in the Tortonian (11–7 Ma using the regional climate model CCLM3.2. We employ relatively high spatial resolution (1° × 1° and adapt the physical boundary conditions such as topography, land-sea distribution and vegetation in the regional model to represent the Late Miocene. As climatological forcing, the output of a Tortonian run with a fully-coupled atmosphere-ocean general circulation model is used. Our results show a stronger-than-present E-Asian winter monsoon wind in the Tortonian, as a result of the enhanced mid-latitude westerly wind of our global forcing and the lowered northern Tibetan Plateau in the regional model. The summer monsoon circulation is generally weakened in our regional Tortonian run compared to today. However, the changes of summer monsoon precipitation exhibit major regional differences. The precipitation decreases in N-China and N-India, but increases in S-China, the western coast and the southern tip of India. This can be attributed to the combined effect of both the regional topographical changes and the other forcings related to our global model. The spread of the dry summer conditions over N-China and NW-India further implies that the monsoonal climate may not be fully established over these regions in the Tortonain. Compared with the global model, the high resolution regional model highlights the spatial differences of the Asian monsoon climate in the Tortonian, and better characterizes the convective activity and its response to topographical changes. It therefore provides a useful and compared to global models complementary tool to improve our understanding of the Asian

  9. Understanding South Asian Monsoon Variability in a Changing Climate

    Science.gov (United States)

    Annamalai, H.; Prasanna, V.; Mohan, T.

    2014-12-01

    Both observations and 20th century coupled model (CMIP3/5) simulations suggest that severe weak monsoon years (seasonal mean rainfall less than 15% of the normal) over South Asia are associated with a developing El Nino. During these years and within the summer season, monsoon breaks last for a prolonged period (> 7 days). Detailed diagnostics show that dry advection is the primary initiator for the dryness while cloud-radiative processes maintain it. In all future RCP projections, a robust signal in the time-mean is a basin-wide SST warming along the equatorial central-eastern Pacific (El Nino-like conditions). Question of interests include: in a warmer planet, what is the probability that the monsoon extremes would increase and intensify? Are there any changes in the dynamical and thermodynamical processes that shape these extremes? To address the above questions, a detalied diagostics of CMIP3/5 solutions in conjunction with a series of idealized numerical experiments were performed in an ensemble mode. Model solutions suggest that compared to present-day, intensity of severe weak monsoons increases, and frequency and intensity of prolonged break conditions also increase. Furthermore, an examination of temporal evolution of area-averaged daily rainfall over South Asia suggests "persistence" of dryness throughout the summer season. Our model solutions imply the dominant role of boundary forcing, enhancing predictability of severe weak monsoons. The actual processes that shape these extremes as well as limitations in the present research, and future directions will be discussed.

  10. Future projection of mean and variability of the Asian Summer Monsoon and Indian Ocean Climate systems

    Energy Technology Data Exchange (ETDEWEB)

    Annamalai, H [IPRC, University of Hawaii

    2014-09-15

    The overall goal of this project is to assess the ability of the CMIP3/5 models to simulate the Indian-Ocean monsoon systems. The PI along with post-docs investigated research issues ranging from synoptic systems to long-term trends over the Asian monsoon region. The PI applied diagnostic tools such as moist static energy (MSE) to isolate: the moist and radiative processes responsible for extended monsoon breaks over South Asia, precursors in the ENSO-monsoon association, reasons for the drying tendency over South Asia and the possible effect on tropical Indian Ocean climate anomalies influencing certain aspects of ENSO characteristics. By diagnosing various observations and coupled model simulations, we developed working hypothesis and tested them by carrying out sensitivity experiments with both linear and nonlinear models. Possible physical and dynamical reasons for model sensitivities were deduced. On the teleconnection front, the ability of CMIP5 models in representing the monsoon-desert mechanism was examined recently. Further more, we have applied a suite of diagnostics and have performed an in depth analysis on CMIP5 integrations to isolate the possible reasons for the ENSO-monsoon linkage or lack thereof. The PI has collaborated with Dr. K.R. Sperber of PCMDI and other CLIVAR Asian-Australian monsoon panel members in understanding the ability of CMIP3/5 models in capturing monsoon and its spectrum of variability. The objective and process-based diagnostics aided in selecting models that best represent the present-day monsoon and its variability that are then employed for future projections. Two major highlights were an invitation to write a review on present understanding monsoons in a changing climate in Nature Climate Change, and identification of an east-west shift in observed monsoon rainfall (more rainfall over tropical western Pacific and drying tendency over South Asia) in the last six decades and attributing that shift to SST rise over the tropical

  11. NUMERICAL SIMULATION OF INFLUENCE OF INDIAN OCEAN SSTA ON WEATHER AND CLIMATE IN ASIAN MONSOON REGION

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Sea surface temperature anomaly (SSTA) exerts great influence on the generation of global weather and climate. Much progress has been made with respect to SSTA in the Pacific Ocean region in contrast to the Indian Ocean. The IAP9L model, which is developed at the Institute of Atmospheric Physics of the Chinese Academy of Science, is used to simulate the influence of the Indian Ocean SSTA on the general circulation and weather/climate anomalies in the monsoon region of Asia. It is found that the warm (cool) SSTA in the equatorial low latitudes of the Indian Ocean triggers winter (summer) teleconnection patterns in middle and higher latitudes of the Northern Hemisphere that are similar to PNA or EAP. They play a very important role in the anomaly of circulation or weather and climate in the middle and lower latitudes of the Asian summer monsoon region. With the warm (cool) SSTA forcing in the Indian Ocean, the Asian summer monsoon sets up at a late (early) date and withdraws at a early (late) date, lasting for a short (long) duration at a weak (strong) intensity. The Indian Ocean SSTA is shown to be an indicator for precipitation variation in China.

  12. The evolution of sub-monsoon systems in the Afro-Asian monsoon region during the Holocene- comparison of different transient climate model simulations

    Science.gov (United States)

    Dallmeyer, A.; Claussen, M.; Fischer, N.; Haberkorn, K.; Wagner, S.; Pfeiffer, M.; Jin, L.; Khon, V.; Wang, Y.; Herzschuh, U.

    2015-02-01

    The recently proposed global monsoon hypothesis interprets monsoon systems as part of one global-scale atmospheric overturning circulation, implying a connection between the regional monsoon systems and an in-phase behaviour of all northern hemispheric monsoons on annual timescales (Trenberth et al., 2000). Whether this concept can be applied to past climates and variability on longer timescales is still under debate, because the monsoon systems exhibit different regional characteristics such as different seasonality (i.e. onset, peak and withdrawal). To investigate the interconnection of different monsoon systems during the pre-industrial Holocene, five transient global climate model simulations have been analysed with respect to the rainfall trend and variability in different sub-domains of the Afro-Asian monsoon region. Our analysis suggests that on millennial timescales with varying orbital forcing, the monsoons do not behave as a tightly connected global system. According to the models, the Indian and North African monsoons are coupled, showing similar rainfall trend and moderate correlation in centennial rainfall variability in all models. The East Asian monsoon changes independently during the Holocene. The dissimilarities in the seasonality of the monsoon sub-systems lead to a stronger response of the North African and Indian monsoon systems to the Holocene insolation forcing than of the East Asian monsoon and affect the seasonal distribution of Holocene rainfall variations. Within the Indian and North African monsoon domain, precipitation solely changes during the summer months, showing a decreasing Holocene precipitation trend. In the East Asian monsoon region, the precipitation signal is determined by an increasing precipitation trend during spring and a decreasing precipitation change during summer, partly balancing each other. A synthesis of reconstructions and the model results do not reveal an impact of the different seasonality on the timing of the

  13. Large-scale urbanization effects on eastern Asian summer monsoon circulation and climate

    Science.gov (United States)

    Chen, Haishan; Zhang, Ye; Yu, Miao; Hua, Wenjian; Sun, Shanlei; Li, Xing; Gao, Chujie

    2016-07-01

    Impacts of large-scale urbanization over eastern China on East Asian summer monsoon circulation and climate are investigated by comparing three 25-year climate simulations with and without incorporating modified land cover maps reflecting two different idealized large-scale urbanization scenarios. The global atmospheric general circulation model CAM4.0 that includes an urban canopy parameterization scheme is employed in this study. The large-scale urbanization over eastern China leads to a significant warming over most of the expanded urban areas, characterized by an increase of 3 K for surface skin temperature, 2.25 K for surface air temperature, significant warming of both daily minimum and daily maximum air temperatures, and 0.4 K for the averaged urban-rural temperature difference. The urbanization is also accompanied by an increase in surface sensible heat flux, a decrease of the net surface shortwave and long-wave radiation, and an enhanced surface thermal heating to the atmosphere in most Eastern Asia areas. It is noted that the responses of the East Asian summer monsoon circulation exhibits an evident month-to-month variation. Across eastern China, the summer monsoon in early summer is strengthened by the large-scale urbanization, but weakened (intensified) over southern (northern) part of East Asia in late summer. Meanwhile, early summer precipitation is intensified in northern and northeastern China and suppressed in south of ~35°N, but late summer precipitation is evidently suppressed over northeast China, the Korean Peninsula and Japan with enhancements in southern China, the South China Sea, and the oceanic region south and southeast of the Taiwan Island. This study highlights the evidently distinct month-to-month responses of the monsoon system to the large-scale urbanization, which might be attributed to different basic states, internal feedbacks (cloud, rainfall) as well as a dynamic adjustment of the atmosphere. Further investigation is required

  14. The influence of land cover change in the Asian monsoon region on present-day and mid-Holocene climate

    Directory of Open Access Journals (Sweden)

    A. Dallmeyer

    2011-02-01

    Full Text Available Using the general circulation model ECHAM5/JSBACH, we investigate the biogeophysical effect of large-scale afforestation and deforestation in the Asian monsoon domain on present-day and mid-Holocene climate. We demonstrate that the applied land cover change does not only modify the local climate but also change the climate in North Africa and the Middle East via teleconnections. Deforestation in the Asian monsoon domain enhances the rainfall in North Africa. In parts of the Sahara summer precipitation is more than doubled. In contrast, afforestation strongly decreases summer rainfall in the Middle East and even leads to the cessation of the rainfall-activity in some parts of this region.

    Regarding the local climate, deforestation results in a reduction of precipitation and a cooler climate as grass mostly has a higher albedo than forests. However, in the core region of the Asian monsoon the decrease of evaporative cooling in the monsoon season overcompensates this signal and results in a net warming. Afforestation has mainly the opposite effect, although the pattern of change is less clear. It leads to more precipitation in most parts of the Asian monsoon domain and a warmer climate except for the southern regions where a stronger evaporation decreases near-surface temperatures in the monsoon season.

    When prescribing mid-Holocene insolation, the pattern of local precipitation change differs. Afforestation particularly increases monsoon rainfall in the region along the Yellow River which was the settlement area of major prehistoric cultures. In this region, the effect of land cover change on precipitation is half as large as the orbitally-induced precipitation change. Thus, our model results reveal that mid- to late-Holocene land cover change could strongly have contributed to the decreasing Asian monsoon precipitation during the Holocene known from reconstructions.

  15. Strong coupling of Asian Monsoon and Antarctic climates on sub-orbital timescales.

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    Chen, Shitao; Wang, Yongjin; Cheng, Hai; Edwards, R Lawrence; Wang, Xianfeng; Kong, Xinggong; Liu, Dianbing

    2016-01-01

    There is increasing evidence that millennial-scale climate variability played an active role on orbital-scale climate changes, but the mechanism for this remains unclear. A (230)Th-dated stalagmite δ(18)O record between 88 and 22 thousand years (ka) ago from Yongxing Cave in central China characterizes changes in Asian monsoon (AM) strength. After removing the 65°N insolation signal from our record, the δ(18)O residue is strongly anti-phased with Antarctic temperature variability on sub-orbital timescales during the Marine Isotope Stage (MIS) 3. Furthermore, once the ice volume signal from Antarctic ice core records were removed and extrapolated back to the last two glacial-interglacial cycles, we observe a linear relationship for both short- and long-duration events between Asian and Antarctic climate changes. This provides the robust evidence of a link between northern and southern hemisphere climates that operates through changes in atmospheric circulation. We find that the weakest monsoon closely associated with the warmest Antarctic event always occurred during the Terminations. This finding, along with similar shifts in the opal flux record, suggests that millennial-scale events play a key role in driving the deglaciation through positive feedbacks associated with enhanced upwelling and increasing CO2. PMID:27605015

  16. Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    OpenAIRE

    Qian, Y.; M. G. Flanner; L. R. Leung; Wang, W

    2010-01-01

    The Tibetan Plateau (TP), the highest and largest plateau in the world, has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. The snowpack and glaciers over the TP provide fresh water to billions of people in Asian countries, but the TP glaciers have been retreating faster than those anywhere else in the world. In this modeling study a series of numerical experiments with a global climate model are designed to simulate radiative forcin...

  17. Climate response of the South Asian monsoon system to anthropogenic aerosols

    Energy Technology Data Exchange (ETDEWEB)

    Ganguly, Dilip; Rasch, Philip J.; Wang, Hailong; Yoon, Jin-Ho

    2012-07-13

    The equilibrium climate response to the total effects (direct, indirect and semi-direct effects) of aerosols arising from anthropogenic and biomass burning emissions on the South Asian summer monsoon system is studied using a coupled atmosphere-slab ocean model. Our results suggest that anthropogenic and biomass burning aerosols generally induce a reduction in mean summer monsoon precipitation over most parts of the Indian subcontinent, strongest along the western coastline of the Indian peninsula and eastern Nepal region, but modest increases also occur over the north western part of the subcontinent. While most of the noted reduction in precipitation is triggered by increased emissions of aerosols from anthropogenic activities, modest increases in the north west are mostly associated with decreases in local emissions of aerosols from forest fire and grass fire sources. Anthropogenic aerosols from outside Asia also contribute to the overall reduction in precipitation but the dominant contribution comes from aerosol sources within Asia. Local emissions play a more important role in the total rainfall response to anthropogenic aerosol sources during the early monsoon period, whereas both local as well as remote emissions of aerosols play almost equally important roles during the later part of the monsoon period. While precipitation responses are primarily driven by local aerosol forcing, regional surface temperature changes over the region are strongly influenced by anthropogenic aerosols from sources further away (non-local changes). Changes in local anthropogenic organic and black carbon emissions by as much as a factor of two (preserving their ratio) produce the same basic signatures in the model's summer monsoon temperature and precipitation responses.

  18. Impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    Science.gov (United States)

    Qian, Y.; Flanner, M. G.; Leung, L.; Wang, W.

    2010-12-01

    The Tibetan Plateau (TP) has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. The snowpack and glaciers over the TP provide fresh water to billions of Asian people, but the TP glaciers have been retreating faster than those anywhere else in the world. In this study a series of experiments with a global climate model are designed to simulate radiative forcing (RF) of black carbon (BC) in snow, and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow on the snowpack over the TP and subsequent impacts on the Asian monsoon climate and hydrological cycle. Results show a large BC content in snow over the TP, especially the southern slope, with concentration larger than 100 µg/kg. Because of high aerosol content in snow and large incident solar radiation, the TP exhibits the largest surface RF induced by BC in snow compared to other snow-covered regions in the world. The BC-induced snow albedo perturbations generate surface RF of 5-15 W/m2 during spring. BC-in-snow increases the surface air temperature by around 1.0oC averaged over the TP and reduces spring snowpack over the TP more than pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer, i.e. a trend toward earlier melt dates. The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1-4 times larger for BC-in-snow than CO2 increase during April-July, indicating that BC-in-snow more efficiently accelerates snowmelt because the increased net solar radiation induced by reduced albedo melts the snow more efficiently than snow melt due to warming in the air. The TP also influences the South (SAM) and East (EAM) Asian monsoon through its thermodynamical forcing. During boreal spring, aerosols are transported by

  19. Simulation of Asian Monsoon Seasonal Variations with Climate Model R42L9/LASG

    Institute of Scientific and Technical Information of China (English)

    王在志; 吴国雄; 吴统文; 宇如聪

    2004-01-01

    The seasonal variations of the Asian monsoon were explored by applying the atmospheric general circulation model R42L9 that was developed recently at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP/CAS). The 20-yr (1979-1998) simulation was done using the prescribed20-yr monthly SST and sea-ice data as required by Atmospheric Model Intercomparison Project (AMIP)Ⅱ in the model. The monthly precipitation and monsoon circulations were analyzed and compared with the observations to validate the model's performance in simulating the climatological mean and seasonal variations of the Asian monsoon. The results show that the model can capture the main features of the spatial distribution and the temporal evolution of precipitation in the Indian and East Asian monsoon areas. The model also reproduced the basic patterns of monsoon circulation. However, some biases exist in this model. The simulation of the heating over the Tibetan Plateau in summer was too strong. The overestimated heating caused a stronger East Asian monsoon and a weaker Indian monsoon than the observations. In the circulation fields, the South Asia high was stronger and located over the Tibetan Plateau. The western Pacific subtropical high was extended westward, which is in accordance with the observational results when the heating over the Tibetan Plateau is stronger. Consequently, the simulated rainfall around this area and in northwest China was heavier than in observations, but in the Indian monsoon area and west Pacific the rainfall was somewhat deficient.

  20. Mid-Holocene Climate Variations Recorded by Palaeolake in Marginal Area of East Asian Monsoon: A Multi-proxy Study

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Traditionally, the mid-Holocene in most parts of China was thought to be warmer with higher precipitation,resulting from a strong Asian summer monsoon. However, some recent researches have proposed a mid-Holocene drought interval of millennial-scale in East Asian monsoon margin areas. Thus whether mid-Holocene was dry or humid remains an open issue. Here, Zhuyeze palaeolake, the terminal lake of the Shiyang River Drainage lying in Asian monsoon marginal areas, was selected for reconstructing the details of climate variations during the Holocene, especially mid-Holocene,on the basis ora sedimentological analysis. Qingtu Lake (QTL) section of 6.92m depth was taken from Zhuyeze palaeolake. Multi-proxy analysis of QTL section, including grain size, carbonate, TOC, C/N and δ13C of organic matter, was used to document regional climatic changes during 9-3 cal ka B.P. The record shows a major environmental change at 9.0-7.8 cal ka B.P., attributed to a climate trend towards warmth and humidity. This event was followed by a typical regional drought event which occurred during 7.8-7.5 cal ka B.P. And a warm and humid climate prevailed from 7.5 to 5.0 cal ka B.P., attributed to the warm/humid Holocene Optimum in this region. After that, the climate gradually became drier.Moreover, comparison of the climate record from this paper with the summer insolation at 30°N indicates that the climate pattern reflecting the Asian monsoon changes was caused by insolation change.

  1. High resolution simulation of the South Asian monsoon using a variable resolution global climate model

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    P Sabin, T.; Krishnan, R.; Ghattas, Josefine; Denvil, Sebastien; Dufresne, Jean-Louis; Hourdin, Frederic; Pascal, Terray

    2013-07-01

    This study examines the feasibility of using a variable resolution global general circulation model (GCM), with telescopic zooming and enhanced resolution (~35 km) over South Asia, to better understand regional aspects of the South Asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation. For this purpose, two sets of ten member realizations are produced with and without zooming using the LMDZ (Laboratoire Meteorologie Dynamique and Z stands for zoom) GCM. The simulations without zoom correspond to a uniform 1° × 1° grid with the same total number of grid points as in the zoom version. So the grid of the zoomed simulations is finer inside the region of interest but coarser outside. The use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields. It is found that the monsoon simulation with high-resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the Western Ghats, the northeastern mountain slopes and northern Bay of Bengal (BOB). A realistic Monsoon Trough (MT) is also noticed in the zoomed simulation, together with remarkable improvements in representing the associated precipitation and circulation features, as well as the large-scale organization of meso-scale convective systems over the MT region. Additionally, a more reasonable simulation of the monsoon synoptic disturbances (lows and disturbances) along the MT is noted in the high-resolution zoomed simulation. On the other hand, the no-zoom version has limitations in capturing the depressions and their movement, so that the MT zone is relatively dry in this case. Overall, the results from this work demonstrate the usefulness of the high-resolution variable resolution LMDZ model in realistically capturing the interactions among the monsoon large-scale dynamics

  2. Holocene South Asian Monsoon Climate Change - Potential Mechanisms and Effects on Past Civilizations

    Science.gov (United States)

    Staubwasser, M.; Sirocko, F.; Grootes, P. M.; Erlenkeuser, H.; Segl, M.

    2002-12-01

    Planktonic oxygen isotope ratios from the laminated sediment core 63KA off the river Indus delta dated with 80 AMS radiocarbon ages reveal significant climate changes in the south Asian monsoon system throughout the Holocene. The most prominent event of the early-mid Holocene occurred after 8.4 ka BP and is within dating error of the GISP/GRIP event centered at 8.2 ka BP. The late Holocene is generally more variable, and shows non-periodic cycles in the multi-centennial frequency band. The largest change of the entire Holocene occurred at 4.2 ka BP and is concordant with the end of urban Harappan civilization in the Indus valley. Opposing isotopic trends across the northern Arabian Sea surface indicate a reduction in Indus river discharge at that time. Consequently, sustained drought may have initiated the archaeologically recorded interval of southeastward habitat tracking within the Harappan cultural domain. The hemispheric significance of the 4.2 ka BP event is evident from concordant climate change in the eastern Mediterranean and the Middle East. The late Holocene cycles in South Asia, which most likely represent drought cycles, vary between 250 and 800 years and are coherent with the evolution of cosmogenic radiocarbon production rates in the atmosphere. This suggests that solar variability is the fundamental cause behind late Holocene rainfall changes at least over south Asia.

  3. Early Holocene Sediment Discharge from Taiwanese Rivers: Intensified Asian Monsoon and Climate Change

    Science.gov (United States)

    Hsu, Ho-Han; Liu, Char-Shine; Milliman, John; Chen, Tzu-Ting; Chang, Jih-Hsin; Wang, Yunshuen

    2016-04-01

    Temporal variations of fluvial sediment discharge can reflect the significant climatic variation. In this study, high-resolution sedimentary records - on the millennial scale - from onshore wells, offshore cores and seismic profiles are used to quantify sediment discharge from small mountainous rivers around Taiwan since the last glacial maximum. While significantly high sediment accumulation rates have been observed in the modern flood plain, shelf and deep-sea basins during the late Pleistocene and Holocene, early Holocene rates are unusually high. In northeast Taiwan, for example, sediment flux from the Lanyang River between 10-12 ka BP appears to have been 10 mt/yr, about 4 fold greater than measured annual discharge prior to 1960. In the southwest Taiwan, the highest sedimentation rate happened during 10-12 ka BP. Long-term average discharge since 8 ka BP has been ~12 mt/yr), less than half the 29 mt/yr that was deposited on the Kaohsiung-Pingtung Plain. These and other sedimentation histories around Taiwan as well as in the South China Sea and the Bay of Bengal indicate that the occurrence of high sediment load cannot be explained solely by general circulation model of sea-level change; climate and climatic change also should be taken into account. We suggest that the intensification of the Asian monsoon, particularly in the case of Taiwan, typhoons, which occurred during the early Holocene may have been the root cause of the increased rainfall and thus increased erosion and sediment delivery. This study reconstructs the long-term sedimentary history of the region since the late Quaternary, especially focuses on the increased sediment discharges during the particularly warm and humid paleo-climatic period in NE and SW Taiwan. Moreover, it could help to better understand and predict fluvial sediment fluxes and their geological and societal impacts in response to future global warming.

  4. Simulation of the future change of East Asian monsoon climate using the IPCC SRES A2 and B2 scenarios

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    In this paper, we applied the newest emission scenarios of the sulfur and greenhouse gases, i.e. Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 and B2 scenarios, to investigating the change of the East Asian climate in the last three decades of the 21st century with an atmosphere-ocean coupled general circulation model. The global warming enlarges the land-sea thermal contrast and, hence, enhances (reduces) the East Asian summer (winter) monsoon circulation. The precipitation from the Yangtze and Huaihe river valley to North China increases significantly. In particular, the strong rainfall increase over North China implies that the East Asian rainy area would expand northward. In addition, from the southeastern coastal area to North China, the rainfall would increase significantly in September, implying that the rainy period of the East Asian monsoon would be prolonged about one month. In July, August and September, the interannual variability of the precipitation enhances evidently over North China, meaning a risk of flooding in the future.

  5. Tracking millennial-scale climate change by analysis of the modern summer precipitation in the marginal regions of the Asian monsoon

    Science.gov (United States)

    Li, Yu; Wang, Nai'ang; Chen, Hongbao; Li, Zhuolun; Zhou, Xuehua; Zhang, Chengqi

    2012-09-01

    The Asian summer monsoon and the westerly winds interact in the mid-latitude regions of East Asia, so that climate change there is influenced by the combined effect of the two climate systems. The Holocene millennial-scale Asian summer monsoon change shows the out-of-phase relationship with the moisture evolution in arid Central Asia. Although much research has been devoted to the long-term climate change, little work has been done on the mechanism. Summer precipitation, in the marginal regions of the Asian monsoon, is strongly affected by the monsoon and the westerly winds. The purpose of this paper is to examine the mechanism of the millennial-scale out-of-phase relationship by modern summer precipitation analysis in the northwest margin of the Asian monsoon (95-110°E, 35-45°N). First, the method of Empirical Orthogonal Function (EOF) analysis was carried out to the 1960-2008 summer rainfall data from 64 stations in that region; then the water vapor transportation and geopotential height field data were studied, in order to explain and understand the factors that influence the summer precipitation; lastly, the East Asian Summer Monsoon Index (EASMI), South Asian Summer Monsoon Index (SASMI), Summer Westerly Winds Index (SWI) were compared with the EOF time series. The results indicate the complicated interannual-scale interaction between the Asian summer monsoon and the westerly winds, which can result in the modern out-of-phase relationship in the study area. This study demonstrates that the interaction between the two climate systems can be considered as a factor for the millennial-scale out-of-phase relationship.

  6. A Possible Role of Solar Radiation and Ocean in the Mid-Holocene East Asian Monsoon Climate

    Institute of Scientific and Technical Information of China (English)

    魏江峰; 王会军

    2004-01-01

    An atmospheric general circulation model (AGCM) and an oceanic general circulation model (OGCM) are asynchronously coupled to simulate the climate of the mid-Holocene period.The role of the solarradiation and ocean in the mid-Holocene East Asian monsoon climate is analyzed and some mechanisms are revealed.At the forcing of changed solar radiation induced by the changed orbital parameters and the changed SST simulated by the OGCM,compared with when there is orbital forcing alone,there is more precipitation and the monsoon is stronger in the summer of East Asia,and the winter temperature increases over China.These agree better with the reconstructed data.It is revealed that the change of solar radiation can displace northward the ITCZ and the East Asia subtropical jet,which bring more precipitation over the south of Tibet and North and Northeast China.By analyzing the summer meridional latent heat transport,it is found that the influence of solar radiation change is mainly to increase the convergence of atmosphere toward the land,and the influence of SST change is mainly to transport more moisture to the sea surface atmosphere.Their synergistic effect on East Asian precipitation is much stronger than the sum of their respective effects.

  7. Climatic Changes and Evaluation of Their Effects on Agriculture in Asian Monsoon Region- A project of GRENE-ei programs in Japan

    Science.gov (United States)

    Mizoguchi, M.; Matsumoto, J.; Takahashi, H. G.; Tanaka, K.; Kuwagata, T.

    2015-12-01

    It is important to predict climate change correctly in regional scale and to build adaptation measures and mitigation measures in the Asian monsoon region where more than 60 % of the world's population are living. The reliability of climate change prediction model is evaluated by the reproducibility of past climate in general. However, because there are many developing countries in the Asian monsoon region, adequate documentations of past climate which are needed to evaluate the climate reproducibility have not been prepared. In addition, at present it is difficult to get information on wide-area agricultural meteorological data which affect the growth of agricultural crops when considering the impact on agriculture of climate. Therefore, we have started a research project entitled "Climatic changes and evaluation of their effects on agriculture in Asian monsoon region (CAAM)" under the research framework of the Green Network of Excellence (GRENE) for the Japanese fiscal years from 2011 to 2015 supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT). This project aims to improve the reliability of future climate prediction and to develop the information platform which will be useful to design adaptation and mitigation strategies in agriculture against the predicted climatic changes in Asian monsoon regions. What is GRENE?Based on the new growth strategy which was approved by the Cabinet of Japan in June 2010, Green Network of Excellence program (GRENE) has started under MEXT from FY 2011. The objectives of this program are that the domestic leading universities work together strategically and promote a comprehensive human resource development and research of the highest level in the world while sharing research resources and research goals. In the field of environmental information, it is required that universities and research institutions, which are working on issues such as adaptation to climate change, cooperate to

  8. Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    Science.gov (United States)

    Qian, Y.; Flanner, M. G.; Leung, L. R.; Wang, W.

    2010-10-01

    The Tibetan Plateau (TP), the highest and largest plateau in the world, has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. The snowpack and glaciers over the TP provide fresh water to billions of people in Asian countries, but the TP glaciers have been retreating faster than those anywhere else in the world. In this modeling study a series of numerical experiments with a global climate model are designed to simulate radiative forcing of black carbon (BC) and dust in snow, and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow on the snowpack over the TP and subsequent impacts on the Asian monsoon climate and hydrological cycle. Simulations results show a large BC content in snow over the TP, especially the southern slope, with concentration larger than 100 μg/kg. Because of the high aerosol content in snow and large incident solar radiation in the low latitude and high elevation, the TP exhibits the largest surface radiative forcing induced by aerosols (e.g. BC, Dust) in snow compared to other snow-covered regions in the world. Simulation results show that the aerosol-induced snow albedo perturbations generate surface radiative forcing of 5-25 W m-2 during spring, with a maximum in April or May. BC-in-snow increases the surface air temperature by around 1.0 °C averaged over the TP and reduces spring snowpack over the TP more than pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates). The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1-4 times larger for BC-in-snow than CO2 increase during April-July, indicating that BC-in-snow more efficiently accelerates snowmelt because the increased net solar radiation

  9. Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    Directory of Open Access Journals (Sweden)

    Y. Qian

    2010-10-01

    Full Text Available The Tibetan Plateau (TP, the highest and largest plateau in the world, has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. The snowpack and glaciers over the TP provide fresh water to billions of people in Asian countries, but the TP glaciers have been retreating faster than those anywhere else in the world. In this modeling study a series of numerical experiments with a global climate model are designed to simulate radiative forcing of black carbon (BC and dust in snow, and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow on the snowpack over the TP and subsequent impacts on the Asian monsoon climate and hydrological cycle. Simulations results show a large BC content in snow over the TP, especially the southern slope, with concentration larger than 100 μg/kg. Because of the high aerosol content in snow and large incident solar radiation in the low latitude and high elevation, the TP exhibits the largest surface radiative forcing induced by aerosols (e.g. BC, Dust in snow compared to other snow-covered regions in the world.

    Simulation results show that the aerosol-induced snow albedo perturbations generate surface radiative forcing of 5–25 W m−2 during spring, with a maximum in April or May. BC-in-snow increases the surface air temperature by around 1.0 °C averaged over the TP and reduces spring snowpack over the TP more than pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates. The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1–4 times larger for BC-in-snow than CO2 increase during April–July, indicating that BC-in-snow more

  10. Parametric Sensitivity Analysis for the Asian Summer Monsoon Precipitation Simulation in the Beijing Climate Center AGCM Version 2.1

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ben; Zhang, Yaocun; Qian, Yun; Wu, Tongwen; Huang, Anning; Fang, Yongjie

    2015-07-15

    In this study, we apply an efficient sampling approach and conduct a large number of simulations to explore the sensitivity of the simulated Asian summer monsoon (ASM) precipitation, including the climatological state and interannual variability, to eight parameters related to the cloud and precipitation processes in the Beijing Climate Center AGCM version 2.1 (BCC_AGCM2.1). Our results show that BCC_AGCM2.1 has large biases in simulating the ASM precipitation. The precipitation efficiency and evaporation coefficient for deep convection are the most sensitive parameters in simulating the ASM precipitation. With optimal parameter values, the simulated precipitation climatology could be remarkably improved, e.g. increased precipitation over the equator Indian Ocean, suppressed precipitation over the Philippine Sea, and more realistic Meiyu distribution over Eastern China. The ASM precipitation interannual variability is further analyzed, with a focus on the ENSO impacts. It shows the simulations with better ASM precipitation climatology can also produce more realistic precipitation anomalies during El Niño decaying summer. In the low-skill experiments for precipitation climatology, the ENSO-induced precipitation anomalies are most significant over continents (vs. over ocean in observation) in the South Asian monsoon region. More realistic results are derived from the higher-skill experiments with stronger anomalies over the Indian Ocean and weaker anomalies over India and the western Pacific, favoring more evident easterly anomalies forced by the tropical Indian Ocean warming and stronger Indian Ocean-western Pacific tele-connection as observed. Our model results reveal a strong connection between the simulated ASM precipitation climatological state and interannual variability in BCC_AGCM2.1 when key parameters are perturbed.

  11. Sensitivity studies on the impacts of Tibetan Plateau snowpack pollution on the Asian hydrological cycle and monsoon climate

    Science.gov (United States)

    Qian, Y.; Flanner, M.; Leung, R.; Wang, W.

    2012-04-01

    The Tibetan Plateau (TP) has long been identified to be critical in regulating the Asian monsoon climate and hydrological cycle. In this modeling study a series of numerical experiments with a global climate model are designed to simulate radiative effect of black carbon (BC) and dust in snow, and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow on the snowpack over the TP and subsequent impacts on the Asian monsoon climate and hydrological cycle. Simulations results show a large BC content in snow over the TP, especially the southern slope. Because of the high aerosol content in snow and large incident solar radiation in the low latitude and high elevation, the TP exhibits the largest surface radiative flux changes induced by aerosols (e.g. BC, Dust) in snow compared to any other snow-covered regions in the world. Simulation results show that the aerosol-induced snow albedo perturbations generate surface radiative flux changes of 5-25 W m-2 during spring, with a maximum in April or May. BC-in-snow increases the surface air temperature by around 1.0oC averaged over the TP and reduces spring snowpack over the TP more than pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates). The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1-4 times larger for BC-in-snow than CO2 increase during April-July, indicating that BC-in-snow more efficiently accelerates snowmelt because the increased net solar radiation induced by reduced albedo melts the snow more efficiently than snow melt due to warming in the air. The TP also influences the South (SAM) and East (EAM) Asian monsoon through its dynamical and thermal forcing. Simulation results show that during boreal spring

  12. Asian Summer Monsoon and its Associated Rainfall Variability in Thailand

    OpenAIRE

    Atsamon Limsakul

    2010-01-01

    The Asian monsoon is an important component of the Earth's climate. Its associated rainfall variability is a crucial fac¬tor for Thailand's socio-economic development, water resources and agricultural management. An analysis shows that the Thailand rainfall annual cycle is in phase with the Indian summer monsoon (ISM) and the western North Pacific summer monsoon (WNPSM). On the basis of the Empirical Orthogonal Function (EOF) analysis, the dominant spatial-temporal interannual variability in ...

  13. Sensitivity of a regional climate model to land surface parameterization schemes for East Asian summer monsoon simulation

    Science.gov (United States)

    Li, Wenkai; Guo, Weidong; Xue, Yongkang; Fu, Congbin; Qiu, Bo

    2015-12-01

    Land surface processes play an important role in the East Asian Summer Monsoon (EASM) system. Parameterization schemes of land surface processes may cause uncertainties in regional climate model (RCM) studies for the EASM. In this paper, we investigate the sensitivity of a RCM to land surface parameterization (LSP) schemes for long-term simulation of the EASM. The Weather Research and Forecasting (WRF) Model coupled with four different LSP schemes (Noah-MP, CLM4, Pleim-Xiu and SSiB), hereafter referred to as Sim-Noah, Sim-CLM, Sim-PX and Sim-SSiB respectively, have been applied for 22-summer EASM simulations. The 22-summer averaged spatial distributions and strengths of downscaled large-scale circulation, 2-m temperature and precipitation are comprehensively compared with ERA-Interim reanalysis and dense station observations in China. Results show that the downscaling ability of RCM for the EASM is sensitive to LSP schemes. Furthermore, this study confirms that RCM does add more information to the EASM compared to reanalysis that imposes the lateral boundary conditions (LBC) because it provides 2-m temperature and precipitation that are with higher resolution and more realistic compared to LBC. For 2-m temperature and monsoon precipitation, Sim-PX and Sim-SSiB simulations are more consistent with observation than simulations of Sim-Noah and Sim-CLM. To further explore the physical and dynamic mechanisms behind the RCM sensitivity to LSP schemes, differences in the surface energy budget between simulations of Ens-Noah-CLM (ensemble mean averaging Sim-Noah and Sim-CLM) and Ens-PX-SSiB (ensemble mean averaging Sim-PX and Sim-SSiB) are investigated and their subsequent impacts on the atmospheric circulation are analyzed. It is found that the intensity of simulated sensible heat flux over Asian continent in Ens-Noah-CLM is stronger than that in Ens-PX-SSiB, which induces a higher tropospheric temperature in Ens-Noah-CLM than in Ens-PX-SSiB over land. The adaptive

  14. The mechanism and scenarios of how mean annual runoff varies with climate change in Asian monsoon areas

    Science.gov (United States)

    Chen, Junxu; Xia, Jun; Zhao, Changsen; Zhang, Shifeng; Fu, Guobin; Ning, Like

    2014-09-01

    Understanding the effects of climate change on runoff is important for the sustainable management of water resources. However, the mechanism of such effects in the Asian monsoon region remains unclear. This study revisits Fu's two-parameter climate elasticity index and enhances it by using the Gardner function to strengthen the former's prediction reliability when the future climate condition is beyond the historical range. Then the improved method was applied to study the elasticity change with temperature and precipitation in the eastern monsoon basins of China, whereas to explore the mechanism of climate change on runoff. Furthermore, the runoff change and the elasticity of the study area from 2020 to 2050 under representative concentration pathways (RCPs) were predicted. Results show that the trend of elasticity change assumes a centrosymmetric picture with the symmetric point (0, 0). Different catchments respond differently to the same climate change scenario: the sensitivity of the Haihe Basin is the highest; those of Yellow, Huaihe, Liaohe, Songhua, Pearl, Yangtze, and Southeast Rivers are lower, in descending order. The changing mode of precipitation and temperature differs greatly to keep the runoff unchanged. For semi-humid regions in which the mean annual temperature ranges from 0.71 °C to 9.0 °C, such as the basins of Songhua, Liaohe, Haihe, and Yellow, a 1 °C increase in temperature requires a corresponding 3.2-4.0% increase in precipitation to keep the runoff unchanged. However, in wet regions, such as the basins of Yangtze, Southeast Rivers, and Pearl, the same change in temperature requires a less than 2.8% increase in precipitation to keep the runoff unchanged. In the future, the runoff in most basins may decrease in different degrees. The decreasing velocity of the runoff is the fastest in the RCP8.5 scenario and the decreasing trend of the runoff slows down under the RCP4.5 and RCP2.6 scenarios. The proposed method can be applied to other

  15. Assessment of South Asian Summer Monsoon Simulation in CMIP5-Coupled Climate Models During the Historical Period (1850-2005)

    Science.gov (United States)

    Prasanna, Venkatraman

    2016-04-01

    This paper evaluates the performance of 29 state-of-art CMIP5-coupled atmosphere-ocean general circulation models (AOGCM) in their representation of regional characteristics of monsoon simulation over South Asia. The AOGCMs, despite their relatively coarse resolution, have shown some reasonable skill in simulating the mean monsoon and precipitation variability over the South Asian monsoon region. However, considerable biases do exist with reference to the observed precipitation and also inter-model differences. The monsoon rainfall and surface flux bias with respect to the observations from the historical run for the period nominally from 1850 to 2005 are discussed in detail. Our results show that the coupled model simulations over South Asia exhibit large uncertainties from one model to the other. The analysis clearly brings out the presence of large systematic biases in coupled simulation of boreal summer precipitation, evaporation, and sea surface temperature (SST) in the Indian Ocean, often exceeding 50 % of the climatological values. Many of the biases are common to many models. Overall, the coupled models need further improvement in realistically portraying boreal summer monsoon over the South Asian monsoon region.

  16. South Asian climate change at the end of urban Harappan (Indus valley) civilization and mechanisms of Holocene monsoon variability

    Science.gov (United States)

    Staubwasser, M.; Sirocko, F.; Erlenkeuser, H.; Grootes, P. M.; Segl, M.

    2003-04-01

    Planktonic oxygen isotope ratios from the well-dated laminated sediment core 63KA off the river Indus delta are presented. The record reveals significant climate changes in the south Asian monsoon system throughout the Holocene. The most prominent event of the early-mid Holocene occurred after 8.4 ka BP and is within dating error of the GISP/GRIP event centered at 8.2 ka BP. The late Holocene is generally more variable and the largest change of the entire Holocene occurred at 4.2 ka BP. This event is concordant with the end of urban Harappan civilization in the Indus valley. Opposing isotopic trends across the northern Arabian Sea surface indicate a reduction in Indus river discharge at that time. Consequently, sustained drought may have initiated the archaeologically recorded interval of southeastward habitat tracking within the Harappan cultural domain. The hemispheric significance of the 4.2 ka BP event is evident from concordant climate change in the eastern Mediterranean and the Middle East. The remainder of the late Holocene shows drought cycles of approximately 700 years that are coherent with the evolution of cosmogenic radiocarbon production rates in the atmosphere. This suggests that solar variability is one fundamental cause behind late Holocene rainfall changes over south Asia.

  17. Synchronicity of the East Asian Summer Monsoon variability and Northern Hemisphere climate change since the last deglaciation

    Directory of Open Access Journals (Sweden)

    T. Shinozaki

    2011-06-01

    Full Text Available Understanding of the mechanism of the East Asian Summer Monsoon (EASM is required for the prediction of climate change in East Asia in a scenario of modern global warming. In this study, we present high-resolution climate records from peat sediments in Northeast Japan to reconstruct the EASM variability based on peat bulk cellulose δ13C since the last deglaciation. We used a 8.8 m long peat sediment core collected from the Tashiro Bog, Northeast Japan. Based on 42 14C measurements, the core bottom reaches ~15.5 ka. δ13C, accumulation rate and accumulation flux time-series correlate well to Greenland ice core δ18O variability, suggesting that the climate record in Northeast Japan is linked to global climate changes. The δ13C record at Tashiro Bog and other paleo-EASM records at Northeast and Southern China consistently demonstrate that hydrological environments were spatially different in mid-high and mid-low latitude regions over the last 15.5 kyr. During global cooling (warming periods, mid-high and mid-low latitude regions were characterized by wet (dry and dry (wet environments, respectively. We suggest that these climatic patterns are related to the migration of the EASM-related rain belt during global climate changes, as a consequence of variations in intensity and location of both the Intertropical Convergence Zone (ITCZ and the Western Pacific Subtropical High (STH. The location of the rain belt largely influences the East Asian hydrological environment. Our δ13C time-series are characterized by a 1230 yr throughout the Holocene and a 680 yr periodicity during the early Holocene. The 1230 yr periodicity is in agreement with North Atlantic ice-rafted debris (IRD events, suggesting a teleconnection between the Northeast Japan and the North Atlantic during the Holocene. In addition, it is the first evidence that the Bond events were recorded in terrestrial sediment in

  18. Abrupt climate change of East Asian Monsoon at 130 kaBP inferred from a high resolution stalagmite δ18O record

    Institute of Scientific and Technical Information of China (English)

    JIANG Xiuyang; WANG Yongjin; KONG Xinggong; WU Jiangying; SHAO Xiaohua; XIA Zhifeng; CHENG Hai

    2005-01-01

    230Th ages and oxygen isotope data of a stalagmite from Shanbao Cave in Hubei Province characterize the East Asian Monsoon precipitation from 133 to127 ka. The decadal-scale high-resolution δ18O record reveals a detailed transitional process from the Penultimate Glaciation to the Last Interglaciation. As established with 230Th dates, the age of the Termination II is determined to be 129.5±1.0 kaBP, which supports the Northern Hemisphere insolation as the triggers for the ice-age cycles. In our δ18O record, the glacial/ interglacial fluctuation reaches about 4‰, almost the same level as in other Asian Monsoon cave stalagmite δ18O records. The transition of the glacial/interglacial period in our record can be recognized as four stepwise stages, among which, a rapid rise of monsoon precipitation follows the stage of "Termination II pause". The rapid rise is synchronous with the abrupt change of global methane concentration, which reflects that an increase in both Asian Monsoon precipitation and tropical wetland plays an important role in the global climate changes.

  19. Mangrove forest degradation indicated by mangrove-derived organic matter in the Qinzhou Bay, Guangxi, China, and its response to the Asian monsoon during the Holocene climatic optimum

    Institute of Scientific and Technical Information of China (English)

    MENG Xianwei; XIA Peng; LI Zhen; LIU Lejun

    2016-01-01

    The response of mangrove ecosystems to the Asian monsoon in the future global warming can be understood by reconstructing the development of mangrove forests during the Holocene climatic optimum (HCO), using proxies preserved in coastal sediments. The total organic matter in sediments of a segmented core, with calibrated age ranges between 5.6 and 7.7 cal. ka BP and corresponding to the HCO, from the Qinzhou Bay in Guangxi, China, is quantitatively partitioned into three end-members according to their sources: mangrove-derived, terrigenous, and marine phytoplanktonic, using a three-end-member model depicted by organic carbon isotope (δ13Corg) and the molar ratio of total organic carbon to total nitrogen (C/N). The percentage of mangrove-derived organic matter (MOM) contribution is used as a proxy for mangrove development. Three visible drops in MOM contribution occurred at ca. 7.3, ca. 6.9, and ca. 6.2 cal. ka BP, respectively, are recognized against a relatively stable and higher MOM contribution level, indicating that three distinct mangrove forest degradations occurred in the Qinzhou Bay during the HCO. The three mangrove forest degradations approximately correspond to the time of the strengthened/weakened Asian winter/summer monsoon. This indicates that even during a period favorable for the mangrove development, such as the HCO, climatic extremes, such as cold and dry events driven by the strengthened/weakened Asian winter/summer monsoon, can trigger the degradation of mangrove forests.

  20. Does Aerosol Weaken or Strengthen the South Asian Monsoon?

    Science.gov (United States)

    Lau, William K.

    2010-01-01

    Aerosols are known to have the ability to block off solar radiation reaching the earth surface, causing it to cool - the so-called solar dimming (SDM) effect. In the Asian monsoon region, the SDM effect by aerosol can produce differential cooling at the surface reducing the meridional thermal contrast between land and ocean, leading to a weakening of the monsoon. On the other hand, absorbing aerosols such as black carbon and dust, when forced up against the steep slopes of the southern Tibetan Plateau can produce upper tropospheric heating, and induce convection-dynamic feedback leading to an advance of the rainy season over northern India and an enhancement of the South Asian monsoon through the "Elevated Heat Pump" (EHP) effect. In this paper, we present modeling results showing that in a coupled ocean-atmosphere-land system in which concentrations of greenhouse gases are kept constant, the response of the South Asian monsoon to dust and black carbon forcing is the net result of the two opposing effects of SDM and EHP. For the South Asian monsoon, if the increasing upper tropospheric thermal contrast between the Tibetan Plateau and region to the south spurred by the EHP overwhelms the reduction in surface temperature contrast due to SDM, the monsoon strengthens. Otherwise, the monsoon weakens. Preliminary observations are consistent with the above findings. We find that the two effects are strongly scale dependent. On interannual and shorter time scales, the EHP effect appears to dominate in the early summer season (May-June). On decadal or longer time scales, the SDM dominates for the mature monsoon (July-August). Better understanding the physical mechanisms underlying the SDM and the EHP effects, the local emission and transport of aerosols from surrounding deserts and arid-regions, and their interaction with monsoon water cycle dynamics are important in providing better prediction and assessment of climate change impacts on precipitation of the Asian monsoon

  1. Tracking South Asian Monsoon in the 21st Century

    Science.gov (United States)

    Rastogi, D.; Mei, R.; Hodges, K. I.; Ashfaq, M.

    2013-05-01

    In this study, we analyze the simulations of the Global Climate Models that are part of the Coupled Model Intercomparison Project Phase 5 (CMIP5) over the South Asian summer monsoon region for the historic (1960-2005) and the 21st century projection (2006-2100) periods. We apply two evaluation matrices namely precipitation recycling ratio analysis and monsoon depressions tracking algorithm to investigate the accuracy of the simulated processes in the GCMs that control the observed spatial and temporal distribution of South Asian summer monsoon rainfall. We sub-select the GCMs for the future period evaluations based on their ability in the simulation of different moisture sources and the accuracy of the low pressure systems tracks that transport moisture over the South Asian land during summer monsoon season in the baseline period. Further, we use selected GCMs to understand the effect of increase in greenhouse forcing on the frequency and tracks of the low-pressure systems during summer monsoon season, and on the moisture sources. These analyses will improve our understanding of the ability of CMIP5 GCMs in the simulation of South Asian summer monsoon dynamics and provide important implications for the reliability of future climate projections over this region.

  2. Asian Eocene monsoons as revealed by leaf architectural signatures

    Science.gov (United States)

    Spicer, Robert A.; Yang, Jian; Herman, Alexei B.; Kodrul, Tatiana; Maslova, Natalia; Spicer, Teresa E. V.; Aleksandrova, Galina; Jin, Jianhua

    2016-09-01

    The onset and development of the Asian monsoon systems is a topic that has attracted considerable research effort but proxy data limitations, coupled with a diversity of definitions and metrics characterizing monsoon phenomena, have generated much debate. Failure of geological proxies to yield metrics capable of distinguishing between rainfall seasonality induced by migrations of the Inter-tropical Convergence Zone (ITCZ) from that attributable to topographically modified seasonal pressure reversals has frustrated attempts to understand mechanisms underpinning monsoon development and dynamics. Here we circumvent the use of such single climate parameter metrics in favor of detecting directly the distinctive attributes of different monsoon regimes encoded in leaf fossils. Leaf form adapts to the prevailing climate, particularly under the extreme seasonal stresses imposed by monsoons, so it is likely that fossil leaves carry a unique signature of past monsoon regimes. Leaf form trait spectra obtained from fossils from Eocene basins in southern China were compared with those seen in modern leaves growing under known climate regimes. The fossil leaf trait spectra, including those derived from previously published fossil floras from northwestern India, were most similar to those found in vegetation exposed to the modern Indonesia-Australia Monsoon (I-AM), which is largely a product of seasonal migrations of the ITCZ. The presence of this distinctive leaf physiognomic signature suggests that although a monsoon climate existed in Eocene time across southern Asia the characteristics of the modern topographically-enhanced South Asia Monsoon had yet to develop. By the Eocene leaves in South Asia had become well adapted to an I-AM type regime across many taxa and points to the existence of a pervasive monsoon climate prior to the Eocene. No fossil trait spectra typical of exposure to the modern East Asia monsoon were seen, suggesting the effects of this system in southern

  3. Sub-seasonal behaviour of Asian summer monsoon under a changing climate: assessments using CMIP5 models

    Science.gov (United States)

    Sooraj, K. P.; Terray, Pascal; Xavier, Prince

    2016-06-01

    Numerous global warming studies show the anticipated increase in mean precipitation with the rising levels of carbon dioxide concentration. However, apart from the changes in mean precipitation, the finer details of daily precipitation distribution, such as its intensity and frequency (so called daily rainfall extremes), need to be accounted for while determining the impacts of climate changes in future precipitation regimes. Here we examine the climate model projections from a large set of Coupled Model Inter-comparison Project 5 models, to assess these future aspects of rainfall distribution over Asian summer monsoon (ASM) region. Our assessment unravels a north-south rainfall dipole pattern, with increased rainfall over Indian subcontinent extending into the western Pacific region (north ASM region, NASM) and decreased rainfall over equatorial oceanic convergence zone over eastern Indian Ocean region (south ASM region, SASM). This robust future pattern is well conspicuous at both seasonal and sub-seasonal time scales. Subsequent analysis, using daily rainfall events defined using percentile thresholds, demonstrates that mean rainfall changes over NASM region are mainly associated with more intense and more frequent extreme rainfall events (i.e. above 95th percentile). The inference is that there are significant future changes in rainfall probability distributions and not only a uniform shift in the mean rainfall over the NASM region. Rainfall suppression over SASM seems to be associated with changes involving multiple rainfall events and shows a larger model spread, thus making its interpretation more complex compared to NASM. Moisture budget diagnostics generally show that the low-level moisture convergence, due to stronger increase of water vapour in the atmosphere, acts positively to future rainfall changes, especially for heaviest rainfall events. However, it seems that the dynamic component of moisture convergence, associated with vertical motion, shows a

  4. Impacts of East Asian aerosols on the Asian monsoon

    Science.gov (United States)

    Bartlett, Rachel; Bollasina, Massimo; Booth, Ben; Dunstone, Nick; Marenco, Franco

    2016-04-01

    Over recent decades, aerosol emissions from Asia have increased rapidly. Aerosols are able to alter radiative forcing and regional hydroclimate through direct and indirect effects. Large emissions within the geographical region of the Asian monsoon have been found to impact upon this vital system and have been linked to observed drying trends. The interconnected nature of smaller regional monsoon components (e.g. the Indian monsoon and East Asian monsoon) presents the possibility that aerosol sources could have far-reaching impacts. Future aerosol emissions are uncertain and may continue to dominate regional impacts on the Asian monsoon. Standard IPCC future emissions scenarios do not take a broad sample of possible aerosol pathways. We investigate the sensitivity of the Asian monsoon to East Asian aerosol emissions. Experiments carried out with HadGEM2-ES use three time-evolving future anthropogenic aerosol emissions scenarios with similar time-evolving greenhouse gases. We find a wetter summer over southern China and the Indochina Peninsula associated with increased sulfate aerosol over China. The southern-flood-northern-drought pattern seen in observations is reflected in these results. India is found to be drier in the summer overall, although wetter in June. These precipitation changes are linked to the increase in sulfate through the alteration of large scale dynamics. Sub-seasonal changes are also seen, with an earlier withdrawal of the monsoon over East Asia.

  5. Transport of short-lived climate forcers/pollutants (SLCF/P) to the Himalayas during the South Asian summer monsoon onset

    International Nuclear Information System (INIS)

    Over the course of six years (2006–2011), equivalent black carbon (eqBC), coarse aerosol mass (PM1–10), and surface ozone (O3), observed during the monsoon onset period at the Nepal Climate Observatory–Pyramid WMO/GAW Global Station (NCO-P, 5079 m a.s.l.), were analyzed to investigate events characterized by a significant increase in these short-lived climate forcers/pollutants (SLCF/P). These events occurred during periods characterized by low (or nearly absent) rain precipitation in the central Himalayas, and they appeared to be related to weakening stages (or ‘breaking’) of the South Asian summer monsoon system. As revealed by the combined analysis of atmospheric circulation, air-mass three-dimensional back trajectories, and satellite measurements of atmospheric aerosol loading, surface open fire, and tropospheric NO x, the large amount of SLCF/P reaching the NCO-P appeared to be related to natural (mineral dust) and anthropogenic emissions occurring within the PBL of central Pakistan (i.e., Thar Desert), the Northwestern Indo-Gangetic plain, and the Himalayan foothills. The systematic occurrence of these events appeared to represent the most important source of SLCF/P inputs into the central Himalayas during the summer monsoon onset period, with possible important implications for the regional climate and for hydrological cycles. (letter)

  6. Arabian Peninsula-North Pacific Oscillation and its association with the Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Using correlation and EOF analyses on sea level pressure from 57-year NCEP-NCAR reanalysis data, the Arabian Peninsula-North Pacific Oscillation (APNPO) is identified. The APNPO reflects the co-variability between the North Pacific high and South Asian summer monsoon low. This teleconnec- tion pattern is closely related to the Asian summer monsoon. On interannual timescale, it co-varies with both the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM); on decadal timescale, it co-varies with the EASM: both exhibit two abrupt climate changes in the middle 1960s and the late 1970s respectively. The possible physical process for the connections between the APNPO and Asian summer monsoon is then explored by analyzing the APNPO-related atmospheric circulations. The results show that with a strong APNPO, the Somali Jet, SASM flow, EASM flow, and South Asian high are all enhanced, and an anomalous anticyclone is produced at the upper level over northeast China via a zonal wave train. Meanwhile, the moisture transportation to the Asian monsoon regions is also strengthened in a strong APNPO year, leading to a strong moisture convergence over India and northern China. All these changes of circulations and moisture conditions finally result in an anoma- lous Asian summer monsoon and monsoon rainfall over India and northern China. In addition, the APNPO has a good persistence from spring to summer. The spring APNPO is also significantly corre- lated with Asian summer monsoon variability. The spring APNPO might therefore provide valuable in- formation for the prediction of Asian summer monsoon.

  7. North Atlantic, ITCZ, and Monsoonal Climate Links

    Science.gov (United States)

    Haug, G. H.; Deplazes, G.; Peterson, L. C.; Brauer, A.; Mingram, J.; Dulski, P.; Sigman, D. M.

    2008-12-01

    Major element chemistry and color data from sediment cores in the anoxic Cariaco Basin off Venezuela record with (sub)annual resolution large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the last 80 ka. These data suggest a direct connection between the position of the ITCZ over northern South America, the strength of trade winds, and the temperature gradient to the high northern latitudes, ENSO, and monsoonal climate in Asia. The mechanisms behind these decadal-scale ITCZ-monsoon swings can be further explored at major climate transitions such as the onset of Younger Dryas cooling at ~12.7 ka, one of the most abrupt climate changes observed in ice core, lake and marine records in the North Atlantic realm and much of the Northern Hemisphere. Annually laminated sediments from ideally record the dynamics of abrupt climate changes since seasonal deposition immediately responds to climate and varve counts accurately estimate the time of change. We compare sub-annual geochemical data from a lake in Western Germany, which provides one of the best-dated records currently available for this climate transition, with the new the Cariaco Basin record and a new and higher resolution record from Lake Huguang Maar in China, and the Greenland ice core record. The Lake Meerfelder Maar record indicates an abrupt increase in storminess, occurring from one year to the next at 12,678 ka BP, coincident with other observed climate changes in the region. We interpret this shift of the wintertime winds to signify an abrupt change in the North Atlantic westerlies to a stronger and more zonal jet. The observed wind shift provides the atmospheric mechanism for the strong temporal link between North Atlantic overturning and European climate during the last deglaciation, tightly coupled to ITCZ migrations observed in the Cariaco Basin sediments, and a stronger east Asian Monsoon winter monsoon as seen in lake Huguang Maar, when cave stalagmite oxygen isotope data

  8. DETERMINATION OF SOUTH CHINA SEA MONSOON ONSET AND EAST ASIAN SUMMER MONSOON INDEX

    Institute of Scientific and Technical Information of China (English)

    GAO-Hui; LIANG Jian-yin

    2006-01-01

    Results of the definition of South China Sea summer monsoon onset date and East Asian summer monsoon index in recent years are summarized in this paper. And more questions to be resolved are introduced later.

  9. South Asian High and Asian-Pacific-American Climate Teleconnection

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Growing evidence indicates that the Asian monsoon plays an important role in affecting the weather and climate outside of Asia. However, this active role of the monsoon has not been demonstrated as thoroughly as has the variability of the monsoon caused by various impacting factors such as sea surface temperature and land surface. This study investigates the relationship between the Asian monsoon and the climate anomalies in the Asian-Pacific-American (APA) sector. A hypothesis is tested that the variability of the upper-tropospheric South Asian high (SAH), which is closely associated with the overall heating of the large-scale Asian monsoon, is linked to changes in the subtropical western Pacific high (SWPH), the midPacific trough, and the Mexican high. The changes in these circulation systems cause variability in surface temperature and precipitation in the APA region. A stronger SAH is accompanied by a stronger and more extensive SWPH. The enlargement of the SWPH weakens the mid-Pacific trough. As a result, the southern portion of the Mexican high becomes stronger. These changes are associated with changes in atmospheric teleconnections, precipitation, and surface temperature throughout the APA region. When the SAH is stronger, precipitation increases in southern Asia, decreases over the Pacific Ocean, and increases over the Central America. Precipitation also increases over Australia and central Africa and decreases in the Mediterranean region. While the signals in surface temperature are weak over the tropical land portion,they are apparent in the mid latitudes and over the eastern Pacific Ocean.

  10. A solar variability driven monsoon see-saw: switching relationships of the Holocene East Asian-Australian summer monsoons

    Science.gov (United States)

    Eroglu, Deniz; Ozken, Ibrahim; McRobie, Fiona; Stemler, Thomas; Marwan, Norbert; Wyrwoll, Karl-Heinz; Kurths, Juergen

    2016-04-01

    The East Asian-Indonesian-Australian monsoon is the predominant low latitude monsoon system, providing a major global scale heat source. Here we apply newly developed non-linear time series techniques on speleothem climate proxies, from eastern China and northwestern Australia and establish relationships between the two summer monsoon regimes over the last ˜9000 years. We identify significant variations in monsoonal activity, both dry and wet phases, at millennial to multi-centennial time scales and demonstrate for the first time the existence of a see-saw antiphase relationship between the two regional monsoon systems. Our analysis attributes this inter-hemispheric linkage to the solar variability that is effecting both monsoon systems.

  11. Asian Summer Monsoon and its Associated Rainfall Variability in Thailand

    Directory of Open Access Journals (Sweden)

    Atsamon Limsakul

    2010-07-01

    Full Text Available The Asian monsoon is an important component of the Earth's climate. Its associated rainfall variability is a crucial fac¬tor for Thailand's socio-economic development, water resources and agricultural management. An analysis shows that the Thailand rainfall annual cycle is in phase with the Indian summer monsoon (ISM and the western North Pacific summer monsoon (WNPSM. On the basis of the Empirical Orthogonal Function (EOF analysis, the dominant spatial-temporal interannual variability in summer monsoon rainfall (Jun.-Sep. during 1975-2006 could be explained by the first two EOF modes, accounting for 34% of the total variance. The EOF1 was spatially dominated by strong positive signals in the central and east, whereas the EOF2 exhibited dipole variability. The coefficient time series of EOF1 significantly correlated posi¬tively with ISM index, but negatively with WNPSM index. The results suggest that summer monsoon rainfall in Thailand is higher (lower than normal during the strengthening (weakening of ISM. In contrast, rainfall in the north-east (central is surplus (deficit during the strengthening (weakening of WNPSM. These findings imply that, on an interannual time scale, ISM and WNPSM exert their influence to a different extent on summer monsoon rainfall in Thailand. A clear picture of linking mechanisms and interactions with another climate mode in the Indo-Pacific sector needs to be understood. This knowledge is essential for effectively adapting to climate-related hazards and rainfall extremes and for better management of water resource and agriculture in Thailand, especially under current/future warming conditions.

  12. The East Asian subtropical summer monsoon: Recent progress

    Science.gov (United States)

    He, Jinhai; Liu, Boqi

    2016-04-01

    The East Asian subtropical summer monsoon (EASSM) is one component of the East Asian summer monsoon system, and its evolution determines the weather and climate over East China. In the present paper, we firstly demonstrate the formation and advancement of the EASSM rainbelt and its associated circulation and precipitation patterns through reviewing recent studies and our own analysis based on JRA-55 (Japanese 55-yr Reanalysis) data and CMAP (CPC Merged Analysis of Precipitation), GPCP (Global Precipitation Climatology Project), and TRMM (Tropical Rainfall Measuring Mission) precipitation data. The results show that the rainy season of the EASSM starts over the region to the south of the Yangtze River in early April, with the establishment of strong southerly wind in situ. The EASSM rainfall, which is composed of dominant convective and minor stratiform precipitation, is always accompanied by a frontal system and separated from the tropical summer monsoon system. It moves northward following the onset of the South China Sea summer monsoon. Moreover, the role of the land-sea thermal contrast in the formation and maintenance of the EASSM is illustrated, including in particular the effect of the seasonal transition of the zonal land-sea thermal contrast and the influences from the Tibetan Plateau and midlatitudes. In addition, we reveal a possible reason for the subtropical climate difference between East Asia and East America. Finally, the multi-scale variability of the EASSM and its influential factors are summarized to uncover possible reasons for the intraseasonal, interannual, and interdecadal variability of the EASSM and their importance in climate prediction.

  13. CMIP5/AMIP GCM simulations of East Asian summer monsoon

    Science.gov (United States)

    Feng, Jinming; Wei, Ting; Dong, Wenjie; Wu, Qizhong; Wang, Yongli

    2014-07-01

    The East Asian summer monsoon (EASM) is a distinctive component of the Asian climate system and critically influences the economy and society of the region. To understand the ability of AGCMs in capturing the major features of EASM, 10 models that participated in Coupled Model Intercomparison Project/Atmospheric Model Intercomparison Project (CMIP5/AMIP), which used observational SST and sea ice to drive AGCMs during the period 1979-2008, were evaluated by comparing with observations and AMIP II simulations. The results indicated that the multi-model ensemble (MME) of CMIP5/AMIP captures the main characteristics of precipitation and monsoon circulation, and shows the best skill in EASM simulation, better than the AMIP II MME. As for the Meiyu/Changma/Baiyu rainbelt, the intensity of rainfall is underestimated in all the models. The biases are caused by a weak western Pacific subtropical high (WPSH) and accompanying eastward southwesterly winds in group I models, and by a too strong and west-extended WPSH as well as westerly winds in group II models. Considerable systematic errors exist in the simulated seasonal migration of rainfall, and the notable northward jumps and rainfall persistence remain a challenge for all the models. However, the CMIP5/AMIP MME is skillful in simulating the western North Pacific monsoon index (WNPMI).

  14. Asian monsoon extremes and humanity's response over the past millennium

    Science.gov (United States)

    Buckley, B. M.; Lieberman, V. B.; Zottoli, B.

    2012-12-01

    The first decade of the 21st century has seen significant development in the production of paleo proxies for the Asian monsoon, exemplified by the Monsoon Asian Drought Atlas that was comprised of more than 300 tree ring chronologies. Noteworthy among them is the Vietnamese cypress tree-ring record which reveals that the two worst droughts of the past 7 centuries, each more than a decade in length, coincided with the demise of the Khmer civilization at Angkor in the early 15th century CE. The 18th century was nearly as tumultuous a period across Southeast Asia, where several polities fell against a backdrop of epic decadal-scale droughts. At this time all of the region's charter states saw rapid realignment in the face of drought, famine, disease and a raft of related and unrelated social issues. Several other droughts, some more extreme but of lesser duration, punctuate the past millennium, but appear to have had little societal impact. Historical documentation is being used not only to provide corroborative evidence of tree-ring reconstructed climate extremes, but to attempt to understand the dynamics of the coupled human-natural systems involved, and to define what kinds of thresholds need to be reached before societies respond. This paleo perspective can assist our analyses of the role of climate extremes in the collapse or disruption of regional societies, a subject of increasing concern given the uncertainties surrounding projections for future climate across the highly populated areas of Asia.

  15. The Joint Aerosol-Monsoon Experiment: A New Challenge to Monsoon Climate Research

    Science.gov (United States)

    Lau, William K. M.

    2008-01-01

    Aerosol and monsoon related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. In recent years, thanks to improved satellite and in-situ observations, and better models, great strides have been made in aerosol, and monsoon research respectively. There is now a growing body of evidence suggesting that interaction of aerosol forcing with water cycle dynamics in monsoon regions may substantially alter the redistribution of energy at the earth surface and in the atmosphere, and therefore significantly impact monsoon rainfall variability and long term trends. In this talk, I will describe issues related to societal needs, scientific background, and challenges in studies of aerosol-water cycle interaction in Asian monsoon regions. As a first step towards addressing these issues, the authors call for an integrated observation and modeling research approach aimed at the interactions between aerosol chemistry and radiative effects and monsoon dynamics of the coupled ocean-atmosphere-land system. A Joint Aerosol-Monsoon Experiment (JAMEX) is proposed for 2007-2011, with an enhanced observation period during 2008-09, encompassing diverse arrays of observations from surface, aircraft, unmanned aerial vehicles, and satellites of physical and chemical properties of aerosols, long range aerosol transport as well as meteorological and oceanographic parameters in the Indo-Pacific Asian monsoon region. JAMEX will leverage on coordination among many ongoing and planned national programs on aerosols and monsoon research in China, India, Japan, Nepal, Italy, US, as well as international research programs of the World Climate Research Program (WCRP) and the World Meteorological Organization (WMO).

  16. Effect of precession on the Asian summer monsoon evolution: A systematic review

    Institute of Scientific and Technical Information of China (English)

    LIU XiaoDong; SHI ZhengGuo

    2009-01-01

    Geological climatic records and model simulations on the Asian summer monsoon climate change induced by insolation forcing of the Earth's precession are systematically reviewed in this paper. The presentation of the questions on the mechanism of the Asian monsoon evolution at the precession band, currently existing debates and future research directions are discussed. Since the early 1980s, more and more observed evidence and simulated results, especially the absolute-dated stalagmite re-cords and orbital-scale transient model runs in the last few years, have indicated that the quasi-20ka period in the Quaternary monsoon climate change is caused by precession. However, debates still exist on the dynamic mechanism how precession affects the Asian monsoon. The "zero phase" hypothesis says that the Asian monsoon is merely controlled by summer insolation in the Northern Hemisphere (NH) while the "latent heat" hypothesis emphasizes the dominant effect of latent heat transport from the Southern Hemisphere (SH) besides the role of the northern insolation. The two hypotheses have separately been supported by some evidence. Although we are cognizant of the importance of northern solar radiation and the remote effect of southern insolation, it has still a long way to go before com-prehensively understanding the evolutionary mechanism of the Asian monsoon. In view of the prob-lems existing in present researches of monsoon-dominated climate change at the precession scale, we propose that studies on the environmental significance of geological monsoon proxies, feedback processes in the long-term transient simulations and intercomparisons between observations and modeling results should be strengthened in the future.

  17. Comparison of East Asian winter monsoon indices

    Directory of Open Access Journals (Sweden)

    Gao Hui

    2007-01-01

    Full Text Available Four East Asian winter monsoon (EAWM indices are compared in this paper. In the research periods, all the indices show similar interannual and decadal-interdecadal variations, with predominant periods centering in 3–4 years, 6.5 years and 9–15 years, respectively. Besides, all the indices show remarkable weakening trends since the 1980s. The correlation coefficient of each two indices is positive with a significance level of 99%. Both the correlation analyses and the composites indicate that in stronger EAWM years, the Siberian high and the higher-level subtropical westerly jet are stronger, and the Aleutian low and the East Asia trough are deeper. This circulation pattern is favorable for much stronger northwesterly wind and lower air temperature in the subtropical regions of East Asia, while it is on the opposite in weaker EAWM years. Besides, EAWM can also exert a remarkable leading effect on the summer monsoon. After stronger (weaker EAWM, less (more summer precipitation is seen over the regions from the Yangtze River valley of China to southern Japan, while more (less from South China Sea to the tropical western Pacific.

  18. The Aerosol-Monsoon Climate System of Asia

    Science.gov (United States)

    Lau, William K. M.; Kyu-Myong, Kim

    2012-01-01

    In Asian monsoon countries such as China and India, human health and safety problems caused by air-pollution are worsening due to the increased loading of atmospheric pollutants stemming from rising energy demand associated with the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon rain associated with flash flood or prolonged drought, has caused major loss of human lives, and damages in crop and properties with devastating societal impacts on Asian countries. Historically, air-pollution and monsoon research are treated as separate problems. However a growing number of recent studies have suggested that the two problems may be intrinsically intertwined and need to be studied jointly. Because of complexity of the dynamics of the monsoon systems, aerosol impacts on monsoons and vice versa must be studied and understood in the context of aerosol forcing in relationship to changes in fundamental driving forces of the monsoon climate system (e.g. sea surface temperature, land-sea contrast etc.) on time scales from intraseasonal variability (weeks) to climate change ( multi-decades). Indeed, because of the large contributions of aerosols to the global and regional energy balance of the atmosphere and earth surface, and possible effects of the microphysics of clouds and precipitation, a better understanding of the response to climate change in Asian monsoon regions requires that aerosols be considered as an integral component of a fully coupled aerosol-monsoon system on all time scales. In this paper, using observations and results from climate modeling, we will discuss the coherent variability of the coupled aerosol-monsoon climate system in South Asia and East Asia, including aerosol distribution and types, with respect to rainfall, moisture, winds, land-sea thermal contrast, heat sources and sink distributions in the atmosphere in seasonal, interannual to climate change time scales. We will show examples of how elevated

  19. Catastrophic drought in East Asian monsoon region during Heinrich event 1

    Science.gov (United States)

    Zhou, Xin; Sun, Liguang; Chu, Yangxi; Xia, Zehui; Zhou, Xinying; Li, Xiangzhong; Chu, Zhuding; Liu, Xiangjun; Shao, Da; Wang, Yuhong

    2016-06-01

    Heinrich event 1 (H1) is an important millennial climate event during the last deglaciation. The substantial decreasing of monsoon strength in the East Asian monsoon region during the H1, as shown by stalagmite δ18O records, has been attributed to the southward shift of the intertropical convergence zone (ITCZ), which is caused by the slowdown/collapse of the Atlantic meridional overturning circulation (AMOC). However, records from different Asian monsoon regions show various trends in precipitation changes during the H1, and these trends cannot be solely interpreted by the southward shift of the ITCZ. In the present study, we reconstructed time-series of East Asian monsoon precipitation between 25,000 and 10,000 a BP from floodplain sediments in the Huai River Basin. A white sediment layer, distinct from other layers in the profile, contains significantly low TOC, tree pollen and fern spore contents, and more positive δ13Corg, and it is deposited during the H1 event. The determined TOC, pollen and δ13Corg time-series, together with previously reported stalagmite δ18O, indicate a catastrophic (severe) drought in Jianghuai Region, one of the East Asian monsoon regions, during the H1. The La Niña condition in tropical Pacific likely also contributes to the catastrophic drought in Jianghuai Region and the precipitation variations in the Asian monsoon region during the H1.

  20. Global Monsoon Dynamics and Climate Change

    Science.gov (United States)

    Zhisheng, An; Guoxiong, Wu; Jianping, Li; Youbin, Sun; Yimin, Liu; Weijian, Zhou; Yanjun, Cai; Anmin, Duan; Li, Li; Jiangyu, Mao; Hai, Cheng; Zhengguo, Shi; Liangcheng, Tan; Hong, Yan; Hong, Ao; Hong, Chang; Juan, Feng

    2015-05-01

    This article provides a comprehensive review of the global monsoon that encompasses findings from studies of both modern monsoons and paleomonsoons. We introduce a definition for the global monsoon that incorporates its three-dimensional distribution and ultimate causes, emphasizing the direct drive of seasonal pressure system changes on monsoon circulation and depicting the intensity in terms of both circulation and precipitation. We explore the global monsoon climate changes across a wide range of timescales from tectonic to intraseasonal. Common features of the global monsoon are global homogeneity, regional diversity, seasonality, quasi-periodicity, irregularity, instability, and asynchroneity. We emphasize the importance of solar insolation, Earth orbital parameters, underlying surface properties, and land-air-sea interactions for global monsoon dynamics. We discuss the primary driving force of monsoon variability on each timescale and the relationships among dynamics on multiple timescales. Natural processes and anthropogenic impacts are of great significance to the understanding of future global monsoon behavior.

  1. Assessment of the Impact of The East Asian Summer Monsoon on the Air Quality Over China

    Science.gov (United States)

    Hao, Nan; Ding, Aijun; Safieddine, Sarah; Valks, Pieter; Clerbaux, Cathy; Trautmann, Thomas

    2016-04-01

    Air pollution is one of the most important environmental problems in developing Asian countries like China. In this region, studies showed that the East Asian monsoon plays a significant role in characterizing the temporal variation and spatial patterns of air pollution, since monsoon is a major atmospheric system affecting air mass transport, convection, and precipitation. Knowledge gaps still exist in the understanding of Asian monsoon impact on the air quality in China under the background of global climate change. For the first time satellite observations of tropospheric ozone and its precursors will be integrated with the ground-based, aircraft measurements of air pollutants and model simulations to study the impact of the East Asian monsoon on air quality in China. We apply multi-platform satellite observations by the GOME-2, IASI, and MOPITT instruments to analyze tropospheric ozone and CO, precursors of ozone (NO2, HCHO and CHOCHO) and other related trace gases over China. Two years measurements of air pollutants including NO2, HONO, SO2, HCHO and CHOCHO at a regional back-ground site in the western part of the Yangtze River Delta (YRD) in eastern China will be presented. The potential of using the current generation of satellite instruments, ground-based instruments and aircraft to monitor air quality changes caused by the East Asian monsoon circulation will be presented. Preliminary comparison results between satellite measurement and limited but valuable ground-based and aircraft measurements will also be showed.

  2. Study on response of ecosystem to the East Asian monsoon in eastern China using LAI data derived from remote sensing information

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jiahua; YAO Fengmei; FU Congbin; YAN Xiaodong

    2004-01-01

    Based on the leaf area index (LAI) data derived from remote sensing information and eco-climate data, the responses of regional ecosystem variations in seasonal and interannual scales to the East Asian monsoon are studied. It is found that the vegetation ecosystems of eastern China are remarkably correlated with the East Asian monsoon in seasonal and interannual scales. In the seasonal timescale, the obvious variations of the vegetation ecosystems occur with the development of the East Asian monsoon from the south in the spring to the north in the autumn. In the interannual scale, high LAI appears in the strong East Asian monsoon year, whereas low LAI is related to the weak East Asian monsoon year. These further lead to the characteristic of "monsoon-driven ecosystem" in the eastern China monsoon region, which can be revealed by LAI.

  3. EFFECT OF THE INDIAN PENINSULA ON THE COURSE OF THE ASIAN TROPICAL SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    徐海明; 何金海; 董敏

    2001-01-01

    In terms of the NCAR Community Climate Model (CCM3), the effect of the Indian Peninsula on the course of the Asian tropical summer monsoon is simulated in this paper, and numerical experimental results show that the Indian Peninsula plays a critical role in the establishment process of the Asian tropical summer monsoon. When the CCM3 includes the Indian Peninsula,the model successfully simulates out the course of the Asian tropical summer monsoon, i.e. the South China Sea (SCS) summer monsoon at first bursts in middle May, while the Indian monsoon just establishes until middle June. However when the Indian Peninsula topography is deleted in the model, the Indian and SCS summer monsoons almost simultaneously establish in late May.Numerical results further indicate that in the former experiment the sensible heating of the Indian Peninsula warms the air above and produces evident temperature contrast between the peninsula and its adjacent SCS and Bay of Bengal (BOB), which results in the strengthening and maintenance of the BOB trough in the low-middle layer of the troposphere in the end of spring and early summer and thus the earliest establishment of the Asian tropical summer monsoon in the SCS in middle May. However, the Indian summer monsoon just establishes until middle June when the strong west wind over the Arabian Sea shifts northwards and cancels out the influence of the northwest flow behind the BOB trough. In the latter experiment the effect of Tibetan Plateau only produces a very weak BOB trough, and thus the SCS and Indian summer monsoons almost simultaneously establish.

  4. Influence of Decadal Variability of Global Oceans on South Asian Monsoon and ENSO-Monsoon Relation

    Science.gov (United States)

    Krishnamurthy, Lakshmi

    This study has investigated the influence of the decadal variability associated with global oceans on South Asian monsoon and El Nino-Southern Oscillation (ENSO)-monsoon relation. The results are based on observational analysis using long records of monsoon rainfall and circulation and coupled general circulation model experiments using the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM) version 4 model. The multi-channel singular spectrum analysis (MSSA) of the observed rainfall over India yields three decadal modes. The first mode (52 year period) is associated with the Atlantic Multidecadal Oscillation (AMO), the second one (21 year) with the Pacific Decadal Oscillation (PDO) and the third mode (13 year) with the Atlantic tripole. The existence of these decadal modes in the monsoon was also found in the control simulation of NCAR CCSM4. The regionally de-coupled model experiments performed to isolate the influence of North Pacific and North Atlantic also substantiate the above results. The relation between the decadal modes in the monsoon rainfall with the known decadal modes in global SST is examined. The PDO has significant negative correlation with the Indian Monsoon Rainfall (IMR). The mechanism for PDO-monsoon relation is hypothesized through the seasonal footprinting mechanism and further through Walker and Hadley circulations. The model results also confirm the negative correlation between PDO and IMR and the mechanism through which PDO influences monsoon. Both observational and model analysis show that droughts (floods) are more likely over India than floods (droughts) when ENSO and PDO are in their warm (cold) phase. This study emphasizes the importance of carefully distinguishing the different decadal modes in the SST in the North Atlantic Ocean as they have different impacts on the monsoon. The AMO exhibits significant positive correlation with the IMR while the Atlantic tripole has significant negative

  5. Regionalization of Tibetan Plateau precipitation and its relation to the Asian Monsoon

    Science.gov (United States)

    Conroy, J. L.; Overpeck, J. T.

    2008-12-01

    Many paleoclimate records from the Tibetan Plateau link past changes in local precipitation to Southwest (SW, or Indian) and East (E) Asian Monsoon variability. However, few of these records are correlated with instrumental records of local or regional monsoon variability. And, although the majority of Tibetan precipitation occurs in the summer months, a dearth of station data limits the connection of instrumental precipitation variability across Tibet to the Asian Monsoon regimes. To properly interpret proxy climate records, a quantitative understanding of Asian Monsoon influences on the Tibetan Plateau is required. With this goal in mind, we investigated precipitation variability across the Tibetan Plateau using monthly gridded merged precipitation (CMAP) and outgoing longwave radiation (OLR) datasets to quantify the relationship between summer precipitation on the Tibetan Plateau and the SW and E Asian Monsoons. Average summer OLR and precipitation are significantly correlated at the 95% confidence level between southwest, northwest, southeast Tibet and the central Himalayas, but average summer OLR and precipitation in northeast Tibet is only significantly correlated with OLR and precipitation in southeastern Tibet. OLR over the central Himalayas, southwest Tibet, and northwest Tibet correlates at the 95% confidence level with the Indian Monsoon Index, and precipitation in the central Himalayas correlates at the 95% confidence level with the Webster-Yang Index of SW Monsoon variability. OLR and precipitation over the central Himalayas, southwest Tibet, and northwest Tibet also significantly correlate with OLR and precipitation over India, as well as surface wind speed, 850 mb zonal, and 850 mb meridional wind speeds over the southwest Arabian Sea. These significant correlations indicate precipitation variability over western Tibet and the central Himalayas is related to SW Asian Monsoon variability. Correlations between southeastern and northeastern Tibet OLR

  6. Asian Summer Monsoon Intraseasonal Variability in General Circulation Models

    Energy Technology Data Exchange (ETDEWEB)

    Sperber, K R; Annamalai, H

    2004-02-24

    The goals of this report are: (1) Analyze boreal summer Asian monsoon intraseasonal variability general circulation models--How well do the models represent the eastward and northward propagating components of the convection and how well do the models represent the interactive control that the western tropical Pacific rainfall exerts on the rainfall over India and vice-versa? (2) Role of air-sea interactions--prescribed vs. interactive ocean; and (3) Mean monsoon vs. variability.

  7. An Abrupt Centennial-Scale Drought Event and Mid-Holocene Climate Change Patterns in Monsoon Marginal Zones of East Asia

    OpenAIRE

    LI Yu; Wang, Nai'ang; Zhang, Chengqi

    2014-01-01

    The mid-latitudes of East Asia are characterized by the interaction between the Asian summer monsoon and the westerly winds. Understanding long-term climate change in the marginal regions of the Asian monsoon is critical for understanding the millennial-scale interactions between the Asian monsoon and the westerly winds. Abrupt climate events are always associated with changes in large-scale circulation patterns; therefore, investigations into abrupt climate changes provide clues for response...

  8. A regional ocean-atmosphere coupled model developed for CORDEX East Asia: assessment of Asian summer monsoon simulation

    Science.gov (United States)

    Zou, Liwei; Zhou, Tianjun

    2016-02-01

    In this study, a developed regional ocean-atmosphere coupled model FROALS was applied to the CORDEX East Asia domain. The performance of FROALS in the simulation of Asian summer monsoon during 1989-2010 was assessed using the metrics developed by the CLIVAR Asian-Australian Monsoon Panel Diagnostics Task Team. The results indicated that FROALS exhibited good performance in simulating Asian summer monsoon climatology. The simulated JJA mean SST biases were weaker than those of the CMIP5 multi-model ensemble mean (MMEM). The skill of FROALS approached that of CMIP5 MMEM in terms of the annual cycle of Asian summer monsoon. The simulated monsoon duration matched the observed counterpart well (with a spatial pattern correlation coefficient of 0.59). Some biases of CMIP5 MMEM were also found in FROALS, highlighting the importance of local forcing and model physics within the Asian monsoon domain. Corresponding to a strong East Asian summer monsoon, an anomalous anticyclone was found over western North Pacific in both observation and simulation. However, the simulated strength was weaker than the observed due to the responses to incorrect sea surface anomalies over the key regions. The model also accurately captured the spatial pattern of the intraseasonal variability variance and the extreme climate indices of Asian summer monsoons, although with larger amplitude. The results suggest that FROALS could be used as a dynamical downscaling tool nested within the global climate model with coarse resolution to develop high-resolution regional climate change projections over the CORDEX East Asia domain.

  9. Deciphering the desiccation trend of the South Asian monsoon hydroclimate in a warming world

    Science.gov (United States)

    Krishnan, R.; Sabin, T. P.; Vellore, R.; Mujumdar, M.; Sanjay, J.; Goswami, B. N.; Hourdin, F.; Dufresne, J.-L.; Terray, P.

    2016-08-01

    Rising propensity of precipitation extremes and concomitant decline of summer-monsoon rains are amongst the most distinctive hydroclimatic signals that have emerged over South Asia since 1950s. A clear understanding of the underlying causes driving these monsoon hydroclimatic signals has remained elusive. Using a state-of-the-art global climate model with high-resolution zooming over South Asia, we demonstrate that a juxtaposition of regional land-use changes, anthropogenic-aerosol forcing and the rapid warming signal of the equatorial Indian Ocean is crucial to produce the observed monsoon weakening in recent decades. Our findings also show that this monsoonal weakening significantly enhances occurrence of localized intense precipitation events, as compared to the global-warming response. A 21st century climate projection using the same high-resolution model indicates persistent decrease of monsoonal rains and prolongation of soil drying. Critical value-additions from this study include (1) realistic simulation of the mean and long-term historical trends in the Indian monsoon rainfall (2) robust attributions of changes in moderate and heavy precipitation events over Central India (3) a 21st century projection of drying trend of the South Asian monsoon. The present findings have profound bearing on the regional water-security, which is already under severe hydrological-stress.

  10. An Index Measuring the Interannual Variation of the East Asian Summer Monsoon--The EAP Index

    Institute of Scientific and Technical Information of China (English)

    黄刚

    2004-01-01

    Based on the EAP (East Asia/Pacific) teleconnection in the summer circulation anomalies over the Northern Hemisphere,an index measuring the strength of the East Asian summer monsoon,i.e.,the socalled EAP index,is defined in this paper.From the analyses of observed data,it is clearly shown that the EAP index defined in this study can well describe the interannual variability of summer rainfall and surfaceair temperature in East Asia,especially in the Yangtze River valley and the Hualhe River valley,Korea,and Japan.Moreover,this index can also reflect the interannual variability of the East Asian summer monsoon system including the monsoon horizontal circulation and the vertical-merldional circulation cell over East Asia.From the composite analyses of climate and monsoon circulation anomalies for high EAP index and for low EAP index,respectively,it is well demonstrated that the EAP index proposed in this study can well measure the strength of the East Asian summer monsoon.

  11. South Asian monsoon: Tug of war on rainfall changes

    Science.gov (United States)

    Singh, Deepti

    2016-01-01

    Precipitation associated with the South Asian summer monsoon has decreased by approximately 7% since 1950, but the reasons for this are unclear. Now research suggests that changes in land-cover patterns and increased emissions from human activities have contributed to this weakening, which is expected to continue in the coming decades.

  12. Late Miocene-Pliocene Asian monsoon intensification linked to Antarctic ice-sheet growth

    Science.gov (United States)

    Ao, Hong; Roberts, Andrew P.; Dekkers, Mark J.; Liu, Xiaodong; Rohling, Eelco J.; Shi, Zhengguo; An, Zhisheng; Zhao, Xiang

    2016-06-01

    Environmental conditions in one of Earth's most densely populated regions, East Asia, are dominated by the monsoon. While Quaternary monsoon variability is reasonably well understood, pre-Quaternary monsoon variability and dynamics remain enigmatic. In particular, little is known about potential relationships between northern hemispheric monsoon response and major Cenozoic changes in Antarctic ice cover. Here we document long-term East Asian summer monsoon (EASM) intensification through the Late Miocene-Pliocene (∼8.2 to 2.6 Ma), and attribute this to progressive Antarctic glaciation. Our new high-resolution magnetic records of long-term EASM intensification come from the Late Miocene-Pliocene Red Clay sequence on the Chinese Loess Plateau; we identify underlying mechanisms using a numerical climate-model simulation of EASM response to an idealized stepwise increase in Antarctic ice volume. We infer that progressive Antarctic glaciation caused intensification of the cross-equatorial pressure gradient between an atmospheric high-pressure cell over Australia and a low-pressure cell over mid-latitude East Asia, as well as intensification of the cross-equatorial sea-surface temperature (SST) gradient. These combined atmospheric and oceanic adjustments led to EASM intensification. Our findings offer a new and more global perspective on the controls behind long-term Asian monsoon evolution.

  13. Dominating Controls for Wetter South Asian Summer Monsoon in the Twenty-First Century

    Energy Technology Data Exchange (ETDEWEB)

    Mei, Rui; Ashfaq, Moetasim; Rastogi, Deeksha; Leung, Lai-Yung R.; Dominguez, Francina

    2015-04-01

    We analyze a suite of Global Climate Models from the 5th Phase of Coupled Models Intercomparison Project (CMIP5) archives to understand the mechanisms behind a net increase in the South Asian summer monsoon precipitation in response to enhanced radiative forcing during the 21st century despite a robust weakening of dynamics governing the monsoon circulation. Combining the future changes in the contributions from various sources, which contribute to the moisture supply over South Asia, with those in monsoon dynamics and atmospheric moisture content, we establish a pathway of understanding that partly explains these counteracting responses to increase in radiative forcing. Our analysis suggests that both regional (local recycling, Arabian Sea, Bay of Bengal) and remote (mainly Indian Ocean) sources contribute to the moisture supply for precipitation over South Asia during the summer season that is facilitated by the monsoon dynamics. Increase in radiative forcing fuels an increase in the atmospheric moisture content through warmer temperatures. For regional moisture sources, the effect of excessive atmospheric moisture is offset by weaker monsoon circulation and uncertainty in the response of the evapotranspiration over land, so anomalies in their contribution to the total moisture supply are either mixed or muted. In contrast, weakening of the monsoon dynamics has less influence on the moisture supply from remote sources that not only is a dominant moisture contributor in the historical period, but is also the net driver of the positive summer monsoon precipitation response in the 21st century. Our results also indicate that historic measures of the monsoon dynamics may not be well suited to predict the non-stationary moisture driven South Asian summer monsoon precipitation response in the 21st century.

  14. Seasonally asymmetric transition of the Asian monsoon in response to ice age boundary conditions

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Hiroaki; Kuroki, Harumitsu; Kamae, Youichi [University of Tsukuba, Graduate School of Life and Environmental Sciences, Tsukuba, Ibaraki (Japan); Ohba, Masamichi [Central Research Institute of Electric Power Industry, Environmental Science Research Laboratory, Abiko (Japan)

    2011-12-15

    Modulation of a monsoon under glacial forcing is examined using an atmosphere-ocean coupled general circulation model (AOGCM) following the specifications established by Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) to understand the air-sea-land interaction under different climate forcing. Several sensitivity experiments are performed in response to individual changes in the continental ice sheet, orbital parameters, and sea surface temperature (SST) in the Last Glacial Maximum (LGM: 21 ka) to evaluate the driving mechanisms for the anomalous seasonal evolution of the monsoon. Comparison of the model results in the LGM with the pre-industrial (PI) simulation shows that the Arabian Sea and Bay of Bengal are characterized by enhancement of pre-monsoon convection despite a drop in the SST encompassing the globe, while the rainfall is considerably suppressed in the subsequent monsoon period. In the LGM winter relative to the PI, anomalies in the meridional temperature gradient (MTG) between the Asian continents minus the tropical oceans become positive and are consistent with the intensified pre-monsoon circulation. The enhanced MTG anomalies can be explained by a decrease in the condensation heating relevant to the suppressed tropical convection as well as positive insolation anomalies in the higher latitude, showing an opposing view to a warmer future climate. It is also evident that a latitudinal gradient in the SST across the equator plays an important role in the enhancement of pre-monsoon rainfall. As for the summer, the sensitivity experiments imply that two ice sheets over the northern hemisphere cools the air temperature over the Asian continent, which is consistent with the reduction of MTG involved in the attenuated monsoon. The surplus pre-monsoon convection causes a decrease in the SST through increased heat loss from the ocean surface; in other words, negative ocean feedback is also responsible for the subsequent weakening of summer

  15. Seasonal cycle of the zonal land-sea thermal contrast and East Asian subtropical monsoon circulation

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Based on analysis of the climatic temperature latitudinal deviation on middle troposphere,its seasonal cycle suggests that due to the rapid warming from eastern China continent to the east of Tibetan Plateau and the heating of Tibetan Plateeu in spring,seasonal transition of the thermal difference between East Asia continent and West Pacific first takes place in the subtropical region with greatest intensity.On the accompanying low troposphere,the prevailing wind turns from northerly in winter to southerly in summer with the convection precipitation occurring at the same time.This maybe indicates the onset of the East Asian subtropical summer monsoon.Consequently,we advice that the seasonal cycle formed by the zonal thermal contrast between Asian continent and West Pacific may be an independent driving force of East Asian SUbtropical monsoon.

  16. Anomalies of the Asian Monsoon Induced by Aerosol Forcings

    Science.gov (United States)

    Lau, William K. M.; Kim, M. K.

    2004-01-01

    Impacts of aerosols on the Asian summer monsoon are studied using the NASA finite volume General Circulation Model (fvGCM), with radiative forcing derived from three-dimensional distributions of five aerosol species i.e., black carbon, organic carbon, soil dust, and sea salt from the Goddard Chemistry Aerosol Radiation and Transport Model (GOCART). Results show that absorbing aerosols, i.e., black carbon and dust, induce large-scale upper-level heating anomaly over the Tibetan Plateau in April and May, ushering in & early onset of the Indian summer monsoon. Absorbing aerosols also I i enhance lower-level heating and anomalous ascent over northern India, intensifying the Indian monsoon. Overall, the aerosol-induced large-scale surface' temperature cooling leads to a reduction of monsoon rainfall over the East Asia continent, and adjacent oceanic regions.

  17. The influence of obliquity in the early Holocene Asian summer monsoon

    Science.gov (United States)

    Wu, Chi-Hua; Lee, Shih-Yu; Chiang, John C. H.; Hsu, Huang-Hsiung

    2016-05-01

    The early Holocene climatic optimum is associated with perihelion precession and high obliquity, though most studies emphasize the former over the latter. Asian monsoon proxy records only decisively show the precessional impact. To explore the obliquity effect, four climate simulations are conducted by fixing orbital parameters of present-day (0K), early Holocene (11K), the lowest obliquity (31K), and 11K's precession and eccentricity with 31K's obliquity (11Kp31Ko). We show that high obliquity significantly augments the precessional impact by shifting the Asian monsoon farther north than present. By contrast, the present-day monsoon seasonality can still be identified in the simulations with low obliquity. We argue that the upper tropospheric (South Asian) and lower tropospheric (North Pacific) high-pressure systems are affected by the subtropical atmospheric heating changes responding to obliquity. As a consequence, associated with the changes in meridional gradients of geopotential height and temperature made by the heating, midlatitude transient eddies and monsoon-midlatitude interactions are modulated.

  18. Simulation of South-Asian Summer Monsoon in a GCM

    Science.gov (United States)

    Ajayamohan, R. S.

    2007-10-01

    Major characteristics of Indian summer monsoon climate are analyzed using simulations from the upgraded version of Florida State University Global Spectral Model (FSUGSM). The Indian monsoon has been studied in terms of mean precipitation and low-level and upper-level circulation patterns and compared with observations. In addition, the model's fidelity in simulating observed monsoon intraseasonal variability, interannual variability and teleconnection patterns is examined. The model is successful in simulating the major rainbelts over the Indian monsoon region. However, the model exhibits bias in simulating the precipitation bands over the South China Sea and the West Pacific region. Seasonal mean circulation patterns of low-level and upper-level winds are consistent with the model's precipitation pattern. Basic features like onset and peak phase of monsoon are realistically simulated. However, model simulation indicates an early withdrawal of monsoon. Northward propagation of rainbelts over the Indian continent is simulated fairly well, but the propagation is weak over the ocean. The model simulates the meridional dipole structure associated with the monsoon intraseasonal variability realistically. The model is unable to capture the observed interannual variability of monsoon and its teleconnection patterns. Estimate of potential predictability of the model reveals the dominating influence of internal variability over the Indian monsoon region.

  19. Asian monsoon variability, cyclicities, and forcing mechanisms

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    5000 to 1200 years BP (Fig. 4). As a consequence strong monsoon rainfall the out flow of the rivers draining the Himalayan Mountains increased at the end of the deglcaiation, and it was larger than today during the lower and mid Holocene. About 5x...

  20. Dominant control of the South Asian monsoon by orographic insulation versus plateau heating.

    Science.gov (United States)

    Boos, William R; Kuang, Zhiming

    2010-01-14

    The Tibetan plateau, like any landmass, emits energy into the atmosphere in the form of dry heat and water vapour, but its mean surface elevation is more than 5 km above sea level. This elevation is widely held to cause the plateau to serve as a heat source that drives the South Asian summer monsoon, potentially coupling uplift of the plateau to climate changes on geologic timescales. Observations of the present climate, however, do not clearly establish the Tibetan plateau as the dominant thermal forcing in the region: peak upper-tropospheric temperatures during boreal summer are located over continental India, south of the plateau. Here we show that, although Tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model, the large-scale South Asian summer monsoon circulation is otherwise unaffected by removal of the plateau, provided that the narrow orography of the Himalayas and adjacent mountain ranges is preserved. Additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm, moist air over continental India from the cold and dry extratropics. These results call for both a reinterpretation of how South Asian climate may have responded to orographic uplift, and a re-evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades. PMID:20075917

  1. Assessing the effects of the Great Eastern China urbanization on the East Asian summer monsoon by coupling an urban canopy model with a Regional Climate Model

    Science.gov (United States)

    Liu, Z.; Xue, Y.; Liu, S.; Oleson, K. W.

    2012-12-01

    The urbanization causes one of the most significant land cover changes. Especially over the eastern China from Beijing to Shanghai, the great urbanization occurs during the past half century.It modifies the physical characteristics of land surface, including land surface albedo, surface roughness length and aerodynamicresistanceand thermodynamic conduction over land. All of these play very important role in regional climate change. Afteremploying several WRF/Urban models to tests land use and land cover change(LUCC) caused by urbanization in East Asia, we decided to introducea urban canopy submodule,the Community Land surface Model urban scheme(CLMU)to the WRF and coupled with the WRF-SSiB3 regional climate model. The CLMU and SSIB share the similar principal to treat the surface energy and water balances and aerodynamic resistance between land and atmosphere. In the urban module, the energy balances on the five surface conditions are considered separately: building roof, sun side building wall, shade side building wall, pervious land surface and impervious road. The surface turbulence calculation is based on Monin-Obukhov similarity theory. We have made further improvements for the urban module. Over each surface condition, a method to calculate sky view factor (SVF) is developed based on the physically process while most urban models simply provide an empirical value for SVF. Our approach along with other improvement in short and long wave radiation transfer improves the accuracy of long-wave and shortwave radiation processing over urban surface. The force-restore approximation is employed to calculate the temperature of each outer surfaces of building. The inner side temperature is used as the restore term and was assigned as a tuning constant. Based on the nature of the force-restore method and our tests, we decide to employ the air mean temperature of last 72 hours as a restore term, which substantially improve the surface energy balance. We evaluate the

  2. Comparative Study of Performance of CMIP3 GCMs in Simulating the East Asian Monsoon Variability

    Directory of Open Access Journals (Sweden)

    Sahana Paul and Huang-Hsiung Hsu

    2012-01-01

    Full Text Available This study evaluates variability of East Asian Monsoon simulated by 24 coupled general circulation models (GCMs participating in Coupled Model Inter-comparison Project 3 (CMIP3. Fifty years (1950 - 1999 of each _ twentieth-century climate simulation are analyzed and compared with observed data. Both East Asian Summer Monsoon (EASM and East Asian Winter Monsoon (EAWM are considered. Suitable indices are selected to analyze EASM and EAWM. The Wang-Fan index, associated with 850 hPa circulation pattern and tripole rainfall pattern are considered to analyze EASM. ICHENW, associated with 850 hPa circulation pattern, IGONGDY, associated with Siberian High, and ISUNBM, associated with 500 hPa East Asian trough are considered for analysis of EAWM. Inter-decadal and inter-annual variability of the EASM and EAWM are major focus of this study. The results indicate that, amplitude of inter-annual component EASM becomes larger after _ The decadal component shows, weakening trend and switching from positive monsoon phase to negative monsoon phase in mid-80s for both EASM and EAWM. The simulated composite differences between weak and strong monsoon decades by models with above mentioned characteristics are compared with observation for further evaluation. The EASM weakening is associated with weaker southwesterly and stronger anti-cyclonic pattern over Western North Pacific and results in more rainfall in south and north China, Korea, Japan and less rainfall in central China. The EAWM weakening is associated with weakening of Siberian High and temperature rise over East Asia. EASM and EAWM matrices are constructed according to the relative merits of GCMs.

  3. The effect of El-Niño on South Asian Monsoon and agricultural production

    Science.gov (United States)

    Mukherjee, A.

    2015-12-01

    Mukherjee A, Wang S.Y.Abstract:The South Asian Monsoon has a prominent and significant impact on South Asian countries like India, Bangladesh, Nepal, Pakistan, Sri Lanka and it is one of the most studied phenomena in the world. The monsoon is historically known to be influenced by El Niño-Southern Oscillation (ENSO). The inter-annual and inter-decadal variability of seasonal precipitation over India strongly depends upon the ENSO phasing. The average southwest monsoon rainfall received during the years with El Niño was found to be less compared to normal years and the average rainfall during the northeast monsoon is higher in coastal Andhra Pradesh. ENSO is anti-correlated with Indian summer monsoon (ISM). The last prominent effect of ENSO on India's monsoon occurred in 2009 with 23% reduction in annual rainfall, reducing summer sown crops such as rice, sugar cane etc. and pushing up food prices. Climatic resources endowment plays a major role in planning agricultural production in tropical and sub-tropical environment especially under rain-fed agriculture, and so contingent crop planning drawn on this relationship would help to mitigate the effects of ENSO episodes in the region. The unexplored area in this domain of research is the changes in the frequency and intensity of ENSO due to global warming and its impact on ENSO prediction and agricultural management practices. We analyze the last 30 years datasets of Pacific SST, and precipitation and air temperature over Southeast Asia to examine the evolution of ENSO teleconnections with ISM, as well as making estimates of drought indices such as Palmer Drought Severity Index. This research can lead toward better crop management strategies in the South Asian monsoon region.

  4. Characteristics, processes, and causes of the spatio-temporal variabilities of the East Asian monsoon system

    Science.gov (United States)

    Huang, Ronghui; Chen, Jilong; Wang, Lin; Lin, Zhongda

    2012-09-01

    Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon (EAM) system are reviewed in this paper. The understanding of the EAM system has improved in many aspects: the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon (EASM) system and the East Asian winter monsoon (EAWM) system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere-ocean interaction and atmosphere-land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere-ocean-land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific (EAP) teleconnection over East Asia and the North Pacific, the "Silk Road" teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study.

  5. Effect of Model Resolution on the Simulation of South Asian Summer Monsoon

    Science.gov (United States)

    Ashfaq, M.; Mei, R.; Touma, D. E.; Rastogi, D.

    2013-12-01

    Most of the Global Climate Models (GCMs) in the Climate Models Inter-comparison Project Phase 5 (CMIP5) do not show substantial improvement in the simulation of South Asian summer monsoon over their predecessors in CMIP3. Such a consistency in GCMs behavior can be due partly to their resolution that has not increased significantly in CMIP5 models compared to that in CMIP3 models. In order to prove this point, we run two configurations of the atmospheric component of the Community Climate System Model Version 4 (CCSM4), one at T85 spectral truncation (~1.5 degrees horizontal grid spacing), and one at T341 spectral truncation (~0.25 degree horizontal grid spacing). Both configuration that consist of 10-years of model integration from 1999 to 2009 use identical model physics, time step and observed sea surface temperatures. Our results show that increase in horizontal grid spacing in CCSM4 substantially improves its representation of South Asian summer monsoon by reducing the errors in the simulation of overall monsoon thermodynamics. We find that high-resolution configuration of CCSM4 has a better representation of meridional temperature gradient in the troposphere that in turn improves the vertical easterly shear during the summer months and the northward movement of the monsoon depressions above 20 N. High-resolution model results also show a noticeable improvement in the representation of the precipitation sourcing over South Asian landmass from Arabian Sea, Bay of Bengal and local recycling, particularly during the monsoon onset phase. Furthermore, we note that the frequency and magnitude of precipitation extremes depends on the horizontal grid spacing of the model. These results highlight the need for high-resolution climate modeling over South Asia.

  6. A Coupled Model Study on the Intensification of the Asian Summer Monsoon in IPCC SRES Scenarios

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The Asian summer monsoon is an important part of the climate system. Investigating the response of the Asian summer monsoon to changing concentrations of greenhouse gases and aerosols will be meaningful to understand and predict climate variability and climate change not only in Asia but also globally. In order to diagnose the impacts of future anthropogenic emissions on monsoon climates, a coupled general circulation model of the atmosphere and the ocean has been used at the Max-Planck-Institute for Meteorology. In addition to carbon dioxide, the major well mixed greenhouse gases such as methane, nitrous oxide, several chlorofluorocarbons, and CFC substitute gases are prescribed as a function of time. The sulfur cycle is simulated interactively, and both the direct aerosol effect and the indirect cloud albedo effect are considered.Furthermore, changes in tropospheric ozone have been pre-calculated with a chemical transport model and prescribed as a function of time and space in the climate simulations. Concentrations of greenhouse gases and anthropogenic emissions of sulfur dioxide are prescribed according to observations (1860-1990) and projected into the future (1990-2100) according to the Scenarios A2 and B2 in Special Report on Emissions Scenarios (SRES, Nakicenovic et al., 2000) developed by the Intergovernmental Panel on Climate Change (IPCC). It is found that the Indian summer monsoon is enhanced in the scenarios in terms of both mean precipitation and interannual variability. An increase in precipitation is simulated for northern China but a decrease for the southern part. Furthermore, the simulated future increase in monsoon variability seems to be linked to enhanced ENSO variability towards the end of the scenario integrations.

  7. Southern Hemisphere imprint for Indo-Asian summer monsoons during the last glacial period as revealed by Arabian Sea productivity records

    Science.gov (United States)

    Caley, T.; Zaragosi, S.; Bourget, J.; Martinez, P.; Malaizé, B.; Eynaud, F.; Rossignol, L.; Garlan, T.; Ellouz-Zimmermann, N.

    2013-11-01

    The monsoon is one of the most important climatic phenomena: it promotes inter-hemispheric exchange of energy and affects the economical prosperity of several countries exposed to its seasonal seesaw. Previous studies in both the Indian and Asian monsoon systems have generally suggested a dominant northern hemispheric (NH) control on summer monsoon dynamics at the scale of suborbital-millennial climatic changes, while the forcing/response of Indian and Asian monsoons at the orbital scale remains a matter of debate. Here, six marine sediment cores distributed across the whole Arabian Sea are used to build a regional surface marine productivity signal. The productivity signal is driven by the intensity of Indian summer monsoon winds. Our results demonstrate the existence of an imprint of suborbital southern hemispheric (SH) temperature changes (i.e. Antarctica) on the Indian summer monsoon during the last glacial period that is generally not recognized. During the last deglaciation, the NH played a more significant role. This suggests that fluctuations in the Indian monsoon are better explained in a bipolar context. The δ18O signal recorded in the Asian monsoon speleothem records could be exported by winds from the Indian summer monsoon region, as recently proposed in modelling exercise, explaining the SH signature observed in Asian cave speleothems. Contrary to the view of a passive response of Indian and Asian monsoons to NH anomalies, the present results appear to suggest that the Indo-Asian summer monsoon plays an active role in amplifying millennial inter-hemispheric asymmetric patterns. Additionally, this study confirms previously observed differences between Indian and Asian speleothem monsoonal records at the orbital-precession scale.

  8. Boreal summer continental monsoon rainfall and hydroclimate anomalies associated with the Asian-Pacific Oscillation

    Science.gov (United States)

    Zhao, Ping; Wang, Bin; Zhou, Xiuji

    2012-09-01

    With the twentieth century analysis data (1901-2002) for atmospheric circulation, precipitation, Palmer drought severity index, and sea surface temperature (SST), we show that the Asian-Pacific Oscillation (APO) during boreal summer is a major mode of the earth climate variation linking to global atmospheric circulation and hydroclimate anomalies, especially the Northern Hemisphere (NH) summer land monsoon. Associated with a positive APO phase are the warm troposphere over the Eurasian land and the relatively cool troposphere over the North Pacific, the North Atlantic, and the Indian Ocean. Such an amplified land-ocean thermal contrast between the Eurasian land and its adjacent oceans signifies a stronger than normal NH summer monsoon, with the strengthened southerly or southwesterly monsoon prevailing over tropical Africa, South Asia, and East Asia. A positive APO implies an enhanced summer monsoon rainfall over all major NH land monsoon regions: West Africa, South Asia, East Asia, and Mexico. Thus, APO is a sensible measure of the NH land monsoon rainfall intensity. Meanwhile, reduced precipitation appears over the arid and semiarid regions of northern Africa, the Middle East, and West Asia, manifesting the monsoon-desert coupling. On the other hand, surrounded by the cool troposphere over the North Pacific and North Atlantic, the extratropical North America has weakened low-level continental low and upper-level ridge, hence a deficient summer rainfall. Corresponding to a high APO index, the African and South Asian monsoon regions are wet and cool, the East Asian monsoon region is wet and hot, and the extratropical North America is dry and hot. Wet and dry climates correspond to wet and dry soil conditions, respectively. The APO is also associated with significant variations of SST in the entire Pacific and the extratropical North Atlantic during boreal summer, which resembles the Interdecadal Pacific Oscillation in SST. Of note is that the Pacific SST anomalies

  9. A new index to describe the tropical Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    We define a new monsoon index (MV) as the product of relative vorticity and equivalent potential temperature using the long-term NCEP/NCAR reanalysis data. The MV index provides new insights into the intraseasonal and interannual variabilities of the broad-scale tropical Asian summer monsoon (TASM), including the South Asian summer monsoon (SASM) and the South China Sea summer monsoon (SCSSM). On the intraseasonal timescale, the pentad-to-pentad MV index bears a close relationship to the broad-scale rainfall in the TASM regions. Among 29 summers from 1979 to 2007, in 23/27 summers the correlation coefficients are higher than 0.7 in the SASM/SCSSM region. However, in fewer than 9 summers, the correlations between the broad-scale rainfall and the existing circulation indices are higher than 0.7. On the interannual timescale, various existing SASM circulation indices are moderately or well correlated with all-India summer monsoon rainfall, whereas their correlations with broad-scale SASM rainfall are weak. In contrast, the summer mean MV index correlates well with the broad-scale SASM rainfall and all-India summer monsoon rainfall (correlation of 0.73 and 0.65, respectively). In the SCSSM region, the summer mean MV index also bears a close relationship to the SCSSM rainfall, although some discrepancies exist during certain years. The composite strong TASM shows a stronger low-tropospheric low pressure in association with the enhanced westerly winds and moisture transfer, stronger convection, and upper-tropospheric easterly winds, which indicate that the MV index can well capture the features of TASM.

  10. A new index to describe the tropical Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    XU ZhongFeng; FU CongBin; QIAN YongFu

    2009-01-01

    We define a new monsoon index (MV) as the product of relative vorticity and equivalent potential tem-perature using the long-term NCEP/NCAR reanalysis data.The MV index provides new insights into the intraseasonal and interannual variabilities of the broad-scale tropical Asian summer monsoon (TASM),including the South Asian summer monsoon (SASM) and the South China Sea summer monsoon (SCSSM).On the intraseasonal timescale,the pentad-to-pentad MV index bears a close relationship to the broad-scale rainfall in the TASM regions.Among 29 summers from 1979 to 2007,in 23/27 summers the correlation coefficients are higher than 0.7 in the SASM/SCSSM region.However,in fewer than 9 summers,the correlations between the broad-scale rainfall and the existing circulation indices are higher than 0.7.On the interannual timescale,various existing SASM circulation indices are moderately or well correlated with all-India summer monsoon rainfall,whereas their correlations with broad-scale SASM rainfall are weak.In contrast,the summer mean MV index correlates well with the broad-scale SASM rainfall and all-India summer monsoon rainfall (correlation of 0.73 and 0.65,respectively).In the SCSSM region,the summer mean MV index also bears a close relationship to the SCSSM rainfall,al-though some discrepancies exist during certain years.The composite strong TASM shows a stronger low-tropospheric low pressure in association with the enhanced westerly winds and moisture transfer,stronger convection,and upper-tropospheric easterly winds,which indicate that the MV index can well capture the features of TASM.

  11. 20th century intraseasonal Asian monsoon dynamics viewed from Isomap

    Science.gov (United States)

    Hannachi, A.; Turner, A. G.

    2013-10-01

    The Asian summer monsoon is a high-dimensional and highly nonlinear phenomenon involving considerable moisture transport towards land from the ocean, and is critical for the whole region. We have used daily ECMWF reanalysis (ERA-40) sea-level pressure (SLP) anomalies on the seasonal cycle, over the region 50-145° E, 20° S-35° N, to study the nonlinearity of the Asian monsoon using Isomap. We have focused on the two-dimensional embedding of the SLP anomalies for ease of interpretation. Unlike the unimodality obtained from tests performed in empirical orthogonal function space, the probability density function, within the two-dimensional Isomap space, turns out to be bimodal. But a clustering procedure applied to the SLP data reveals support for three clusters, which are identified using a three-component bivariate Gaussian mixture model. The modes are found to appear similar to active and break phases of the monsoon over South Asia in addition to a third phase, which shows active conditions over the western North Pacific. Using the low-level wind field anomalies, the active phase over South Asia is found to be characterised by a strengthening and an eastward extension of the Somali jet. However during the break phase, the Somali jet is weakened near southern India, while the monsoon trough in northern India also weakens. Interpretation is aided using the APHRODITE gridded land precipitation product for monsoon Asia. The effect of large-scale seasonal mean monsoon and lower boundary forcing, in the form of ENSO, is also investigated and discussed. The outcome here is that ENSO is shown to perturb the intraseasonal regimes, in agreement with conceptual ideas.

  12. The spatial-temporal patterns of Asian summer monsoon precipitation in response to Holocene insolation change: a model-data synthesis

    Science.gov (United States)

    Jin, Liya; Schneider, Birgit; Park, Wonsun; Latif, Mojib; Khon, Vyacheslav; Zhang, Xiaojian

    2014-02-01

    Paleoclimate proxy records of precipitation/effective moisture show spatial-temporal inhomogeneous over Asian monsoon and monsoon marginal regions during the Holocene. To investigate the spatial differences and diverging temporal evolution over monsoonal Asia and monsoon marginal regions, we conduct a series of numerical experiments with an atmosphere-ocean-sea ice coupled climate model, the Kiel Climate Model (KCM), for the period of Holocene from 9.5 ka BP to present (0 ka BP). The simulations include two time-slice equilibrium experiments for early Holocene (9.5 ka BP) and present-day (0 ka BP), respectively and one transient simulation (HT) using a scheme for model acceleration regarding to the Earth's orbitally driven insolation forcing for the whole period of Holocene (from 9.5 to 0 ka BP). The simulated summer precipitation in the equilibrium experiments shows a tripole pattern over monsoonal Asia as depicted by the first modes of empirical orthogonal function (EOF1) of H0K and H9K. The transient simulation HT exhibits a wave train pattern in the summer precipitation across the Asian monsoon region associated with a gradually decreased trend in the strength of Asian summer monsoon, as a result of the response of Asian summer monsoon system to the Holocene orbitally-forced insolation change. Both the synthesis of multi-proxy records and model experiments confirm the regional dissimilarity of the Holocene optimum precipitation/effective moisture over the East Asian summer monsoon region, monsoon marginal region, and the westerly-dominated areas, suggesting the complex response of the regional climate systems to Holocene insolation change in association with the internal feedbacks within climate system, such as the air-sea interactions associated with the El Nino/Southern Oscillation (ENSO) and shift of the Intertropical Convergence Zone (ITCZ) in the evolution of Asian summer monsoon during the Holocene.

  13. Searching for a fingerprint of global warming in the Asian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Stephenson, D.B.; Douville, H.; Kumar, K.R. [University of Reading, Reading (United Kingdom). Dept. of Meteorology

    2001-07-01

    This study investigates possible trends in several large-scale indices that describe the Asian summer monsoon. Results from recent atmospheric general circulating experiments are used to provide clues as to how the monsoon might be changing due to the effects of global warming. Interestingly, this study has found that the large-scale wind shear monsoon indices have been decreasing at a rate of 0.1-0.3% per year (based on NCEP/NCAR (National Centre for Atmospheric Research) analyses 1958-98) in quantitative agreement with recent results from doubled CO{sub 2} simulations made using several state-of-the-art climate models. Nevertheless, despite the weakening of the monsoon circulation, all-India rainfall shows no clear trend in either the model results or in the observation re-analyses from 1958-98. Multiple regression is used to separte out the dynamical contribution from the observed all-India rainfall index, and a clear increasing trend then emerges in the non-dynamical residual. A simple dimensionless multivariate monsoon index is proposed that could be of use in monitoring global warming changes in the monsoon. 31 refs., 2 figs., 3 tabs.

  14. Changing Hydrological Cycle in Asian Monsoon Region in Relation to Water Resources

    Science.gov (United States)

    Kabat, P.

    2006-12-01

    Water is a key resource for sustainable development in the Monsoon Asian Region. Frequent occurrence of flood disasters related to increasing Asian monsoon climate variability, progressing land degradation associated with anomalous monsoon dry climate and land overexploitation, increasing water use due to rapid social/economic development, and water pollution under the development of industrialization, urbanization and intensive agriculture, all pose fundamental questions about mid- and long term future carrying capacity of water systems in this key-region of the globe. We review some of the most recent data and methodological insights about how the hydrological cycle and hydroclimate in monsoon Asia is changing or has already changed in association with the global warming (GHG increase). Next,we analyze how regional-scale anthropogenic impacts such land cover/use changes, forest fire, dust increase, affect the hydrological cycle and water resources in the monsoon Asia and Northern China. The issues addressed in the presentation include: (i)the current regional hydrological cycle, especially causal chains leading to observable changes in droughts and floods;(ii)how the water cycle and the extremes may respond to future drivers of global change;(iii) feedbacks in the coupled system as they affect the hydrological cycle; (iv)the uncertainties in the predictions of coupled climate-hydrological- land use models and (v)the future vulnerability of water as a resource. We argue for a substantial increase of international collaborative research efforts into integrated impact assessment of climate change and human activity on water systems in this region.

  15. Future Projection and Associated Uncertainty of the East Asian Summer Monsoon

    Science.gov (United States)

    Chen, J.; Bordoni, S.

    2014-12-01

    The regional climate change of the East Asian summer monsoon is investigated in the Coupled Model Inter-comparison Project - Phase 5 (CMIP5) archive in the context of the moist static energy budget. In the greenhouse gas forcing scenario, the reduction of radiative cooling and the increase of continental surface temperature occur much more rapidly than changes in sea surface temperatures (SSTs). Without changes in SSTs, the rainfall in the oceanic monsoon region decreases, despite an increase in the land-sea thermal contrast traditionally considered as a fundamental driver of monsoons. The reduction in precipitation is robust amongst all CMIP5 models and is primarily attributable to a weakening of the subtropical westerly jet. The weakening of the jet, in turn, can be explained by changes in upper-level eddy momentum flux convergence and thermal wind balance. On longer time scales, SSTs increase, as does monsoon rainfall. This delayed precipitation increase is primarily driven by the thermodynamic contribution to precipitation changes, by which wet regions get wetter and dry regions get drier. Dynamical changes due to changes in circulation play a secondary effect. These results clearly highlight deficits of commonly proposed geo-engineering schemes as climate mitigation strategies, which, by reducing the surface warming without sequestration of CO2, might still result in dramatic changes in rainfall, especially in heavily populated monsoonal regions. Similar analyses will be applied to other subtropical convergence zones in the Earth's atmosphere.

  16. Inter-decadal variations,causes and future projection of the Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    Ding Yihui; Si Dong; Sun Ying; Liu Yanju; Song Yafang

    2014-01-01

    The present paper presents a concise summary of our recent studies on the Asian summer monsoon, with highting decadal and inter-decadal scales. The studies on the long-term variations of the Asian summer monsoon and its impacts on the change in the summer precipitation in China are reviewed. Moreover,recent changes in the Asian summer monsoon and summer precipitation in East Asia (including Meiyu precipitation) are discussed. Finally,the future changes of the Asian summer monsoon are also pointed out in this paper.

  17. Understanding the regional anthropogenic signature in weakening of the south Asian Summer Monsoon

    Science.gov (United States)

    TP, S.

    2014-12-01

    The evidence from observation shows that South Asia underwent a widespread drying from the last five to six decades during the summer. The underlying reasons are unclear, whether this trend is due to natural or anthropogenic activities. Using a state-of-the-art global variable resolution climate model with high-resolution zooming over South-Asia, we decomposed the regional factors responsible for the weakening of monsoon circulation and rainfall. To address this issue we conducted several long simulations from 1886 to 2095, with and without anthropogenic forcing. The simulation provides key information about the regional responses to changes in south Asian summer monsoon, which leads to the decline in mean monsoon, and enhancement in the occurrence of localized extreme precipitation events in a warming climate. Further the 21st century climate projection using the same high-resolution model indicates persistent decrease of monsoonal rains due to land-atmosphere feedbacks in a warming environment. This would have severe impacts on agriculture, water resources and ecosystem over South Asia.

  18. Speleothem Evidence for Temporal-Spatial Variation in East Asian Summer Monsoon since Medieval Warm Period

    Science.gov (United States)

    Li, H.-C.; Chu, P. C.; Fan, C. W.

    2012-04-01

    Published annual-to-decadal resolution stalagmite δ18O records since AD 900 from six caves (Dongge, Furong, Heshang, Buddha, Shihua and Wanxiang) in China were analyzed to detect temporal and spatial variability of the East Asian Summer Monsoon strength which strongly affects wet/dry conditions in eastern China. The empirical mode decomposition method (Huang et al., 1998) was used to obtain trends of the six cave records. After the base trend was determined, δ18O anomalies of each record were computed by subtracting the base trend. Mean δ18O anomaly values of the detrended time series for each cave record were calculated for four periods: (1) medieval warm period (MWD, AD 900 - 1250), (2) little ice age phase-1 (LIA-1, AD 1250 -1550), (3) little ice age phase-2 (LIA-2, AD 1550 - 1850), and (4) modern period (MD-1, AD 1850 - 2000). From these anomalies, the temporal and spatial variability of wet/dry conditions has been identified. Positive values of the mean δ18O anomalies indicating drier conditions appeared in lower Yangtze River Drainage Area and Southeast Coast Area during MD-1, LIA-1 and MWD, whereas negative values existed in North, South and Yangtze areas of the eastern China. The results agree with Dryness/Wetness index reconstructed by Chinese historic records in general. These results illustrate that wet and dry conditions in different regions of the eastern China could be opposite under the monsoon influence, so that no single speleothem δ18O record could represent monsoonal climate in this vast region. The climatic patterns in the monsoonal region can either warm/wet (cold/dry) or cold/wet (warm/dry) on annual-to-centennial scales. A 128-yr periodic cycle exists in all six cave records, whereas 64-yr and 42-yr periodicities appear in the Shihua, Heshang and Dongge records. These cycles may reflect the influence of the solar activity on the East Asian Summer Monsoon.

  19. Multi-Satellite Synergy for Aerosol Analysis in the Asian Monsoon Region

    Science.gov (United States)

    Ichoku, Charles; Petrenko, Maksym

    2012-01-01

    Atmospheric aerosols represent one of the greatest uncertainties in environmental and climate research, particularly in tropical monsoon regions such as the Southeast Asian regions, where significant contributions from a variety of aerosol sources and types is complicated by unstable atmospheric dynamics. Although aerosols are now routinely retrieved from multiple satellite Sensors, in trying to answer important science questions about aerosol distribution, properties, and impacts, researchers often rely on retrievals from only one or two sensors, thereby running the risk of incurring biases due to sensor/algorithm peculiarities. We are conducting detailed studies of aerosol retrieval uncertainties from various satellite sensors (including Terra-/ Aqua-MODIS, Terra-MISR, Aura-OMI, Parasol-POLDER, SeaWiFS, and Calipso-CALIOP), based on the collocation of these data products over AERONET and other important ground stations, within the online Multi-sensor Aerosol Products Sampling System (MAPSS) framework that was developed recently. Such analyses are aimed at developing a synthesis of results that can be utilized in building reliable unified aerosol information and climate data records from multiple satellite measurements. In this presentation, we will show preliminary results of. an integrated comparative uncertainly analysis of aerosol products from multiple satellite sensors, particularly focused on the Asian Monsoon region, along with some comparisons from the African Monsoon region.

  20. The effects of monsoons and climate teleconnections on the Niangziguan Karst Spring discharge in North China

    Science.gov (United States)

    Zhang, Juan; Hao, Yonghong; Hu, Bill X.; Huo, Xueli; Hao, Pengmei; Liu, Zhongfang

    2016-03-01

    Karst aquifers supply drinking water for 25 % of the world's population, and they are, however, vulnerable to climate change. This study is aimed to investigate the effects of various monsoons and teleconnection patterns on Niangziguan Karst Spring (NKS) discharge in North China for sustainable exploration of the karst groundwater resources. The monsoons studied include the Indian Summer Monsoon, the West North Pacific Monsoon and the East Asian Summer Monsoon. The climate teleconnection patterns explored include the Indian Ocean Dipole, E1 Niño Southern Oscillation, and the Pacific Decadal Oscillation. The wavelet transform and wavelet coherence methods are used to analyze the karst hydrological processes in the NKS Basin, and reveal the relations between the climate indices with precipitation and the spring discharge. The study results indicate that both the monsoons and the climate teleconnections significantly affect precipitation in the NKS Basin. The time scales that the monsoons resonate with precipitation are strongly concentrated on the time scales of 0.5-, 1-, 2.5- and 3.5-year, and that climate teleconnections resonate with precipitation are relatively weak and diverged from 0.5-, 1-, 2-, 2.5-, to 8-year time scales, respectively. Because the climate signals have to overcome the resistance of heterogeneous aquifers before reaching spring discharge, with high energy, the strong climate signals (e.g. monsoons) are able to penetrate through aquifers and act on spring discharge. So the spring discharge is more strongly affected by monsoons than the climate teleconnections. During the groundwater flow process, the precipitation signals will be attenuated, delayed, merged, and changed by karst aquifers. Therefore, the coherence coefficients between the spring discharge and climate indices are smaller than those between precipitation and climate indices. Further, the fluctuation of the spring discharge is not coincident with that of precipitation in most

  1. The vorticity and angular momentum budgets of Asian summer monsoon

    Indian Academy of Sciences (India)

    P L S Rao; U C Mohanty; P V S Raju; M A Arain

    2004-09-01

    The study delineates the vorticity and angular momentum balances of Asian summer monsoon during the evolution and established phases. It also elucidates the differences between these balances in the National Centre for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis and the National Centre for Medium Range Weather Forecasts (NCM- RWF) analysis fields. The NCEP/NCAR reanalysis for a 40 year period (1958-97) and the NCM- RWF analysis for a three year (1994-96) period are made use of for the purpose. The time mean summer monsoon circulation is bifurcated into stable mean and transient eddy components and the mean component is elucidated. The generation of vorticity due to stretching of isobars balances most of the vorticity transported out of the monsoon domain during the evolution period. However, during the established period, the transportation by the relative and planetary vorticity components exceeds the generation due to stretching. The effective balancing mechanism is provided by vorticity generation due to sub-grid scale processes. The flux convergence of omega and relative momenta over the monsoon domain is effectively balanced by pressure torque during the evolution and established phases. Nevertheless, the balance is stronger during the established period due to the increase in the strength of circulation. Both the NCMRWF and NCEP fields indicate the mean features related to vorticity and angular momentum budgets realistically. Apart from the oceanic bias (strong circulation over oceans rather than continents), the summer monsoon circulation indicated by the NCEP is feeble compared to NCMRWF. The significant terms in the large-scale budgets of vorticity and angular momentum enunciate this aspect.

  2. Simulation of the Indian and East-Asian summer monsoon in the ECMWF model: Sensitivity to horizontal resolution

    Energy Technology Data Exchange (ETDEWEB)

    Sperber, K.R.; Potter, G.L.; Boyle, J.S. [Lawrence Livermore National Lab., CA (United States); Hameed, S. [State Univ. of New York, Stony Brook, NY (United States). Inst. for Terrestrial and Planetary Atmospheres

    1993-11-01

    The ability of the ECMWF model (Cycle 33) to simulate the Indian and East Asian summer monsoon is evaluated at four different horizontal resolutions: T21, T42, T63, and T106. Generally, with respect to the large scale features of the circulation, the largest differences among the simulations occur at T42 relative to T21. However, on regional scales, important differences among the high frequency temporal variabilitY serve as a further critical test of the model`s ability to simulate the monsoon. More generally, the results indicate the importance of evaluating high frequency time scales as a component of the climate system. T106 best captures both the spatial and temporal characteristics of the Indian and East Asian Monsoon, while T42 fails to correctly simulate the sequence and development of synoptic scale milestones that characterize the monsoon flow. In particular, T106 is superior at simulating the development and migration of the monsoon trough over the Bay of Bengal. In the T42 simulation, the development of the monsoon occurs one month earlier than typically observed. At this time the trough is incorrectly located adjacent to the east coast of India which results in an underestimate of precipitation over the Burma/Thailand region. This early establishment of the monsoon trough affects the evolution of the East-Asian monsoon and yields excessive preseason rainfall over the Mei-yu region. EOF analysis of precipitation over China indicates that T106 best simulates the Mei-yu mode of variability associated with an oscillation of the rainband that gives rise to periods of enhanced rainfall over the Yangize River Valley. The coarse resolution of T21 precludes simulation of the aforementioned regional scale monsoon flows.

  3. Structure and Propagation Characteristics of Climatological Mean Kinetic Energy of Disturbance of Intraseasonal Oscillation in Asian Summer Monsoon Zone

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    [Objective] The research aimed to study the structure and propagation characteristics of climatological mean kinetic energy of disturbance of intraseasonal oscillation in Asian summer monsoon zone. [Method] When South China Sea monsoon started to break out, the kinetic energy of intraseasonal oscillation disturbance in the monsoon zone was analyzed, especially the researches about the variation of South China Sea monsoon, the development of Indian monsoon and the advancement of East Asian monsoon. [Result] ...

  4. Holocene weak summer East Asian monsoon intervals in subtropical Taiwan and their global synchronicity

    Directory of Open Access Journals (Sweden)

    K. Selvaraj

    2008-08-01

    Full Text Available Sedimentary total organic carbon and carbon-to-nitrogen ratio records from the subalpine Retreat Lake in NE Taiwan reveal four centennial periods (~8–8.3, 5.1–5.7, 4.5–~2.1, and 2–1.6 kyr BP of relatively reduced summer East Asian monsoon (EAM precipitation that were superimposed on the insolation-dependent, long-term decreasing monsoon trend during the middle and late Holocene while early Holocene monsoon strength was controlled by glacial boundary conditions. Strikingly, all weak monsoon events correlate with the timings of low sea surface temperature in the tropical Pacific, maxima of hematite stained-grains in the sediments of North Atlantic, reduced formation of North Atlantic Deep Water, and low concentrations of atmospheric methane over Greenland, suggesting a globally well-connected postglacial climate (from ca. 8.6 kyr BP onwards. Persistent linkage of weak summer EAM-tropical Pacific and North Atlantic cooling-reduced global wetland extent during these intervals is believed to be driven by coupled ocean-atmosphere interactions, especially reduced heat and moisture transport and enhanced El Niño-Southern Oscillation in the tropical Pacific, as well as solar activity. Overall similarity of summer EAM with diverse proxy records and their coincidence to abrupt changes witnessed in other paleorecords across the world imply that the centennial-scale reorganizations in the tropical Pacific climate dynamics may have been playing an important role, of course closely in phase with solar variations and North Atlantic climate, in the Holocene summer EAM and, by extension, low-latitude's monsoon instability.

  5. Asian-Pacific Oscillation index and variation of East Asian summer monsoon over the past millennium

    Institute of Scientific and Technical Information of China (English)

    ZHOU XiuJi; ZHAO Ping; LIU Ge

    2009-01-01

    To study the long-term variation of the East Asian summer monsoon (EASM), the Asian-Pacific Oscil-lation index (I_(APO)), representing a zonal thermal contrast between Asia and the North Pacific, is recon-structed over the past millennium. During the Little Ice Age (LIA), the variability of the reconstructed IAPO is closely linked to dry-wet anomalies in eastern China on the centennial scale. This correlation pattern is consistent with the observation during the current period, which suggests that the recon-structed IAPO may generally represent the centennial-scale variation of the EASM and rainfall anomalies over eastern China during the LIA.

  6. Investigating the history of East Asian monsoon and climate during the last glacial–interglacial period (0–140 000 years) : mineralogy and geochemistry of ODP Sites 1143 and 1144, South China Sea

    OpenAIRE

    Tamburini, P; Adatte, Thierry; Föllmi, Karl B.; Bernasconi, Stefano M; Steinmann, P.

    2005-01-01

    Monsoon climate is an important component of the global climatic system. A comprehensive understanding of its variability over glacial–interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate, continental weathering and productivity. A detailed multiproxy study, including bulk and clay mineralogy, grain-size analysis, phosphorus geochemistry (SEDEX extraction), organic matter characterization, and nitrogen stable isotop...

  7. Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

    Directory of Open Access Journals (Sweden)

    L. Guo

    2014-12-01

    aerosol emissions also plays a role in declining monsoon rainfall. The disparity between the response of monsoon rainfall to increasing aerosol emissions in models containing direct aerosol effects only and those also containing indirect effects needs to be urgently investigated since the suggested future decline in Asian anthropogenic aerosol emissions inherent to the representative concentration pathways (RCPs used for future climate projection may turn out to be optimistic. In addition, both groups of models show declining rainfall over China, also relating to local aerosol mechanisms. We hypothesize that aerosol emissions over China are large enough, in the CMIP5 models, to cause declining monsoon rainfall even in the absence of indirect aerosol effects. The same is not true for India.

  8. Impacts of 20th century aerosol emissions on the South Asian monsoon in the CMIP5 models

    Science.gov (United States)

    Guo, L.; Turner, A. G.; Highwood, E. J.

    2015-06-01

    plays a role in declining monsoon rainfall. The disparity between the response of monsoon rainfall to increasing aerosol emissions in models containing direct aerosol effects only and those also containing indirect effects needs to be urgently investigated since the suggested future decline in Asian anthropogenic aerosol emissions inherent to the representative concentration pathways (RCPs) used for future climate projection may turn out to be optimistic. In addition, both groups of models show declining rainfall over China, also relating to local aerosol mechanisms. We hypothesize that aerosol emissions over China are large enough, in the CMIP5 models, to cause declining monsoon rainfall even in the absence of indirect aerosol effects. The same is not true for India.

  9. Three exceptionally strong East-Asian summer monsoon events during glacial times in the past 470 kyr

    Directory of Open Access Journals (Sweden)

    D.-D. Rousseau

    2009-04-01

    characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

  10. Three exceptionally strong East-Asian summer monsoon events during glacial conditions in the past 470 kyr

    Directory of Open Access Journals (Sweden)

    D.-D. Rousseau

    2008-12-01

    characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

  11. 亚洲季风区铁杉属现代分布区及其气候特征%Modern Geographical Distribution of Tsuga and Its Climatic Conditions in the Asian Monsoon Region

    Institute of Scientific and Technical Information of China (English)

    杨青松; 星耀武; 周浙昆

    2009-01-01

    铁杉属在亚洲主要分布于亚洲季风区东部,间断分布于中国大陆、台湾岛以及日本列岛(除北海道).在中国大陆间断分布在西南山区(横断山区和部分东喜马拉雅)、中部山区(秦岭-大巴山区)和东南山区(华东山地).亚洲季风区铁杉属的现代分布环境要求年降水量范围为720~2 103 mm,生长季降水量为635~1 489 mm;年均温范围为5.8~18.2℃,冬季月均温为-2.7~11.5℃,年最冷月均温为-3.7~10.9℃,年最暖月均温为13.0~28.2℃,气温年较差为9.7~25.4℃.亚洲季风区铁杉属的现代地理分布与气候要素值相互关系的分析表明,无铁杉分布的朝鲜半岛及其邻近的我国东北山地和山东山地降水量均大于700 mm,基本上能够满足铁杉属生长的水分条件;而朝鲜半岛及其邻近的我国东北山地和山东山地的气温年较差明显大于铁杉属分布区的值,同时两地的冬季月均温和年最冷月均温明显低于铁杉属分布区的值,这也是这些地区没有铁杉属分布的主要气候原因.总之,这些亚洲季风区水分条件能够满足铁杉属生长需要,但冬季温度(包括冬季月平均温度和年最冷月均温)和气温年较差无法满足铁杉属生长需要,导致这些地区无铁杉属现代分布记录.%In Asia, Tsuga is mainly distributed in the Asian Monsoon region, and intermittently distributed in Mainland China, Taiwan Central Ranges and Japanese Archipelago (except Hokkaido). In Mainland China, it is discontinuously distributed in the southwestern mountains (the Hengduan Mountains and a part of the Eastern Himalayas), the central mountains (the Qinling Mountains and the Daba Mountains) and the southeastern mountains (the East China mountains) . In its modern geographical distribution, Tsuga growth requires following climatic conditions: annual precipitation (AP) range of 720-2 103 mm, growing season precipitation (GP) range of 635-1 489 mm, annual mean

  12. Slow and fast annual cycles of the Asian summer monsoon in the NCEP CFSv2

    Science.gov (United States)

    Shin, Chul-Su; Huang, Bohua

    2016-07-01

    The climatological Asian summer monsoon (ASM) is decomposed into the slow and fast annual cycles (SAC and FAC). The FAC represents the abrupt onset and breaks phase-locked to the ASM seasonal progression. This study evaluates how well the NCEP Climate Forecast System version 2 (CFSv2) simulates the SAC and FAC over the Indian and East Asia monsoon regions (IMR and EAMR). The simulated SACs are in good agreement with observations in both regions. The FAC also represents the northward propagation in both observations and CFSv2. It is further demonstrated that the FAC is associated with a thermodynamic air-sea interaction. In particular, the different roles played by the wind-evaporation-SST (WES) feedback may account for the faster propagation in the IMR than the EAMR. However, compared with observations, the simulated FAC shows earlier monsoon onset and long-lasting stronger dry and wet phases in the IMR but delayed monsoon onset with weaker and less organized FAC in the EAMR. These reversed behaviors may originate from a warm (cold) SST bias in the IMR (EAMR) in boreal spring and enhanced by an overly sensitive surface evaporation to wind changes in the CFSv2. As a result, the warm spring SST bias in the IMR initiates a strong WES feedback and changes of solar insolation during boreal summer, which leads to a cold SST bias in early fall. On the other hand, the cold spring SST bias in the EAMR accounts for a weaker air-sea coupling, which in turn results in a warm SST bias after the withdrawal of the monsoon.

  13. Characteristics of the Onset of the Asian Summer Monsoon and the Importance of Asian-Australian "Land Bridge"

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Based on summarizing previous achievements and using data as long and new as possible, the onset characteristics of Asian summer monsoon and the role of Asian-Australian "land bridge" in the onset of summer monsoon are further discussed. In particular, the earliest onset area of Asian summer monsoon is comparatively analyzed, and the sudden and progressive characteristics of the onset of summer monsoon in different regions are discussed. Furthermore, the relationships among such critical events during the onset of Asian summer monsoon as the splitting of subtropical high belt over the Bay of Bengal (BOB), the initiation of convection over Indo-China Peninsula, the westward advance, reestablishment of South Asian High, and the rapid northward progression of convection originated from Sumatra in early summer are studied. The important impact of the proper collocation of the latent heating over Indo-China Peninsula and the sensible heating over Indian Peninsula on the splitting of the subtropical high belt, the deepening of BOB trough, the activating of Sri Lanka vortex (twin vortexes in the Northern and Southern Hemispheres),and the subsequent onset of South China Sea summer monsoon are emphasized.

  14. Atmospheric Circulation Characteristics Associated with the Onset of Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The onset of the Asian summer monsoon has been a focus in the monsoon study for many years. In this paper, we study the variability and predictability of the Asian summer monsoon onset and demonstrate that this onset is associated with specific atmospheric circulation characteristics. The outbreak of the Asian summer monsoon is found to occur first over the southwestern part of the South China Sea (SCS)and the Malay Peninsula region, and the monsoon onset is closely related to intra-seasonal oscillations in the lower atmosphere. These intra-seasonal oscillations consist of two low-frequency vortex pairs, one located to the east of the Philippines and the other over the tropical eastern Indian Ocean. Prior to the Asian summer monsoon onset, a strong low-frequency westerly emerges over the equatorial Indian Ocean and the low-frequency vortex pair develops symmetrically along the equator. The formation and evolution of these low-frequency vortices are important and serve as a good indicator for the Asian summer monsoon onset. The relationship between the northward jumps of the westerly jet over East Asia and the Asian summer monsoon onset over SCS is investigated. It is shown that the northward jump of the westerly jet occurs twice during the transition from winter to summer and these jumps are closely related to the summer monsoon development. The first northward jump (from 25°-28°N to around 30°N) occurs on 8 May on average, about 7 days ahead of the summer monsoon onset over the SCS. It is found that the reverse of meridional temperature gradient in the upper-middle troposphere (500-200 hPa) and the enhancement and northward movement of the subtropical jet in the Southern Hemispheric subtropics are responsible for the first northward jump of the westerly jet.

  15. The Asian monsoon over the past 640,000 years and ice age terminations

    Science.gov (United States)

    Cheng, Hai; Edwards, R. Lawrence; Sinha, Ashish; Spötl, Christoph; Yi, Liang; Chen, Shitao; Kelly, Megan; Kathayat, Gayatri; Wang, Xianfeng; Li, Xianglei; Kong, Xinggong; Wang, Yongjin; Ning, Youfeng; Zhang, Haiwei

    2016-06-01

    Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record’s length and temporal precision allow us to test the idea that insolation changes caused by the Earth’s precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record’s timing, the terminations are separated by four or five precession cycles, supporting the idea that the ‘100,000-year’ ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and ‘unfinished terminations’.

  16. The Asian monsoon over the past 640,000 years and ice age terminations.

    Science.gov (United States)

    Cheng, Hai; Edwards, R Lawrence; Sinha, Ashish; Spötl, Christoph; Yi, Liang; Chen, Shitao; Kelly, Megan; Kathayat, Gayatri; Wang, Xianfeng; Li, Xianglei; Kong, Xinggong; Wang, Yongjin; Ning, Youfeng; Zhang, Haiwei

    2016-06-30

    Oxygen isotope records from Chinese caves characterize changes in both the Asian monsoon and global climate. Here, using our new speleothem data, we extend the Chinese record to cover the full uranium/thorium dating range, that is, the past 640,000 years. The record's length and temporal precision allow us to test the idea that insolation changes caused by the Earth's precession drove the terminations of each of the last seven ice ages as well as the millennia-long intervals of reduced monsoon rainfall associated with each of the terminations. On the basis of our record's timing, the terminations are separated by four or five precession cycles, supporting the idea that the '100,000-year' ice age cycle is an average of discrete numbers of precession cycles. Furthermore, the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands, and is nearly in anti-phase with summer boreal insolation. These observations indicate that insolation, in part, sets the pace of the occurrence of millennial-scale events, including those associated with terminations and 'unfinished terminations'. PMID:27357793

  17. South Asian summer monsoon variability during the last ˜54 kyrs inferred from surface water salinity and river runoff proxies

    Science.gov (United States)

    Gebregiorgis, D.; Hathorne, E. C.; Sijinkumar, A. V.; Nath, B. Nagender; Nürnberg, D.; Frank, M.

    2016-04-01

    The past variability of the South Asian Monsoon is mostly known from records of wind strength over the Arabian Sea while high-resolution paleorecords from regions of strong monsoon precipitation are still lacking. Here, we present records of past monsoon variability obtained from sediment core SK 168/GC-1, which was collected at the Alcock Seamount complex in the Andaman Sea. We utilize the ecological habitats of different planktic foraminiferal species to reconstruct freshwater-induced stratification based on paired Mg/Ca and δ18O analyses and to estimate seawater δ18O (δ18Osw). The difference between surface and thermocline temperatures (ΔT) and δ18Osw (Δδ18Osw) is used to investigate changes in upper ocean stratification. Additionally, Ba/Ca in G. sacculifer tests is used as a direct proxy for riverine runoff and sea surface salinity (SSS) changes related to monsoon precipitation on land. Our Δδ18Osw time series reveals that upper ocean salinity stratification did not change significantly throughout the last glacial suggesting little influence of NH insolation changes. The strongest increase in temperature gradients between the mixed layer and the thermocline is recorded for the mid-Holocene and indicate the presence of a significantly shallower thermocline. In line with previous work, the δ18Osw and Ba/Ca records demonstrate that monsoon climate during the LGM was characterized by a significantly weaker southwest monsoon circulation and strongly reduced runoff. Based on our data the South Asian Summer Monsoon (SAM) over the Irrawaddyy strengthened gradually after the LGM beginning at ˜18 ka. This is some 3 kyrs before an increase of the Ba/Ca record from the Arabian Sea and indicates that South Asian Monsoon climate dynamics are more complex than the simple N-S displacement of the ITCZ as generally described for other regions. Minimum δ18Osw values recorded during the mid-Holocene are in phase with Ba/Ca marking a stronger monsoon precipitation

  18. Climate change at the 4.2 ka BP termination of the Indus valley civilization and Holocene south Asian monsoon variability

    Science.gov (United States)

    Staubwasser, M.; Sirocko, F.; Grootes, P. M.; Segl, M.

    2003-04-01

    Planktonic oxygen isotope ratios off the Indus delta reveal climate changes with a multi-centennial pacing during the last 6 ka, with the most prominent change recorded at 4.2 ka BP. Opposing isotopic trends across the northern Arabian Sea surface at that time indicate a reduction in Indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south Asia. The 4.2 ka event is coherent with the termination of urban Harappan civilization in the Indus valley. Thus, drought may have initiated southeastward habitat tracking within the Harappan cultural domain. The late Holocene drought cycles following the 4.2 ka BP event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14C production rates. This suggests that solar variability is one fundamental cause behind Holocene rainfall changes over south Asia.

  19. Urban heat mitigation by roof surface materials during the East Asian summer monsoon

    Science.gov (United States)

    Lee, Seungjoon; Ryu, Youngryel; Jiang, Chongya

    2015-12-01

    Roof surface materials, such as green and white roofs, have attracted attention in their role in urban heat mitigation, and various studies have assessed the cooling performance of roof surface materials during hot and sunny summer seasons. However, summers in the East Asian monsoon climate region are characterized by significant fluctuations in weather events, such as dry periods, heatwaves, and rainy and cloudy days. This study investigated the efficacy of different roof surface materials for heat mitigation, considering the temperatures both at and beneath the surface of the roof covering materials during a summer monsoon in Seoul, Korea. We performed continuous observations of temperature at and beneath the surface of the roof covering materials, and manual observation of albedo and the normalized difference vegetation index for a white roof, two green roofs (grass (Poa pratensis) and sedum (Sedum sarmentosum)), and a reference surface. Overall, the surface temperature of the white roof was significantly lower than that of the grass and sedum roofs (1.1 °C and 1.3 °C), whereas the temperature beneath the surface of the white roof did not differ significantly from that of the grass and sedum roofs during the summer. The degree of cloudiness significantly modified the surface temperature of the white roof compared with that of the grass and sedum roofs, which depended on plant metabolisms. It was difficult for the grass to maintain its cooling ability without adequate watering management. After considering the cooling performance and maintenance efforts for different environmental conditions, we concluded that white roof performed better in urban heat mitigation than grass and sedum during the East Asian summer monsoon. Our findings will be useful in urban heat mitigation in the region.

  20. Impacts of the East Asian Monsoon on springtime dust concentrations over China

    Science.gov (United States)

    Lou, Sijia; Russell, Lynn M.; Yang, Yang; Xu, Li; Lamjiri, Maryam A.; DeFlorio, Michael J.; Miller, Arthur J.; Ghan, Steven J.; Liu, Ying; Singh, Balwinder

    2016-07-01

    We use 150 year preindustrial simulations of the Community Earth System Model to quantify the impacts of the East Asian Monsoon strength on interannual variations of springtime dust concentrations over China. The simulated interannual variations in March-April-May (MAM) dust column concentrations range between 20-40% and 10-60% over eastern and western China, respectively. The dust concentrations over eastern China correlate negatively with the East Asian Monsoon (EAM) index, which represents the strength of monsoon, with a regionally averaged correlation coefficient of -0.64. Relative to the strongest EAM years, MAM dust concentrations in the weakest EAM years are higher over China, with regional relative differences of 55.6%, 29.6%, and 13.9% in the run with emissions calculated interactively and of 33.8%, 10.3%, and 8.2% over eastern, central, and western China, respectively, in the run with prescribed emissions. Both interactive run and prescribed emission run show the similar pattern of climate change between the weakest and strongest EAM years. Strong anomalous northwesterly and westerly winds over the Gobi and Taklamakan deserts during the weakest EAM years result in larger transport fluxes, and thereby increase the dust concentrations over China. These differences in dust concentrations between the weakest and strongest EAM years (weakest-strongest) lead to the change in the net radiative forcing by up to -8 and -3 W m-2 at the surface, compared to -2.4 and +1.2 W m-2 at the top of the atmosphere over eastern and western China, respectively.

  1. East Asian Monsoon and paleoclimatic data analysis: a vegetation point of view

    Directory of Open Access Journals (Sweden)

    J. Guiot

    2008-06-01

    Full Text Available First we review several syntheses of paleodata (pollen, lake-levels showing the climate variations in China and Mongolia from the last glacial maximum to Present and in particular the precipitation increase at mid Holocene related to enhanced monsoon. All these results concur to a much enhanced monsoon on most of China during the first half of the Holocene. Second we present, in some details, a temporal study of a core (Lake Bayanchagan, Inner Mongolia located in an arid region at the edge of the present East Asian Monsoon (EAM influence and then sensitive to climatic change. This study involves pollen data together with other macro-remains and stable isotope curve to obtain a robust climate reconstruction. This study shows a long wet period between 11 000 and 5000 years BP divided in two parts, a warmer one from 11 000 and 8000 (marked by large evapotranspiration and a cooler one more favourable to forest expansion. Third, we present a spatial study based on pollen data only and covering all China and Mongolia at 6000 years BP, but using a mechanistic modelling approach, in an inverse mode. It has the advantage to take into account environmental context different from the present one (lower atmospheric CO2, different seasonality. This study shows temperature generally cooler than present one in southern China, but a significant warming was found over Mongolia, and a slightly higher in northeast China. Precipitation was generally higher than today in southern, northeast China, and northern Mongolia, but lower or similar to today in northwest China and north China. Enhanced EAM was then found in the southern half of China and in northeast China.

  2. Forced and internal modes of variability of the East Asian summer monsoon

    Directory of Open Access Journals (Sweden)

    J. Liu

    2008-05-01

    Full Text Available The modern instrumental record (1979–2006 is analyzed in an attempt to reveal the dynamical structure and origins of the major modes of interannual variability of East Asian summer monsoon (EASM and to elucidate their fundamental differences with the major modes of seasonal variability. These differences are instrumental in understanding of the forced (say orbital and internal (say interannual modes of variability in EASM. We show that the leading mode of interannual variation, which accounts for about 39% of the total variance, is primarily associated with decaying phases of major El Nino, whereas the second mode, which accounts for 11.3% of the total variance, is associated with the developing phase of El Nino/La Nina. The EASM responds to ENSO in a nonlinear fashion with regard to the developing and decay phases of El Nino. The two modes are determined by El Nino/La Nina forcing and monsoon-warm ocean interaction, or essentially driven by internal feedback processes within the coupled climate system. For this internal mode, the intertropical convergence zone (ITCZ and subtropical EASM precipitations exhibit an out-of-phase variations; further, the Meiyu in Yangtze River Valley is also out-of-phase with the precipitation in the central North China.

    In contrast, the slow and fast annual cycles forced by the solar radiation show an in-phase correlation between the ITCZ and subtropical EASM precipitation. Further, the seasonal march of precipitation displays a continental-scale northward advance of a rain band (that tilts in a southwest-northeastward direction over the entire Indian and East Asian summer monsoon from mid-May toward the end of July. This uniformity in seasonal advance suggests that the position of the northern edge of the summer monsoon or the precipitation over the central North China may be an adequate measure of the monsoon intensity for the forced mode, while the intensity of the internal mode of EASM variability

  3. Fast and Slow Responses of the South Asian Monsoon System to Anthropogenic Aerosols

    Energy Technology Data Exchange (ETDEWEB)

    Ganguly, Dilip; Rasch, Philip J.; Wang, Hailong; Yoon, Jin-Ho

    2012-09-25

    Using a global climate model with fully predictive aerosol life cycle, we investigate the fast and slow responses of the South Asian monsoon system to anthropogenic aerosol forcing. Our results show that the feedbacks associated with sea surface temperature (SST) change caused by aerosols play a more important role than the aerosol's direct impact on radiation, clouds and land surface (rapid adjustments) in shaping the total equilibrium climate response of the monsoon system to aerosol forcing. Inhomogeneous SST cooling caused by anthropogenic aerosols eventually reduces the meridional tropospheric temperature gradient and the easterly shear of zonal winds over the region, slowing down the local Hadley cell circulation, decreasing the northward moisture transport, and causing a reduction in precipitation over South Asia. Although total responses in precipitation are closer to the slow responses in general, the fast component dominates over land areas north of 25°N. Our results also show an east-west asymmetry in the fast responses to anthropogenic aerosols causing increases in precipitation west of 80°E but decreases east of it.

  4. The Joint Aerosol-Monsoon Experiment (JAMEX): A Core Element for the Asian Monsoon Year (2008-2009)

    Science.gov (United States)

    Lau, WIlliam K. M.

    2007-01-01

    The objective of the Joint Aerosol-Monsoon Experiment (JAMEX) is to unravel the physical mechanisms and multi-scale interactions associated with aerosol-monsoon water cycle in the Asian Indo-Paczj?c region towards improved prediction of rainfall in land regions of the Asian monsoon. JAMEX will be planned as a five-year (2007-201 1) multi-national aerosol-monsoon research project, aimed at promoting collaboration, partnership and alignment of ongoing and planned national and international programs. Two coordinated special observing periods (SOP), covering the pre-monsoon (April-May) and the monsoon (June-August) periods is tentatively targeted for 2008 and 2009. The major work on validation and reference site coordination will take place in 2007 through the spring of 2008. A major science workshop is planned after SOP-I1 in 2010. Modeling and satellite data utilization studies will continue throughout the entire period to help in design of the observation arrays and measurement platforms for SOPS. The tentative time schedule, including milestones and research activities is shown in Fig. 1. One of the unique aspects of JAMEX is that it stems from grass-root scientific and societal imperatives, and it bridges a gap in existing national and international research programs. Currently we have identified 10 major national and international projects/programs separately for aerosols and monsoon research planned in the next five years in China, India, Japan, Italy, and the US, that could be potential contributors or partners with JAMEX. These include the Asian-Indo- Pacific Ocean (AIPO) Project and Aerosol Research Project from China, Monsoon Asian Hydro- Atmospheric Science Research and predication Initiative (MAHASRI) from Japan, Continental Tropical Convergence Zone (CTCZ) and Severe Thunderstorm: Observations and Regional Modeling (STORM) from India, Share-Asia from Italy, Atmospheric Brown Cloud (ABC), Pacific Aerosol-Cloud-Dust Experiment (PACDEX), East Asia Study of

  5. Changes in the south Asian monsoon low level jet during recent decades and its role in the monsoon water cycle

    Science.gov (United States)

    Aneesh, S.; Sijikumar, S.

    2016-02-01

    June-September mean wind at 850 hPa from ERA-Interim, MERRA and NCEP2 reanalyses shows an increasing trend in the south Asian monsoon Low Level Jet (LLJ) during 1980-2014. In the sub-seasonal scale, the LLJ during July and September exhibits increasing trend, while August shows a decreasing trend. Lesser changes in surface pressure over heat low region and weaker Bay of Bengal convection lead to weakening of LLJ during August while an intense heat low during September results stronger LLJ. The associated moisture transport changes affect the monsoon hydrological cycle with decreasing precipitation during August and increasing precipitation during September.

  6. Different impacts of the two types of El Niño on Asian summer monsoon onset

    International Nuclear Information System (INIS)

    In this study, we investigate the features of Asian summer monsoon onset during the decaying phases of central Pacific (CP) and eastern Pacific (EP) types of El Niño. The Asian summer monsoon onset is late during the EP El Niño while it is generally normal during the CP El Niño. Compared to the CP El Niño, the EP El Niño exerts a stronger impact on the climate over the Indian Ocean and the western North Pacific. Warmer sea surface temperature (SST) develops in boreal spring in the southern Indian Ocean and thus forms a large cross-equatorial SST gradient during the EP El Niño, which induces asymmetric patterns of winds and precipitation over the Indian Ocean. The asymmetric precipitation and circulation patterns contribute to a late monsoon onset. In addition, the anomalous anticyclone over the western North Pacific during the EP El Niño also contributes to late onset of the monsoon. (letter)

  7. The peatlands developing history in the Sanjiang Plain, NE China, and its response to East Asian monsoon variation

    Science.gov (United States)

    Zhang, Zhenqing; Xing, Wei; Wang, Guoping; Tong, Shouzheng; Lv, Xianguo; Sun, Jimin

    2015-06-01

    Studying the peatlands accumulation and carbon (C) storage in monsoonal areas could provide useful insights into the response of C dynamics to climate variation in the geological past. Here, we integrated 40 well-dated peat/lake sediment cores to reveal the peatlands evolution history in the Sanjiang Plain and examine its links to East Asian monsoon variations during the Holocene. The results show that 80% peatlands in the Sanjiang Plain initiated after 4.7 ka (1 ka = 1000 cal yr BP), with the largest initiating frequency around 4.5 ka. The mean C accumulation rate of peatlands in the Sanjiang Plain exhibits a synchronous increase with the peatlands expansion during the Holocene. Such a peatlands expanding and C accumulating pattern corresponds well to the remarkable drying event subsequent to the Holocene monsoon maximum. We suggest that in addition to the locally topographic conditions, Holocene variations of East Asian summer monsoon (especially its associated precipitation) have played a critical role in driving the peatlands initiation and expansion in the Sanjiang Plain.

  8. Distinct effects of anthropogenic aerosols on the East Asian summer monsoon between multidecadal strong and weak monsoon stages

    Science.gov (United States)

    Xie, Xiaoning; Wang, Hongli; Liu, Xiaodong; Li, Jiandong; Wang, Zhaosheng; Liu, Yangang

    2016-06-01

    Because industrial emissions of anthropogenic aerosols over East Asia have greatly increased in recent decades, the interactions between atmospheric aerosols and the East Asian summer monsoon (EASM) have attracted enormous attention. To further understand the aerosol-EASM interaction, we investigate the impacts of anthropogenic aerosols on the EASM during the multidecadal strong (1950-1977) and weak (1978-2000) EASM stages using the Community Atmospheric Model 5.1. Numerical experiments are conducted for the whole period, including the two different EASM stages, with present day (PD, year 2000) and preindustrial (PI, year 1850) aerosol emissions, as well as the observed time-varying aerosol emissions. A comparison of the results from PD and PI shows that, with the increase in anthropogenic aerosols, the large-scale EASM intensity is weakened to a greater degree (-9.8%) during the weak EASM stage compared with the strong EASM stage (-4.4%). The increased anthropogenic aerosols also result in a significant reduction in precipitation over North China during the weak EASM stage, as opposed to a statistically insignificant change during the strong EASM stage. Because of greater aerosol loading and the larger sensitivity of the climate system during weak EASM stages, the aerosol effects are more significant during these EASM stages. These results suggest that anthropogenic aerosols from the same aerosol emissions have distinct effects on the EASM and the associated precipitation between the multidecadal weak and strong EASM stages.

  9. The First Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons

    Energy Technology Data Exchange (ETDEWEB)

    Sperber, K R; Yasunari, T

    2005-07-27

    In 2004 the Joint Scientific Committee (JSC) that provides scientific guidance to the World Climate Research Programme (WCRP) requested an assessment of (1) WCRP monsoon related activities and (2) the range of available observations and analyses in monsoon regions. The purpose of the assessment was to (a) define the essential elements of a pan-WCRP monsoon modeling strategy, (b) identify the procedures for producing this strategy, and (c) promote improvements in monsoon observations and analyses with a view toward their adequacy, and addressing any undue redundancy or duplication. As such, the WCRP sponsored the ''1st Pan-WCRP Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoons'' at the University of California, Irvine, CA, USA from 15-17 June 2005. Experts from the two WCRP programs directly relevant to monsoon studies, the Climate Variability and Predictability Programme (CLIVAR) and the Global Energy and Water Cycle Experiment (GEWEX), gathered to assess the current understanding of the fundamental physical processes governing monsoon variability and to highlight outstanding problems in simulating the monsoon that can be tackled through enhanced cooperation between CLIVAR and GEWEX. The agenda with links to the presentations can be found at: http://www.clivar.org/organization/aamon/WCRPmonsoonWS/agenda.htm. Scientific motivation for a joint CLIVAR-GEWEX approach to investigating monsoons includes the potential for improved medium-range to seasonal prediction through better simulation of intraseasonal (30-60 day) oscillations (ISO's). ISO's are important for the onset of monsoons, as well as the development of active and break periods of rainfall during the monsoon season. Foreknowledge of the active and break phases of the monsoon is important for crop selection, the determination of planting times and mitigation of potential flooding and short-term drought. With a few exceptions simulations of ISO are

  10. Reexamining the barrier effect of Tibetan Plateau on the South Asian summer monsoon

    Directory of Open Access Journals (Sweden)

    G.-S. Chen

    2013-08-01

    Full Text Available The Tibetan Plateau has been conventionally treated as an elevated heat source driving the Asian monsoon system, especially for the South Asian monsoon. Numerous model simulations with general circulation models (GCMs support this hypothesis with the finding that the Asian monsoon system is weak or absent with all elevated topographies removed. A recent model simulation shows that the South Asian summer monsoon circulation is little affected with only the Himalayas (no Tibetan Plateau kept as a barrier, leading to a hypothesis of the barrier "blocking" mechanism of the Tibetan Plateau. In this paper, a new series of experiments are designed to reexamine this barrier effect. We find that with the barrier, the large-scale summer monsoon circulation over South Asia is simulated in general agreement with the full Tibetan Plateau, which is consistent with the previous finding. However there remains significant differences in both wind field and precipitation field elsewhere, suggesting a role of the full Tibetan Plateau as well. Moreover, the proposed barrier "blocking" mechanism is not found in our experiments. The energy of the low-level air and the convection is lower/weaker over the Indian subcontinent in the full Tibetan Plateau experiment than that in the no-Tibetan Plateau experiment or the barrier only experiment, which is opposite to the barrier "blocking" hypothesis. Instead, there is a similar candle-like latent heating in the middle troposphere along the south edge of the Tibetan Plateau in both the full Tibetan Plateau and the barrier experiments, whereas this "candle heating" disappears in the no-Tibetan Plateau experiment. We propose that this candle heating is the key to understand the mechanisms of the Tibetan Plateau on the South Asian monsoon. Future studies are needed to check the source of the "candle heating" and its effect on the Asian monsoon.

  11. Contribution of oceanic and vegetation feedbacks to Holocene climate change in monsoonal Asia

    Directory of Open Access Journals (Sweden)

    A. Dallmeyer

    2010-04-01

    Full Text Available The impact of vegetation-atmosphere and ocean-atmosphere interactions on the mid- to late Holocene climate change as well as their synergy is studied for different parts of the Asian monsoon region, giving consideration to the large climatic and topographical heterogeneity in that area. We concentrate on temperature and precipitation changes as the main parameters describing monsoonal influenced climates. For our purpose, we analyse a set of coupled numerical experiments, performed with the comprehensive Earth system model ECHAM5/JSBACH-MPIOM under present-day and mid-Holocene (6 k orbital configurations (Otto et al., 2009b. The temperature change caused by the insolation forcing reveals an enhanced seasonal cycle, with a pronounced warming in summer (0.58 K and autumn (1.29 K and a cooling in the other seasons (spring: -1.32 K; winter: -0.97 K. Most of this change can be attributed to the direct response of the atmosphere, but the ocean, whose reaction has a lagged seasonal cycle (warming in autumn and winter, cooling in the other seasons, strongly modifies the signal. The simulated contribution of dynamic vegetation is small and most effective in winter, where it slightly warms the near-surface atmosphere (approx. 0.03 K. The temperature difference attributed to the synergy is on average positive, but also small. Concerning the precipitation, the most remarkable change is the postponement and enhancement of the Asian monsoon (0.46 mm/day in summer, 0.53 mm/day in autumn, mainly related to the direct atmospheric response. On regional average, the interactive ocean (ca. 0.18 mm/day amplifies the direct effect, but tends to weaken the East Asian summer monsoon and strongly increases the Indian summer monsoon rainfall rate (0.68 mm/day. The influence of dynamic vegetation on precipitation is comparatively small (<0.04 mm/day. The synergy effect has no influence, on average.

  12. Impacts of Global Warming on Hydrological Cycles in the Asian Monsoon Region

    Institute of Scientific and Technical Information of China (English)

    Koji DAIRAKU; Seita EMORI; Toru NOZAWA

    2008-01-01

    The hydrologic changes and the impact of these changes constitute a fundamental global-warmingrelated concern. Faced with threats to human life and natural ecosystems, such as droughts, floods, and soil erosion, water resource planners must increasingly make future risk assessments. Though hydrological predictions associated with the global climate change are already being performed, mainly through the use of GCMs, coarse spatial resolutions and uncertain physical processes limit the representation of terrestrial water/energy interactions and the variability in such systems as the Asian monsoon. Despite numerous studies, the regional responses of hydrologic changes resulting from climate change remains inconclusive. In this paper, an attempt at dynamical downscaling of future hydrologic projection under global climate change in Asia is addressed. The authors conducted present and future Asian regional climate simulations which were nested in the results of Atmospheric General Circulation Model (AGCM) experiments. The regional climate model could capture the general simulated features of the AGCM. Also, some regional phenomena such as orographic precipitation, which did not appear in the outcome of the AGCM simulation, were successfully produced. Under global warming, the increase of water vapor associated with the warmed air temperature was projected. It was projected to bring more abundant water vapor to the southern portions of India and the Bay of Bengal, and to enhance precipitation especially over the mountainous regions, the western part of India and the southern edge of the Tibetan Plateau. As a result of the changes in the synoptic flow patterns and precipitation under global warming, the increases of annual mean precipitation and surface runoff were projected in many regions of Asia. However, both the positive and negative changes of seasonal surface runoff were projected in some regions which will increase the flood risk and cause a mismatch between water

  13. Three centuries of Myanmar monsoon climate variability inferred from teak tree rings

    Science.gov (United States)

    D'Arrigo, Rosanne; Palmer, Jonathan; Ummenhofer, Caroline C.; Kyaw, Nyi Nyi; Krusic, Paul

    2011-12-01

    Asian monsoon extremes critically impact much of the globe’s population. Key gaps in our understanding of monsoon climate remain due to sparse coverage of paleoclimatic information, despite intensified recent efforts. Here we describe a ring width chronology of teak, one of the first high-resolution proxy records for the nation of Myanmar. Based on 29 samples from 20 living trees and spanning from 1613-2009, this record, from the Maingtha forest reserve north of Mandalay, helps fill a substantial gap in spatial coverage of paleoclimatic records for monsoon Asia. Teak growth is positively correlated with rainfall and Palmer Drought Severity Index variability over Myanmar, during and prior to the May-September monsoon season (e.g., r = 0.38 with Yangon rainfall, 0.001, n 68). Importantly, this record also correlates significantly with larger-scale climate indices, including core Indian rainfall (23°N, 76°E a particularly sensitive index of the monsoon), and the El Niño-Southern Oscillation (ENSO). The teak ring width value following the so-called 1997-98 El Niño of the Century suggests that this was one of the most severe droughts in the past ˜300 years in Myanmar. Evidence for past dry conditions inferred for Myanmar is consistent with tree-ring records of decadal megadroughts developed for Thailand and Vietnam. These results confirm the climate signature related to monsoon rainfall in the Myanmar teak record and the considerable potential for future development of climate-sensitive chronologies from Myanmar and the broader region of monsoon Asia.

  14. Global warming and the weakening of the Asian summer monsoon circulation: assessments from the CMIP5 models

    Science.gov (United States)

    Sooraj, K. P.; Terray, Pascal; Mujumdar, M.

    2015-07-01

    The evolution of the Asian summer monsoon (ASM) in a global warming environment is a serious scientific and socio-economic concern since many recent studies have demonstrated the weakening nature of large-scale tropical circulation under anthropogenic forcing. But, how such processes affect the ASM circulation and rainfall is still a matter of debate. This study examines the climate model projections from a selected set of Coupled Model Inter-comparison Project 5 (CMIP5) models to provide a unified perspective on the future ASM response. The results indicate a robust reduction in the large-scale meridional gradient of temperature (MGT) at upper levels (200 hPa) over the ASM region, associated with enhanced ascendance and deep tropospheric heating over the equatorial Pacific in the future climate. The differential heating in the upper troposphere, with concomitant increase (decrease) in atmospheric stability (MGT), weakens the ASM circulation, promotes a northward shift of the monsoon circulation and a widening of the local Hadley cell in the eastern Indian sector. An examination of the water vapour budget indicates the competing effects of the thermodynamic (moisture convergence) and dynamics processes (monsoon circulation) on future ASM rainfall changes. The former component wins out over the later one and leads to the intensification of Indian monsoon rainfall in the CMIP5 projections. However, the diagnostics further show a considerable offset due to the dynamic component.

  15. Identification of tipping elements of the Indian Summer Monsoon using climate network approach

    Science.gov (United States)

    Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

    2015-04-01

    Spatial and temporal variability of the rainfall is a vital question for more than one billion of people inhabiting the Indian subcontinent. Indian Summer Monsoon (ISM) rainfall is crucial for India's economy, social welfare, and environment and large efforts are being put into predicting the Indian Summer Monsoon. For predictability of the ISM, it is crucial to identify tipping elements - regions over the Indian subcontinent which play a key role in the spatial organization of the Indian monsoon system. Here, we use climate network approach for identification of such tipping elements of the ISM. First, we build climate networks of the extreme rainfall, surface air temperature and pressure over the Indian subcontinent for pre-monsoon, monsoon and post-monsoon seasons. We construct network of extreme rainfall event using observational satellite data from 1998 to 2012 from the Tropical Rainfall Measuring Mission (TRMM 3B42V7) and reanalysis gridded daily rainfall data for a time period of 57 years (1951-2007) (Asian Precipitation Highly Resolved Observational Data Integration Towards the Evaluation of Water Resources, APHRODITE). For the network of surface air temperature and pressure fields, we use re-analysis data provided by the National Center for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR). Second, we filter out data by coarse-graining the network through network measures, and identify tipping regions of the ISM. Finally, we compare obtained results of the network analysis with surface wind fields and show that occurrence of the tipping elements is mostly caused by monsoonal wind circulation, migration of the Intertropical Convergence Zone (ITCZ) and Westerlies. We conclude that climate network approach enables to select the most informative regions for the ISM, providing realistic description of the ISM dynamics with fewer data, and also help to identify tipping regions of the ISM. Obtained tipping elements deserve a

  16. Leaf physiognomy and climate: Are monsoon systems different?

    Science.gov (United States)

    Jacques, Frédéric M. B.; Su, Tao; Spicer, Robert A.; Xing, Yaowu; Huang, Yongjiang; Wang, Weiming; Zhou, Zhekun

    2011-03-01

    Our understanding of past climatic changes depends on our ability to obtain reliable palaeoclimate reconstructions. Climate Leaf Analysis Multivariate Program (CLAMP) uses the physiognomy of woody dicot leaf assemblages to quantitatively reconstruct terrestrial palaeoclimates. However, the present calibrations do not always allow us to reconstruct correctly the climate of some regions due to differing palaeofloristic histories. Present calibrations are also inappropriate for regions experiencing strong monsoon regimes. To help solve this problem, we have established a new calibration that can accommodate monsoonal climates in Asia. Our new calibration is based on the Physg3brcAZ dataset with 45 new Chinese sites added. These Chinese sites are taken from humid to mesic vegetations across China, and all are influenced by monsoonal conditions to some extent. They plot in a distinct part of physiognomic space, whether they are analysed as passive or active samples. The standard deviations for the new monsoonal calibration (1.25 °C for MAT and 217.7 mm for GSP) are in the same range as those observed for previous calibrations. The new monsoonal calibration was tested using a cross validation procedure. The estimates derived from the new monsoonal calibration (PhysgAsia1) for the Chinese sites are more accurate than those obtained from the Physg3brcAZ calibration, especially for the moisture related parameters. The mean absolute error for GSP of the Chinese sites is 294.6 mm in the new monsoonal calibration, whereas it was 1609.6 mm in the Physg3brcAZ calibration. Results for the three wettest months and three driest months are also more accurate and precise, which allows us to study the seasonality of the precipitation, and hence the monsoon. The new monsoonal calibration also gives accurate results for enthalpy reconstruction. Enthalpy is a parameter that is used for palaeoaltimetry, the new calibration is therefore useful for studies of land surface height changes in

  17. Astronomical and Hydrological Perspective of Mountain Impacts on the Asian Summer Monsoon

    Science.gov (United States)

    He, Bian; Wu, Guoxiong; Liu, Yimin; Bao, Qing

    2015-12-01

    The Asian summer monsoon has great socioeconomic impacts. Understanding how the huge Tibetan and Iranian Plateaus affect the Asian summer monsoon is of great scientific value and has far-reaching significance for sustainable global development. One hypothesis considers the plateaus to be a shield for monsoon development in India by blocking cold-dry northerly intrusion into the tropics. Based on astronomical radiation analysis and numerical modeling, here we show that in winter the plateaus cannot block such a northerly intrusion; while in summer the daily solar radiation at the top of the atmosphere and at the surface, and the surface potential temperature to the north of the Tibetan Plateau, are higher than their counterparts to its south, and such plateau shielding is not needed. By virtue of hydrological analysis, we show that the high energy near the surface required for continental monsoon development is maintained mainly by high water vapor content. Results based on potential vorticity-potential temperature diagnosis further demonstrate that it is the pumping of water vapor from sea to land due to the thermal effects of the plateaus that breeds the Asian continental monsoon.

  18. How can aerosols affect the Asian summer monsoon? Assessment during three consecutive pre-monsoon seasons from CALIPSO satellite data

    Directory of Open Access Journals (Sweden)

    J. Kuhlmann

    2010-02-01

    Full Text Available The impact of aerosols above and around the Tibetan Plateau on the Asian Summer Monsoon during pre-monsoon seasons March-April-May 2007, 2008, and 2009 is investigated by means of remote sensing and radiative transfer modelling. Four source regions are found to be responsible for the high aerosol loading around the Tibetan Plateau: the Taklamakan Desert, the Ganges Plains, the Indus Plains, and the Arabian Sea. CALIPSO lidar satellite data, providing vertically resolved images of aerosols, shows aerosol concentrations to be highest in the lower 5 km of the atmosphere with only little amounts reaching the Tibetan Plateau altitude. Using a radiative transfer model we find that aerosol plumes reduce shortwave radiation throughout the Monsoon region in the seasonal average by between 20 and 30 W/m2. Peak shortwave heating in the lower troposphere reaches 0.2 K/day. In higher layers this shortwave heating is partly balanced by longwave cooling. Although high-albedo surfaces, such as deserts or the Tibetan Plateau, increase the shortwave heating by around 10%, the overall effect is strongest close to the aerosol sources. A strong elevated heating which could influence large-scale monsoonal circulations as suggested by previous studies is not found.

  19. How can aerosols affect the Asian summer monsoon? Assessment during three consecutive pre-monsoon seasons from CALIPSO satellite data

    Directory of Open Access Journals (Sweden)

    J. Kuhlmann

    2010-05-01

    Full Text Available The impact of aerosols above and around the Tibetan Plateau on the Asian Summer Monsoon during pre-monsoon seasons March-April-May 2007, 2008, and 2009 is investigated by means of remote sensing and radiative transfer modelling. Four source regions are found to be responsible for the high aerosol loading around the Tibetan Plateau: the Taklamakan Desert, the Ganges Plains, the Indus Plains, and the Arabian Sea. CALIPSO lidar satellite data, providing vertically resolved images of aerosols, shows aerosol concentrations to be highest in the lower 5 km of the atmosphere with only little amounts reaching the Tibetan Plateau altitude. Using a radiative transfer model we find that aerosol plumes reduce shortwave radiation throughout the Monsoon region in the seasonal average by between 20 and 30 W/m2. Peak shortwave heating in the lower troposphere reaches 0.2 K/day. In higher layers this shortwave heating is partly balanced by longwave cooling. Although high-albedo surfaces, such as deserts or the Tibetan Plateau, increase the shortwave heating by around 10%, the overall effect is strongest close to the aerosol sources. A strong elevated heating which could influence large-scale monsoonal circulations as suggested by previous studies is not found.

  20. Characteristics of Clay Minerals in the Northern South China Sea and Its Implications for Evolution of East Asian Monsoon since Miocene

    Institute of Scientific and Technical Information of China (English)

    Wan Shiming; Li Anchun; Xu Kehui; Yin Xueming

    2008-01-01

    Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows

  1. Response of the Asian Summer Monsoon to Weakening of Atlantic Thermohaline Circulation

    Institute of Scientific and Technical Information of China (English)

    Lu Riyu; Buwen DONG

    2008-01-01

    Various paleocllimate records have shown that the Asian monsoon was punctuated by numerous sub-orbital time-scale events,,and these events were coeval with those that happened in the North Atlantic..This study investigates the Asian summer monsoon responses to the Atlantic 0cean forcing by applying an additional freshwater flux into the North Atlantic.The simulated results indicate that the cold North Atlantic and warm South Atlantic induced by the weakened Atlantic thermohaline circulation(THC)due to the freshwater flux lead to significantly suppressed Asian summer monsoon.The authors analyzed the detailed processes of the Atlantic Ocean forcing on the Asian summer monsoon,and found that the atmospheric teleconnection in the eastern and central North Pacific and the atmosphere-ocean interaction in the tropical North Pacific play the most crucial role.Enhanced precipitation in the subtropical North Pacific extends the effects of Atlantic Ocean forcing from the eastern Pacific into the western Pacific,and the atmosphere-ocean jinteraction in the tropical Pacific and Indian 0pcean intensifies the circulation and precipitation anomalies in the Pacific and East Asia.

  2. The effect of the Asian Monsoon to the atmospheric boundary layer over the Tibetan Plateau

    Science.gov (United States)

    Li, Maoshan; Su, Zhongbo; Chen, Xuelong; Zheng, Donghai; Sun, Fanglin; Ma, Yaoming; Hu, Zeyong

    2016-04-01

    Modulation of the diurnal variations in the convective activities associated with day-by-day changes of surface flux and soil moisture was observed in the beginning of the monsoon season on the central Tibetan plateau (Sugimoto et al., 2008) which indicates the importance of land-atmosphere interactions in determining convective activities over the Tibetan plateau. Detailed interaction processes need to be studied by experiments designed to evaluate a set of hypotheses on mechanisms and linkages of these interactions. A possible function of vegetation to increase precipitation in cases of Tibetan High type was suggested by Yamada and Uyeda (2006). Use of satellite derived plateau scale soil moisture (Wen et al., 2003) enables the verification of these hypotheses (e.g. Trier et al. 2004). To evaluate these feedbacks, the mesoscale WRF model will be used because several numerical experiments are being conducted to improve the soil physical parameterization in the Noah land surface scheme in WRF so that the extreme conditions on the Tibetan plateau could be adequately represented (Van der Velde et al., 2009) such that the impacts on the structure of the atmospheric boundary layer can be assessed and improved. The Tibetan Observational Research Platform (TORP) operated by the Institute of Tibetan Plateau (Ma et al., 2008) will be fully utilized to study the characteristics of the plateau climate and different aspects of the WRF model will be evaluated using this extensive observation platform (e.g. Su et al., 2012). Recently, advanced studies on energy budget have been done by combining field and satellite measurements over the Tibetan Plateau (e.g. Ma et al., 2005). Such studies, however, were based on a single satellite observation and for a few days over an annual cycle, which are insufficient to reveal the relation between the land surface energy budget and the Asian monsoon over the Tibetan plateau. Time series analysis of satellite observations will provide the

  3. Air pollution episodes associated with East Asian winter monsoons

    International Nuclear Information System (INIS)

    A dozen multi-day pollution episodes occur from October to February in Hanoi, Vietnam due to prolonged anticyclonic conditions established after the northeast monsoon surges (cold surges). These winter pollution episodes (WPEs) account for most of the 24-h PM10 exceedances and the highest concentrations of gaseous pollutants in Hanoi. In this study, WPEs were investigated using continuous air quality monitoring data and information on upper-air soundings and air mass trajectories. The 24-h pollutant concentrations are lowest during cold surges; concurrently rise thereafter reaching the highest levels toward the middle of a monsoon cycle, then decline ahead of the next cold surge. Each monsoon cycle usually proceeds through a dry phase and a humid phase as Asiatic continental cold air arrives in Hanoi through inland China then via the East China Sea. WPEs are associated with nighttime radiation temperature inversions (NRTIs) in the dry phase and subsidence temperature inversions (STIs) in the humid phase. In NRTI periods, the rush hour pollution peak is more pronounced in the evening than in the morning and the pollution level is about two times higher at night than in daytime. In STI periods, broad morning and evening traffic peaks are observed and pollution is as high at night as in daytime. The close association between pollution and winter monsoon meteorology found in this study for the winter 2003-04 may serve as a basis for advance warning of WPEs and for forecasting the 24-h pollutant concentrations. - Highlights: → Dozen pollution episodes from Oct. to Feb in Hanoi associated with anticyclones after monsoon surges. → 24-h concentrations of PM10, SO2, NO2, CO rise after surge and decline ahead of the next. → Episodes caused by nighttime radiation and subsidence inversions in dry and humid monsoon phases. → Distinct diurnal variations of pollutant concentrations observed in the two periods. → Close pollution-meteorology association serve as a basis

  4. Hydrological changes of DOM composition and biodegradability of rivers in temperate monsoon climates

    Science.gov (United States)

    Shin, Yera; Lee, Eun-Ju; Jeon, Young-Joon; Hur, Jin; Oh, Neung-Hwan

    2016-09-01

    The spatial and hydrological dynamics of dissolved organic matter (DOM) composition and biodegradability were investigated for the five largest rivers in the Republic of Korea (South Korea) during the years 2012-2013 using incubation experiments and spectroscopic measurements, which included parallel factor analysis (PARAFAC). The lower reaches of the five rivers were selected as windows showing the integrated effects of basin biogeochemistry of different land use under Asian monsoon climates, providing an insight on consistency of DOM dynamics across multiple sites which could be difficult to obtain from a study on an individual river. The mean dissolved organic carbon (DOC) concentrations of the five rivers were relatively low, ranging from 1.4 to 3.4 mg L-1, due to the high slope and low percentage of wetland cover in the basin. Terrestrial humic- and fulvic-like components were dominant in all the rivers except for one, where protein-like compounds were up to ∼80%. However, terrestrial components became dominant in all five of the rivers after high precipitation during the summer monsoon season, indicating the strong role of hydrology on riverine DOM compositions for the basins under Asian monsoon climates. Considering that 64% of South Korea is forested, our results suggest that the forests could be a large source of riverine DOM, elevating the DOM loads during monsoon rainfall. Although more DOM was degraded when DOM input increased, regardless of its sources, the percent biodegradability was reduced with increased proportions of terrestrially derived aromatic compounds. The shift in DOM quality towards higher percentages of aromatic terrestrial compounds may alter the balance of the carbon cycle of coastal ecosystems by changing microbial metabolic processes if climate extremes such as heavy storms and typhoons become more frequent due to climate change.

  5. Implications of East Asian summer and winter monsoons for interannual aerosol variations over central-eastern China

    Science.gov (United States)

    Cheng, Xugeng; Zhao, Tianliang; Gong, Sunling; Xu, Xiangde; Han, Yongxiang; Yin, Yan; Tang, Lili; He, Hongchang; He, Jinhai

    2016-03-01

    Air quality change is generally driven by two factors: pollutant emissions and meteorology, which are difficult to distinguish via observations. To identify the contribution of meteorological factor to air quality change, an aerosol simulation from 1995 to 2004 with the global air quality model GEM-AQ/EC was designed without year-to-year changes in the anthropogenic aerosol (including sulfate and organic and black carbon) emissions over the 10-year span. To assess the impact of interannual variations of East Asian monsoon (EAM) on air quality change in China, this modeling study focused on the region of central-eastern China (CEC), a typical East Asian monsoon (EAM) region with high anthropogenic aerosol emissions. The simulation analysis showed that the interannual variability in surface aerosols over CEC was driven by fluctuation in meteorological factors associated with EAM changes. Large amplitudes of interannual variability in surface aerosol concentrations reaching 20-30% relative to the 10-year averages were found over southern CEC in summer and over northern CEC in winter. The weakened near-surface winds of EAMs in both summer and winter were significantly correlated with aerosol increases over most areas of CEC. The summer and winter monsoon changes enhance the surface aerosol concentrations with increasing trend rates exceeding 30% and 40% over the southern and northern CEC region, respectively, during the 10 years. The composite analyses of aerosol concentrations in weak and strong monsoon years revealed that positive anomalies in surface aerosol concentrations during weak summer monsoon years were centered over the vast CEC region from the North China Plain to the Sichuan Basin, and the anomaly pattern with "northern higher" and "southern lower" surface aerosol levels was distributed over CEC in weak winter monsoon years. Aerosol washout by summer monsoon rainfall exerted an impact on CEC aerosol distribution in summer; aerosol dry depositions in

  6. Multi-scale Holocene Asian monsoon variability deduced from a twin-stalagmite record in southwestern China

    Science.gov (United States)

    Huang, Wei; Wang, Yongjin; Cheng, Hai; Edwards, Richard Lawrence; Shen, Chuan-Chou; Liu, Dianbing; Shao, Qingfeng; Deng, Chao; Zhang, Zhenqiu; Wang, Quan

    2016-07-01

    We present two isotopic (δ18O and δ13C) sequences of a twin-stalagmite from Zhuliuping Cave, southwestern China, with 230Th dates from 14.6 to 4.6 ka. The stalagmite δ18O record characterizes orbital- to decadal-scale variability of Asian summer monsoon (ASM) intensity, with the Holocene optimum period (HOP) between 9.8 and 6.8 ka BP which is reinforced by its co-varying δ13C data. The large multi-decadal scale amplitude of the cave δ18O indicates its high sensitivity to climate change. Four centennial-scale weak ASM events during the early Holocene are centered at 11.2, 10.8, 9.1 and 8.2 ka. They can be correlated to cold periods in the northern high latitudes, possibly resulting from rapid dynamics of atmospheric circulation associated with North Atlantic cooling. The 8.2 ka event has an amplitude more than two-thirds that of the Younger Dryas (YD), and is significantly stronger than other cave records in the Asia monsoon region, likely indicating a more severe dry climate condition at the cave site. At the end of the YD event, the δ13C record lags the δ18O record by 300-500 yr, suggesting a multi-centennial slow response of vegetation and soil processes to monsoon enhancement.

  7. The rise of the Himalaya enforced the diversification of SE Asian ferns by altering the monsoon regimes

    Directory of Open Access Journals (Sweden)

    Wang Li

    2012-11-01

    Full Text Available Abstract Background The rise of high mountain chains is widely seen as one of the factors driving rapid diversification of land plants and the formation of biodiversity hotspots. Supporting evidence was reported for the impact of the rapid rise of the Andean mountains but this hypothesis has so far been less explored for the impact of the “roof of the world”. The formation of the Himalaya, and especially the rise of the Qinghai–Tibetan Plateau in the recent 20 million years, altered the monsoon regimes that dominate the current climates of South East Asia. Here, we infer the hypothesis that the rise of Himalaya had a strong impact on the plant diversity in the biodiversity hotspot of the Southwest Chinese Mountains. Results Our analyses of the diversification pattern of the derived fern genus Lepisorus recovered evidence for changes in plant diversity that correlated with the strengthening of South East Asian monsoon. Southwest China or Southwest China and Japan was recovered as the putative area of origin of Lepisorus and enhancing monsoon regime were found to shape the early diversification of the genus as well as subsequent radiations during the late Miocene and Pliocene. Conclusions We report new evidence for a coincidence of plant diversification and changes of the climate caused by the uplift of the Himalaya. These results are discussed in the context of the impact of incomplete taxon sampling, uncertainty of divergence time estimates, and limitations of current methods used to assess diversification rates.

  8. Evaluation of global climate models for Indian monsoon climatology

    International Nuclear Information System (INIS)

    The viability of global climate models for forecasting the Indian monsoon is explored. Evaluation and intercomparison of model skills are employed to assess the reliability of individual models and to guide model selection strategies. Two dominant and unique patterns of Indian monsoon climatology are trends in maximum temperature and periodicity in total rainfall observed after 30 yr averaging over India. An examination of seven models and their ensembles reveals that no single model or model selection strategy outperforms the rest. The single-best model for the periodicity of Indian monsoon rainfall is the only model that captures a low-frequency natural climate oscillator thought to dictate the periodicity. The trend in maximum temperature, which most models are thought to handle relatively better, is best captured through a multimodel average compared to individual models. The results suggest a need to carefully evaluate individual models and model combinations, in addition to physical drivers where possible, for regional projections from global climate models. (letter)

  9. Seasonal Transition Features of Large-Scale Moisture Transport in the Asian-Australian Monsoon Region

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Using NCEP/NCAR reanalysis data for the period of 1957-2001, the climatological seasonal transition features of large-scale vertically integrated moisture transport (VIMT) in the Asian-Australian monsoon region are investigated in this paper. The basic features of the seasonal transition of VIMT from winter to summer are the establishment of the summertime "great moisture river" pattern (named the GMR pattern)and its eastward expansion, associated with a series of climatological events which occurred in some "key periods", which include the occurrence of the notable southerly VIMT over the Indochina Peninsula in mid March, the activity of the low VIMT vortex around Sri Lanka in late April, and the onset of the South China Sea summer monsoon in mid May, among others. However, during the transition from summer to winter, the characteristics are mainly exhibited by the establishment of the easterly VIMT belt located in the tropical area, accompanied by some events occurring in "key periods". Further analyses disclose a great difference between the Indian and East Asian monsoon regions when viewed from the meridional migration of the westerly VIMT during the seasonal change process, according to which the Asian monsoon region can be easily divided into two parts along the western side of the Indochina Peninsula and it may also denote different formation mechanisms between the two regions.

  10. Atmospheric methane observed from space over the Asian monsoon: implications for emission from Asian rice paddies

    Science.gov (United States)

    Hayashida, S.; Yoshizaki, S.; Frankenberg, C.; Yan, X.

    2010-12-01

    More than 40% of anthropogenic emissions of methane, the second most important greenhouse gas, is estimated to be from agricultural sources, including rice cultivation. Unfortunately, the strength of individual sources of methane remains uncertain, despite the importance of its effect in global warming. Here we focus on the Asian monsoon region to improve our understanding of methane emission from rice paddy fields. This region contains about 90% of the world’s rice fields. We analyze the temporal and spatial distribution of atmospheric methane concentrations observed from space and compare it with ground-based measurements and bottom-up emission inventory data coupled with rice field maps. Recently, Frankenberg et al. [2008] derived an updated version of methane concentration from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY: SCIA hereafter) instrument onboard ENVISAT. This showed a clear signature of methane enhancement over the Asian monsoon. As SCIA retrievals include all involve column densities, we carefully examined potential biases and variability due to the gradient of methane concentration over source regions by comparing these data with ground-based measurements at 53 stations of the WDCGG network. After evaluating the bias and variability of methane concentration over the source regions, we examined selected areas where rice paddies were highly concentrated, and the methane emission inventories were estimated to be large. The sampled areas were North and South India, Bangladesh, Myanmar, Thailand, South China, and the Sichuan Basin. All of these are known to be major rice cultivation areas. The time series of monthly mean SCIA retrievals were compared with the emission inventory data for rice cultivation archived in the GISS dataset and Yan et al. [2009], as well as with precipitation data (Huffman et al., 1997). The phase of seasonal variation of SCIA retrievals corresponded closely to those of emission

  11. The Summer Monsoon Onset over the Tropical Eastern Indian Ocean: The Earliest Onset Process of the Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The onset process of the tropical eastern Indian Ocean (TEIO) summer monsoon (TEIOSM) and its relationship with the cross-equatorial flows are investigated via climatological analysis. Climatologically,results indicate that the earliest onset process of the Asian summer monsoon occurs over the TEIO at pentad 22 (April 15-20). Unlike the abrupt onset of the South China Sea (SCS) summer monsoon, the TEIOSM onset process displays a stepwise advance. Moreover, a close relationship between the TEIOSM development and the northward push of the cross-equatorial flows over 80°-90°E is revealed. A difference vorticity center, together with the counterpart over the southern Indian Ocean, constitutes a pair of difference cyclonic vortices, which strengthens the southwesterly wind over the TEIO and the northerly wind to the west of the Indian Peninsula from the end of March to late May. Therefore, the occurrence of the southwesterly wind over the TEIO is earlier than its counterpart over the tropical western Indian Ocean, and the cross-equatorial flows emerge firstly over the TEIO rather than over the Somali area.The former increases in intensity during its northward propagation, which provides a precondition for the TEIOSM onset and its northward advance.

  12. Feedback Attributions to the Interannual Variation of the Dominant Modes of the East Asian Winter Monsoon

    Science.gov (United States)

    Li, Yana; Yang, Song

    2016-04-01

    This study investigates the interannual variation and feedback attributions of the East Asian Winter Monsoon for the period of 1979-2013. The variations of winter mean surface air temperature are dominated by two distinct principal modes, which account for 70.9% of the total variance. The interannual variation of the northern mode features high correlations with the variations of the Arctic Oscillation, the Siberia High, and the tropoical Indian Ocean Dipole, while the southern mode is strongly linked to the East Asia trough and the atmospheric circulation over the northwestern Pacific. To find the main factors which affect the two different modes, this study decomposes the surface air temperature interannual variation into various feedback attributions by applying a climate feedback-response analysis method. The results indicate that the surface cooling associated with the northern mode is mainly contributed by the feedback processes of atmospheric dynamics, cloud, and sensible heating. For the southern mode, the surface cooling is mainly attributed to the atmospheric dynamic process, sensible heating, and water vapor, while the oceanic dynamics and heat storage process induces a negative effect that warms the surface.

  13. Impact of different Asian source regions on the composition of the Asian monsoon anticyclone and of the extratropical lowermost stratosphere

    Science.gov (United States)

    Vogel, B.; Günther, G.; Müller, R.; Grooß, J.-U.; Riese, M.

    2015-12-01

    The impact of different boundary layer source regions in Asia on the chemical composition of the Asian monsoon anticyclone, considering its intraseasonal variability in 2012, is analysed by simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS) using artificial emission tracers. The horizontal distribution of simulated CO, O3, and artificial emission tracers for India/China are in good agreement with patterns found in satellite measurements of O3 and CO by the Aura Microwave Limb Sounder (MLS). Using in addition, correlations of artificial emission tracers with potential vorticity demonstrates that the emission tracer for India/China is a very good proxy for spatial distribution of trace gases within the Asian monsoon anticyclone. The Asian monsoon anticyclone constitutes a horizontal transport barrier for emission tracers and is highly variable in location and shape. From the end of June to early August, a northward movement of the anticyclone and, during September, a strong broadening of the spatial distribution of the emission tracer for India/China towards the tropics are found. In addition to the change of the location of the anticyclone, the contribution of different boundary source regions to the composition of the Asian monsoon anticyclone in the upper troposphere strongly depends on its intraseasonal variability and is therefore more complex than hitherto believed. The largest contributions to the composition of the air mass in the anticyclone are found from northern India and Southeast Asia at a potential temperature of 380 K. In the early (mid-June to mid-July) and late (September) period of the 2012 monsoon season, contributions of emissions from Southeast Asia are highest; in the intervening period (early August), emissions from northern India have the largest impact. Our findings show that the temporal variation of the contribution of different convective regions is imprinted in the chemical composition of the Asian monsoon

  14. Role of Atmospheric Circulation and Westerly Jet Changes in the mid-Holocene East Asian Summer Monsoon

    Science.gov (United States)

    Kong, W.; Chiang, J. C. H.

    2014-12-01

    The East Asian Summer Monsoon (EASM) varies on inter-decadal to interglacial-glacial timescales. The EASM is stronger in the mid-Holocene than today, and these changes can be readily explained by orbitally-driven insolation increase during the boreal summer. However, a detailed understanding of the altered seasonal evolution of the EASM during this time is still lacking. In particular, previous work has suggested a close link between seasonal migration of the EASM and that of the mid-latitude westerlies impinging on the Tibetan Plateau. In this study, we explore, this problem in PMIP3 climate model simulations of the mid-Holocene, focusing on the role of atmospheric circulation and in particular how the westerly jet modulates the East Asia summer climate on paleoclimate timescales. Analysis of the model simulations suggests that, compared to the preindustrial simulations, the transition from Mei-Yu to deep summer rainfall occurs earlier in the mid-Holocene. This is accompanied by an earlier weakening and northward shift of westerly jet away from the Tibetan Plateau. The variation in the strength and the 3-D structure of the westerly jet in the mid-Holocene is summarized. We find that changes to the monsoonal rainfall, westerly jet and meridional circulation covary on paleoclimate timescales. Meridional wind changes in particular are tied to an altered stationary wave pattern, resembling today's the so-called 'Silk Road' teleconnection pattern, riding along the westerly jet. Diagnostic analysis also reveals changes in moist static energy and eddy energy fluxes associated with the earlier seasonal transition of the EASM. Our analyses suggest that the westerly jet is critical to the altered dynamics of the East Asian summer monsoon during the mid-Holocene.

  15. IMPACTS OF THE ONSET OF THE SOUTHEAST ASIAN SUMMER MONSOON ON THE BEGINNING OF THE RAINY SEASON IN YUNNAN

    Institute of Scientific and Technical Information of China (English)

    JU Jian-hua; ZHAO Er-xu; LU Jun-mei

    2006-01-01

    @@ 1 INTRODUCTION Summer monsoon in Southeast Asia can cause large-scale precipitation in the region in early summer,which is featured by prevailing low-level southwesterly from the Bay of Bengal to South China Sea (SCS). It has characteristics of its own as well as those of Asian monsoons in general.

  16. The observed impacts of South Asian summer monsoon on the near-surface turbulent heat exchange over the Southeast Tibet

    Science.gov (United States)

    Zhou, Libo

    2016-04-01

    The Southeast Tibet is an important region of the Tibetan Plateau bearing the interaction between the Tibetan and the neighbor atmospheric systems. The South Asian summer monsoon (SASM) as a basic climate system in Asia could impact the local atmosphere and the near-surface heat exchange process in the Southeast Tibet. An observational campaign, OSEP2013, was carried out in this region during SASM in 2013. The atmospheric parameters and turbulent heat fluxes were observed and averaged over three different land surfaces of the inhomogeneous landscape during the observation campaign. Results show clear SASM impacts on the local atmosphere and near-surface heat exchange in the Southeast Tibet. The South Asian summer monsoon was onset on June 1, 2013, and experienced a south phase and north phase during OSEP2013. The convection and humidity were increased in the Southeast Tibet by SASM, especially during the north phase. The observation domain received low radiation energy due to the convective clouds brought by SASM, and the soil and air temperatures were lowered as consequence. In addition, the air humidity was increased over this region by the wet air transportation of SASM circulation. The sensible and latent heat transfers were decreased by the low land-air temperature difference and high air humidity during SASM. The latent heat transfer dominated the total heat transfer in the Southeast Tibet due to the low sensible heat transfer in the SASM situation, and the domination was increased as the sensible heat transfer was further decreased during the SASM north phase.

  17. An abrupt centennial-scale drought event and mid-holocene climate change patterns in monsoon marginal zones of East Asia.

    Science.gov (United States)

    Li, Yu; Wang, Nai'ang; Zhang, Chengqi

    2014-01-01

    The mid-latitudes of East Asia are characterized by the interaction between the Asian summer monsoon and the westerly winds. Understanding long-term climate change in the marginal regions of the Asian monsoon is critical for understanding the millennial-scale interactions between the Asian monsoon and the westerly winds. Abrupt climate events are always associated with changes in large-scale circulation patterns; therefore, investigations into abrupt climate changes provide clues for responses of circulation patterns to extreme climate events. In this paper, we examined the time scale and mid-Holocene climatic background of an abrupt dry mid-Holocene event in the Shiyang River drainage basin in the northwest margin of the Asian monsoon. Mid-Holocene lacustrine records were collected from the middle reaches and the terminal lake of the basin. Using radiocarbon and OSL ages, a centennial-scale drought event, which is characterized by a sand layer in lacustrine sediments both from the middle and lower reaches of the basin, was absolutely dated between 8.0-7.0 cal kyr BP. Grain size data suggest an abrupt decline in lake level and a dry environment in the middle reaches of the basin during the dry interval. Previous studies have shown mid-Holocene drought events in other places of monsoon marginal zones; however, their chronologies are not strong enough to study the mechanism. According to the absolutely dated records, we proposed a new hypothesis that the mid-Holocene dry interval can be related to the weakening Asian summer monsoon and the relatively arid environment in arid Central Asia. Furthermore, abrupt dry climatic events are directly linked to the basin-wide effective moisture change in semi-arid and arid regions. Effective moisture is affected by basin-wide precipitation, evapotranspiration, lake surface evaporation and other geographical settings. As a result, the time scales of the dry interval could vary according to locations due to different geographical

  18. The Asian Monsoon Links to Solar Changes and the Intertropical Convergence Zone and 1300 Years of Chinese Human Susceptibility

    Science.gov (United States)

    Yu, E.; Hsu, Y.; Lee, T.

    2011-12-01

    Here we present a new paleoclimatic record from a sediment core recovered in Lake Liyutan in central Taiwan over the last 1300 years. The age model is based on 2 AMS 14C dates. Adjustments of age were using the well-dated records from a near by lake sediment core. The Lake Liyutan sediments record the strength of the summer monsoon in two independent ways: (1) the magnetic parameters (ARM/χ, ARM, anhysteresis remenent magnetization; χ, Volume susceptibility) and magnetic susceptibility, and (2) total organic carbon content, organic C/N elemental ratio and δ13Corg of the sediments as a result of changes in different organic matter origins and terrigenous detritus dilution due to precipitation. All the proxy records are 10 to 30- year-resolution. Weaker summer monsoon phases reconstructed from the Lake Liyutan correlate with higher δ18O at Dongge and Hulu caves, which indicates lower summer precipitation rates. Moreover, it is interesting to find that the strong winter monsoon from the Lake Huguang Maar records show a synchronous relationship with weaker summer monsoon from the caves and the Lake Liyutan. From the coincidence in timing, these records were explained by migrations in the intertropical convergence zone. In addition, the weak Asian summer monsoon in the Lake Liyutan corresponds with lowering Northern Hemisphere summer insolation recorded at Dongge cave. Climate variations influenced the agricultural productivity, health risk, and conflict level of preindustrial societies. We note that, on the basis of our new lake record, major changes in Chinese dynasties occurred when the summer monsoon strength was weaker and rainfall was reduced. The Tang dynasty began to ebb in the eighth century, and it fully collapsed in AD907, then the dynastic transitions to the Five Dynasties and Ten Kingdoms period. The weak summer monsoon and reduced rainfall was indicated in the coincidence in timing of the sediment core LYT-3A from Lake Liyutan during 1100 - 1000BP. In

  19. Long-term variations in the South Asian monsoon annual cycle: the role of regional anthropogenic aerosol forcing

    Science.gov (United States)

    Bollasina, Massimo; Ming, Yi

    2013-04-01

    Detection and attribution of long-term variations of the South Asian monsoon is of extreme importance. Indeed, even small changes in the onset and duration of the monsoon season or in the spatial distribution of the seasonal mean precipitation may severely impact agriculture, health, water availability, ecosystems, and economy for a substantial fraction of the world's population. In the past decades emissions of aerosols have dramatically increased over South Asia due to rapid urbanization and population growth. As a result, the study of the impact of anthropogenic aerosols on the monsoon has recently emerged as one of the topics of highest priority in the scientific community. This study makes use of a state-of-the-art coupled climate model, the GFDL CM3, to investigate two aspects of the aerosol influence on the 20th-century changes in the monsoon. The model has fully-interactive aerosols and a representation of both direct and indirect effects. Aerosols are responsible for the advancement of the monsoon onset over India, leading, in agreement with observations, to enhanced precipitation in June over most parts of the subcontinent. Our experiments show that the earlier onset is preceded in early spring by a strong aerosol forcing over the Bay of Bengal and Indonesia and associated atmospheric circulation anomalies. The latter triggers thermodynamical changes over the northwestern part of the Subcontinent in May and June, including enhanced surface heating, which in turn drive the movement of the monsoon to the west. We also performed historical experiments with time-evolving radiative forcings aimed at isolating the contribution of regional versus remote anthropogenic aerosol emissions on the observed 20th century widespread drying of the Indian monsoon. Indian-only aerosol sources are found to play a predominant role in generating suppressed rainfall over the subcontinent, especially during early summer. Remote aerosols contribute, although in a minor way, to

  20. NUMERICAL SIMULATION OF LAG INFLUENCE OF ENSO ON EAST-ASIAN MONSOON

    Institute of Scientific and Technical Information of China (English)

    龙振夏; 李崇银

    2001-01-01

    By prescribing sea surface temperature anomalies (SSTAs) over eastern equatorial Pacific in January-March, the lag influence of ENSO (El Nino and La Nina) on monsoon over East Asia has been studied. The results suggest that, due to the excitation of atmospheric low-frequency oscillation by the SSTA, ENSO has significant lag influence on the monsoon over East Asia.During the summer after El Nino, the subtropical high over western Pacific is intensified and shows the northward and westward displacement, meanwhile, the rainfall over East China is below normal, especially in North China; during the winter after El Nino, both the Asian trough and the winter monsoon over East Asia are strengthened. During the summer after La Nina, the anomalous subtropical high prevails over the lower reaches of Yangtze (Changjiang) River, the rainfall between Yangtze and Huaihe Rivers is below normal; during the winter after La Nina,both the Asian trough and the winter monsoon over East Asia are weaker. Compared with La Nina, the effect of El Nino is stronger, but it is not always opposite to the one of La Nina.

  1. Impact of El Nino on Large-scale Circulation of Southeast Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    白学志; 吴爱明

    2003-01-01

    Multi year SST and NCEP/NCAR reanalyzed wind data were employed to study the impacts of El Nino on the Southeast Asian summer monsoon (SEASM). It was found that the impacts of El Nino on the SEASM differed distinctly from those on the East Asian summer monsoon (EASM) and the Indian summer monsoon (ISM). Composite analysis indicated that the "gear point" of coupling between the Indo monsoon circulation and the Pacific Walker circulation was located in the western margins of Southeast Asia when the developing stage of El Nino events covered the boreal summer. The anomalous circulations in the lower and upper troposphere and divergent circulation are all favorable for the strengthening of the SEASM during this period. Following the evolution of El Nino, the "gear point" of the two cells shifted eastward tothe central Pacific when the mature or decaying period of El Nino events covered the boreal summer. The anomalous circulations are favorable for the weakening of the SEASM. The anomalous indexes of intensity of SEASM accord well withthe above results. Additionally, the difference of SSTA patterns in the tropical Indo Pacific Ocean between the two stages of the El Nino may play an important role.

  2. Carbonate leaching processes in the Red Clay Formation, Chinese Loess Plateau: Fingerprinting East Asian summer monsoon variability during the late Miocene and Pliocene

    Science.gov (United States)

    He, Tong; Chen, Yang; Balsam, William; Qiang, Xiaoke; Liu, Lianwen; Chen, Jun; Ji, Junfeng

    2013-01-01

    High-resolution variations in carbonate minerals from the Jiaxian Red Clay section, located at the northern limit of the present East Asian summer monsoon (EASM) on Chinese Loess Plateau were quantified using Fourier transform infrared spectroscopy. We analyzed a large quantity of sediments dated from the late Miocene to Pliocene (8.2-2.6 Ma). The carbonates in this interval show high-frequency variations alternating between leached and calcareous horizons. The low carbonate contents and high values of magnetic susceptibility and high Rb/Sr ratios were found in the leached zones, a pattern that is consistent with that observed in the overlying Quaternary loess-paleosol sequences. This pattern suggests that East Asian Monsoon (EAM) rainwater enhanced leaching and accumulation processes of carbonate minerals in the Red Clay Formation in a way similar to the loess-paleosol sequence. Seven alternating leached and calcareous zones are identified, suggesting oscillations of the EASM and East Asian winter monsoon intervals. The calcareous zones were also found to have high Zr/Rb ratio. These indications of shifts from a strong EASM to East Asian winter monsoon dominance correlate well with the cooling transition indicated by deep sea δ18O isotopes. This evidence suggests that the EAM was active during the late Miocene and Pliocene and was similar to the Quaternary monsoon. The presence of a strong EAM during the Pliocene Warm Period also raises questions about the hypothesis that past and future warm climate conditions could produce a permanent El Niño-like state.

  3. An Analysis of Interdecadal Variations of the Asian-African Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    SONG Yan; JI Jinjun; SUN Xia

    2008-01-01

    The response of the Asian-African summer monsoon(AASM)to the fast global warming in the 1980s is studied based on several datasets,which span a long time period of nearly 100 yr,with two special periods 1980-1985 and 1990-1995 being focused on.Wavelet analyses are employed to explore the interdecadal variations of the AASM.It is found that after the mid-1980s.the global annual mean surface temperature rises more significantly and extensively over most parts of the African Continent,north of the Indian Ocean,and the Eurasian Continent excluding the Tibetan Plateau.Correspondingly,the global precipitation pattern alters with increased rainfall seen over the Sahel and North China in 1990-1995,though it is not recovered to the level of the rainy period before the mid-1960s.Changes of monsoonal circulations between the pre-and post-1980s periods display that,after the fast global warming of the 1980s,the African summer monsoon intensifies distinctly,the Indian summer monsoon weakens a little bit,and the East Asian summer monsoon remains almost unchanged.The summer precipitation over the Asian-African Monsoon Belt(AAMB)does not change in phase coherently with the variations of the monsoonal circulations.Wavelet analyses of the land-sea thermal contrast and precipitation over North China and the Sahel indicate that interdecadal signals are dominant and in positive phases in the 1960s.1eading to an overall enhanced interdecadal variation of the AASM,although the 1960s witnesses a global cooling.In the 1980s,however,in the context of a fast global warming,interdecadal signals are in opposite phases,and they counteract with each other.1cading to a weakened interdecadal variation of the AASM.After the mid-1960s.the AASM weakened remarkably,whereas after the mid-1980s,the AASM as a whole did not strengthen uniformly and synchronously,because it is found that the interannual variations of the AASM in the 1980s are stronger than those in the 1960s,and they superimposed on the

  4. Clay mineral records of East Asian monsoon evolution during late Quaternary in the southern South China Sea

    Institute of Scientific and Technical Information of China (English)

    LIU Zhifei; C. Colin; A. Trentesaux; D. Blamart

    2005-01-01

    High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 190 ka during late Quaternary from core MD01-2393 off the Mekong River in the southern South China Sea are reported to reconstruct a history of East Asian monsoon evolution.The dominating clay mineral components indicate a strong glacial-interglacial cyclicity, with high glacial illite, chlorite, and kaolinite contents and high interglacial smectites content. The provenance analysis indicates the direct input of clay minerals via the Mekong River drainage basin.Illite and chlorite derived mainly from the upper reach of the Mekong River, where physical erosion of meta-sedimentary rocks is dominant. Kaolinite derived mainly from active erosion of inhered clays from reworked sediments in the middle reaches. Smectites originated mainly through bisiallitic soils in the middle to lower reaches of the Mekong River. The smectites/(illite+chlorite)and smectites/kaolinite ratios are determined as mineralogical indicators of East Asian monsoon variations. Relatively high ratios occur during interglacials and indicate strengthened summer-monsoon rainfall and weakened winter-monsoon winds; relatively lower ratios happened in glacials, indicating intensified winter monsoon and weakened summer monsoon. The evolution of the summer and winter monsoons provides an almost linear response to the summer insolation of the Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.

  5. Book Review: Late Cenozoic Climate Change in Asia: Loess, Monsoon and Monsoon-arid Environment Evolution

    Science.gov (United States)

    Clemens, Steven C.

    2015-01-01

    Loess-Paleosol deposits drape >500,000 km2 of eastern China, spanning environments from the humid, monsoon-influenced regions near the coast to the arid, westerlies-dominated regions inland. Sections, up to hundreds of meters thick, are exposed in deeply incised river valleys and can be accessed as well by drilling. Combined, the high sedimentation rates and extensive geographic coverage make these sections unique among global terrestrial sediment archives. The Chinese loess-paleosol sequences, and the arid interior regions to the northwest, record diverse aspects of geologic and environmental change ranging from the tectonic evolution of the Tibetan Plateau (106 year time scale) through glacial-interglacial scale changes in global ice volume and greenhouse gasses (105 year time scale) on down through the orbital (104 years) to millennial and centennial scale events (103-102 year) relevant to the underpinnings of human interactions with changing environmental pressures. 'Late Cenozoic Climate Chang in Asia: Loess, Monsoon and Monsoon-arid Environment Evolution' is a timely contribution that synthesizes findings derived from the extensive work in these areas, places the findings in the broader context of global climate change and helps to define avenues for future research.

  6. Upper-tropospheric CO and O3 budget during the Asian summer monsoon

    Science.gov (United States)

    Barret, Brice; Sauvage, Bastien; Bennouna, Yasmine; Le Flochmoen, Eric

    2016-07-01

    During the Asian summer monsoon, the circulation in the upper troposphere/lower stratosphere (UTLS) is dominated by the Asian monsoon anticyclone (AMA). Pollutants convectively uplifted to the upper troposphere are trapped within this anticyclonic circulation that extends from the Pacific Ocean to the Eastern Mediterranean basin. Among the uplifted pollutants are ozone (O3) and its precursors, such as carbon monoxide (CO) and nitrogen oxides (NOx). Many studies based on global modeling and satellite data have documented the source regions and transport pathways of primary pollutants (CO, HCN) into the AMA. Here, we aim to quantify the O3 budget by taking into consideration anthropogenic and natural sources. We first use CO and O3 data from the MetOp-A/IASI sensor to document their tropospheric distributions over Asia, taking advantage of the useful information they provide on the vertical dimension. These satellite data are used together with MOZAIC tropospheric profiles recorded in India to validate the distributions simulated by the global GEOS-Chem chemistry transport model. Over the Asian region, UTLS monthly CO and O3 distributions from IASI and GEOS-Chem display the same large-scale features. UTLS CO columns from GEOS-Chem are in agreement with IASI, with a low bias of 11 ± 9 % and a correlation coefficient of 0.70. For O3, the model underestimates IASI UTLS columns over Asia by 14 ± 26 % but the correlation between both is high (0.94). GEOS-Chem is further used to quantify the CO and O3 budget through sensitivity simulations. For CO, these simulations confirm that South Asian anthropogenic emissions have a more important impact on enhanced concentrations within the AMA (˜ 25 ppbv) than East Asian emissions (˜ 10 ppbv). The correlation between enhanced emissions over the Indo-Gangetic Plain and monsoon deep convection is responsible for this larger impact. Consistently, South Asian anthropogenic NOx emissions also play a larger role in producing O3 within

  7. Post-Pliocene establishment of the present monsoonal climate in SW China: evidence from the late Pliocene Longmen megaflora

    Science.gov (United States)

    Su, T.; Jacques, F. M. B.; Spicer, R. A.; Liu, Y.-S.; Huang, Y.-J.; Xing, Y.-W.; Zhou, Z.-K.

    2013-08-01

    The paleoclimate of the late Pliocene Longmen flora from Yongping County located at the southeastern boundary of the Qinghai-Tibet Plateau was reconstructed using two leaf-physiognomy-based methods, i.e., leaf margin analysis (LMA) and Climate Leaf Analysis Multivariate Program (CLAMP), to understand the paleoclimate condition and geographical pattern of monsoonal climate in southwestern China during the late Pliocene. The mean annual temperatures (MATs) estimated by LMA and CLAMP are 17.4 ± 3.3 °C and 17.4 ± 1.3 °C, respectively, compared with 15.9 °C at present. Meanwhile, the growing season precipitation (GSP) estimated by CLAMP is 1735.5 ± 217.7 mm in the Longmen flora, compared with 986.9 mm nowadays. The calculated monsoon intensity index (MSI) of the Longmen flora is significantly lower than that of today. These results appear consistent with previous studies on the late Pliocene floras in western Yunnan based on the coexistence approach (CA), and further suggest that there was a slightly warmer and much wetter climate during the late Pliocene than the present climate in western Yunnan. We conclude that the significant change of the monsoonal climate might have been resulted from the continuous uplift of mountains in western Yunnan, as well as the intensification of the eastern Asian winter monsoon, both occurring concurrently in the post-Pliocene period.

  8. Post-Pliocene establishment of the present monsoonal climate in SW China: evidence from the late Pliocene Longmen megaflora

    Directory of Open Access Journals (Sweden)

    T. Su

    2013-04-01

    Full Text Available The paleoclimate of the late Pliocene Longmen flora from Yongping County located at the southeastern boundary of the Qinghai-Tibet Plateau was reconstructed using two leaf physiognomy based methods, i.e. Leaf Margin Analysis (LMA and Climate Leaf Analysis Multivariate Program (CLAMP, to understand the paleoclimate condition and geographical pattern of monsoonal climate in southwestern China during the late Pliocene. The mean annual temperatures (MATs estimated by LMA and CLAMP are 17.4 ± 3.3 °C and 17.4 ± 1.3 °C, respectively, compared with 15.9 °C at present. Meanwhile, the growing season precipitation (GSP estimated by CLAMP is 1735.5 ± 217.7 mm in the Longmen flora, compared with 986.9 mm nowadays. The calculated monsoon index (MSI of the Longmen flora is significantly lower than that of today. These results appear consistent with previous studies based on the coexistence approach (CA, and further suggest that there was a slightly warmer and much wetter climate during the late Pliocene than the present climate in western Yunnan. We conclude that the significant change of the monsoonal climate might have been resulted from the continuous uplift of mountains in western Yunnan, as well as the intensification of eastern Asian winter monsoon, both occurring concurrently in the post-Pliocene period.

  9. Multi-Decadal Modulations in the Variability of the East Asian Summer Monsoon

    Science.gov (United States)

    Nakamura, H.; Machimura, T.; Ogawa, S.; Kosaka, Y.; Nishii, K.; Miyasaka, T.

    2015-12-01

    The East Asian summer monsoon fluctuates from its climatological activity on monthly and interannual time scales, and the most dominant pattern of the variability is known as the Pacific-Japan (PJ) pattern. Characterized by a meridional teleconnection in anomalous activity of the Meiyu/Baiu rainband, tropical storms and a surface subtropical anticyclone (the Bonin High) in between, the PJ pattern exerts substantial influence on summertime climatic conditions over East Asia and the western North Pacific. Despite the recent warming trend observed in its background state, no assessment thus far has been made on how substantially the PJ has undergone, if any, multi-decadal modulations in its structure and/or dominance. Through an EOF analysis applied to a new dataset of global atmospheric reanalysis (JRA-55), the predominance of the PJ pattern is confirmed as being extracted in the leading EOF of lower-tropospheric monthly vorticity anomalies over 55 recent years. Both efficient barotropic/baroclinic energy conversion from the climatological-mean state and efficient generation of available potential energy through anomalous convective activity over the tropical western Pacific are shown to be essential for the maintenance of the monthly atmospheric anomalies of the PJ pattern over the entire 55-year period. At the same time, however, the same EOF analysis as above but applied separately to each of the sub-periods reveals a distinct signature of long-term modulations in amplitude and thus the dominance of the PJ pattern. While being extracted in the first EOF up to the 1980s, the PJ pattern is extracted in the second EOF in the period since the 1990s with marked reductions in both the variance fraction explained and the efficiency of energy conversion/generation. The resultant modulations of the summertime meridional teleconnection are also discussed with implications for future changes.

  10. Analysis of Basic Features of the Onset of the Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In this paper, a relatively systematic climatological research on the onset of the Asian tropical summer monsoon (ATSM) was carried out. Based on a unified index of the ATSM onset, the advance of the whole ATSM was newly made and then the view that the ATSM firstly breaks out over the tropical eastern Indian Ocean and the middle and southern Indo-China Peninsula was further documented, which was in the 26th pentad (about May 10), then over the South China Sea (SCS) in the 28th pentad. It seems that the ATSM onset over the two regions belongs to the different stages of the same monsoon system. Then, the onset mechanism of ATSM was further investigated by the comprehensive analysis on the land-sea thermodynamic contrast, intraseasonal oscillation, and so on, and the several key factors which influence the ATSM onset were put forward. Based on these results, a possible climatological schematic map that the ATSM firstly breaks out over the tropical eastern Indian Ocean, the Indo-China Peninsula, and the SCS was also presented, namely seasonal evolution of the atmospheric circulation was the background of the monsoon onset; the enhancement and northward advance of the convections, the sensible heating and latent heating over the Indo-China Peninsula and its neighboring areas, the dramatic deepening of the India-Burma trough, and the westerly warm advection over the eastern Tibetan Plateau were the major driving forces of the summer monsoon onset, which made the meridional gradient of the temperature firstly reverse over this region and ascending motion develop. Then the tropical monsoon and precipitation rapidly developed and enhanced. The phase-lock of the 30-60-day and 10-20-day low frequency oscillations originated from different sources was another triggering factor for the summer monsoon onset. It was just the common effect of these factors that induced the ATSM earliest onset over this region.

  11. On the robustness of relationship between ENSO and East Asian Summer Monsoon

    Science.gov (United States)

    Sun, Xuguang; Yang, Xiuqun; Greatbatch, Richard; Park, Wonsun

    2016-04-01

    In observations, the leading mode of variability of East Asian summer monsoon (EASM) features enhanced precipitation along the Yangtze River Valley, and mainly occurs in El Nino decaying summer (Sun et al. 2010). Kiel Climate Model (KCM) developed by Park et al. (2009) in GEOMAR, Germany is capable of reproducing these EASM characteristics in its 1000-year twentieth century equivalent (20C) control simulation. Moreover, consistent with the results of ERA-40 reanalysis data, the 1000-year 20C simulation of KCM also demonstrates an unstable relationship of EASM and ENSO, and the reason is particularly investigated in this study. The simulated El Nino events are selected and grouped into 4 categories according to their intensities and their relationships with EASM, i.e., Strong ENSO Strong Relation (SESR), Strong ENSO Weak Relation (SEWR), Weak ENSO Strong Relation (WESR) and Weak ENSO Weak Relation (WEWR). Their comparisons indicate that in situations of strong EASM-ENSO relationship, the suppressed precipitation in the northwest Pacific is more significant, so are the major components of EASM, such as western Pacific anticyclone (WPA) anomaly, the western Pacific subtropical high (WPSH), and the East Asian subtropical westerly jet (EASWJ) regardless of strong or weak ENSO, and vice versa. As for the strong ENSO, the robust EASM-ENSO relation mainly comes from the mid-eastern tropical Pacific where obvious large positive ENSO SST anomalies exist. However, it is primarily from the much warmer tropical Indian Ocean for the weak ENSO. Furthermore, correlation results show that EASM-ENSO relationship is getting more robust when much warmer interdecadal SST anomalies appear in the tropical Indian Ocean, tropical Atlantic Ocean and mid-western off-equatorial Pacific Ocean, which causes remarkably reduced convection and precipitation over the western Pacific, and then enhanced WPA anomaly, WPSH and EASWJ. Finally, the interdecadal changes of oceanic and atmospheric basic

  12. Millennial-Scale Asian Monsoon Influenced Longjie Lake Evolution during Marine Isotope Stage 3, Upper Stream of Changjiang (Yangtze River, China

    Directory of Open Access Journals (Sweden)

    Chaozhu Li

    2015-01-01

    Full Text Available Millennial-scale climate change in Asian monsoon region during MIS 3 has been studied using stalagmite, loess, and peat sediments. However, records from more materials are essential to further illustrate dynamics of these events. In the present study, a time-series of grain size covering 60–30 ka was reconstructed from lake sediments in the Yunnan Province, southwestern China. The time-series contains 14 obvious millennial-scale events during the period. On millennial-scale, the grain size record is generally consistent with mean stalagmite δ18O from Hulu Cave, grain size of Gulang loess sequence, Chinese Loess Plateau, and Greenland ice core δ18O. The results show that the millennial-scale variation was well compared with the Dansgaard-Oeschger (DO events, indicating that those global events were well documented in lake sediments in the Asian monsoon region. Because the grain size can be used as a proxy for water discharge, we suggest that signal of the DO events might be transmitted to lake evolution by Asian monsoon.

  13. Grain-size records at ODP Site 1146 from the northern South China Sea: Implications on the East Asian monsoon evolution since 20 Ma

    Institute of Scientific and Technical Information of China (English)

    WAN; ShiMing; LI; AnChun; Jan-Berend; W.; STUUT; XU; FangJian

    2007-01-01

    273 samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea (SCS) were analyzed for grain-size distributions using grain-size class vs. standard deviation method and end-member modeling algorithm (EMMA) in order to investigate the evolution of the East Asian monsoon since about 20 Ma. 10-19 μm/1.3-2.4 μm, the ratio of two grain-size populations with the highest variability through time was used to indicate East Asian winter monsoon intensity relative to summer monsoon. The mass accumulation rate of the coarsest end member EM1 (eolian), resulting from EMMA, can be used as a proxy of winter monsoon strength and Asian inland aridity, and the ratio of EM1/(EM2+EM3) as a proxy of winter monsoon intensity relative to summer monsoon. The combined proxies show that a profound enhancement of East Asian winter monsoon strength and winter monsoon intensity relative to summer monsoon occurred at about 8 Ma, and it is possible that the summer monsoon simultaneously intensified with winter monsoon at 3 Ma. Our results are well consistent with the previous studies in loess, eolian deposion in the Pacifc, radiolarians and planktonic foraminifera in the SCS. The phased uplift of the Himalaya-Tibetan Plateau may have played a significant role in strengthening the Asian monsoon at 8 Ma and 3 Ma.

  14. Summer Asian-Pacific Oscillation and Its Relationship with Atmospheric Circulation and Monsoon Rainfall

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ping; CHEN Junming; XIAO Dong; NAN Sulan; ZOU Yan; ZHOU Botao

    2008-01-01

    Using the ERA-40 data and numerical simulations, this study investigated the teleconnection over the extratropical Asian-Pacific region and its relationship with the Asian monsoon rainfall and the climatological characteristics of tropical cyclones over the western North Pacific, and analyzed impacts of the Tibetan Plateau (TP) heating and Pacific sea surface temperature (SST) on the teleconnection. The Asian-Pacific oscillation (APO) is defined as a zonal seesaw of the tropospheric temperature in the midlatitudes of the Asian-Pacific region. When the troposphere is cooling in the midlatitudes of the Asian continent, it is warming in the midlatitudes of the central and eastern North Pacific; and vice versa. The APO also appears in the stratosphere, but with a reversed phase. Used as an index of the thermal contrast between Asia and the North Pacific, it provides a new way to explore interactions between the Asian and Pacific atmospheric circulations. The APO index exhibits the interannual and interdecadal variability. It shows a downward trend during 1958-2001, indicating a weakening of the thermal contrast, and shows a 5.5-yr oscillation period. The formation of the APO is associated with the zonal vertical circulation caused by a difference in the solar radiative heating between the Asian continent and the North Pacific. The numerical simulations further reveal that the summer TP heating enhances the local tropospheric temperature and upward motion, and then strengthens downward motion and decreases the tropospheric temperature over the central and eastern North Pacific. This leads to the formation of the APO. The Pacific decadal oscillation and El Nino/La Nina over the tropical eastern Pacific do not exert strong influences on the APO. When there is an anomaly in the summer APO, the South Asian high, the westerly jet over Eurasia, the tropical easterly jet over South Asia, and the subtropical high over the North Pacific change significantly, with anomalous Asian

  15. Wetting and greening Tibetan Plateau in early summer since the late 1970s due to advanced Asian summer monsoon onset

    Science.gov (United States)

    Zhang, Wenxia; Zhou, Tianjun; Zhang, Lixia

    2016-04-01

    Known as the "the world water tower", the Tibetan Plateau (TP) is the origin of the ten largest rivers in Asia, breeding more than 1.4 billion people, and exerts substantial influences on water resources, agriculture, and ecosystems in downstream countries. This region is one of the most susceptible areas around the world to changing climate due to the high elevation. Observed evidence have shown significant climate changes over the TP, including surface air warming and moistening, glaciers shrinking, winds stilling, solar dimming, and atmospheric heat source weakening. However, as an essential part of the hydrological cycle, precipitation changes on the TP remain an ambiguous picture. Changes in precipitation vary largely with different seasons, time periods and climate zones considered. This study shows a robust increase in precipitation amount over the TP in May, when the rainy season starts, over the period 1979-2014 (31% relative to the climatology). The wetting trend is spatially consistent over the south-eastern TP, to which both precipitation frequency and intensity contribute. Circulation trends show that the wetting TP in May is resulted from the advanced onset of Asian summer monsoon, which onsets 1~2 pentads earlier since 1979. It intensified water vapor transport from the Bay of Bengal (BOB) to south of the TP in May and local anomalous convection. This relationship is further validated by the significant correlation coefficient (0.47) between the onset dates of Asian summer monsoon (particularly the BOB summer monsoon, 0.68) and precipitation over the south-eastern TP in May. The wetting TP in May has further exerted profound impacts on the hydrological cycle and ecosystem, such as moistening the soil and animating vegetation activities throughout early summer. Both decadal variations of soil moisture (from May to June) and Normalized Difference Vegetation Index (NDVI) (from May to July) coincide well with that of precipitation over the south

  16. The Earliest Onset Areas and Mechanism of the Tropical Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    QIAN Yongfu; ZHANG Yan; JIANG Jing; YAO Yonghong; XU Zhongfeng

    2005-01-01

    The multi-yearly averaged pentad meteorological fields at 850 hPa of the NCEP/NCAR reanalysis dada and the TBB fields of the Japan Meteorological Agency during 1980-1994 are analyzed. It is found that if the pentad is taken as the time unit of the monsoon onset, then the tropical Asian summer monsoon (TASM) onsets earliest, simultaneously and abruptly over the whole area in the Bay of Bengal (BOB), the Indo-China Peninsula (ICP), and the South China Sea (SCS), east of 90°E, in the 27th to 28th pentads of a year (Pentads 3 to 4 in May), while it onsets later in the India Peninsula (IP) and the Arabian Sea (AS), west of 90°E. The TASM bursts first at the south end of the IP in the 30th to 31st pentads near 10°N, and advances gradually northward to the whole area, by the end of June. Analysis of the possible mechanism depicts that the rapid changes of the surface sensible heat flux, air temperature, and pressure in spring and early summer in the middle to high latitudes of the East Asian continent between 100°E and 120°E are crucially responsible for the earliest onset of the TASM in the BOB to the SCS areas. It is their rapid changes that induce a continental depression to form and break through the high system of pressure originally located in the above continental areas. The low depression in turn introduces the southwesterly to come into the BOB to the SCS areas, east of 90°E, and thus makes the SCS summer monsoon (SCSSM)burst out earliest in Asia. In the IP to the AS areas, west of 90°E, the surface sensible heat flux almost does not experience obvious change during April and May, which makes the tropical Indian summer monsoon (TISM) onset later than the SCSSM by about a month. Therefore, it is concluded that the meridian of 90°E is the demarcation line between the South Asian summer monsoon (SASM, i.e., the TISM) and the East Asian summer monsoon (EASM, including the SCSSM).Besides, the temporal relations between the TASM onset and the seasonal variation

  17. A major reorganization of Asian climate by the early Miocene

    Directory of Open Access Journals (Sweden)

    Z. T. Guo

    2008-08-01

    Full Text Available The global climate system experienced a series of drastic changes during the Cenozoic. In Asia, these include the climate transformation from a zonal pattern to a monsoon-dominated pattern, the disappearance of typical subtropical aridity, and the onset of inland deserts. Despite major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes.

    This paper addresses these issues mainly based on two lines of evidence. First, we compiled newly collected data from geological indicators of the Cenozoic environment in China as paleoenvironmental maps of ten intervals. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the maps within the Miocene indicate that this change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted to tropical-subtropical regions. The latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalance in evolution of polar ice-sheets between the two hemispheres.

    Secondly, we examine the relevant depositional and soil forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with emphasis on the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which have been constantly maintained during the past 22 Ma. Grain-size gradients between loess sections indicate northerly dust-carrying winds from northern sources, a clear indication of an Asian winter monsoon system. Meanwhile, well-developed Luvisols show evidence that moisture from the oceans reached northern China. This evidence shows the coexistence of two kinds of

  18. Aerosol-Water Cycle Interaction: A New Challenge in Monsoon Climate Research

    Science.gov (United States)

    Lau, William K. M.

    2006-01-01

    Long recognized as a major environmental hazard, aerosol is now known to have strong impacts on both regional and global climate. It has been estimated that aerosol may reduce by up to 10% of the seasonal mean solar radiation reaching the earth surface, producing a global cooling effect that opposes global warming (Climate Change 2001). This means that the potential perils that humans have committed to global warming may be far greater than what we can detect at the present. As a key component of the Earth climate system, the water cycle is profoundly affected by the presence of aerosols in the atmosphere. Through the so-called "direct effect", aerosol scatters and/or absorbs solar radiation, thus cooling the earth surface and changing the horizontal and vertical radiational heating contrast in the atmosphere. The heating contrast drives anomalous atmospheric circulation, resulting in changes in convection, clouds, and rainfall. Another way aerosol can affect the water cycle is through the so-called "indirect effects", whereby aerosol increases the number of cloud condensation nuclei, prolongs life time of clouds, and inhibits the growth of cloud drops to raindrops. This leads to more clouds, and increased reflection of solar radiation, and further cooling at the earth surface. In monsoon regions, the response of the water cycle to aerosol forcing is especially complex, not only because of presence of diverse mix of aerosol species with vastly different radiative properties, but also because the monsoon is strongly influenced by ocean and land surface processes, land use, land change, as well as regional and global greenhouse warming effects. Thus, sorting out the impacts of aerosol forcing, and interaction with the monsoon water cycle is a very challenging problem. In this talk, I will offer some insights into how aerosols may impact the Asian monsoon based on preliminary results from satellite observations and climate model experiments. Specifically, I will

  19. Long-term changes in the relationship between stratospheric circulation and East Asian Winter Monsoon

    Science.gov (United States)

    Wei, K.

    2015-12-01

    Using two generations of reanalysis datasets from the NCAR, ECMWF, and JMA, we showed that on the interannual timescale the two leading modes of the East Asian winter monsoon (EAWM) are associated with tropospheric annular mode (AM) and stratospheric polar vortex (SPV), respectively. The relationship between AM and the first EAWM mode remained stable during 1958 to 2013, whereas that between SPV and the second EAWM mode increased since the late 1980s. The SPV-related circulation and planetary wave activities are intensified in the latter period. We suggested that this change might be caused by the global warming and ozone depletion.

  20. Comparison of the impact of the Arctic Oscillation and Eurasian teleconnection on interannual variation in East Asian winter temperatures and monsoon

    Science.gov (United States)

    Lim, Young-Kwon; Kim, Hae-Dong

    2016-04-01

    The large-scale impacts of the Arctic Oscillation (AO) and the Eurasian teleconnection (EU) on the East Asian winter climate are compared for the past 34 winters, focusing on (1) interannual monthly to seasonal temperature variability, (2) East Asian winter monsoon (EAWM), and (3) the Siberian high (SH) and cold surge. Regression analysis reveals warming by AO and cooling by EU over mid-latitude East Asia during their positive phase and vice versa (i.e., warm phase: +AO, -EU; cold phase: -AO, +EU). The EU impact was found to be comparable to the AO impact. For example, warm (cold) months during the warm (cold) AO phase are found clearly when the AO is in the same warm (cold) EU phase. No significant correlation was found between East Asian temperature and the AO when the warm (cold) AO coincided with the cold (warm) EU. The well-known relationship of strong (weak) SH during the cold (warm) AO phase was observed significantly more often when the AO was in the same cold (warm) EU phase. Also, the indices of EAWM, cold surge, and SH were more highly correlated with the EU than with the AO. The advective temperature change and associated circulation demonstrate that the large-scale field including the SH over the mid-latitude Asian inland is better represented by the EU, influencing the East Asian climate. These results suggest that the impact of EU should be considered more important than previously thought for a better understanding of East Asian winter temperature and monsoon variability.

  1. 中国全新世气候变迁相位差与亚洲季风及西风带的联系%The Asynchronous Nature of Holocene Climate Variability in China and Its Linkage to Asian Monsoon and the Westerly

    Institute of Scientific and Technical Information of China (English)

    吴永红; 郑祥民; 周立旻

    2012-01-01

    Different regions controlled by different dominant climatic factors show different characteristics of Holocene climate change.By the study of these mechanisms,we can have a very clear understanding on the developing process and the mutual coupling relation between the natural elements,as well as the impact of mechanism on climate.Through comparative analysis of Holocene climate changes in different regions of China,it is found out that the characteristics of Holocene climate changes in Northwest China and the Loess Plateau generally show that there are a dry and cold climate in the early Holocene,a warm and humid climate in mid-Holocene,a climate deterioration in the late Holocene,and two monsoon strengthening appearing in the southwest monsoon region and the eastern monsoon region during the Holocene.But the strengthening of the southwest monsoon is about 3~4 ka earlier than that of southeast monsoon.This paper argues that the characteristics of Holocene climate changes on the Loess Plateau and Northwest China are alike which may be due to the same climate system that affects them.While,the contrast of Holocene climate changes in Southwest Monsoon region and Eastern Monsoon region is pretty good which may indicate that both the strengthening and weakening of Southwest Monsoon and Southeast Monsoon are controlled the same by the north-south movement of planetary wind belt during Holocene.But the strengthening of the southeast monsoon delayed because of the huge heat capacity of ocean,resulting in the asynchrony of Holocene climate changes in Southeast Monsoon region and Southwest Monsoon region.%不同区域由于其主导气候影响因素的差异而表现出不同的全新世气候变化特征,对这些机制的研究,可以很好地理解各种自然要素的发展变化过程、气候影响机制及相互耦合关系。通过中国不同区域全新世气候变化研究成果的对比分析,发现黄土高原区与西北干旱区全新世期间气候特征

  2. The mean evolution and variability of the Asian summer monsoon: comparison of ECMWF and NCEP/NCAR reanalyses

    Energy Technology Data Exchange (ETDEWEB)

    Annamalai, H.; Hodges, K.; Slingo, J.M.; Sperber, K.R.

    1999-04-21

    The behavior of the Asian Summer Monsoon is compared using the European Centre for Medium Range Weather Forecasts Reanalysis (ERA) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis (Kalnay et al. 1996). The goals of this paper are to identify common features between the reanalyses, to assess their robustness for model validation, and especially to use reanalyses to develop their understanding of the mean evolution of the Asian Summer Monsoon and the characteristics of its interannual and intraseasonal variability (Annamalai et al. 1999).

  3. A PV-based determination of the transport barrier in the Asian summer monsoon anticyclone

    Directory of Open Access Journals (Sweden)

    F. Ploeger

    2015-04-01

    Full Text Available The Asian summer monsoon provides an important pathway of tropospheric source gases and pollution into the lower stratosphere. This transport is characterized by deep convection and steady upwelling, combined with confinement inside a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS. In this paper, we show that a barrier to horizontal transport along the 380 K isentrope in the monsoon anticyclone can be determined from the potential vorticity (PV field, following the polar vortex criterion by Nash et al. (1996. Due to large dynamic variability of the anticyclone, the corresponding maximum in the PV gradient is weak and additional constraints are needed (e.g., time averaging. Notwithstanding, PV contours in the monsoon anticyclone agree well with contours of trace gas mixing ratios (CO, O3 and mean age from model simulations with a Lagrangian chemistry transport model (CLaMS and MLS satellite observations. Hence, the PV-based transport barrier reflects the separation between air inside the anticyclone core and the background atmosphere well. For the summer season 2011 we find an average PV value of 3.6 PVU for the transport barrier in the anticyclone on the 380 K isentrope.

  4. Interdecadal variation of East Asian summer monsoon and drought/flood distribution over eastern China in the last 159 years

    Institute of Scientific and Technical Information of China (English)

    LI Qian; WEI Fengying; LI Dongliang

    2011-01-01

    Based on the drought/flood grades of 90 meterological stations over eastern China and summer average sea-level pressure (SLP) during 1850-2008 and BPCCA statistical methods,the coupling relationship between the drought/flood grades and the East Asian summer SLP is analyzed.The East Asian summer monsoon index which is closely related with interdecadal variation of drought/flood distribution over eastern China is defined by using the key areas of SLP.The impact of the interdecadal variation of the East Asian summer monsoon on the distribution of drought/flood over eastern China in the last 159 years is researched.The results show that there are four typical drought and flood spatial distribution patterns in eastern China,i.e.the distribution of drought/flood in southern China is contrary to the other regions,the distribution of drought/flood along the Huanghe River-Huaihe River Valley is contrary to the Yangtze River Valley and regions south of it,the distribution of drought/flood along the Yangtze River Valley and Huaihe River Valley is contrary to the other regions,the distribution of drought/flood in eastern China is contrary to the western.The main distribution pattern of SLP in summer is that the strength of SLP is opposite in Asian continent and West Pacific.It has close relationship between the interdecadal variation of drought/flood distribution patterns over eastern China and the interdecadal variation of the East Asian summer monsoon which was defined in this paper,but the correlation is not stable and it has a significant difference in changes of interdecadal phase.When the East Asian summer monsoon was stronger (weaker),regions north of the Yangtze River Valley was more susceptible to drought (flood),the Yangtze River Valley and regions south of it were more susceptible to flood (drought) before the 1920s; when the East Asian summer monsoon was stronger (weaker),the regions north of the Yangtze River Valley was prone to flood (drought),the Yangtze River

  5. South Asian Summer Monsoon and Its Relationship with ENSO in the IPCC AR4 Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Annamalai, H; Hamilton, K; Sperber, K R

    2005-09-07

    , suggesting a lack of predictability of the decadal modulation of the monsoon-ENSO relationship. The analysis was repeated for each of the four models using results from integrations in which the atmospheric CO{sub 2} concentration was raised to twice pre-industrial values. From these ''best'' models in the double CO{sub 2} simulations there are increases in both the mean monsoon rainfall over the Indian sub-continent (by 5-25%) and in its interannual variability (5-10%). We find for each model that the ENSO-monsoon correlation in the global warming runs is very similar to that in the 20th century runs, suggesting that the ENSO-monsoon connection will not weaken as global climate warms. This result, though plausible, needs to be taken with some caution because of the diversity in the simulation of ENSO variability in the coupled models we have analyzed. The implication of the present results for monsoon prediction are discussed.

  6. Interdecadal shift in the relationship between the East Asian summer monsoon and tropical SST

    Science.gov (United States)

    Li, J.; Ding, R.; Wu, Z.; Feng, J.; Ha, K.

    2012-04-01

    Interdecadal shift in the interannual relationship between the East Asian summer monsoon (EASM) and the tropical sea surface temperature (SST) anomalies (SSTA) is investigated. The result shows that a notable feature is the enhanced relationship between the previous winter El Niño-Southern Oscillation (ENSO) and the following EASM in the past 60 years, which is opposite to the weakening relationship between the Indian summer monsoon (ISM) and ENSO since 1970s. It is also found that pronounced changes in the interannual relationship between the EASM and summer SSTA over the tropical Indian Ocean (IO) happen in the late 1970s. Besides, an enhanced relationship between the previous autumn-winter SSTA over western tropical IO and the following EASM occurs in the late 1970s. The observational and numerical evidences manifest that spring North Atlantic Oscillation (NAO) may exert notable impacts on the enhancement of the EASM-ENSO relationship. Anomalous spring NAO induces a tripole SSTA pattern in North Atlantic which persists into ensuring summer. The tripole SSTA excites downstream teleconnections of a distinct Rossby wave train prevailing over the northern Eurasia and a simple Gill-Matsuno-type quadrupole response over western Pacific. The former modulates the blocking highs over the Ural Mountain and the Okhotsk Sea. The latter enhances the linkage between the western Pacific subtropical high (WPSH) and ENSO. The co-effects of the two teleconnection patterns help to strengthen (or weaken) the subtropical Meiyu-Baiu-Changma front, the primary rain-bearing system of the EASM. As such, spring NAO is tied to the strengthened connection between ENSO and the EASM. It can be seen from the correlations of the EASM index (EASMI) with the summer IO SSTA between 1953-1975 and 1978-2000 that the SSTA pattern similar to the positive Indian Ocean Dipole (IOD) shows a strongly positive correlation with the EASMI in 1953-1975, but in 1978-2000, significant negative correlation

  7. The East Asian Summer Monsoon at mid-Holocene: results from PMIP3 simulations

    Directory of Open Access Journals (Sweden)

    W. Zheng

    2013-02-01

    Full Text Available Ten Coupled General Circulation Models (CGCMs participated in the third phase of Paleoclimate Modelling Intercomparison Project (PMIP3 are assessed for the East Asian Summer Monsoon (EASM in both the pre-Industrial (PI, 0 ka and mid-Holocene (MH, 6 ka simulations. Results show that the PMIP3 model median captures well the large-scale characteristics of the EASM, including the two distinct features of the Meiyu rainbelt and the stepwise meridional displacement of the monsoonal rainbelt. At mid-Holocene, the PMIP3 model median shows significant warming (cooling during boreal summer (winter over Eurasia continent that are dominated by the changes of insolation. However, the PMIP3 models fail to simulate a warmer annual mean and winter surface air temperature (TAS over eastern China as derived from proxy records. The EASM at MH are featured by the changes of large-scale circulation over Eastern China while the changes of precipitation are not significant over its sub-domains of the Southern China and the lower reaches of Yangzi River. The inter-model differences for the monsoon precipitation can be associated with different configurations of the changes in large-scale circulation and the water vapour content, of which the former determines the sign of precipitation changes. The large model spread for the TAS over Tibetan Plateau has a positive relationship with the precipitation in the lower reaches of Yangzi River, yet this relationship does not apply to those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation. Except that the PMIP3 model median captured the warming of annual mean TAS over Tibetan Plateau, no significant improvements can be concluded when compared with the PMIP2 models results.

  8. Prediction of daily modes of South Asian monsoon variability and its association with Indian and Pacific Ocean SST in the NCEP CFS V2

    Science.gov (United States)

    Shahi, Namendra Kumar; Rai, Shailendra; Pandey, D. K.

    2016-02-01

    The prediction capability of daily modes of variability for South Asian monsoon from climate forecast system version 2 of national centers for environmental prediction with respect to observed precipitation has been assessed. The space-time structure of the daily modes for summer monsoon rainfall has been identified by using multi-channel singular spectrum analysis (MSSA). The MSSA is applied on daily anomalies of rainfall data over the South Asian monsoon region (40°E-160°E, 30°S-35°N) for the period of 2001-2013 with a lag window of 61 days for June-July-August-September season. The broad spectrum around 45 and 50 days was obtained from the observed and model data during the time domain of our study. The space-time structure of the modes obtained from the model shows good resemblance with respect to the observation. The observed northeastward propagation of oscillatory mode is well simulated by the model. The significant improvement in the space-time structure, period of oscillation, and propagation of oscillatory modes was found in the model. The observed connectivity of oscillatory and persisting modes with the sea surface temperature of Indian and Pacific Ocean has also been investigated and it was found that the model is able to predict it reasonably well.

  9. The effect of sea surface temperature bias in the PMIP2 AOGCMs on mid-Holocene Asian monsoon enhancement

    Energy Technology Data Exchange (ETDEWEB)

    Ohgaito, Rumi [Frontier Research Center for Global Change, JAMSTEC, Yokohama (Japan); Abe-Ouchi, A. [Frontier Research Center for Global Change, JAMSTEC, Yokohama (Japan); The University of Tokyo, Center for Climate System Research, Kashiwa (Japan)

    2009-12-15

    The effect of bias on control simulation is a significant issue for climate change modeling studies. We investigated the effect of the sea surface temperature (SST) bias in present day (0 ka) Atmosphere-Ocean Coupled General Circulation Model (AOGCM) simulations on simulations of the mid-Holocene (6 ka, i.e., 6,000 years before present) Asian monsoon enhancement. Because changes in ocean heat transport have a negligible effect on the 6 ka Asian monsoon (Ohgaito and Abe-Ouchi in Clim Dyn 29(1):39-50, 2007), we used an Atmospheric General Circulation Model (AGCM) rather than an AOGCM. Simulations using the AGCM coupled to a mixed layer ocean model (MLM) were conducted for 0 and for 6 ka with different ocean heat transport estimated from the climatological SST of the 0 ka simulations from nine Paleoclimate Modeling Intercomparison Project (PMIP) phase 2 (PMIP2) AOGCMs (henceforth ''MA'' is used to refer to experiments using the AGCM coupled with the MLM). No correlation between MA and the corresponding PMIP2 was seen in the 0 ka precipitation and it was not very strong for the 6 ka precipitation enhancement. Thus, the influences from the different AGCMs play a substantial role on the 0 ka precipitation and the 6 ka precipitation enhancement. The sensitivity experiments indicated that it was the pattern of the 0 ka SST bias which played a dominant role in the 0 ka precipitation and the 6 ka precipitation enhancement, not the difference in the mean value of the SST bias. The distributions of the 6 ka precipitation enhancements for the nine PMIP2 AOGCMs and nine MA experiments were compared. These showed that the effects of SST bias on 6 ka precipitation enhancement among the AOGCMs were not negligible. The effects of biases among the AGCMs were not negligible either, but of comparable size. That is, improvements in both the SST bias and the AGCM contribute to simulate better 6 ka monsoon. (orig.)

  10. Systematic errors in the simulation of the Asian summer monsoon: the role of rainfall variability on a range of time and space scales

    Science.gov (United States)

    Martin, Gill; Levine, Richard; Klingaman, Nicholas; Bush, Stephanie; Turner, Andrew; Woolnough, Steven

    2015-04-01

    Despite considerable efforts worldwide to improve model simulations of the Asian summer monsoon, significant biases still remain in climatological seasonal mean rainfall distribution, timing of the onset, and northward and eastward extent of the monsoon domain (Sperber et al., 2013). Many modelling studies have shown sensitivity to convection and boundary layer parameterization, cloud microphysics and land surface properties, as well as model resolution. Here we examine the problems in representing short-timescale rainfall variability (related to convection parameterization), problems in representing synoptic-scale systems such as monsoon depressions (related to model resolution), and the relationship of each of these with longer-term systematic biases. Analysis of the spatial distribution of rainfall intensity on a range of timescales ranging from ~30 minutes to daily, in the MetUM and in observations (where available), highlights how rainfall biases in the South Asian monsoon region on different timescales in different regions can be achieved in models through a combination of the incorrect frequency and/or intensity of rainfall. Over the Indian land area, the typical dry bias is related to sub-daily rainfall events being too infrequent, despite being too intense when they occur. In contrast, the wet bias regions over the equatorial Indian Ocean are mainly related to too frequent occurrence of lower-than-observed 3-hourly rainfall accumulations which result in too frequent occurrence of higher-than-observed daily rainfall accumulations. This analysis sheds light on the model deficiencies behind the climatological seasonal mean rainfall biases that many models exhibit in this region. Changing physical parameterizations alters this behaviour, with associated adjustments in the climatological rainfall distribution, although the latter is not always improved (Bush et al., 2014). This suggests a more complex interaction between the diabatic heating and the large

  11. Simulation of the interface between the Indian summer monsoon and the East Asian summer monsoon: Intercomparison between MPI-ESM and ECHAM5/MPI-OM

    Science.gov (United States)

    Guo, Yiran; Cao, Jie; Li, Hui; Wang, Jian; Ding, Yuchao

    2016-03-01

    The time-mean and interannual variability of the interface between the Indian summer monsoon and East Asian summer monsoon (IIE) was assessed using both Max-Planck-Institute Earth System Model (MPI-ESM) and ECHAM5/MPI-OM and by calculating diagnostics and skill metrics around the IIE area. Progress has been made in modeling these aspects by moving from ECHAM5/MPI-OM to MPI-ESM. MPI-ESM is more skillful than ECHAM5/MPI-OM in modeling the time-mean state and the extreme condition of the IIE. Though simulation of the interannual variability significantly deviates to some extent in both MPI-ESM and ECHAM5/MPI-OM, MPI-ESM-LR shows better skill in reflecting the relationship among sea surface temperature anomalies over the Pacific, circulation anomalies over East Asia, and IIE variability. The temperature becomes warmer under the RCP2.6 and RCP8.5 scenarios in comparison with the historical experiments, but the position of the IIE and the key physical process in relation to the IIE variability almost remains the same, suggesting that the Indian summer monsoon tends to change in phase with the East Asian summer monsoon under each RCP scenario. The relatively realistic description of the physical processes modulated by terrain in MPI-ESM may be one of the most important reasons why MPI-ESM performs better in simulating the IIE.

  12. Workshop on Monsoon Climate Systems: Toward Better Prediction of the Monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Sperber, K R; Yasunari, T

    2005-12-20

    The Earth's monsoon systems are the life-blood of more than two-thirds of the world's population through the rainfall they provide to the mainly agrarian societies they influence. More than 60 experts gathered to assess the current understanding of monsoon variability and to highlight outstanding problems simulating the monsoon.

  13. Modeling the East Asian climate during the last glacial maximum

    Institute of Scientific and Technical Information of China (English)

    赵平; 陈隆勋; 周秀骥; 巩远发; 韩余

    2003-01-01

    Using the CCM3 global climate model of National Center for AtmosphericResearch(NCAR), this paper comparatively analyzes the characteristics of East Asian monsoon and surface water condition and the expansion of glacier on the Qinghai-Xizang(Tibetan) Plateau(QXP) between the present and the last glacial maximum(LGM). It is found that the winter monsoon is remarkably stronger during the LGM than at present in the north part of China and the western Pacific but varies little in the south part of China. The summer monsoon remarkably weakens inSouth China Sea and the south part of China during the LGM and has no remarkable changes in the north part of China between the present and the LGM. Due to thealternations of the monsoons during the LGM, the annual mean precipitation significantly decreases in the northeast of China and the most part of north China and the Loess Plateau and the eastern QXP, which makes the earth surface lose more water and becomes dry, especially in the eastern QXP and the western Loess Plateau. In some areas of the middle QXP the decrease of evaporation at the earth surface causes soil to become wetter during the LGM than at present, which favorsthe water level of local lakes to rise during the LGM. Additionally, compared to the present, the depth of snow cover increases remarkably on the most part of the QXP during the LGM winter. The analysis of equilibrium line altitude(ELA) of glaciers on the QXP, calculated on the basis of the simulated temperature and precipitation, shows that although a less decrease of air temperature was simulated during the LGM in this paper, the balance between precipitation and air temperature associated with the atmospheric physical processes in the model makes the ELA be 300-900 m lower during the LGM than at present, namely going down fromthe present ELA above 5400 m to 4600-5200 m during the LGM, indicating a unified ice sheet on the QXP during the LGM.

  14. An 8.1Ma calcite record of Asian summer monsoon evolution on the Chinese central Loess Plateau

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Carbonates in loess-red clay sequences consist mainly of calcite and dolomite. The EDTA analysis of carbonates in different size fractions and magnetic susceptibility reveal that calcite is a sensitive index of summer monsoon. The chemical analysis of carbonates and calcite from an 8.1 Ma loess-red clay sequence at Chaona on the Chinese central Loess Plateau shows that the evolution of the Asian summer monsoon experienced four stages, namely 8.1―5.5 Ma, 5.5―2.8 Ma, 2.8―1.5 Ma and 1.5―0 Ma, with increasing intensification and fluctuation, suggesting a possible combining impacts of uplift of the Tibetan Plateau and global changes on the Asian summer monsoon.

  15. Preferred response of the East Asian summer monsoon to local and non-local anthropogenic sulphur dioxide emissions

    Science.gov (United States)

    Dong, Buwen; Sutton, Rowan T.; Highwood, Eleanor J.; Wilcox, Laura J.

    2016-03-01

    In this study, the atmospheric component of a state-of-the-art climate model (HadGEM2-ES) that includes earth system components such as interactive chemistry and eight species of tropospheric aerosols considering aerosol direct, indirect, and semi-direct effects, has been used to investigate the impacts of local and non-local emissions of anthropogenic sulphur dioxide on the East Asian summer monsoon (EASM). The study focuses on the fast responses (including land surface feedbacks, but without sea surface temperature feedbacks) to sudden changes in emissions from Asia and Europe. The initial responses, over days 1-40, to Asian and European emissions show large differences. The response to Asian emissions involves a direct impact on the sulphate burden over Asia, with immediate consequences for the shortwave energy budget through aerosol-radiation and aerosol-cloud interactions. These changes lead to cooling of East Asia and a weakening of the EASM. In contrast, European emissions have no significant impact on the sulphate burden over Asia, but they induce mid-tropospheric cooling and drying over the European sector. Subsequently, however, this cold and dry anomaly is advected into Asia, where it induces atmospheric and surface feedbacks over Asia and the Western North Pacific (WNP), which also weaken the EASM. In spite of very different perturbations to the local aerosol burden in response to Asian and European sulphur dioxide emissions, the large scale pattern of changes in land-sea thermal contrast, atmospheric circulation and local precipitation over East Asia from days 40 onward exhibits similar structures, indicating a preferred response, and suggesting that emissions from both regions likely contributed to the observed weakening of the EASM. Cooling and drying of the troposphere over Asia, together with warming and moistening over the WNP, reduces the land-sea thermal contrast between the Asian continent and surrounding oceans. This leads to high sea level

  16. Impact of cloud radiative heating on East Asian summer monsoon circulation

    International Nuclear Information System (INIS)

    The impacts of cloud radiative heating on the East Asian Summer Monsoon (EASM) over southeastern China (105°–125°E, 20°–35°N) are addressed by using the Community Atmosphere Model version 5 (CAM5). Sensitivity experiments demonstrate that the radiative heating of clouds leads to a positive effect on the local EASM circulation over southeastern China. Without the radiative heating of clouds, the EASM circulation and precipitation would be much weaker than that in normal conditions. The longwave heating of clouds dominates the changes of EASM circulation. The positive effect of clouds on EASM circulation is explained by the thermodynamic energy equation, i.e. the different heating rate between cloud base and cloud top enhances the convective instability over southeastern China, which consequently enhances updraft. The strong updraft would further result in a southward meridional wind above the center of the updraft through Sverdrup vorticity balance. (letter)

  17. Land-Use and Land-Cover Change and Associated Changes in Hydrological Cycle and Energy Exchange Processes in Monsoon Asian Region (Invited)

    Science.gov (United States)

    Jain, A.; Liang, M.; Barman, R.; Erickson, M.; Cao, L.; Bala, G.

    2009-12-01

    The climate system is affected by land-use and land-cover changes (LULCC) through changes in hydrological cycle, energy exchange processes and soil biogeochemistry. These changes affect climate both at global and regional scales. Here, we use the terrestrial component of the Integrated Science Assessment Model (ISAM), with satellite data to examine the effects of LULCC and other terrestrial ecosystem processes on variability in soil hydrology and energy fluxes in monsoon Asian region. ISAM’s energy and hydrology processes have been adapted from the Common Land Model (CoLM) and the Community Land Model (CLM 3.5), respectively. CoLM uses a two-big-leaf scheme for modeling canopy temperature, photosynthesis and stomatal conductance, improving CO2 and water flux estimates. The soil/snow hydrology, incorporated from CLM3.5 (10 layers for soil and up to 5 layers for snow) improves runoff and ground water table predictions. This talk will focus on describing the results of a series of modeling experiments investigating the influence of LULCC on terrestrial moisture flux, latent and sensible heat fluxes, and continental runoff (surface & subsurface) in monsoon Asian region. These experiments were conducted based on measured activities of LULCC and observed atmospheric forcings over the last century.

  18. Relationships between ENSO and East Asian-western North Pacific monsoon: observations versus 18 CMIP5 models

    Science.gov (United States)

    Wu, B.

    2014-12-01

    The relationships between ENSO and the East Asian-western North Pacific monsoon during ENSO mature winter and decaying summer are studied by examining the pre-industrial control runs of 18 global climate models (GCMs) that participated in the phase five of the Coupled Model Intercomparison Project (CMIP5). In the observation, the tropical western North Pacific (WNP) is dominated by an anomalous anticyclone (cyclone) during El Niño (La Niña) mature winter, referred to as WNPAC (WNPC). WNPAC is asymmetric with WNPC. Multi-model assessments support the idea that the asymmetry results from the combined effects of the asymmetric remote forcing from the equatorial central-eastern Pacific and the asymmetric local sea surface temperature (SST) anomalies. It has been proposed that the asymmetric circulation anomalies over the tropical WNP have a contribution to the asymmetric decaying rates between El Niño and La Niña. The mechanism works in the CMIP5 models. Those models that can (cannot) simulate the asymmetry between WNPAC and WNPC tend to reproduce ENSO with asymmetric (symmetric) decaying rates. In the observation, WNPAC maintains throughout El Niño decaying summer. The maintenance of WNPAC primarily relies on the local forcing of underlying cold SST anomalies in the early summer, remaining from preceding winter and spring, whereas to remote forcing from the tropical Indian Ocean in the late summer. The two mechanisms are reproduced by the multi-model ensemble mean. The scatter diagrams for the CMIP5 models demonstrate that the response of WNPAC to the remote forcing from the tropical Indian Ocean intensifies from June to July, concurring with the establishment of the climatological WNP monsoon trough.

  19. Characterization of non-methane hydrocarbons in Asian summer monsoon outflow observed by the CARIBIC aircraft

    Directory of Open Access Journals (Sweden)

    A. K. Baker

    2010-07-01

    Full Text Available Between April and December 2008 the CARIBIC commercial aircraft conducted monthly measurement flights between Frankfurt, Germany and Chennai, India. These flights covered the period of the Asian summer monsoon (June–September, during which enhancements in a number of atmospheric species were observed in monsoon outflow. In addition to in situ measurements of trace gases and aerosols, whole air samples were collected during the flights, and these were subsequently analyzed for a suite of trace gases that included the non-methane hydrocarbons. Non-methane hydrocarbons are relatively short-lived compounds and the large enhancements in their mixing ratios in the upper troposphere over Southwest Asia between June and September, sometimes more than double their spring and fall means, provides qualitative evidence for the influence of convectively uplifted boundary layer air. The particularly large enhancements of the combustion tracers benzene and ethyne, along with the similarity of their ratios to carbon monoxide and emission ratios from the burning of household biofuels, indicate a strong influence of biofuel burning to NMHC emissions in this region. Conversely, the ratios of ethane and propane to carbon monoxide, along with the ratio between i-butane and n-butane, indicate a significant source of these compounds from the use of LPG and natural gas, and comparison to previous campaigns suggests that this source could be increasing. Photochemical aging patterns of NMHCs showed that the CARIBIC samples were collected in two distinctly different regions of the monsoon circulation: a southern region where air masses had been recently influenced by low level contact and a northern region, where air parcels had spent substantial time in transit in the upper troposphere before being probed. Estimates of age using ratios of individual NMHCs have ranges of 3–6 d in the south and 9–12 d in the north.

  20. Sensitivity of surface radiation budget to clouds over the Asian monsoon region

    Indian Academy of Sciences (India)

    S Balachandran; M Rajeevan

    2007-04-01

    Using the ISCCP–FD surface radiative flux data for the summer season (June to September) of the period 1992 to 1995, an analysis was done to understand the role of clouds on the surface radiation budget over the Asian monsoon region. At the top of atmosphere (TOA) of convective regions of the Asian monsoon region, the short wave radiative forcing (SWCRF) and long wave radiative forcing (LWCRF) do not cancel each other resulting in occurrence of the net cloud radiative forcing values exceeding −30W/m2. This type of imbalance between SWCRF and LWCRF at TOA is reflected down on the earth surface–atmosphere system also as an imbalance between surface netcloud radiative forcing (NETCRF) and atmospheric NETCRF. Based on the regression analysis of the cloud effects on the surface radiation budget quantities, it has been observed that generally, the variance explained by multiple type cloud data is 50% more than that of total cloud cover alone. In case of SWCRF, the total cloud cover can explain about 3% (7%) of the variance whereas the three cloud type descriptions of clouds can explain about 44% (42%) of the variance over oceanic (land) regions. This highlights the importance of cloud type information in explaining the variations of surface radiation budget. It has been observed that the clouds produce more cooling effect in short-wave band than the warming effect in long-wave band resulting in a net cooling at the surface. Over the oceanic region, variations in high cloud amount contribute more to variations in SWCRF while over land regions both middle and high cloud variations make substantial contributions to the variations in both SWCRF and NETCRF.

  1. Impacts of the East Asian monsoon on lower tropospheric ozone over coastal South China

    International Nuclear Information System (INIS)

    The impact of the East Asian monsoon (EAM) on climatology and interannual variability of tropospheric ozone (O3) over the coastal South China was investigated by analyzing 11 years of ozonesonde data over Hong Kong with the aid of Lagrangian dispersion modeling of carbon monoxide and calculation of an EAM index. It was found that the seasonal cycle of O3 in the lower troposphere is highly related to the EAM over the study region. Ozone enhancements in the free troposphere are associated with the monsoon-induced transport of pollutants of continental anthropogenic and biomass burning origins. Lower tropospheric O3 levels showed high interannual variability, with an annual averaged amplitude up to 61% of averaged concentrations in the boundary layer (0–1 km altitudes) and 49% below 3 km altitude. In spring and autumn, the interannual variability in boundary layer O3 levels was predominately influenced by the EAM intensity, with high O3 mixing ratios associated with northeasterly circulation anomalies. (letter)

  2. Vertical Structures of Atmospheric Properties in Southeast Tibet during the South Asian Summer Monsoon in 2013

    Institute of Scientific and Technical Information of China (English)

    周立波; 李斐; 朱金焕; 邹捍; 马舒坡; 李鹏

    2016-01-01

    In June 2013, a field experiment was conducted in Southeast Tibet in which the air temperature, moisture, and wind were measured by using a GPS sounding system. In the present study, based on these observations and ERA-Interim reanalysis data, the vertical structures of these atmospheric properties and the possible influence of the South Asian summer monsoon (SASM) were investigated. On average, the temperature had a lapse rate of 6.8℃ km−1 below the tropopause of 18.0 km. A strong moisture inversion occurred at the near-surface, with a strength of 1.7 g kg−1 (100 m)−1 for specific humidity. During the observation period, the SASM experienced a south phase and a north phase in the middle and by the end of June, respectively. The monsoon’s evolution led to large changes in convection and circulation over Southeast Tibet, which further affected the local thermal, moisture, and circulation conditions. The strong convection resulted in an elevated tropopause height over Southeast Tibet during the north phase of the SASM, and the large-scale warm and wet air masses delivered by the monsoon caused high local temperature and moisture conditions.

  3. The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century

    Science.gov (United States)

    Sperber, K. R.; Annamalai, H.; Kang, I.-S.; Kitoh, A.; Moise, A.; Turner, A.; Wang, B.; Zhou, T.

    2013-11-01

    The boreal summer Asian monsoon has been evaluated in 25 Coupled Model Intercomparison Project-5 (CMIP5) and 22 CMIP3 GCM simulations of the late twentieth Century. Diagnostics and skill metrics have been calculated to assess the time-mean, climatological annual cycle, interannual variability, and intraseasonal variability. Progress has been made in modeling these aspects of the monsoon, though there is no single model that best represents all of these aspects of the monsoon. The CMIP5 multi-model mean (MMM) is more skillful than the CMIP3 MMM for all diagnostics in terms of the skill of simulating pattern correlations with respect to observations. Additionally, for rainfall/convection the MMM outperforms the individual models for the time mean, the interannual variability of the East Asian monsoon, and intraseasonal variability. The pattern correlation of the time (pentad) of monsoon peak and withdrawal is better simulated than that of monsoon onset. The onset of the monsoon over India is typically too late in the models. The extension of the monsoon over eastern China, Korea, and Japan is underestimated, while it is overestimated over the subtropical western/central Pacific Ocean. The anti-correlation between anomalies of all-India rainfall and Niño3.4 sea surface temperature is overly strong in CMIP3 and typically too weak in CMIP5. For both the ENSO-monsoon teleconnection and the East Asian zonal wind-rainfall teleconnection, the MMM interannual rainfall anomalies are weak compared to observations. Though simulation of intraseasonal variability remains problematic, several models show improved skill at representing the northward propagation of convection and the development of the tilted band of convection that extends from India to the equatorial west Pacific. The MMM also well represents the space-time evolution of intraseasonal outgoing longwave radiation anomalies. Caution is necessary when using GPCP and CMAP rainfall to validate (1) the time

  4. Response of the Asian summer monsoon to changes in El Niño properties

    Science.gov (United States)

    Annamalai, H.; Liu, P.

    2005-04-01

    Diagnostics from observed precipitation and National Centers for Environmental Prediction-National Center for Atmospheric Research re-analysis products reveal that after the 1976-77 climate shift in the Pacific there was a dramatic change in the response of the Indian summer monsoon (ISM) to El Niño, particularly during the months of July and August. Based on 1950-75 (PRE76) and 1977-2001 (POST76) El Niño composites: the western North Pacific monsoon (WNPM) was stronger than normal in both periods; the ISM was weaker than normal during the entire monsoon season in PRE76, but in POST76 was weaker only during the onset and withdrawal phases. In terms of observed sea surface temperature (SST) during July-August, the major differences between the two periods are the presence of cold SST anomalies over the Indo-Pacific warm pool and the intensity of warm SST anomalies in the central Pacific in POST76. The effect of these differences on the ISM is investigated in a suite of experiments with an Atmospheric General Circulation Model (AGCM) that has a realistic monsoon precipitation climatology.Separate ten-member ensemble simulations with the AGCM were conducted for PRE76 and POST76 El Niño events with SST anomalies inserted as follows: (i) tropical Indo-Pacific (TIP), (ii) tropical Pacific only (TPO), and (iii) tropical Indian Ocean only (TIO). Qualitatively, TPO solutions reproduce the observed differences in the monsoon response in both periods. Specifically, during July-August of POST76 the cold SST anomalies in conjunction with remote subsidence suppress precipitation (3-5 mm day-1) over the maritime continent and equatorial central Indian Ocean. Inclusion of Indian Ocean SST anomalies in the TIP runs further suppresses precipitation over the entire equatorial Indian Ocean. The low-level anticyclonic circulation anomalies that develop as a Rossby-wave response to these convective anomalies increase the south-westerlies over the northern Indian Ocean, and favour a

  5. Variability of Moisture Sources and Moisture Transport in the East Asian Monsoon System

    Science.gov (United States)

    Fremme, Astrid; Sodemann, Harald

    2016-04-01

    The rainfall of the East Asian Monsoon is of key importance for livelihoods in the densely populated area of China, Japan and Korea. The interplay of many factors, including land surface processes, makes monsoon precipitation difficult to predict. To contribute to improved precipitation prediction we investigate the atmospheric mechanisms importing moisture to the region. In previous studies moisture transport has mainly been analysed by examining a combination of temperature, pressure, winds and water vapour content. However this has been done without linking precipitation to its moisture sources directly. In this project we use the Lagrangian particle dispersion model FLEXPART and the diagnostic tool WaterSip to analyse ERA Interim reanalysis data to obtain a link between precipitation and its moisture sources. The total atmospheric mass is subdivided into millions air parcels, which are traced backwards for 20 days for each rainfall event in the 34 year ERA-Interim period. Specific humidity changes are interpreted as evaporation and precipitation in the area beneath the parcel with the help of a sophisticated accounting method related to target precipitation. Results on the relationship between source and sink areas reflect changes in the conditions of the source regions and in moisture transport. We investigate the moisture transport mechanisms for both seasonal and inter-annual variations during the study period 1979-2013. Preliminary results show that the sources for precipitation in the Yangtze River Valley (YRV) in China have a clear seasonal cycle in terms of location and evaporation conditions. Land areas outside the YRV Region contribute most of the moisture. The second largest source is inside the YRV region itself. For monthly means the sum of all direct oceanic sources rarely exceeds 20%. Recycling of moisture from land surfaces outside the target regions therefore seems to play a pivotal role in the East Asian Monsoon's moisture budget. Contrasting

  6. Possible relationship between East Asian summer monsoon and western North Pacific tropical cyclone genesis frequency

    Science.gov (United States)

    Choi, Ki-Seon; Cha, Yumi; Kim, Hae-Dong; Kang, Sung-Dae

    2016-04-01

    In the present study, the fact that strong positive correlations have existed between East Asian summer monsoons (EASMs) and western North Pacific tropical cyclone (TC) genesis frequency over the last 37 years was found. To figure out the cause of these correlations, 7 years (positive East Asian summer monsoon index (EASMI) phase) that have the highest values and 7 years (negative EASMI phase) that have the lowest values in the normalized EASM index were selected and the differences in averages between the two phases were analyzed. In the positive EASMI phase, TCs mainly occurred in the northwestern waters of the tropical and subtropical western North Pacific and showed a tendency to move from the far eastern waters of the Philippines, pass the East China Sea, and move northward toward Korea and Japan. On the 500 hPa streamline, whereas anomalous anticyclones developed in the East Asia middle-latitude region, anomalous cyclones developed in the tropical and subtropical western North Pacific. Therefore, in this phase, whereas EASMs were weakened, western North Pacific summer monsoons (WNPSMs) were strengthened so that some more TCs could occur. In addition, in the case of the East China Sea and the southern waters of Japan located between the two anomalous pressure systems, TCs could move some more toward the East Asia middle-latitude region in this phase. According to an analysis of the 850 hPa relative vorticity, negative anomalies were strengthened in the East Asia middle-latitude region while positive anomalies were strengthened in the region south to 25 N. Therefore, in the positive EASMI phase, whereas EASMs were weakened, WNPSMs were strengthened so that some more TCs could occur. According to an analysis of the 850 and 200 hPa horizontal divergence, whereas anomalous downward flows were strengthened in the East Asia middle-latitude region, anomalous upward flows were strengthened in the tropical and subtropical western North Pacific. According to an analysis

  7. Recent trends and tele-connections among South and East Asian summer monsoons in a warming environment

    Science.gov (United States)

    Preethi, B.; Mujumdar, M.; Kripalani, R. H.; Prabhu, Amita; Krishnan, R.

    2016-06-01

    Recent trends, variations and tele-connections between the two large regional sub-systems over the Asian domain, the South Asian and the East Asian monsoons are explored using data for the 1901-2014 period. Based on trend analysis a dipole-type configuration with north-drought and south-flood over South as well as East Asia is observed. Two regions over South Asia, one exhibiting a significant decreasing trend in summer monsoon rainfall over northeast India and the other significant increasing trend over the northern parts of the west coast of India are identified. Similarly two regions over East Asia, one over South Korea-southern parts of Japan and the other over South China are also identified both indicating a significant increasing trend in the summer monsoon rainfall. These trends are examined post 1970s. Possible factors associated with the recent trends are explored. Analysis of sea surface temperature (SST), mean sea level pressure and winds at lower troposphere indicates that the entire monsoon flow system appears to have shifted westwards, with the monsoon trough over South Asia indicating a westward shift by about 2-3° longitudes and the North Pacific Subtropical High over East Asia seems to have shifted by about 5-7° longitudes. These shifts are consistent with the recent rainfall trends. Furthermore, while the West Indian Ocean SSTs appear to be related with the summer monsoon rainfall over northern parts of India and over North China, the West Pacific SSTs appear to be related with the rainfall over southern parts of India and over South Korea- southern Japan sector.

  8. Sensitivity of Asian climate change to radiative forcing during the last millennium in a multi-model analysis

    Science.gov (United States)

    Shi, Zhengguo; Xu, Tingting; Wang, Hongli

    2016-04-01

    The outputs of last millennium (A.D. 850-1850) experiments from seven climate models of the Paleoclimate Modeling Intercomparison Project 3, have been used to analyze decadal to centennial climatic variations over Asia, including the Indian monsoon, the East Asian monsoon and the westerly jet. In particular, the differences between the Medieval Warm Period (MWP, A.D. 901-1200) and the Little Ice Age (LIA, A.D. 1551-1850) are focused on. Statistically, significant temperature contrasts between the MWP and LIA are simulated by all of the models, and larger temperature deviations occur during colder periods. Although discrepancies exist, stronger Indian and East Asian summer monsoon circulations, as well as a stronger Asian westerly jet stream in winter, are found during the MWP compared to the LIA, in most of the models. These changes primarily originate from different atmospheric thermal structures over the two periods, which occur in response to the external radiative forcings. However, the monsoon-associated precipitation is quite complicated, with distinctly different patterns simulated among the models. There are phase differences in the multi-decadal variability of precipitation among the models, which consistently fail to detect a weakening in the precipitation at the minima of the radiative forcings. Only limited models are able to simulate the quasi-100-year solar cycles in the changes of precipitation over India and East Asia. Thus, although the climate system is certainly affected by external radiative forcings, our results imply that the natural forcings may not exert such a substantial influence on the Asian monsoon rainfall, or the models may underestimate the response.

  9. Variations of the Summer Somali and Australia Cross-Equatorial Flows and the Implications for the Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    ZHU Yali

    2012-01-01

    The temporal variations during 1948-2010 and vertical structures of the summer Somali and Australia cross-equatorial flows (CEFs) and the implications for the Asian summer monsoon were explored in this study.The strongest southerly and northerly CEFs exist at 925 hPa and 150 hPa level,respectively.The low-level Somali (LLS) CEFs were significantly connected with the rainfall in most regions of India (especially the monsoon regions),except in a small area in southwest India.In comparison to the climatology,the lowlevel Australia (LLA) CEFs exhibited stronger variations at interannual time scale and are more closely connected to the East Asian summer monsoon circulation than to the LLS CEFs.The East Asian summer monsoon circulation anomalies related to stronger LLA CEFs were associated with less water vapor content and less rainfall in the region between the middle Yellow River and Yangtze River and with more water vapor and more rainfall in southern China.The sea-surface temperature anomalies east of Australia related to summer LLA CEFs emerge in spring and persist into summer,with implications for the seasonal prediction of summer rainfall in East Asia.The connection between the LLA CEFs and East Asian summer monsoon rainfall may be partly due to its linkage with El Nino-Southern Oscillation.In addition,both the LLA and LLS CEFs exhibited interdecadal shifts in the late 1970s and the late 1990s,consistent with the phase shifts of Pacific Decadal Oscillation (PDO).

  10. Predictability experiments for the Asian summer monsoon: Impact of SST anomalies on interannual and intraseasonal variability

    International Nuclear Information System (INIS)

    The effects of SST anomalies on the interannual and intraseasonal variability of the Asian summer monsoon have been studied by multivariate statistical analyses of 850-hPa wind and rainfall yields simulated in a set of ensemble integrations of the ECMWF atmospheric GCM, referred to as the PRISM experiments. The simulations used observed SSTs (PRISM-O), covering 9 years characterised by large variations of the ENSO phenomenon in the 1980's and the early 1990's. A parallel set of simulations was also performed with climatological SSTs (PRISM-C), thus enabling the influence of SST forcing on the modes of interannual and intraseasonal variability to be investigated. As in observations, the model's interannual variability is dominated by a zonally-oriented mode which describes the north-south movement of the tropical convergence zone (TCZ). This mode appears to be independent of SST forcing and its robustness between the PRISM-O and PRISM-C simulations suggests that it is driven by internal atmospheric dynamics. On the other hand, the second mode of variability, which again has a good correspondence with observed patterns, shows a clear relationship with the ENSO cycle. Since the mode related to ENSO accounts for only a small part of the total variance, the notion of a quasi-linear superposition of forced and unforced modes of variability may not provide an appropriate interpretation of monsoon interannual variability. Consequently, the possibility of a non-linear influence has been investigated by exploring the relationship between interannual and intraseasonal variability. As in other studies, a common mode of interannual and intraseasonal variability has been found, in this case describing the north-south transition of the TCZ associated with monsoon active/break cycles. Although seasonal-mean values of the Principal Component (PC) timeseries associated with the leading intraseasonal mode shows no significant correlation with ENSO, the 2-dimensional probability

  11. An ocean-atmosphere interaction mechanism for the active break cycle of the Asian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, P.V.; Sabin, T.P. [Cochin University of Science and Technology, Department of Atmospheric Sciences, Cochin (India)

    2008-05-15

    A typical active-break cycle of the Asian summer monsoon is taken as beginning with maximum SST (pentad 0) over the north Bay of Bengal when the oceans to its west and east from longitude 40 -160 E, and between latitudes 10 and 25 N (area A) also has maximum SST. During this pentad the recently found 'Cold Pool' of the Bay of Bengal (between latitudes 3 N and 10 N) has its minimum SST. An area of convection takes genesis over the Bay of Bengal immediately after pentad 0 in the zone of large SST gradient north of the Cold Pool and it pulls the monsoon Low Level Jetstream (LLJ) through peninsular India. Convection and the LLJ westerlies then spread to the western Pacific Ocean during pentads 1-4 taken as the active phase of the monsoon during which convection and LLJ have grown in a positive feed back process. The cyclonic vorticity to the north of the LLJ axis is hypothesized to act as a flywheel maintaining the convection during the long active phase against the dissipating effect of atmospheric stabilization by each short spell of deep convection. By the end of pentad 4 the SST over area A has cooled and the convection weakens there, when the LLJ turns clockwise over the Arabian Sea and flows close to the equator in the Indian ocean. A band of convection develops at pentad 5 between the equator and latitude 10 S over the Indian ocean and it is nourished by the cyclonic vorticity of the LLJ now near the equator and the moisture supply through it. This is taken as the break monsoon phase lasting for about three to four pentads beginning from pentad 5 of a composite active-break cycle of 40 day duration. With reduced wind and convection over the area A during the break phase, solar radiation and light winds make the SST there warm rapidly and a new active-break cycle begins. SST, convection, LLJ and the net heat flux at the ocean surface have important roles in this new way of looking at the active-break cycle as a coupled ocean-atmosphere phenomenon. (orig.)

  12. Predictability experiments for the Asian summer monsoon: impact of SST anomalies on interannual and intraseasonal variability

    International Nuclear Information System (INIS)

    The effects of SST anomalies on the interannual and intraseasonal variability of the Asian summer monsoon have been studied by multivariate statistical analyses of 850-hPa wind and rainfall fields simulated in a set of ensemble integrations of the ECMWF atmospheric GCM, referred to as the PRISM experiments. The simulations used observed SSTs (PRISM-O), covering 9 years characterised by large variations of the ENSO phenomenon in the 1980's and the early 1990's. A parallel set of simulations was also performed with climatological SSTs (PRISM-C), thus enabling the influence of SST forcing on the modes of interannual and intraseasonal variability to be investigated. As in observations, the model's interannual variability is dominated by a zonally-oriented mode which describes the north-south movement of the tropical convergence zone (TCZ). This mode appears to be independent of SST forcing and its robustness between the PRISM-O and PRISM-C simulations suggests that it is driven by internal atmospheric dynamics. On the other hand, the second mode of variability, which again has a good correspondence with observed patterns, shows a clear relationship with the ENSO cycle. Since the mode related to ENSO accounts for only a small part of the total variance, the notion of a quasi-linear superposition of forced and unforced modes of variability may not provide an appropriate interpretation of monsoon interannual variability. Consequently, the possibility of a non-linear influence has been investigated by exploring the relationship between interannual and intraseasonal variability. As in other studies, a common mode of interannual and intraseasonal variability has been found, in this case describing the north-south transition of the TCZ associated with monsoon active/break cycles. Although seasonal-mean values of the Principal Component (PC) timeseries associated with the leading intraseasonal mode shows no significant correlation with ENSO, the 2-dimensional probability

  13. Quaternary biogenic opal records in the South China Sea: Linkages to East Asian monsoon, global ice volume and orbital forcing

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Particulate fluxes investigated in the central South China Sea (SCS) during 1993―1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470―900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420―450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The vari- ability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ 18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and

  14. Classification of typical summer rainfall patterns in the East China monsoon region and their association with the East Asian summer monsoon

    Science.gov (United States)

    Yang, Liu; Zhao, Junhu; Feng, Guolin

    2016-06-01

    In this study, the summer rainfall patterns in the East China monsoon region during 1951-2015 were objectively classified into four typical categories: the northern China rainfall pattern (NCP), the intermediate rainfall pattern (IRP), the Yangtze River rainfall pattern (YRP), and the South China rainfall pattern (SCP). The periods of the four patterns show significant decadal characteristics. The NCP occurred mainly between the late 1950s and the early 1980s, and the IRP in the late 1950s to the early 1970s and the 2000s. The YRP occurred mainly between the 1980s and the 1990s, and the SCP between the mid-1990s and the early 21st century. The relationship between the East Asian summer monsoon index (EASM I WF) and the four rainfall patterns was comparatively analyzed. The results confirmed that the four rainfall patterns have obvious differences in the EASM. In the NCP, IRP, or SCP years, the EASM I WF primarily showed a positive phase and a strong summer monsoon; in the YRP years, the EASM I WF primarily showed a negative phase and a weak summer monsoon.

  15. Seasonal and Intraseasonal Variations of East Asian Summer Monsoon Precipitation Simulated by a Regional Air-Sea Coupled Model

    Institute of Scientific and Technical Information of China (English)

    FANG Yongjie; ZHANG Yaocun; HUANG Anning; LI Bo

    2013-01-01

    The performance of a regional air sea coupled model,comprising the Regional Integrated Environment Model System (RIEMS) and the Princeton Ocean Model (POM),in simulating the seasonal and intraseasonal variations of East Asian summer monsoon (EASM) rainfall was investigated.Through comparisons of the model results among the coupled model,the uncoupled RIEMS,and observations,the impact of air sea coupling on simulating the EASM was also evaluated.Results showed that the regional air sea coupled climate model performed better in simulating the spatial pattern of the precipitation climatology and produced more realistic variations of the EASM rainfall in terms of its amplitude and principal EOF modes.The coupled model also showed greater skill than the uncoupled RIEMS in reproducing the principal features of climatological intraseasonal oscillation (CISO) of EASM rainfall,including its dominant period,intensity,and northward propagation.Further analysis indicated that the improvements in the simulation of the EASM rainfall climatology and its seasonal variation in the coupled model were due to better simulation of the western North Pacific Subtropical High,while the improvements of CISO simulation were owing to the realistic phase relationship between the intraseasonal convection and the underlying SST resulting from the air sea coupling.

  16. A detailed East Asian monsoon history surrounding the ‘Mystery Interval’ derived from three Chinese speleothem records

    Science.gov (United States)

    Zhang, Weihong; Wu, Jiangying; Wang, Yi; Wang, Yongjin; Cheng, Hai; Kong, Xinggong; Duan, Fucai

    2014-07-01

    The ‘Mystery Interval’ (MI, 17.5-14.5 ka) was the first stage of the last deglaciation, a key interval for understanding mechanisms of glacial-interglacial cycles. To elucidate possible causes of the MI, here we present three high-resolution, precisely dated oxygen-isotope records of stalagmites from Qingtian and Hulu Caves in China, reflecting changes in the East Asian summer monsoon (EASM) then. Based on well-established chronologies using precise 230Th dates and annual-band counting results, the two-cave δ18O profiles of ~ 7-yr resolution match well at decadal timescales. Both of the two-cave records document an abrupt weakening (2‰ of δ18O rise within 20 yr) in the EASM at ~ 16.1 ka, coinciding with the transition of the two-phased MI reconstructed from New Mexico's Lake Estancia. Our results indicate that the maximum southward displacement of the Intertropical Convergence Zone and associated southward shift of polar jet stream may generate this two-phase feature of the MI during that time. We also discover a linear relationship among decreasing EASM intensity, rising atmospheric CO2 and weakening Atlantic Meridional Overturning Circulation between the MI and Younger Dryas episodes, suggesting a strong coupling of atmospheric/oceanic circulations in response to the millennial-scale forcing, which in turn regulates global climate changes and carbon cycles.

  17. Glacial to Holocene swings of the Australian-Indonesian monsoon

    NARCIS (Netherlands)

    Mohtadi, M.; Oppo, D.W.; Steinke, S.; Stuut, J.B.W.; De Pol-Holz, R.; Hebbeln, D.; Lückge, A.; Stuut, J.B.W.; De-Pol-Holz, R.

    2011-01-01

    The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region(1). However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present

  18. Simulation of different types of ENSO impacts on South Asian Monsoon in CCSM4

    Science.gov (United States)

    Islam, Siraj ul; Tang, Youmin

    2016-04-01

    It has been found in observation that there are different types of influences of El Nino Southern Oscillation (ENSO) on the South Asian Monsoon (SAM). A correct description and representation of these teleconnections is critical for climate models to simulate and predict SAM. In this study, we examine these teleconnections in NCAR CAM4 and CCSM4 models, including the strength and weakness of these models in preserving different types of ENSO-SAM relationships. By using observational and simulation dataset, the composite analysis, based on specific selection criteria, is performed for both SAM rainfall and the eastern equatorial Pacific sea surface temperature (SST) anomalies. Anomalous SAM rainfall is characterized in three different types i.e. the indirect influence of the SST anomalies of preceding winter (DJF-only), direct influence of the SST anomalies of concurrent summer (JJAS-only) and the combined influence of both preceding winter and concurrent summer (DJF&JJAS). The analysis reveals that CAM4 uncoupled simulation can reasonably well reproduce the anomalous SAM rainfall in DJF-only and DJF&JJAS types whereas the model fails to simulate the anomalous rainfall in the JJAS-only type. The better performance of CAM4, particularly in DJF&JJAS type, comes from its realistic simulation of moisture content and thermal contrast. Its failure to preserve the ENSO-SAM relationship of JJAS-only type is due to the absence of ENSO induced warming in Northern Indian Ocean via atmospheric circulation which is indirectly linked to the lack of air-sea coupling. The role of Indian Ocean in controlling the ENSO-SAM teleconnections of the DJF&JJAS type is further investigated using CAM4 sensitivity experiments. It is found that in absence of Indian Ocean SST, the anomalous SAM summer rainfall suppresses in the DJF&JJAS type, suggesting the important modulation by Indian Ocean SST probably through the preceding winter equatorial Pacific SST forcing and the atmospheric

  19. Response of Asian summer monsoon duration to orbital forcing under glacial and interglacial conditions: Implication for precipitation variability in geological records

    Science.gov (United States)

    Shi, Zhengguo

    2016-05-01

    The responses of Asian summer monsoon and associated precipitation to orbital forcing have been intensively explored during the past 30 years, but debate still exists regarding whether or not the Asian monsoon is controlled by northern or southern summer insolation on the precessional timescale. Various modeling studies have been conducted that support the potential roles played by the insolation in both hemispheres. Among these previous studies, however, the main emphasis has been on the Asian monsoon intensity, with the response of monsoon duration having received little consideration. In the present study, the response of the rainy season duration over different monsoon areas to orbital forcing and its contribution to total annual precipitation are evaluated using an atmospheric general circulation model. The results show that the durations of the rainy seasons, especially their withdrawal, in northern East Asia and the India-Bay of Bengal region, are sensitive to precession change under interglacial-like conditions. Compared to those during stronger boreal summer insolation, the Asian monsoon-associated rainy seasons at weaker insolation last longer, although the peak intensity is smaller. This longer duration of rainfall, which results from the change in land-ocean thermal contrast associated with atmospheric diabatic heating, can counterbalance the weakened intensity in certain places and induce an opposite response of total annual precipitation. However, the duration effect of Asian monsoon is limited under glacial-like conditions. Nevertheless, monsoon duration is a factor that can dominate the orbital-scale variability of Asian monsoon, alongside the intensity, and it should therefore receive greater attention when attempting to explain orbital-scale monsoon change.

  20. South China Sea Surface Waters During the Late Pleistocene: Records of the Relationship Between South East Asian Monsoon Variability and Glacial-Interglacial Cycles

    Science.gov (United States)

    McIntyre, K.; Oppo, D.

    2001-05-01

    One of the major goals of Ocean Drilling Program Leg 184 in the South China Sea was to recover sediment records that could be used to examine the history of the South East Asian monsoon relative to external variation in the global climate, on both orbital and millennial timescales. Examinations of how monsoonal variability in this region interacts with larger changes in global climate speak to the ongoing debate about the role of the tropical and equatorial regions in climate change. In order to reconstruct this interaction we have generated a new 700 kyr record of planktonic foraminiferal (G. ruber) oxygen and carbon isotopes from Ocean Drilling Program site 1145 in the South China Sea (19° 35.04'N, 117° 37.86'E, 3175 m. water depth). The oxygen isotope record reflects both global ice volume and a composite of sea surface salinity and temperature that varies in response to monsoonally driven changes in sea surface circulation and regional precipitation. The carbon isotopic record reflects changes in local productivity and global changes in the carbon budget. Since our record has both a strong 100-kyr glacial component and a strong precessional component, it allows us to examine the interaction between high-latitude glacial influence and local precessional influence on the South East Asian monsoon. As seen at other sites in the South China Sea, there is an overall increase in sedimentation rates coming toward the present. Sedimentation rates at this site decrease threefold at 400 Ka, with sedimentation rates ~6 cm/kyr prior to this time and rates of ~20 cm/kyr after. As a consequence, temporal resolution for the latter part of the record varies between 400 and 1000 years, and is >2000 years before 400 ka. We find that sub-Milankovitch variability in both oxygen and carbon isotopes is consistently high throughout glacial-interglacial cycles, +/-0.6 ‰ in δ 18O and +/-0.4 ‰ in δ 13C. Over the last 400 kyrs we find both variability on 3-4 kyr timescales and on

  1. Summer climate of Madagascar and monsoon pulsing of its vortex

    Science.gov (United States)

    Jury, Mark R.

    2016-02-01

    This study analyzes the climate of Madagascar (12°-26°S, 43°-50°E) and its relation to the Indian Ocean during austral summer (Dec-Mar). Moisture converges onto a standing easterly wave and floods are prevalent in late summer. All-island daytime land temperatures exceed 38 °C in October and are ~4 °C above sea temperatures during summer. Analysis of thermally induced diurnal convection and circulation revealed inflow during the afternoon recirculated from the southeastern mountains and the warm Mozambique Channel. Summer rainfall follows latent and sensible heat flux during the first half of the day, and gains a surplus by evening via thunderstorms over the western plains. At the inter-annual time-scale, 2.3 years oscillations in all-island rainfall appear linked with the stratospheric quasi-biennial oscillation and corresponding 80 Dobson Unit ozone fluctuations during flood events. Wet spells at frequencies from 11-27 days derive from locally-formed tropical cyclones and NW-cloud bands. Flood case studies exhibit moisture recycling in the confluence zone between the sub-tropical anticyclone and the lee-side vortex. Hovmoller analysis of daily rainfall reinforces the concept of local generation and pulsing by cross-equatorial (Indian winter) monsoon flow rather than zonal atmospheric waves. Since the surface water budget is critical to agriculture in Madagascar, this study represents a further step to understand its meso-scale summer climate.

  2. The resolution sensitivity of the South Asian monsoon and Indo-Pacific in a global 0.35° AGCM

    Science.gov (United States)

    Johnson, Stephanie J.; Levine, Richard C.; Turner, Andrew G.; Martin, Gill M.; Woolnough, Steven J.; Schiemann, Reinhard; Mizielinski, Matthew S.; Roberts, Malcolm J.; Vidale, Pier Luigi; Demory, Marie-Estelle; Strachan, Jane

    2016-02-01

    The South Asian monsoon is one of the most significant manifestations of the seasonal cycle. It directly impacts nearly one third of the world's population and also has substantial global influence. Using 27-year integrations of a high-resolution atmospheric general circulation model (Met Office Unified Model), we study changes in South Asian monsoon precipitation and circulation when horizontal resolution is increased from approximately 200-40 km at the equator (N96-N512, 1.9°-0.35°). The high resolution, integration length and ensemble size of the dataset make this the most extensive dataset used to evaluate the resolution sensitivity of the South Asian monsoon to date. We find a consistent pattern of JJAS precipitation and circulation changes as resolution increases, which include a slight increase in precipitation over peninsular India, changes in Indian and Indochinese orographic rain bands, increasing wind speeds in the Somali Jet, increasing precipitation over the Maritime Continent islands and decreasing precipitation over the northern Maritime Continent seas. To diagnose which resolution-related processes cause these changes, we compare them to published sensitivity experiments that change regional orography and coastlines. Our analysis indicates that improved resolution of the East African Highlands results in the improved representation of the Somali Jet and further suggests that improved resolution of orography over Indochina and the Maritime Continent results in more precipitation over the Maritime Continent islands at the expense of reduced precipitation further north. We also evaluate the resolution sensitivity of monsoon depressions and lows, which contribute more precipitation over northeast India at higher resolution. We conclude that while increasing resolution at these scales does not solve the many monsoon biases that exist in GCMs, it has a number of small, beneficial impacts.

  3. The Influence of the East Asian Winter Monsoon on Indonesian Rainfall During the Past 60,000 Years

    Science.gov (United States)

    Konecky, B. L.; Russell, J. M.; Vogel, H.; Bijaksana, S.; Huang, Y.

    2013-12-01

    The Indo-Pacific Warm Pool (IPWP) invigorates the oceanic-atmospheric circulation in the tropics, with far-reaching climate impacts that extend into the high latitudes. A growing number of deglacial proxy reconstructions from the Maritime Continent and its surrounding seas have revealed the importance of both high- and low-latitude climate processes to IPWP rainfall during the deglaciation and the Holocene. However, few records extend beyond the Last Glacial Maximum (LGM), making it difficult to assess regional rainfall characteristics and monsoon interactions under the glacial/interglacial boundary conditions of the Pleistocene. Proxy reconstructions of the oxygen and hydrogen isotopic composition of rainfall (δ18O/δDprecip) have proven useful in understanding millennial to orbital scale changes in the climate of the Maritime Continent, but the tendency for δ18O/δDprecip in this region to reflect regional and/or remote climate processes has highlighted the need to reconstruct δ18O/δDprecip alongside independent proxies for continental rainfall amount. Here we present a reconstruction of δDprecip using leaf wax compounds preserved in the sediments of Lake Towuti, Central Sulawesi, from 60,000 years before present (kyr BP) to today. Our δDprecip reconstruction provides a precipitation isotopic counterpart to multi-proxy geochemical reconstructions of surface hydrology and vegetation characteristics from the same sediment cores, enabling for the first time an independent assessment of both continental rainfall intensity and δDprecip from this region on glacial/interglacial timescales. We find that orbital-scale variations in δDprecip and rainfall intensity are strongly tied to the East Asian Winter Monsoon (EAWM), which is an important contributor to the band of convection over the Maritime Continent during austral summer. Unlike today, however, severely dry conditions in Central Sulawesi during the Last Glacial Maximum were accompanied by a strengthened

  4. Assessing how seasonal hydrological balance has changed during the warming 20th century in the montane forests of Southeast Asian monsoon region using a stable isotope dendroclimatology approach

    Science.gov (United States)

    Zhu, M.; Stott, L. D.

    2010-12-01

    Tropical montane forests act as water catchment and host of biodiversity in the Southeast Asian monsoon region, and understanding how their hydrological conditions change with global warming is vitally important. Global climate model simulations project enhanced moisture cycle in the tropics, which would cause stronger summer monsoon precipitations, but on the other hand the adiabatic lapse rate would be shifted towards a moister condition (amplification of warming at high elevation), inhibiting dry season orographic lifting cloud/fog formation (lifting cloud base hypothesis), enhancing evapo-transpiration, and leading to a net moisture loss during winter dry season. In this study, we have attempted to investigate how the seasonal moisture balance in Southeast Asia has evolved in response to these influences through the 20th century using the oxygen isotopic composition (δ18O) of subannual tree cellulose samples extracted from the annual rings of pine trees that grow in Doi Chiang Dao, a limestone mountain in northern Thailand. At this location the δ18O of cellulose exhibits distinctive annual cycles of up to 12‰, which is primarily a reflection of both the so-called ‘isotope amount effect’ that is associated with the strong monsoon precipitation during summer wet season and the moisture availability from different sources during winter dry season. We have demonstrated that tree cellulose δ18O could be used as a proxy for regional monsoon strength by showing that the annual mean cellulose δ18O correlate significantly with All India Rainfall, Webster-Yang monsoon index, as well as with both local and regional monsoon precipitation. ENSO is the dominant influence on interannual rainfall variability and this is well expressed in the interannual cellulose δ18O record. Using a 21-year moving window correlation analysis we find a weakening of ENSO influence after 1980, coinciding with the most rapid atmospheric warming. We expect to analyze older trees to

  5. The Eurasian ice sheet reinforces the East Asian summer monsoon during the interglacial 500 000 years ago

    OpenAIRE

    Qiuzhen Yin; Berger, A; E. Driesschaert; Goosse, H.; Loutre, M. F.; Crucifix, M.

    2008-01-01

    Deep-sea and ice-core records show that interglacial periods were overall less "warm" before about 420 000 years ago than after, with relatively higher ice volume and lower greenhouse gases concentration. This is particularly the case for the interglacial Marine Isotope Stage 13 which occurred about 500 000 years ago. However, by contrast, the loess and other proxy records from China suggest an exceptionally active East Asian summer monsoon during this interglacial. A three-dimensio...

  6. Recent intensification of the South and East Asian monsoon contrast associated with an increase in the zonal tropical SST gradient

    Science.gov (United States)

    Yun, Kyung-Sook; Lee, June-Yi; Ha, Kyung-Ja

    2014-07-01

    Observed analysis of the 35 years of 1979-2013 reveals considerable interdecadal change and significant recent intensification in the difference of convective precipitation between the South Asian monsoon (SAM) and East Asian monsoon (EAM) systems during the major summer monsoon season (June-July). We propose that the recent strengthening of the zonal gradient of sea surface temperature (SST) between the Indian Ocean, western Pacific, and eastern Pacific is a possible cause for the intensification of the convective precipitation contrast. It is noted that the strengthening of the zonal SST gradient associated with the recent mega-La Niña trend tends to reinforce the negative connection between SAM and EAM systems by inducing enhanced convection over the maritime continent and then facilitating the northwestward emanation of Rossby waves. Consequently, a cyclonic circulation anomaly that effectively changes the local Hadley circulation has been formed over the SAM region, resulting in the noticeable difference between the SAM and EAM. The years 2013 and 1983 are further investigated as the strongest extreme years for positive and negative phases of submonsoon contrast, respectively. The result confirms that the meridional dipole height pattern along the Asian Jet stream, which is caused by the strong zonal gradient of tropical SST, serves as a key trigger in strengthening the submonsoon contrast.

  7. Glacial to Holocene swings of the Australian-Indonesian monsoon

    OpenAIRE

    M. Mohtadi; Oppo, D. W.; Steinke, S.; De Pol-Holz, R.; Hebbeln, D.; Lückge, A.; Stuut, J.B.W.; De-Pol-Holz, R.

    2011-01-01

    The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region(1). However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive ...

  8. Holocene East Asian summer monsoon records in northern China and their inconsistency with Chinese stalagmite δ18O records

    Science.gov (United States)

    Liu, Jianbao; Chen, Jianhui; Zhang, Xiaojian; Chen, Fahu

    2016-04-01

    Monsoon precipitation over China exhibits large spatial differences. It has been found that a significantly enhanced East Asian summer monsoon (EASM) is characterized by increased rainfall in northern China and by reduced rainfall in southern China, and this relationship occurs on different time scales during the Holocene. This study presents results from a diverse range of proxy paleoclimatic records from northern China where precipitation variability is traditionally considered as an EASM proxy. Our aim is to evaluate the evolution of the EASM during the Holocene and to compare it with all of the published stalagmite δ18O records from the Asian Monsoon region in order to explore the potential mechanism(s) controlling the Chinese stalagmite δ18O. We found that the intensity of the EASM during the Holocene recorded by the traditional EASM proxy of moisture (or precipitation) records from northern China are significantly different from the Chinese stalagmite δ18O records. The EASM maximum occurred during the mid-Holocene, challenging the prevailing view of an early Holocene EASM maximum mainly inferred from stalagmite δ18O records in eastern China. In addition, all of the well-dated Holocene stalagmite δ18O records, covering a broad geographical region, exhibit a remarkably similar trend of variation and are statistically well-correlated on different time scales, thus indicating a common signal. However, in contrast with the clear consistency in the δ18O values in all of the cave records, both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal-to- centennial time scales over eastern China. In addition, both paleoclimatic records and modeling results suggest that Holocene East Asian summer monsoon precipitation reached a maximum at different periods in different regions of China. Thus the stalagmite δ18O records from the EASM region should not be regarded as a reliable indicator of the strength of the East

  9. Characteristics of Thermal and Geopotential Height Differences Between Continent and Ocean and Its Role in the Strength of the Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    Andrea Silverman; SUN Jilin

    2005-01-01

    The interdecadal factors affecting the summer monsoon winds over Somalia and the South China Sea were studied. Global geopotential heights and wind velocity fields of the 850-hPa and 200-hPa pressure levels, as well as sea surface temperature anomaly data and correlation coefficients were analyzed. The monsoons over Somalia and the South China Sea were found to be two different monsoon systems, operating on different mechanisms and being affected by different oceanatmosphere interactions. The intensity of the Asian subtropical summer monsoon is influenced by the intensity of the summer monsoon over Somalia in the month of June and by the intensity of the summer monsoon over the South China Sea in the months of June and July. The summer monsoon wind strength over Somalia is affected by regional factors, such as the heating of the Tibetan plateau, and by global mechanisms, such as the subtropical heat exchange with Antarctica. The summer monsoon over the South China Sea is affected by different ocean-atmosphere interactions. The Somalia and subtropical summer monsoons have wind blowing down the pressure gradient from area over ocean to that over land, like typical summer monsoons. The South China Sea summer monsoon has winds that blow down the pressure gradient from area over land to that over ocean. The South China Sea summer monsoon is affected by the Kuroshio Current off the east coast of Japan.

  10. Observations of PAN and its confinement in the Asian summer monsoon anticyclone in high spatial resolution

    Science.gov (United States)

    Ungermann, Jörn; Ern, Mandfred; Kaufmann, Martin; Müller, Rolf; Spang, Reinhold; Ploeger, Felix; Vogel, Bärbel; Riese, Martin

    2016-07-01

    This paper presents an analysis of trace gases in the Asian summer monsoon (ASM) region on the basis of observations by the CRISTA infrared limb sounder taken in low-earth orbit in August 1997. The spatially highly resolved measurements of peroxyacetyl nitrate (PAN) and O3 allow a detailed analysis of an eddy-shedding event of the ASM anticyclone. We identify enhanced PAN volume mixing ratios (VMRs) within the main anticyclone and within the eddy, which are suitable as a tracer for polluted air originating in India and China. Plotting the retrieved PAN VMRs against potential vorticity (PV) and potential temperature reveals that the PV value at which the PAN VMRs exhibit the strongest decrease with respect to PV increases with potential temperature. These PV values might be used to identify the extent of the ASM. Using temperature values also derived from CRISTA measurements, we also computed the location of the thermal tropopause according to the WMO criterion and find that it confines the PAN anomaly vertically within the main ASM anticyclone. In contrast, the shed eddy exhibits enhanced PAN VMRs for 1 to 2 km above the thermal tropopause. Using the relationship between PAN as a tropospheric tracer and O3 as a stratospheric tracer to identify mixed air parcels, we further found the anticyclone to contain few such air parcels, whereas the region between the anticyclone and the eddy as well as the eddy itself contains many mixed air parcels. In combination, this implies that while the anticyclone confines polluted air masses well, eddy shedding provides a very rapid horizontal transport pathway of Asian pollution into the extratropical lowermost stratosphere with a timescale of only a few days.

  11. Holocene Asian monsoon evolution revealed by a pollen record from an alpine lake on the southeastern margin of the Qinghai-Tibetan Plateau, China

    Science.gov (United States)

    Zhang, Enlou; Wang, Yongbo; Sun, Weiwei; Shen, Ji

    2016-02-01

    We present the results of pollen analyses from a 1105 cm long sediment core from Wuxu Lake in southwestern China, which depict the variations of the East Asian winter monsoon (EAWM) and the Indian summer monsoon (ISM) during the last 12.3 ka. During the period of 12.3 to 11.3 cal ka BP, the dominance of Betula forest and open alpine shrub and meadow around Wuxu Lake indicates a climate with relatively cold winters and dry summers, corresponding to the Younger Dryas event. Between 11.3 and 10.4 cal ka BP, further expansion of Betula forest and the retreat of alpine shrubs and meadows reflect a greater seasonality with cold winters and gradually increasing summer precipitation. From 10.4 to 4.9 cal ka BP, the dense forest understory, together with the gradual decrease in Betula forest and increase in Tsuga forest, suggest that the winters became warmer and summer precipitation was at a maximum, corresponding to the Holocene climatic optimum. Between 4.9 and 2.6 cal ka BP, Tsuga forest and alpine shrubs and meadows expanded significantly, reflecting relatively warm winters and decreased summer precipitation. Since 2.6 cal ka BP, reforestation around Wuxu Lake indicates a renewed humid period in the late Holocene; however, the vegetation in the catchment may also have been affected by grazing activity during this period. The results of our study are generally consistent with previous findings; however, the timing and duration of the Holocene climatic optimum from different records are inconsistent, reflecting real contrast in local rainfall response to the ISM. Overall, the EAWM is broadly in-phase with the ISM on the orbital timescale, and both monsoons exhibit a trend of decreasing strength from the early to late Holocene, reflecting the interplay of solar insolation receipt between the winter and summer seasons and El Niño-Southern Oscillation strength in the tropical Pacific.

  12. Mid-Holocene variability of the East Asian monsoon based on bulk organic δ13C and C/N records from the Pearl River estuary, southern China

    Science.gov (United States)

    Yu, F.; Zong, Y.; Lloyd, J. M.; Leng, M. J.; Switzer, A. D.; Yim, W. W.; Huang, G.

    2012-12-01

    Understanding the mid-Holocene dynamics of the East Asian monsoon (EAM) is integral to modelling the Holocene development of the global climate system (Webster et al., 1998). Thus the mid-Holocene EAM history was reconstructed using bulk organic carbon isotopes (δ13C), total carbon to total nitrogen (C/N) ratios and total organic carbon (TOC) from a sediment core (UV1), at a mean resolution of 7-10 years, from the Pearl River estuary, southern China. Sedimentary δ13C, C/N and TOC from the Pearl River estuary is a good indicator of changes in monsoonal precipitation strength (Zong et al., 2006; Yang et al., 2010; Yu et al., 2010), eg sediments buried during a period of high precipitation exhibit a high proportion of terrigenous sediments, and have low δ13C and high C/N, and vice versa (Yu et al., 2010). Results suggest a general decreasing trend in monsoonal precipitation from 6650 to 2215 cal yr BP because of the weakening Northern Hemisphere insolation most likely related to the current precession circle (An, 2000). Superimposed on this trend are apparent dry-wet oscillations at centennial to millennial timescales most likely in response to solar activity. Mismatch between δ13C and results from the Dongge Cave in southern China at millennial-timescale oscillations (Wang et al., 2005), may indicate that the δ13C from the Pearl River estuary reveals changes in precipitation in a broader area than the δ18O from Dongge Cave does. Reference An Z (2000) The history and variability of the East Asian paleomonsoon climate. Quaternary Science Reviews 19: 171-187. Wang Y, Cheng H, Edwards RL, He Y, Kong X, An Z, Wu J, Kelly MJ, Dykoski CA and Li X (2005) The Holocene Asian Monsoon: Links to Solar Changes and North Atlantic Climate. Science 308: 854-857. Webster PJ, Magaña VO, Palmer TN, Shukla J and Tomas RA (1998) Monsoons: Processes, predictability, and the prospects for prediction. Journal of Geophysical Research 103(C7): 14451-14510. Yang S, Tang M, Yim WWS, Zong

  13. Evapotranspiration of rubber (Hevea brasiliensis) under the highly seasonal rainfall regime of the Asian monsoon in mainland Southeast Asia

    Science.gov (United States)

    Giambelluca, T. W.; Mudd, R. G.; Liu, W.; Kobayashi, N.; Ziegler, A. D.; Miyazawa, Y.; Kumagai, T.; Huang, M.

    2012-12-01

    The Asian Monsoon dominates the climate of the mainland Southeast Asia (MSEA) region, characterized by a highly seasonal rainfall regime in which 80-90% of annual rainfall occurs during the 6-month (May-October) wet season. The accompanying extremes in soil moisture, solar radiation, and vapor pressure deficit exert strong controls on ecosystem fluxes, including evapotranspiration (ET). Rubber (Hevea brasiliensis), the major commercial crop currently replacing traditional agriculture and secondary forests in MSEA is a native of the equatorial Amazon rainforest, and differs physiologically from the dominant native SE Asian forest tree species. It sheds its leaves in the middle of the dry season and flushes new leaves before the onset of the wet season. In some areas, rubber cultivation is suspected of having caused changes in local climate and watershed processes, including a dramatic downward trend in fog frequency and large increases in surface runoff and soil erosion (Wu et al., 2001, Int. J. Sust. Dev. World Ecol. 8:337-345). Guardiola-Claramonte et al. (2008, Ecohydrology 1:13-22; 2010, Ecohydrology 3:306-314) noted striking differences in the timing and rate of dry season root-water extraction under rubber as compared with other vegetation types. To investigate the environmental impacts of rubber, eddy covariance flux towers were installed to monitor energy, water, and carbon exchange at rubber plantation sites in northeastern Thailand and Cambodia. Results of the first two years of observations at the sites indicate that controls on ET differ between wet and dry seasons, with varying responses to energy, soil moisture, canopy wetness, and leaf area. Despite the long dry season and loss of leaves for several weeks, rubber accumulates exceptionally high annual ET totals, exceeding those of natural forest and other plant functional types in the region. The phenology of rubber represents a disruption of the land-atmosphere interactions of native and other non

  14. Predictability of the East Asian Winter Monsoon Interannual Variability as Indicated by the DEMETER CGCMS

    Institute of Scientific and Technical Information of China (English)

    LI Fei; WANG Huijun

    2012-01-01

    The interannual variability of East Asian winter monsoon (EAWM) circulation from the Development of a European Multi-Model Ensemble (MME) System for Seasonal to Inter-Annual Prediction (DEMETER)hindcasts was evaluated against observation reanalysis data.We evaluated the DEMETER coupled general circulation models (CGCMs)' retrospective prediction of the typical EAWM and its associated atmospheric circulation.Results show that the EAWM can be reasonably predicted with statistically significant accuracy,yet the major bias of the hindcast models is the underestimation of the related anomalies.The temporal correlation coefficient (TCC) of the MME-produced EAWM index,defined as the first EOF mode of 850-hPa air temperature within the EAWM domain (20°-60°N,90° 150°E),was 0.595.This coefficient was higher than those of the corresponding individual models (range:0.39-0.51) for the period 1969-2001; this result indicates the advantage of the super-ensemble approach.This study also showed that the ensemble models can reasonably reproduce the major modes and their interannual variabilities for sea level pressure,geopotential height,surface air temperature,and wind fields in Eurasia.Therefore,the prediction of EAWM interannual variability is feasible using multimodel ensemble systems and that they may also reveal the associated mechanisms of the EAWM interannual variability.

  15. Predictability experiments for the Asian summer monsoon impact of SST anomalies on interannual and intraseasonal variability

    CERN Document Server

    Molteni, F; Ferranti, L; Slingo, J M

    2003-01-01

    The effects of SST anomalies on the interannual and intraseasonal variability of the Asian summer monsoon have been studied by multivariate statistical analyses of 850-hPa wind and rainfall fields simulated in a set of ensemble integrations of the ECMWF atmospheric GCM, referred to as the PRISM experiments. The simulations used observed SSTs (PRISM-O), covering 9 years characterised by large variations of the ENSO phenomenon in the 1980's and the early 1990's. A parallel set of simulations was also performed with climatological SSTs (PRISM-C), thus enabling the influence of SST forcing on the modes of interannual and intraseasonal variability to be investigated. As in observations, the model's interannual variability is dominated by a zonally-oriented mode which describes the north-south movement of the tropical convergence zone (TCZ). This mode appears to be independent of SST forcing and its robustness between the PRISM-O and PRISM-C simulations suggests that it is driven by internal atmospheric dynamics. O...

  16. Impact of the North Atlantic sea surface temperature tripole on the East Asian summer monsoon

    Science.gov (United States)

    Zuo, Jinqing; Li, Weijing; Sun, Chenghu; Xu, Li; Ren, Hong-Li

    2013-07-01

    A strong (weak) East Asian summer monsoon (EASM) is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer, which has positive (negative) SST anomalies in the northwestern North Atlantic and negative (positive) SST anomalies in the subpolar and tropical ocean. The mechanisms responsible for this linkage are diagnosed in the present study. It is shown that a barotropic wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer. This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains, which has a substantial effect on the EASM. Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing. Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation (NAO), the relationships between these two factors and the EASM are also examined. It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole, which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO. The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.

  17. A major reorganization of Asian climate by the early Miocene

    OpenAIRE

    Z. T. Guo; Sun, B; Z. S. Zhang; Peng, S. Z.; G. Q. Xiao; Ge, J. Y.; Q. Z. Hao; Qiao, Y. S.; M. Y. Liang; Liu, J F; Q. Z. Yin; Wei, J. J.

    2008-01-01

    The global climate system experienced a series of drastic changes during the Cenozoic. In Asia, these include the climate transformation from a zonal pattern to a monsoon-dominated pattern, the disappearance of typical subtropical aridity, and the onset of inland deserts. Despite major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes....

  18. Using a WRF simulation to examine regions where convection impacts the Asian summer monsoon anticyclone

    Directory of Open Access Journals (Sweden)

    N. K. Heath

    2013-09-01

    Full Text Available The Asian summer monsoon is a prominent feature of the global circulation that is associated with an upper-level anticyclone (ULAC that stands out vividly in satellite observations of trace gases. The ULAC also is an important region of troposphere-to-stratosphere transport. We ran the Weather Research and Forecasting (WRF model at convective-permitting scales (4 km grid spacing between 10–20 August 2012 to understand the role of convection in transporting boundary layer air into the upper-level anticyclone. Such high-resolution modeling of the Asian ULAC previously has not been documented in the literature. Comparison of our WRF simulation with reanalysis and satellite observations showed that WRF simulated the atmosphere sufficiently well to be used to study convective transport into the ULAC. A back-trajectory analysis based on hourly WRF output showed that > 90% of convectively influenced parcels reaching the ULAC came from the Tibetan Plateau (TP and the southern slope (SS of the Himalayas. A distinct diurnal cycle is seen in the convective trajectories, with their greatest impact occurring between 1600–2300 local solar time. This finding highlights the role of "everyday" diurnal convection in transporting boundary layer air into the ULAC. WRF output at 15 min intervals was produced for 16 August to examine the convection in greater detail. This high-temporal output revealed that the weakest convection in the study area occurred over the TP. However, because the TP is at 3000–5000 m a.m.s.l., its convection does not have to be as strong to reach the ULAC as in lower altitude regions. In addition, because the TP's elevated heat source is a major cause of the ULAC, we propose that convection over the TP and the neighboring SS is ideally situated geographically to impact the ULAC. The vertical mass flux of water vapor into the ULAC also was calculated. Results show that the TP and SS regions dominate other Asian regions in transporting

  19. Asian monsoon and Indian Ocean evolution during Heinrich and Dansgaard-Oeschger events

    Science.gov (United States)

    Bard, Edouard; Böning, Philipp; Tachikawa, Kazuyo; Garcia, Marta; Ménot, Guillemette; Fagault, Yoann; Rostek, Frauke; Licari, Laetitia; Pichevin, Laetitia; Martinez, Philippe

    2014-05-01

    multiple proxies in order to build a detailed and reliable record of the monsoon and ventilation patterns. The identification of significant paleoclimate events should also take into account the stratigraphic resolution of the records. For example, the high-resolution Fe and CaCO3 profiles based on XRF scanner exhibit the rather short DO event #9 that lasted less than 200 yr. By contrast, this event is more difficult to detect in geochemical records measured on discrete samples at lower resolution. Paleo-proxies are often complex indicators of environmental conditions with additional biological, chemical or physical imprints superimposed on the main paleoceanographic control. These imperfections justify a multi-proxy approach relying on the assumption that only common features are robust paleoclimate events. In addition, the comparison of different proxy responses provides insight on the spread and mechanisms of paleoceanographic changes. The case of DO event #12 in core MD04-2876 provides a clear illustration. This prominent DO interstadial lasted about three millennia and is characterized by the highest planktonic productivity over the past 50 kyr (highest values for TOC, TN, chlorins, marine GDGTs, δ15N, U, Mo, Cd; lowest values for CaCO3, Sr/Ca and aragonite/calcite ratios). During this interval, the productivity changes were so large that they significantly affected the deeper record (TOC, TN, δ15N, Mo…) suggesting a vertical extension of the OMZ down to more than 2 km water depth. Moreover, several paleoceanographic proxies exhibit a complex behavior in the middle of the DO-12 event with thresholds values or even a transient reversal (TOC, TN, U, Mo, Cd, lycopane, crenarchaeol/caldarchaeol, benthic foraminiferal number). This shows that the biological productivity was strongly affected, in strength and species distribution, during this prominent maximum of the Asian monsoon. Overall, our multiproxy approach provides a consistent image and shows radical changes at

  20. Contribution of the east-west thermal heating contrast to the South Asian Monsoon and consequences for its variability

    Energy Technology Data Exchange (ETDEWEB)

    Kucharski, Fred; Barimalala, Rondrotiana; Yoo, Jin Ho [Abdus Salam International Centre for Theoretical Physics, Earth System Physics Section, Trieste (Italy); Bracco, Annalisa [EAS, Georgia Institute of Technology, Atlanta, GA (United States)

    2011-08-15

    The focus of this paper is to assess the relative role of the north-south and east-west contrasts in atmospheric heating for the maintenance of the South Asian summer monsoon climatology. The juxtaposition of the Eurasian land mass and the Indian Ocean is responsible for the north-south contrast, while the greater diabatic heating above the western Pacific compared to the one over the African and the tropical South Atlantic Ocean region introduces the east-west gradient. With a series of idealized atmospheric general circulation model experiments, it is found that both contrasts contribute to the maintenance of the South Asian monsoon climatology, but their impact varies at regional scales. The surface atmospheric cyclone and precipitation over northern India are mainly due to the north-south contrast. On the other hand, when the Indian Ocean sea surface temperatures are close to their climatological mean values, the low-level cyclone and consequent rainfall activity in the Bay of Bengal and southern India result from the east-west gradient. The physical mechanism relays on the southern part of the upper-level South Asian monsoon high being forced by the east-west diabatic heating contrast via Sverdrup balance. The east-west heating difference controls also the strength of the Tropical Easterly Jet. Finally, the contribution of the El Nino Southern Oscillation to the interannual variability of the Indian monsoon is interpreted as the result of a longitudinal shift of one of the centers of diabatic heating contributing to the east-west contrast. (orig.)

  1. ITCZ and ENSO pacing on East Asian winter monsoon variation during the Holocene: Sedimentological evidence from the Okinawa Trough

    Science.gov (United States)

    Zheng, Xufeng; Li, Anchun; Wan, Shiming; Kao, Shuhji; Kuhn, Gerhard

    2016-04-01

    Deep-sea fan sediments provide an excellent geological archive for paleoenvironment reconstruction. Grain size, clay mineral and elemental (Ti, Fe, Ca) compositions were measured for a core retrieved from a submarine fan in the Okinawa Trough. Varimax-rotated Principal Component Analysis (V-PCA) on time-evolution of grain size spectrum reveals that, since the Holocene, sediment was transported mainly by the benthic nepheloid layer (33%) and upper layers (33%) which is driven by the East Asian winter monsoon (EAWM). The intensification of the Kuroshio Current during the Holocene, masks the fluvial signal of the summer monsoon and obstructs clay minerals derived from the Yellow River, a major contributor prior to 12 ka BP. A new grain size index (GSI), which represents the EAWM well, exhibits a negative correlation with the δ18O record in Dongge Cave, China during the Holocene when sea level was relatively steady. This anticorrelation suggests the southward migration of the Intertropical Convergence Zone (ITCZ). The consistency among our records and rainfall records in Peru, Ti counts in the Cariaco Basin, monsoon records in Oman and the averaged summer insolation pattern at 30°N further support the ITCZ's impact on monsoon systems globally. Cross-Correlation Analyses for GSI and log(Ti/Ca) against δ18O record in Dongge Cave reveal a decoupling between the East Asian winter and summer monsoon during 5500-2500 cal yr BP, with greater complexity in the last 2500 years. This can be attributed to exacerbated ENSO mode fluctuations and possibly anthropogenic interference superimposed on insolation and ITCZ forcing.

  2. Interhemispheric atmospheric mass oscillation and its relation to interannual variations of the Asian monsoon in boreal summer

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Using NCEP/NCAR reanalysis and precipitation records of Chinese stations, we have investigated the relationship of interhemispheric oscillation of air mass (IHO) with global lower-level circulation and monsoon anomalies in boreal summer. Our results show that the summer IHO explains a greater portion of variance in the abnormal distribution of atmospheric mass over 30°S-60°N as well as the Antarctic. The IHO strongly correlates to the variations of sea level pressure (SLP) in these regions. It is shown that IHO has some influences on both atmospheric mass transports and water vapor fluxes over 30°S-60°N in association with three anomalous cyclonic circulations over land areas of the eastern hemisphere, which is in close relation to the changes in summer monsoon intensity in eastern Asia and western Africa. Composites of summer rainfall anomalies in China for high and low IHO-index years indicate that the eastern Asian summer monsoon is more intense, with positive precipitation anomaly centers in northern and northeastern parts of China, as opposed to the negative center over the mid-lower reaches of the Yangtze River (MLRYR) in stronger IHO years. In weak IHO years, a feeble summer monsoon appears in eastern Asia, leading to positive center of precipitation anomalies displaced into the MLRYR. Furthermore, a teleconnection in wind fields between the western African and eastern Asian monsoon regions was observed in the middle and higher troposphere in the scenario of IHO. The anomalous cyclonic (anticyclonic) circulations along the path of this Africa-East Asia teleconnection were found to be just over the diabatic heating (cooling) centers, suggesting that diabatic forcings are responsible for the formation of this Africa-East Asia teleconnection.

  3. School Climate, Discrimination, and Depressive Symptoms among Asian American Adolescents

    Science.gov (United States)

    Wang, Cixin; Atwal, Kavita

    2015-01-01

    The current study examined a multidimensional, developmental, and transactional model for depressive symptoms among Asian American adolescents using longitudinal data from 1,664 Asian American adolescents in the Children of Immigrants Longitudinal Study (CILS). Specifically, the relationships among school climate, acculturation, perceived…

  4. Spatiotemporal variability of rainfall extremes in monsoonal climates - examples from the South American Monsoon and the Indian Monsoon Systems (Invited)

    Science.gov (United States)

    Bookhagen, B.; Boers, N.; Marwan, N.; Malik, N.; Kurths, J.

    2013-12-01

    Monsoonal rainfall is the crucial component for more than half of the world's population. Runoff associated with monsoon systems provide water resources for agriculture, hydropower, drinking-water generation, recreation, and social well-being and are thus a fundamental part of human society. However, monsoon systems are highly stochastic and show large variability on various timescales. Here, we use various rainfall datasets to characterize spatiotemporal rainfall patterns using traditional as well as new approaches emphasizing nonlinear spatial correlations from a complex networks perspective. Our analyses focus on the South American (SAMS) and Indian (ISM) Monsoon Systems on the basis of Tropical Rainfall Measurement Mission (TRMM) using precipitation radar and passive-microwave products with horizontal spatial resolutions of ~5x5 km^2 (products 2A25, 2B31) and 25x25 km^2 (3B42) and interpolated rainfall-gauge data for the ISM (APHRODITE, 25x25 km^2). The eastern slopes of the Andes of South America and the southern front of the Himalaya are characterized by significant orographic barriers that intersect with the moisture-bearing, monsoonal wind systems. We demonstrate that topography exerts a first-order control on peak rainfall amounts on annual timescales in both mountain belts. Flooding in the downstream regions is dominantly caused by heavy rainfall storms that propagate deep into the mountain range and reach regions that are arid and without vegetation cover promoting rapid runoff. These storms exert a significantly different spatial distribution than average-rainfall conditions and assessing their recurrence intervals and prediction is key in understanding flooding for these regions. An analysis of extreme-value distributions of our high-spatial resolution data reveal that semi-arid areas are characterized by low-frequency/high-magnitude events (i.e., are characterized by a ';heavy tail' distribution), whereas regions with high mean annual rainfall have a

  5. Forms of the Tibetan Plateau uplift and regional differences of the Asian monsoon-arid environmental evolution-A modeling perspective

    Institute of Scientific and Technical Information of China (English)

    LIU Xiao-dong; YIN Zhi-yong

    2011-01-01

    Tectonic uplift of the Tibetan Plateau (TP) is a major event in the recent geological history of the earth, which produced far-reaching impacts on the Asian and global climates and environments. Since the 1970s, with the development of theories in planetary fluid dynamics and the improvement of computational environment, numerical simulation based on general circulation models (GCMs) has become an increasingly effective tool in investigations of the physical mechanisms and evolutionary processes of paleoclimate associated with the TP uplift. In this paper, we provide a timely review on representative works in the past four decades on the paleoclimatic responses to the plateau uplift. Numerical simulations to study the paleoclimatic effects of the plateau uplift experienced three stages with increasing complexity: 1) plateau uplift as a whole in a single episode, as represented by the no-mountain/with-mountain experiments; 2) phased uplift in which the uplifting process was divided into multiple stages and within each the plateau rose by a certain proportion of its current height; and 3) sub-regional uplift, in which the focus was the effects of the uplift of a certain area within the TP, such as the northern Tibetan Plateau. These studies discovered the cause-effect relations between the plateau uplift and paleoclimate change, especially for the effects on the evolution of Asian monsoon system and aridiifcation of inland Asia. In this review, we also included examples of current on-going studies, such as the relative impacts of the Himalayas vs. those of the TP as the rain barrier and comparative studies on the paleoclimatic effects of the uplifts of the TP and African highland. Toward the end, we identiifed ifve areas as the focus of future research regarding the TP uplift: 1) the differences in the evolutionary processes of the South Asian and East Asian monsoons in response to the Himalayas–TP uplift at the regional and sub-regional scales; 2) climatic

  6. Cyclic changes of Asian monsoon intensity during the early mid-Holocene from annually-laminated stalagmites, central China

    Science.gov (United States)

    Liu, Dianbing; Wang, Yongjin; Cheng, Hai; Edwards, R. L.; Kong, Xinggong

    2015-08-01

    Climate during the early Holocene was highly variable due to the complex interplay of external and internal forcing mechanisms. The relative importance for them on the Asian monsoon (AM) evolution yet remains to be resolved. Here we present two-to six-yr-resolution oxygen isotope (δ18O) records of five stalagmites, four of which are annually-laminated, from Qingtian Cave, central China, revealing detailed AM variability between 10.9 and 6.1 ka BP. Over the contemporaneous periods, the δ18O records agree well with each other at multi-decadal to centennial timescales. When pieced together with the previously published isotopic data from the same cave, the final δ18O record reveals detailed AM variability from the last deglaciation to the mid-Holocene, consistent with other cave records. The most striking feature of the δ18O record is the recurrence of centennial-scale oscillations, especially during the annually-counted period (8.8-6.1 ka BP). Cross-wavelet analyses between the δ18O record and solar proxies show strong coherence at 200-yr cycle, suggesting that solar output was actively involved as a primary contributor. The AM depression at 8.2 ka BP is indistinguishable in amplitude and pattern from a series of weak AM events after 8 ka BP. We speculate that these centennial-scale AM changes might be regulated by the positive feedbacks of oceanic/atmospheric interactions to the solar activity under the condition of the retreat of continental ice-sheets.

  7. The effect of regional changes in anthropogenic aerosols on rainfall of the East Asian Summer Monsoon

    Directory of Open Access Journals (Sweden)

    L. Guo

    2013-02-01

    Full Text Available The response of East Asian Summer Monsoon (EASM precipitation to long term changes in regional anthropogenic aerosols (sulphate and black carbon is explored in an atmospheric general circulation model, the atmospheric component of the UK High-Resolution Global Environment Model v1.2 (HiGAM. Separately, sulphur dioxide (SO2 and black carbon (BC emissions in 1950 and 2000 over East Asia are used to drive model simulations, while emissions are kept constant at year 2000 level outside this region. The response of the EASM is examined by comparing simulations driven by aerosol emissions representative of 1950 and 2000. The aerosol radiative effects are also determined using an off-line radiative transfer model. During June, July and August, the EASM was not significantly changed as either SO2 or BC emissions increased from 1950 to 2000 levels. However, in September, precipitation is significantly decreased by 26.4% for sulphate aerosol and 14.6% for black carbon when emissions are at the 2000 level. Over 80% of the decrease is attributed to changes in convective precipitation. The cooler land surface temperature over China in September (0.8 °C for sulphate and 0.5 °C for black carbon due to increased aerosols reduces the surface thermal contrast that supports the EASM circulation. However, mechanisms causing the surface temperature decrease in September are different between sulphate and BC experiments. In the sulphate experiment, the sulphate direct and the 1st indirect radiative effects contribute to the surface cooling. In the BC experiment, the BC direct effect is the main driver of the surface cooling, however, a decrease in low cloud cover due to the increased heating by BC absorption partially counteracts the direct effect. This results in a weaker land surface temperature response to BC changes than to sulphate changes. The resulting precipitation response is also weaker, and the responses of the monsoon circulation

  8. THE CLIMATIC CHARACTERISTICS OF SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA I.40-YEAR AVERAGE

    Institute of Scientific and Technical Information of China (English)

    冯瑞权; 王安宇; 吴池胜; 林建恒; 古志明; 林文实; 谭志文

    2002-01-01

    By using 40-year NCEP reanalysis daily data (1958-1997),we have analyzed the climatic characteristics of summer monsoon onset in the South China Sea (105(E ~120(E,5(N~20(N,to be simplified as SCS in the text followed) pentad by pentad (5 days).According to our new definition,in the monsoon area of the SCS two of the following conditions should be satisfied:1) At 850hPa,the southwest winds should be greater than 2m/s.2) At 850 hPa,should be greater than 335(K.The new definition means that the summer monsoon is the southwest winds with high temperature and high moisture.The onset of the SCS summer monsoon is defined to start when one half of the SCS area (105(E~120(E,5(N~20(N) is controlled by the summer monsoon.The analyzed results revealed the following:1) The summer monsoon in the SCS starts to build up abruptly in the 4th pentad in May.2) The summer monsoon onset in the SCS is resulted from the development and intensification of southwesterly monsoon in the Bay of Bengal.3) The onset of the summer monsoon and establishment of the summer monsoon rainfall season in the SCS occur simultaneously.4) During the summer monsoon onset in the SCS,troughs deepen and widen quickly in the lower troposphere of the India;the subtropical high in the Western Pacific moves eastward off the SCS in the middle troposphere;the easterly advances northward over the SCS in the upper troposphere.

  9. The Eurasian ice sheet reinforces the East Asian summer monsoon during the interglacial 500 000 years ago

    Directory of Open Access Journals (Sweden)

    Qiuzhen Yin

    2008-05-01

    Full Text Available Deep-sea and ice-core records show that interglacial periods were overall less "warm" before about 420 000 years ago than after, with relatively higher ice volume and lower greenhouse gases concentration. This is particularly the case for the interglacial Marine Isotope Stage 13 which occurred about 500 000 years ago. However, by contrast, the loess and other proxy records from China suggest an exceptionally active East Asian summer monsoon during this interglacial. A three-dimension Earth system Model of Intermediate complexity was used to understand this seeming paradox. The astronomical forcing and the remnant ice sheets present in Eurasia and North America were taken into account in a series of sensitivity experiments. Expectedly, the seasonal contrast is larger and the East Asian summer monsoon is reinforced compared to Pre-Industrial time when Northern Hemisphere summer is at perihelion. Surprisingly, the presence of the Eurasian ice sheet was found to reinforce monsoon, too, through a south-eastwards perturbation planetary wave. The trajectory of this wave is influenced by the Tibetan plateau.

  10. Climate proofing infrastructure in Bangladesh : the incremental cost of limiting future inland monsoon flood damage

    OpenAIRE

    Dasgupta, Susmita; Huq, Mainul; Khan, Zahirul Huq; Masud, Md. Sohel; Ahmed, Manjur Murshed Zahid; Mukherjee, Nandan; Pandey, Kiran

    2010-01-01

    Two-thirds of Bangladesh is less than 5 meters above sea level, making it one of the most flood prone countries in the world. Severe flooding during a monsoon causes significant damage to crops and property, with severe adverse impacts on rural livelihoods. Future climate change seems likely to increase the destructive power of monsoon floods. This paper examines the potential cost of offs...

  11. Precisely dated multidecadally resolved Asian summer monsoon dynamics 113.5-86.6 thousand years ago

    Science.gov (United States)

    Jiang, Xiuyang; Wang, Xiaoyan; He, Yaoqi; Hu, Hsun-Ming; Li, Zhizhong; Spötl, Christoph; Shen, Chuan-Chou

    2016-07-01

    We present a new 230Th-dated absolute chronology of Asian summer monsoon (ASM) variability from 113.5 to 86.6 kyr BP (before 1950 AD). This integrated multidecadally resolved record, based on 1435 oxygen isotope data and 46 230Th dates with 2-sigma errors as low as ±0.3 kyr from three stalagmites collected in Sanxing Cave, southwestern China, can be a new reference for calibrating paleoclimate proxy sequences. The Sanxing δ18O record follows the 23 kyr precessional cycle of insolation and is punctuated by prominent millennial-scale oscillations of the Chinese Interstadials (CIS) 25 to 22, corresponding to Greenland Interstadials (GIS) 25 to 22. The onset of CIS 25, 24, 23 and 22 is dated to 113.1 ± 0.4, 108.1 ± 0.3, 103.7 ± 0.3 and 91.4 ± 0.6 kyr BP in the Sanxing record, respectively. The end of CIS 24 and CIS 22 is constrained to 105.5 ± 0.4 and 87.7 ± 0.3 kyr BP, respectively. A centennial-scale precursor event at 104.1 ± 0.3 kyr BP preceding CIS 23 is clearly registered. These events in the Sanxing record are synchronous with those identified in stalagmites from the European Alps (NALPS), except for the onset of GIS 25 and the end of GIS 22, and differ by up to 2.3 kyr from the corresponding ones in Greenland ice core records. The high degree of similarity of the δ18O records between Sanxing Cave and Greenland supports a Northern Hemisphere forcing of the ASM. The anti-phase relationship of δ18O records between Sanxing stalagmites and Antarctic ice cores suggests an additional ASM linkage to the Southern Hemisphere.

  12. An optimal index for measuring the effect of East Asian winter monsoon on China winter temperature

    Science.gov (United States)

    Hu, Chundi; Yang, Song; Wu, Qigang

    2015-11-01

    Extreme cold events occur frequently in China. The authors define a representative yet simple index to reveal the monthly changes in China winter temperature associated with the East Asian winter monsoon (EAWM), which is represented by both the leading empirical orthogonal function (EOF) mode and the country-mean temperature index of Chinese 160 gauge stations. A combined technique of correlation and multivariate EOF (Corr-MVEOF) analyses is applied to capture the dominant coupled patterns of EAWM circulation system. Based on the atmospheric circulation features captured by the leading Corr-MVEOF mode, a new EAWM index referred to as CNWMI is derived by using a stepwise regression analysis. The CNWMI highlights the importance of (1) the Mongolia-Siberian High (MSH) and its southward expansion and (2) the Asia-wide meridional dipole anomaly of 500 hPa geopotential height. Compared with the 27 existing EAWM indices, the CNWMI not only best represents the leading modes of both EAWM circulation system and China winter temperature, but also reasonably tracks the intraseasonal-to-interdecadal variations of EAWM so that the monthly intensity of EAWM can be monitored conveniently. In particular, the Aleutian low (AL) is not strongly related to the MSH and may not be responsible for the variability of EAWM/MSH. Moreover, the indices that are highly correlated with the temperature over southern East Asia do not show significant relationships with the AL, which is different from the conventional concept that a strong EAWM/MSH is linked to a deepened AL. In contrast, the anomalous Australia-Maritime Continent low is in good agreement with the variation of EAWM/MSH.

  13. A NAO-ENSO-based seasonal prediction model for East Asian summer monsoon

    Science.gov (United States)

    Li, Jianping; Wu, Zhiwei; Feng, Juan; Zheng, Fei; Xu, Hanlie; Wang, Bin; Jin, Fei-Fei

    2013-04-01

    The observational analysis shows that the relationship between the preceding winter El Niño-Southern Oscillation (ENSO) and the following East Asian summer monsoon (EASM) in the past 60 years is strengthened. Both the observational and numerical evidences demonstrate that spring North Atlantic Oscillation (NAO) may exert significant influences on the enhancement of the EASM-ENSO relationship. Anomalous spring NAO may cause a tripole SSTA pattern in North Atlantic which can persist into ensuring summer from spring. In summer, the tripole SSTA impacts EASM through two pathways. One is the tripole SSTA pattern excites the Atlantic-Eurasian (AEA) teleconnection which is a distinct Rossby wave train prevailing over the Atlantic and northern Eurasia. As a result, the blocking highs over the Ural Mountain and the Okhotsk Sea can be modulated. Another is it can force a simple Gill-Matsuno-type quadrupole response over western Pacific, consequently, the linkage between the western Pacific subtropical high (WPSH) and ENSO is enhanced. The co-effects of the two teleconnection patterns help to strengthen (or weaken) the subtropical Meiyu-Baiu-Changma front, the primary rain-bearing system of the EASM. As such, spring NAO is tied to the strengthened connection between ENSO and the EASM. Then we may establish a NAO-ENSO-based seasonal prediction model for EASM. The hindcast experiments show a good performances of this prediction model for EASM. The NAO-ENSO-based model is employed to make seasonal prediction for EASM strength and summer rainfall over middle reach of Yangtze river in 2012, and the results show a good performance of the approach, implying the model could be a useful tool for seasonal prediction of EASM.

  14. Impact of the North Atlantic Sea Surface Temperature Tripole on the East Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    ZUO Jinqing; LI Weijing; SUN Chenghu; XU Li; REN Hong-Li

    2013-01-01

    A strong (weak) East Asian summer monsoon (EASM) is usually concurrent with the tripole pattern of North Atlantic SST anomalies on the interannual timescale during summer,which has positive (negative)SST anomalies in the northwestern North Atlantic and negative (positive) SST anomalies in the subpolar and tropical ocean.The mechanisms responsible for this linkage are diagnosed in the present study.It is shown that a barotropic wave-train pattern occurring over the Atlantic-Eurasia region likely acts as a link between the EASM and the SST tripole during summer.This wave-train pattern is concurrent with geopotential height anomalies over the Ural Mountains,which has a substantial effect on the EASM.Diagnosis based on observations and linear dynamical model results reveals that the mechanism for maintaining the wave-train pattern involves both the anomalous diabatic heating and synoptic eddy-vorticity forcing.Since the North Atlantic SST tripole is closely coupled with the North Atlantic Oscillation (NAO),the relationships between these two factors and the EASM are also examined.It is found that the connection of the EASM with the summer SST tripole is sensitive to the meridional location of the tripole,which is characterized by large seasonal variations due to the north-south movement of the activity centers of the NAO.The SST tripole that has a strong relationship with the EASM appears to be closely coupled with the NAO in the previous spring rather than in the simultaneous summer.

  15. Indigenous vegetation burning practices and their impact on the climate of the northern Australian monsoon region

    Directory of Open Access Journals (Sweden)

    K.-H. Wyrwoll

    2013-08-01

    Full Text Available Here we pose the question: was there a downturn in summer monsoon precipitation over northern Australia due to Aboriginal vegetation practices over prehistoric time scales? In answering this question we consider the results from a global climate model incorporating ocean, land, ice, atmosphere and vegetation interactions, reducing the total vegetation cover over northern Australia by 20% to simulate the effects of burning. The results suggest that burning forests and woodlands in the monsoon region of Australia led to a shift in the regional climate, with a delayed monsoon onset and reduced precipitation in the months preceding the "full" monsoon. We place these results in a global context, drawing on model results from five other monsoon regions, and note that although the precipitation response is highly varied, there is a general but region specific climate response to reduced vegetation cover in all cases. Our findings lead us to conclude that large-scale vegetation modification over millennial time-scales due to indigenous burning practices, would have had significant impacts on regional climates. With this conclusion comes the need to recognise that the Anthropocene saw the impact of humans on regional-scale climates and hydrologies at much earlier times than generally recognized.

  16. Indigenous vegetation burning practices and their impact on the climate of the northern Australian monsoon region

    Science.gov (United States)

    Wyrwoll, K.-H.; McRobie, F. H.; Notaro, M.; Chen, G.

    2013-08-01

    Here we pose the question: was there a downturn in summer monsoon precipitation over northern Australia due to Aboriginal vegetation practices over prehistoric time scales? In answering this question we consider the results from a global climate model incorporating ocean, land, ice, atmosphere and vegetation interactions, reducing the total vegetation cover over northern Australia by 20% to simulate the effects of burning. The results suggest that burning forests and woodlands in the monsoon region of Australia led to a shift in the regional climate, with a delayed monsoon onset and reduced precipitation in the months preceding the "full" monsoon. We place these results in a global context, drawing on model results from five other monsoon regions, and note that although the precipitation response is highly varied, there is a general but region specific climate response to reduced vegetation cover in all cases. Our findings lead us to conclude that large-scale vegetation modification over millennial time-scales due to indigenous burning practices, would have had significant impacts on regional climates. With this conclusion comes the need to recognise that the Anthropocene saw the impact of humans on regional-scale climates and hydrologies at much earlier times than generally recognized.

  17. Monsoon variability of ultraviolet radiation (UVR) attenuation and bio-optical factors in the Asian tropical coral-reef waters

    Science.gov (United States)

    Mizubayashi, Keiko; Kuwahara, Victor S.; Segaran, Thirukanthan C.; Zaleha, Kassim; Effendy, A. W. M.; Kushairi, M. R. M.; Toda, Tatsuki

    2013-07-01

    The East coast of Peninsular Malaysia is strongly influenced by the North-East (NE) monsoon, and may significantly influence the optical environment of coral-reef ecosystems. However, our knowledge of temporal variability, including episodic events, of environmental factors in Asian tropical regions is still limited. The objectives of this study were to (1) observe temporal variability in ultraviolet radiation (UVR) and photosynthetically active radiation (PAR) attenuation and (2) determine the bio-optical factors regulating the optical environment in shallow coral-reef waters. Downwelling UVR and PAR irradiance and in situ bio-optical factors were measured monthly near Bidong Island on the East coast of Peninsular Malaysia from June 2010 to June 2011. The NE monsoon was recognized between November 2010 and January 2011. The highest diffuse attenuation coefficient at 305 nm was 2.05 ± 0.03 m-1 in a coral-reef area on December 2010. The most significant bio-optical factor at 305, 380, 440 nm during the NE monsoon season was CDOM (89 ± 8% at 305 nm, 84 ± 9% at 380 nm and 49 ± 17% at 440 nm). All UVR attenuation coefficients showed significant correlations with the CDOM absorption coefficients (aCDOM). CDOM with relatively low S275-295 during the NE monsoon season (0.0177 ± 0.0020 nm-1) suggests terrestrial sources, which is also supported by the correlation between salinity and aCDOM(305). A significant correlation between S275-295 and the carbon specific absorbance coefficient (a*(305)) suggest the potential to measure DOC optically in these waters. The high CDOM during the NE monsoon season may have an important role to reduce harmful UVR exposure reaching benthic communities.

  18. Indian monsoon and the elevated-heat-pump mechanism in a coupled aerosol-climate model

    Science.gov (United States)

    D'Errico, Miriam; Cagnazzo, Chiara; Fogli, Pier Giuseppe; Lau, William K. M.; Hardenberg, Jost; Fierli, Federico; Cherchi, Annalisa

    2015-09-01

    A coupled aerosol-atmosphere-ocean-sea ice climate model is used to explore the interaction between aerosols and the Indian summer monsoon precipitation on seasonal-to-interannual time scales. Results show that when increased aerosol loading is found on the Himalayas slopes in the premonsoon period (April-May), intensification of early monsoon rainfall over India and increased low-level westerly flow follow, in agreement with the elevated-heat-pump mechanism. The increase in rainfall during the early monsoon season has a cooling effect on the land surface. In the same period, enhanced surface cooling may also be amplified through solar dimming by more cloudiness and aerosol loading, via increased dust transported by low-level westerly flow. The surface cooling causes subsequent reduction in monsoon rainfall in July-August over India. The time-lagged nature of the reasonably realistic response of the model to aerosol forcing suggests that absorbing aerosols, besides their potential key roles in impacting monsoon water cycle and climate, may influence the seasonal variability of the Indian summer monsoon.

  19. Quantitative Estimation of the Impact of European Teleconnections on Interannual Variation of East Asian Winter Temperature and Monsoon

    Science.gov (United States)

    Lim, Young-Kwon; Kim, Hae-Dong

    2014-01-01

    The impact of European teleconnections including the East AtlanticWest Russia (EA-WR), the Scandinavia (SCA), and the East Atlantic (EA) on East Asian winter temperature variability was quantified and compared with the combined effect of the Arctic Oscillation (AO), the Western Pacific (WP), and the El-Nino Southern Oscillation (ENSO), which are originated in the Northern Hemispheric high-latitudes or the Pacific. Three European teleconnections explained 22-25 percent of the total monthly upper-tropospheric height variance over Eurasia. Regression analysis revealed warming by EA-WR and EA and cooling by SCA over mid-latitude East Asia during their positive phase and vice versa. Temperature anomalies were largely explained by the advective temperature change process at the lower troposphere. The average spatial correlation over East Asia (90-180E, 10-80N) for the last 34 winters between observed and reconstructed temperature comprised of AO, WP and ENSO effect (AWE) was approximately 0.55, and adding the European teleconnection components (ESE) to the reconstructed temperature improved the correlation up to approximately 0.64. Lower level atmospheric structure demonstrated that approximately five of the last 34 winters were significantly better explained by ESE than AWE to determine East Asian seasonal winter temperatures. We also compared the impact between EA-WR and AO on the 1) East Asian winter monsoon, 2) cold surge, and 3) the Siberian high. These three were strongly coupled, and their spatial features and interannual variation were somewhat better explained by EA-WR than AO. Results suggest that the EA-WR impact must be treated more importantly than previously thought for a better understanding of East Asian winter temperature and monsoon variability.

  20. Bay of Bengal Monsoon Experiment (BOBMEX) — A component of the Indian Climate Research Programme (ICRP)

    Indian Academy of Sciences (India)

    D R Sikka; P Sanjeeva Rao

    2000-06-01

    The Indian Climate Research Programme (ICRP) focuses on the study of climate variability and its impact on agriculture. To address the role of the Bay of Bengal in monsoon variability, a process study was organised during July-August 1999, deploying research ships, buoys, INSAT, coastal radar and conventional observational systems to collect information about the coupled ocean-atmosphere system over the warm waters of the Bay of Bengal. The paper gives the background of the ICRP and the organisation and implementation of the Bay of Bengal Monsoon Experiment (BOBMEX) in its field phase.

  1. Future projection of Indian summer monsoon variability under climate change scenario: An assessment from CMIP5 climate models

    Science.gov (United States)

    Sharmila, S.; Joseph, S.; Sahai, A. K.; Abhilash, S.; Chattopadhyay, R.

    2015-01-01

    In this study, the impact of enhanced anthropogenic greenhouse gas emissions on the possible future changes in different aspects of daily-to-interannual variability of Indian summer monsoon (ISM) is systematically assessed using 20 coupled models participated in the Coupled Model Inter-comparison Project Phase 5. The historical (1951-1999) and future (2051-2099) simulations under the strongest Representative Concentration Pathway have been analyzed for this purpose. A few reliable models are selected based on their competence in simulating the basic features of present-climate ISM variability. The robust and consistent projections across the selected models suggest substantial changes in the ISM variability by the end of 21st century indicating strong sensitivity of ISM to global warming. On the seasonal scale, the all-India summer monsoon mean rainfall is likely to increase moderately in future, primarily governed by enhanced thermodynamic conditions due to atmospheric warming, but slightly offset by weakened large scale monsoon circulation. It is projected that the rainfall magnitude will increase over core monsoon zone in future climate, along with lengthening of the season due to late withdrawal. On interannual timescales, it is speculated that severity and frequency of both strong monsoon (SM) and weak monsoon (WM) might increase noticeably in future climate. Substantial changes in the daily variability of ISM are also projected, which are largely associated with the increase in heavy rainfall events and decrease in both low rain-rate and number of wet days during future monsoon. On the subseasonal scale, the model projections depict considerable amplification of higher frequency (below 30 day mode) components; although the dominant northward propagating 30-70 day mode of monsoon intraseasonal oscillations may not change appreciably in a warmer climate. It is speculated that the enhanced high frequency mode of monsoon ISOs due to increased GHG induced warming

  2. The footprint of Asian monsoon dynamics in the mass and energy balance of a Tibetan glacier

    Directory of Open Access Journals (Sweden)

    T. Mölg

    2012-08-01

    Full Text Available Determinations of glacier-wide mass and energy balance are still scarce for the remote mountains of the Tibetan Plateau, where field measurements are challenging. Here we run and evaluate a physical, distributed mass balance model for Zhadang glacier (central Tibet, 30° N, based on in-situ measurements over 2009–2011 and an uncertainty estimate by Monte Carlo and ensemble strategies. The model application aims to provide the first quantification of how the Indian Summer Monsoon (ISM impacts an entire glacier over the various stages of the monsoon's annual cycle. We find a strong and systematic ISM footprint on the interannual scale. Early (late monsoon onset causes higher (lower accumulation, and reduces (increases the available energy for ablation primarily through changes in absorbed shortwave radiation. By contrast, only a weak footprint exists in the ISM cessation phase. Most striking though is the core monsoon season: local mass and energy balance variability is fully decoupled from the active/break cycle that defines large-scale atmospheric variability during the ISM. Our results demonstrate quantitatively that monsoon onset strongly affects the ablation season of glaciers in Tibet. However, we find no direct ISM impact on the glacier in the main monsoon season, which has not been acknowledged so far. This result also adds cryospheric evidence that regional modification of the large-scale monsoon flow prevails on the Tibetan Plateau in summer.

  3. Energy partitioning and environmental influence factors in different vegetation types in the GEWEX Asian Monsoon Experiment

    Science.gov (United States)

    Liu, Fengshan; Tao, Fulu; Li, Shenggong; Zhang, Shuai; Xiao, Dengpan; Wang, Meng

    2014-12-01

    Environmental influences upon energy balance in areas of different vegetation types (i.e., forest at Kog-Ma in Thailand and at Yakutsk in Russia, grassland at Amdo in Chinese Tibet and at Arvaikheer in Mongolia, and mixed farmland at Tak in Thailand) in the GEWEX Asian Monsoon Experiment were investigated. The sites we investigated are geographically and climatologically different; and consequently had quite large variations in temperature ( T), water vapor pressure deficit (VPD), soil moisture (SM), and precipitation (PPT). During May-October, the net radiation flux ( R n) (in W·m-2) was 406.21 at Tak, 365.57 at Kog-Ma, 390.97 at Amdo, 316.65 at Arvaikheer, and 287.10 at Yakutsk. During the growing period, the R n partitioned into latent heat flux ( λE/ R n) was greater than that partitioned into sensible heat flux ( H/ R n) at Tak and at Kog-Ma. In contrast, λE/ R n was lower than H/ R n at Arvaikheer, H/ R n was less than λE/ R n between DOY 149 and DOY 270 at Amdo, and between DOY 165 and DOY 235 at Yakutsk. The R n partitioned into ground heat flux was generally less than 0.15. The short-wave albedo was 0.12, 0.18, and 0.20 at the forest, mixed land, and grass sites, respectively. At an hourly scale, energy partitions had no correlation with environmental factors, based on average summer halfhourly values. At a seasonal scale energy partitions were linearly correlated (usually p<0.05) with T, VPD, and SM. The λE/ R n increased with increases in SM, T, and VPD at forest areas. At mixed farmlands, λE/ R n generally had positive correlations with SM, T, and VPD, but was restrained at extremely high values of VPD and T. At grasslands, λE/ R n was enhanced with increases of SM and T, but was decreased with VPD.

  4. Relationship between sea level pressures of the winter tropical western Pacific and the subsequent Asian summer monsoon

    Science.gov (United States)

    Wu, Bingyi; Wang, Dongxiao; Huang, Ronghui

    2003-07-01

    Using monthly mean National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data for the period 1958 1996, based on a new circulation index in the tropical western Pacific region, this paper investigates extreme winter circulation conditions in the northwestern Pacific and their evolution. The results show that the extreme winter circulation anomaly in the northwestern Pacific exhibits a strong association with those appearing in the high latitudes of the Northern Hemisphere including the northern Asian continent, part of the Barents Sea, and the northeastern Pacific. As the season progresses, an anticyclonic (cyclonic) circulation anomaly appearing in the north-western Pacific gradually moves northeastwards and extends westwards. Its axis in the west-east direction is also stretched. Therefore, easterly (westerly) anomalies in the southern part of the anticyclonic (cyclonic) circulation anomaly continuously expand westwards to the peninsula of India. Therefore, the South Asian summer monsoon would be weaker (stronger). Simultaneously, another interesting phenomenon is the evolution of SLP anomalies. As the season progresses (from winter to the following summer), SLP anomalies originating from the tropical western Pacific gradually move towards, and finally occupy the Asian continent, and further influence the thermal depression over the Asian continent in the following summer.

  5. Effect of climate change on seasonal monsoon in Asia and its impact on the variability of monsoon rainfall in Southeast Asia

    Institute of Scientific and Technical Information of China (English)

    Yen Yi Loo; Lawal Billa; Ajit Singh

    2015-01-01

    Global warming and climate change is one of the most extensively researched and discussed topical issues affecting the environment. Although there are enough historical evidence to support the theory that climate change is a natural phenomenon, many research scientists are widely in agreement that the increase in temperature in the 20th century is anthropologically related. The associated effects are the variability of rainfall and cyclonic patterns that are being observed globally. In Southeast Asia the link between global warming and the seasonal atmospheric flow during the monsoon seasons shows varying degree of fuzziness. This study investigates the impact of climate change on the seasonality of monsoon Asia and its effect on the variability of monsoon rainfall in Southeast Asia. The comparison of decadal variation of precipitation and temperature anomalies before the 1970s found general increases which were mostly varying. But beyond the 1970s, global precipitation anomalous showed increases that almost corresponded with increases in global temperature anomalies for the same period. There are frequent changes and a shift westward of the Indian summer monsoon. Although precipitation is observed to be 70%below normal levels, in some areas the topography affects the intensity of rainfall. These shifting phenomenon of other monsoon season in the region are impacting on the variability of rainfall and the onset of monsoons in Southeast Asia and is predicted to delay for 15 days the onset of the monsoon in the future. The variability of monsoon rainfall in the SEA region is observed to be decadal and the frequency and intensity of intermittent flooding of some areas during the monsoon season have serious consequences on the human, financial, infrastructure and food security of the region.

  6. Earth as diode: monsoon source of the orbital ~100 ka climate cycle

    Directory of Open Access Journals (Sweden)

    R. Y. Anderson

    2010-08-01

    Full Text Available A potential source for Earth's enigmatic ~100 ka climate cycle, which is found in many ancient geological records at low latitudes and also in the pacing of glaciation during the late Pleistocene, is traced to a climatic rectifying process inherent in the monsoon. Seasonal information needed to identify the rectifying mechanism is preserved within varves of a continuous, 200 ka recording of annual maximum surface temperature (Tmax from the equator of Western Pangea. Specific seasonal reactions recorded in varves show how the monsoon reacted to seasonal differences in insolation at equinox to produce a 11.7 ka semi-precession cycle in Tmax. At solstice, anti-phasing of insolation in the Northern and Southern Hemispheres, intensified and focused by a highly asymmetric Pangea relative to the equator, produced a strong equatorial maritime monsoon that performed a nonlinear rectifying function similar to that of a simple rectifying diode. Expressed in the resulting varve series are substantial cycles in Tmax of 100 ka, 23.4 ka, and 11.7 ka. Importantly, any external or internal forcing of the tropical (monsoon climate system at higher-than-orbital frequencies (e.g. solar, ENSO should also be amplified at Milankovitch frequencies by the monsoon.

  7. A high-resolved record of the Asian Summer Monsoon from Dongge Cave, China for the past 1200 years

    Science.gov (United States)

    Zhao, Kan; Wang, Yongjin; Edwards, R. Lawrence; Cheng, Hai; Liu, Dianbing; Kong, Xinggong

    2015-08-01

    Two annually-laminated and 230Th-dated stalagmite oxygen isotope (δ18O) records from Dongge Cave, China, provided a high-resolution Asian Summer Monsoon (ASM) history for the past 1200 years. A close similarity between annual band thickness and stable isotope analyses (δ13C and δ18O) suggests the calcite δ18O is most likely a proxy associated with ASM precipitation. The two duplicated stalagmite δ18O records show that the ASM varies at a periodicity of ∼220 years, concordant with a dominant cycle of solar activity. A period of strong ASM activity occurred during the Spörer Minimum (1450-1550 A.D.), followed by a striking drop circa 1580 A.D., potentially consistent with the social unrest in the final decades of China's Ming Dynasty (1368-1644 A.D.). Centennial-scale changes in ASM precipitation over the last millennium match well with changes in tropical Atlantic sea surface temperatures (SSTs) and South American summer monsoon precipitation. Our findings suggest that variations in low-latitude monsoon precipitation are probably driven by shifts in the mean position of the intertropical convergence zone (ITCZ), which is further mediated by solar activity and tropical SSTs.

  8. RAMA: The Research Moored Array for African-Asian-Australian Monsoon Analysis and Prediction (including supplement)

    Digital Repository Service at National Institute of Oceanography (India)

    McPhaden, M.J.; Meyers, G.; Ando, K.; Masumoto, Y.; Murty, V.S.N.; Ravichandran, M.; Syamsudin, F.; Vialard, J.; Yu, L.; Yu, W.

    -atmosphere interactions, and intense seasonal rains over the Indian subcontinent, Southeast Asia, East Africa, and Australia. Recurrence of these monsoon rains is critical to agricultural production that supports a third of the world’s population. The Indian Ocean also...

  9. AN EAST ASIAN SUBTROPICAL SUMMER MONSOON INDEX DEFINED BY MOISTURE TRANSPORT

    Institute of Scientific and Technical Information of China (English)

    LIANG Ping; TANG Xu; HE Jin-hai; CHEN Long-xun

    2008-01-01

    Using daily NCEP/NCAR reanalysis dataset and observation rainfall data in China for the 1971- 2000 period, a subtropical summer monsoon index has been defined by meridional moisture transport of the total atmosphere column. Results show that the subtropical summer monsoon index defined by the difference of meridional moisture transport between South China and North China can be used to describe the intensity of the subtropical summer monsoon. High (low) index is corresponding to strong (weak) subtropical summer monsoon. And the new index is well related to the summer rainfall over the middle and lower reaches of Yangtze River. In addition, the convergence of moisture transport from the west Pacific via the South China Sea and that from the North China may be responsible for the anomalously excessive summer rainfall over the middle and lower reaches of Yangtze River.

  10. Temporal Variations of the Spring Persistent Rains and South China Sea Sub-high and Their Correlations to the Circulation and Precipitation of the East Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    WAN Rijin; WANG Tongmei; WU Guoxiong

    2008-01-01

    National Meteorological Information Center (NMIC) rainfall data and NCEP/NCAR dally circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains (SPR) and the decay-pentad time index of the South China Sea (SCS) sub-high. These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon (EASM). Results show that, the summer rainfall over southeastern China decreases when SPR onset is late. For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau (TP) strengthens, which makes abnormal anti-cyclonic circulation (cyclonic convergent circulation weakens) appear over southeastern China. When the decay of SCS sub-high delays, abnormal flood prevails over the middle and lower reaches of the Yangtze River (MLYR) and to the south. That is mainly caused by EASM weakening while SCS sub-high strengthening, then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley. The two indexes have high correlations with multivariate ENSO index (MEI) in March, indicating that the climate abnormity in East Asia is rclated to global climate abnormity tightly. The two time indexes are independent of each other, which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM. From this point of view, we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.

  11. Tropospheric Ozone Variability during the East Asian Summer Monsoon as Observed by Satellite (IASI), Aircraft (MOZAIC) and Ground Stations

    Science.gov (United States)

    Safieddine, S.; Boynard, A.; Hao, N.; Huang, F.; Wang, L.; Ji, D.; Barret, B.; Ghude, S. D.; Coheur, P.-F.; Hurtmans, D.; Clerbaux, C.

    2015-11-01

    Satellite measurements from the thermal Infrared Atmospheric Sounding Interferometer (IASI), the Measurements of OZone and water vapor by in-service AIrbus airCraft (MOZAIC), as well as observations from ground based stations, are used to assess the tropospheric ozone (O3) variability during the East Asian Summer Monsoon (EASM). Six years [2008-2013] of IASI data analysis reveals the ability of the instrument to detect the onset and the progression of the monsoon reflected by a decrease in the tropospheric [0-6] km O3 column due to the EASM, and to reproduce this decrease from one year to the other. Focusing on the period of May-August 2011, taken as an example year, IASI data show clear inverse relationship between tropospheric [0-6] km O3 on one hand and meteorological parameters such as cloud cover, relative humidity and wind speed, on the other hand. Aircraft data from the MOZAIC project at Hyderabad, Nanjing and Guangzhou are used to validate the IASI data and to assess the effect of the monsoon on the vertical distribution of the tropospheric O3 at different locations. Results show good agreement with a correlation coefficient of 0.74 between the [0-6] km O3 column derived from IASI and MOZAIC. The aircraft data show a decrease in the tropospheric O3 that is more important in the free troposphere than in the boundary layer and at Hyderabad than at the other two Chinese cities. Ground station data at different locations in India and China show a spatiotemporal dependence on meteorology during the monsoon, with decrease up to 22 ppbv in Hyderabad, and up to 5 ppbv in the North China Plain.

  12. Trapping, chemistry, and export of trace gases in the South Asian summer monsoon observed during CARIBIC flights in 2008

    Science.gov (United States)

    Rauthe-Schöch, Armin; Baker, Angela K.; Schuck, Tanja J.; Brenninkmeijer, Carl A. M.; Zahn, Andreas; Hermann, Markus; Stratmann, Greta; Ziereis, Helmut; van Velthoven, Peter F. J.; Lelieveld, Jos

    2016-03-01

    The CARIBIC (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container) passenger aircraft observatory performed in situ measurements at 10-12 km altitude in the South Asian summer monsoon anticyclone between June and September 2008. These measurements enable us to investigate this atmospheric region (which so far has mostly been observed from satellites) using the broad suite of trace gases and aerosol particles measured by CARIBIC. Elevated levels of a variety of atmospheric pollutants (e.g. carbon monoxide, total reactive nitrogen oxides, aerosol particles, and several volatile organic compounds) were recorded. The measurements provide detailed information about the chemical composition of air in different parts of the monsoon anticyclone, particularly of ozone precursors. While covering a range of 3500 km inside the monsoon anticyclone, CARIBIC observations show remarkable consistency, i.e. with distinct latitudinal patterns of trace gases during the entire monsoon period. Using the CARIBIC trace gas and aerosol particle measurements in combination with the Lagrangian particle dispersion model FLEXPART, we investigated the characteristics of monsoon outflow and the chemical evolution of air masses during transport. The trajectory calculations indicate that these air masses originated mainly from South Asia and mainland Southeast Asia. Estimated photochemical ages of the air were found to agree well with transport times from a source region east of 90-95° E. The photochemical ages of the air in the southern part of the monsoon anticyclone were systematically younger (less than 7 days) and the air masses were mostly in an ozone-forming chemical mode. In its northern part the air masses were older (up to 13 days) and had unclear ozone formation or destruction potential. Based on analysis of forward trajectories, several receptor regions were identified. In addition to predominantly westward transport, we found evidence for

  13. Effects of Mountain Uplift on East Asian Summer Climate Investigated by a Coupled Atmosphere Ocean GCM.

    Science.gov (United States)

    Kitoh, Akio

    2004-02-01

    To study the effects of progressive mountain uplift on East Asian summer climate, a series of coupled general circulation model (CGCM) experiments were performed. Eight different mountain heights were used: 0% (no mountain), 20%, 40%, 60%, 80%, 100% (control run), 120%, and 140%. The land sea distribution is the same for all experiments and mountain heights are varied uniformly over the entire globe.Systematic changes in precipitation pattern and circulation fields as well as sea surface temperature (SST) appeared with progressive mountain uplift. In summertime, precipitation area moves inland on the Asian continent with mountain uplift, while the Pacific subtropical anticyclone and associated trade winds become stronger. The mountain uplift resulted in an SST increase over the western tropical Pacific and the Maritime Continent and an SST decrease over the western Indian Ocean and the central subtropical Pacific. There is a drastic change in the East Asian circulations with the threshold value at the 60% mountain height. With the mountain height below 60%, the southwesterly monsoon flow from the Indian Ocean becomes strong by uplift and transports moisture toward East Asia, forming the baiu rainband. With higher mountain heights, intensified subtropical trade winds transport moisture from the Pacific into the Asian continent.In order to investigate how the SST change affected the results presented herein, additional experiments were performed with the same experimental design but with the atmospheric GCM (AGCM). A comparison between CGCM and AGCM experiments revealed that major features such as a shift in precipitation inland and an appearance of the baiu rainband by higher orography were reproduced similarly in both the AGCM and the CGCM. However, there was a qualitatively as well as quantitatively different feature. The anticyclonic circulation anomalies in the lower troposphere, which appeared by mountain uplift in the tropical western Pacific in the CGCM

  14. A major reorganization of Asian climate regime by the early Miocene

    Directory of Open Access Journals (Sweden)

    Z. T. Guo

    2008-05-01

    Full Text Available The global climate system has experienced a series of drastic changes during the Cenozoic. These include the climate transformation in Asia, from a zonal pattern to a monsoon-dominant pattern, the disappearance of subtropical aridity related to a planetary circulation system and the onset of inland deserts in central Asia. Despite of the major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persist relative to the timing, behaviors and underlying causes.

    This paper addresses these issues mainly based on two lines of evidence. Firstly, we newly collected the available Cenozoic geological indicators of environment in China to compile the paleoenvironmental maps of ten intervals with a more detailed examination within the Oligocene and Miocene. In confirming the earlier observation that a zonal climate pattern was transformed into a monsoonal one, the new maps within the Miocene indicate that this major change was achieved by the early Miocene, roughly consistent with the onset of loess deposition in China. Although a monsoon-like regime would have existed in the Eocene, it was restricted in the tropical-subtropical regions. The observed latitudinal oscillations of the climate zones during the Paleogene are likely attributable to the imbalanced evolution of polar ice-sheets between the two hemispheres.

    Secondly, we examine the relevant depositional and soil-forming processes of the Miocene loess-soil sequences to determine the circulation characteristics with special emphasis given to the early Miocene. Continuous eolian deposition in the middle reaches of the Yellow River since the early Miocene firmly indicates the formation of inland deserts, which has been constantly maintained in the past 22 Ma. Inter-section grain-size gradients indicate northerly dust-carrying winds and source location, as is regarded as the main criteria of the Asian winter monsoon

  15. Eocene prevalence of monsoon-like climate over eastern China reflected by hydrological dynamics

    Science.gov (United States)

    Wang, Dehai; Lu, Shicong; Han, Shuang; Sun, Xiaoyan; Quan, Cheng

    2013-01-01

    Hydrological dynamics of sedimentary basins are essential for understanding regional climatic pattern in the geological past. In previous qualitative studies lithologically depending on the occurrence of featured sedimentary rocks, the Eocene climate of China had been subdivided into three latitudinal zones, with one subtropical high-controlled arid zone throughout middle China, and two humid zones respectively in the north and south. However, recent advances on mammalian fauna distribution, plant fossil-based quantitative paleoclimatic reconstruction, and modeling experiment jointly suggest that the relatively humid monsoonal climate might have prevailed over the territory. Here we examine and compare sedimentary sequences of 10 Eocene sections across eastern China, and hence the lake level fluctuations, to discuss the nature of climate type. Our results show that, instead of the categorically zonal pattern, the hydroclimate dynamics is intensified landward. This is demonstrated by the fact that, in contrast to the wide developed coal layers around the periphery, evaporites are growingly occurred endocentrically to the central part of middle China. However, although we have had assumed that all evaporites are indicator of extreme aridity, the highly oscillated climate in the central part of middle China was humid in the majority of the Eocene, distinct from permanent arid as seen in deserts or steppe along modern horse latitude. From the upcountry distribution pattern of the Eocene hydrological dynamics, it appears that the relatively dry climate in central China was caused by the impact of continentality or rain shadow effect under monsoonal, or monsoon-like climate.

  16. Abrupt climate change in southeast tropical Africa influenced by Indian monsoon variability and ITCZ migration

    Science.gov (United States)

    Tierney, Jessica E.; Russell, James M.

    2007-08-01

    The timing and magnitude of abrupt climate change in tropical Africa during the last glacial termination remains poorly understood. High-resolution paleolimnological data from Lake Tanganyika, Southeast Africa show that wind-driven seasonal mixing in the lake was reduced during the Younger Dryas, Inter-Allerød Cool Period, Older Dryas, and Heinrich Event 1, suggesting a weakened southwest Indian monsoon and a more southerly position of the Inter-Tropical Convergence Zone over Africa during these intervals. These events in Lake Tanganyika, coeval with millennial and centennial-scale climate shifts in the high latitudes, suggest that changes in ITCZ location and Indian monsoon strength are important components of abrupt global climate change and that their effects are felt south of the equator in Africa. However, we observe additional events in Lake Tanganyika of equal magnitude that are not correlated with high-latitude changes, indicating the potential for abrupt climate change to originate from within tropical systems.

  17. Review of monsoons, interannual variability and decadal trends that underpin climate prediction

    OpenAIRE

    Susanto, D.; Vinayachandran, P.; Hacker, P.; Masumoto, Y.; Webster, P.; Godfrey, S; Meyers, G

    2002-01-01

    Understanding and predicting the interannual variations of the whole monsoon climate system has been, and will continue to be, one of the major reasons for studying the oceanography of the Indian Ocean; but there are other reasons. Knowledge about Indian Ocean current systems may have diverse practical applications, from fisheries through search and rescue to management of Exclusive Economic Zones. Our discussion mainly concerns the open ocean and the climate applications, but the resul...

  18. Strong coupling of centennial-scale changes of Asian monsoon and soil processes derived from stalagmite δ18O and δ13C records, southern China

    Science.gov (United States)

    Liu, Dianbing; Wang, Yongjin; Cheng, Hai; Edwards, R. Lawrence; Kong, Xinggong; Li, Ting-Yong

    2016-05-01

    The paleoclimate application of speleothem δ13C is influenced by site-specific processes. Here we present four stalagmite δ13C records from two caves in southern China, covering early and late Marine Isotope Stage (MIS) 3 and the Holocene, to investigate the spatio-temporal pattern of calcite δ13C changes and the relationship with Asian monsoon (AM) variability. In each growth period, precessional- to millennial-scale changes are clear in the δ18O record. In contrast, millennial variability is absent in the δ13C record, which characterizes persistent centennial oscillations. However, centennial-scale δ18O variations agree well with those of δ13C, with a larger amplitude in δ13C changes (about twice that of δ18O). This suggests that soil humidity balance associated with regional hydrological circulations is important for these centennial δ13C changes, although evaporation-related kinetic fractionation can induce concurrent enrichments in δ18O and δ13C. In frequency, the detrended δ18O and δ13C records are coupled at a periodicity of about 300 yr during the last glacial period and 150 yr during the Holocene. Those centennial-scale δ13C variations are generally consistent with Greenland temperature variability, indicating a climate response over broad regions. Thus, strong co-variation of δ18O and δ13C records should have a climatic origin, even if it is amplified by kinetic effects.

  19. Assessment of Seasonal Energy Efficiency Strategies of a Double Skin Façade in a Monsoon Climate Region

    Directory of Open Access Journals (Sweden)

    Choongwan Koo

    2013-08-01

    Full Text Available As climate change and global warming have become two of the most significant environmental issues today, the double-skin façade (DSF is getting considerable attention as an energy-efficient passive design. This study is aimed at assessing the seasonal energy efficiency strategies of a DSF targeting library facilities in the climate region with hot summers and cold winters. Toward this end, this study was conducted in four steps: (i establishment of seasonal energy-efficient strategies; (ii application of seasonal energy-efficient strategies; (iii analysis of energy saving effect by season; and (iv life cycle cost and life cycle CO2 analyses for selecting an optimal DSF. Results show that a shaft box DSF energy model (EMS #2, which applied winter strategies, was optimal with an energy saving rate of 4.13%, while a multi-story DSF energy model (EMM #5, which applied summer strategies, was optimal with an energy saving rate of 12.67%. In terms of savings to investment ratio (SIR40 and breakeven point (BEP40, the multi-story DSF (3.20; 9 years was superior. The results of this study can be used for (i seasonal energy efficiency strategies of a DSF in East Asian monsoon climates, and (ii as a guideline for the application of a DSF both in existing and new buildings.

  20. A dipole pattern in the Indian and Pacific oceans and its relationship with the East Asian summer monsoon

    International Nuclear Information System (INIS)

    This study demonstrates a robust relationship between the Indo-Pacific warm pool (IPWP) and North Pacific Ocean dipole (IPOD) and the East Asian summer monsoon (EASM) using observational datasets and sensitivity tests from the Community Atmosphere Model version 3.1 of the National Center for Atmospheric Research. The IPOD, which is a significant pattern of boreal summer SSTA in the Indian and Pacific oceans characterized by positive (negative) sea-surface temperature anomalies (SSTA) in the North Pacific and negative (positive) SSTA in the IPWP, appears around May, intensifies in the following months, and weakens in September. In summers with a positive IPOD phase, the western Pacific subtropical high (WPSH) weakens and shrinks with the axis of the WPSH ridge moving northwards, which favours an intensified EASM and a decrease in summer rainfall in the Yangtze River valley, and vice versa. (letter)

  1. Probabilistic versus Deterministic Skill in Predicting the Western North Pacific- East Asian Summer Monsoon Variability with Multi-Model Ensembles

    Science.gov (United States)

    Yang, D.; Yang, X. Q.; Xie, Q.; Zhang, Y.; Ren, X.; Tang, Y.

    2015-12-01

    Based on the historical forecasts of three quasi-operational multi-model ensemble (MME) systems, this study assesses the superiorities of the coupled MME over its contributing single-model ensembles (SMEs) and over the uncoupled atmospheric MME in predicting the seasonal variability of the Western North Pacific-East Asian summer monsoon. The seasonal prediction skill of the monsoon is measured by Brier skill score (BSS) in the sense of probabilistic forecast as well as by anomaly correlation (AC) in the sense of deterministic forecast. The probabilistic forecast skill of the MME is found to be always significantly better than that of each participating SME, while the deterministic forecast skill of the MME is even worse than that of some SME. The BSS is composed of reliability and resolution, two attributes characterizing probabilistic forecast skill. The probabilistic skill increase of the MME is dominated by the drastic improvement in reliability, while resolution is not always improved, similar to AC. A monotonous resolution-AC relationship is further found and qualitatively understood, whereas little relationship can be identified between reliability and AC. It is argued that the MME's success in improving the reliability possibly arises from an effective reduction of biases and overconfidence in forecast distributions. The coupled MME is much more skillful than the uncoupled atmospheric MME forced by persisted sea surface temperature (SST) anomalies. This advantage is mainly attributed to its better capability in capturing the evolution of the underlying seasonal SST anomaly.

  2. Indian Monsoon Depression: Climatology and Variability

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Jin-Ho; Huang, Wan-Ru (Judy)

    2012-03-09

    The monsoon climate is traditionally characterized by large seasonal rainfall and reversal of wind direction (e.g., Krishnamurti 1979). Most importantly this rainfall is the major source of fresh water to various human activities such as agriculture. The Indian subcontinent resides at the core of the Southeast Asian summer monsoon system, with the monsoon trough extended from northern India across Indochina to the Western Tropical Pacific (WTP). Large fraction of annual rainfall occurs during the summer monsoon season, i.e., June - August with two distinct maxima. One is located over the Bay of Bengal with rainfall extending northwestward into eastern and central India, and the other along the west coast of India where the lower level moist wind meets the Western Ghat Mountains (Saha and Bavardeckar 1976). The rest of the Indian subcontinent receives relatively less rainfall. Various weather systems such as tropical cyclones and weak disturbances contribute to monsoon rainfall (Ramage 1971). Among these systems, the most efficient rain-producing system is known as the Indian monsoon depression (hereafter MD). This MD is critical for monsoon rainfall because: (i) it occurs about six times during each summer monsoon season, (ii) it propagates deeply into the continent and produces large amounts of rainfall along its track, and (iii) about half of the monsoon rainfall is contributed to by the MDs (e.g., Krishnamurti 1979). Therefore, understanding various properties of the MD is a key towards comprehending the veracity of the Indian summer monsoon and especially its hydrological process.

  3. Orbital control of the western North Pacific summer monsoon

    Science.gov (United States)

    Wu, Chi-Hua; Chiang, John C. H.; Hsu, Huang-Hsiung; Lee, Shih-Yu

    2016-02-01

    Orbital forcing exerts a strong influence on global monsoon systems, with higher summer insolation leading to stronger summer monsoons in the Northern Hemisphere. However, the associated regional and seasonal changes, particularly the interaction between regional monsoon systems, remain unclear. Simulations using the Community Earth System Model demonstrate that the western North Pacific (WNP) summer monsoon responds to orbital forcing opposite to that of other major Northern Hemisphere monsoon systems. Compared with its current climate state, the simulated WNP monsoon and associated lower-tropospheric trough is absent in the early Holocene when the precession-modulated Northern Hemisphere summer insolation is higher, whereas the summer monsoons in South and East Asia are stronger and shift farther northward. We attribute the weaker WNP monsoon to the stronger diabatic heating of the summer Asian monsoon—in particular over the southern Tibetan Plateau and Maritime Continent—that in turn strengthens the North Pacific subtropical high through atmospheric teleconnections. By contrast, the impact of the midlatitude circulation changes on the WNP monsoon is weaker when the solar insolation is higher. Prior to the present WNP monsoon onset, the upper-tropospheric East Asian jet stream weakens and shifts northward; the monsoon onset is highly affected by the jet-induced high potential vorticity intrusion. In the instance of the extreme perihelion-summer, the WNP monsoon is suppressed despite a stronger midlatitude precursor than present-day, and the midlatitude circulation response to the enhanced South Asian precipitation is considerable. These conditions indicate internal monsoon interactions of an orbital scale, implying a potential mechanistic control of the WNP monsoon.

  4. 谁驱动T亚洲季风的演化:一个瞬变模拟试验的启示%WHAT IS DRIVING THE ASIAN MONSOON EVOLUTION: INSPIRATIONS FROM A TRANSIENT SIMULATION

    Institute of Scientific and Technical Information of China (English)

    石正国; 刘晓东

    2009-01-01

    亚洲季风演化受到地球轨道参数强迫,尤其是岁差所引起日射变化的显著影响,但关于其驱动机制的争议仍然存在,且集中在"零相位"和"南半球潜热"两种假说上.两个假说都得到了部分地质证据的支持,因此亟需相应的数值模拟,尤其是长期瞬变试验的检验.长期瞬变模拟试验可以对气候的连续演变进行模拟,并能与地质证据进行对比,有助于深入认识亚洲季风系统演化的内在物理机制.但由于计算能力的匮乏,过去的古季风数值模拟多为"时间片"模拟,这使得季风变迁机理研究受到限制.文章通过一个海-气耦合模式的长期瞬变试验,讨论了轨道日射的变化特征,证明过去280ka亚洲夏季风降水对日射有十分显著的响应.且与北半球初夏日射变化相位接近,部分支持了"零相位"假说.同时,模拟结果还揭示了随意选取日射参考标尺会导致缺乏内在物理机制的位相关系,合理选择日射参考以及明确地质记录的气候学意义在古季风强迫-响应机制研究中十分重要.%How the orbital-scale Asian monsoon has developed during the Quaternary is still an open question up to now. Geological records and numerical simulations have demonstrated that the evolution of the Asian monsoon system is significantly influenced by the insolation variation induced by the Earth's orbital parameters. In the low-latitude region, owing to the dominance of precession in the variability of solar radiation, most researches have focused on the evolution of monsoonal climate with quasi-2Oka precession cycles. However, debates still exist on the mechanism how precession affects the Asian monsoon. At present,there are two hypotheses on this question: "Zero phase" and "Sothem Hemispheric latent heat", proposed by John Kutzbach and Steven Clemens, respectively, which are both supported by several geological proxies. The main attention is paid to whether the Asian monsoon

  5. Observations of Non-Methane Hydrocarbons Over India During the Asian Summer Monsoon Period: Results from CARIBIC

    Science.gov (United States)

    Baker, A. K.; Schuck, T. J.; Slemr, F.; Brenninkmeijer, C. A.

    2008-12-01

    The CARIBIC project (Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container, www.caribic-atmospheric.com) involves the monthly deployment of an instrument container equipped to make atmospheric measurements from onboard a long-range commercial airliner. Since December 2004, flights for the second phase of CARIBIC have been aboard a Lufthansa Airbus A340-600 traveling between Frankfurt, Germany and destinations in Asia, North America and South America. The instrument package housed in the container (1.5 ton) is fully automated and during each monthly set of flights carries out a variety of real-time trace gas and aerosol measurements, and also collects 28 air samples, which are analyzed upon return to the laboratory. Routine measurements made from the sampling flasks include non-methane hydrocarbon (NMHC) analysis, and these measurements provide the basis for the data presented here. Between April and September of 2008, the container was deployed monthly on two sequential roundtrip flights between Frankfurt and Chennai, India. To achieve greater resolution, air samples were collected only on the first of the roundtrip flights, with 14 samples collected on the flight to Chennai and 14 collected on the return. These flights provided the opportunity to study the composition of the upper troposphere in this region during the Asian summer monsoon period (typically June-September), which is characterized by anticyclonic circulation in the upper troposphere coupled with deep convection. Samples collected during the monsoon period exhibit elevated levels of NMHCs relative to samples collected outside of the monsoon period, with enhancements in ethyne and benzene being more substantial than enhancements in the alkanes. Enhanced mixing ratios are observed between 15N and 40N, and correspond to enhancements in other trace gases, namely methane and CO. Ethyne in particular is strongly correlated with both methane and CO in this region

  6. South Asian Summer Monsoon Rainfall Variability and Trend: Its Links to Indo-Pacific SST Anomalies and Moist Processes

    Science.gov (United States)

    Prasanna, V.

    2016-01-01

    The warm (cold) phase of El Niño (La Niña) and its impact on all Indian Summer Monsoon rainfall (AISMR) relationship is explored for the past 100 years. The 103-year (1901-2003) data from the twentieth century reanalysis datasets (20CR) and other major reanalysis datasets for southwest monsoon season (JJAS) is utilized to find out the simultaneous influence of the El Niño Southern Oscillation (ENSO)-AISMR relationship. Two cases such as wet, dry monsoon years associated with ENSO(+) (El Niño), ENSO(-) (La Niña) and Non-ENSO (neutral) events have been discussed in detail using observed rainfall and three-dimensional 20CR dataset. The dry and wet years associated with ENSO and Non-ENSO periods show significant differences in the spatial pattern of rainfall associated with three-dimensional atmospheric composite, the 20CR dataset has captured the anomalies quite well. During wet (dry) years, the rainfall is high (low), i.e. 10 % above (below) average from the long-term mean and this wet or dry condition occur both during ENSO and Non-ENSO phases. The Non-ENSO year dry or wet composites are also focused in detail to understand, where do the anomalous winds come from unlike in the ENSO case. The moisture transport is coherent with the changes in the spatial pattern of AISMR and large-scale feature in the 20CR dataset. Recent 50-year trend (1951-2000) is also analyzed from various available observational and reanalysis datasets to see the influence of Indo-Pacific SST and moist processes on the South Asian summer monsoon rainfall trend. Apart from the Indo-Pacific sea surface temperatures (SST), the moisture convergence and moisture transport among India (IND), Equatorial Indian Ocean (IOC) and tropical western pacific (WNP) is also important in modifying the wet or dry cycles over India. The mutual interaction among IOC, WNP and IND in seasonal timescales is significant in modifying wet and dry cycles over the Indian region and the seasonal anomalies.

  7. South Asian Summer Monsoon Rainfall Variability and Trend: Its Links to Indo-Pacific SST Anomalies and Moist Processes

    Science.gov (United States)

    Prasanna, V.

    2016-06-01

    The warm (cold) phase of El Niño (La Niña) and its impact on all Indian Summer Monsoon rainfall (AISMR) relationship is explored for the past 100 years. The 103-year (1901-2003) data from the twentieth century reanalysis datasets (20CR) and other major reanalysis datasets for southwest monsoon season (JJAS) is utilized to find out the simultaneous influence of the El Niño Southern Oscillation (ENSO)-AISMR relationship. Two cases such as wet, dry monsoon years associated with ENSO(+) (El Niño), ENSO(-) (La Niña) and Non-ENSO (neutral) events have been discussed in detail using observed rainfall and three-dimensional 20CR dataset. The dry and wet years associated with ENSO and Non-ENSO periods show significant differences in the spatial pattern of rainfall associated with three-dimensional atmospheric composite, the 20CR dataset has captured the anomalies quite well. During wet (dry) years, the rainfall is high (low), i.e. 10 % above (below) average from the long-term mean and this wet or dry condition occur both during ENSO and Non-ENSO phases. The Non-ENSO year dry or wet composites are also focused in detail to understand, where do the anomalous winds come from unlike in the ENSO case. The moisture transport is coherent with the changes in the spatial pattern of AISMR and large-scale feature in the 20CR dataset. Recent 50-year trend (1951-2000) is also analyzed from various available observational and reanalysis datasets to see the influence of Indo-Pacific SST and moist processes on the South Asian summer monsoon rainfall trend. Apart from the Indo-Pacific sea surface temperatures (SST), the moisture convergence and moisture transport among India (IND), Equatorial Indian Ocean (IOC) and tropical western pacific (WNP) is also important in modifying the wet or dry cycles over India. The mutual interaction among IOC, WNP and IND in seasonal timescales is significant in modifying wet and dry cycles over the Indian region and the seasonal anomalies.

  8. Climate Change Signal Analysis for Northeast Asian Surface Temperature

    Institute of Scientific and Technical Information of China (English)

    Jeong-Hyeong LEE; Byungsoo KIM; Keon-Tae SOHN; Won-Tae KOWN; Seung-Ki MIN

    2005-01-01

    Climate change detection, attribution, and prediction were studied for the surface temperature in the Northeast Asian region using NCEP/NCAR reanalysis data and three coupled-model simulations from ECHAM4/OPYC3, HadCM3, and CCCma GCMs (Canadian Centre for Climate Modeling and Analysis general circulation model). The Bayesian fingerprint approach was used to perform the detection and attribution test for the anthropogenic climate change signal associated with changes in anthropogenic carbon dioxide (CO2) and sulfate aerosol (SO42-) concentrations for the Northeast Asian temperature. It was shown that there was a weak anthropogenic climate change signal in the Northeast Asian temperature change. The relative contribution of CO2 and SOl- effects to total temperature change in Northeast Asia was quantified from ECHAM4/OPYC3 and CCCma GCM simulations using analysis of variance. For the observed temperature change for the period of 1959-1998, the CO2 effect contributed 10%-21% of the total variance and the direct cooling effect of SO42- played a less important role (0% 7%) than the CO2effect. The prediction of surface temperature change was estimated from the second CO2+SO24- scenario run of ECHAM4/OPYC3 which has the least error in the simulation of the present-day temperature field near the Korean Peninsula. The result shows that the area-mean surface temperature near the Korean Peninsula will increase by about 1.1° by the 2040s relative to the 1990s.

  9. Vertical structure of cumulonimbus towers and intense convective clouds over the South Asian region during the summer monsoon season

    Science.gov (United States)

    Bhat, G. S.; Kumar, Shailendra

    2015-03-01

    The vertical structure of radar reflectivity factor in active convective clouds that form during the South Asian monsoon season is reported using the 2A25 version 6 data product derived from the precipitation radar measurements on board the Tropical Rainfall Measuring Mission satellite. We define two types of convective cells, namely, cumulonimbus towers (CbTs) and intense convective cells (ICCs). CbT is defined referring to a reflectivity threshold of 20 dBZ at 12 km altitude and is at least 9 km thick. ICCs are constructed referring to reflectivity thresholds at 8 km and 3 km altitudes. Cloud properties reported here are based on 10 year climatology. It is observed that the frequency of occurrence of CbTs is highest over the foothills of Himalayas, plains of northern India and Bangladesh, and minimum over the Arabian Sea and equatorial Indian Ocean west of 90°E. The regional differences depend on the reference height selected, namely, small in the case of CbTs and prominent in 6-13 km height range for ICCs. Land cells are more intense than the oceanic ones for convective cells defined using the reflectivity threshold at 3 km, whereas land versus ocean contrasts are not observed in the case of CbTs. Compared to cumulonimbus clouds elsewhere in the tropics, the South Asian counterparts have higher reflectivity values above 11 km altitude.

  10. Relationship between tropical cyclone activities in the Northwest Pacific area and the summer monsoon rainfall in the Northeast Asian region

    Science.gov (United States)

    Choi, Ki-Seon; Cha, Yu-Mi; Kang, Sung-Dae; Kim, Hae-Dong

    2015-07-01

    The study surveys the tropical cyclone (TC) activities in the Northwestern Pacific region during the summer monsoon season (SMS) (June-July) in the Northeast Asian region (North China, Korea, and Japan). The positive (negative) SMS rainfall years in the region show that not only the TC genesis frequency, but also the TC frequency which affects the Northeast Asian countries, are low (high) in the tropical and subtropical northwest Pacific. That is, the TCs mainly move to the southern part of China or up to the east sea far from Japan in the positive SMS rainfall years. The study analyzes the difference between the two groups in the 500 hPa streamline to investigate TC activities for the groups. The large-scale anomalous anticyclone and the anomalous cyclone were enlarged in the tropical and subtropical Northwestern Pacific and from Manchuria to the eastern Japan, respectively. Due to such anomalous pressure system patterns being strengthened during the positive SMS rainfall years, the tropical Northwestern Pacific below 20°N fortified anomalous easterlies, causing a lot of TCs during those years to move to the southern part of China along with these anomalous steering flows (anomalous easterlies). In addition, the anomalous anticyclone that is located in the tropical and subtropical Northwestern Pacific caused a low TC genesis frequency during the positive SMS rainfall years.

  11. Relationship between Sea Level Pressures of the Winter Tropical Western Pacific and the Subsequent Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    武炳义; 王东晓; 黄荣辉

    2003-01-01

    Using monthly mean National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data for the period 1958-1996, based on a new circulation index in the tropical western Pacific region, this paper investigates extreme winter circulation conditions in thenorthwestern Pacific and their evolution. The results show that the extreme winter circulation anomalyin the northwestern Pacific exhibits a strong association with those appearing in the high latitudes of theNorthern Hemisphere including the northern Asian continent, part of the Barents Sea, and the northeasternPacific. As the season progresses, an anticyclonic (cyclonic) circulation anomaly appearing in the north-western Pacific gradually moves northeastwards and extends westwards. Its axis in the west-east directionis also stretched. Therefore, easterly (westerly) anomalies in the southern part of the anticyclonic (cyclonic)circulation anomaly continuously expand westwards to the peninsula of India. Therefore, the South Asiansummer monsoon would be weaker (stronger). Simultaneously, another interesting phenomenon is theevolution of SLP anomalies. As the season progresses (from winter to the following summer), SLP anoma-lies originating from the tropical western Pacific gradually move towards, and finally occupy the Asiancontinent, and further influence the thermal depression over the Asian continent in the following summer.

  12. Asian Aspirations for Climate Regime Beyond 2012

    International Nuclear Information System (INIS)

    This report is based on the second round of 'The Asia-Pacific Consultations on Climate Regime Beyond 2012' in 2006 to further advance the frank exchange of opinions of policy makers, academics, and the private sector on specific issues of high priority to the region. These include: energy security and development, Clean Development Mechanism (CDM), technology development and transfer, and adaptation. This report presents a summary of what has been learnt through the current consultations, interviews, and questionnaire surveys with policy makers and climate policy researchers across the region

  13. Nonlinear effect on the East Asian summer monsoon due to two coexisting anthropogenic forcing factors in eastern China: an AGCM study

    Science.gov (United States)

    Deng, Jiechun; Xu, Haiming

    2016-06-01

    Two anthropogenic forcing factors dominate in eastern China: aerosols and urban land cover. Usually, aerosols induce surface cooling while urban land cover causes surface warming. It is important to explore whether or not a nonlinear effect may result from the coexistence of these two opposing effects, and to what extent such nonlinear effect may become significant in affecting the climate change in East Asia. In this study, the Community Atmosphere Model version 5.1 (CAM5.1) coupled with the Community Land Model version 4 (CLM4) is employed to investigate the nonlinear effect on the East Asian summer monsoon due to the coexistence of aerosols and urban land cover. The anthropogenic forcing can be studied by including only aerosol emissions, only urban land cover, or a combination of the two in eastern China. The nonlinear effect obtained in CAM5.1 is evident in eastern China to offset the urbanization effect. Large-scale atmospheric response produces anomalous upward motion and increases total cloud amount and precipitation. This increased total cloud amount and its associated negative shortwave cloud forcing in turn significantly decrease surface air temperature and cool the troposphere, especially in northern China, resulting in a reduced land-sea thermal contrast, which acts to weaken the prevailing southwesterly wind over the Yangtze River Valley and southwestern China and to enhance the wind over the northern South China Sea. The nonlinear effect also indirectly excites strong convection over southern China, leading to a pronounced increase in summer precipitation.

  14. Climate contributions to vegetation variations in Central Asian drylands

    DEFF Research Database (Denmark)

    Zhou, Yu; Zhang, Li; Fensholt, Rasmus; Wang, Kun; Vitkovskaya, Irina; Tian, Feng

    2015-01-01

    Central Asia comprises a large fraction of the world's drylands, known to be vulnerable to climate change. We analyzed the inter-annual trends and the impact of climate variability in the vegetation greenness for Central Asia from 1982 to 2011 using GIMMS3g normalized difference vegetation index...... could be explained by the changes in the socio-economic structure resulted from the USSR collapse in late 1991. Our results clearly illustrate the combined influence of climatic/anthropogenic contributions on vegetation growth in Central Asian drylands. Due to the USSR collapse, this region represents a...... unique case study of the vegetation response to climate changes under different climatic and socio-economic conditions....

  15. Rapid interhemispheric climate links via the Australasian monsoon during the last deglaciation.

    Science.gov (United States)

    Ayliffe, Linda K; Gagan, Michael K; Zhao, Jian-xin; Drysdale, Russell N; Hellstrom, John C; Hantoro, Wahyoe S; Griffiths, Michael L; Scott-Gagan, Heather; St Pierre, Emma; Cowley, Joan A; Suwargadi, Bambang W

    2013-01-01

    Recent studies have proposed that millennial-scale reorganization of the ocean-atmosphere circulation drives increased upwelling in the Southern Ocean, leading to rising atmospheric carbon dioxide levels and ice age terminations. Southward migration of the global monsoon is thought to link the hemispheres during deglaciation, but vital evidence from the southern sector of the vast Australasian monsoon system is yet to emerge. Here we present a 230thorium-dated stalagmite oxygen isotope record of millennial-scale changes in Australian-Indonesian monsoon rainfall over the last 31,000 years. The record shows that abrupt southward shifts of the Australian-Indonesian monsoon were synchronous with North Atlantic cold intervals 17,600-11,500 years ago. The most prominent southward shift occurred in lock-step with Heinrich Stadial 1 (17,600-14,600 years ago), and rising atmospheric carbon dioxide. Our findings show that millennial-scale climate change was transmitted rapidly across Australasia and lend support to the idea that the 3,000-year-long Heinrich 1 interval could have been critical in driving the last deglaciation. PMID:24309539

  16. Evidence for signiifcant climate impacts in monsoonal Asia at 8.2 ka from multiple proxies and model simulations

    Institute of Scientific and Technical Information of China (English)

    MORRILL Carrie; WAGNER Amy J; OTTO-BLIESNER Bette L; ROSENBLOOM Nan

    2011-01-01

    Given the likelihood of future reductions in the strength of the Atlantic Meridional Overturning Circulation (AMOC), it is important to document how changes in the AMOC have altered climate patterns in the past and to assess the skill of coupled climate models in reproducing these teleconnections. Of past abrupt changes in the AMOC, the 8.2 ka event provides a particularly useful case study because its duration, magnitude of AMOC reduction and background climate state are closest to conditions expected in the future. In this research, we present an expanded proxy synthesis of the 8.2 ka event in monsoonal Asia, including new high-resolution lake and bog records, more sites from the East Asia monsoon region and proxies of winter monsoon strength. We compare proxy evidence with a new simulation of the 8.2 ka event using the Community Climate System Model version 3 (CCSM3) and prescribing North Atlantic freshwater forcing according to the latest reconstructions. We ifnd clear and objectively-determined evidence for 8.2 ka climate anomalies at nearly all of the fourteen proxy sites, emphasizing the strong and widespread impacts of the event in monsoonal Asia during both summer and winter seasons. The model simulation corroborates that these anomalies, described generally as a weakening of the summer monsoon and strengthening of the winter monsoon, were likely caused by a reduction of the AMOC. Examination of regional anomalies in East Asia reveals some spatial heterogeneity, however, that in the model simulation is caused by contraction of the seasonal migration of the subtropical monsoon front. The duration of climate anomalies at 8.2 ka in monsoonal Asia, both in proxy records and the model simulation, generally matches the duration of the event in Greenland ice core δ18O, further supporting a tight connection to the North Atlantic.

  17. A quick cooling event of the East Asian monsoon responding to Heinrich Event 1: Evidence from stalagmite

    Institute of Scientific and Technical Information of China (English)

    WANG; Yongjin

    2002-01-01

    [1]Heinrich, H., Origin and consequences of cyclic ice rafting in the northeast Atlantic Ocean during the past 130000 years, Quaternary Research, 1988, 29: 142.[2]Broecker, W. S., Massive iceberg discharges as triggers for global climate change, Nature, 1994, 372: 421.[3]Porter, S. C., An, Z. S., Correlation between climate events in the North Atlantic and China during the last glaciation, Nature, 1995, 375: 305.[4]Mu, X. N., Xu, H. K., Mu, D. C. et al., Discovery of Homo erectus Remains from Tangshan, Nanjing and its significance, Acta Palaeontologica Sinica (in Chinese), 1993, 32(4): 393.[5]Wang, Y. J., Cheng, H., Lu, C. L. et al., TIMS U-series ages of speleothems from the Tangshan caves, Nanjing, Chinese Science Bulletin, 1999, 44(21): 1987.[6]Qin, X. G., Liu, T. S., Tang, M. et al., Grey characteristics of microbanding of stalagmite in Shihua Cave, Beijing and its climatic signification (I)--The study of microstructure of microbanding, Science in China, Ser. D, 1998, 41(2): 151.[7]McCrea, J. M., The isotopic chemistry of carbonates and a paleotemperature-scale, Journal of Chemical Physics, 1950, 18: 849.[8]Bar-Matthews, M., Ayalon, A., Matthews, A. et al., Carbon and oxygen isotope study of the active water-carbonate system in a karstic Mediterranean cave: implications for paleoclimate research in semiarid regions, Geochimica et Cosmochimica Acta, 1996, 60: 337.[9]Zheng, S. H., Hou F. G., Ni, B. L., Study on hydrogen and oxygen isotope of precipitation in China, Chinese Science Bulletin (in Chinese), 1983, 13: 801.[10]Hoffmann, G., Heimann, M., Water isotope modeling in the Asian monsoon region, Quaternary International, 1997, 37: 115.[11]O'Neil, J. R., Clayton, R. N., Mayeda, T. K., Oxygen isotope fractionation in divalent metal carbonates, Journal of Chemical Physics, 1969, 51: 5547.[12]Li, H. C., Ku. T. L., Stott, L. D., Applications of interannual-resolution stable isotope records of speleothem: climatic

  18. Influence of the Asian monsoon on net ecosystem carbon exchange in two major ecosystems in Korea

    Directory of Open Access Journals (Sweden)

    H. Kwon

    2010-05-01

    Full Text Available Considering the feedback in radiation, temperature, and soil moisture with alterations in rainfall patterns, the influence of the changing monsoon on Net Ecosystem CO2 Exchange (NEE can be critical to the estimation of carbon balance in Asia. In this paper, we examined CO2 fluxes measured by the eddy covariance method from 2004 to 2008 in two major ecosystems in the KoFlux sites in Korea, i.e., the Gwangneung Deciduous forest (GDK and the Haenam Farmland (HFK. Our objectives were to identify the repeatability of the mid-season depression of NEE encountered at the two sites based on the single-year observation, and to further scrutinize its cause, effect, and interannual variability by using multi-year observations. In both GDK and HFK sites, the mid-season depression of NEE was reproduced each year but with different timing, magnitude, and mechanism. At the GDK site, a predominant factor causing the mid-season depression was a decreased solar radiation and the consequent reduction in Gross Primary Productivity (GPP during the summer monsoon period. At the HFK site, however, the monsoonal effect was less pronounced and the apparent mid-season depression was mainly a result of the management practices such as cultivation of spring barley and rice transplantation. Other flux observation sites in East Asia also showed a decline in radiation but with a lesser degree during the monsoon season, resulting in less pronounced depression in NEE. In our study, the observed depressions in NEE caused both GDK and HFK sites to become a weaker carbon sink or even a source in the middle of the growing season. On average, the GDK site (with maximum leaf area index of ~5 was a weak carbon sink with NEE of −84 gC m−2 y−1. Despite about 20% larger GPP (of 1321 gC m−2y−1 in comparison with the GDK site, the HFK site (with maximum leaf area index of 3–4 was a weaker carbon sink with NEE of

  19. Modeling efforts to improve the Asian Summer Monsoon representation in a coupled ocean-atmosphere tropical-channel model

    Science.gov (United States)

    Samson, G.; Masson, S. G.; Durand, F.; Terray, P.; Berthet, S.; Jullien, S.

    2015-12-01

    The Asian Summer Monsoon (ASM) simulated over the 1989-2009 period with a new 0.75° coupled ocean-atmosphere tropical-channel (45°S-45°N) model based on WRF and NEMO models is presented. The model biases are comparable to those commonly found in coupled global coupled models (CGCMs): the Findlater jet is too weak, precipitations are underestimated over India while they are overestimated over South-East Asia and the Maritime Continent. The ASM onset is delayed by several weeks, an error which is also very common in current CGCMs. We show that land surface temperature errors are a major source of the ASM low-level circulation and rainfall biases in our model: a cold bias over the Middle-East region weakens the Findlater jet while a warm bias over India strengthens the monsoon circulation in the Bay of Bengal. To explore the origins of those biases and their relationship with the ASM, a series of sensitivity experiments is presented. First, we show that changing the land surface albedo representation in our model directly influences the ASM characteristics by reducing the cold bias in the Middle-East region. It improves the "heat low" representation, which has direct implication on the Findlater jet strength and precipitation over India. Furthermore, the ASM onset is shifted back by almost one month in agreement with observations. Second, a parameterization of the convective cloud-radiative feedback is introduced in the atmospheric model. It acts to reduce the warm bias present in convective regions such as India and favors the monsoon northward migration. As a consequence, the dry bias is reduced in this region. Finally, horizontal resolution is increased from 0.75° to 0.25° for both oceanic and atmospheric models to assess the sensitivity of the ASM biases to the model resolution. Large-scale model errors persist at higher resolution, but are significantly attenuated. Precipitation is improved in mountainous areas with strong orographic control, but also in

  20. Global Monsoon and Long-Term climate Changes

    Institute of Scientific and Technical Information of China (English)

    WANG Pinxian

    2009-01-01

    @@ The core in the current "Global Warming" debate is how to discriminate the anthropogenic from natural warming. To answer this question, we have to know the natural trend of climate changes, an issue on which scientists' opinions diverge incredibly. Some scientists tell us that the next ice age will not come in some 50 thousands years (Berger & Loutre, 2002), but others believe that new glaciation would have been upon us several thousands years ago, should it be not postponed by early human impact (Ruddiman, 2003). Climatologists now talking on "global warming" warned about "global cooling" over 30 years ago.

  1. Evaluation of Forecast Performance on Asian Summer Monsoon Low Level Wind Using TIGGE Dataset

    Science.gov (United States)

    Ruoyun, Niu

    2016-04-01

    The forecast performance of EASM (East Asia summer monsoon) and SASM (South Asia summer monsoon) for six TIGGE (the THORPEX Interactive Grand Global Ensemble) centers in the summers of 2008-2013 are evaluated to reflect the current predictability of the state-of-the-art numerical weather prediction. The results show that EASM is overestimated by all the TIGGE centers (except the Canadian Meteorological Center, CMC). SASM is also over-predicted by ECMWF (the European Center for Medium-Range Weather Forecasts), CMA (the China Meteorological Administration) and CMC but conversely under-predicted by JMA (the Japan Meteorological Agency), Additionally, SASM is overestimated for the early lead times and underestimated for the longer lead times by NCEP (the National Centers for Environmental Prediction) and UKMO (the United Kingdom Meteorological Office (UKMO). Further analysis suggests such biases are likely to the associated with those in the related land-sea thermal contrasts. EASM surge is basically overestimated by NCEP and CMA and mainly underestimated by the others. The bias predictabilities for SASM surge are similar to that of SASM. The peaks of SASM and EASM including their surges are mainly underestimated while the valleys are mostly overestimated. By comparison, ECMWF and UKMO have overall the highest forecast skills in predicting SASM and EASM and both have respective advantages. All the TIGGE centers generally show higher skills in predicting SASM than EASM. The forecast skills of SASM and EASM are superior to that of their respective surges. Moreover, the bias-correction forecast skills tend to be improved with higher correlation coefficients in raw forecast verification.

  2. Formation of the Summertime Ozone Valley over the Tibetan Plateau: The Asian Summer Monsoon and Air Column Variations

    Institute of Scientific and Technical Information of China (English)

    BIAN Jianchun; YAN Renchang; CHEN Hongbin; L(U) Daren; Steven T. MASSIE

    2011-01-01

    The summertime ozone valley over the Tibetan Plateau is formed by two influences,the Asian summer monsoon (ASM) and air column variations. Total ozone over the Tibetan Plateau in summer was ~33 Dobson units (DU) lower than zonal mean values over the ocean at the same latitudes during the study period 2005-2009. Satellite observations of ozone profiles show that ozone concentrations over the ASM region have lower values in the upper troposphere and lower stratosphere (UTLS) than over the non-ASM region. This is caused by frequent convective transport of low-ozone air from the lower troposphere to the UTLS region combined with trapping by the South Asian High.This offset contributes to a ~20-DU deficit in the ozone column over the ASM region.In addition,along the same latitude,total ozone changes identically with variations of the terrain height,showing a high correlation with terrain heights over the ASM region,which includes both the Tibetan and Iranian plateaus.This is confirmed by the fact that the Tibetan and Iranian plateaus have very similar vertical distributions of ozone in the UTLS,but they have different terrain heights and different total-column ozone levels.These two factors (lower UTLS ozone and higher terrain height) imply 40 DU in the lower-ozone column,but the Tibetan Plateau ozone column is only ~33 DU lower than that over the non-ASM region.This fact suggests that the lower troposphere has higher ozone concentrations over the ASM region than elsewhere at the same latitude,contributing ~7 DU of total ozone,which is consistent with ozonesonde and satellite observations.

  3. Influence of the East Asian winter monsoon on interannual variations of wintertime aerosol concentrations over East Asia during 1980-2013

    Science.gov (United States)

    Jeong, Jaein; Park, Rokjin

    2016-04-01

    The monsoon circulation influence the spatial and temporal variations of aerosol concentrations. In this study, we examine the effect of the East Asian winter monsoon (EAWM) on wintertime aerosol concentrations in East Asia during 1980-2013 using observed PM10 concentrations and a global 3-D chemical transport model (GEOS-Chem) driven by the assimilated MERRA meteorological data. We find that the observed and simulated surface aerosol concentrations have strong negative (positive) correlations with the EAWM over the northeast (southeast) Asia. Differences in aerosol concentrations between the strong and weak monsoon years are up to 25% over the northeast Asia (30°-55°N, 110°-160°E), where the strong monsoon years show much lower aerosol concentrations than those of the weak monsoon years. On the other hand, the opposite patterns are found over the southeast Asia (20°-30°N, 110°-160°E). The EAWM appears to play a significant role in the inter-annual variability of aerosol concentrations and thus its change would be crucial to predict wintertime aerosol concentrations and their future changes over East Asia.

  4. Asian anthropogenic dust and its climate effect (Invited)

    Science.gov (United States)

    Huang, J.; Liu, J.; Chen, B.

    2013-12-01

    Anthropogenic dust originates mainly from areas of localized human disturbance, such as traffic-on-roads, agricultural fields, grazing, military installations, construction sites, and off-road vehicle areas. To understand historical and possible future changes in dust emissions, the percentage of atmospheric dust load originating from anthropogenic source and its distribution must be quantified. CALIPSO lidar, which shoots a laser into the atmosphere, provides new insight into the detection of anthropogenic dust emission. Here, we present the distribution of Asian anthropogenic dust emissions and its relation to human activity by using CALIPSO lidar measurements. We found that the local anthropogenic dust aerosols account for significant portion of the total dust burden in the atmosphere. The anthropogenic dust emissions mainly occur over the heavy human activity and poor ecosystem region, such as semi-arid region. The impact of Asian anthropogenic dust on regional climate will also be discussed in this talk.

  5. Asian Change in the Context of Global Climate Change

    Science.gov (United States)

    Galloway, James N.; Melillo, Jerry M.

    1998-09-01

    Nearly two-thirds of the world's population live in Asia, and many countries in that region are currently undergoing very rapid industrial, agricultural and economic development. The Framework Convention on Climate Change constrains developed countries with regard to their future emissions of greenhouse gases, but recognizes the special needs of developing countries. There is growing appreciation of the ways in which developing countries in the Asian region both contribute to global changes (by altering biogeochemical pathways and cycles) and are themselves affected by those changes. This volume uses the intellectual efforts and findings of the International Geosphere-Biosphere Programme (IGBP) community to provide the first integrated analysis of the interactions between global change and Asian change, giving particular attention to China's role. The book will be of interest to readers in a wide range of academic disciplines (natural sciences and socio-economic) and for those involved in national and international policy development relevant to global change.

  6. Impact of high resolution land surface initialization in Indian summer monsoon simulation using a regional climate model

    Science.gov (United States)

    Unnikrishnan, C. K.; Rajeevan, M.; Rao, S. Vijaya Bhaskara

    2016-06-01

    The direct impact of high resolution land surface initialization on the forecast bias in a regional climate model in recent years over Indian summer monsoon region is investigated. Two sets of regional climate model simulations are performed, one with a coarse resolution land surface initial conditions and second one used a high resolution land surface data for initial condition. The results show that all monsoon years respond differently to the high resolution land surface initialization. The drought monsoon year 2009 and extended break periods were more sensitive to the high resolution land surface initialization. These results suggest that the drought monsoon year predictions can be improved with high resolution land surface initialization. Result also shows that there are differences in the response to the land surface initialization within the monsoon season. Case studies of heat wave and a monsoon depression simulation show that, the model biases were also improved with high resolution land surface initialization. These results show the need for a better land surface initialization strategy in high resolution regional models for monsoon forecasting.

  7. THE CLIMATIC CHARACTERISTICS OF SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA Ⅰ40—YEAR AVERAGE

    Institute of Scientific and Technical Information of China (English)

    冯瑞权; 林建恒

    2002-01-01

    By using 40-year NCEP reanalysis daily data91958-1997),we have analyzed the climatic characteristics of summer monsoon onset in the South China Sea(1050°E-120°E,5°N-20°N,to be simplified as SCS in the text followed) pentad y pentad(5 days),According to our new definition,in the monsoon area of the SCS two of the following conditions should be satistied:1)At 850hPa,the southwest winds should be greater than 2m/s.2)At 850 hPa.θse should e greater than 335°K.The new definition means that the summermonsoon is the southwest winds high temperature and high moisture.The onset of the SCS summer monsoon is defined to start when one half of the SCS area(105°E-120°E,5°N-20°N)is controlled by the summer monsoon.The analyzed results revealed the following:1) The summer monsoon in the SCS starts to build up abruptly in the 4th pentad in May.2) The summer monsoon onset in the SCS is resulted from the development and intensification of southwesterly monsoon in the Bay of Bengal.3) The onset of the summer monsoon and establishment of the summer monsoon rainfall season in the SCS occur simultaneously.4) During the summer monsoon onset in the SCS,troughs deepen and widen quickly in the lower troposphere of the India:the subtropical high in the Western pacific moves eastward off the SCS in the middle troposphere:the easterly advances northward over the SCS in the upper troposphere.

  8. Fudo: An East Asian Notion of Climate and Sustainability

    Directory of Open Access Journals (Sweden)

    Jin Baek

    2013-09-01

    Full Text Available My paper discusses an East Asian notion of climate and its significance for sustainability. A particular reference is the environmental philosophy of Tetsuro Watsuji (1889–1960, a Japanese philosopher who reflected upon the meaning of climate, or “fudo” in the Sino-Japanese linguistic tradition. Watsuji sees fudo not merely as a collection of natural features—climatic, scenic, and topographical—of a given land, but also as the metaphor of subjectivity, or “who I am”. Furthermore, this self-discovery through fudo is never private but collective. By referring to a phenomenological notion of “ek-sistere”, or “to be out among other ‘I’s”, Watsuji demonstrates the pervasiveness of a climatic phenomenon and the ensuing inter-personal joining of different individuals to shape a collective sustainable measure in response to the phenomenon. My paper lastly concretizes the significance of fudo and its inter-personal ethical basis for sustainability by dwelling upon cross-ventilation in Japanese vernacular residential architecture. Cross-ventilation emerges only through what Watsuji calls “selfless openness” between different rooms predicated upon the joining of different ‘I’s soaked in hotness and humidity. Watsuji’s fudo thus offers a lesson that without considering the collective humane characteristic of a natural climatic phenomenon, any sustainable act is flawed and inefficient.

  9. Projected hydrologic changes in monsoon-dominated Himalaya Mountain basins with changing climate and deforestation

    Science.gov (United States)

    Neupane, Ram P.; White, Joseph D.; Alexander, Sara E.

    2015-06-01

    In mountain headwaters, climate and land use changes affect short and long term site water budgets with resultant impacts on landslide risk, hydropower generation, and sustainable agriculture. To project hydrologic change associated with climate and land use changes in the Himalaya Mountains, we used the Soil and Water Assessment Tool (SWAT) calibrated for the Tamor and Seti River basins located at eastern and western margins of Nepal. Future climate change was modeled using averaged temperature and precipitation for 2080 derived from Special Report on Emission Scenarios (SRES) (B1, A1B and A2) of 16 global circulation models (GCMs). Land use change was modeled spatially and included expansion of (1) agricultural land, (2) grassland, and (3) human settlement area that were produced by considering existing land use with projected changes associated with viability of elevation and slope characteristics of the basins capable of supporting different land use type. From these simulations, higher annual stream discharge was found for all GCM-derived scenarios compared to a baseline simulation with maximum increases of 13 and 8% in SRES-A2 and SRES-A1B for the Tamor and Seti basins, respectively. On seasonal basis, we assessed higher precipitation during monsoon season in all scenarios that corresponded with higher stream discharge of 72 and 68% for Tamor and Seti basins, respectively. This effect appears to be geographically important with higher influence in the eastern Tamor basin potentially due to longer and stronger monsoonal period of that region. However, we projected minimal changes in stream discharge for the land use scenarios potentially due to higher water transmission to groundwater reservoirs associated with fractures of the Himalaya Mountains rather than changes in surface runoff. However, when combined the effects of climate and land use changes, discharge was moderately increased indicating counteracting mechanisms of hydrologic yield in these mountains

  10. Intraseasonal-to-interannual variability of the Indian Monsoon: the present climate and future projections of climate change

    Science.gov (United States)

    Carvalho, L. V.; Jones, C.; Cannon, F.

    2014-12-01

    The Asia Monsoon is among Earth's most intriguing and spectacular phenomena. The Indian Monsoon System (IMS) is a regional manifestation this continental-scale phenomenon with complex characteristics and predictive challenges. India exhibits one of the largest rates of population growth that relies on IMS cycle for water supply. Thus, understanding the temporal variability of the IMS is essential to realistically predict the impacts of climate change on Asia's water resources and food security. Here we investigate intraseasonal-to-interannual variability of the IMS in the climate of the 20th century using the Climate Forecast System Reanalysis (CFSR) and examine future scenarios of climate change using the high spatial resolution models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) project. IMS is characterized with a large-scale index continuous in time and obtained by performing combined EOF analysis (CEOF) of variables that characterize the monsoon cycle: precipitation, low level circulation at 10 m, specific humidity and temperature at 2m. CFSR is used to derive the index (1979-2013). Projections of the CEOF onto the tropical rainfall measuring mission (TRMM) indicate that the first CEOF captures the large-scale features of the South and East Asia Monsoon. The second CEOF is associated with the IMS and its time coefficient is used as large-scale index for the IMS (LIMS). LIMS realistically defines IMS onset and withdrawal, and its amplitude associates with total seasonal precipitation. Moreover, the spectral analysis of the ISMI shows peaks on intraseasonal timescales that are related to IMS's active and break phases. Moreover, we demonstrate that LIMS identifies the interannual variability of IMS and can be used to investigate floods and droughts that have occurred over India. Similar approach is used to investigate the skill of the CMIP5 models in realistically simulating active and break phases of the IMS in the 'historic' run (1951-2005). We

  11. Assessment of the Indian summer monsoon in the WRF regional climate model

    Science.gov (United States)

    Raju, Attada; Parekh, Anant; Chowdary, J. S.; Gnanaseelan, C.

    2014-08-01

    The performance of the regional climate model, Weather Research and Forecasting in simulating the three dimensional moist and thermodynamic structure of Indian summer monsoon (ISM) during 2001-2011 is examined in this study. The model could simulate monsoon elements and convective precipitation zones over ISM region with some overestimation. Statistical analysis of sub-regional precipitation indicates that model has better skill over the monsoon core region with correlation of 0.7 and root mean square error of 2.3 mm day-1 with respect to observations. The model simulated seasonal mean vertical structures of temperature and water vapour mixing ratio (WVMR) are consistent with the Atmospheric Infrared Sounder observations. However, the core of low level jet is shifted southward in the model due to unrealistic convective heating over the lower latitudes of Indian Ocean and southern peninsular India. The tropical easterly jet is confined to 15°N in the model, which is due to the midtropospheric cold bias over the Tibetan region. The meridional asymmetric bias of sea level pressure (SLP) in model leads to weaker vertical wind shear, limiting the northward migration of maximum rain band to south of 23°N. These discrepancies have marked effects on the proper simulation of monsoon climate. The large scale spatial patterns of SLP, precipitation and winds during active and break spells are well simulated by the model. The lead-lag evolution of vertical structure of model temperature shows baroclinic structure during the active phase. It is evident from the observations that enhanced (suppressed) convection is generally preceded by a low-level moist (dry) anomaly and followed by a low-level dry (moist) anomaly. The model is inadequately representing the temporal evolution of vertical moist and thermodynamic processes. The evolution of vertical structures of temperature and WVMR is better simulated in the break phase compared to that of active phase. The evolution of

  12. Land surface coupling in regional climate simulations of the West African monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Steiner, Allison L. [University of Michigan, Department of Atmospheric, Oceanic and Space Sciences, Ann Arbor, MI (United States); Pal, Jeremy S. [Loyola Marymount University, Department of Civil Engineering and Environmental Science, Los Angeles, CA (United States); Rauscher, Sara A.; Giorgi, Filippo [Abdus Salam International Centre for Theoretical Physics, Earth System Physics - Weather and Climate Group, Trieste (Italy); Bell, Jason L.; Sloan, Lisa C. [University of California, Department of Earth and Planetary Sciences, Santa Cruz, CA (United States); Diffenbaugh, Noah S. [Purdue University, Purdue Climate Change Research Center and Department of Earth and Atmospheric Sciences, West Lafayette, IN (United States); Boone, Aaron [CNRS/GAME, CNRM Meteo-France, Toulouse (France)

    2009-11-15

    Coupling of the Community Land Model (CLM3) to the ICTP Regional Climate Model (RegCM3) substantially improves the simulation of mean climate over West Africa relative to an older version of RegCM3 coupled to the Biosphere Atmosphere Transfer Scheme (BATS). Two 10-year simulations (1992-2001) show that the seasonal timing and magnitude of mean monsoon precipitation more closely match observations when the new land surface scheme is implemented. Specifically, RegCM3-CLM3 improves the timing of the monsoon advance and retreat across the Guinean Coast, and reduces a positive precipitation bias in the Sahel and Northern Africa. As a result, simulated temperatures are higher, thereby reducing the negative temperature bias found in the Guinean Coast and Sahel in RegCM3-BATS. In the RegCM3-BATS simulation, warmer temperatures in northern latitudes and wetter soils near the coast create excessively strong temperature and moist static energy gradients, which shifts the African Easterly Jet further north than observed. In the RegCM3-CLM3 simulation, the migration and position of the African Easterly Jet more closely match reanalysis winds. This improvement is triggered by drier soil conditions in the RegCM3-CLM3 simulation and an increase in evapotranspiration per unit precipitation. These results indicate that atmosphere-land surface coupling has the ability to impact regional-scale circulation and precipitation in regions exhibiting strong hydroclimatic gradients. (orig.)

  13. Effect of the early and late onset of summer monsoon over the Bay of Bengal on Asian precipitation in May

    Science.gov (United States)

    Xing, Nan; Li, Jianping; Wang, Lanning

    2015-12-01

    The impact of early and late Bay of Bengal (BoB) summer monsoon (BoBSM) onset on Asian precipitation in May is investigated. When the BoBSM occurs earlier (later), May rainfall tends to be enhanced (suppressed) in the southern Indian peninsula (SIP), the Indochinese peninsula (ICP), southwest China (SWC) and the South China Sea (SCS), while south China (SC) rainfall tends to be suppressed (enhanced). When the BoBSM occurs earlier than the climatological mean (late April), strong convective activity emerges earlier over the BoB, which causes local strong convective heating earlier. Then, earlier spread of heating in the BoB towards both sides leads to earlier retreat of the subtropical highs in the western Pacific (WPSH) and Indian Ocean outwards the BoB. Thus, compared to the climatological mean, the two subtropical highs present larger retreat outwards the BoB and smaller meridional extent over the SCS and Arabian Sea in May, which contributes to positive heating anomalies over the SCS and Arabian Sea. Therefore, anomalous cyclonic circulations occur over the BoB, SCS and Arabian Sea in May. Anomalous cyclonic circulation is favorable for low-level convergence over the SIP, and thus resulting in local heavy rainfall. Associated with cyclonic circulation anomalies over the BoB and SCS, anomalous low-level convergent winds and ascending flows favor positive precipitation anomalies in the ICP, SWC, and SCS, while anomalous northeasterlies and descending flows affected by the southward retreat of the WPSH lessen SC rainfall. In late onset years the opposite occurs.

  14. Probabilistic versus deterministic skill in predicting the western North Pacific-East Asian summer monsoon variability with multimodel ensembles

    Science.gov (United States)

    Yang, Dejian; Yang, Xiu-Qun; Xie, Qian; Zhang, Yaocun; Ren, Xuejuan; Tang, Youmin

    2016-02-01

    Based on historical forecasts of three quasi-operational multimodel ensemble (MME) systems, this study assesses the superiority of coupled MME over contributing single-model ensembles (SMEs) and over uncoupled atmospheric MME in predicting the Western North Pacific-East Asian summer monsoon variability. The probabilistic and deterministic forecast skills are measured by Brier skill score (BSS) and anomaly correlation (AC), respectively. A forecast-format-dependent MME superiority over SMEs is found. The probabilistic forecast skill of the MME is always significantly better than that of each SME, while the deterministic forecast skill of the MME can be lower than that of some SMEs. The MME superiority arises from both the model diversity and the ensemble size increase in the tropics, and primarily from the ensemble size increase in the subtropics. The BSS is composed of reliability and resolution, two attributes characterizing probabilistic forecast skill. The probabilistic skill increase of the MME is dominated by the dramatic improvement in reliability, while resolution is not always improved, similar to AC. A monotonic resolution-AC relationship is further found and qualitatively explained, whereas little relationship can be identified between reliability and AC. It is argued that the MME's success in improving the reliability arises from an effective reduction of the overconfidence in forecast distributions. Moreover, it is examined that the seasonal predictions with coupled MME are more skillful than those with the uncoupled atmospheric MME forced by persisting sea surface temperature (SST) anomalies, since the coupled MME has better predicted the SST anomaly evolution in three key regions.

  15. Regional Glacier Sensitivity to Climate Change in the Monsoonal Himalaya: Implications for Water Resources

    Science.gov (United States)

    Rupper, S.; Maurer, J. M.; Schaefer, J. M.; Tsering, K.; Rinzin, T.; Dorji, C.; Johnson, E. S.; Cook, E. R.

    2014-12-01

    The rapid retreat of many glaciers in the monsoonal Himalaya is of potential societal concern. However, the retreat pattern in the region has been very heterogeneous, likely due in part to the inherent heterogeneity of climate and glaciers within the region. Assessing the impacts of glacier change on water resources, hydroelectric power, and hazard potential requires a detailed understanding of this potentially complex spatial pattern of glacier sensitivity to climate change. Here we quantify glacier surface-mass balance and meltwater flux across the entire glacierized region of the Bhutanese watershed using a full surface-energy and -mass balance model validated with field data. We then test the sensitivity of the glaciers to climatic change and compare the results to a thirty-year record of glacier volume changes. Bhutan is chosen because it (1) sits in the bulls-eye of the monsoon, (2) has >600 glaciers that exhibit the extreme glacier heterogeneity typical of the Himalayas, and (3) faces many of the economic and hazard challenges associated with glacier changes in the Himalaya. Therefore, the methods and results from this study should be broadly applicable to other regions of the monsoonal Himalaya. Our modeling results show a complex spatial pattern of glacier sensitivity to changes in climate across the Bhutanese Himalaya. However, our results also show that 90% of the total meltwater flux, and that these glaciers are uniformly the glaciers most sensitive to changes in temperature (and less sensitive to other climate variables). We compare these results to a thirty-year record of glacier volume changes over the same region. In particular, we extract DEMs and orthorectified imagery from 1976 historical spy satellite images and 2006 ASTER images. DEM differencing shows that the glaciers that have changed most over the past thirty years also have the highest modeled temperature sensitivity. These results suggest that, despite the complex glacier heterogeneity in

  16. Transient coupling relationships of the Holocene Australian monsoon

    CERN Document Server

    McRobie, Fiona H; Wyrwoll, Karl-Heinz

    2015-01-01

    The modern-day northwest Australian summer monsoon is dynamically coupled to other regional monsoon systems and inflows from the Indian Ocean, however, the nature of these relationships over longer time scales is uncertain. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Ni\\~no-related proxy records, has been qualitative, relying on `curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices which correspond to physically-based mechanisms. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9,000 years. The res...

  17. Impact of Tibetan Plateau uplift on Asian climate and stable oxygen isotopes in precipitation

    Science.gov (United States)

    Botsyun, Svetlana; Sepulchre, Pierre; Risi, Camille; Donnadieu, Yannick

    2016-04-01

    Surface elevation provides crucial information for understanding both geodynamic mechanisms of Earth's interior and influence of mountains growth on climate. Stable oxygen isotopes paleoaltimetry is considered to be a very efficient technic for reconstruction of the elevation history of mountains belts, including Tibetan Plateau and the Himalayas. This method relies on the difference between δ18O of paleo-precipitation reconstructed using the natural archives, and modern measured values for the point of interest. However, stable-isotope paleoaltimetry is potentially hampered by the fact that the presumed constancy of altitude-δ18O relationships through time might not be valid and climate changes affects δ18O in precipitation. We use the isotope-equipped atmospheric general circulation model LMDZ-iso for modeling Asia climate variations and associated δ18O in precipitation linked with Himalayas and Tibetan Plateau uplift. Experiments with reduced height over the Tibetan Plateau and the Himalayas have been designed. For the purpose of understanding where and how simulated complex climatic changes linked with the growth of mountains affect δ18O in precipitation we develop a theoretical expression for the precipitation composition. Our results show that modifying Tibetan Plateau height alters large-scale atmospheric dynamics including monsoon circulation and subsidence and associated climate variables, namely temperature, precipitation, relative humidity and cloud cover. In turn, δ18O signal decomposition results show that the isotopic signature of rainfall is very sensitive to climate changes related with the growth of the Himalayas and Tibetan Plateau, notably changes in relative humidity and precipitation amount. Topography appears to be the main controlling factor for only 40{%} of the sites where previous paleoelevation studies have been performed. Change of moisture sources linked with Asian topography uplift is shown to be not sufficient to yield a strong

  18. Stable isotopes in monsoon precipitation and water vapour in Nagqu, Tibet, and their implications for monsoon moisture

    Science.gov (United States)

    He, Siyuan; Richards, Keith

    2016-09-01

    Understanding climate variations over the Qinghai-Tibetan plateau has become essential because the high plateau sustains various ecosystems and water sources, and impacts on the Asian monsoon system. This paper provides new information from isotopic signals in meteoric water and atmospheric water vapour on the Qinghai-Tibetan Plateau using high frequency observation data over a relatively short period. The aim is to explore temporal moisture changes and annual variations at the onset and during the summer monsoon season at a transitional site with respect to the monsoon influence. Data show that high frequency and short period observations can reveal typical moisture changes from the pre-monsoon to the monsoon seasons (2010), and the large variation in isotopic signals in different years with respect to active/inactive periods during a mature phase of the monsoon (2011), especially inferring from the temporal changes in the d-excess of precipitation and its relationship with δ18O values, when higher d-excess is found in the pre-monsoon precipitation. In this transition zone on a daily basis, δ18O values in precipitation are controlled mainly by the amount of rainfall during the monsoon season, while temperature seems more important before the onset of monsoon. Furthermore, the "amount effect" is significant for night-time rain events. From comparison of signals in both the precipitation and water vapour, an inconsistent relationship between d-excess values suggests various moisture fluxes are active in a short period. The temporal pattern of isotopic signal change from the onset of the monsoon to the mature monsoon phase provides information about the larger circulation dynamics of the Asian monsoon.

  19. Extreme Rainfall Indices for Tropical Monsoon Countries in Southeast Asia

    OpenAIRE

    Kusumastuti, C.; Weesakul, S.

    2014-01-01

    Southeast Asian countries have the possibility to have rainfall and number of extreme rainfall event change due to future climate variation. This paper proposed three extreme rainfall indices as a modification of climate extremes indices from CLIMDEX Project by researchers at the Climate Change Research Centre (CCRC), the University of New South Wales (UNSW). The proposed indices aim to be used as a parameter for observing extreme rainfall events in tropical monsoon countries. Eleven extreme ...

  20. Sediment concentration rating curves for a monsoonal climate: upper Blue Nile

    Science.gov (United States)

    Moges, Mamaru A.; Zemale, Fasikaw A.; Alemu, Muluken L.; Ayele, Getaneh K.; Dagnew, Dessalegn C.; Tilahun, Seifu A.; Steenhuis, Tammo S.

    2016-07-01

    Information on sediment concentration in rivers is important for design of reservoirs and for environmental applications. Because of the scarcity of continuous sediment data, methods have been developed to predict sediment loads based on few discontinuous measurements. Traditionally, loads are being predicted using rating curves that relate sediment load to discharge. The relationship assumes inherently a unique relationship between concentration and discharge and therefore although performing satisfactorily in predicting loads, it may be less suitable for predicting concentration. This is especially true in the Blue Nile Basin of Ethiopia where concentrations decrease for a given discharge with the progression of the rainy monsoon phase. The objective of this paper is to improve the sediment concentration predictions throughout the monsoon period for the Ethiopian highlands with a modified rating type equation. To capture the observed sediment concentration pattern, we assume that the sediment concentration was at the transport limit early in the rainy season and then decreases linearly with effective rainfall towards source-limited concentration. The modified concentration rating curve was calibrated for the four main rivers in the Lake Tana basin where sediment concentrations affect fish production and tourism. Then the scalability of the rating type equation was checked in three 100 ha watersheds for which historic data were available. The results show that for predicting sediment concentrations, the (modified) concentration rating curve was more accurate than the (standard) load rating curve as expected. In addition loads were predicted more accurately for three of the four rivers. We expect that after more extensive testing over a wider geographical area, the proposed concentration rating curve will offer improved predictions of sediment concentrations in monsoonal climates.

  1. Sediment concentration rating curves for a monsoonal climate: upper Blue Nile Basin

    Science.gov (United States)

    Moges, M. A.; Zemale, F. A.; Alemu, M. L.; Ayele, G. K.; Dagnew, D. C.; Tilahun, S. A.; Steenhuis, T. S.

    2015-12-01

    Information on sediment content in rivers is important for design of reservoirs and for environmental applications. Because of scarcity of continuous sediment data, methods have been developed to predict sediment loads based on few discontinuous measurements. Traditionally, loads are being predicted using rating curves that relate sediment load to discharge. The relationship assumes inherently a unique relationship between concentration and discharge and therefore although performing satisfactorily in predicting loads, it may be less suitable for predicting concentration. This is especially true in the Blue Nile basin of Ethiopia where concentrations decrease for a given discharge with the progression of the rainy monsoon phase. The objective of this paper is to improve the sediment concentration predictions throughout the monsoon period for the Ethiopian highlands with a modified rating type equation. To capture the observed sediment concentration pattern, we assume that the sediment concentration was at the transport limit early in the rainy season and then decrease linearly with effective rainfall towards source limited concentration. The modified concentration rating curve was calibrated for the four main rivers in the Lake Tana basin where sediment concentrations affect fish production and tourism. Then the scalability of the rating type equation was checked in three 100-ha watersheds for which historic data was available. The results show, that for predicting sediment concentrations, the (modified) concentration rating curve was more accurate than the (standard) load rating curve as expected. In addition loads were predicted more accurately for three of the four rivers. We expect that after more extensive testing over a wider geographical area, the proposed concentration rating curve will offer improved predictions of sediment concentrations in monsoonal climates.

  2. Different orbital rhythms in the Asian summer monsoon records from North and South China during the Pleistocene

    NARCIS (Netherlands)

    Ao, H.; Dekkers, M.J.; Xiao, G.; Yang, X.; Qin, L.; Liu, X; Qiang, X.; Chang, H.; Zhao, H.

    2012-01-01

    Here we construct a Pleistocene astronomical timescale for the Nihewan fluvio–lacustrine sediments (North China), via tuning a stacked summer monsoon index generated from grain size and low-field magnetic susceptibility records to orbital obliquity and precession. Combining the summer monsoon record

  3. KZai 02 pollen record, an insight into West African monsoon fluctuations during the Last Climatic Cycle

    Science.gov (United States)

    Dalibard, M.; Popescu, S.; Maley, J.; Suc, J.

    2012-12-01

    Climate of the circum-Atlantic intertropical zone is driven by the ocean/atmosphere dynamics in response to variations of yearly insolation. These latitudes correspond to the convergence of the Hadley cells expressed on earth surface by intense trade winds and in lower troposphere by the African easterly jet making the edges of the intertropical zone relatively dry, while humidity is concentrated near the Equator. This phenomenon generates a precipitation front, known as the InterTropical Convergence Zone (ITCZ), the oscillations of which regulate the latitudinal vegetation distribution. Pollen record of core KZai 02 (Guinea Gulf) allows high resolution reconstruction of variations of past ecosystems over Central Africa during the Last Climatic Cycle. Plant taxa recorded in pollen analyses have been clustered according to their ecological requirements and African phytogeography. Fluctuations of these groups inform on precipitation intensity and their distribution during the last 130 ka. During Glacials, an open vegetation made of Cyperaceae marshes developed in the central Zaire/Congo Basin, surrounded by savannah on borders and afromontane forests on reliefs. Composition and distribution of vegetation indicate a decrease in monsoon activity and the strengthening of the precipitation front in the center of the basin. Interglacial phases are characterized by rain forest expansion over Central Africa in response to a precipitation enhancement associated with a northward shift of the rainfall front. Replacement of afromontane forest and marsh ecosystems by savannah then lowland pioneering, warm-temperate and rain forests characterized glacial/interglacial transitions. This succession suggests the increasing influence of at least two climatic parameters: the water availability and temperature and/or CO2 fluctuation. Spectral analysis applied to vegetation groups evidences the forcing of insolation, mainly driven by precession, on the West African monsoon system. Sub

  4. Global monsoon in a geological perspective

    Institute of Scientific and Technical Information of China (English)

    WANG PinXian

    2009-01-01

    Monsoon is now considered as a global system rather than regional phenomena only. For over 300 years, monsoon has been viewed as a gigantic land-sea breeze, but now satellite and conventional observations support an alternative hypothesis which considers monsoon as a manifestation of sea-sonal migration of the intertropical convergence zone (ITCZ) and, hence, a climate system of the global scale. As a low-latitude climate system, monsoon exists over all continents but Antarctica, and through all the geological history at least since the Phenorozoic. The time is ripe for systematical studies of monsoon variations in space and time.As evidenced by the geological records, the global monsoon is controlled by the Wilson cycle on the tectonic time scale (106-108a). A "Mega-continent" produces "Mega-monsoon", and its breakdown leads to weakening of the monsoon Intensity. On the time scales of 104-105 a, the global monsoon displays the precessional cycles of~20 ka and eccentricity cycles of 100- and 400-ka, i.e. the orbital cycles. On the time scales of 103 a and below, the global monsoon intensity is modulated by solar cy-cles and other factors. The cyclicity of global monsoon represents one of the fundamental factors re-sponsible for variations in the Earth surface system as well as for the environmental changes of the human society. The 400-ka long eccentricity cycles of the global monsoon is likened to "heartbeat" of the Earth system, and the precession cycle of the global monsoon was responsible for the collapse of several Asian and African ancient cultures at~4000 years ago, whereas the Solar cycles led to the de-mise of the Maya civilization about a thousand years ago. Therefore, paleoclimatology should be fo-cused not only on the high-latitude processes centered at ice cap variations, but also on the low-latitude processes such as monsoons, as the latter are much more common in the geological history compared to the glaciations.

  5. Monsoons, history of

    Digital Repository Service at National Institute of Oceanography (India)

    Niitsuma, N.; Naidu, P.D.

    The evolution of the Asian monsoon started at around 9.5 Ma, in response to the uplift of the Himalayas. The monsoonal intensity reached its maximum at around 5 Ma, and from that time the associated easterly trade winds caused intense upwelling...

  6. Sedimentary characteristics of terrigenous debris at site MD05-2905 in the northeastern part of the South China Sea since 36 ka and evolution of the East Asian monsoon

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Sediments with high sedimentation rate at site MD05-2905 in the Northeastern slope of the South China Sea provide unique materials for a high-resolution study on the paleoenvironment.Based on precise dating of AMS 14C,grain size analysis of terrigenous debris at core MD05-2905 was conducted after organic matter,biological carbonate and biogenic opal were removed.The results show that 15.5-63.5 μm coarse grain size ingredients may indicate East Asian winter monsoon changes and that 2-9 μm fine grain size ingredients may be used as a proxy of evolution of the East Asian summer monsoon.The results of grain size analysis,which suggest East Asian monsoon intensity,reveal that a winter monsoon dominated the glacial regime and a summer monsoon dominated the Holocene regime.It was also shown that the summer monsoon increased gradually,experienced several abrupt changes and reached a culmination in the early Holocene (11200-8500 a B.P.) since 36 ka.Controlled by precession periodicity,it may be related with the amount of solar radiation at the highest stage,which needs further study.

  7. Glacier Sensitivity to Climate Change in the Monsoonal Himalaya: Past, Present, and Future

    Science.gov (United States)

    Rupper, S.; Maurer, J.; Schaefer, J. M.; Cook, E. R.; Putnam, A. E.; Krusic, P.; Smith, R. G.

    2013-12-01

    Glaciers are particularly sensitive to climate change, making them vulnerable elements of the environment. Of potential concern for societies is the rapid glacier retreat of Himalayan glaciers. However, the temporally short and spatially sparse instrumental records of climate, and arguably shorter and sparser glacier records, make it extremely difficult to quantify glacier sensitivity to climatic change or to place recent glacier changes into a longer, historical context. Here we address many of these issues by quantifying the glacier-climate sensitivity in the Bhutanese Himalaya over the past 800 years using a combination of remote sensing data, paleoclimate data, glacier modeling, and glacial geochronology. Bhutan is chosen for two key reasons. First, Bhutan exemplifies an area where little data on glacier changes are available and where it is logistically difficult to obtain field-based studies, a common problem for many regions of the Himalayas. Thus the methods developed here will be directly applicable to other regions. Second, glaciers in Bhutan, just as neighboring glaciers in India, Nepal, and Southwest China, sit in the bulls-eye of high snow accumulation glaciers. Sensitivity tests using a surface energy- and mass-balance model show that high accumulation regions are extremely temperature-sensitive. Therefore, Bhutan's glaciers form a highly suitable natural laboratory to investigate glacier sensitivity and response to temperature change in the monsoonal Himalaya. In this study, we map Bhutan glacierized area and volume changes over the past forty years, and show significant changes and rapid retreat of these glaciers over this period of time. In addition, we map the former glacier extents for key glacierized regions of Bhutan, and produce a 10Be chronology for glacier fluctuations for one region. Finally, we model the glacierized changes over the past 800 years using Bhutan tree-ring temperature reconstructions as climate input. Our results show that

  8. Assessing the Capabilities of Three Regional Climate Models over CORDEX Africa in Simulating West African Summer Monsoon Precipitation

    OpenAIRE

    Akinsanola, A. A.; K. O. Ogunjobi; Gbode, I. E.; Ajayi, V. O.

    2015-01-01

    This study evaluates the ability of three Regional Climate Models (RCMs) used in Coordinated Regional Climate Downscaling Experiment (CORDEX) to simulate the characteristics of rainfall pattern during the West Africa Summer Monsoon from 1998 to 2008. The seasonal climatology, annual rainfall cycles, and wind fields of the RCMs output were assessed over three homogenous subregions and validated using precipitation data from eighty-one (81) ground observation stations and TRMM satellite data. F...

  9. Emergent properties of climate-vegetation feedbacks in the North American Monsoon Macrosystem

    Science.gov (United States)

    Mathias, A.; Niu, G.; Zeng, X.

    2012-12-01

    The ability of ecosystems to adapt naturally to climate change and associated disturbances (e.g. wildfires, spread of invasive species) is greatly affected by the stability of feedback interactions between climate and vegetation. In order to study climate-vegetation interactions, such as CO2 and H2O exchange in the North American Monsoon System (NAMS), we plan to couple a community land surface model (NoahMP or CLM) used in regional climate models (WRF) with an individual based, spatially explicit vegetation model (ECOTONE). Individual based modeling makes it possible to link individual plant traits with properties of plant communities. Community properties, such as species composition and species distribution arise from dynamic interactions of individual plants with each other, and with their environment. Plants interact with each other through intra- and interspecific competition for resources (H2O, nitrogen), and the outcome of these interactions depends on the properties of the plant community and the environment itself. In turn, the environment is affected by the resulting change in community structure, which may have an impact on the drivers of climate change. First, we performed sensitivity tests of ECOTONE to assess its ability to reproduce vegetation distribution in the NAMS. We compared the land surface model and ECOTONE with regard to their capability to accurately simulate soil moisture, CO2 flux and above ground biomass. For evaluating the models we used the eddy-correlation sensible and latent heat fluxes, CO2 flux and observations of other climate and environmental variables (e.g. soil temperature and moisture) from the Santa Rita experimental range. The model intercomparison helped us understand the advantages and disadvantages of each model, providing us guidance for coupling the community land surface model (NoahMP or CLM) with ECOTONE.

  10. A major reorganization of Asian climate regime by the early Miocene

    OpenAIRE

    Z. T. Guo; Sun, B; Z. S. Zhang; Peng, S. Z.; G. Q. Xiao; Ge, J. Y.; Q. Z. Hao; Qiao, Y. S.; M. Y. Liang; Liu, J F; Q. Z. Yin; Wei, J. J.

    2008-01-01

    The global climate system has experienced a series of drastic changes during the Cenozoic. These include the climate transformation in Asia, from a zonal pattern to a monsoon-dominant pattern, the disappearance of subtropical aridity related to a planetary circulation system and the onset of inland deserts in central Asia. Despite of the major advances in the last two decades in characterizing and understanding these climate phenomena, disagreements persi...

  11. Impact of modified soil thermal characteristic on the simulated monsoon climate over south Asia

    Indian Academy of Sciences (India)

    Pankaj Kumar; Ralf Podzun; Stefan Hagemann; Daniela Jacob

    2014-02-01

    In the present study, the influence of soil thermal characteristics (STC) on the simulated monsoon climate over south Asia is analyzed. The study was motivated by a common warm temperature bias over the plains of northern India that has been noticed in several global and regional climate models. To address this warm bias and its relation to STC, two sensitivity experiments have been performed with the regional climate model REMO of the Max Planck Institute for Meteorology. The control experiment uses the standard soil thermal characteristic of the model that corresponds to a moist soil. The second experiment uses modified STC that characterize a dry soil, which is more representative of the considered region, as a large part of the region has arid, semi-arid or subtropical summer wet conditions. Both experiments were conducted over 20 years using re-analysis data as lateral boundary conditions. Results show that using the modified STC the predominant regional warm bias has reduced substantially, leading to a better and more realistic surface temperature compared to observations over south Asia. Although, the magnitude of bias has reduced, the warm bias still exists over the region suggesting that other atmospheric and land surface processes also play a role, such as aerosols and irrigation. These need to be addressed adequately in future modeling studies over the region.

  12. Distress under Duress: The Relationship between Campus Climate and Depression in Asian American College Students.

    Science.gov (United States)

    Cress, Christine M.; Ikeda, Elaine K.

    2003-01-01

    Student perceptions of negative campus climate were predictive of Asian American students' depression levels in spite of students' entering proclivities toward depression and in spite of varying institutional types. Higher education institutions that are perceived by students to discriminate against individuals may put their Asian American…

  13. Seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in the southern South China Sea under the influence of the East Asian monsoon

    Directory of Open Access Journals (Sweden)

    L. Zhou

    2015-04-01

    Full Text Available To examine seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in oligotrophic tropical waters under the influence of seasonal reversing monsoon, dilution experiments were conducted during the summer 2009 (21 May to 9 June and winter 2010 (9 to 18 November in the southern South China Sea (SSCS. The results showed that environmental variables, phytoplankton biomass, phytoplankton growth rate (μ, microzooplankton grazing rate (m, and correlationship (coupling between the μ and m, but the microzooplankton grazing impact on phytoplankton (m/μ significantly varied between the two seasons. Higher relative preference index (RPI for and m on the larger-sized (>3 μm phytoplankton than pico-phytoplankton (m were significantly correlated with salinity and dissolved inorganic nutrients, which indicated that salient seasonal variations in the phytoplankton growth and microzooplankton grazing in the SSCS were closely related to the environmental variables under the influence of the East Asian monsoon. We propose that intermittent arrivals of the northeast winter monsoon could lead to the low μ and m, and the decoupling between the μ and m in the SSCS, through influencing nutrient supply to the surface water, and inducing surface seawater salinity decrease. The low m/μ (<50% on average indicates low remineralization of organic matter mediated by microzooplankton and the increased importance of the phytoplankton-mesozooplankton grazing pathway, and thus probably accounts for part of the high vertical biogenic particle fluxes in the prevailing periods of the monsoons in the SSCS. The size-selective grazing suggests that microzooplankton grazing contributes to the pico-phytoplankton dominance in the oligotrophic tropical waters such as that of the SSCS.

  14. Precipitation sensitivity to regional SST in a regional climate simulation during the West African monsoon for two dry years

    Energy Technology Data Exchange (ETDEWEB)

    Messager, C. [Laboratoire des Transferts en Hydrologie et Environnement - Unite Mixte de Recherche 5564 CNRS-UJF-INPG-IRD, BP53, 38041 Grenoble Cedex 9 (France); Gallee, H. [Laboratoire de Glaciologie et de Geophysique de l' Environnement - Unite propre FRE2192 CNRS, 54, rue Moliere, 38042 Saint Martin d' Heres Cedex (France); Brasseur, O. [Cellule Interregionale de l' Environnement, 10-11, Avenue des Arts, 1210 Bruxelles (Belgium)

    2004-03-01

    The influence on precipitation of regional sea surface temperature (SST) during a drought period of the West African monsoon is determined, using a regional climate model (RCM). The results from three simulations of two realistic dry years are compared. The first two experiments are initialised and nested respectively in 1983 and 1984 reanalysis data sets. The third experiment is a hybrid simulation of 1983 which is the same as the first experiment except that the SST field is the 1984 SST. Precipitation from the RCM is compared with several precipitation data sets and, as in observations, the RCM reasonably simulates the West African monsoon (seasonal cycle and monsoon sub-period) for the two different years. In particular, the model reproduces stage by stage the motion of the monsoon band well: installation phase, high rain period with abrupt northward shift of the rain band, and the retreat southward phase. Interannual variability and wet or dry tendencies are also represented. The most significant effect of SST is shown by the hybrid simulation, when the regional SST appears as a major factor in the seasonal and interannual monsoon precipitation regime over the African continent (up to 12 N) although this influence is modulated both by the surface conditions (soil and vegetation) and by the reanalysis flow introduced at the lateral boundaries. Dynamically, a warmer SST leads to a decrease in the magnitude of the African Easterly Jet and an increase in northward equivalent water content transport (from equator to 12 N). (orig.)

  15. 大气环流模式CAM4对亚洲气候的高分辨率模拟%A high resolution simulation on Asian climate by Community Atmosphere Model 4

    Institute of Scientific and Technical Information of China (English)

    沙莹莹; 石正国

    2016-01-01

    Background, aim, and scope Asian climate is characterized by the Indian monsoon, the East Asian monsoon and inland aridity, which is complex and sensitive to global change. The formation and variation of the climate system are correlated with lots of external forcings, such as solar radiation, land-sea distribution and ice sheet. The Tibetan Plateau is also demonstrated to have a vital effect on the Asian monsoons and inland aridity. Besides the large scale plateau, the meso- and small-scale mountains also show great inlfuence. These mountains not only affect the regional precipitation and circulation, but also inlfuence large scale weather systems such as monsoons and westerly jet lfow. The climate model CAM4 is with much higher resolution, it can relfect a more realistic topography and resolute those meso- and small-scale mountains to evaluate the climate effect of them.Materials and methods The precipitation data is a daily database from Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources of Japan. Its spatial resolution is 0.25°×0.25° from 1951 to 2007. Other meteorological variables such as sea level pressure, horizontal wind and temperature is from ERA-Interim reanalysis data of European Center for Medium-Range Weather Forecasts(ECMWF). The reanalysis data is from 1979 to present with a resolution of 0.75°×0.75°. Besides the meteorological data, the climate model we used to simulate is the CAM4. The CAM4 is the sixth generation of the NCAR atmospheric general climate model. The horizontal resolution is 0.47°×0.63° (latitude×longitude) in the simulation.Results With the apparently increased resolution of global climate model, the modeling result conducted by CAM4 with high resolution is compared with APHRO precipitation and ERA-Interim reanalysis data to evaluate whether and in what extent the simulating capability is improved. (1) The CAM4 with high resolution can well simulates the large scale

  16. Transient coupling relationships of the Holocene Australian monsoon

    Science.gov (United States)

    McRobie, F. H.; Stemler, T.; Wyrwoll, K.-H.

    2015-08-01

    The northwest Australian summer monsoon owes a notable degree of its interannual variability to interactions with other regional monsoon systems. Therefore, changes in the nature of these relationships may contribute to variability in monsoon strength over longer time scales. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Niño-related proxy records, have been qualitative, relying on 'curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9000 years. The resulting networks demonstrate the existence of coupling relationships between regional monsoon systems on millennial time scales, but also highlight the transient nature of teleconnections during this period. In the context of the northwest Australian summer monsoon, we recognise a shift in coupling relationships from strong interhemispheric links with East Asian and ITCZ-related proxy records in the mid-Holocene to significantly weaker coupling in the later Holocene. Although the identified links cannot explain the underlying physical processes leading to coupling between regional monsoon systems, this method provides a step towards understanding the role that changes in teleconnections play in millennial-to orbital-scale climate variability.

  17. Diatom response to climate forcing of a deep, alpine lake (Lugu Hu, Yunnan, SW China) during the Last Glacial Maximum and its implications for understanding regional monsoon variability

    Science.gov (United States)

    Wang, Qian; Yang, Xiangdong; Anderson, N. John; Zhang, Enlou; Li, Yanling

    2014-02-01

    The Yunnan Plateau of southwest China is strongly influenced by the Asian monsoon and is a critical area in terms of determining its development and variability since the Last Glacial Maximum. High-resolution diatom analysis of a 14C-dated sediment core retrieved from Lugu Lake, Yunnan provides a detailed history of palaeoenvironment changes from 30,000 to 10,000 cal. yr BP. A model of climate-diatom interactions (linking thermal stratification, ice cover and catchment-derived nutrients) is proposed to explain the observed changes. Prior to 24,500 cal. yr BP the dominance of the planktonic Cyclotella rhomboideo-elliptica indicates a period of stable stratification and low nutrient levels, with a moderate change of temperature and precipitation in the southwest monsoon region. During the LGM (24,500-14,500 cal. yr BP), the loss of the planktonic diatoms and a switch to small Fragilaria spp. suggest an altered thermal regime in the lake (i.e. weaker stratification and possibly ice cover). From ˜18,000 cal. yr BP, the expansion of planktonic taxa (Stephanodiscus and the Asterionella formosa) and increased %TOC are indicative of increased nutrient availability reflecting altered vegetation and soil processes due to rising regional temperatures. After 14,500 cal. yr BP, a rapid reversal to dominance by planktonic diatoms indicates a further increase in temperature and continued development of catchment vegetation and soils. The abrupt changes in diatom species composition around 24,500 and 14,500 cal. yr BP suggest that the ecological status of the lake exceeded limnological thresholds. Interestingly, however, the Younger Dryas event is not clearly recognizable in either the diatom or pollen records in the Lugu Lake sediment record. In a partial redundancy analysis, 44.2% of the variability in the total diatom assemblages in the period 30,000-10,000 cal. yr BP was accounted for by changes in summer solar radiation. The relationships between the diatom assemblages and

  18. Temporal dynamics of precipitation in an extreme mid-latitude monsoonal climate

    Science.gov (United States)

    Grigorieva, E. A.; de Freitas, C. R.

    2014-04-01

    Trends of precipitation over the twentieth century are examined by a variety of methods to more fully describe how precipitation has changed in the Russian Far East. Data used are considered to represent conditions of the extreme monsoonal climate of the high-to-mid-latitude climate of the Russian Far East region for the period 1911 to 2005. The study examines within-year characteristics of the 95-year time series. The results show variability of precipitation is high in all months, but especially so during the cold season. Trends in the data indicate that both the wettest and driest months of the year are getting wetter. There are some distinct shifts in the trend patterns. Most noticeable is a shift from positive trends to negative trends. Overall, the results show the highest twentieth century precipitation in the early 1960s and in the late 1970s, with a general decrease since the mid-1980s. This differs from trends and means for Russia as a whole. The results also show standard normals to be different from a complete record of monthly precipitation data. Further, it may not enough to use a limited period times series such as a 30-year normal to represent a steady average for a year or a season, as the mean changes through time; in particular, for a steady cold season, mean one should use the full period.

  19. Role of atmospheric heating over the South China Sea and western Pacific regions in modulating Asian summer climate under the global warming background

    Science.gov (United States)

    He, Bian; Yang, Song; Li, Zhenning

    2016-05-01

    The response of monsoon precipitation to global warming, which is one of the most significant climate change signals at the earth's surface, exhibits very distinct regional features, especially over the South China Sea (SCS) and adjacent regions in boreal summer. To understand the possible atmospheric dynamics in these specific regions under the global warming background, changes in atmospheric heating and their possible influences on Asian summer climate are investigated by both observational diagnosis and numerical simulations. Results indicate that heating in the middle troposphere has intensified in the SCS and western Pacific regions in boreal summer, accompanied by increased precipitation, cloud cover, and lower-tropospheric convergence and decreased sea level pressure. Sensitivity experiments show that middle and upper tropospheric heating causes an east-west feedback pattern between SCS and western Pacific and continental South Asia, which strengthens the South Asian High in the upper troposphere and moist convergence in the lower troposphere, consequently forcing a descending motion and adiabatic warming over continental South Asia. When air-sea interaction is considered, the simulation results are overall more similar to observations, and in particular the bias of precipitation over the Indian Ocean simulated by AGCMs has been reduced. The result highlights the important role of air-sea interaction in understanding the changes in Asian climate.

  20. Bias reduction in decadal predictions of West African monsoon rainfall using regional climate models

    Science.gov (United States)

    Paxian, A.; Sein, D.; Panitz, H.-J.; Warscher, M.; Breil, M.; Engel, T.; Tödter, J.; Krause, A.; Cabos Narvaez, W. D.; Fink, A. H.; Ahrens, B.; Kunstmann, H.; Jacob, D.; Paeth, H.

    2016-02-01

    The West African monsoon rainfall is essential for regional food production, and decadal predictions are necessary for policy makers and farmers. However, predictions with global climate models reveal precipitation biases. This study addresses the hypotheses that global prediction biases can be reduced by dynamical downscaling with a multimodel ensemble of three regional climate models (RCMs), a RCM coupled to a global ocean model and a RCM applying more realistic soil initialization and boundary conditions, i.e., aerosols, sea surface temperatures (SSTs), vegetation, and land cover. Numerous RCM predictions have been performed with REMO, COSMO-CLM (CCLM), and Weather Research and Forecasting (WRF) in various versions and for different decades. Global predictions reveal typical positive and negative biases over the Guinea Coast and the Sahel, respectively, related to a southward shifted Intertropical Convergence Zone (ITCZ) and a positive tropical Atlantic SST bias. These rainfall biases are reduced by some regional predictions in the Sahel but aggravated by all RCMs over the Guinea Coast, resulting from the inherited SST bias, increased westerlies and evaporation over the tropical Atlantic and shifted African easterly waves. The coupled regional predictions simulate high-resolution atmosphere-ocean interactions strongly improving the SST bias, the ITCZ shift and the Guinea Coast and Central Sahel precipitation biases. Some added values in rainfall bias are found for more realistic SST and land cover boundary conditions over the Guinea Coast and improved vegetation in the Central Sahel. Thus, the ability of RCMs and improved boundary conditions to reduce rainfall biases for climate impact research depends on the considered West African region.

  1. The verification of millennial-scale monsoon water vapor transport channel in northwest China

    Science.gov (United States)

    Li, Yu; Zhang, Chengqi; Wang, Yue

    2016-05-01

    Long-term changes of the Asian summer monsoon water vapor transport play a pivotal role in the variability of monsoon precipitation. Paleo-climate simulations have shown that there is an important monsoon vapor transport channel in western China. Previous studies mostly focused on the correlation between monsoon precipitation and intensity. Little research has been done on the verification of the water vapor channel. Compared with speleothem and lacustrine systems, the hydrological cycle of land surface sediments is more directly related to the monsoon water vapor. In this study, we used carbonate δ18O and organic matter δ13C of the surface eolian sediments from the piedmont of the northern Qilian Mountains to verify the monsoon water vapor on the Holocene millennial-scale. Two surface sedimentary sections were selected to study paleo-monsoon water vapor transport. Proxy data, including carbonate δ18O and organic matter δ13C of surface eolian sediments, as well as total organic matter and carbonate content were obtained from the two eolian sections. We also synthesized transient simulations of the CCSM3 and the Kiel climate models. The PMIP 3.0 project and TRACE isotopic simulations were also compared with the reconstructed monsoon water vapor transport. Our findings indicate that the strength of the Holocene Asian summer monsoon is consistent with the water vapor transport in western China that has significant impacts to long-term monsoon precipitation in northern China. This study verifies a significant millennial-scale correlation between the monsoon strength and monsoon water vapor transport intensity along the eastern Qinghai-Tibet Plateau.

  2. SUNYA Regional Climate Model Simulations of East Asia Summer Monsoon: Effects of Cloud Vertical Structure on the Surface Energy Balance

    OpenAIRE

    Wei Gong and Wei-Chyung Wang

    2007-01-01

    We used the State University of New York at Albany (SUNYA) regional climate model to study the effect of cloud vertical distribution in affecting the surface energy balance of the East Asia summer monsoon (EASM). Simulations were conducted for the summers of 1988 and 1989, during which large contrast in the intra-seasonal cloud radiative forcing (CRF) was observed at the top of the atmosphere. The model results indicate that both the high and low clouds are persistent throughout the summe...

  3. Latitudinal distributions of activities in atmospheric aerosols, deposition fluxes, and soil inventories of 7Be in the East Asian monsoon zone

    International Nuclear Information System (INIS)

    Activities of atmospheric aerosols, bulk deposition fluxes, and undisturbed soil inventories of 7Be were investigated in China's East Asian monsoon zone at various latitudes ranging from 23.8°N to 43.5°N. The annual latitudinal distributions of 7Be concentrations in aerosols follow a distribution pattern which looks similar to a normal distribution with the maxima occurring in the mid-latitude region. Simultaneous measurements of 7Be at various latitudes suggest that atmospheric circulation may play an important role in the latitudinal distributions of 7Be in surface air. Latitude and wet precipitation are the main factors controlling the bulk 7Be depositional fluxes. Significant seasonal variations in 7Be depositional fluxes in Beijing, a mid-latitude city, were observed with the highest flux in summer and the lowest in winter, whereas less seasonality were found in the high- and the low-latitude cities. The highest 7Be inventory in undisturbed soils in summer also occurred at a mid-latitudinal area in the East Asian monsoon zone. Precipitation is the main factor controlling the 7Be soil inventory in Qingdao with the highest values occurring in autumn followed by summer. - Highlights: • 7Be in atmospheric aerosols, rainfall, and soils were measured at different latitudes. • The annual maxima of 7Be concentrations in aerosols occurred at ∼40°N. • Spring and autumn are seasons of high atmospheric 7Be with maxima at 30°N. • The annual maxima of 7Be deposition fluxes occurred at ∼40°N. • High rainfall in summer is the main cause of higher 7Be soil inventory

  4. The zonal movement of the Indian-East Asian summer monsoon interface in relation to the land-sea thermal contrast anomaly over East Asia

    Science.gov (United States)

    Tao, Yun; Cao, Jie; Lan, Guangdong; Su, Qin

    2016-05-01

    Based on atmospheric circulation reanalysis, global gridded precipitation, and outgoing longwave radiation datasets, this study reveals the physical process through which the land-sea thermal contrast over East Asia interrelates with the variability of the interface between the Indian summer monsoon and East Asian summer monsoon (IIE). The results indicate that the release of latent heating exerted by the low-frequency variability of anomalous land-sea thermal contrast is one of the most important physical processes correlating with the zonal movement of the IIE, in which the release of latent heating over eastern East Asia makes the greatest contribution. When a lower apparent moisture sink occurs over the South China Sea but a higher one over southern China, an anomalously positive land-sea thermal contrast is formed. An anomalous convergent zone in relation to the positive land-sea thermal contrast, located in the eastern part of the IIE, will favor the IIE to move more eastward than normal, and vice versa. An anomalous divergent zone located in the eastern part of the IIE will benefit the IIE to shift more westward than normal. Experiments using a linear baroclinic model confirm the physical processes revealed by the observational analysis.

  5. Simulation of South Asian aerosols for regional climate studies

    Science.gov (United States)

    Nair, Vijayakumar S.; Solmon, Fabien; Giorgi, Filippo; Mariotti, Laura; Babu, S. Suresh; Moorthy, K. Krishna

    2012-02-01

    Extensive intercomparison of columnar and near-surface aerosols, simulated over the South Asian domain using the aerosol module included in the regional climate model (RegCM4) of the Abdus Salam International Centre for Theoretical Physics (ICTP) have been carried out using ground-based network of Sun/sky Aerosol Robotic Network (AERONET) radiometers, satellite sensors such as Moderate Resolution Imaging Spectroradiometer (MODIS) and Multiangle Imaging Spectroradiometer (MISR), and ground-based black carbon (BC) measurements made at Aerosol Radiative Forcing over India (ARFI) network stations. In general, RegCM4 simulations reproduced the spatial and seasonal characteristics of aerosol optical depth over South Asia reasonably well, particularly over west Asia, where mineral dust is a major contributor to the total aerosol loading. In contrast, RegCM4 simulations drastically underestimated the BC mass concentrations over most of the stations, by a factor of 2 to 5, with a large spatial variability. Seasonally, the discrepancy between the measured and simulated BC tended to be higher during winter and periods when the atmospheric boundary layer is convectively stable (such as nighttime and early mornings), while during summer season and during periods when the boundary layer is convectively unstable (daytime) the discrepancies were much lower, with the noontime values agreeing very closely with the observations. A detailed analysis revealed that the model does not reproduce the nocturnal high in BC, observed at most of the Indian sites especially during winter, because of the excessive vertical transport of aerosols under stable boundary layer conditions. As far as the vertical distribution was concerned, the simulated vertical profiles of BC agreed well with airborne measurements during daytime. This comprehensive validation exercise reveals the strengths and weaknesses of the model in simulating the spatial and temporal heterogeneities of the aerosol fields over

  6. Rainfall variability, climate change and regionalization in the African monsoon region

    International Nuclear Information System (INIS)

    This summary recalls some results at the end of the AMMA international experiment (2003-2010) in terms of variability of the African monsoon at the intra-seasonal to multi-decadal scales and of climate prospective. The results confirmed the weight of surface temperatures and marine tele-connections for inter-annual and decadal fluctuations and stressed the importance of atmospheric variability. They also described the dominant modes of intra-seasonal variability as their interactions with the surface. Several hypotheses involving memory effects related to soil water and vegetation, particularly in boreal spring and autumn have also been made. Prospective analysis from model output suggests rainfall surplus around 2050 over the Eastern-central Sahel and relative deficit to the West. Phase 2 of AMMA (2010-2020) will focus more on aspects that have a high social impact in direct collaboration with meteorological services predictability, prediction scores, operational indicators, evaluation of the part of anthropogenic forcing in the current and future variations. (authors)

  7. Bias correction of the CCSM4 for improved regional climate modeling of the North American monsoon

    Science.gov (United States)

    Meyer, Jonathan D. D.; Jin, Jiming

    2016-05-01

    This study investigates how a form of bias correction using linear regression improves the limitations of the community climate system model (CCSM) version 4 when it is dynamically downscaled with the Weather Research and Forecasting (WRF) model for the North American monsoon (NAM). Long-term biases in the CCSM dataset were removed using the climate forecast system reanalysis (CFSR) dataset as a baseline, from which a physically consistent set of bias-corrected variables were created. To quantitatively identify the effects of CCSM data on the NAM simulations, three 32-year climatologies were generated with WRF driven by (1) CFSR, (2) original CCSM, and (3) bias-corrected CCSM data. The WRF-CFSR simulations serve as a baseline for comparison. With the bias correction, onset dates simulated by WRF bias-corrected CCSM data were generally within a week of the WRF-CFSR climatology, while WRF using the original CCSM data occur up to 3-4 weeks too early over the core of the NAM. Additionally, bias-correction led to improvements in the mature phase of the NAM, reducing August root-mean-square-error values by 26 % over the core of the NAM and 36 % over the northern periphery. Comparison of the CFSR and the bias-corrected CCSM climatologies showed marked consistency in the general evolution of the NAM system. Dry biases in the NAM precipitation existed in each climatology with the original CCSM performing the poorest when compared to observations. The poor performance of the original CCSM simulations stem from biases in the thermodynamic profile supplied to the model through lateral boundary conditions. Bias-correction improved the excessive capping inversions, and mid-level mixing ratio dry biases (2-3 g kg-1) present in the CCSM simulations. Improvements in the bias-corrected CCSM data resulted in greater convective activity and a more representative seasonal distribution of precipitation.

  8. Temporal derivative of Total Solar Irradiance and anomalous Indian summer monsoon: An empirical evidence for a Sun–climate connection

    Digital Repository Service at National Institute of Oceanography (India)

    Agnihotri, R.; Dutta, K.; Soon, W.

    , 1309–1321. Le Mou¨el, J.-L., Courtillot, V., Blanter, E., Shnirman, M., 2008. Evidence for a solar signature in 20th-century temperature data from the USA and Europe. Comptes Rendus Geoscience 340, 421–430. Lean, J., 2000. Evolution of the Sun’s... on global climate through changes in precipitation distribution, it is manda- tory to understand the magnitude and pattern of natural variability in Indian monsoonal precipitation on interdecadal and longer (Shaviv, 2008) that result in the observed climate...

  9. Inter-comparison of deep convection over the Tibetan Plateau-Asian Monsoon Region and subtropical North America in boreal summer using CloudSat/CALIPSO data

    Science.gov (United States)

    Luo, Y.; Zhang, R.; Qian, W.; Luo, Z.

    2010-12-01

    Deep convection at the Tibetan Plateau-Southern Asian Monsoon Region (TP-SAMR) is analyzed using CloudSat and CALIPSO data for the boreal summer season (June-August) from 2006 to 2009. Three sub-regions - the Tibetan Plateau (TP), southern slope of the Plateau (PSS), and southern Asian monsoon region (SAMR) - are defined and deep convection properties are compared among these sub-regions. To cast them in a broader context, we also bring in four additional regions that bear some similarity to the TP-SAMR: East Asia (EA), tropical northwestern Pacific (NWP), west and east North America (WNA, ENA). The principal findings are as follows: 1) Compared to the other two sub-regions of the TP-SAMR, deep convection at the TP is shallower, less frequent, and embedded in smaller-size convection systems, but the cloud tops are more densely packed. These characteristics of deep convection at the TP are closely related to the significantly lower level of neutral buoyancy (LNB) and much drier atmosphere. 2) In a broader context where all seven regions are brought together, deep convection at the two tropical regions (NWP and SAMR; mostly over ocean) is similar in many regards. Similar conclusion can be drawn among the four subtropical continental regions (TP, EA, WNA, and ENA). However, tropical oceanic and subtropical land regions present some significant contrasts: deep convection in the latter region occurs less frequently, has lower cloud tops but comparable or slightly higher tops of large radar echo, and is embedded in smaller systems. The cloud tops of the subtropical land regions are generally more densely packed. Hence, the difference between TP and SAMR is more of a general contrast between subtropical land regions and tropical oceanic regions during the boreal summer. 3) Deep convection at the PSS possesses some uniqueness of its own because of the distinctive terrain (slopes) and moist low-level monsoon flow. 4) Results from comparison between the daytime and the

  10. Impact of GCM boundary forcing on regional climate modeling of West African summer monsoon precipitation and circulation features

    Science.gov (United States)

    Kebe, Ibourahima; Sylla, Mouhamadou Bamba; Omotosho, Jerome Adebayo; Nikiema, Pinghouinde Michel; Gibba, Peter; Giorgi, Filippo

    2016-05-01

    In this study, the latest version of the International Centre for Theoretical Physics Regional Climate Model (RegCM4) driven by three CMIP5 Global Climate Models (GCMs) is used at 25 km grid spacing over West Africa to investigate the impact of lateral boundary forcings on the simulation of monsoon precipitation and its relationship with regional circulation features. We find that the RegCM4 experiments along with their multimodel ensemble generally reproduce the location of the main precipitation characteristics over the region and improve upon the corresponding driving GCMs. However, the provision of different forcing boundary conditions leads to substantially different precipitation magnitudes and spatial patterns. For instance, while RegCM4 nested within GFDL-ESM-2M and HadGEM2-ES exhibits some underestimations of precipitation and an excessively narrow Intertropical Convergence Zone, the MPI-ESM-MR driven run produces precipitation spatial distribution and magnitudes more similar to observations. Such a superior performance originates from a much better simulation of the interactions between baroclinicity, temperature gradient and African Easterly Jet along with an improved connection between the Isentropic Potential Vorticity, its gradient and the African Easterly Waves dynamics. We conclude that a good performing GCM in terms of monsoon dynamical features (in this case MPI-ESM-MR) is needed to drive RCMs in order to achieve a better representation of the West Africa summer monsoon precipitation.

  11. Sensitivity of the African and Asian Monsoons to Mid-Holocene Insolation and Data-Inferred Surface Changes.

    Science.gov (United States)

    Texier, Delphine; de Noblet, Nathalie; Braconnot, Pascale

    2000-01-01

    Orbital forcing alone is not sufficient to explain the massive northward penetration of monsoon rains in Africa shown by data during the mid-Holocene (6000 yr ago). Feedbacks associated with changes in SSTs and land surface cover may be necessary to produce a sufficient increase in the monsoon. A step toward a better understanding of the respective role of oceans and land surfaces is to design sensitivity studies with prescribed forcings, inferred from observations. In the first study, SSTs are lowered in the upwelling regions offshore of West Africa and Somalia, and increased in the Bay of Bengal and South China Sea. In the second simulation, the modern Sahara desert is replaced by a combination of xerophytic woods/scrub and grassland.In both cases the amount of water vapor advected from oceanic sources is increased north of 10°N in Africa in response to the increased land-sea temperature contrast, thereby enhancing rainfall. But the magnitude of the simulated changes is much larger when land surface is modified. The lower albedo (compared to desert) increases the amount of radiation absorbed by the surface in northern Africa and warms it up, and the larger roughness length increases both the sensible and latent heat fluxes. Moreover, vegetation is more efficient in recycling water than a bare soil, and the release of latent heat in the atmosphere increases convection, which in turn helps maintain the onshore oceanic advection. The monsoon season is then lengthened by 1-2 months compared to all other simulations reported in the paper.The intensity of monsoon rains is also modified in Asia in both sensitivity experiments. Warmer SSTs in the Bay of Bengal and South China Sea reduce the land-sea contrast and therefore the inland penetration of monsoon rains. Changes in the position of the main large-scale convergence area in the case of a green Sahara enhances the precipitation in India.Changes are also discussed in terms of atmospheric circulation. For example, the

  12. Decoupled warming and monsoon precipitation in East Asia over the last deglaciation

    NARCIS (Netherlands)

    Peterse, F.; Prins, M.A.; Beets, C.J.; Troelstra, S.R.; Zheng, H.; Gu, Z.; Schouten, S.; Sinninghe Damsté, J.S.

    2011-01-01

    Our understanding of the continental climate development in East Asia is mainly based on loess–paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes (δ18O) of stalagmites from several Chinese caves. Based on these records, it is thought that East Asian Summer M

  13. The reconstructed Indonesian warm pool sea surface temperatures from tree rings and corals: Linkages to Asian monsoon drought and El Niño-Southern Oscillation

    Science.gov (United States)

    D'Arrigo, Rosanne; Wilson, Rob; Palmer, Jonathan; Krusic, Paul; Curtis, Ashley; Sakulich, John; Bijaksana, Satria; Zulaikah, Siti; Ngkoimani, La Ode; Tudhope, Alexander

    2006-09-01

    The west Pacific warm pool is the heat engine for the globe's climate system. Its vast moisture and heat exchange profoundly impact conditions in the tropics and higher latitudes. Here, September-November sea surface temperature (SST) variability is reconstructed for the warm pool region (15°S-5°N, 110-160°E) surrounding Indonesia using annually resolved teak ring width and coral δ18O records. The reconstruction dates from A.D. 1782-1992 and accounts for 52% of the SST variance over the most replicated period. Significant correlations are found with El Niño-Southern Oscillation (ENSO) and monsoon indices at interannual to decadal frequency bands. Negative reconstructed SST anomalies coincide with major volcanic eruptions, while other noteworthy extremes are at times synchronous with Indian and Indonesian monsoon drought, particularly during major warm ENSO episodes. While the reconstruction adds to the sparse network of proxy reconstructions available for the tropical Indo-Pacific, additional proxies are needed to clarify how warm pool dynamics have interacted with global climate in past centuries to millennia.

  14. FEATURES AND COMPARISONS OF THE QUASI-BIENNIAL VARIATIONS IN THE ASIA-PACIFIC MONSOON SUBSYSTEMS

    Institute of Scientific and Technical Information of China (English)

    ZHENG Bin; LI Chun-hui; LIN Ai-lan; GU De-jun

    2009-01-01

    The National Centers for Environmental Prediction (NCEP) reanalysis data Climate Diagnostics Center Merged Analysis of Precipitation (CMAP) results,and NOAA Extended Reconstructed Sea Surface Temperature (SST),have been utilized in this paper to study the quasi-biennial variations in Asia-Pacific monsoon subsystems and associated SST anomalies (SSTA) and wind anomalies. Four monsoon indices are computed fi,om NCEP/National Center for Atmospheric Research (NCAR) reanalysis to represent the South Asian monsoon (SAM),South China Sea summer monsoon (SCSSM),Western North Pacific monsoon (WNPM) and East Asian monsoon (EAM),respectively. The quasi-biennial periods are very significant in Asia-Pacific monsoons (as discovered by power spectrum analysis),and for SAM and EAM---with moderate effects by EI Ni(n)o-Southern Oscillation (ENSO)---the quasi-biennial periods are the most important factor. For SCSSM and WNPM (once again due to the effects of ENSO),the quasi-biennial periods are of secondary durations. There are obvious interdecadal variations in the quasi-biennial modes of the Asia-Pacific monsoon,so in the negative phase the biennial modes will not be significant or outstanding. The wind anomalies and SSTA associated with the biennial modes are very different in the SAM. WNPM and EAM regions. Since the WNPM and SCSSM are very similar in the biennial modes,they can be combined into one subsystem,called SCS/WNPM.

  15. Evolution of Vertical Moist Thermodynamic Structure Associated with the Indian Summer Monsoon 2010 in a Regional Climate Model

    Science.gov (United States)

    Raju, A.; Parekh, Anant; Gnanaseelan, C.

    2014-07-01

    The 2010 boreal summer marked a worldwide abnormal climate. An unprecedented heat wave struck East Asia in July and August 2010. In addition to this, the tropical Indian Ocean was abnormally warm during the summer of 2010. Several heavy rainfall events and associated floods were also reported in the Indian monsoon region. During the season, the monsoon trough (an east-west elongated area of low pressure) was mostly located south of its normal position and monsoon low pressure systems moved south of their normal tracks. This resulted in an uneven spatial distribution with above-normal rainfall over peninsular and Northwest India, and deficient rainfall over central and northeastern parts of India, thus prediction (and simulation) of such anomalous climatic summer season is important. In this context, evolution of vertical moist thermodynamic structure associated with Indian summer monsoon 2010 is studied using regional climate model, reanalysis and satellite observations. This synergised approach is the first of its kind to the best of our knowledge. The model-simulated fields (pressure, temperature, winds and precipitation) are comparable with the respective in situ and reanalysis fields, both in intensity and geographical distribution. The correlation coefficient between model and observed precipitation is 0.5 and the root-mean-square error (RMSE) is 4.8 mm day-1. Inter-comparison of model-simulated fields with satellite observations reveals that the midtropospheric temperature [Water vapour mixing ratio (WVMR)] has RMSE of 0.5 K (1.6 g kg-1), whereas the surface temperature (WVMR) has RMSE of 3.4 K (2.2 g kg-1). Similarly, temporal evolution of vertical structure of temperature with rainfall over central Indian region reveals that the baroclinic nature of monsoon is simulated by the model. The midtropospheric warming associated with rainfall is captured by the model, whereas the model failed to capture the surface response to high and low rainfall events. The

  16. Reconstruction of the Holocene monsoon climate variability in the Arabian Sea based on alkenone sea surface temperature, primary productivity and denitrification proxies

    OpenAIRE

    Böll, A.

    2014-01-01

    The Indian monsoon climate influences large parts of the world’s population. But relatively little is known about its decadal to centennial scale variation at time scales of societal relevance. The aim of this study was to reconstruct the Holocene history of summer and winter monsoon variability in high-resolution by analyzing sediment cores from different locations in the Arabian Sea (northern Indian Ocean). Oceanic properties and biogeochemical processes in the Arabian Sea, such as sea surf...

  17. Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951–2005 using a regional climate model

    OpenAIRE

    S. Halder; Saha, S K; Dirmeyer, P. A.; Chase, T N; Goswami, B. N.

    2015-01-01

    Daily moderate rainfall events, that constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 till 2005. Mean and extreme near surface daily temperature during the monsoon season have also increased by a maximum of 1–1.5 °C. Using simulations made with a high-resolution regional climate model (RegCM4) with prescribed vegetation cover of 1950 and 2005, it is demonstrated that part ...

  18. Applications of an Indian Ocean Observing System to Climate Impacts and Resource Predictions in Surrounding Countries in the Context of ENSO-Monsoon Teleconnections

    OpenAIRE

    Jury, M.; Gadgil, S; Meyers, G; Ragoonaden, S.; Reason, C.; Sribimawati, T.; Tangang, F.

    2000-01-01

    We explore the path between Indian Ocean observations and monsoon dynamics, the societal impacts of interannual climate variations and applications of resource predictions in southeastern Africa, the Mascarene Islands, India, southeast Asia and Australia. Recent progress in understanding ocean dynamics associated with SST variation is reviewed. The global El Niño-Southern Oscillation (ENSO) affects monsoon winds and ocean temperatures in a manner consistent with, but lagging, the ...

  19. Inverse correlation between ancient winter and summer monsoons in East Asia?

    Institute of Scientific and Technical Information of China (English)

    ZHOU BoTao; ZHAO Ping

    2009-01-01

    There is a scientific debate on the relationship between ancient winter and summer monsoons in East Asia. Some scholars think that East Asian winter and summer monsoons are anti-correlated, and oth-ers think not. For this reason, this study is motivated to assess their linkage from the paleoclimate simulation perspective, through analyzing the Last Glacial Maximum (LGM) and mid-Holocene (MH) climate simulated by CCSM3 model. Compared to the present climate, the Aleutian low is found to be deepened and the East Asian winter monsoon (EAWM) is stronger during the LGM winter. The Pacific high in summer is noticed to be weakened and the East Asian summer monsoon (EASM) is weaker at the LGM. During the MH, the Aleutian low and the Asian high in winter are intensified, and the Asian low and the Pacific high in summer are enhanced, indicating that the EAWM and EASM are both stronger than today. Therefore, the EAWM is not always negatively correlated to the EASM. Their relationship may be different at different geological stages. It can be obtained at least from the numerical simulation results that the EAWM and the EASM is negatively correlated during the cooling period, while positively correlated during the warming period.

  20. Influence of the Asian Monsoon on net ecosystem carbon exchange in two major plant functional types in Korea

    Directory of Open Access Journals (Sweden)

    H. Kwon

    2009-11-01

    Full Text Available Considering the feedback loops in radiation, temperature, and soil moisture with alterations in rainfall patterns, the influence of the changing monsoon on net ecosystem CO2 exchange can be critical to the estimation of carbon balance in Asia. In this paper, we examined the eddy covariance CO2 fluxes observed from 2004 to 2008 in two major plant functional types in KoFlux, i.e., the Gwangneung deciduous forest (GDK site and the Haenam farmland (HFK site. The objectives of the study were to (1 quantify the net ecosystem CO2 exchange (NEE, ecosystem respiration (RE, and gross primary production (GPP, (2 examine their interannual patterns, and (3 assess the mechanism for the coupling of carbon and water exchange associated with the summer monsoon. The GDK site, which had a maximum leaf area index (LAI of ~5, was on average a relatively weak carbon sink with NEE of −84 gC m−2 y−1, RE of 1028 gC m−2 y−1, and GPP of 1113 gC m−2 y−1. Despite about 20% larger GPP (of 1321 gC m−2 y−1 in comparison with the GDK site, the HFK site (with the maximum LAI of 3 to 4 was a weaker carbon sink with NEE of −58 gC m−2 y−1 because of greater RE of 1263 gC m−2 y−1. In both sites, the annual patterns of NEE and GPP had a striking "mid-season depression" each year with two distinctive peaks of different timing and magnitude, whereas RE did not. The mid-season depression at the GDK site occurred typically from early June to late August, coinciding with the season of summer monsoon when the solar radiation decreased substantially due to frequent rainfalls and cloudiness. At the HFK site, the mid-season depression began earlier in May and continued until the end of July due to land use management (e.g., crop rotation in addition to such disturbances as summer monsoon and typhoons

  1. Seasonal variability of chlorophyll-a and oceanographic conditions in Sabah waters in relation to Asian monsoon--a remote sensing study.

    Science.gov (United States)

    Abdul-Hadi, Alaa; Mansor, Shattri; Pradhan, Biswajeet; Tan, C K

    2013-05-01

    A study was conducted to investigate the influence of Asian monsoon on chlorophyll-a (Chl-a) content in Sabah waters and to identify the related oceanographic conditions that caused phytoplankton blooms at the eastern and western coasts of Sabah, Malaysia. A series of remote sensing measurements including surface Chl-a, sea surface temperature, sea surface height anomaly, wind speed, wind stress curl, and Ekman pumping were analyzed to study the oceanographic conditions that lead to large-scale nutrients enrichment in the surface layer. The results showed that the Chl-a content increased at the northwest coast from December to April due to strong northeasterly wind and coastal upwelling in Kota Kinabalu water. The southwest coast (Labuan water) maintained high concentrations throughout the year due to the effect of Padas River discharge during the rainy season and the changing direction of Baram River plume during the northeast monsoon (NEM). However, with the continuous supply of nutrients from the upwelling area, the high Chl-a batches were maintained at the offshore water off Labuan for a longer time during NEM. On the other side, the northeast coast illustrated a high Chl-a in Sandakan water during NEM, whereas the northern tip off Kudat did not show a pronounced change throughout the year. The southeast coast (Tawau water) was highly influenced by the direction of the surface water transport between the Sulu and Sulawesi Seas and the prevailing surface currents. The study demonstrates the presence of seasonal phytoplankton blooms in Sabah waters which will aid in forecasting the possible biological response and could further assist in marine resource managements. PMID:22930185

  2. Precise dating of East-Asian-Monsoon D/O events during 95―56 ka BP: Based on stalagmite data from Shanbao Cave at Shennongjia, China

    Institute of Scientific and Technical Information of China (English)

    XIA ZhiFeng; KONG XingGong; JIANG XiuYang; CHENG Hai

    2007-01-01

    Based on 23 U/Th analyses and 532 oxygen isotopic data, an averaged 80-a stalagmite oxygen isotopic composition series was established through 95 to 56 thousand years before present (ka BP) from two speleothems in Shanbao Cave, Shennongjia, central China. Shanbao Cave record (referred to as SB record) replicates well with Hulu Cave record, extending the characteristics of millennial oscillations in East-Asian-Summer-Monsoon (EASM) to the past 95 ka. The trend of the SB record generally follows mid-July solar insolation at 65°N, suggesting that mid-high northern latitude insolation, in the first order, controls changes of EASM intensity. Millennial oscillations of EASM recorded in the stalagmites are well related to the Greenland interstadials referred to as Dansgaard/Oeschger (D/O) events from 1 to 22, indicating that rapid ocean-atmosphere reorganization in North Atlantic has a remote effect in EASM. The well-dated D/O events by stalagmites probably provide an absolute calibration for chronologies of Greenland ice cores. The timings of D/O events in the SB record are different variously from those in Greenland ice cores. For D/O 19 and 20, the age offsets between the stalagmites' and the Greenland ice cores' record are significant, larger than the uncertainties of uranium-series dating. The two events in the SB record are younger than those in North GRIP time scale by 1―2 ka, and older than the counterparts in GISP2 by approximately 3―4 ka. A comparison between the SB and Brazil stalagmite record shows an anti-phase relation in millennial-scale monsoon precipitation between the two localities. This supports a mode for the coupled ocean-atmosphere "See-saw".

  3. Precise dating of East-Asian-Monsoon D/O events during 95―56 ka BP: Based on stalagmite data from Shanbao Cave at Shennongjia, China

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Based on 23 U/Th analyses and 532 oxygen isotopic data, an averaged 80-a stalagmite oxygen isotopic composition series was established through 95 to 56 thousand years before present (ka BP) from two speleothems in Shanbao Cave, Shennongjia, central China. Shanbao Cave record (referred to as SB record) replicates well with Hulu Cave record, extending the characteristics of millennial oscillations in East-Asian-Summer-Monsoon (EASM) to the past 95 ka. The trend of the SB record generally follows mid-July solar insolation at 65°N, suggesting that mid-high northern latitude insolation, in the first or- der, controls changes of EASM intensity. Millennial oscillations of EASM recorded in the stalagmites are well related to the Greenland interstadials referred to as Dansgaard/Oeschger (D/O) events from 1 to 22, indicating that rapid ocean-atmosphere reorganization in North Atlantic has a remote effect in EASM. The well-dated D/O events by stalagmites probably provide an absolute calibration for chro- nologies of Greenland ice cores. The timings of D/O events in the SB record are different variously from those in Greenland ice cores. For D/O 19 and 20, the age offsets between the stalagmites’ and the Greenland ice cores’ record are significant, larger than the uncertainties of uranium-series dating. The two events in the SB record are younger than those in North GRIP time scale by 1―2 ka, and older than the counterparts in GISP2 by approximately 3―4 ka. A comparison between the SB and Brazil stalag- mite record shows an anti-phase relation in millennial-scale monsoon precipitation between the two localities. This supports a mode for the coupled ocean-atmosphere "See-saw".

  4. Characteristics of a persistent "pool of inhibited cloudiness" and its genesis over the Bay of Bengal associated with the Asian summer monsoon

    Science.gov (United States)

    Nair, Anish Kumar M.; Rajeev, K.; Sijikumar, S.; Meenu, S.

    2011-07-01

    Using spatial and vertical distributions of clouds derived from multi-year spaceborne observations, this paper presents the characteristics of a significant "pool of inhibited cloudiness" covering an area of >106 km2 between 3-13° N and 77-90° E over the Bay of Bengal (BoB), persisting throughout the Asian summer monsoon season (ASM). Seasonal mean precipitation rate over the "pool" is vault-like structure at the "pool" with little cloudiness below ~7 km, indicating that this "pool" is almost fully contributed by the substantially reduced or near-absence of low- and middle-level clouds. This suggest the absence of convection in the "pool" region. Spaceborne scatterometer observations show divergence of surface wind at the "pool" and convergence at its surroundings, suggesting the existence of a mini-circulation embedded in the large-scale monsoon circulation. Reanalysis data shows a mini-circulation extending between the surface and ~3 km altitude, but its spatial structure does not match well with that inferred from the above observations. Sea surface at the south BoB during ASM is sufficiently warm to trigger convection, but is inhibited by the subsidence associated with the mini-circulation, resulting in the "pool". This mini-circulation might be a dynamical response of the atmosphere to the substantial spatial gradient of latent heating by large-scale cloudiness and precipitation at the vast and geographically fixed convective zones surrounding the "pool". Subsidence at the "pool" might contribute to the maintenance of convection at the above zones and be an important component of ASM that is overlooked hitherto.

  5. Coastal dunefields of south Brazil as a record of climatic changes in the South American Monsoon System

    Science.gov (United States)

    Mendes, Vinícius Ribau; Giannini, Paulo César Fonseca

    2015-10-01

    Southern Brazil coastal dunefields are undergoing a stabilization process that appears to be influenced by climate change. Although this process is relatively well known in the literature, the precise climatic mechanisms involved were not fully understood until now. Here, we propose a new method for integrating meteorological data with dunefield morphology analyses by remote sensing to better understand the impacts of recent climate change on dunefield dynamics. Based on this approach, three successive morphological phases were identified for the Santa Catarina central coast dunefields since 1938: (i) increased sand saturation; (ii) reduced sand saturation with consequent accelerated dune migration; and (iii) decelerated dune migration with trends of stabilization by the vegetation cover. For the coastal dunefields of southern Brazil, the stabilization process can be explained mechanistically by an increase in precipitation and decrease of wind power, both of which were correlated with the intensification of the South American Monsoon System.

  6. Regional Climate Model Sensitivity to Domain Size for the Simulation of the West African Summer Monsoon Rainfall

    OpenAIRE

    Browne, Nana A. K.; Sylla, Mouhamadou B.

    2012-01-01

    We use the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM3) to study the impact of different domain sizes on the simulation of the West African summer monsoon rainfall and circulation features. RegCM3 simulates drier conditions over the default domain (RegCM-D1) and its westward extension (RegCM-D2), much less dryness over the eastward extended domain (RegCM-D3) and excessive wetness in the domain extended northward into the extratropical regions (RegCM-D4)....

  7. Climate risk management in Central Asian agriculture. A situation analysis

    Energy Technology Data Exchange (ETDEWEB)

    Pawlowski, Ira

    2012-03-15

    The region of Central Asia, and in particularly the agricultural sector, is extremely vulnerable to climate change risks. The countries have started to develop adaptation strategies and climate risk management strategies, most of them described in the National Communications on the United Nations Framework Convention on Climate Change. These and other efforts are presented and commented in this paper.

  8. Tropical Indian Ocean response to the decay phase of El Niño in a coupled model and associated changes in south and east-Asian summer monsoon circulation and rainfall

    Science.gov (United States)

    Chowdary, Jasti S.; Parekh, Anant; Kakatkar, Rashmi; Gnanaseelan, C.; Srinivas, G.; Singh, Prem; Roxy, M. K.

    2016-08-01

    This study investigates the response of tropical Indian Ocean (TIO) sea surface temperature (SST) to El Niño decay phase and its impacts on South and East Asian summer monsoon in the National Centers for Environmental Prediction Climate Forecast System version 2 free run. The TIO basin-wide warming induced by El Niño at its peak phase (winter; DJF) and next spring (MAM + 1) are reasonably well captured by the model but with weak magnitude. This TIO basin-wide SST warming persists until summer (JJA + 1) and exert strong impact on summer monsoon rainfall and circulation as revealed in the observations. However, TIO SST anomalies are very weak in the model during the El Niño decaying summers. Though El Niño decay is delayed by 2 months in the model, decay of TIO SST warming is faster than the observations. Anomalous latent heat loss from ocean and a feeble southern TIO Rossby waves associated with weak wind response to El Niño are mainly accountable for rapid decay of TIO SST warming by mid-summer in the model. This suggests that JJA + 1 TIO SST response to El Niño decay phase in the model is poorly represented. The model is able to capture the SST anomalies associated with the northwest Pacific anticyclone at the peak phase of El Niño but fail to maintain that during the decay phase in MAM + 1 and JJA + 1. It is found that precipitation and circulation anomalies associated with TIO SST warming over the South and East Asian regions are disorganized in the model during the decay phase of El Niño. Rainfall anomalies over the southwest TIO, west coast of India, northern flank of northwest Pacific anticyclone and over Japan in JJA + 1 are poorly represented by the model. Analysis of lower troposphere stream function and rotational wind component reveals that northwest Pacific anticyclone shifted far eastward to the date line in the model during JJA + 1 unlike in the observations. Anomalous divergence observed over the western TIO and convergence in the northwest

  9. Indian monsoon variability on millennial-orbital timescales

    Science.gov (United States)

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R. Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F. M.

    2016-04-01

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ18O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ18O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales.

  10. Observational and modeling studies of impacts of the South China Sea monsoon on the monsoon rainfall in the middle-lower reaches of the Yangtze River during summer

    Science.gov (United States)

    Jin, Lijun; Zhao, Ping

    2012-04-01

    Based on the ERA-40 and NCEP/NCAR reanalysis data, the NOAA Climate Prediction Center's merged analysis of precipitation (CMAP), and the fifth-generation PSU/NCAR Mesoscale Model version 3 (MM5v3), we defined a monsoon intensity index over the East Asian tropical region and analyzed the impacts of summer (June-July) South China Sea (SCS) monsoon anomaly on monsoon precipitation over the middle-lower reaches of the Yangtze River (MLRYR) using both observational data analysis and numerical simulation methods. The results from the data analysis show that the interannual variations of the tropical monsoon over the SCS are negatively correlated with the southwesterly winds and precipitation over the MLRYR during June-July. Corresponding to stronger (weaker) tropical monsoon and precipitation, the southwesterly winds are weaker (stronger) over the MLRYR, with less (more) local precipitation. The simulation results further exhibit that when changing the SCS monsoon intensity, there are significant variations of monsoon and precipitation over the MLRYR. The simulated anomalies generally consist with the observations, which verifies the impact of the tropical monsoon on the monsoon precipitation over the MLRYR. This impact might be supported by certain physical processes. Moreover, when the tropical summer monsoon is stronger, the tropical anomalous westerly winds and positive precipitation anomalies usually maintain in the tropics and do not move northward into the MLRYR, hence the transport of water vapor toward southern China is weakened and the southwest flow and precipitation over southern China are also attenuated. On the other hand, the strengthened tropical monsoon may result in the weakening and southward shift of the western Pacific subtropical high through self-adjustment of the atmospheric circulation, leading to the weakening of the monsoon flows and precipitation over the MLRYR.

  11. Impact of typhoons on the UTLS ozone and water vapor distribution within the Asian summer monsoon anticyclone during the SWOP campaign in Lhasa 2013

    Science.gov (United States)

    Li, Dan; Vogel, Bärbel; Bian, Jianchun; Müller, Rolf

    2016-04-01

    During the sounding water vapor, ozone, and particle (SWOP) campaign during the Asian Summer Monsoon (ASM) organized by the Institute of Atmospheric Physics, Chinese Academy of Sciences, ozone and water vapor profiles were measured by balloon-borne sensors in Lhasa (29.66°N, 91.14°E, elevation 3,650 m), China in August 2013. Totally, 23 soundings were launched, half of which show some deviations from the typical relationship between ozone and water vapor in the tracer-tracer correlation in the upper troposphere and lower stratosphere (UTLS). 20-day backward trajectories of each sounding were calculated using the trajectory module of the Chemical Lagrangian Model of the Stratosphere (CLaMS) to analyse these deviations. Our results demonstrate that during this period three typhoons (Jebi, Utor, and Trami) occurred over the Northwest Pacific Ocean, which have impacts on the vertical structure of ozone and water vapor by transporting the maritime airmasses from the boundary layer. These airmasses with poor ozone were transported to the UTLS by the strong uplift associated with the typhoons, and then entered the ASM anticyclone. Thereafter, air parcels arrived at the observation site through two main pathways: first rotational subsidence, during which air parcels decend slowly along a circle following the anticyclone flow with a timescale of one week, and second direct horizontal transport from the location of the typhoon to the station, where air parcels are transported directly towards the station within approximately three days.

  12. Future changes and uncertainties in Asian monsoon precipitation simulated by multi-physics and multi-SST ensemble experiments with high-resolution MRI-AGCMs

    Science.gov (United States)

    Kitoh, A.; Endo, H.; Ose, T.; Mizuta, R.; Kusunoki, S.

    2012-12-01

    We provide future change projections and their uncertainty in mean and extreme precipitation in the Asian monsoon region. Time-slice experiments using a 20-km-mesh atmospheric general circulation (AGCM) were performed both in the present-day (1979-2003) and the future (2075-2099). To assess the uncertainty of the projections, 12 ensemble projections (i.e., combination of 3 different cumulus schemes and 4 different sea surface temperature (SST) change patterns) were conducted using 60-km-mesh AGCMs. Mean and extreme precipitation will generally increase in the future in South Asia and Southeast Asia, but their changes show marked differences among the projections, suggesting some uncertainty in their changes over these regions. In East Asia, northwestern China and Bangladesh, in contrast, mean and extreme precipitation show consistent increases among the projections, suggesting their increases are reliable for this model framework. Further investigation by analysis of variance (ANOVA) revealed that the uncertainty in the precipitation changes in South Asia and Southeast Asia are derived mainly from differences in the cumulus schemes, with an exception in the Maritime Continent where the uncertainty originates mainly from the differences in the SST pattern used.

  13. Relative contributions of the Tibetan Plateau thermal forcing and the Indian Ocean Sea surface temperature basin mode to the interannual variability of the East Asian summer monsoon

    Science.gov (United States)

    Hu, Jun; Duan, Anmin

    2015-11-01

    Investigating the relationships among different factors impacting the East Asian summer monsoon (EASM) is urgent for improving its predictability. In the present study, two factors, the Tibetan Plateau (TP) atmospheric thermal forcing and the Indian Ocean sea surface temperature basin mode (IOBM), are selected to compare their relative contributions to the interannual variability of the EASM. Both statistical methods and numerical experiments are used to separate and compare their respective influences under realistic circumstances. The results indicate that the IOBM mainly drives an anticyclonic anomaly over the northwestern Pacific in the lower troposphere, which is consistent with the dominant mode of the EASM circulation system. Meanwhile, influences from the TP thermal forcing are primarily on the anticyclonic anomaly over the TP in the upper troposphere, together with the enhanced southwesterly over southern China and a northerly anomaly over northern China in the lower troposphere. Moreover, the TP thermal forcing seems to play a more important role than the IOBM in affecting the main rainfall belt of the EASM, which extends from the middle and lower reaches of the Yangtze River to Japan. Such a rainfall pattern anomaly is directly related to the anomalous northerly over northern China and the resultant stronger moisture convergence over the main rainfall belt region when a strong TP thermal forcing occurs. In addition, the IOBM can increase the precipitation over the southeastern TP during its positive phase and hence enhance the in situ atmospheric heat source to a certain degree.

  14. Hydroxy fatty acids in fresh snow samples from northern Japan: long-range atmospheric transport of Gram-negative bacteria by Asian winter monsoon

    Science.gov (United States)

    Tyagi, P.; Yamamoto, S.; Kawamura, K.

    2015-12-01

    Hydroxy fatty acids (FAs) in fresh snow from Sapporo, one of the heaviest snowfall regions in the world, have been studied to ascertain the airborne bacterial endotoxin concentrations and their biomass. The presence of β-hydroxy FAs (C9-C28), constituents of the Gram-negative bacterium (GNB), suggests long-range transport of soil microbes. Likewise, the occurrence of α- and ω-hydroxy FAs (C9-C30 and C9-C28, respectively) in snow reveals their contribution from epicuticular waxes and soil microorganisms. Estimated endotoxin and GNB mass can aid in assessing their possible impacts on the diversity and functioning of aquatic and terrestrial ecosystems, as well as lethal effects on pedestrians through dispersal of microbes. Air mass back trajectories together with hydroxy FAs reveal their sources from Siberia, the Russian Far East and northern China by the Asian monsoon. This study highlights the role of fresh snow that reduces the human health risk of GNB and endotoxin by the scavenging from air.

  15. Using unmanned aircraft to measure the impact of pollution plumes on atmospheric heating rates and cloud properties during the Cheju ABC Plume-Asian Monsoon Experiment (CAPMEX)

    Science.gov (United States)

    Venkata Ramana, M.; Ramanathan, V.; Nguyen, H.; Xu, Y.; Pistone, K.; Corrigan, C.; Feng, Y.; Zhu, A.; Kim, S.; Yoon, S.; Carmichael, G. R.; Schauer, J. J.

    2009-12-01

    The CAPMEX (Cheju ABC Plume-Asian Monsoon Experiment) campaign took place off the Coast of Cheju Island in South Korea to take advantage of the unique event associated with the shutdown of anthropogenic emissions surrounding Beijing during the Olympics in summer 2008. CAPMEX studied pollution plumes before, during, and after the Beijing reductions using ground-level and high-elevation measurements, i.e., from unmanned aircrafts. Additionally, the campaign documented the effect on solar heating and clouds due to aerosols carried by the long range transport of pollution plumes. The unmanned aerial vehicle (UAV) measurement component of this campaign took place during Aug 9 to Sept 30, 2008. The AUAV payload was mission-specific and was outfitted to perform a particular set of measurements. These measurements include aerosol concentration, aerosol size distribution, aerosol absorption, cloud drop size distribution, solar radiation fluxes (visible and broadband), and spectral radiative fluxes. Throughout the CAPMEX experiment, long-range transport of aerosols from Beijing, Shanghai and Marine plumes were sampled in aerosol layers up to 3-4 km above sea level. During this period, we captured both heavy and light pollution events and witnessed air masses from both pristine oceanic sources and from major cities including Beijing and Shanghai. Analysis of specific plumes allowed us to quantify the impact of anthropogenic pollution on heating rates and cloud properties.

  16. Seasonal variations in surface ozone as influenced by Asian summer monsoon and biomass burning in agricultural fields of the northern Yangtze River Delta

    Science.gov (United States)

    Tang, Haoye; Liu, Gang; Zhu, Jianguo; Han, Yong; Kobayashi, Kazuhiko

    2013-03-01

    Surface ozone (O3) concentration was measured continuously at an agricultural site of Jiangdu in the northern Yangtze River Delta (YRD), China for the period from March 2007 to December 2011. Extremely high O3 concentrations ([O3]) were frequently observed in May and June with the highest hourly mean of 144 ppb. The monthly 7-h mean of [O3] showed a bimodal pattern in the seasonal change with peaks in June and October. The depression of [O3] in summer was due mostly to the monsoonal climate, which was adverse to photochemical O3 generation. Analyses of the wind direction and air mass trajectories showed that pollutants from the industrialized area of YRD were carried by the prevailing wind, causing an increased [O3] in the spring, whereas, in the summer, frequent incursions of maritime air mass diluted the high [O3] in the polluted air mass. Furthermore, it was found that extensive open crop residue burning in central eastern China made a significant contribution to the peak [O3] in June. The increase of [O3] by the residue burning in June was estimated to be 39% on sunny days and 27% on rainy days. The inter-annual variation of [O3] showed that [O3] in June tends to be lower in the years with more maritime air mass incursions, and the lowest [O3] in June 2008 could be partially attributed to the low frequency of residue burning events. This study has thus demonstrated that the variations in marine air mass incursions as influenced by the monsoonal climate and the open crop residue burning are the major determinants of the seasonal trends in surface [O3] across the agricultural areas of the northern YRD.

  17. Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India)

    Science.gov (United States)

    Reuter, M.; Piller, W. E.; Harzhauser, M.; Kroh, A.

    2013-09-01

    Climate change has an unknown impact on tropical cyclones and the Asian monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as a recorder of tropical cyclone activity along the NW Indian coast during the late Oligocene warming period (~ 27-24 Ma). Proxy data providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system at the Oligocene-Miocene boundary. The vast shell concentrations are comprised of a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deeper to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished, each recording a relative storm wave base. (1) A shallow storm wave base is shown by nearshore molluscs, reef corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclinid foraminifers, Eupatagus echinoids and corallinacean algae; and (3) a deep storm wave base is represented by an Amussiopecten bivalve-Schizaster echinoid assemblage. These wave base depth estimates were used for the reconstruction of long-term tropical storm intensity during the late Oligocene. The development and intensification of cyclones over the recent Arabian Sea is primarily limited by the atmospheric monsoon circulation and strength of the associated vertical wind shear. Therefore, since the topographic boundary conditions for the Indian monsoon already existed in the late Oligocene, the reconstructed long-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~ 26 Ma followed by a period of monsoon weakening during the peak of the late

  18. Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India

    Directory of Open Access Journals (Sweden)

    M. Reuter

    2013-09-01

    Full Text Available Climate change has an unknown impact on tropical cyclones and the Asian monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin as a recorder of tropical cyclone activity along the NW Indian coast during the late Oligocene warming period (~ 27–24 Ma. Proxy data providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system at the Oligocene–Miocene boundary. The vast shell concentrations are comprised of a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deeper to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished, each recording a relative storm wave base. (1 A shallow storm wave base is shown by nearshore molluscs, reef corals and Clypeaster echinoids; (2 an intermediate storm wave base depth is indicated by lepidocyclinid foraminifers, Eupatagus echinoids and corallinacean algae; and (3 a deep storm wave base is represented by an Amussiopecten bivalve-Schizaster echinoid assemblage. These wave base depth estimates were used for the reconstruction of long-term tropical storm intensity during the late Oligocene. The development and intensification of cyclones over the recent Arabian Sea is primarily limited by the atmospheric monsoon circulation and strength of the associated vertical wind shear. Therefore, since the topographic boundary conditions for the Indian monsoon already existed in the late Oligocene, the reconstructed long-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~ 26 Ma followed by a period of monsoon weakening during the

  19. Validating the dynamic downscaling ability of WRF for East Asian summer climate

    Science.gov (United States)

    Gao, Jiangbo; Hou, Wenjuan; Xue, Yongkang; Wu, Shaohong

    2015-12-01

    To better understand the regional climate model (RCM) performance for East Asian summer climate and the influencing factors, this study evaluated the dynamic downscaling ability of the Weather Research Forecast (WRF) RCM. According to the comprehensive comparison studies on different physical processes and experimental settings, the optimal combination of WRF model setups can be obtained for East Asian precipitation and temperature simulations. Furthermore, based on the optimal combination, when compared with climate observations, WRF shows high ability to downscale NCEP DOE Reanalysis-2, which provided initial and lateral boundary conditions for the WRF, especially for the precipitation simulation due to the better simulated low-level water vapor flux. However, the strengthened Western North Pacific Subtropical High (WPSH) from WRF simulation results in the positive anomaly for summer rainfall.

  20. Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

    Directory of Open Access Journals (Sweden)

    S. Fadnavis

    2015-06-01

    Full Text Available The Asian summer monsoon involves complex transport patterns with large scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS. We employ the global chemistry-climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide species PAN, NOx, and HNO3 from various monsoon regions, to the UTLS over Southern Asia and vice versa. Simulated long term seasonal mean mixing ratios are compared with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding aboard ENVISAT(MIPAS-E and aircraft campaigns during the monsoon season (June–September in order to evaluate the model's ability to reproduce these transport patterns. The model simulations show that there are three regions which contribute substantial pollution to the South Asian UTLS: the Asian summer monsoon (ASM, the North American Monsoon (NAM and the West African monsoon (WAM. However, penetration due to ASM convection reaches deeper into the UTLS as compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere. Remote transport also occurs in the extratropical upper troposphere where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and be lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. The intense convective activity in the monsoon regions is associated with lightning and thereby the formation of additional NOx. This also affects the distribution of PAN in the UTLS. According to sensitivity simulations with and without lightning, increase in concentrations of PAN (~ 40%, HNO3 (75%, NOx (70% and ozone (30% over the regions of convective transport, especially over equatorial Africa and America and comparatively less over the ASM. This indicates that

  1. Mutual interaction between the West African Monsoon on the summer Mediterranean climate

    Science.gov (United States)

    Gaetani, M.; Baldi, M.; Dalu, G. A.

    2009-04-01

    Many studies have show that the West African Monsoon (WAM) is teleconnected with neighbouring regions, as the Mediterranean (Med) basin and the Tropical Atlantic, but also it is sensitive to the perturbations occurring even in remote regions, as the Indian sub-continent and the Tropical Pacific, these teleconnections being active on several time-scales, from intraseasonal to multidecadal. The WAM plays also an active role in the regional atmospheric circulation, inducing significant changes in rainfall, moisture, temperature, and wind distribution up to the North Africa. Within this framework, recent works were focused on the teleconnection between WAM and Med. WAM is strengthened by the north-easterly advection of moisture from the Med Sea, and, since the subsiding monsoonal air often invades the Med, there is a 2-way interaction between WAM and Med summer circulation. We study these interactions, applying SVD analysis to global NCEP Reanalysis and to rainfall data from CMAP, during the extended monsoonal season from May to October, on interannual and on intraseasonal time-scale. Dynamical features are explored using composite analysis, focusing on the role of this connection in the heat waves occurrence in the Med. We find that a strong WAM intensifies the Hadley meridional circulation, with a strengthening of the north Atlantic anticyclone and a weakening, even blocking, of the westerly flow in the Med. A deep inland penetration of WAM produces a northern shift of the Libyan anticyclone, with subsidence and high pressure affecting mainly the western Med. The positive feedback is due to the intensification of north-easterly flow from the eastern Med, which, reaching the Sahara desert, intensifies the intertropical front, favouring abundant monsoonal precipitation because of the added moist air.

  2. Intercomparison of Deep Convection over the Tibetan Plateau-Asian Monsoon Region and Subtropical North America in Boreal Summer Using CloudSat/CALIPSO Data

    Science.gov (United States)

    Luo, Y.; Zhang, R.; Qian, W.; Luo, Z.

    2012-04-01

    Deep convection in the Tibetan Plateau-southern Asian monsoon region (TP-SAMR) is analyzed using CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data for the boreal summer season (June-August) from 2006 to 2009. Three subregions are defined—the TP, the southern slope of the plateau (PSS), and the SAMR—and deep convection properties (such as occurrence frequency, internal vertical structure, system size, and local environment) are compared among these subregions. To cast them in a broader context, four additional regions that bear some similarity to the TP-SAMR are also discussed: East Asia (EA), tropical northwestern Pacific (NWP), and western and eastern North America (WNA and ENA, respectively). The principal findings are as follows: 1) Compared to the other two subregions of the TP-SAMR, deep convection over the TP is shallower, less frequent, and embedded in smaller-size convection systems, but the cloud tops are more densely packed. These characteristics of deep convection over the TP are closely related to the unique local environment, namely, a significantly lower level of neutral buoyancy (LNB) and much drier atmosphere. 2) In a broader context in which all seven regions are brought together, deep convection in the two tropical regions (NWP and SAMR; mostly over ocean) is similar in many regards. A similar conclusion can be drawn among the four subtropical continental regions (TP, EA, WNA, and ENA). However, tropical oceanic and subtropical land regions present some significant contrasts: deep convection in the latter region occurs less frequently, has lower cloud tops but comparable or slightly higher tops of large radar echo (e.g., 0 and 10 dBZ), and is embedded in smaller systems. The cloud tops of the subtropical land regions are generally more densely packed.Hence, the difference between the TP and SAMRismore of a general contrast between subtropical land regions and tropical oceanic regions during the

  3. The global monsoon across timescales: coherent variability of regional monsoons

    Science.gov (United States)

    Wang, P. X.; Wang, B.; Cheng, H.; Fasullo, J.; Guo, Z. T.; Kiefer, T.; Liu, Z. Y.

    2014-11-01

    Monsoon has earned increasing attention from the climate community since the last century, yet only recently have regional monsoons been recognized as a global system. It remains a debated issue, however, as to what extent and at which timescales the global monsoon can be viewed as a major mode of climate variability. For this purpose, a PAGES (Past Global Changes) working group (WG) was set up to investigate the concept of the global monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional monsoons can vary coherently, although not perfectly, at various timescales, varying between interannual, interdecadal, centennial, millennial, orbital and tectonic timescales, conforming to the global monsoon concept across timescales. Within the global monsoon system, each subsystem has its own features, depending on its geographic and topographic conditions. Discrimination between global and regional components in the monsoon system is a key to revealing the driving factors in monsoon variations; hence, the global monsoon concept helps to enhance our understanding and to improve future projections of the regional monsoons. This paper starts with a historical review of the global monsoon concept in both modern and paleo-climatology, and an assessment of monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various timescales, providing evidence of the coherent global monsoon system. The paper concludes with a projection of future monsoon shifts in a warming world. The synthesis will be followed by a companion paper addressing driving mechanisms and outstanding issues in global monsoon studies.

  4. West African monsoon intraseasonal activity and its daily precipitation indices in regional climate models: diagnostics and challenges

    Science.gov (United States)

    Poan, E. D.; Gachon, P.; Dueymes, G.; Diaconescu, E.; Laprise, R.; Seidou Sanda, I.

    2016-02-01

    The West African monsoon intraseasonal variability has huge socio-economic impacts on local populations but understanding and predicting it still remains a challenge for the weather prediction and climate scientific community. This paper analyses an ensemble of simulations from six regional climate models (RCMs) taking part in the coordinated regional downscaling experiment, the ECMWF ERA-Interim reanalysis (ERAI) and three satellite-based and observationally-constrained daily precipitation datasets, to assess the performance of the RCMs with regard to the intraseasonal variability. A joint analysis of seasonal-mean precipitation and the total column water vapor (also called precipitable water—PW) suggests the existence of important links at different timescales between these two variables over the Sahel and highlights the relevance of using PW to follow the monsoon seasonal cycle. RCMs that fail to represent the seasonal-mean position and amplitude of the meridional gradient of PW show the largest discrepancies with respect to seasonal-mean observed precipitation. For both ERAI and RCMs, spectral decompositions of daily PW as well as rainfall show an overestimation of low-frequency activity (at timescales longer than 10 days) at the expense of the synoptic (timescales shorter than 10 days) activity. Consequently, the effects of the African Easterly Waves and the associated mesoscale convective systems are substantially underestimated, especially over continental regions. Finally, the study investigates the skill of the models with respect to hydro-climatic indices related to the occurrence, intensity and frequency of precipitation events at the intraseasonal scale. Although most of these indices are generally better reproduced with RCMs than reanalysis products, this study indicates that RCMs still need to be improved (especially with respect to their subgrid-scale parameterization schemes) to be able to reproduce the intraseasonal variance spectrum adequately.

  5. SEACIONS During the 2012 Asian Monsoon: A Strategic Approach to Determining Convective Impacts on Tropospheric Ozone and TTL Gravity Waves

    Science.gov (United States)

    Thompson, Anne M. (Principal Investigator); Young, George S. (Principal Investigator); Morris, Gary; Johnson, Bryan; Oltmans, Samuel; Selkirk, Henry B.

    2016-01-01

    Purpose of making ozone and water vapor profiles measurements in SEAC4RS is to give consistent coverage of the vertical structure at fixed sites to (1) complement 2 campaign aircraft sampling; (2) ground-truth satellite measurements of H O and ozone; (3) provide profiles for model evaluation; (4) study processes responsible for day-to-day variability at each site. Revised objective for 2013, due to cancellation of the 2012 and 2013 plans to operate in Southeast Asia: rapidly re-configure the original "SEACIONS," Southeast Asian Consortium for Intensive Ozonesonde Network Study, to a SouthEast American plan (SEACIONS) for collecting daily ozonesonde data during DC-8 and ER-2 flights throughout the southeastern US. As in previous IONS (2004, 2006, 2008), students were trained at St Louis, Tallahassee, Houston, Penn State, Huntsville, Socorro. Images of the soundings and related flight-planning products were posted each day at NASA and Penn State (PSU) websites. With the aircraft based at Ellington Field (Houston), water CFH (cryogenic frost-point hygrometer) sondes in addition to ozonesondes, were to be taken launched at that site.

  6. Evolution of South China Sea Summer Monsoon During SCSMEX-98: An Application of TRMM Data for Regional Hydro-Climate Studies

    Science.gov (United States)

    Lau, K.-M.; Li, Xiaofan; Einaudi, Franco (Technical Monitor)

    2000-01-01

    Evolution of South China Sea (SCS) summer monsoon in May-June, 1998 is investigated by using NASA/Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR) data and the SCS Monsoon Experiment (SCSMEX) data. The five-day mean moisture budget over the SCS region, and TMI surface rain rate, winds and divergence are calculated for the periods of pre-monsoon, onset, mature, and break. Results show that the SCS monsoon onset is triggered by the southward-propagating mid-latitude frontal system and the eastward-propagating intraseasonal oscillations. The disastrous flooding over the Yangtze River Basin in 1998 is caused mainly by the massive moisture transport by the lower-tropospheric prevailed westerly winds associated with the depression over the Bay of Bengal. The TRMM PR data are used to calculate the vertical distribution of fractional cover of Corrected Z-factor. Before the onset, the fractional cover 1-2% of 20-30 dBz appears around 2 km, indicating marine status clouds, During the monsoon onset and mature, the factional cover 34% of 25-35 dBz occurs below 6 km, indicating strong convection. The factional cover 5% of 20 dBz is around 8 km, which is indicative of large stratiform ice clouds. Yangtze River (YR) floods occurred as a part of the evolution of the East Asian summer monsoon. The rain rate over the YR shows out of phase with rainfall over the SCS. The vertical structures and statistical properties of clouds over the YR are compared with those over the SCS.

  7. Simulation of the West African monsoon onset using the HadGEM3-RA regional climate model

    Science.gov (United States)

    Diallo, Ismaïla; Bain, Caroline L.; Gaye, Amadou T.; Moufouma-Okia, Wilfran; Niang, Coumba; Dieng, Mame D. B.; Graham, Richard

    2014-08-01

    The performance of the Hadley Centre Global Environmental Model version 3 regional climate model (HadGEM3-RA) in simulating the West African monsoon (WAM) is investigated. We focus on performance for monsoon onset timing and for rainfall totals over the June-July-August (JJA) season and on the model's representation of the underlying dynamical processes. Experiments are driven by the ERA-Interim reanalysis and follow the CORDEX experimental protocol. Simulations with the HadGEM3 global model, which shares a common physical formulation with HadGEM3-RA, are used to gain insight into the causes of HadGEM3-RA simulation errors. It is found that HadGEM3-RA simulations of monsoon onset timing are realistic, with an error in mean onset date of two pentads. However, the model has a dry bias over the Sahel during JJA of 15-20 %. Analysis suggests that this is related to errors in the positioning of the Saharan heat low, which is too far south in HadGEM3-RA and associated with an insufficient northward reach of the south-westerly low-level monsoon flow and weaker moisture convergence over the Sahel. Despite these biases HadGEM3-RA's representation of the general rainfall distribution during the WAM appears superior to that of ERA-Interim when using Global Precipitation Climatology Project or Tropical Rain Measurement Mission data as reference. This suggests that the associated dynamical features seen in HadGEM3-RA can complement the physical picture available from ERA-Interim. This approach is supported by the fact that the global HadGEM3 model generates realistic simulations of the WAM without the benefit of pseudo-observational forcing at the lateral boundaries; suggesting that the physical formulation shared with HadGEM3-RA, is able to represent the driving processes. HadGEM3-RA simulations confirm previous findings that the main rainfall peak near 10°N during June-August is maintained by a region of mid-tropospheric ascent located, latitudinally, between the cores of

  8. Synergies in the Asian energy system: Climate change, energy security, energy access and air pollution

    International Nuclear Information System (INIS)

    We use the MESSAGE model to examine multiple dimensions of sustainable development for three Asian regions in a set of scenarios developed for the Asian Modelling Exercise. Using climate change mitigation as a starting point for the analysis, we focus on the interaction of climate and energy with technology choice, energy security, energy access, and air pollution, which often have higher policy priority than climate change. Stringent climate policies drive the future energy supply in Asia from being dominated by coal and oil to a more diversified system based mostly on natural gas, coal with CCS, nuclear and renewable energy. The increase in diversity helps to improve the energy security of individual countries and regions. Combining air pollution control policies and universal energy access policies with climate policy can further help to reduce both outdoor and indoor air pollution related health impacts. Investments into the energy system must double by 2030 to achieve stringent climate goals, but are largely offset by lower costs for O and M and air pollution abatement. Strong focus on end-use efficiency also helps lowering overall total costs and allows for limiting or excluding supply side technologies from the mitigation portfolio. Costs of additional energy access policies and measures are a small fraction of total energy system costs. - Highlights: ► Half of added investments in energy offset by lower costs for O and M and air pollution. ► Costs for achieving universal energy access much smaller than energy system costs. ► Combined emissions and access policies further reduce air pollution impacts on health. ► Strong focus on end-use efficiency allows for more flexibility on energy sources. ► Stringent climate policy can improve energy security of Asian regions.

  9. Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

    Directory of Open Access Journals (Sweden)

    S. Fadnavis

    2014-08-01

    Full Text Available The Asian summer monsoon involves complex transport patterns with large scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS. We employ the global chemistry–climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide reservoir species PAN, NOx, and HNO3 from various monsoon regions, to the UTLS over Southern Asia and vice versa. The model is evaluated with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-E and aircraft campaigns during the monsoon season (June–September. There are three regions which contribute substantial pollution to the UTLS during the monsoon: the Asian summer monsoon (ASM, the North American Monsoon (NAM and the West African monsoon (WAM. However, penetration due to ASM convection is deeper into the UTLS as compared to NAM and WAM outflow. The circulation in these monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere. Remote transport also occurs in the extratropical upper troposphere where westerly winds drive North American and European pollutants eastward to partly merge with the ASM plume. Strong ASM convection transports these remote and regional pollutants into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. The intense convective activity in the monsoon regions is associated with lightning generation and thereby the emission of NOy species. This will affect the distribution of PAN in the UTLS. The estimates of lightning produced PAN, HNO3, NOx and ozone obtained from control and lightning-off simulations shows high percentage changes over the regions of convective transport especially equatorial Africa and America and comparatively less over the ASM. This indicates higher anthropogenic pollution transport from the ASM region into the UTLS.

  10. Sediment transport process and East Asian monsoon evolution during the last 410 kyr in the northern South China Sea: a multi-proxy approach

    Science.gov (United States)

    Chen, Quan; Liu, Zhifei; Kissel, Catherine

    2015-04-01

    Terrigenous detrital materials buried at sea is a book documenting their whole life, including the continental environment where they originated from and the transport process they experienced. In order to reconstruct the East Asian monsoon evolution in late Quaternary, we need to read this book correctly. The key problem is to well understand the proxies and pick the right ones, because most of them are affected by several factors. In this study, clay and magnetic mineralogical measurements and geochemical XRF analyses were conducted on Core MD12-3432 taken from the northern South China Sea at 2125 m water depth during the CIRCEA cruise organized within Franco-Chinese LIA-MONOCL framework on board the R.V. Marion Dufresne. The age model is derived from both carbonate and magnetic stratigraphy. The clearly identified Laschamp and Iceland Basin geomagnetic excursions are used as tie points. Coupled earth magnetic field paleointensity and carbonate content record calibrated from XRF core scanned calcium intensity, we established a robust age model, indicating that Core MD12-3432 covers the last 410 kyr with an average sedimentation rate of 12.4 cm/kyr. The calibrated XRF-scan data provide high-resolution Ti/Ca, Al/Si and K/Al ratios. Ti/Ca and Al/Si ratios vary in phase, indicating strong clastic flux and short transport distances during glacials. Variations in K/Al ratio show an independent pattern, suggesting that temperature-driven chemical weathering is not the main control factor. Special attention needs therefore to be paid to the transport process. For that purpose, anisotropy of magnetic susceptibility was measured on discrete samples at 50 cm intervals. Orientations of the principal anisotropy axes could be reconstructed, using the NRM declination to orient the core in the horizontal plane. The maximum axis is relatively well oriented in the stratigraphic plane of the sedimentary magnetic fabric. A 90° shift is observed at the MIS 5-6 boundary, suggesting a

  11. Effects of urban land-use change in East China on the East Asian summer monsoon based on the CAM5.1 model

    Science.gov (United States)

    Ma, Hongyun; Jiang, Zhihong; Song, Jie; Dai, Aiguo; Yang, Xiuqun; Huo, Fei

    2016-05-01

    The effects of urban land-use change in East China on the East Asian summer monsoon (EASM) are investigated using a Community Atmosphere Model Version 5.1. The results show that the urban land-use change in East China causes spatially-varying changes in surface net radiation and heat fluxes, atmospheric circulation, and water budgets. It results in significant surface warming (cooling) and precipitation decrease (increase) in a large region north (south) of 30°N. Urban expansion agglomerated in (29°-41°N, 110°-122°E) alters the surface energy budget and warms the surface, resulting in strengthened southwesterly airflow south of 25°N and increased convergence below the mid-troposphere between 20° and 30°N. A concomitant northward downdraft associated with the increased convection generates an anomalous high pressure north of 30°N. Meanwhile, the downdraft not only produces adiabatic warming but also inhibits the dynamic condition for precipitation formation. The anomalous high pressure formed in North China prevents the southwesterly airflow from advancing northward, leading to increase the convergence and precipitation in South China. These changes reduce the meridional temperature gradient in the mid-lower troposphere and weaken the westerly airflow near 30°N. In addition, horizontal transport of vorticity north of 35°N weakens significantly, which leads to an anomalous barotropic structure of anticyclonic there. As a result, the anomalous anticyclonic circulation and descent north of 30°N are strengthened. At the same time, the anomalous cyclonic circulation and ascent south of 30°N are enhanced. These process induced by the thermal state changes due to urbanization weakens the EASM.

  12. Observed Variability of Summer Precipitation Pattern and Extreme Events in East China Associated with Variations of the East Asian Summer Monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lei; Qian, Yun; Zhang, Yaocun; Zhao, Chun; Leung, Lai-Yung R.; Huang, Anning; Xiao, Chuliang

    2016-06-30

    This paper presents a comprehensive analysis of interannual and interdecadal variations of summer precipitation and precipitation-related extreme events in China associated with variations of the East Asian summer monsoon (EASM) from 1979-2012. A high-quality daily precipitation dataset covering 2287 weather stations in China is analyzed. Based on the precipitation pattern analysis using empirical orthogonal functions, three sub-periods of 1979-1992 (period I), 1993-1999 (period II) and 2000-2012 (period III) are identified to be representative of the precipitation variability. Similar significant variability of the extreme precipitation indices is found across four sub-regions in eastern China. The spatial patterns of summer mean precipitation, the number of days with daily rainfall exceeding 95th percentile precipitation (R95p) and the maximum number of consecutive wet days (CWD) anomalies are consistent, but opposite to that of maximum consecutive dry days (CDD) anomalies during the three sub-periods. However, the spatial patterns of hydroclimatic intensity (HY-INT) are notably different from that of the other three extreme indices, but highly correlated to the dry events. The changes of precipitation anomaly patterns are accompanied by the change of the EASM regime and the abrupt shift of the position of the west Pacific subtropical high around 1992/1993 and 1999/2000, respectively, which influence the moisture transport that contributes most to the precipitation anomalies. Lastly, the EASM intensity is linked to sea surface temperature anomaly over the tropical Indian and Pacific Ocean that influences deep convection over the oceans.

  13. The representation of low-level clouds during the West African monsoon in weather and climate models

    Science.gov (United States)

    Kniffka, Anke; Hannak, Lisa; Knippertz, Peter; Fink, Andreas

    2016-04-01

    The West African monsoon is one of the most important large-scale circulation features in the tropics and the associated seasonal rainfalls are crucial to rain-fed agriculture and water resources for hundreds of millions of people. However, numerical weather and climate models still struggle to realistically represent salient features of the monsoon across a wide range of scales. Recently it has been shown that substantial errors in radiation and clouds exist in the southern parts of West Africa (8°W-8°E, 5-10°N) during summer. This area is characterised by strong low-level jets associated with the formation of extensive ultra-low stratus clouds. Often persisting long after sunrise, these clouds have a substantial impact on the radiation budget at the surface and thus the diurnal evolution of the planetary boundary layer (PBL). Here we present some first results from a detailed analysis of the representation of these clouds and the associated PBL features across a range of weather and climate models. Recent climate model simulations for the period 1991-2010 run in the framework of the Year of Tropical Convection (YOTC) offer a great opportunity for this analysis. The models are those used for the latest Assessment Report of the Intergovernmental Panel on Climate Change, but for YOTC the model output has a much better temporal resolution, allowing to resolve the diurnal cycle, and includes diabatic terms, allowing to much better assess physical reasons for errors in low-level temperature, moisture and thus cloudiness. These more statistical climate model analyses are complemented by experiments using ICON (Icosahedral non-hydrostatic general circulation model), the new numerical weather prediction model of the German Weather Service and the Max Planck Institute for Meteorology. ICON allows testing sensitivities to model resolution and numerical schemes. These model simulations are validated against (re-)analysis data, satellite observations (e.g. CM SAF cloud and

  14. The West African monsoon: Contribution of the AMMA multidisciplinary programme to the study of a regional climate system.

    Science.gov (United States)

    Lebel, T.; Janicot, S.; Redelsperger, J. L.; Parker, D. J.; Thorncroft, C. D.

    2015-12-01

    The AMMA international project aims at improving our knowledge and understanding of the West African monsoon and its variability with an emphasis on daily-to-interannual timescales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on water resources, health and food security for West African nations. The West African monsoon (WAM) has a distinctive annual cycle in rainfall that remains a challenge to understand and predict. The location of peak rainfall, which resides in the Northern Hemisphere throughout the year, moves from the ocean to the land in boreal spring. Around the end of June there is a rapid shift in the location of peak rainfall between the coast and around 10°N where it remains until about the end of August. In September the peak rainfall returns equatorward at a relatively steady pace and is located over the ocean again by November. The fact that the peak rainfall migrates irregularly compared to the peak solar heating is due to the interactions that occur between the land, the atmosphere and the ocean. To gain a better understanding of this complex climate system, a large international research programme was launched in 2002, the biggest of its kind into environment and climate ever attempted in Africa. AMMA has involved a comprehensive field experiment bringing together ocean, land and atmospheric measurements, on timescales ranging from hourly and daily variability up to the changes in seasonal activity over a number of years. This presentation will focus on the description of the field programme and its accomplishments, and address some key questions that have been recently identified to form the core of AMMA-Phase 2.

  15. Climate field reconstruction of East Asian spring temperature

    Directory of Open Access Journals (Sweden)

    M. Ohyama

    2012-08-01

    Full Text Available We describe a first attempt of dendroclimatic field reconstruction, based upon five ring-width chronologies from living trees, in Japan and Korea. Mean March–May temperature derived from a gridded land air temperature dataset (CRUTEM3 between 35–40° E and 125–140° N was reconstructed for the period of 1784–1990 AD. The reconstruction accounted for 19.4% of the temperature variance in the calibration period. This reconstruction showed remarkably similar fluctuations to regional dendroclimatic reconstructions in Japan and Korea, indicating the past spatial coherency of spring temperatures in the region. The reconstruction was validated against other climate proxies. A fairly good agreement was found with cold periods as estimated from documentary records in China and Japan. The west-Japan temperature series recovered also showed a reasonable agreement with the reconstruction. These comparisons revealed that climatic field reconstruction using tree-ring chronologies in this area offers a good potential for reconstructing long-term and large-scale past temperature patterns for East Asia.

  16. Predicting Monsoonal-Driven Stream Discharge and Sediment Yield in Himalaya Mountain Basins with Changing Climate and Deforestation

    Science.gov (United States)

    Neupane, R. P.; White, J. D.

    2014-12-01

    Short and long term effects of site water availability impacts the spectrum of management outcomes including landslide risk, hydropower generation, and sustainable agriculture in mountain systems heavily influenced by climate and land use changes. Climate change and land use may predominantly affect the hydrologic cycle of mountain basins as soil precipitation interception is affected by land cover. Using the Soil and Water Assessment Tool, we estimated stream discharge and sediment yield associated with climate and land use changes for two Himalaya basins located at eastern and western margins of Nepal that included drainages of the Tamor and Seti Rivers. Future climate change was modeled using average output of temperature and precipitation changes derived from Special Report on Emission Scenarios (B1, A1B & A2) of 16 global circulation models for 2080 as meteorological inputs into SWAT. Land use change was modeled spatially and included 1) deforestation, 2) expansion of agricultural land, and 3) increased human settlement that were produced by considering current land use with projected changes associated with viability of elevation and slope characteristics of the basins capable of supporting different land use types. We found higher annual stream discharge in all GCM-derived scenarios compared to the baseline with maximum increases of 13 and 8% in SRES-A2 and SRES-A1B for the Tamor and Seti basins, respectively. With 7% of original forest land removed, sediment yield for Tamor basin was estimated to be 65% higher, but increased to 124% for the SRES-B1 scenario. For the Seti basin, 4% deforestation yielded 33% more sediment for the SRES-A1B scenario. Our results indicated that combined effects of future, intensified monsoon rainfall with deforestation lead to dramatic potential for increased stream discharge and sediment yield as rainfall on steep slopes with thin exposed soils increases surface runoff and soil erosion in the Himalayas. This effect appears to

  17. The contribution of CEOP data to the understanding and modeling of monsoon systems

    Science.gov (United States)

    Lau, William K. M.

    2005-01-01

    CEOP has contributed and will continue to provide integrated data sets from diverse platforms for better understanding of the water and energy cycles, and for validating models. In this talk, I will show examples of how CEOP has contributed to the formulation of a strategy for the study of the monsoon as a system. The CEOP data concept has led to the development of the CEOP Inter-Monsoon Studies (CIMS), which focuses on the identification of model bias, and improvement of model physics such as the diurnal and annual cycles. A multi-model validation project focusing on diurnal variability of the East Asian monsoon, and using CEOP reference site data, as well as CEOP integrated satellite data is now ongoing. Similar validation projects in other monsoon regions are being started. Preliminary studies show that climate models have difficulties in simulating the diurnal signals of total rainfall, rainfall intensity and frequency of occurrence, which have different peak hours, depending on locations. Further more model diurnal cycle of rainfall in monsoon regions tend to lead the observed by about 2-3 hours. These model bias offer insight into lack of, or poor representation of key components of the convective,and stratiform rainfall. The CEOP data also stimulated studies to compare and contrasts monsoon variability in different parts of the world. It was found that seasonal wind reversal, orographic effects, monsoon depressions, meso-scale convective complexes, SST and land surface land influences are common features in all monsoon regions. Strong intraseasonal variability is present in all monsoon regions. While there is a clear demarcation of onset, breaks and withdrawal in the Asian and Australian monsoon region associated with climatological intraseasonal variability, it is less clear in the American and Africa monsoon regions. The examination of satellite and reference site data in monsoon has led to preliminary model experiments to study the impact of aerosol on

  18. Cyclone trends constrain monsoon variability during Late Oligocene sea level highstands (Kachchh Basin, NW India

    Directory of Open Access Journals (Sweden)

    M. Reuter

    2013-01-01

    Full Text Available Important concerns about the consequences of climate change for India are the potential impact on tropical cyclones and the monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin as an indicator of tropical cyclone activity along the NW Indian coast during the Late Oligocene warming period (~27–24 Ma. Direct proxies providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system in the Early Miocene. The vast shell concentrations comprise a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deep to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished each recording a relative storm wave base depth. (1 A shallow storm wave base is shown by nearshore mollusks, corals and Clypeaster echinoids; (2 an intermediate storm wave base depth is indicated by lepidocyclind foraminifers, Eupatagus echinoids and corallinaceans; and (3 a deep storm wave base is represented by an Amussiopecten–Schizaster echinoid assemblage. Vertical changes in these skeletal associations give evidence of gradually increasing tropical cyclone intensity in line with third-order sea level rise. The intensity of cyclones over the Arabian Sea is primarily linked to the strength of the Indian monsoon. Therefore and since the topographic boundary conditions for the Indian monsoon already existed in the Late Oligocene, the longer-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~26 Ma followed by a period of monsoon weakening during the peak of the Late Oligocene

  19. Sensitivity of East Asian Climate to the Progressive Uplift and Expansion of the Tibetan Plateau Under the Mid-Pliocene Boundary Conditions

    Institute of Scientific and Technical Information of China (English)

    JIANG Dabang; DING Zhongli; Helge DRANGE; GAO Yongqi

    2008-01-01

    A global atmospheric general circulation model has been used to perform eleven idealized numerical experimenta,i.e.,TP00,TPl0,…,TPl00,corresponding to different percentages of the Tibetan Plateau altitude.The aim is to explore the sensitivity of East Asian climate to the uplift and expansion of the Tibetan Plateau under the reconstructed boundary conditions for the mid-Pliocene about 3 Ma ago.When the plateau is progressively uplifted,global annual surface temperature is gradually declined and statistically significant cooling signals emerge only in the Northern Hemisphere,especially over and around the Tibetan Plateau.with larger magnitudes over land than over the oceans.0n the contrary,annual surface temperature rises notably over Central Asia and most parts of Africa,as well as over northeasternmost Eurasia in the experiments TP60 to TP100.Meanwhile.the plateau uplift also leads to annual precipitation augmentation over the Tibetan Plateau but a reduction in northern Asia,the Indian Peninsula,much of Central Asia,parts of western Asia and the southern portions of northeastern Europe.Additionally,it is found that an East Asian summer monsoon system similar to that of the present initially exists in the TP60 and is gradually intensified with the continued plateau uplift.At 850 hPa the plateau uplift induces an anomalous cyclonic circulation around the Tibetan Plateau in summertime and two anomalous westerly currents respectively located to the south and north of the Tibetan Plateau in wintertime.In the mid-troposphere,similar-to-modern spatial pattern of summertime western North Pacific subtropical high is only exhibited in the experiments TP60 to TP100,and the East Asian trough is steadily deepened in response to the progressive uplift and expansion of the Tibetan Plateau.

  20. Climate regime of Asian glaciers revealed by GAMDAM glacier inventory

    Science.gov (United States)

    Sakai, A.; Nuimura, T.; Fujita, K.; Takenaka, S.; Nagai, H.; Lamsal, D.

    2015-05-01

    Among meteorological elements, precipitation has a large spatial variability and less observation, particularly in high-mountain Asia, although precipitation in mountains is an important parameter for hydrological circulation. We estimated precipitation contributing to glacier mass at the median elevation of glaciers, which is presumed to be at equilibrium-line altitude (ELA) such that mass balance is zero at that elevation, by tuning adjustment parameters of precipitation. We also made comparisons between the median elevation of glaciers, including the effect of drifting snow and avalanche, and eliminated those local effects. Then, we could obtain the median elevation of glaciers depending only on climate to estimate glacier surface precipitation. The calculated precipitation contributing to glacier mass can elucidate that glaciers in arid high-mountain Asia receive less precipitation, while much precipitation makes a greater contribution to glacier mass in the Hindu Kush, the Himalayas, and the Hengduan Shan due to not only direct precipitation amount but also avalanche nourishment. We classified glaciers in high-mountain Asia into summer-accumulation type and winter-accumulation type using the summer-accumulation ratio and confirmed that summer-accumulation-type glaciers have a higher sensitivity than winter-accumulation-type glaciers.

  1. Relation of peer effects and school climate to substance use among Asian American adolescents.

    Science.gov (United States)

    Ryabov, Igor

    2015-07-01

    Using a nationally representative, longitudinal sample of Asian American late adolescents/young adults (ages 18-26), this article investigates the link between peer effects, school climate, on the one hand, and substance use, which includes tobacco, alcohol, and other illicit mood altering substance. The sample (N = 1585) is drawn from the National Longitudinal Study of Adolescent Health (Waves I and III). The study is set to empirically test premises of generational, social capital and stage-environment fit theories. The exploratory variables include individual-level (immigrant generation status, ethnic origin, co-ethnic and co-generational peers - peers from the same immigrant generation) as well as school-level measures (average school socio-economic status and school climate). Multilevel modeling (logistic and negative binomial regression) was used to estimate substance use. Results indicate that preference for co-generational friends is inversely associated with frequency of cannabis and other illicit drug use and preference for co-ethnic peers is inversely associated with other illicit drug use. We also find that school climate is a strong and negative predictor of frequency of cannabis and other illicit drug use as well as of heavy episodic drinking. In terms of policy, these findings suggest that Asian American students should benefit from co-ethnic and co-generational peer networks in schools and, above all, from improving school climate. PMID:25996088

  2. Inter-hemispheric eco-climatic connections in the Americas: A possible influence of a longer dry season over the Amazon forests on the North American monsoon

    Science.gov (United States)

    Arias, P. A.; Fu, R.; Vera, C.; Rojas, M.

    2014-12-01

    Recent studies have identified a lengthening of the dry season over the southern Amazon during the last three decades. This work suggests that this lengthening is correlated with an earlier demise of the North American monsoon, mainly observed after the mid 1990's. In addition, changes in both systems appear to be induced by common forcing factors at different time scales, like the shifting patterns of El Niño-Southern Oscillation anomalies, the westward expansion of the North Atlantic Subtropical High, and the global warming influence. However, whether the observed changes of dry season rainfall deficit over the Amazonia could influence the retreat of the North American monsoon is not clear. This work aims to identify the processes that could enable a possible influence of a longer and stronger dry season in the Amazon forests on the cross-equatorial flow and the demise of the North American monsoon. To address this possible inter-hemispheric link may be important in understanding the future climate variability of the American monsoons when the effects of anthropogenic forced change and conversion from Amazon forests to savannah become more dominant. The latter would be particularly relevant in order to understand the role of ecosystem changes on modulating climate over the Americas.

  3. Formation MicroScanner (FMS) data and orbital cycle records: preliminary interpretation from the Asian Monsoon IODP Expedition 346

    Science.gov (United States)

    Johanna, Lofi; Grizel, Jimenez Soto; Ryuji, Tada; Murray Richard, W.; Alvarez Zarikian Carlos, A.; Martin, Ziegler

    2015-04-01

    Recently, IODP Expedition 346 (29 July-27 September 2013) drilled seven sites in in the marginal sea bordered by the Eurasian continent, the Korean Peninsula, and the Japanese Islands, as well as two closely spaced sites in the East China Sea. Expedition 346 was the first scientific drilling expedition ever to focus exclusively on the climate system in this region. During the expedition, the Formation MicroScanner (FMS) downhole logging tool was deployed, providing high-resolution electrical resistivity-based images of borehole walls. Features such as bedding, slump folding and bioturbation can be resolved. Here we analyze FMS image resistivity data collected at Site U1425 that extend back to the Miocene. Analysis allowed the recognition of several FMS intervals, with vertical extension ranging from several tens of centimeters to a few meters, with an apparent cyclicity. These FMS intervals correlate well with other downhole logs (Total Gamma Ray, Uranium, Thorium, Potassium and density). Conductive intervals generally correlate with low gamma ray and low density log values. Conversely, more resistive intervals generally correlate with higher values in the gamma ray and bulk density logs. This relationship can be interpreted in terms of the relative abundance of terrigenous clay/diatoms in the sediment. Clay has high K and Th contents and relatively higher density and lower porosity than higher diatom-rich sediment. Consequently, with the exception of sporadic ash and dolomite layers, conductive intervals in the FMS images tend to reflect intervals enriched in diatoms, whereas resistive intervals reflect relative high-terrigenous clay content. An apparent cyclic nature, with several orders of cycles on the FMS images, is locally clearly observed. The cyclic pattern consists of ~4-8 m thick resistive intervals alternating with conductive intervals, generally correlating in core with laminated (diatomite or carbonate rich) intervals. These conductive intervals often

  4. Impact of warming climate on the monsoon and water resources of a western Himalayan watershed in the Upper Indus Basin

    Science.gov (United States)

    Khan, Asif; Richards, Keith S.; Parker, Geoffrey T.; McRobie, Allan; Booij, Martijn J.

    2015-04-01

    This study discusses the impact of a warming climate on the monsoon and on water resources in the Astore watershed, a major tributary of the Upper Indus Basin (UIB). It uses precipitation and temperature time series data from climatic stations, European Reanalysis (ERA) interim precipitation data, and monthly river flow data, all for the 1984-2009 period. Monthly average temperature data show statistically significant increasing trends for November-June through this period, while June and July, which experience episodic and intense precipitation, show statistically significant but opposing trends between the first and second halves of the period. To examine precipitation and flow data in more detail, two equal sub-periods were defined; 1984-1996 (T1) and 1997-2009 (T2). Basin-wide average annual precipitation (based on ERA data) declined by ~29% from 1481 mm/yr in T1 to 1148 inT2, whereas during the same periods flows declined by only ~17% (1245 to 1061 mm/yr), suggesting an increase in glacier melt in the T2 period. Spring to early summer flows increased during the T2 period concomitant with shift in the streamflow peak from July to June. Increasing spring discharge, the shift in timing of annual peak discharge, and an increase in the glacial melt component in river flows have been accompanied by a depletion of glacial storage within the Astore watershed, especially in the T2 period. If recent trends in climate and river flow continue in the future, then river flows will eventually decrease more sharply once the glacial reserves can no longer provide sustained nourishment to the river waters. Thus, there is a vital need to prepare and adopt policies for water resource management and reservoir operation that support sustainable development, agricultural expansion, and increased hydro-power generation.

  5. Reconstructing Monsoon Variations in India - Evidence from Speleothems

    Science.gov (United States)

    Breitenbach, S. F.; Lechleitner, F.; Plessen, B.; Marwan, N.; Cheng, H.; Adkins, J. F.; Haug, G. H.

    2012-12-01

    Indian summer monsoon (ISM) rainfall is of vital importance for ca. one fifth of the world's population, yet little is known about the factors governing its variability. Changing seasonality and/or rainfall intensity have profound impacts on the well-being of Asian agriculture-based societies. Most proxy-records from the Indian realm lack temporal resolution and age control sufficient to allow detailed analysis of high-frequency ISM rainfall variations. Low spatial coverage further restricts understanding spatial differences and the interactions between subsystems of the Asian summer monsoon, limiting understanding, not to mention reliable forecasting. Here, we summarize available information on rainfall changes over India, as reflected in speleothems. Suitable stalagmites offer highly precise chronologies and multi-proxy time series. Oxygen isotope and greyscale time series can track ISM intensity. Using published and new records from NE India, we present evidence for significant rainfall changes during the Holocene. Available proxy records show that while long-term ISM rainfall pattern changed in concert with supra-regional variations of the Asian summer monsoon, sub-decadal-scale ISM variations are influenced by local and regional influences. Complex network analysis of Indian and Chinese proxy data reveals that during the Medieval Warm Period ISM and East Asian summer monsoon (EASM) were more tightly linked, with a seemingly strong ISM influence on the EASM. During the cooler Little Ice Age however, the ISM and EASM connection weakened and local effects exerted influence on both sub-systems of the Asian monsoon. In order to allow detailed insights in spatio-temporal variations of the ISM and external teleconnections, precisely dated high-resolution time series must be obtained from various places in the Indian peninsula and beyond. Only a combination of high temporal and spatial coverage will allow assessments of the likelihood of drought recurrence in a given

  6. Resilience and Vulnerability of Southeast Asian Societies to Climate Variability in the Pre-Modern Era

    Science.gov (United States)

    Kaplan, J. O.

    2014-12-01

    Climate variability and projected future climate change has led to growing interest in understanding societal responses to changes in environmental conditions, and identifying societies that are particularly vulnerable or resilient to external shocks. To investigate this question it is instructive to look into the past, where we have examples of civilizational decline that have been hypothesized to be linked to climate variability or change. The Khmer Empire of the late 1st and early 2nd Millennium AD is an excellent example of a society that may have been affected by climate: After constructing the world's largest urban area in pre-modern time at Angkor, the site was largely abandoned after ~600 years of occupation. To investigate the vulnerability and resilience of Southeast Asian societies and test hypotheses about the importance of climate impacts on societies, I developed a new process-based model of human subsistence and demography for preindustrial Southeast Asia. The model is driven by topography, soils, vegetation and climate, and accounts for the range of subsistence lifestyles that were present at the time, from semi-nomadic shifting cultivators to complex irrigation-based urban polities. I use high-resolution gridded climate reconstructions from the Southeast Asian Drought Atlas to modulate the baseline climate input data and simulate the effects of periodic drought on potential food production and overall landscape-level carrying capacity. Results show that subsistence lifestyle may have had a large influence on the vulnerability or resilience of a society to climate variability. Complex societies with a large built infrastructure were more vulnerable to excessive rainfall as opposed to drought, while drought most affected small-scale sedentary farming communities that lacked trade networks for basic foodstuffs. Shifting cultivators could generally survive periods of unfavorable climate by concentrating more on foraging to collect food as opposed to

  7. Nature, Origin, Potential Composition, and Climate Impact of the Asian Tropopause Aerosol Layer (ATAL)

    Science.gov (United States)

    Fairlie, T. D.; Vernier, J.-P.; Thomason, L. W.; Natarajan, M.; Bedka, K.; Wienhold, F.; Bian J.; Martinsson, B.

    2015-01-01

    Satellite observations from SAGE II and CALIPSO indicate that summertime aerosol extinction has more than doubled in the Asian Tropopause Aerosol Layer (ATAL) since the late 1990s. Here we show remote and in-situ observations, together with results from a chemical transport model (CTM), to explore the likely composition, origin, and radiative forcing of the ATAL. We show in-situ balloon measurements of aerosol backscatter, which support the high levels observed by CALIPSO since 2006. We also show in situ measurements from aircraft, which indicate a predominant carbonaceous contribution to the ATAL (Carbon/Sulfur ratios of 2- 10), which is supported by the CTM results. We show that the peak in ATAL aerosol lags by 1 month the peak in CO from MLS, associated with deep convection over Asia during the summer monsoon. This suggests that secondary formation and growth of aerosols in the upper troposphere on monthly timescales make a significant contribution to ATAL. Back trajectory calculations initialized from CALIPSO observations provide evidence that deep convection over India is a significant source for ATAL through the vertical transport of pollution to the upper troposphere.

  8. Modulation of the East Asian Monsoon by ENSO on a Decadal Time Scale%年代际尺度厄尔尼诺南方涛动(ENSO)对东亚夏季风的调制作用

    Institute of Scientific and Technical Information of China (English)

    詹涛; 周鑫; 李峨; 张俊; 张海燕; 谢远云; 马永法

    2014-01-01

    东亚夏季风变化规律和驱动机制的研究是气候研究的重要方向,对较长时间尺度上东亚夏季风的变化进行进一步分析能够提供重要线索。采用前人重建的过去2000年和尚洞高分辨率石笋氧同位素(δ18 O)记录,通过奇异谱方法分解之后进行重建,发现前4个组分重建的序列反映了百年以上尺度东亚夏季风的演化,而组分5~16重建的序列则与年代际尺度上厄尔尼诺南方涛动(El Ni n~o Southern Oscillation ENSO)的变化良好相关,反映了这一时间尺度上ENSO 对东亚夏季风的调制作用。组分5~16重建的过去2000年序列中显著的77年和44年周期可能是 ENSO 传递的太阳活动信号。%Variance and mechanism of changes in the East Asian summer monsoon (EASM)are im-portant topics in climate study,and more researches on long-term changes in the EASM can provide use-ful information.In the present study,we use Singular Spectrum Analysis (SSA)method to decompose time-series of stalagmiteδ1 8 O in the past 2000 years,and then reconstruct centennial scale and multi-dec-adal scale time-series.The results show that the centennial scale variation indicates the evolution of the EASM,and the multi-decadal change is well correlated with the El Ni n~o Southern Oscillation (ENSO) variance.The significant 77-year and 44-year cycles in the multi-decadal time-series might be signals of solar activity transported by ENSO.

  9. Climatic control on extreme sediment transfer from Dokriani Glacier during monsoon, Garhwal Himalaya (India)

    Science.gov (United States)

    Kumar, Amit; Verma, Akshaya; Dobhal, Dwarika Prasad; Mehta, Manish; Kesarwani, Kapil

    2014-02-01

    In the Himalayas, most of the glaciers are covered by thick debris, especially in the ablation zone. Supraglacial debris cover might play an important role for sediment budget of the glaciated area or for the ablation of ice masses mantled in debris. During summer season, proglacial meltwater carries considerable amount of suspended sediment. The deglaciated area provides a ready source of sediment during Indian Summer Monsoon (ISM). The heavy sediment load from the glaciers affects the hydropower generation, irrigation and drinking water supply. Therefore, to understand the sediment delivery from glaciated basins, characteristics and variation of the suspended sediment concentrations in the proglacial meltwater stream, Dokriani Glacier, have been monitored during the ablation season (May-September). Suspended sediment samples were collected near the snout of Dokriani Glacier, Garhwal Himalaya, in 2010 and 2011. Results show that mean monthly suspended sediment concentrations (SSC) were 1499, 2303, 3845 and 1649 mg/l for the months June, July, August, and September, respectively, indicating highest concentration in August followed by July. Over the period of recording, daily mean suspended concentration in the melt stream varied from 13-9798.2 mg/l, which is very high, caused due to a flash flood event during the monitoring period. The mean daily suspended sediment concentration was computed to be 2196 mg/l. The suspended sediment concentration begins to increase with discharge from May and reduces in September. Present study provides TRMM (Tropical Rainfall Measuring Mission) derived and field based hydro-meteorological insight about severe rainstorms during the years 2010 and 2011 in the study area, which transported large amounts of sediment.

  10. Feedback of observed interannual vegetation change: a regional climate model analysis for the West African monsoon

    Science.gov (United States)

    Klein, Cornelia; Bliefernicht, Jan; Heinzeller, Dominikus; Gessner, Ursula; Klein, Igor; Kunstmann, Harald

    2016-06-01

    West Africa is a hot spot region for land-atmosphere coupling where atmospheric conditions and convective rainfall can strongly depend on surface characteristics. To investigate the effect of natural interannual vegetation changes on the West African monsoon precipitation, we implement satellite-derived dynamical datasets for vegetation fraction (VF), albedo and leaf area index into the Weather Research and Forecasting model. Two sets of 4-member ensembles with dynamic and static land surface description are used to extract vegetation-related changes in the interannual difference between August-September 2009 and 2010. The observed vegetation patterns retain a significant long-term memory of preceding rainfall patterns of at least 2 months. The interannual vegetation changes exhibit the strongest effect on latent heat fluxes and associated surface temperatures. We find a decrease (increase) of rainy hours over regions with higher (lower) VF during the day and the opposite during the night. The probability that maximum precipitation is shifted to nighttime (daytime) over higher (lower) VF is 12 % higher than by chance. We attribute this behaviour to horizontal circulations driven by differential heating. Over more vegetated regions, the divergence of moist air together with lower sensible heat fluxes hinders the initiation of deep convection during the day. During the night, mature convective systems cause an increase in the number of rainy hours over these regions. We identify this feedback in both water- and energy-limited regions of West Africa. The inclusion of observed dynamical surface information improved the spatial distribution of modelled rainfall in the Sahel with respect to observations, illustrating the potential of satellite data as a boundary constraint for atmospheric models.

  11. Climatic control on extreme sediment transfer from Dokriani Glacier during monsoon, Garhwal Himalaya (India)

    Indian Academy of Sciences (India)

    Amit Kumar; Akshaya Verma; Dwarika Prasad Dobhal; Manish Mehta; Kapil Kesarwani

    2014-02-01

    In the Himalayas, most of the glaciers are covered by thick debris, especially in the ablation zone. Supraglacial debris cover might play an important role for sediment budget of the glaciated area or for the ablation of ice masses mantled in debris. During summer season, proglacial meltwater carries considerable amount of suspended sediment. The deglaciated area provides a ready source of sediment during Indian Summer Monsoon (ISM). The heavy sediment load from the glaciers affects the hydropower generation, irrigation and drinking water supply. Therefore, to understand the sediment delivery from glaciated basins, characteristics and variation of the suspended sediment concentrations in the proglacial meltwater stream, Dokriani Glacier, have been monitored during the ablation season (May– September). Suspended sediment samples were collected near the snout of Dokriani Glacier, Garhwal Himalaya, in 2010 and 2011. Results show that mean monthly suspended sediment concentrations (SSC) were 1499, 2303, 3845 and 1649 mg/l for the months June, July, August, and September, respectively, indicating highest concentration in August followed by July. Over the period of recording, daily mean suspended concentration in the melt stream varied from 13–9798.2 mg/l, which is very high, caused due to a flash flood event during the monitoring period. The mean daily suspended sediment concentration was computed to be 2196 mg/l. The suspended sediment concentration begins to increase with discharge from May and reduces in September. Present study provides TRMM (Tropical Rainfall Measuring Mission) derived and field based hydro-meteorological insight about severe rainstorms during the years 2010 and 2011 in the study area, which transported large amounts of sediment.

  12. Influence of upper ocean on Indian summer monsoon rainfall: studies by observation and NCEP climate forecast system (CFSv2)

    Science.gov (United States)

    Chaudhari, Hemantkumar S.; Pokhrel, Samir; Rahman, H.; Dhakate, A.; Saha, Subodh K.; Pentakota, S.; Gairola, R. M.

    2016-08-01

    This study explores the role played by ocean processes in influencing Indian summer monsoon rainfall (ISMR) and compares the observed findings with National Centers for Environmental Prediction (NCEP)-coupled model Climate Forecast System, version 2 (CFSv2). The excess and deficit ISMR clearly brings out the distinct signatures in sea surface height (SSH) anomaly, thermocline and mixed layer depth over north Indian Ocean. CFSv2 is successful in simulating SSH anomalies, especially over Arabian Sea and Bay of Bengal region. CFSv2 captures observed findings of SSH anomalies during flood and drought (e.g., Rossby wave propagation which reaches western Bay of Bengal (BoB) during flood years, Rossby wave propagation which did not reach western BoB during drought). It highlights the ability of CFSv2 to simulate the basic ocean processes which governs the SSH variability. These differences are basically generated by upwelling and downwelling caused by the equatorial and coastal Kelvin and Rossby waves, thereby causing difference in SSH anomaly and thermocline, and subsequently modifying the convection centers, which dictates precipitation over the Indian subcontinent region. Since the observed SSH anomaly and thermal structure show distinct characteristic features with respect to strong and weak ISMR variability, the assimilation of real ocean data in terms of satellite products (like SSHA from AVISO/SARAL) bestow great promise for the future improvement.

  13. New climate change scenarios reveal uncertain future for Central Asian glaciers

    Directory of Open Access Journals (Sweden)

    A. F. Lutz

    2012-11-01

    Full Text Available Central Asian water resources largely depend on (glacier melt water generated in the Pamir and Tien Shan mountain ranges, located in the basins of the Amu and Syr Darya rivers, important life lines in Central Asia and the prominent water source of the Aral Sea. To estimate future water availability in the region, it is thus necessary to project the future glacier extent and volume in the Amu and Syr Darya river basins. The aim of this study is to quantify the impact of uncertainty in climate change projections on the future glacier extent in the Amu and Syr Darya river basins. The latest climate change projections provided by the fifth Coupled Model Intercomparison Project (CMIP5 generated for the upcoming fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC are used to model future glacier extent in the Central Asian region for the two large river basins. The outcomes are compared to model results obtained with the climate change projections used for the fourth IPCC assessment (CMIP3. We use a regionalized glacier mass balance model to estimate changes in glacier extent as a function of glacier size and projections of temperature and precipitation. The model is developed for implementation in (large scale hydrological models, when the spatial model resolution does not allow for modelling of individual glaciers and data scarcity is an issue. Both CMIP3 and CMIP5 model simulations point towards a strong decline in glacier extent in Central Asia. However, compared to the CMIP3 projections, the CMIP5 projections of future glacier extent in Central Asia provide a wider range of outcomes, mostly owing to greater variability in precipitation projections among the latest suite of climate models. These findings have great impact on projections of the timing and quantity of water availability in glacier melt dominated rivers in the region. Uncertainty about the size of the decline in glacier extent remains large, making

  14. Potential Impact of South Asian Anthropogenic Aerosols on Northern Hemisphere Climate

    Science.gov (United States)

    Bollasina, M. A.; Ming, Y.; Ramaswamy, V.

    2014-12-01

    South Asia has one of the world's highest aerosol loading due to the dramatic increase of anthropogenic emissions from the 1950s associated with rapid urbanization and population growth. The possible large-scale impact of the late 20th century increase of South Asian aerosol emissions on climate away from the source regions was studied by means of historical ensemble experiments with a state-of-the-art coupled climate model with fully interactive aerosols and a representation of both direct and indirect aerosol effects. The key characteristics of the northern hemisphere responses are examined separately for winter and summer, and show that regional aerosols induce significant planetary-scale teleconnection patterns. In both seasons, the large-scale aerosol imprint originates from substantial changes in the regional precipitation distribution. During the winter, in response to anomalous surface cooling in the northern Indian Ocean, aerosols cause a westward shift of convection over the eastern Indian Ocean and compensating subsidence to the west and over the Maritime continent. During the summer, aerosols are collocated with rainfall, and cause a widespread drying over South Asia mostly by indirect effects. In both cases, the impact of the regional diabatic heating anomaly propagates remotely by exciting a northern hemisphere wave-train which, enhanced by regional feedbacks, leads to remarkable changes in near-surface climate, including circulation and temperature, over Eurasia, the northern Pacific and North America. Depending on the region, the induced anomalies may have opposite signs between the two seasons, and may thus contribute to reinforcing or dampening those due greenhouse gases. These results underscore the potential influence of Asian aerosols on global climate, which is a compelling problem as regional aerosol loading will continue to be large in the coming decades.

  15. The Role of the Persian Gulf in Shaping Southwest Asian Surface Climate

    Science.gov (United States)

    Pal, J. S.; Eltahir, E. A. B.

    2015-12-01

    Summer surface climate of the Persian Gulf region is characterized by hot and humid conditions. Despite such conditions - which in other regions tends to trigger moist convection - typically this region experiences clear sky conditions and very little rainfall in the summer. In this study, we customize the MIT Regional Climate Model specifically for the Southwest Asia region and apply it at a 25-km grid spacing using reanalysis boundary conditions for present-day climate (1975-2005). Specific customizations include accurate representations of surface albedo and emissivity as well as mineral dust processes, all of which improve model bias. To assess the role of the Persian Gulf in shaping the region's climate, a 30-year experiment is performed without the Persian Gulf characterized. Results suggest that observed conditions over the Persian Gulf are due to a combination of physical processes involving adiabatic and diabatic descent. First, virtually clear sky conditions, due to subsidence during summer associated with the rising air motion over the monsoon region to the east, suppress upward motion and deep convection and increase incoming solar radiation. Second, the low surface albedo of the Persian Gulf results in enhanced absorption of solar radiation and total heat flux. Third, high evaporation rates increase water vapor, and therefore trap heat at the surface via the greenhouse effect for water vapor. Fourth, the relatively shallow boundary layer over the Persian Gulf concentrates water vapor and heat close to the surface. These combined factors maximize the total flux of heat in the boundary layer and hence moist static energy over the Persian Gulf.

  16. Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951-2005 using a regional climate model

    Science.gov (United States)

    Halder, Subhadeep; Saha, Subodh K.; Dirmeyer, Paul A.; Chase, Thomas N.; Nath Goswami, Bhupendra

    2016-05-01

    Daily moderate rainfall events, which constitute a major portion of seasonal summer monsoon rainfall over central India, have decreased significantly during the period 1951 through 2005. On the other hand, mean and extreme near-surface daily temperature during the monsoon season have increased by a maximum of 1-1.5 °C. Using simulations made with a high-resolution regional climate model (RegCM4) and prescribed land cover of years 1950 and 2005, it is demonstrated that part of the changes in moderate rainfall events and temperature have been caused by land-use/land-cover change (LULCC), which is mostly anthropogenic. Model simulations show that the increase in seasonal mean and extreme temperature over central India coincides with the region of decrease in forest and increase in crop cover. Our results also show that LULCC alone causes warming in the extremes of daily mean and maximum temperatures by a maximum of 1-1.2 °C, which is comparable with the observed increasing trend in the extremes. Decrease in forest cover and simultaneous increase in crops not only reduces the evapotranspiration over land and large-scale convective instability, but also contributes toward decrease in moisture convergence through reduced surface roughness. These factors act together in reducing significantly the moderate rainfall events and the amount of rainfall in that category over central India. Additionally, the model simulations are repeated by removing the warming trend in sea surface temperatures over the Indian Ocean. As a result, enhanced warming at the surface and greater decrease in moderate rainfall events over central India compared to the earlier set of simulations are noticed. Results from these additional experiments corroborate our initial findings and confirm the contribution of LULCC in the decrease in moderate rainfall events and increase in daily mean and extreme temperature over India. Therefore, this study demonstrates the important implications of LULCC over

  17. A University-Level Curriculum in Climate Change for SE Asia and the Asian Pacific

    Science.gov (United States)

    Furniss, M. J.; Saah, D. S.; Hines, S. J.; Radel, C. A.; McGroddy, M. E.; Ganz, D. J.

    2014-12-01

    A university-level curriculum has been developed for the SE Asia and Asia Pacific region and is currently being implemented by 12+ universities; in Vietnam, Cambodia, Laos, Thailand, Malaysia, and Papua New Guinea. The curriculum is supported by USAID (U.S. Agency for International Development) through the LEAF program (Lowering Emissions in Asian Forests), under the technical leadership of the U.S. Forest Service. Four modules have been developed: Basic Climate Change, Low-Emissions Land Use Planning, Social and Environmental Soundness, and Carbon Measurement and Monitoring. This presentation will focus on the Basic Climate Change module. This is a survey course that covers a wide range of climate change topics, including causes, effects, and responses. The level of detail in each of the covered topics is calibrated to current issues in the region. The module is elaborated in English and will be translated into the national language of the participating countries. The module is designed to be flexible and can be tailored to both degree and non-degree programs; as well as for trainings for natural resources professionals and policy-makers. Important training topics can be selected as short course trainings for practitioners and leaders working on climate change.

  18. Monsoon extremes and society over the past millennium on mainland Southeast Asia

    Science.gov (United States)

    Buckley, Brendan M.; Fletcher, Roland; Wang, Shi-Yu Simon; Zottoli, Brian; Pottier, Christophe

    2014-07-01

    The early 21st century has seen vigorous scientific interest in the Asian monsoon and significant development of paleo-proxies of monsoon strength. These include the Monsoon Asian Drought Atlas - a 700-year, gridded reconstruction of hydroclimate derived from 327 tree ring records - and several long speleothem records from China and India. Similar progress has been made on the study of monsoon climate dynamics through re-analysis data products and General Circulation Model diagnostics. The story has emerged of a variable monsoon over the latter Holocene, with extended droughts and anomalously wet episodes that occasionally and profoundly influenced the course of human history. We focus on Southeast Asia where an anomalous period of unstable climate coincided with the demise of the capital of the Khmer Empire at Angkor between the 14th and the 16th centuries, and we suggest that protracted periods of drought and deluge rain events, the latter of which damaged Angkor's extensive water management systems, may have been a significant factor in the subsequent transfer of the political capital away from Angkor. The late 16th and early 17th century experienced climate instability and the collapse of the Ming Dynasty in China under a period of drought, while Tonkin experienced floods and droughts throughout the 17th century. The 18th century was a period of great turmoil across Southeast Asia, when all of the region's polities saw great unrest and rapid realignment during one of the most extended periods of drought of the past millennium. New paleo-proxy records and the incorporation of historical documentation will improve future analyses of the interaction between climate extremes, social behavior and the collapse or disruption of regional societies, a subject of increasing concern given the uncertainties surrounding projections for future climate.

  19. CHANGES IN EAST ASIAN SUMMER MONSOON DURING THE HOLOCENE RECORDED BY STALAGMITE δ18O RECORDS FROM LIAONING PROVINCE%全新世东亚夏季风演化的辽宁暖和洞石笋δ18O记录

    Institute of Scientific and Technical Information of China (English)

    吴江滢; 汪永进; 董进国

    2011-01-01

    Nuanhe Cave(41°20'N,124°55'E)locates at Huanren county in Liaoning Province,a typical site influenced by the East Asian monsoon. The climates here are characterized by cold/dry atmospheric circulation during the winter and warm/humid air masses during the summer. The seasonal temperature ranges between -13℃ (Jan. )and 22 ℃ ( Jul. ). The mean annual precipitation at the site is between 800mm and 900mm,60% of which falls between June and September. Relative humidity in the cave is 100% (measured on Jun.,2008) and the cave temperature(61) keeps constant through a year and approximates a mean annual value.Four stalagmites(NH5 ,NH12,NH13 and NH20)were collected in the deep site of the cave. These stalagmites vary from 60mm ( NH13 ) to 157mm ( NH5 ) in length. Their vertical sections are all in candle shapes and the diameters vary between 20 ~54mm at the top and 105 ~ 150mm near the base. Each stalagmite is pure calcite,no porous on the polished surface, and composed of typical coalescent columnar-fabric crystals. Under the binocular microscope, we observed an apparent hiatus at the depth of 14mm in NH13, supported by our dating result that indicates the stalagmite ceased to growth between 3. 3kaB. P. And 1. 8kaB. P. We also found a hiatus at the depth of 20mm in NH20. We focus our oxygen analysis on the section below the depth of the hiatus. There is no evidence for hiatuses in any other stalagmites.A composite δ18O profile, pieced all data (16 230Th ages and 433 pairs of oxygen isotope data) measured from the four stalagmites, provides a continuous history of the East Asian Summer Monsoon ( EASM ) intensity for the period from 10. 5kaB. P. To 3. 36kaB. P. And 1. 9kaB. P. To 0. 3kaB. P. ( relative to 1950A. D. ). The δ18O measurements were run at Isotope Laboratory of Nanjing Normal University with on-line automated carbonate preparation system ( Kiel Carbonate Device) linked to Finnigan MAT-253 , yielding a standard deviation error of 0. 06%o. The 230Th dates

  20. Quaternary Indus River Terraces as Archives of Summer Monsoon Variability

    Science.gov (United States)

    Jonell, Tara N.; Clift, Peter D.

    2013-04-01

    If we are to interpret the marine stratigraphic record in terms of evolving continental environmental conditions or tectonics, it is essential to understand the transport processes that bring sediment from mountain sources to its final marine depocenter. We investigate the role that climate plays in modulating this flux by looking at the Indus River system, which is dominated by the strong forcing of the Asian monsoon and the erosion of the western Himalaya. Lake, paleoceanographic, and speleothem records offer high-resolution reconstructions of monsoon intensity over millennial timescales. These proxies suggest the monsoon reached peak intensity at ~9-10 ka in central India, followed by a steady decline after ~7 ka, with a steep decline after 4 ka. New lake core records (Tso Kar and Tso Moriri), however, suggest a more complex pattern of monsoon weakening between 7-8 ka in the Greater Himalayan region, which contrasts with a time of strong monsoon in central India. This indicates that the floodplains of the major river systems may not experience the same climatic conditions as their mountain sources, resulting in different geomorphologic responses to climate change. Earlier research has established that the northern part of the Indus floodplain adjacent to the mountains experienced incision after ~10 ka. Incision and reworking is even more intense in the Himalayas but its timing is not well-constrained. High altitude river valleys, at least north of the Greater Himalaya, appear to be sensitive to monsoon strength because they lie on the periphery of the Himalayan rain shadow. These valleys may be affected by landslide damming during periods of strong monsoonal precipitation, such as slightly after the monsoon maximum from 9-10 ka. Damming of these river valleys provides sediment storage through valley-filling and later sediment release through gradual incision or dam-bursting. Terraces of a major tributary to the Indus, the Zanskar River, indicate valley

  1. Transport pathways of peroxyacetyl nitrate in the upper troposphere and lower stratosphere from different monsoon systems during the summer monsoon season

    Science.gov (United States)

    Fadnavis, S.; Semeniuk, K.; Schultz, M. G.; Kiefer, M.; Mahajan, A.; Pozzoli, L.; Sonbawane, S.

    2015-10-01

    The Asian summer monsoon involves complex transport patterns with large-scale redistribution of trace gases in the upper troposphere and lower stratosphere (UTLS). We employ the global chemistry-climate model ECHAM5-HAMMOZ in order to evaluate the transport pathways and the contributions of nitrogen oxide species peroxyacetyl nitrate (PAN), NOx and HNO3 from various monsoon regions, to the UTLS over southern Asia and vice versa. Simulated long-term seasonal mean mixing ratios are compared with trace gas retrievals from the Michelson Interferometer for Passive Atmospheric Sounding aboard ENVISAT(MIPAS-E) and aircraft campaigns during the monsoon season (June-September) in order to evaluate the model's ability to reproduce these transport patterns. The model simulations show that there are three regions which contribute substantial pollution to the South Asian UTLS: the Asian summer monsoon (ASM), the North American monsoon (NAM) and the West African monsoon (WAM). However, penetration due to ASM convection reaches deeper into the UTLS compared to NAM and WAM outflow. The circulation in all three monsoon regions distributes PAN into the tropical latitude belt in the upper troposphere (UT). Remote transport also occurs in the extratropical UT where westerly winds drive North American and European pollutants eastward where they can become part of the ASM convection and lifted into the lower stratosphere. In the lower stratosphere the injected pollutants are transported westward by easterly winds. Sensitivity experiments with ECHAM5-HAMMOZ for simultaneous NOx and non-methane volatile organic compounds (NMVOCs) emission change (-10 %) over ASM, NAM and WAM confirm similar transport. Our analysis shows that a 10 % change in Asian emissions transports ~ 5-30 ppt of PAN in the UTLS over Asia, ~ 1-10 ppt of PAN in the UTLS of northern subtropics and mid-latitudes, ~ 7-10 ppt of HNO3 and ~ 1-2 ppb of ozone in UT over Asia. Comparison of emission change over Asia, North

  2. Impact of high resolution land surface initialization in Indian summer monsoon simulation using a regional climate model

    Indian Academy of Sciences (India)

    C K Unnikrishnan; M Rajeevan; S Vijaya Bhaskara Rao

    2016-06-01

    The direct impact of high resolution land surface initialization on the forecast bias in a regional climatemodel in recent years over Indian summer monsoon region is investigated. Two sets of regional climatemodel simulations are performed, one with a coarse resolution land surface initial conditions and secondone used a high resolution land surface data for initial condition. The results show that all monsoonyears respond differently to the high resolution land surface initialization. The drought monsoon year2009 and extended break periods were more sensitive to the high resolution land surface initialization.These results suggest that the drought monsoon year predictions can be improved with high resolutionland surface initialization. Result also shows that there are differences in the response to the land surfaceinitialization within the monsoon season. Case studies of heat wave and a monsoon depression simulationshow that, the model biases were also improved with high resolution land surface initialization. Theseresults show the need for a better land surface initialization strategy in high resolution regional modelsfor monsoon forecasting.

  3. The Asian American College Experience at a Diverse Institution: Campus Climate as a Predictor of Sense of Belonging

    Science.gov (United States)

    Wells, Alison V.; Horn, Catherine

    2015-01-01

    Assessing campus climate is an important factor in understanding the persistence and satisfaction of all students. This investigation extends this research stream by examining the relationship between perceptions of campus and overall sense of belonging of Asian American students on a diverse campus. Administrators may use the information gained…

  4. Summer monsoon moisture variability over China and Mongolia during the past four centuries

    Science.gov (United States)

    Li, Jinbao; Cook, Edward R.; Chen, Fahu; Davi, Nicole; D'Arrigo, Rosanne; Gou, Xiaohua; Wright, Wiliam E.; Fang, Keyan; Jin, Liya; Shi, Jiangfeng; Yang, Tao

    2009-11-01

    A great impediment of Asian monsoon (AM) climate studies is the general lack of long-term observations of large-scale monsoon variability. Here we present a well-verified reconstruction of temporal changes in the dominant summer moisture pattern over China and Mongolia (CM), based on a network of tree-ring chronologies (1600-1991). The reconstruction reveals significant changes in the large-scale AM over the past four centuries, which coincide with dramatic episodes in Chinese history over the period of record. These episodes include the fall of the Ming Dynasty (AD 1644) and the catastrophic famine during China's Great Leap Forward (1958-1961). Overall, the reconstructed AM strength corresponds well with Northern Hemisphere temperature proxies over the past four centuries. Yet, this relationship has broken down in recent decades, raising the possibility that the major driving force of monsoon dynamics has shifted from natural to anthropogenic in nature.

  5. SUNYA Regional Climate Model Simulations of East Asia Summer Monsoon: Effects of Cloud Vertical Structure on the Surface Energy Balance

    Directory of Open Access Journals (Sweden)

    Wei Gong and Wei-Chyung Wang

    2007-01-01

    Full Text Available We used the State University of New York at Albany (SUNYA regional climate model to study the effect of cloud vertical distribution in affecting the surface energy balance of the East Asia summer monsoon (EASM. Simulations were conducted for the summers of 1988 and 1989, during which large contrast in the intra-seasonal cloud radiative forcing (CRF was observed at the top of the atmosphere. The model results indicate that both the high and low clouds are persistent throughout the summer months in both years. Because of large cloud water, low clouds significantly reduce the solar radiation flux reaching the surface, which nevertheless still dominate the surface energy balance, accounting for more than 50% of the surface heating. The low clouds also contribute significantly the downward longwave radiation to the surface with values strongly dependent on the cloud base temperature. The presence of low clouds effectively decreases the temperature and moisture gradients near surface, resulting in a substantial decrease in the sensible and latent heat fluxes from surface, which partially compensate the decrease of the net radiative cooling of the surface. For example, in the two days, May 8 and July 11 of 1988, the total cloud cover of 80% is simulated, but the respective low cloud cover (water was 63% (114 gm-2 and 22% (21 gm-2. As a result, the downward solar radiation is smaller by 161 Wm-2 in May 8. On the other hand, the cloud temperature was _ lower, yielding 56 Wm-2 smaller downward longwave radiation. The near surface temperature and gradient is more than _ smaller (and moisture gradient, leading to 21 and 81 Wm-2 smaller sensible heat and latent heat fluxes. It is also demonstrated that the model is capable to reproduce the intraseasonal variation of shortwave CRF, and catches the relationship between total cloud cover and SW CRF. The model results show the dominance of high cloud on the regional mean longwave CRF and low cloud on the intra

  6. Tracking moisture pathways to Asia since the late Cretaceous: The competing influences of westerly and monsoonal dynamics

    Science.gov (United States)

    Caves, Jeremy; Bayshashov, Bolat; Zhamangara, Aizhan; Ritch, Andrea; Ibarra, Daniel; Gao, Yuan; Sjostrom, Derek; Page Chamberlain, C.

    2016-04-01

    stable isotopes from paleosol and lacustrine carbonates from the Zaysan Basin (Kazakhstan), which lies windward of the greater India-Asia collisional system. These data suggest that a rainfall gradient from inland to coastal Asia is a long-lasting feature of Asian climate. In contrast, stable isotope records from inland Asia track stable isotope records from basins windward of the Tian Shan and Altai ranges. We conclude that the mid-latitude westerlies have been a sustained source of moisture for much of Central Asia and that north-south monsoonal circulation has not persistently extended into Central Asia since the late Cretaceous.

  7. A climate change-induced threat to the ecological resilience of a subtropical monsoon evergreen broad-leaved forest in Southern China.

    Science.gov (United States)

    Zhou, Guoyi; Peng, Changhui; Li, Yuelin; Liu, Shizhong; Zhang, Qianmei; Tang, Xuli; Liu, Juxiu; Yan, Junhua; Zhang, Deqiang; Chu, Guowei

    2013-04-01

    Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought-induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of China's forested land. In this study, we describe how the monsoon evergreen broad-leaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broad-leaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long-term climate change. PMID:23504896

  8. The effect of absorbing aerosols on Indian monsoon circulation and rainfall: A review

    Science.gov (United States)

    Sanap, S. D.; Pandithurai, G.

    2015-10-01

    Aerosol, an uncertain component of the climate system, has attracted wide attention among the researchers due to its role in hydrological cycle and radiation budget in a changing climate. According to IPCC 5th assessment report, current understanding of aerosol-cloud-precipitation interaction is low to moderate, as a result they are not well represented in the climate models, and in turn are recognized as major uncertainties in the future climate projections. In South Asian monsoon regions, the aerosol forcing response to water cycle is even more complicated. Substantial amount of transported dust from Middle East countries and adjacent deserts get accumulated over Indian subcontinent (mainly North India and Indo Gangetic Plains; IGP) and further coated with black carbon (BC) produced from local emission, which make the atmospheric physics and chemistry of the aerosol more complex over the region. Here we review earlier studies and recapitulate our current understanding of absorbing aerosols on Indian monsoon circulation and rainfall from observational evidences and variety of numerical model simulations. This review begins with current understanding of the absorbing aerosols and interactions with Indian summer monsoon, followed by discussion on various working hypotheses, observational and modeling perspective, local and remote impacts. The key open questions and suggestions for future research priorities are delineated to improve the current understanding about the relationship between absorbing aerosols and Indian summer monsoon.

  9. Desert Dust and Monsoon Rain

    Science.gov (United States)

    Lau, William K. M.; K