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Sample records for asian summer monsoon

  1. 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.

  2. 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 ...

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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).

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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] ...

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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).

  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. 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.

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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).

  15. 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

    Full Text Available Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon, respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4 than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. The cold-aridiphilous individuals indicate the so-called Asian winter monsoon regime and predominantly occur during glacials, when dust is deposited. The thermal-humidiphilous mollusks are prevalent during interglacial or interstadial conditions of the Asian summer monsoon, when soil formation takes place. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr, respectively. The L5 and L4 events appear to be the strongest (high counts. Similar variations have also been identified in the Xifeng sequence, distant enough from Luochuan, but also in Lake Baikal further North, to suggest that this phenomenon is regional rather than local. The indicators of the summer monsoon within the glacial intervals imply a strengthened East-Asian monsoon interpreted as corresponding to marine isotope stages 12, 10 and 6, respectively. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which

  16. 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

    Full Text Available Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon, respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4 than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. The cold-aridiphilous individuals indicate the so-called Asian winter monsoon regime and predominantly occur during glacials, when dust is deposited. The thermal-humidiphilous mollusks are prevalent during interglacial or interstadial conditions of the Asian summer monsoon, when soil formation takes place. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr, respectively. The L5 and L4 events appear to be the strongest (high counts. Similar variations have also been identified in the Xifeng sequence, distant enough from Luochuan, but also in Lake Baikal further North, to suggest that this phenomenon is regional rather than local. The indicators of the summer monsoon within the glacial intervals imply a strengthened East-Asian monsoon interpreted as corresponding to marine isotope stages 6, 10 and 12, respectively. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which

  17. 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.

  18. 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.

  19. 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.

  20. 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)

  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  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. 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.

  11. 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.

  12. 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.

  13. 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

  14. 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.)

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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...

  1. 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...

  2. 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.

  3. 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.

  4. 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

  5. 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.

  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. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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.

  16. 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.

  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. 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)

  19. 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.

  20. 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.

  1. 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.

  2. 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

    In this paper we use the extensive integrations produced for the IPCC Fourth Assessment Report (AR4) to examine the relationship between ENSO and the monsoon at interannual and decadal timescales. We begin with an analysis of the monsoon simulation in the 20th century integrations. Six of the 18 models were found to have a reasonably realistic representation of monsoon precipitation climatology. For each of these six models SST and anomalous precipitation evolution along the equatorial Pacific during El Nino events display considerable differences when compared to observations. Out of these six models only four (GFDL{_}CM{_}2.0, GFDL{_}CM{_}2.1, MRI, and MPI{_}ECHAM5) exhibit a robust ENSO-monsoon contemporaneous teleconnection, including the known inverse relationship between ENSO and rainfall variations over India. Lagged correlations between the all-India rainfall (AIR) index and Nino3.4 SST reveal that three models represent the timing of the teleconnection, including the spring predictability barrier which is manifested as the transition from positive to negative correlations prior to the monsoon onset. Furthermore, only one of these three models (GFDL{_}CM{_}2.1) captures the observed phase lag with the strongest anticorrelation of SST peaking 2-3 months after the summer monsoon, which is partially attributable to the intensity of simulated El Nino itself. We find that the models that best capture the ENSO-monsoon teleconnection are those that correctly simulate the timing and location of SST and diabatic heating anomalies in the equatorial Pacific, and the associated changes to the equatorial Walker Circulation during El Nino events. The strength of the AIR-Nino3.4 SST correlation in the model runs waxes and wanes to some degree on decadal timescales. The overall magnitude and timescale for this decadal modulation in most of the models is similar to that seen in observations. However, there is little consistency in the phase among the realizations

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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

  9. 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.

  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. 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. 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

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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)

  12. 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

  13. 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.

  14. Identifying the northernmost summer monsoon location in East Asia

    Institute of Scientific and Technical Information of China (English)

    Hu Haoran; Qian Weihong

    2007-01-01

    An integrated index which can be used to indicate the advance of subtropical summer monsoon in East Asia has been proposed in this paper. The index was combined by three variables including precipitation, wind and pseudo-equivalent potential temperature. The northernmost summer monsoon location (NSML) was identified by using this index annually. It was found that the NSML experienced an interdecadal shift in the period 1977-1979 based on the annual index analysis from 1961 to 2001. A comparison of the NSML with other four summer monsoon indices has also been made. The result showed that the NSML could well represent the interannual and interdecadal variability of summer monsoon precipitation in North China (beyond 35°N), while other four indices could well indicate the precipitation anomalies of East Asian summer monsoon along the Yangtze River valley (around 30°N).

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. 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.

  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. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. Indian summer monsoon rainfall characteristics during contrasting monsoon years.

    Digital Repository Service at National Institute of Oceanography (India)

    Varikoden, H.; RameshKumar, M.R.; Babu, C.A.

    % in the central and western coastal regions. In a wet monsoon year, about 35–45 % of rainfall is contributed during June and July in most parts of India. During these years, the influence of features in the Pacific Ocean played vital role on the Indian summer...

  11. 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.

  12. 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.

  13. A Large Scale Index to Characterize the Indian Summer Monsoon

    Science.gov (United States)

    Cannon, F. G.; Carvalho, L. V.; Jones, C.; Bookhagen, B.

    2012-12-01

    Seasonal rainfall associated with the Indian summer monsoon is the primary water source for the central and eastern Himalaya, while the western Himalaya receives significant amounts of precipitation during the winter season. Typically, the monsoon season begins in the eastern lowlands during June, migrates northwest across the Ganges plains, is bounded by the Himalayan orographic barrier to the north, and lasts until approximately mid-October. By the end of the monsoon season, the accumulated rainfall contributes to over 80% of the total annual precipitation in the central and eastern Himalayan regions. Consequently, the seasonal variability of mountain runoff depends on the onset, duration, and intensity of the monsoon and short-to-long term variations in these factors play a fundamental role in the region's hydrologic cycle. The objective task of this research is to develop detailed diagnostic analyses to characterize climatological variability of the summer monsoon system over high Asian mountains during 1979-present. Primarily, we apply a combined empirical orthogonal function to seasonal variations in circulation, temperature and moisture. Previous research has shown that important mechanisms of monsoonal variability include low level (surface - 850 hPa) specific humidity, temperature, zonal and meridional wind components, and precipitation. This project utilizes daily CFSR reanalysis data for the aforementioned variables from 1979 to 2010 at a one-degree spatial resolution over the Indian sub-continent (5°-45°N and 60°-90°E). We also employ precipitation data from various sources including APHRODITE, TRMM, GPCP, and station data to comprehensively investigate the validity of our index through various precipitation data acquisition methods. Based on the time coefficient of the second EOF of surface level humidity, temperature, and zonal and meridional wind, we construct the proposed monsoon index and define the onset, demise, and intraseasonal variations

  14. 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

    ability of the newly coupled model by two runs: one without and one with the urban canopy module. The coupled model is integrated from March through September, covering a summer monsoon season. The preliminary results show more significant urban heat island (UHI) effect over urban areas with the urban canopy model. The existence of the UHIs enhances the convection in lower atmosphere, affects the water vapor transportation and precipitation of the surrounding area, consistent with the phenomena that occur in urban areas. We further test the effect of urbanization on the monsoon by introducing two maps, one with and one without urbanization and the effect of the urbanization on the monsoon evolution and low level circulation will be discussed in the presentation.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. Weakening of Indian Summer Monsoon in Recent Decades

    Institute of Scientific and Technical Information of China (English)

    WU Bingyi

    2005-01-01

    The analysis of 43 years of NCEP-NCAR reanalysis data and station observations reveals the connections between tropospheric temperature variations and the weakening of the Indian summer monsoon circulation. The Indian summer monsoon variation is strongly linked to tropospheric temperature over East Asia, showing significant positive correlations of mean tropospheric temperature with all-Indian summer rainfall and the monsoon circulation intensity. The result shows that Indian summer monsoon circulation underwent two weakening processes in recent decades. The first occurred in circa the mid-1960s, and the other occurred in circa the late 1970s. The finding indicates that the mean tropospheric temperature may play a crucial role in the weakening of the Indian summer monsoon intensity via changing land-sea thermal contrast. The role of the tropospheric temperature contrast between East Asia and the tropical area from the eastern Indian Ocean to the tropical western Pacific is to weaken the Indian summer monsoon circulation.

  1. 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

  2. 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

  3. 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.

  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. 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

  6. 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.

  7. 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

  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. Role of Ocean in the Variability of Indian Summer Monsoon Rainfall

    Science.gov (United States)

    Joseph, Porathur V.

    2014-05-01

    Asian summer monsoon sets in over India after the Intertropical Convergence Zone moves across the equator to the northern hemisphere over the Indian Ocean. Sea surface temperature (SST) anomalies on either side of the equator in Indian and Pacific oceans are found related to the date of monsoon onset over Kerala (India). Droughts in the June to September monsoon rainfall of India are followed by warm SST anomalies over tropical Indian Ocean and cold SST anomalies over west Pacific Ocean. These anomalies persist till the following monsoon which gives normal or excess rainfall (tropospheric biennial oscillation). Thus, we do not get in India many successive drought years as in sub-Saharan Africa, thanks to the ocean. Monsoon rainfall of India has a decadal variability in the form of 30-year epochs of frequent (infrequent) drought monsoons occurring alternately. Decadal oscillations of monsoon rainfall and the well-known decadal oscillation in SST of the Atlantic Ocean (also of the Pacific Ocean) are found to run parallel with about the same period close to 60 years and the same phase. In the active-break cycle of the Asian summer monsoon, the ocean and the atmosphere are found to interact on the time scale of 30-60 days. Net heat flux at the ocean surface, monsoon low-level jetstream (LLJ) and the seasonally persisting shallow mixed layer of the ocean north of the LLJ axis play important roles in this interaction. In an El Niño year, the LLJ extends eastwards up to the date line creating an area of shallow ocean mixed layer there, which is hypothesised to lengthen the active-break (AB) cycle typically from 1 month in a La Niña to 2 months in an El Niño year. Indian monsoon droughts are known to be associated with El Niños, and long break monsoon spells are found to be a major cause of monsoon droughts. In the global warming scenario, the observed rapid warming of the equatorial Indian ocean SST has caused the weakening of both the monsoon Hadley circulation and

  10. 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.

  11. 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.

  12. Air sea interaction during summer monsoon period of 1979

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.

    of the summer monsoon over the Kerala Coast. (2) The weak zonal anomalies of SSTs off the Somali and Arabian coasts and the weak temperature gradient prevalent throughout the monsoon season in the Arabian Sea, Bay of Bengal and Indian Ocean are associated...

  13. Summer monsoon rainfall prediction for India - Some new ideas

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    Present methods of forecasting of mean Indian rainfall for summer monsoon season are critically examined. Considering the wide variations in mean seasonal rainfalls (more than 5 to less than 400 cm) and crops in various regions of India...

  14. 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.

  15. Did aboriginal vegetation burning impact on the Australian summer monsoon?

    Science.gov (United States)

    Notaro, Michael; Wyrwoll, Karl-Heinz; Chen, Guangshan

    2011-06-01

    Aboriginal vegetation burning practices and their role in the Australian environment remains a central theme of Australian environmental history. Previous studies have identified a decline in the Australian summer monsoon during the late Quaternary and attributed it to land surface-atmosphere feedbacks, related to Aboriginal burning practices. Here we undertake a comprehensive, ensemble model evaluation of the effects of a decrease in vegetation cover over the summer monsoon region of northern Australia. Our results show that the climate response, while relatively muted during the full monsoon, was significant for the pre-monsoon season (austral spring), with decreases in precipitation, higher surface and ground temperatures, and enhanced atmospheric stability. These early monsoon season changes can invoke far-reaching ecological impacts and set-up land surface-atmosphere feedbacks that further accentuate atmospheric stability.

  16. The Indian summer monsoon as revealed by NCMRWF system

    Indian Academy of Sciences (India)

    P L S Rao; U C Mohanty; P V S Raju; Gopal Iyengar

    2003-03-01

    In this study, we present the mean seasonal features of the Indian summer monsoon circulation in the National Centre for Medium Range Weather Forecasting (NCMRWF) global data assimilation and forecast system. The large-scale budgets of heat and moisture are examined in the analyzed and model atmosphere. The daily operational analyses and forecasts (day 1 through day 5) produced for the summer seasons comprising June, July and August of 1995 and 1993 have been considered for the purpose. The principal aim of the study is two-fold. Primarily, to comprehend the influence of the systematic errors over the Indian summer monsoon, secondarily, to analyze the performance of the model in capturing the interseasonal variability. The heat and moisture balances show reduction in the influx of heat and moisture in the model forecasts compared to the analyzed atmosphere over the monsoon domain. Consequently, the diabatic heating also indicates reducing trend with increase in the forecast period. In effect, the strength of Indian summer monsoon, which essentially depends on these parameters, weakens considerably in the model forecasts. Despite producing feeble monsoon circulation, the model captures interseasonal variability realistically. Although, 1995 and 1993 are fairly normal monsoon seasons, the former received more rainfall compared to the latter in certain pockets of the monsoon domain. This is clearly indicated by the analyzed and model atmosphere in terms of energetics.

  17. 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

  18. 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.

  19. Inter-decadal Shift of East Asian Summer Monsoon in the Early 1990s%20世纪90年代初东亚夏季风的年代际转型

    Institute of Scientific and Technical Information of China (English)

    唐佳; 武炳义

    2012-01-01

    Using JRA-25 and NCEP/NCAR reanalysis data from 1979 to 2009, dominant modes of summer season (June-August) 850 hPa wind field variability over East Asia is revealed by means of the complex vector empirical orthogonal function method. The two reanalysis data are consistent with the description of the first East Asian summer monsoon (EASM) mode, whereas the first mode had been studied, showing that the first mode could not reflect the inter-decadal shift of Chinese summer precipitation in the early 1990s. Consequently, the inter-decadal shift feature of the second EASM mode is deeply analyzed, as well as its effect on summer precipitation in China. Moreover, the possible external forcing factors exerting effects on the inter-decadal shift of EASM are discussed. Results show that, EASM which is revealed,by two sets of reanalysis data to have undergone one inter-decadal shift in the early 1990s. The inter-decadal shift time of EASM is consistent with the inter-decadal shift time of summer precipitation in China. EASM is closely related to the mid-high latitude atmospheric circulation anomalies. Corresponding anomalous 500 hPa geopotential height fields show an anomalous quasi-zonal teleconnection pattern in northern Eurasia, whereas the distribution of summer precipitation anomalies show a meridional dipole pattern. Accompanied by the inter-decadal shift of EASM, after the early 1990s, summer precipitation decreases in the majority of northern China, especially in north of the northeast and the area between the Yangtze River and the Yellow River in the vicinity of 105° E. While summer precipitation increases significantly in South China and the Huaihe River Basin. From the perspective of dynamic, the characteristics of inter-decadal shift of summer precipitation in China are described. The difference distribution of summer 500 hPa geopotential height fields between two periods (1993-2009 and 1979-1992) show northern Eurasian quasi-zonal teleconnection pattern, then

  20. In-phase transition from the winter monsoon to the summer monsoon over East Asia: Role of the Indian Ocean

    Science.gov (United States)

    Wang, Lin; Wu, Renguang

    2012-06-01

    Analysis of observations shows that the weak East Asian winter monsoon (EAWM) to weak East Asian summer monsoon (EASM) transitions mainly occur in El Niño decaying years whereas strong EAWM (denoting stronger northerly winds along East Asian coast) to strong EASM (denoting less precipitation along the Meiyu-Baiu rainband) transitions all occur in non-El Niño-Southern Oscillation (ENSO) years during the period 1979-2009. This new finding implies that ENSO is not indispensable to the in-phase EAWM to the EASM transitions. The present study reveals an important role of the Indian Ocean in the strong EAWM to strong EASM transitions and proposes a possible mechanism for these transitions. A strong EAWM induces more precipitation over the Maritime Continent, and the associated anomalous heating excites a Gill-Matsuno type pattern in the tropics. The resultant wind and cloud changes enhance latent heat flux and reduce downward shortwave radiation over the northwestern Indian Ocean in winter, which leads to SST cooling. The cold SST anomalies persist to summer and excite an anomalous cyclone over the subtropical western North Pacific, leading to a strong EASM. The above processes also operate in the weak EAWM to weak EASM transitions during which El Niño impacts dominate but with additional contributions from the EAWM. The results of observational analysis are confirmed by numerical experiments with a coupled model.

  1. 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

  2. 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.

  3. 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

  4. 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.

  5. Did Aboriginal vegetation burning affect the Australian summer monsoon?

    Science.gov (United States)

    Balcerak, Ernie

    2011-08-01

    For thousands of years, Aboriginal Australians burned forests, creating grasslands. Some studies have suggested that in addition to changing the landscape, these burning practices also affected the timing and intensity of the Australian summer monsoon. Different vegetation types can alter evaporation, roughness, and surface reflectivity, leading to changes in the weather and climate. On the basis of an ensemble of experiments with a global climate model, Notaro et al. conducted a comprehensive evaluation of the effects of decreased vegetation cover on the summer monsoon in northern Australia. They found that although decreased vegetation cover would have had only minor effects during the height of the monsoon season, during the premonsoon season, burning-induced vegetation loss would have caused significant decreases in precipitation and increases in temperature. Thus, by burning forests, Aboriginals altered the local climate, effectively extending the dry season and delaying the start of the monsoon season. (Geophysical Research Letters, doi:10.1029/2011GL047774, 2011)

  6. 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.

  7. Anomalous behaviour of the Indian summer monsoon 2009

    Indian Academy of Sciences (India)

    B Preethi; J V Revadekar; R H Kripalani

    2011-10-01

    The Indian subcontinent witnessed a severe monsoon drought in the year 2009. India as a whole received 77% of its long period average during summer monsoon season (1 June to 30 September) of 2009, which is the third highest deficient all India monsoon season rainfall year during the period 1901–2009. Therefore, an attempt is made in this paper to study the characteristic features of summer monsoon rainfall of 2009 over the country and to investigate some of the possible causes behind the anomalous behaviour of the monsoon. Presence of El Niño like conditions in the Pacific and warming over the equatorial Indian Ocean altered the circulation patterns and produced an anomalous low level convergence and ascending motion over the Indian Ocean region and large scale subsidence over the Indian landmass. Furthermore, the crossequatorial flow was weak, the monsoon was dominated by the slower 30–60 day mode, and the synoptic systems, which formed over the Bay of Bengal and the Arabian Sea, did not move inland. All the above features resulted in less moisture supply over the Indian landmass, resulting in subdued rainfall activity leading to a severe monsoon drought during 2009.

  8. Effect of dust on the iNdian summer monsoon

    Science.gov (United States)

    Maharana, Pyarimohan; Priyadarshan Dimri, Ashok

    2015-04-01

    The atmospheric dust plays a major role in deciding the radiation balance over the earth. The dust scatters the light, acts as cloud condensation nuclei, and hence helps in the formation of different types of clouds. This property of the dust has a long term effect on the Indian summer monsoon and its spatial distribution. India receives around 80% of its annual rainfall during summer monsoon and around 50% of the Indian population depends upon the monsoonal rain for the agricultural activities. The rain also has an important contribution to the industry, water resource management, ground water recharge, provide relief from the heat and also play a major role in deciding the socio-economic condition of a major part of the population. Two sets of simulations (control and dust chemistry simulation) are made to analyze the effect of dust on the Indian summer monsoon. Both the simulations nicely represent the spatial structure of different meteorological parameters. The magnitude of the pressure gradient, circulation and the precipitation is more during the JJAS for the dust chemistry simulation except for the temperature climatology. The analysis of the pre-monsoon and May temperature climatology reflects that the heating of the land mass is more in the dust chemistry simulation as compared to the control simulation, which is providing the strength to the monsoon flow during JJAS. The dust simulation shows that it increases the hydrological cycle over the Indian land mass.

  9. 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.

  10. Investigation of summer monsoon rainfall variability in Pakistan

    Science.gov (United States)

    Hussain, Mian Sabir; Lee, Seungho

    2016-01-01

    This study analyzes the inter-annual and intra-seasonal rainfall variability in Pakistan using daily rainfall data during the summer monsoon season (June to September) recorded from 1980 to 2014. The variability in inter-annual monsoon rainfall ranges from 20 % in northeastern regions to 65 % in southwestern regions of Pakistan. The analysis reveals that the transition of the negative and positive anomalies was not uniform in the investigated dataset. In order to acquire broad observations of the intra-seasonal variability, an objective criterion, the pre-active period, active period and post-active periods of the summer monsoon rainfall have demarcated. The analysis also reveals that the rainfall in June has no significant contribution to the increase in intra-seasonal rainfall in Pakistan. The rainfall has, however, been enhanced in the summer monsoon in August. The rainfall of September demonstrates a sharp decrease, resulting in a high variability in the summer monsoon season. A detailed examination of the intra-seasonal rainfall also reveals frequent amplitude from late July to early August. The daily normal rainfall fluctuates significantly with its maximum in the Murree hills and its minimum in the northwestern Baluchistan.

  11. 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...

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Development of summer monsoon and onset of continuous rains over central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Varkey, M.J.

    A new interpretation of the start of summer monsoon along central west coast of India is presented in this paper. Many authors misinterpret onset of continuous rains as start of summer monsoon front, These two are different phenomena, continuous...

  19. 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

  20. 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.

  1. Possible Impacts of the Arctic Oscillation on the Interdecadal Variation of Summer Monsoon Rainfall in East Asia

    Institute of Scientific and Technical Information of China (English)

    JU Jianhua; L(U) Junmei; CAO Jie; REN Juzhang

    2005-01-01

    The influences of the wintertime AO (Arctic Oscillation) on the interdecadal variation of summer monsoon rainfall in East Asia were examined. An interdecadal abrupt change was found by the end of the 1970s in the variation of the AO index and the leading principal component time series of the summer rainfall in East Asia. The rainfall anomaly changed from below normal to above normal in central China, the southern part of northeastern China and the Korean peninsula around 1978. However,the opposite interdecadal variation was found in the rainfall anomaly in North China and South China.The interdecadal variation of summer rainfall is associated with the weakening of the East Asia summer monsoon circulation. It is indicated that the interdecadal variation of the AO exerts an influence on the weakening of the monsoon circulation. The recent trend in the AO toward its high-index polarity during the past two decades plays important roles in the land-sea contrast anomalies and wintertime precipitation anomaly. The mid- and high-latitude regions of the Asian continent are warming, while the low-latitude regions are cooling in winter and spring along with the AO entering its high-index polarity after the late 1970s. In the meantime, the precipitation over the Tibetan Plateau and South China is excessive, implying an increase of soil moisture. The cooling tendency of the land in the southern part of Asia will persist until summer because of the memory of soil moisture. So the warming of the Asian continent is relatively slow in summer. Moreover, the Indian Ocean and Pacific Ocean, which are located southward and eastward of the Asian land, are warming from winter to summer. This suggests that the contrast between the land and sea is decreased in summer. The interdecadal decrease of the land-sea heat contrast finally leads to the weakening of the East Asia summer monsoon circulation.

  2. Summer precipitation anomalies in Asia and North America induced by Eurasian non-monsoon land heating versus ENSO

    Science.gov (United States)

    Zhao, Ping; Wang, Bin; Liu, Jiping; Zhou, Xiuji; Chen, Junming; Nan, Sulan; Liu, Ge; Xiao, Dong

    2016-02-01

    When floods ravage Asian monsoon regions in summer, megadroughts often attack extratropical North America, which feature an intercontinental contrasting precipitation anomaly between Asia and North America. However, the characteristics of the contrasting Asian-North American (CANA) precipitation anomalies and associated mechanisms have not been investigated specifically. In this article, we firmly establish this summer CANA pattern, providing evidence for a significant effect of the land surface thermal forcing over Eurasian non-monsoon regions on the CANA precipitation anomalies by observations and numerical experiments. We show that the origin of the CANA precipitation anomalies and associated anomalous anticyclones over the subtropical North Pacific and Atlantic has a deeper root in Eurasian non-monsoon land surface heating than in North American land surface heating. The ocean forcing from the ENSO is secondary and tends to be confined in the tropics. Our results have strong implications to interpretation of the feedback of global warming on hydrological cycle over Asia and North America. Under the projected global warming due to the anthropogenic forcing, the prominent surface warming over Eurasian non-monsoon regions is a robust feature which, through the mechanism discussed here, would favor a precipitation increase over Asian monsoon regions and a precipitation decrease over extratropical North America.

  3. Summer precipitation anomalies in Asia and North America induced by Eurasian non-monsoon land heating versus ENSO.

    Science.gov (United States)

    Zhao, Ping; Wang, Bin; Liu, Jiping; Zhou, Xiuji; Chen, Junming; Nan, Sulan; Liu, Ge; Xiao, Dong

    2016-01-01

    When floods ravage Asian monsoon regions in summer, megadroughts often attack extratropical North America, which feature an intercontinental contrasting precipitation anomaly between Asia and North America. However, the characteristics of the contrasting Asian-North American (CANA) precipitation anomalies and associated mechanisms have not been investigated specifically. In this article, we firmly establish this summer CANA pattern, providing evidence for a significant effect of the land surface thermal forcing over Eurasian non-monsoon regions on the CANA precipitation anomalies by observations and numerical experiments. We show that the origin of the CANA precipitation anomalies and associated anomalous anticyclones over the subtropical North Pacific and Atlantic has a deeper root in Eurasian non-monsoon land surface heating than in North American land surface heating. The ocean forcing from the ENSO is secondary and tends to be confined in the tropics. Our results have strong implications to interpretation of the feedback of global warming on hydrological cycle over Asia and North America. Under the projected global warming due to the anthropogenic forcing, the prominent surface warming over Eurasian non-monsoon regions is a robust feature which, through the mechanism discussed here, would favor a precipitation increase over Asian monsoon regions and a precipitation decrease over extratropical North America. PMID:26916258

  4. What drives the global summer monsoon over the past millennium?

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jian [Chinese Academy of Sciences, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Nanjing (China); Wang, Bin [University of Hawaii at Manoa, Department of Meteorology, Honolulu, HI (United States); University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Yim, So-Young; Lee, June-Yi [University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Jhun, Jong-Ghap [Seoul National University, School of Earth and Environmental Sciences/Research Institute of Oceanography, Seoul (Korea, Republic of); Ha, Kyung-Ja [Pusan National University, Division of Earth Environmental System, Busan (Korea, Republic of)

    2012-09-15

    The global summer monsoon precipitation (GSMP) provides a fundamental measure for changes in the annual cycle of the climate system and hydroclimate. We investigate mechanisms governing decadal-centennial variations of the GSMP over the past millennium with a coupled climate model's (ECHO-G) simulation forced by solar-volcanic (SV) radiative forcing and greenhouse gases (GHG) forcing. We show that the leading mode of GSMP is a forced response to external forcing on centennial time scale with a globally uniform change of precipitation across all monsoon regions, whereas the second mode represents internal variability on multi-decadal time scale with regional characteristics. The total amount of GSMP varies in phase with the global mean temperature, indicating that global warming is accompanied by amplification of the annual cycle of the climate system. The northern hemisphere summer monsoon precipitation (NHSMP) responds to GHG forcing more sensitively, while the southern hemisphere summer monsoon precipitation (SHSMP) responds to the SV radiative forcing more sensitively. The NHSMP is enhanced by increased NH land-ocean thermal contrast and NH-minus-SH thermal contrast. On the other hand, the SHSMP is strengthened by enhanced SH subtropical highs and the east-west mass contrast between Southeast Pacific and tropical Indian Ocean. The strength of the GSMP is determined by the factors controlling both the NHSMP and SHSMP. Intensification of GSMP is associated with (a) increased global land-ocean thermal contrast, (b) reinforced east-west mass contrast between Southeast Pacific and tropical Indian Ocean, and (c) enhanced circumglobal SH subtropical highs. The physical mechanisms revealed here will add understanding of future change of the global monsoon. (orig.)

  5. 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.

  6. 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

  7. 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

  8. Himalayan River Terraces as A Landscape Response to Quaternary Summer Monsoon Variability

    Science.gov (United States)

    Jonell, T. N.; Clift, P. D.

    2013-12-01

    In order to interpret marine sedimentary archives as records of the erosional response to Asian monsoon variability, we must first recognize how transport processes affect the storage and release of sediment to the ocean. River terraces, such as found in the Greater Himalaya, provide a pivotal role in the source-to-sink story, because this is where sediment storage occurs and is likely modulated. We investigate the role that climate plays in controlling erosion and sediment flux to the Indus delta and fan by looking at the Indus River system, which is dominated by the strong forcing of the Asian monsoon, as well as winter Westerly winds. Paleoceanographic, speleothem, and lacustrine records indicate that summer monsoon intensity was strong from 29 to 37 ka, decreased after that time until ~16 ka, reached maximum intensity from 8 to 10 ka, and then weakened until ~3 ka. Some lacustrine records, however, indicate a more complex pattern of monsoon variability in the Greater Himalaya, which contrasts with monsoonal forcing in central India. This disagreement suggests that floodplains of major river systems may not experience the same climatic conditions as their mountain sources, resulting in contrasting landscape responses to climate change. High altitude river valleys, at least north ofthe Greater Himalaya, appear to be sensitive to monsoon strength because they lie on the periphery of the present rainfall maximum, in the Himalayan rain shadow. These steep river valleys may be affected by landslide damming during periods of increase moisture transport and strong monsoonal precipitation, where damming provides sediment storage through valley-filling and later sediment release through gradual incision or dam-bursting. The Zanskar River, a major tributary to the upper Indus River, provides a record of the erosional response of mountain river valleys to these extreme phases through river terracing. New OSL ages from alluvial terraces indicate reworking of sediment and

  9. 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

    Full Text Available Comparison of single-forcing varieties of 20th century historical experiments in a subset of models from the Fifth Coupled Model Intercomparison Project (CMIP5 reveals that South Asian summer monsoon rainfall increases towards the present day in Greenhouse Gas (GHG-only experiments with respect to pre-industrial levels, while it decreases in anthropogenic aerosol-only experiments. Comparison of these single-forcing experiments with the all-forcings historical experiment suggests aerosol emissions have dominated South Asian monsoon rainfall trends in recent decades, especially during the 1950s to 1970s. The variations in South Asian monsoon rainfall in these experiments follows approximately the time-evolution of inter-hemispheric temperature gradient over the same period, suggesting a contribution from the large-scale background state relating to the asymmetric distribution of aerosol emissions about the equator. By examining the twenty-five available all-forcings historical experiments, we show that models including aerosol indirect effects dominate the negative rainfall trend. Indeed, models including only the direct radiative effect of aerosol show an increase in monsoon rainfall, consistent with the dominance of increasing greenhouse gas emissions and planetary warming on monsoon rainfall in those models. For South Asia, reduced rainfall in the models with indirect effects is related to decreased evaporation at the land surface rather than from anomalies in horizontal moisture flux, suggesting the impact of indirect effects on local aerosol emissions. This is confirmed by examination of aerosol loading and cloud droplet number trends over the South Asia region. Thus while remote aerosols and their asymmetric distribution about the equator play a role in setting the inter-hemispheric temperature distribution on which the South Asian monsoon, as one of the global monsoons, operates, the addition of indirect aerosol effects acting on very local

  10. 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

    Comparison of single-forcing varieties of 20th century historical experiments in a subset of models from the Fifth Coupled Model Intercomparison Project (CMIP5) reveals that South Asian summer monsoon rainfall increases towards the present day in Greenhouse Gas (GHG)-only experiments with respect to pre-industrial levels, while it decreases in anthropogenic aerosol-only experiments. Comparison of these single-forcing experiments with the all-forcings historical experiment suggests aerosol emissions have dominated South Asian monsoon rainfall trends in recent decades, especially during the 1950s to 1970s. The variations in South Asian monsoon rainfall in these experiments follows approximately the time evolution of inter-hemispheric temperature gradient over the same period, suggesting a contribution from the large-scale background state relating to the asymmetric distribution of aerosol emissions about the equator. By examining the 24 available all-forcings historical experiments, we show that models including aerosol indirect effects dominate the negative rainfall trend. Indeed, models including only the direct radiative effect of aerosol show an increase in monsoon rainfall, consistent with the dominance of increasing greenhouse gas emissions and planetary warming on monsoon rainfall in those models. For South Asia, reduced rainfall in the models with indirect effects is related to decreased evaporation at the land surface rather than from anomalies in horizontal moisture flux, suggesting the impact of indirect effects on local aerosol emissions. This is confirmed by examination of aerosol loading and cloud droplet number trends over the South Asia region. Thus, while remote aerosols and their asymmetric distribution about the equator play a role in setting the inter-hemispheric temperature distribution on which the South Asian monsoon, as one of the global monsoons, operates, the addition of indirect aerosol effects acting on very local aerosol emissions also

  11. 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.

  12. Teleconnection between the Indian summer monsoon onset and the Meiyu over the Yangtze River Valley

    Institute of Scientific and Technical Information of China (English)

    LIU YunYun; DING YiHui

    2008-01-01

    Based on the Indian and Chinese precipitation data and the NCEP-NCAR reanalysis circulation data,the relationship between the Indian summer monsoon (ISM) onset and the Meiyu over the Yangtze River Valley has been discussed by the methods of correlation analysis and composite analysis. The results show that the date of ISM onset over Kerala in the southwestern coast of the Indian Peninsula is about two weeks earlier than the beginning of the Meiyu over the Yangtze River Valley. After the outbreak of ISM,the teleconnection mode sets up from the western coast of India via the Bay of Bengal (BOB) to the Yangtze River Valley and southern Japan. It is different both in time and space from the teleconnection mode which is from the northwest of India via the Tibetan Plateau to northern China. The former mode is defined as the "south" teleconnection of the Asian summer monsoon,forming in the period of ISM onset; while the latter mode is called the "north" teleconnection,mainly occurring in the Asian monsoon culminant period. During the process of the "south" teleconnection's formation,the Asian monsoon circulation has experienced a series of important changes: ISM onset,the northward movement of the south Asia high (SAH),the onset vortex occurrence,the eastward extension of the stronger tropical westerly belt,and the northeastward jump of the western Pacific subtropical high(WPSH),etc. Consequently,since ISM sets up over Kerala,the whole Asian continent is covered by the upper SAH after about two weeks,while in the mid- and lower troposphere,a strong wind belt forms from the Arabian Sea via the southern India,BOB and the South China Sea (SCS),then along the western flank of WPSH,to the Yangtze River Valley and southern Japan. With the northward moving of the subtropical jet streams,the upper westerly jet stream and the low level jet have been coupled vertically over east Asia,while the Yangtze River Valley happens to locate in the ascending motion area between the upper jet

  13. Active and break spells of the Indian summer monsoon

    Indian Academy of Sciences (India)

    M Rajeevan; Sulochana Gadgil; Jyoti Bhate

    2010-06-01

    In this paper, we suggest criteria for the identification of active and break events of the Indian summer monsoon on the basis of recently derived high resolution daily gridded rainfall dataset over India (1951–2007). Active and break events are defined as periods during the peak monsoon months of July and August, in which the normalized anomaly of the rainfall over a critical area, called the monsoon core zone exceeds 1 or is less than −1.0 respectively, provided the criterion is satisfied for at least three consecutive days. We elucidate the major features of these events. We consider very briefly the relationship of the intraseasonal fluctuations between these events and the interannual variation of the summer monsoon rainfall. We find that breaks tend to have a longer life-span than active spells. While, almost 80% of the active spells lasted 3–4 days, only 40% of the break spells were of such short duration. A small fraction (9%) of active spells and 32% of break spells lasted for a week or longer. While active events occurred almost every year, not a single break occurred in 26% of the years considered. On an average, there are 7 days of active and break events from July through August. There are no significant trends in either the days of active or break events. We have shown that there is a major difference between weak spells and long intense breaks. While weak spells are characterized by weak moist convective regimes, long intense break events have a heat trough type circulation which is similar to the circulation over the Indian subcontinent before the onset of the monsoon. The space-time evolution of the rainfall composite patterns suggests that the revival from breaks occurs primarily from northward propagations of the convective cloud zone. There are important differences between the spatial patterns of the active/break spells and those characteristic of interannual variation, particularly those associated with the link to ENSO. Hence, the

  14. Circulation Patterns of Summer Monsoon Corresponding to Two Kinds of Indices over the South China Sea

    Institute of Scientific and Technical Information of China (English)

    SUN Jilin; WANG Dongxiao

    2002-01-01

    The characteristics of circulation corresponding to two kinds of indices of summer monsoon onset over the South China Sea (SCS) have been discussed using the reanalysis data of the National Centers for Environmental Prediction-National Center for Atmospheric Research. It is found that there are two patterns of deep convection that occur at different locationsand influence the summer monsoon onset over the SCS. One is over the Asia continent and the western Pacific corresponding to the southwesterly of summer monsoon prevailing over the northern and central part of the SCS, while the other is near the Philippines that affects the westerly summer monsoon as prevailing over the central and southern part of the SCS. Since these two kinds of convection affecting the summer monsoon onset do not always occur together, thus the summer monsoon onset time is different when determined by various indices.

  15. Future precipitation extremes during summer monsoon in southern Pakistan

    Science.gov (United States)

    Zahid, Maida; Lucarini, Valerio

    2016-04-01

    Extreme precipitation events are considered as a hydro-meteorological hazard resulting in colossal damage worldwide. In Pakistan, the extreme precipitation events have increased in the recent decades particularly in the southern part (Sindh province). This region did not receive substantial amount of precipitation earlier, but now experiencing urban flooding almost every year causing loss of life, property, crops and infrastructure. The region lacks the information regarding the recurrence of extreme precipitation events. Therefore, there is a strong need for a reliable information of extremes over the upcoming decades for better regional planning. Although statistical methods based on extreme value theory (EVT) are the most relevant ones to study the extremes, but they are never been applied in Pakistan. To address this shortcoming, we use the peak over threshold (POT) approach to compute the return levels (RLs) of precipitation extremes, and also identify the regions most prone to them. In this study, we analyzed the summer monsoon daily precipitation measured at nine weather stations of Pakistan Meteorological Department over the period 1980-2013. The summer monsoon (JJAS) is preferred for the analysis, because most of the extreme precipitation occurs during this period. We apply POT approach to model the daily precipitation above a selected threshold for each station. Then, we estimate return levels (RLs) of precipitation extremes during summer monsoon in southern Pakistan (Sindh) for the next 5, 25, 50 and 100-years. Lastly, we compare the 5-years with 100-years RLs to indicate the stations most vulnerable to precipitation extremes in future. This work is funded by the Climate KIC, European Institute of Innovation and Technology, Germany.

  16. 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.

  17. Amplification of ENSO effects on Indian summer monsoon by absorbing aerosols

    Science.gov (United States)

    Kim, Maeng-Ki; Lau, William K. M.; Kim, Kyu-Myong; Sang, Jeong; Kim, Yeon-Hee; Lee, Woo-Seop

    2016-04-01

    In this study, we present observational evidence, based on satellite aerosol measurements and MERRA reanalysis data for the period 1979-2011, indicating that absorbing aerosols can have strong influence on seasonal-to-interannual variability of the Indian summer monsoon rainfall, including amplification of ENSO effects. We find a significant correlation between ENSO (El Nino Southern Oscillation) and aerosol loading in April-May, with La Nina (El Nino) conditions favoring increased (decreased) aerosol accumulation over northern India, with maximum aerosol optical depth over the Arabian Sea and Northwestern India, indicative of strong concentration of dust aerosols transported from West Asia and Middle East deserts. Composite analyses based on a normalized aerosol index (NAI) show that high concentration of aerosol over northern India in April-May is associated with increased moisture transport, enhanced dynamically induced warming of the upper troposphere over the Tibetan Plateau, and enhanced rainfall over northern India and the Himalayan foothills during May-June, followed by a subsequent suppressed monsoon rainfall over all India, consistent with the elevated heat pump (EHP) hypothesis (Lau et al. in Clim Dyn 26:855-864, 2006. doi: 10.1007/s00382-006-0114-z). Further analyses from sub-sampling of ENSO years, with normal (1-σ) NAI over northern India respectively show that the EHP may lead to an amplification of the Indian summer monsoon response to ENSO forcing, particularly with respect to the increased rainfall over the Himalayan foothills, and the warming of the upper troposphere over the Tibetan Plateau. Our results suggest that absorbing aerosol, particular desert dusts can strongly modulate ENSO influence, and possibly play important roles as a feedback agent in climate change in Asian monsoon regions.

  18. Analysis of the seasonal ozone budget and the impact of the summer monsoon on the northeastern Qinghai-Tibetan Plateau

    Science.gov (United States)

    Zhu, Bin; Hou, Xuewei; Kang, Hanqing

    2016-02-01

    Seasonal variations in ozone (O3) and the impact of the East Asian summer monsoon at Mount Waliguan (WLG) in the northeastern Qinghai-Tibetan Plateau (TP) and in the surrounding regions were analyzed for 1997-2007 using a global chemical transport model coupled with O3 tagging simulations. The model-simulated O3 and its precursors agreed well with observed values. An O3 budget analysis combined with O3 tagging results implied that photochemistry over the TP and long-range transport of O3 from East Asia, Europe, and Africa were responsible for the surface O3 summer maximum at WLG. In June, the contribution of O3 from the TP was 11.8 ppbv, and the total contribution of O3 transport from eastern China, Japan, Korean Peninsula, Europe, and Africa was 22.7 ppbv. At 400 mb, the O3 exports from the stratosphere, Europe, Africa, and the Americas seemed to be the main sources of O3 at WLG. The contributions to surface O3 from deep convection process and lightning-induced photochemistry at WLG were both low in summer and are unlikely to be the key processes or contributors for the O3 peak. At several mountain sites in southeast East Asia, the increasing summer monsoon index was related to a decreasing trend for O3 from spring onward at Mount Tai and Mount Huang. At Mount Hua and WLG, regional O3 accumulated over the monsoon's northernmost marginal zone under the influence of the East Asian summer monsoon and TP thermal circulation; this is most likely a key reason for the O3 summer maxima.

  19. Effects of South China Sea/western North Pacific summer monsoon on tropospheric biennial oscillation (TBO)

    Institute of Scientific and Technical Information of China (English)

    Zheng Bin; Gu De-Jun; Lin Ai-Lan; Li Chun-Hui

    2007-01-01

    Severed theories have been developed to explain tropical biennial oscillation (TBO), as an air-sea interactive system to impact Asian and global weather and climate, and some models have been established to produce a TBO. A simple 5-box model, with almost all the key processes associated with TBO, can produce a TBO by including air-sea interactions in the monsoon regions. Despite that, the South China Sea/western North Pacific summer monsoon (SCS/WNPSM), a very important monsoon subsystem, is neglected. In this paper, based on the dynamical framework of 5-box model, the term of SCS/WNPSM has been added and a 6-box model has been developed. Comparing the difference of TBO sensibilities with several key parameters, air-sea coupling coefficient α, SST-thermocline feedback coefficient γ and wind-evaporation feedback coefficient λ, between the modified model and original model, TBO is more sensible to the parameters in the new model. The results imply that the eastern Pacific and local wind-evaporation play more important roles in the TBO when including SCS/WNPSM.

  20. 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’.

  1. 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

  2. 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

  3. Active and break events of Indian summer monsoon during 1901-2014

    Digital Repository Service at National Institute of Oceanography (India)

    Pai, D.S.; Sridhar, L.; RameshKumar, M.R.

    . Dyn., vol.46(11); 2016; 3921-3939 Active and Break Events of Indian Summer Monsoon during 1901-2014 D.S. Pai*, Latha Sridhar* and M. R. Ramesh Kumar** *India Meteorological Department, Pune **National Institute of Oceanography, Goa Contact e... words: Monsoon break and active spells, monsoon depression, gridded daily rainfall, decadal variation 2 1 Introduction Over India, the large scale rainfall during the SW monsoon season (June-September) is received in spells with intermediate dry...

  4. 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.

  5. 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

  6. 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.

  7. Seasonal prediction of Indian summer monsoon: Sensitivity to persistent SST

    Indian Academy of Sciences (India)

    Sukanta Kumar Das; Sanjib Kumar Deb; C M Kishtawal; Pradip Kumar Pal

    2013-10-01

    In the present study, the assessment of the Community Atmosphere Model (CAM) developed at National Centre for Atmospheric Research (NCAR) for seasonal forecasting of Indian Summer Monsoon (ISM) with different persistent SST is reported. Towards achieving the objective, 30-year model climatology has been generated using observed SST. Upon successful simulation of climatological features of ISM, the model is tested for the simulation of ISM 2011 in forecast mode. Experiments have been conducted in three different time-phases, viz., April, May and June; using different sets of initial conditions (ICs) and the persistent SSTs of the previous months of the time-phases. The spatial as well as temporal distribution of model simulated rainfall suggest a below normal monsoon condition throughout the season in all the experiments. However, the rainfall anomaly shows some positive signature over north-east part of India in the month of June and August whereas the central Indian landmass had positive anomaly during August and September. The monthly accumulated All-India rainfall (AIR) over land for June to September 2011 are predicted to be 101% (17.6 cm), 86% (24.3 cm), 83% (21.0 cm) and 95% (15.5 cm) of normal AIR, respectively. This makes the seasonal accumulated AIR 78.4 cm which is 11% below the normal rainfall of 87.6 cm. The model prediction for the months of June and July is comparable with the observation; however, the simulation would not be able to capture the high rainfall during August and September. The intention behind this work is to assess the shortcomings in the CAM model prediction, which can later be improved for future monsoon forecast experiments.

  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. Hydrography of the eastern Arabian Sea during summer monsoon 2002

    Indian Academy of Sciences (India)

    D Shankar; S S C Shenoi; R K Nayak; P N Vinayachandran; G Nampoothiri; A M Almeida; G S Michael; M R Ramesh Kumar; D Sundar; O P Sreejith

    2005-10-01

    Hydrographic observations in the eastern Arabian Sea (EAS)during summer monsoon 2002 (during the first phase of the Arabian Sea Monsoon Experiment (ARMEX))include two approximately fortnight-long CTD time series.A barrier layer was observed occasionally during the two time series. These ephemeral barrier layers were caused by in situ rainfall,and by advection of low-salinity (high-salinity)waters at the surface (below the surface mixed layer).These barrier layers were advected away from the source region by the West India Coastal Current and had no discernible effect on the sea surface temperature.The three high-salinity water masses,the Arabian Sea High Salinity Water (ASHSW),Persian Gulf Water (PGW),and Red Sea Water (RSW),and the Arabian Sea Salinity Minimum also exhibited intermittency:they appeared and disappeared during the time series.The concentration of the ASHSW,PGW,and RSWdecreased equatorward,and that of the RSW also decreased offshore.The observations suggest that the RSW is advected equatorward along the continental slope off the Indian west coast.

  10. Meteorological fields variability over the Indian seas in pre and summer monsoon months during extreme monsoon seasons

    Indian Academy of Sciences (India)

    U C Mohanty; R Bhatla; P V S Raju; O P Madan; A Sarkar

    2002-09-01

    In this study, the possible linkage between summer monsoon rainfall over India and surface meteorological fields (basic fields and heat budget components) over monsoon region (30° E-120°E, 30°S-30°N) during the pre-monsoon month of May and summer monsoon season (June to September) are examined. For this purpose, monthly surface meteorological fields anomaly are analyzed for 42 years (1958-1999) using reanalysis data of NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research). The statistical significance of the anomaly (difference) between the surplus and deficient monsoon years in the surface meteorological fields are also examined by Student's t-test at 95% confidence level. Significant negative anomalies of mean sea level pressure are observed over India, Arabian Sea and Arabian Peninsular in the pre-monsoon month of May and monsoon season. Significant positive anomalies in the zonal and meridional wind (at 2m) in the month of May are observed in the west Arabian Sea off Somali coast and for monsoon season it is in the central Arabian Sea that extends up to Somalia. Significant positive anomalies of the surface temperature and air temperature (at 2m) in the month of May are observed over north India and adjoining Pakistan and Afghanistan region. During monsoon season this region is replaced by significant negative anomalies. In the month of May, significant positive anomalies of cloud amount are observed over Somali coast, north Bay of Bengal and adjoining West Bengal and Bangladesh. During monsoon season, cloud amount shows positive anomalies over NW India and north Arabian Sea. There is overall reduction in the incoming shortwave radiation flux during surplus monsoon years. A higher magnitude of latent heat flux is also found in surplus monsoon years for the month of May as well as the monsoon season. The significant positive anomaly of latent heat flux in May, observed over southwest Arabian Sea, may be considered

  11. Long range prediction of Indian summer monsoon rainfall

    Indian Academy of Sciences (India)

    A A Munot; K Krishna Kumar

    2007-02-01

    The search for new parameters for predicting the all India summer monsoon rainfall (AISMR) has been an important aspect of long range prediction of AISMR. In recent years NCEP/NCAR reanalysis has improved the geographical coverage and availability of the data and this can be easily updated. In this study using NCEP/NCAR reanalysis data on temperature, zonal and meridional wind at different pressure levels, few predictors are identified and a prediction scheme is developed for predicting AISMR. The regression coeffcients are computed by stepwise multiple regression procedure. The final equation explained 87% of the variance with multiple correlation coeffcient (MCC), 0.934. The estimated rainfall in the El-Nino year of 1997 was -1.7% as against actual of 4.4%. The estimated rainfall deficiency in both the recent deficient years of 2002 and 2004 were -19.5% and -8.5% as against observed -20.4% and -11.5% respectively.

  12. 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.

  13. Origin of summer monsoon rainfall identified by δ18O in precipitation

    Institute of Scientific and Technical Information of China (English)

    PANG Hongxi; HE Yuanqing; ZHANG Zhonglin; LU Aigang; GU Juan; ZHAO Jingdong

    2005-01-01

    A negative correlation between δ18O in monsoon precipitation and f, the ratio of precipitable water in monsoon region to that in water source area, is hypothesized.Using the Rayleigh model, a new method for identifying origin of summer monsoon rainfall is developed based on the hypothesis. In order to validate the method, the isotopic data at New Delhi, a typical station in the southwest monsoon region, and Hong Kong, a typical station in the southeast monsoon region, were collected and analyzed for case studies.The case studies indicate that the water source areas of the monsoon rainfall at the two stations identified by the method are accordant with the general atmosphere circulation patterns. The method developed in this paper is significantly important for tracing the origin of summer monsoon precipitation.

  14. 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.

  15. 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.

  16. 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

  17. Indian summer monsoon precipitating clouds: role of microphysical process rates

    Science.gov (United States)

    Hazra, Anupam; Chaudhari, Hemantkumar S.; Pokhrel, Samir; Saha, Subodh K.

    2016-04-01

    The budget analysis of microphysical process rates based on Modern Era Retrospective-analysis for Research and Applications (MERRA) products are presented in the study. The relative importance of different microphysical process rates, which is crucial for GCMs, is investigated. The autoconversion and accretion processes are found to be vital for Indian Summer Monsoon (ISM). The map-to-map correlations are examined between observed precipitation and MERRA reanalysis. The pattern correlations connote the fidelity of the MERRA datasets used here. Results of other microphysical parameters (e.g. ice water content from CloudSat, high cloud fraction from CALIPSO and MODIS, latent heating from TRMM, cloud ice mixing ratio from MERRA) are presented in this study. The tropospheric temperature from reanalysis product of MERRA and NCEP are also analyzed. Furthermore, the linkages between cloud microphysics production rates and dynamics, which are important for North-South tropospheric temperature gradient for maintaining the ISM circulation, are also discussed. The study demonstrates the microphysical process rates, which are actually responsible for the cloud hydrometeors and precipitation formation on the monsoon intraseasonal oscillations timescale. Cloud to rain water auto-conversion and snow accretion rates are the dominant processes followed by the rain accretion. All these tendency terms replicates the similar spatial patterns as that of precipitation. The quantification of microphysical process rates and precipitation over different regions are shown here. The freezing rate is also imperative for the formation of cloud ice as revealed by the observation. Freezing rates at upper level and snow accretion at middle level may have effect on latent heating release. Further it can modulate the north-south temperature gradient which can influence the large-scale monsoon dynamics. The rain water evaporation is also considered as a key aspect for controlling the low level

  18. 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.

  19. Possible role of pre-monsoon sea surface warming in driving the summer monsoon onset over the Bay of Bengal

    Science.gov (United States)

    Li, Kuiping; Liu, Yanliang; Yang, Yang; Li, Zhi; Liu, Baochao; Xue, Liang; Yu, Weidong

    2016-08-01

    Sea surface temperature (SST) reaches its annual maximum just before the summer monsoon onset and collapses soon after in the central areas of the Bay of Bengal (BoB). Here, the impact of the peak in the pre-monsoon SST on triggering the earliest monsoon onset in the BoB is investigated, with a focus on the role they play in driving the first-branch northward-propagating intra-seasonal oscillations (FNISOs) over the equatorial Eastern Indian Ocean (EIO). During the calm pre-monsoon period, sea surface warming in the BoB could increase the surface equivalent potential temperature (θe) in several ways. Firstly, warming of the sea surface heats the surface air through sensible heating, which forces the air temperature to follow the SST. The elevated air surface temperature accounts for 30 % of the surface θe growth. Furthermore, the elevated air temperature raises the water vapor capacity of the surface air to accommodate more water vapor. Constrained by the observation that the surface relative humidity is maintained nearly constant during the monsoon transition period, the surface specific humidity exhibits a significant increase, according to the Clausius-Clapeyron relationship. Budget analysis indicates that the additional moisture is primarily obtained from sea surface evaporation, which also exhibits a weak increasing trend due to the sea surface warming. In this way, it contributes about 70 % to the surface θe growth. The rapid SST increase during the pre-monsoon period preconditions the summer monsoon onset over the BoB through its contributions to significantly increase the surface θe, which eventually establishes the meridional asymmetry of the atmospheric convective instability in the EIO. The pre-established greater convective instability leads to the FNISO convections, and the summer monsoon is triggered in the BoB region.

  20. Variation of Methane, Water Vapor and Clouds over Tibetan PlateauUnder the Impact of Asian Summer Monsoon%季风影响下的青藏高原上空甲烷、水汽及云的变化

    Institute of Scientific and Technical Information of China (English)

    熊效振; 张莹; 陈良富; 占瑞芬; 李建平

    2011-01-01

    In order to understand the impact of Monsoon to the transport of water vapor and trace gases, an analysis of the relationship between mid-uppertropospheric methane (CH4), water vapor, cloud amounts and cloud top height with the monsoon index was made by using the AIRS CH4 data from 2003 to 2010, and the water vapor and cloud data from MODIS on EOS/Aqua. The results indicated that, during the Asian Summer Monsoon (ASM), the variations of water vapor, cloud amounts and cloud top heights are closely correlated with the monsoon index. Due to the strong convection over the Tibetan Plateau (TP), more water vapor is transported to the TP, resulting in more cloud amounts and the elevated cloud top height. Correspondingly, the CH4 transported leads to the increase of the CH4 concentration in the mid-upper troposphere and its accumulation over the TP under the constraint by the strong Tibetan anticyclone. The occurrence of the CH4 maximum is about one month late than Monsoon Index. With the withdrawal of the ASM and the dissipation of anticyclone, the maximum of CH4 disappears rapidly. These results suggested that the strong convection over the TP is one of the major factors controlling the formation of CH4 plume. As a long life trace gas, CH4 has the potential to be used as a tracer to help the study the ASM and the dynamic of anticyclone.%为进一步了解季风对于水汽及其它大气成分的输送作用,利用美国Aqua卫星上AIRS反演的甲烷(CH4)和MODIS反演的水汽、云高和云量等卫星观测资料,分析了2003至2010年中国青藏高原上空CH4、水汽和云在季风期间的变化及其与季风指数的关系.研究发现:夏季(6月至9月)高原上空水汽、云量和云顶高度的变化与季风指数有很好的相关;在强对流影响下,输送到高原上空的水汽增多,引起云量增多,云顶高度增加,而向上输送的甲烷引起高原上空CH4浓度增加,并在青藏高压强大的反气旋的阻塞下CH4不断积累,

  1. 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

  2. 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

  3. 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.

  4. 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

  5. Seasonal prediction of East Asian summer rainfall using a multi-model ensemble system

    Science.gov (United States)

    Ahn, Joong-Bae; Lee, Doo-Young; Yoo, Jin‑Ho

    2015-04-01

    Using the retrospective forecasts of seven state-of-the-art coupled models and their multi-model ensemble (MME) for boreal summers, the prediction skills of climate models in the western tropical Pacific (WTP) and East Asian region are assessed. The prediction of summer rainfall anomalies in East Asia is difficult, while the WTP has a strong correlation between model prediction and observation. We focus on developing a new approach to further enhance the seasonal prediction skill for summer rainfall in East Asia and investigate the influence of convective activity in the WTP on East Asian summer rainfall. By analyzing the characteristics of the WTP convection, two distinct patterns associated with El Niño-Southern Oscillation developing and decaying modes are identified. Based on the multiple linear regression method, the East Asia Rainfall Index (EARI) is developed by using the interannual variability of the normalized Maritime continent-WTP Indices (MPIs), as potentially useful predictors for rainfall prediction over East Asia, obtained from the above two main patterns. For East Asian summer rainfall, the EARI has superior performance to the East Asia summer monsoon index or each MPI. Therefore, the regressed rainfall from EARI also shows a strong relationship with the observed East Asian summer rainfall pattern. In addition, we evaluate the prediction skill of the East Asia reconstructed rainfall obtained by hybrid dynamical-statistical approach using the cross-validated EARI from the individual models and their MME. The results show that the rainfalls reconstructed from simulations capture the general features of observed precipitation in East Asia quite well. This study convincingly demonstrates that rainfall prediction skill is considerably improved by using a hybrid dynamical-statistical approach compared to the dynamical forecast alone. Acknowledgements This work was carried out with the support of Rural Development Administration Cooperative Research

  6. 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.

  7. Emission sources contributing to tropospheric ozone over equatorial Africa during the summer monsoon

    Directory of Open Access Journals (Sweden)

    I. Bouarar

    2011-05-01

    Full Text Available A global chemistry-climate model LMDz_INCA is used to investigate the contribution of African and Asian emissions to tropospheric ozone over central and West Africa during the summer monsoon. The model results show that ozone in this region is most sensitive to lightning NOx and to central African biomass burning emissions. However, other emission categories also contribute significantly to regional ozone. The maximum ozone changes due to lightning NOx occur in the upper troposphere between 400 hPa and 200 hPa over West Africa and downwind over the Atlantic Ocean. Biomass burning emissions mainly influence ozone in the lower and middle troposphere over central Africa, and downwind due to westward transport. Biogenic emissions of volatile organic compounds, which can be uplifted from the lower troposphere into higher altitudes by the deep convection that occurs over West Africa during the monsoon season, dominate the ozone changes in the upper troposphere and lower stratosphere region. Convective uplift of soil NOx emissions over the Sahel region also makes a significant contribution to ozone in the upper troposphere. Concerning African anthropogenic emissions, they make a lower contribution to ozone compared to the other emission categories. The model results indicate that most ozone changes due to African emissions occur downwind, especially over the Atlantic Ocean, far from the emission regions. The influence of Asian emissions should also be taken into account in studies of the ozone budget over Africa since they make a considerable contribution to ozone concentrations above 150 hPa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report estimates of anthropogenic emissions for 2030 over Africa and Asia, the model calculations suggest largest changes in ozone due to the growth of emissions over Asia than over Africa over the next 20 years.

  8. 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.

  9. Long range forecasting of summer monsoon rainfall from SST in the central equatorial Indian Ocean

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Murthy, T.V.R.

    pressure change at Bombay during Winter to pre-monsoon and Sea Surface Temperature (SST) over Pacific and Indian Ocean regions. The relationship between SST in the Central Equatorial Indian Ocean (CEIO) and all India Summer Monsoon Rainfall using the data...

  10. Coastal processes at the southern tip of India during summer monsoon 2005

    Digital Repository Service at National Institute of Oceanography (India)

    Smitha, B.R.; VimalKumar, K.G.; Sanjeevan, V.N.

    In situ temperature and wind data, during summer monsoon 2005, bring out some interesting features like, the existence of a purely wind driven upweiling system at the southern tip (ST), very adjacent to another remotely forced upweiling system...

  11. Relationships between Indian summer monsoon rainfall and ice cover over selected oceanic regions

    Digital Repository Service at National Institute of Oceanography (India)

    Gopinathan, C.K.

    The variations in oceanic ice cover at selected polar regions during 1973 to 1987 have been analysed in relation to the seasonal Indian summer monsoon rainfall. The ice cover over the Arctic regions in June has negative relationship (correlation...

  12. 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

    needed temporal and spatial coupling and means for validation of mesoscale model simulations (Zhong et al., 2009, 2011). When these time series are integrated into energy balance analyses methods (Su, 2002, 2005) with reanalysis data, plateau scale diurnal radiative and turbulence fluxes can be generated (Oku et al., 2005; Su et al., 2010) for the study of the boundary layer atmospheric structures at plateau scale. As such regional land-atmosphere feedbacks and atmospheric boundary layer structures can be studied. The quantification of the multi-scale atmospheric boundary layer and land surface processes over the heterogeneous underlying surface of the Tibetan Plateau is a challenging problem that remains unsettled despite many years of efforts. Using field observation, truth investigation, land surface process parameterization and meso-scale simulation, the dynamical and thermal uniform function of the atmospheric boundary layer and its effect to the atmospheric boundary layer will be analyzed in this research. Results The different characteristics of the Boundary layer with Asia monsoon season exchange over TP The height of atmospheric boundary layer was higher before monsoon season than it in summer. It was around 3-4 km above the ground in spring, while it was 1-2 km during monsoon season. It due to sensible heat flux was stronger in spring than it in summer. Using wavelet analysis method, we decomposed the wind include horizontal and vertical velocity from radiosounding observational data. The reason of high boundary layer height was disclosed. Compared to the observation, the output of model was underestimation during spring, while it was reasonable in summer monsoon. The effect of the Asian Monsoon to the precipitation on the TP Numerical simulation of climate on the TP was implemented for the whole year of 2008 using WRF-Noah model. The output of the WRF model is compared to TRMM data set for precipitation and ERA-interim land product for soil moisture. Modeled

  13. Water vapour flux divergence over the Arabian Sea during 1987 summer monsoon using satellite data

    Digital Repository Service at National Institute of Oceanography (India)

    Vinayachandran, P.N.; RameshKumar, M.R.

    WATERVAPOURFLUXDIVERGENCEOVERTHE ARABIAN SEA DURING 1987 SUMMER MONSOON USING SATELLITE DATA (Research Note) P. N. VINAYACHANDRAN and M. R. RAMESH KUMAR Physical Oceanography Division, National Institute of Oceanography, Dona Paula 403004, Goa, India (Received in final form... 19 September, 1989) Abstract. The evaporation rates over the Arabian Sea (AS) for the summer monsoon months (June to September) of 1987 have been computed using the bulk-aerodynamic formula. The satellite derived precipitation from the INSAT-1B...

  14. 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.)

  15. On the relationship between convection intensity of South China Sea summer monsoon and air-sea temperature difference in the tropical oceans

    Institute of Scientific and Technical Information of China (English)

    LIN Ailan; LIANG Jianyin; GU Dejun; WANG Dongxiao

    2004-01-01

    The annual, interannual and inter-decadal variability of convection intensity of South China Sea (SCS) summer monsoon and air-sea temperature difference in the tropical ocean is analyzed, and their relationship is discussed using two data sets of 48-a SODA (simple ocean data assimilation) and NCEP/NCAR. Analyses show that in wintertime Indian Ocean (WIO), springtime central tropical Pacific (SCTP) and summertime South China Sea-West Pacific (SSCSWP), air-sea temperature difference is significantly associated with the convection intensity of South China Sea summer monsoon. Correlation of the inter-decadal time scale (above 10 a) is higher and more stable. There is interdecadal variability of correlation in scales less than 10 a and it is related with the air-sea temperature difference itself for corresponding waters. The inter-decadal variability of the convection intensity during the South China Sea summer monsoon is closely related to the inter-decadal variability of the general circulation of the atmosphere. Since the late period of the 1970s, in the lower troposphere, the cross-equatorial flow from the Southern Hemisphere has intensified. At the upper troposphere layer, the South Asian high and cross-equatorial flow from the Northern Hemisphere has intensified at the same time. Then the monsoon cell has also strengthened and resulted in the reinforcing of the convection of South China Sea summer monsoon.

  16. Late Glacial to Holocene Indian Summer Monsoon Variability Based upon Sediment Records Taken from the Bay of Bengal

    Directory of Open Access Journals (Sweden)

    Harunur Rashid

    2011-01-01

    Full Text Available Paleoclimatic records from the Bay of Bengal are rare. We reconstruct the sea-surface temperature (SST and salinity from paired S18O and Mg/Ca measurements in planktonic foraminifera Globigerinoides ruber from the western Bay of Bengal core VM29-19. Our data suggest that SST and seawater S18O (S18Osw were ~3C colder and ~0.6 o/oo depleted, respectively, during the Last Glacial Maximum (LGM compared to the early Holocene. The most enriched S18Osw values were found between 18.2 and 15.6 ka interval. Depleted LGM S18Osw values suggest a wet climate which freshened the Bay of Bengal sea surface. Our data further indicate that the monsoon was stronger in the Bolling/Allerod and weaker in the Younger Dryas periods. The most depleted early Holocene S18Osw values suggest that the monsoon was stronger and wetter resulting in a humid climate. After ~5 ka the Indian summer monsoon weakened significantly, indicating less dilution of the sea surface by the Ganges-Brahmaputra-Meghna outflow and/or less direct rainfall. We hypothesize that the prevailing late Holocene dry climate may have caused the diminishment and subsequent abandonment of the settlements of the great Indus Valley Civilizations. Our Bay of Bengal climate records are consistent with those from the Andaman Sea, corroborating broad regional changes in the Indian summer monsoon during the last 25 ka. The general pattern and timing of monsoon variability in the Bay of Bengal and Andaman Sea seems to parallel the Arabian Sea, Africa, and Asian ice cores and speleothem records suggesting that a common tropical forcing may have induced these abrupt climate changes.

  17. Indian summer monsoon simulations with CFSv2: a microphysics perspective

    Science.gov (United States)

    Chaudhari, Hemantkumar S.; Hazra, Anupam; Saha, Subodh K.; Dhakate, Ashish; Pokhrel, Samir

    2016-07-01

    The present study explores the impact of two different microphysical parameterization schemes (i.e. Zhao and Carr, Mon Wea Rev 125:1931-1953, 1997:called as ZC; Ferrier, Amer Meteor Soc 280-283, 2002: called as BF) of National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) on Indian summer monsoon (ISM). Critical relative humidity (RHcrit) plays a crucial role for the realistic cloud formation in a general circulation model (GCM). Hence, impact of RHcrit along with microphysical scheme on ISM is evaluated in the study. Model performance is evaluated in terms of simulation of rainfall, lower and upper tropospheric circulations, cloud fraction, cloud condensate and outgoing longwave radiation (OLR). Climatological mean features of rainfall are better represented by all the sensitivity experiments. Overall, ZC schemes show relatively better rainfall patterns as compared to BF schemes. BF schemes along with 95 % RHcrit (called as BF95) show excess precipitable water over Indian Ocean basin region, which seems to be unrealistic. Lower and upper tropospheric features are well simulated in all the sensitivity experiments; however, upper tropospheric wind patterns are underestimated as compared to observation. Spatial pattern and vertical profile of cloud condensate is relatively better represented by ZC schemes as compared to BF schemes. Relatively more (less) cloud condensate at upper level has lead to relatively better (low) high cloud fraction in ZC (BF) simulation. It is seen that OLR in ZC simulation have great proximity with observation. ZC (BF) simulations depict low (high) OLR which indicates stronger (weaker) convection during ISM period. It implies strong (weak) convection having stronger (weaker) updrafts in ZC (BF). Relatively more (less) cloud condensate at upper level of ZC (BF) may produce strong (weak) latent heating which may lead to relatively strong (weak) convection during ISM. The interaction among microphysics

  18. Validation of Seasonal Forecast of Indian Summer Monsoon Rainfall

    Science.gov (United States)

    Das, Sukanta Kumar; Deb, Sanjib Kumar; Kishtawal, C. M.; Pal, Pradip Kumar

    2015-06-01

    The experimental seasonal forecast of Indian summer monsoon (ISM) rainfall during June through September using Community Atmosphere Model (CAM) version 3 has been carried out at the Space Applications Centre Ahmedabad since 2009. The forecasts, based on a number of ensemble members (ten minimum) of CAM, are generated in several phases and updated on regular basis. On completion of 5 years of experimental seasonal forecasts in operational mode, it is required that the overall validation or correctness of the forecast system is quantified and that the scope is assessed for further improvements of the forecast over time, if any. The ensemble model climatology generated by a set of 20 identical CAM simulations is considered as the model control simulation. The performance of the forecast has been evaluated by assuming the control simulation as the model reference. The forecast improvement factor shows positive improvements, with higher values for the recent forecasted years as compared to the control experiment over the Indian landmass. The Taylor diagram representation of the Pearson correlation coefficient (PCC), standard deviation and centered root mean square difference has been used to demonstrate the best PCC, in the order of 0.74-0.79, recorded for the seasonal forecast made during 2013. Further, the bias score of different phases of experiment revealed the fact that the ISM rainfall forecast is affected by overestimation in predicting the low rain-rate (less than 7 mm/day), but by underestimation in the medium and high rain-rate (higher than 11 mm/day). Overall, the analysis shows significant improvement of the ISM forecast over the last 5 years, viz. 2009-2013, due to several important modifications that have been implemented in the forecast system. The validation exercise has also pointed out a number of shortcomings in the forecast system; these will be addressed in the upcoming years of experiments to improve the quality of the ISM prediction.

  19. Summer monsoon onset over Kerala: New definition and prediction

    Indian Academy of Sciences (India)

    D S Pai; Rajeevan M Nair

    2009-04-01

    The summer monsoon onset over Kerala (MOK)marks the beginning of the rainy season for the country.Associated with the MOK,significant transitions of large scale atmospheric and oceanic circulation patterns are observed over the Asia –Pacific region.In this study,a new method for the objective identification of MOK,based on large scale circulation features and rainfall over Kerala,is discussed.Further,a set of empirical models based on the principal component regression (PCR)technique was developed for the prediction of the date of MOK by keeping in mind the IMD ’s operational forecasting service requirements.Predictors for the models were derived using correlation analysis from the thermal,convective and circulation patterns.Only five predictors pertaining to the second half of April were used in the first model (Model-1)so that the prediction of MOK can be prepared by the end of April itself.The second model (Model-2)used four additional predictors pertaining up to the first half of May along with two predictors used in the Model-1 for update prediction at the end of the first half of May.To develop each of the PCR models, Principal Components Analysis (PCA)of the respective predictor data was carried out followed by regression analysis of first two principal components (PCs)with the date of MOK.Both these models showed good skill in predicting the date of MOK during the independent test period of 1997 –2007.The root mean square error (RMSE)of the predictions from both the models during the independent test period was about four days which was nearly half the RMSE of the predictions based on climatology.

  20. Effects of the Tibetan Plateau on the onsetof the summer monsoon in South Asia: The role of the air-sea interaction

    Science.gov (United States)

    Abe, Manabu; Hori, Masatake; Yasunari, Tetsuzo; Kitoh, Akio

    2013-02-01

    Using both a coupled atmosphere-ocean general circulation model (GCM) and an atmospheric GCM, we investigate the effects of the Tibetan Plateau (TP) on the onset of the South Asian summer monsoon by conducting simulations with and without the TP. In the coupled GCM, the presence of the TP causes the monsoon onset to occur approximately 15 days later in the Arabian Sea (AS) and India (ID) and approximately 10 days earlier in the Bay of Bengal (BB). These changes are attributed to different atmospheric circulation patterns and different conditions within the adjacent oceans, such as the AS and the BB. When the TP is included, lower sea surface temperatures (SSTs) in the AS contribute to a stable lower atmosphere, which suppresses convection over the AS and ID in May. In contrast, low pressure over South Asia, caused by the TP, induces a southwesterly toward the BB that transports a substantial amount of water vapor to the BB. This flow results in an earlier monsoon in the BB. Without the TP, higher SSTs that are formed in the AS in May destabilize the lower atmosphere and create a depression, resulting in an earlier onset of the monsoon over the AS and ID. Consequently, the cyclonic circulation spreads abruptly to the BB, and precipitation begins to increase over the BB. Therefore, the air-sea interaction in the adjacent ocean under the influence of the TP strongly modulates the onset of the South Asian summer monsoon. This modulation was verified by the atmospheric GCM experiments.

  1. A THEORETICAL STUDY ON THE MULTIPLE EQUILIBRIA OF TROPICAL ATMOSPHERE AND THEIR RELATION TO THE ONSET OF THE SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    ZHAO Nan; DING Yi-hui; Masaaki Takahashi; SHEN Xin-yong

    2006-01-01

    Multiple equilibria and their stability in tropical atmosphere are investigated through β -plane barotropic models with consideration of heating and dissipation. We have derived the solutions of the model equations corresponding to the multiple equilibria or the steady flows first, and then establish the criteria for the stability of steady flow by use of the Liapunov direct Method. When these criteria are applied to the solutions of equilibria obtained, stable flows, which are closely related to the different patterns of quasi-stationary circulation in the tropical region, are found. The configurations of these stable flows and the shift between two of them as season changes provide quite reasonable explanations to many fundamental problems of tropical circulation features such as the catastrophe mechanism of the onset and the break-active cycle of the Asian summer monsoon. It follows that the onset or the abrupt transition of the Asian summer monsoon could be attributed to the multiple equilibrium property of the tropical circulation resulted from the advective nonlinearity, which provide another explanation among others.

  2. 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.

  3. Emission sources contributing to tropospheric ozone over Equatorial Africa during the summer monsoon

    Directory of Open Access Journals (Sweden)

    I. Bouarar

    2011-12-01

    Full Text Available A global chemistry-climate model LMDz_INCA is used to investigate the contribution of African and Asian emissions to tropospheric ozone over Central and West Africa during the summer monsoon. The model results show that ozone in this region is most sensitive to lightning NOx and to Central African biomass burning emissions. However, other emission categories also contribute significantly to regional ozone. The maximum ozone changes due to lightning NOx occur in the upper troposphere between 400 hPa and 200 hPa over West Africa and downwind over the Atlantic Ocean. Biomass burning emissions mainly influence ozone in the lower and middle troposphere over Central Africa, and downwind due to westward transport. Biogenic emissions of volatile organic compounds, which can be uplifted from the lower troposphere to higher altitudes by the deep convection that occurs over West Africa during the monsoon season, lead to maximum ozone changes in the lower stratosphere region. Soil NOx emissions over the Sahel region make a significant contribution to ozone in the lower troposphere. In addition, convective uplift of these emissions and subsequent ozone production are also an important source of ozone in the upper troposphere over West Africa. Concerning African anthropogenic emissions, they only make a small contribution to ozone compared to the other emission categories. The model results indicate that most ozone changes due to African emissions occur downwind, especially over the Atlantic Ocean, far from the emission regions. The import of Asian emissions also makes a considerable contribution to ozone concentrations above 150 hPa and has to be taken into account in studies of the ozone budget over Africa. Using IPCC AR5 (Intergovernmental Panel on Climate Change; Fifth Assessment Report estimates of anthropogenic emissions for 2030 over Africa and Asia, model calculations show larger changes in ozone over Africa due to

  4. Impacts of Urbanization on Indian Summer Monsoon Rainfall

    Science.gov (United States)

    Shastri, H. K.; Ghosh, S.; Karmakar, S.

    2013-12-01

    Rapid urbanisation all around the world is a matter of concern to the scientific community. The fast growing urban areas carries out huge anthropogenic activities that burdens natural environment and its resources like air-water quality and space, thus have different climatology to their rural surroundings. World Urbanization Prospects 2005 annual report described 20th century as witnessing a rapid urbanization of the world's population. Though urbanization is a worldwide phenomenon, it is especially prevalent in India, where urban areas have experienced an unprecedented rate of growth with level of urbanization increased from 17.23 % to 31.16% in year 1951 to 2011and the number of cities with population more than one million has grown from 5 to 53 over the same time. We take up an observational study to understand influence of urbanisation on mesoscale circulations and resulting convection, thus nature of precipitation around urban areas. The spatially distributed analysis of gridded daily precipitation data over the country is carried out to identify nature of trends in selected statistics of Indian summer monsoon precipitation and examine its association with urban land cover to have an impact on precipitation statistics. We evaluate explicit changes around urban land use in context of 40 large Indian urban areas. Further we assess local-urban climatic signals in the point level rainfall observations with model based analysis of two nearby locations under similar climatic conditions but differing largely in terms of urbanisation. The results of gridded data analysis indicate an overall tendency towards decrease in mean precipitation however, rainfall activities are enhanced around urban areas across different climate zones of the country. Though trends observed in selected climatic parameters revealed great degree of spatial inter variability in selected precipitation statistics over the country, they accounts a greater degree of inclination for occurrence under

  5. Observed changes in the characteristics of Active and Break Spells in the Indian Summer Monsoon

    Science.gov (United States)

    Singh, D.; Tsiang, M.; Rajaratnam, B.; Diffenbaugh, N. S.

    2013-12-01

    South Asia is home to about 24% of the world's population and is one of the world's most disaster prone regions. The majority of the people in this region depend on agriculture for their livelihood. Substantial variability in the South Asian Summer Monsoon occurs on an intraseasonal timescale (30-60 day) during which it fluctuates between spells of heavy (active spells) and low rainfall (breaks or weak spells). Considering the potentially severe implications of such rainfall variations, we quantify historical changes in the active and break spell characteristics in an effort to understand how these events are likely to respond to future anthropogenic forcings using the 1degx1deg gridded rainfall dataset. We find a decreasing trend in peak season rainfall since 1951 and a statistically significant shift in the rainfall distribution, suggesting greater extremes. Consequently, our results suggest an intensification of the active spells and more frequent occurrence of break spells at the 95% significance level. To understand the cause of these changes, we explore the environmental parameters in the North Indian Ocean and the Western Pacific that influence the occurrence of such events over the core monsoon region. We use the NCEP/NCAR Reanalysis 1 (1948-present) to do a composite analysis for two periods - 1951-1980 and 1981-2011. First, we examine the energetics of the baroclinic instabilities that initiate cyclonic depressions in the northern Bay of Bengal and the net moisture flux into the region. Further, sea surface temperatures are known to influence the characteristics of active and break spells. Therefore, next, we study sea surface temperature patterns in the Bay of Bengal and the equatorial western Pacific preceding breaks. We also examine the persistence of breaks through the diabatic heating anomalies over this region.

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

    Science.gov (United States)

    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

  7. 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

  8. RELATIONSHIPS BETWEEN AUTUMN INDIAN OCEAN DIPOLE MODE AND THE STRENGTH OF SCS SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    LI Dong-hui; ZHANG Gui; ZHU Yi-min; TAN Yan-ke; WANG Xue-zhong

    2007-01-01

    Based on 1948 - 2004 monthly Reynolds Sea Surface Temperature (SST) and NCEP/NCAR atmospheric reanalysis data, the relationships between autumn Indian Ocean Dipole Mode (IODM) and the strength of South China Sea (SCS) Summer Monsoon are investigated through the EOF and smooth correlation methods. The results are as the following. (1) There are two dominant modes of autumn SSTA over the tropical Indian Ocean. They are the uniformly signed basin-wide mode (USBM) and Indian Ocean dipole mode (IODM), respectively. The SSTA associated with USBM are prevailing decadal to interdecadal variability characterized by a unanimous pattern, while the IODM mainly represents interannual variability of SSTA. (2) When positive (negative) IODM exists over the tropical Indian Ocean during the preceding fall,the SCS summer monsoon will be weak (strong). The negative correlation between the interannual variability of IODM and that of SCS summer monsoon is significant during the warm phase of long-term trend but insignificant during the cool phase. (3) When the SCS summer monsoon is strong (weak), the IODM will be in its positive (negative) phase during the following fall season. The positive correlation between the interannual variability of SCS summer monsoon and that of IODM is significant during both the warm and cool phase of the long-term trend, but insignificant during the transition between the two phases.

  9. 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.

  10. Multi-year model simulations of mineral dust distribution and transport over the Indian subcontinent during summer monsoon seasons

    Science.gov (United States)

    Sijikumar, S.; Aneesh, S.; Rajeev, K.

    2016-08-01

    Aerosol distribution over the Arabian Sea and the Indian subcontinent during the northern hemispheric summer is dominated by mineral dust transport from the West Asian desert regions. The radiative impact of these dust plumes is expected to have a prominent role in regulating the Asian Summer Monsoon circulation. While satellite observations have provided information in the spatial distribution of aerosols over the oceanic regions during the season, their utility over the land is rather limited. This study examines the transport of mineral dust over the West Asian desert, the Indian subcontinent and the surrounding oceanic regions during the summer monsoon season with the help of a regional scale model, WRF-Chem. Geographical locations of prominent dust sources, altitude ranges of mineral dust transport and their inter-annual variations are examined in detail. Multi-year model simulations were carried out during 2007 to 2012 with a model integration from 15 May to 31 August of each year. Six-year seasonal mean (June to August) vertically integrated dust amount from 1000 to 300 hPa level shows prominent dust loading over the eastern parts of Arabian desert and the northwestern part of India which are identified as two major sources of dust production. Large latitudinal gradient in dust amount is observed over the Arabian Sea with the largest dust concentration over the northwestern part and is primarily caused by the prevailing northwesterly wind at 925 hPa level from the Arabian desert. The model simulations clearly show that most of the dust distributed over the Indo-Gangetic plane originates from the Rajasthan desert located in the northwestern part of India, whereas dust observed over the central and south peninsular India and over the Arabian Sea are mainly transported from the Arabian desert. Abnormal dust loading is observed over the north Arabian Sea during June 2008. This has been produced as a result of the low pressure system (associated with the onset of

  11. Multi-year model simulations of mineral dust distribution and transport over the Indian subcontinent during summer monsoon seasons

    Science.gov (United States)

    Sijikumar, S.; Aneesh, S.; Rajeev, K.

    2015-12-01

    Aerosol distribution over the Arabian Sea and the Indian subcontinent during the northern hemispheric summer is dominated by mineral dust transport from the West Asian desert regions. The radiative impact of these dust plumes is expected to have a prominent role in regulating the Asian Summer Monsoon circulation. While satellite observations have provided information in the spatial distribution of aerosols over the oceanic regions during the season, their utility over the land is rather limited. This study examines the transport of mineral dust over the West Asian desert, the Indian subcontinent and the surrounding oceanic regions during the summer monsoon season with the help of a regional scale model, WRF-Chem. Geographical locations of prominent dust sources, altitude ranges of mineral dust transport and their inter-annual variations are examined in detail. Multi-year model simulations were carried out during 2007 to 2012 with a model integration from 15 May to 31 August of each year. Six-year seasonal mean (June to August) vertically integrated dust amount from 1000 to 300 hPa level shows prominent dust loading over the eastern parts of Arabian desert and the northwestern part of India which are identified as two major sources of dust production. Large latitudinal gradient in dust amount is observed over the Arabian Sea with the largest dust concentration over the northwestern part and is primarily caused by the prevailing northwesterly wind at 925 hPa level from the Arabian desert. The model simulations clearly show that most of the dust distributed over the Indo-Gangetic plane originates from the Rajasthan desert located in the northwestern part of India, whereas dust observed over the central and south peninsular India and over the Arabian Sea are mainly transported from the Arabian desert. Abnormal dust loading is observed over the north Arabian Sea during June 2008. This has been produced as a result of the low pressure system (associated with the onset of

  12. Determination of summer monsoon onset and its related large-scale circulation characteristics over Pakistan

    Science.gov (United States)

    Latif, M.; Syed, F. S.

    2016-08-01

    The onset of summer monsoon over the Core Monsoon Region of Pakistan (CMRP) has been investigated in this study using observational daily rainfall and Precipitable Water (PW) data sets. An objective criterion is proposed to define monsoon onset dates by employing Precipitation Index and Normalized Precipitable Water Index techniques. The climatological mean summer monsoon onset dates over CMRP based on daily rainfall data sets are observed to be 1 July and 30 June in the station and gridded data sets, respectively. Whereas the daily PW-based climatological mean onset date is 30 June. The year-wise onset dates determined through station and gridded rainfall data sets are very similar but these dates differ in case of PW-based onsets. The evolution of large-scale circulation anomalies and thermodynamic structure leading monsoon onset over Pakistan shows that a strong positive temperature and geopotential height anomalies appear over the northwestern part of the core region in the upper atmosphere. This warm geopotential height anomaly gets strengthen as the monsoon onset approaches. The temperature anomalies are barotropic whereas the geopotential height anomalies are baroclinic with the presence of low level anticyclone over the Tibetan Plateau. A moisture convergence zone along the foothill of Himalayas and low level moisture convergence zone over the north Arabian Sea set the stage for the moisture carrying monsoon winds to blow inland towards CMRP. The moisture is mainly supplied from the Arabian Sea, as the low pressure system approaches CMRP from the Bay of Bengal.

  13. 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

  14. 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.

  15. Changes in the in-phase relationship between the Indian and subsequent Australian summer monsoons during the past five decades

    Directory of Open Access Journals (Sweden)

    J.-Y. Yu

    2007-10-01

    Full Text Available This study examines the decadal changes in the in-phase relationship between Indian summer monsoon and the subsequent Australian summer monsoon using observational data from 1950–2005. The in-phase relationship is the tendency for a strong Indian summer monsoon to be followed by a strong Australian summer monsoon and vice versa. It is found that the in-phase relationship was weak during the late 1950s and early 1960s, strengthened to a maximum in the early 1970s just before the 1976/77 Pacific climate shift, then declined until the late 1990s. Pacific SST anomalies are noticed to have strong persistence from boreal to austral summer, providing the memory to connect the Indian and subsequent Australian summer monsoon. The simultaneous correlation between the Pacific SST anomalies and the Indian summer monsoon is always strong. It is the weakening and strengthening of the simultaneous correlation between the Australian summer monsoon and the Pacific SST anomalies that contributes to the decadal variations of the in-phase monsoon relation. This study suggests that the interaction between the Australian monsoon and the Pacific Ocean is crucial to tropical climate variability and has experienced significant changes over the past five decades.

  16. Moisture source for summer monsoon rainfall over India

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Rao, D.P.

    that the average evaporation and precipitation rates over the Arabian Sea during SW monsoon season are 2.78 and 2.21 (X 10 sup(10) tons/day) respectively. This suggests that the possible contribution from evaporation towards the moisture transport across the west...

  17. Seasonal forecasting of Bangladesh summer monsoon rainfall using simple multiple regression model

    Indian Academy of Sciences (India)

    Md Mizanur Rahman; M Rafiuddin; Md Mahbub Alam

    2013-04-01

    In this paper, the development of a statistical forecasting method for summer monsoon rainfall over Bangladesh is described. Predictors for Bangladesh summer monsoon (June–September) rainfall were identified from the large scale ocean–atmospheric circulation variables (i.e., sea-surface temperature, surface air temperature and sea level pressure). The predictors exhibited a significant relationship with Bangladesh summer monsoon rainfall during the period 1961–2007. After carrying out a detailed analysis of various global climate datasets; three predictors were selected. The model performance was evaluated during the period 1977–2007. The model showed better performance in their hindcast seasonal monsoon rainfall over Bangladesh. The RMSE and Heidke skill score for 31 years was 8.13 and 0.37, respectively, and the correlation between the predicted and observed rainfall was 0.74. The BIAS of the forecasts (% of long period average, LPA) was −0.85 and Hit score was 58%. The experimental forecasts for the year 2008 summer monsoon rainfall based on the model were also found to be in good agreement with the observation.

  18. 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.

  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. Indian summer monsoon rainfall variability in global coupled ocean-atmospheric models

    Energy Technology Data Exchange (ETDEWEB)

    Preethi, B.; Krishna Kumar, K. [Indian Institute of Tropical Meteorology, Pune (India); Kripalani, R.H. [Pukyong National University, Department of Environmental and Atmospheric Sciences, Busan (Korea, Republic of)

    2010-12-15

    Performance of seven fully coupled models in simulating Indian summer monsoon climatology as well as the inter-annual variability was assessed using multi member 1 month lead hindcasts made by several European climate groups as part of the program called Development of a European multi-model ensemble system for seasonal-to-inter-annual prediction (DEMETER). Dependency of the model simulated Indian summer monsoon rainfall and global sea surface temperatures on model formulation and initial conditions have been studied in detail using the nine ensemble member simulations of the seven different coupled ocean-atmosphere models participated in the DEMETER program. It was found that the skills of the monsoon predictions in these hindcasts are generally positive though they are very modest. Model simulations of India summer monsoon rainfall for the earlier period (1959-1979) are closer to the 'perfect model' (attainable) score but, large differences are observed between 'actual' skill and 'perfect model' skill in the recent period (1980-2001). Spread among the ensemble members are found to be large in simulations of India summer monsoon rainfall (ISMR) and Indian ocean dipole mode (IODM), indicating strong dependency of model simulated Indian summer monsoon on initial conditions. Multi-model ensemble performs better than the individual models in simulating ENSO indices, but does not perform better than the individual models in simulating ISMR and IODM. Decreased skill of multi-model ensemble over the region indicates amplification of errors due to existence of similar errors in the individual models. It appears that large biases in predicted SSTs over Indian Ocean region and the not so perfect ENSO-monsoon (IODM-monsoon) tele-connections are some of the possible reasons for such lower than expected skills in the recent period. The low skill of multi-model ensemble, large spread among the ensemble members of individual models and the not so

  1. The link between interannual variation of the South China Sea summer monsoon onset and summer precipitation in Shandong Province

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    Relationship between the onset date of South China Sea (SCS) summer monsoon and the summer rainfall in Shandong Province was examined by comprehensive analysis to establish a conceptual model of the link. If the summer monsoon occurs earlier, the 500 hPa level would induce the teleconnection of Eurasian pattern in the summer (June-August), which indicates that the western Pacific subtropical high is displaced northward further than usual, the Siberian high is intensified and the Okhotsk low is deepened. Under such circumstance, Shandong, located in the west side of the subtropical high and in front of the mid-Siberia high, would be expected to have a wet summer because it is quite possible for cold and warm air to meet and interact with each other in Shandong. Statistical analysis revealed that the 500 hPa anomalies over Korea and Japan were sensitive to the SCS monsoon onset date and very important to precipitation in Shandong, and that the convective activities over the deep water basin in the SCS in 24-26 pentads significantly influenced the position of the ridge lineof the western Pacific subtropical high. These findings yielded better understanding of the causative mechanisms involved in the precipitation generation, so that the knowledge gained can possibly be applied for long-lead forecast.

  2. Relationship between tropospheric temperature and Indian summer monsoon rainfall as simulated by RegCM3

    Science.gov (United States)

    Pattnayak, K. C.; Panda, S. K.; Saraswat, Vaishali; Dash, S. K.

    2016-05-01

    Relationship between rainfall and tropospheric temperature (TT) has been examined over the Indian subcontinent during four seasons of the year using Regional Climate Model Version 3.0 (RegCM3). The model has been integrated at 55 km horizontal resolution over India during the years 1980-2000 with prescribed lateral boundary forcing from the 40 years re-analysis (ERA40) of the European Centre for Medium-range Weather Forecasts. Results of this study show that RegCM3 in general is able to capture the spatial distributions of rainfall in all the seasons as compared to the corresponding IMD0.5 gridded rainfall. The model has simulated warmer TT over the Himalayan region in all the seasons as compared to ERA40. However, it is well captured over the peninsular India and the oceanic regions. In the model, larger warming by about 0.5 °C over the northwest and Central India in the summer monsoon months might have lead to lower surface pressure there. Also, the vertical extent of the monsoon trough is found to be up to 500 hPa in the model as compared to that in NCEP/NCAR reanalysis. As a consequence, the simulated monsoon circulation and rainfall are stronger than those observed. The two most important rainfall seasons, the summer monsoon and winter are reasonably well simulated with correlation coefficients (CC) of 0.60 and 0.59 respectively significant at 99 % confidence level with the corresponding observed values of IMD0.5. Further, Indian summer monsoon rainfall (ISMR) and TT during the contrasting monsoon years are also close to their respective observed values. Temporal CCs between the TT over Tibet, Pakistan and Central India during the summer monsoon season and gridded ISMR values reveals that the TT over Pakistan has been better correlated with the ISMR than those over Tibet and Central India. This relationship has been well supported by the model simulations.

  3. Variations in the Teleconnection of ENSO and Summer Rainfall in Northern China: A Role of the Indian Summer Monsoon(.

    Science.gov (United States)

    Feng, Song; Hu, Qi

    2004-12-01

    Observational studies have created a dilemma on how El Niño Southern Oscillation (ENSO) may have affected interannual variations of summer rainfall in northern China; some suggested a consistent effect while others showed a complete lack of effect. This dilemma is resolved in this study, which shows that ENSO has affected the summer rainfall in northern China and the effect has varied at multidecadal scales. The question of how the ENSO teleconnection with northern China rainfall variation was established is addressed, and an answer pointing to the Indian summer monsoon as a “facilitator” connecting ENSO and northern China rainfall variation is examined. The Indian monsoon circulation interacted with the regional circulations in northern China in some epochs and such interaction was interrupted in other epochs. When the interaction was active, the Indian monsoon variations originating from ENSO, during El Niño or La Niña, was extended to affect the rainfall variation in northern China, creating a teleconnection of ENSO with northern China rainfall. When the interaction weakened or was inactive, the ENSO effect languished. Additional analyses were done to address the related question of why the interactions have alternated. The alternation was suggested to result from variations of the large-scale circulation in the Eurasian continent. The circulation anomalies showed lowering (rising) 500-hPa geopotential height centered at Mongolia and western China in some epochs, enhancing cyclonic (anticyclonic) rotation in mid- and low-level winds and creating (disrupting) a moisture convoy from the Indian monsoon region to northern China and synergetic convergence/divergence anomalies in the monsoon region and in northern China. Results of this study contribute to the understanding of interannual and multidecadal variations of the summer rainfall in the semiarid region of northern China.

  4. 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

  5. Enhancement of seasonal prediction of East Asian summer rainfall related to the western tropical Pacific convection

    Science.gov (United States)

    Lee, D. Y.; Ahn, J. B.; Yoo, J. H.

    2014-12-01

    The prediction skills of climate model simulations in the western tropical Pacific (WTP) and East Asian region are assessed using the retrospective forecasts of seven state-of-the-art coupled models and their multi-model ensemble (MME) for boreal summers (June-August) during the period 1983-2005, along with corresponding observed and reanalyzed data. The prediction of summer rainfall anomalies in East Asia is difficult, while the WTP has a strong correlation between model prediction and observation. We focus on developing a new approach to further enhance the seasonal prediction skill for summer rainfall in East Asia and investigate the influence of convective activity in the WTP on East Asian summer rainfall. By analyzing the characteristics of the WTP convection, two distinct patterns associated with El Niño-Southern Oscillation (ENSO) developing and decaying modes are identified. Based on the multiple linear regression method, the East Asia Rainfall Index (EARI) is developed by using the interannual variability of the normalized Maritime continent-WTP indices (MPIs), as potentially useful predictors for rainfall prediction over East Asia, obtained from the above two main patterns. For East Asian summer rainfall, the EARI has superior performance to the East Asia summer monsoon index (EASMI) or each MP index (MPI). Therefore, the regressed rainfall from EARI also shows a strong relationship with the observed East Asian summer rainfall pattern. In addition, we evaluate the prediction skill of the East Asia reconstructed rainfall obtained by statistical-empirical approach using the cross-validated EARI from the individual models and their MME. The results show that the rainfalls reconstructed from simulations capture the general features of observed precipitation in East Asia quite well. This study convincingly demonstrates that rainfall prediction skill is considerably improved by using the statistical-empirical method compared to the dynamical models

  6. Zonal propagation of kinetic energy and convection in the South China Sea and Indian monsoon regions in boreal summer

    Institute of Scientific and Technical Information of China (English)

    CHEN; Longxun; GAO; Hui; HE; Jinhai; TAO; Shiyan; JIN; Zuhu

    2004-01-01

    Zonal propagation of kinetic energy (KE) and convection in the South China Sea (SCS) and Indian summer monsoon areas are examined in present study. Results suggest that the SCS and Indian summer monsoon prevailed regions (5-15°N) are dominated by the southwesterly wind, however, the disturbances of KE at 850 hPa and convection are observed mainly coming from the western Pacific Ocean (140-150°E), after passing through the SCS, and westward propagated into the Bay of Bengal (90-100°E). In the Indian summer monsoon domain, where the disturbances of KE are found mainly coming from the Arabian Sea (AS) and eastward propagated into the Bay of Bengal. Therefore, the SCS and the Indian summer monsoon are quite different in zonal propagation of KE and convection. The SCS summer monsoon is mainly affected by the KE and convection coming from the tropical western Pacific. The Indian summer monsoon, however, can be partly influenced by the AS and the SCS summer monsoon. The analysis also suggests that the interaction region between the SCS and the Indian summer monsoon is around 90-95°E, rather than 105°E as proposed by earlier studies.

  7. Differences in heat budgets of the near-surface Arabian Sea and Bay of Bengal: Implications for the summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.

    An analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during the summer monsoon (June-September). In the Arabian Sea the winds associated with the summer monsoon are stronger...

  8. 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

  9. Why is Bay of Bengal warmer than Arabian Sea during the summer monsoon?

    Digital Repository Service at National Institute of Oceanography (India)

    Shenoi, S.S.C.; Shankar, D.; Shetye, S.R.

    The near-surface Bay of Bengal remains significantly warmer than the Arabian Sea during summer monsoon (June-September). Analysis of the heat budgets of the near-surface Arabian Sea and Bay of Bengal shows significant differences between them during...

  10. Trace metal dynamics in zooplankton from the Bay of Bengal during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Rejomon, G.; DineshKumar, P.K.; Nair, M.; Muraleedharan, K.R.

    Trace metal (Fe, Co, Ni, Cu, Zn, Cd, and Pb) concentrations in zooplankton from the mixed layer were investigated at 8 coastal and 20 offshore stations in the western Bay of Bengal during the summer monsoon of 2003. The ecotoxicological importance...

  11. 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.

  12. Seminal role of stratiform clouds in large-scale aggregation of tropical rain in boreal summer monsoon intraseasonal oscillations

    Science.gov (United States)

    Kumar, Siddharth; Arora, Anika; Chattopadhyay, R.; Hazra, Anupam; Rao, Suryachandra A.; Goswami, B. N.

    2016-04-01

    Modification of the vertical structure of non-adiabatic heating by significant abundance of the stratiform rain in the tropics has been known to influence the large-scale circulation. However, the role of the stratiform rain on the space-time evolution of the observed Boreal summer monsoon intraseasonal oscillations (MISO) has so far been ignored. In the present study, we unravel a feedback mechanism through which the stratiform component of the rain leads to aggregation (organization) of rain on the MISO scale, making it an indispensable component of the MISO evolution dynamics. Using TRMM 3A25 monthly mean data (between 1998 and 2013), the ratio between convective and stratiform rain (RCS) is shown to be strongly related to the total rainfall. Further, composites of rainfall and circulation anomalies corresponding to high (low) values of RCS over the Central India or over the Equatorial Indian Ocean show spatial structures remarkably similar to that associated with the MISOs. Analyzing lead-lag relationship between the convective rain, the stratiform rain and the large scale moisture convergence with respect to peak active (break) spells from daily modern era retrospective-analysis for research and applications data, we unravel that the initial isolated convective elements spawn the stratiform rain which in turn modifies the vertical distribution of heating and leads to stronger large scale moisture convergence thereby producing more convective elements and more stratiform rain ultimately leading to aggregation of rain on the MISO scale. Our finding indicates that large and persisting systematic biases in simulating the summer monsoon rainfall over the Asian monsoon region by climate models are likely to be related to the systematic biases in simulating the MISOs which in turn are related to the serious underestimation of stratiform rain in most climate models.

  13. Ozone and carbon monoxide over India during the summer monsoon: regional emissions and transport

    Science.gov (United States)

    Ojha, Narendra; Pozzer, Andrea; Rauthe-Schöch, Armin; Baker, Angela K.; Yoon, Jongmin; Brenninkmeijer, Carl A. M.; Lelieveld, Jos

    2016-03-01

    We compare in situ measurements of ozone (O3) and carbon monoxide (CO) profiles from the CARIBIC program with the results from the regional chemistry transport model (WRF-Chem) to investigate the role of local and regional emissions and long-range transport over southern India during the summer monsoon of 2008. WRF-Chem successfully reproduces the general features of O3 and CO distributions over the South Asian region. However, absolute CO concentrations in the lower troposphere are typically underestimated. Here we investigate the influence of local relative to remote emissions through sensitivity simulations. The influence of 50 % increased CO emissions over South Asia leads to a significant enhancement (upto 20 % in July) in upper tropospheric CO in the northern and central Indian regions. Over Chennai in southern India, this causes a 33 % increase in surface CO during June. However, the influence of enhanced local and regional emissions is found to be smaller (5 %) in the free troposphere over Chennai, except during September. Local to regional emissions are therefore suggested to play a minor role in the underestimation of CO by WRF-Chem during June-August. In the lower troposphere, a high pollution (O3: 146.4 ± 12.8, CO: 136.4 ± 12.2 nmol mol-1) event (15 July 2008), not reproduced by the model, is shown to be due to transport of photochemically processed air masses from the boundary layer in southern India. A sensitivity simulation combined with backward trajectories indicates that long-range transport of CO to southern India is significantly underestimated, particularly in air masses from the west, i.e., from Central Africa. This study highlights the need for more aircraft-based measurements over India and adjacent regions and the improvement of global emission inventories.

  14. Current status of multimodel superensemble and operational NWP forecast of the Indian summer monsoon

    Indian Academy of Sciences (India)

    Akhilesh Kumar Mishra; T N Krishnamurti

    2007-10-01

    In the last thirty years great strides have been made by large-scale operational numerical weather prediction models towards improving skills for the medium range time-scale of 7 days.This paper illustrates the use of these current forecasts towards the construction of a consensus multimodel forecast product called the superensemble.This procedure utilizes 120 of the recent-past forecasts from these models to arrive at the training phase statistics. These statistics are described by roughly 107 weights.Use of these weights provides the possibility for real-time medium range forecasts with the superensemble.We show the recent status of this procedure towards real-time forecasts for the Asian summer monsoon.The member models of our suite include ECMWF,NCEP/EMC, JMA,NOGAPS (US Navy),BMRC,RPN (Canada)and an FSU global spectral forecast model. We show in this paper the skill scores for day 1 through day 6 of forecasts from standard variables such as winds,temperature,500 hPa geopotential height,sea level pressure and precipitation.In all cases we noted that the superensemble carries a higher skill compared to each of the member models and their ensemble mean.The skill matrices we use include the RMS errors,the anomaly correlations and equitable threat scores.For many of these forecasts the improvements of skill for the superensemble over the best model was found to be quite substantial.This real-time product is being provided to many interested research groups.The FSU multimodel superensemble,in real- time,stands out for providing the least errors among all of the operational large scale models.

  15. Evaluation of the ENSEMBLES multi-model seasonal forecasts of Indian summer monsoon variability

    Energy Technology Data Exchange (ETDEWEB)

    Rajeevan, M.; Unnikrishnan, C.K. [National Atmospheric Research Laboratory, Gadanki (India); Preethi, B. [Indian Institute of Tropical Meteorology, Pune (India)

    2012-06-15

    The performance of the new multi-model seasonal prediction system developed in the frame work of the ENSEMBLES EU project for the seasonal forecasts of India summer monsoon variability is compared with the results from the previous EU project, DEMETER. We have considered the results of six participating ocean-atmosphere coupled models with 9 ensemble members each for the common period of 1960-2005 with May initial conditions. The ENSEMBLES multi-model ensemble (MME) results show systematic biases in the representation of mean monsoon seasonal rainfall over the Indian region, which are similar to that of DEMETER. The ENSEMBLES coupled models are characterized by an excessive oceanic forcing on the atmosphere over the equatorial Indian Ocean. The skill of the seasonal forecasts of Indian summer monsoon rainfall by the ENSEMBLES MME has however improved significantly compared to the DEMETER MME. Its performance in the drought years like 1972, 1974, 1982 and the excess year of 1961 was in particular better than the DEMETER MME. The ENSEMBLES MME could not capture the recent weakening of the ENSO-Indian monsoon relationship resulting in a decrease in the prediction skill compared to the ''perfect model'' skill during the recent years. The ENSEMBLES MME however correctly captures the north Atlantic-Indian monsoon teleconnections, which are independent of ENSO. (orig.)

  16. Combined influence of remote and local SST forcing on Indian Summer Monsoon Rainfall variability

    Science.gov (United States)

    Chakravorty, Soumi; Gnanaseelan, C.; Pillai, P. A.

    2016-02-01

    The combined influence of tropical Indian Ocean (TIO) and Pacific Ocean (TPO) sea surface temperature (SST) anomalies on Indian summer monsoon rainfall (ISMR) variability is studied in the context of mid-1970s regime shift. The rainfall pattern on the various stages of monsoon during the developing and decaying summer of El Niño is emphasized. Analysis reveals that ISMR anomalies during El Niño developing summer in epoch-1 (1950-1979) are mainly driven by El Niño forcing throughout the season, whereas TIO SST exhibits only a passive influence. On the other hand in epoch-2 (1980-2009) ISMR does not show any significant relation with Pacific during the onset phase of monsoon whereas withdrawal phase is strongly influenced by El Niño. Again the eastern Indian Ocean cooling and westward shift in northwest Pacific (NWP) cyclonic circulation during epoch-2 have strong positive influence on the rainfall over the central and eastern India during the matured phase of monsoon. ISMR in the El Niño decaying summer does not show any significant anomalies in epoch-1 as both Pacific and Indian Ocean warming dissipate by the summer. On the other hand in epoch-2 ISMR anomalies are significant and display strong variability throughout the season. In the onset phase of monsoon, central and east India experience strong negative precipitation anomalies due to westward extension of persistent NWP anticyclone (forced by persisting Indian Ocean warming). The persistent TIO warming induces positive precipitation anomalies in the withdrawal phase of monsoon by changing the atmospheric circulation and modulating the water vapour flux. Moisture budget analysis unravels the dominant processes responsible for the differences between the two epochs. The moisture convergence and moisture advection are very weak (strong) over Indian land mass during epoch-1 (epoch-2) in El Niño decaying summer. The changing moisture availability and convergence play important role in explaining the weakening

  17. NUMERICAL SIMULATION EXPERIMENTS OF THE IMPACTS OF LOCAL LAND-SEA THERMODYNAMIC CONTRASTS ON THE SCS SUMMER MONSOON ONSET

    Institute of Scientific and Technical Information of China (English)

    任雪娟; 钱永甫

    2003-01-01

    The important effects of local land-sea thermodynamic contrast between the South China Sea (SCS) and Indochina Peninsula on SCS summer monsoon onset are preliminarily studied by using two sets of SSTA tests and two ideal tests in regional climate model. The result shows that warm SST in the SCS in winter and spring is favorable for the formation of monsoon circulation throughout all levels of the atmosphere over the sea, which hastens the onset of SCS summer monsoon. The effects of cold SST are generally the opposite. The local land-sea contrast in the SCS is one of the possible reasons for SCS summer monsoon onset. Superposed upon large-scale land-sea thermodynamic differences, it facilitates the formation of out-breaking onset characteristics of SCS summer monsoon in the SCS area.

  18. 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

  19. 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.

  20. 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.

  1. Significant influence of the boreal summer monsoon flow on the Indian Ocean response during dipole events

    Science.gov (United States)

    Raghavan, Krishnan; Panickal, Swapna

    2010-05-01

    A majority of positive Indian Ocean Dipole (IOD) events in the last 50-years were accompanied by enhanced summer-monsoon circulation and above-normal precipitation over central-north India. Given that IODs peak during boreal-autumn following the summer-monsoon season, this study examines the role of the summer-monsoon flow on the Indian Ocean (IO) response using a suite of ocean model experiments and supplementary data-diagnostics. The present results indicate that if the summer-monsoon Hadley-type circulation strengthens during positive-IOD events, then the strong off-equatorial south-easterly winds over the northern flanks of the intensified Australian High can effectively promote upwelling in the south-eastern tropical Indian Ocean and amplify the zonal-gradient of the IO heat-content response. While it is noted that a strong-monsoon cross-equatorial flow by itself may not generate a dipole-like response, a strengthening (weakening) of monsoon easterlies to the south-of-equator during positive-IOD events tends to reinforce (hinder) the zonal-gradient of the upper-ocean heat-content response. The findings show that an intensification of monsoonal-winds during positive-IOD periods produces nonlinear amplification of easterly wind-stress anomalies to the south-of-equator due to the nonlinear dependence of wind-stress on wind-speed. It is noted that such an off-equatorial intensification of easterlies over SH enhances upwelling in the eastern IO off Sumatra-Java; and the thermocline shoaling provides a zonal pressure-gradient which drives anomalous eastward equatorial under-currents (EUC) in the sub-surface. Furthermore, the combination of positive-IOD and stronger-than-normal monsoonal flow favors intensification of shallow transient meridional-overturning circulation in the eastern IO; and enhances the feed of cold subsurface off-equatorial waters to the EUC. References: P. Swapna and R. Krishnan 2008: Geophy. Res. Lett. 35, L14S04, doi: 10.1029/ 2008GL033430 R

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. Simulation of Indian summer monsoon using the Japan Meteorological Agency’s seasonal ensemble prediction system

    Indian Academy of Sciences (India)

    Kailas Sonawane; O P Sreejith; D R Pattanaik; Mahendra Benke; Nitin Patil; D S Pai

    2015-03-01

    The performance of a dynamical seasonal forecast system is evaluated for the prediction of summer monsoon rainfall over the Indian region during June–September (JJAS) by using hindcast of the Japan Meteorological Agency (JMA) seasonal ensemble prediction system (EPS) model, based on five ensembles of March, April and May initial states for a period of 32 years (1979–2010). The hindcast climatology during JJAS simulates the mean monsoon circulation at lower and upper tropospheres very well in JMA model using March, April and May ensembles with a more realistic simulation of Webster and Yang’s broad scale monsoon circulation index. The JMA hindcast climatology during JJAS simulates the rainfall maxima over the west-coast of India and the head Bay of Bengal reasonably well, although, the latter is slightly shifted southwestward. Associated with better forecast skills of El Nino in the JMA model, the interannual variability of All India Summer Monsoon Rainfall (AISMR) during the 32-year period has also been very well simulated with a high significant (99% level) correlation in April ensemble followed by that of March and May ensembles. Thus, the present analysis indicates that the JMA seasonal forecast model can prove to be a useful tool for the dynamical seasonal forecast of AISMR.

  7. 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.

  8. Discrepancies in Different Precipitation Data Products in the Bay of Bengal during Summer Monsoon Season

    OpenAIRE

    Li Qi; Yuqing Wang

    2015-01-01

    In the east Bay of Bengal (BoB), the precipitation maximum always lies near the eastern coast on the windward side of Mountain Araka Yoma in the summer monsoon season. In this study, different precipitation products are compared in terms of their representation of the offshore rainfall maximum feature in this region. Climatologically, all products examined present similar rainfall distribution except for the CMAP. Significant discrepancies among different products are found in the interannual...

  9. Waves in the nearshore waters of northern Arabian Sea during the summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    SanilKumar, V.; Singh, J.; Pednekar, P.S.; Gowthaman, R.

    comparative performance survey of methods used for estimating directional wave spectra from heave-pitch-roll data. Proceedings Coastal Engineering Conference, pp. 62-75. Besnard, J.C., Benoit, M., 1994. Representative directional wave parameters - Review...: Ocean Eng., vol.38(2-3); 2011; 382-388 Waves in the nearshore waters of northern Arabian Sea during the summer monsoon V. Sanil Kumar*, Jai Singh, P. Pednekar and R. Gowthaman Ocean Engineering, National Institute of Oceanography (Council...

  10. On the role of the cross equatorial flow on summer monsoon rainfall over India using NCEP/NCAR reanalysis data

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Shenoi, S.S.C.; Schluessel, P.

    The role of the cross equatorial flow from the southern Indian Ocean on the Indian Summer monsoon is examined using the National Centre for Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) data for the period January...

  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. Detecting human impacts on the flora, fauna, and summer monsoon of Pleistocene Australia

    Directory of Open Access Journals (Sweden)

    G. H. Miller

    2007-08-01

    Full Text Available The moisture balance across northern and central Australia is dominated by changes in the strength of the Australian Summer Monsoon. Lake-level records that record changes in monsoon strength on orbital timescales are most consistent with a Northern Hemisphere insolation control on monsoon strength, a result consistent with recent modeling studies. A weak Holocene monsoon relative to monsoon strength 65–60 ka, despite stronger forcing, suggests a changed monsoon regime after 60 ka. Shortly after 60 ka humans colonized Australia and all of Australia's largest mammals became extinct. Between 60 and 40 ka Australian climate was similar to present and not changing rapidly. Consequently, attention has turned toward plausible human mechanisms for the extinction, with proponents for over-hunting, ecosystem change, and introduced disease. To differentiate between these options we utilize isotopic tracers of diet preserved in eggshells of two large, flightless birds to track the status of ecosystems before and after human colonization. More than 800 dated eggshells of the Australian emu (Dromaius novaehollandiae, an opportunistic, dominantly herbivorous feeder, provide a 140-kyr dietary reconstruction that reveals unprecedented reduction in the bird's food resources about 50 ka, coeval in three distant regions. These data suggest a tree/shrub savannah with occasionally rich grasslands was converted abruptly to the modern desert scrub. The diet of the heavier, extinct Genyornis newtoni, derived from >550 dated eggshells, was more restricted than in co-existing Dromaius, implying a more specialized feeding strategy. We suggest that generalist feeders, such as Dromaius, were able to adapt to a changed vegetation regime, whereas more specialized feeders, such as Genyornis, became extinct. We speculate that ecosystem collapse across arid and semi-arid zones was a consequence of systematic burning by early humans

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. Processes and Mechanisms in Simulations of the Mid-holocene African Summer Monsoon Circulation

    Science.gov (United States)

    Tomas, R. A.; Otto-Bliesner, B.

    2006-12-01

    Proxy reconstructions indicate that the Sahel and Sahara regions were considerably wetter during the early and middle Holocene (about 12 to 5 thousand years ago) than they are presently. Kutzbach (1981) and Kutzbach and Otto-Bliesner (1982) tested whether changes in the Earth's orbital parameters could have caused these climatic changes seen in the observed records. Using a low-resolution general circulation model and orbital parameters that describe conditions 9000 years ago, they found that the increased solar radiation during the summer months caused an intensified monsoon circulation over the African-Eurasian land mass. During the past 25 years, as general circulation models and coupled climate models have evolved, these experiments have been repeated, these results have been reconfirmed and our understanding of what parts of the climate system are important for the anomalous monsoon circulation has been refined. Yet, questions remain about the details of the processes and mechanisms that are important for producing the anomalous monsoon in climate model simulations and there are still some significant discrepancies between simulations and proxy records. We examine simulations of the African summer monsoon made using the latest version of the Community Climate System Model (CCSM3) developed at the National Center for Atmospheric Research (NCAR) forced with orbital parameters and greenhouse gas concentrations appropriate for 6 ka and pre-industrial periods following the protocols established by the Paleoclimate Modeling Intercomparison Project II (PMIP-2). Results from three sets of experiments are presented. In the first, we test to determine to what extent the SST's simulated by CCSM3 influence the anomalous monsoon circulation using a stand alone atmospheric model forced with 6ka orbital parameters but prescribed SST's taken from CCSM3 simulations of the 6ka and pre-industrial periods. In the second, we explore a more fundamental question regarding what

  18. Spatio-temporal variability of summer monsoon rainfall over Orissa in relation to low pressure systems

    Indian Academy of Sciences (India)

    M Mohapatra; U C Mohanty

    2006-04-01

    The summer monsoon rainfall over Orissa occurs mostly due to low pressure systems (LPS)developing over the Bay of Bengal and moving along the monsoon trough.A study is hence undertaken to find out characteristic features of the relationship between LPS over different regions and rainfall over Orissa during the summer monsoon season (June-September).For this purpose,rainfall and rainy days over 31 selected stations in Orissa and LPS days over Orissa and adjoining land and sea regions during different monsoon months and the season as a whole over a period of 20 years (1980-1999)are analysed.The principal objective of this study is to find out the role of LPS on spatial and temporal variability of summer monsoon rainfall over Orissa. The rainfall has been significantly less than normal over most parts of Orissa except the eastern side of Eastern Ghats during July and hence during the season as a whole due to a significantly less number of LPS days over northwest Bay in July over the period of 1980-1999.The seasonal rainfall shows higher interannual variation (increase in coefficient of variation by about 5%)during 1980-1999 than that during 1901-1990 over most parts of Orissa except northeast Orissa.Most parts of Orissa,especially the region extending from central part of coastal Orissa to western Orissa (central zone)and western side of the Eastern Ghats get more seasonal monsoon rainfall with the development and persistence of LPS over northwest Bay and their subsequent movement and persistence over Orissa.The north Orissa adjoining central zone also gets more seasonal rainfall with development and persistence of LPS over northwest Bay.While the seasonal rainfall over the western side of the Eastern Ghats is adversely affected due to increase in LPS days over west central Bay,Jharkhand and Bangladesh,that over the eastern side of the Eastern Ghats is adversely affected due to increase in LPS days over all the regions to the north of Orissa.There are signi

  19. An East Asian land-sea atmospheric heat source difference index and its relation to general circulation and summer rainfall over China

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Using a monthly precipitation dataset of 160 stations over China and a daily and monthly National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset from 1961 to 2006, we here define an East Asian land-sea atmospheric heat source difference index ILSQD and investigate its relationship to summer rainfall in China and East Asian general circulation. The results show that ILSQD more closely reflects the anomalous variations in summer monsoon phenomena; in the high-index (HI) cases, the strong low-level southerlies over East China and the strong high-level westerlies over middle latitudes indicate an active summer monsoon, and vice versa in the low-index (LI) cases. This index also reflects summer rainfall anomalies over East China; in the HI (LI) cases rainfall increases (decreases) over North China and at the same time decreases (increases) over the mid-lower Yangtze River valley and the southern Yangtze River. Hence, ILSQD can be utilized as a summer monsoon index. There is also remarkable correlation between ILSQD in March and the following summer rainfall over the mid-lower Yangtze River valley. Finally, the Community Atmospheric Model Version 3.1 (CAM3.1) of NCAR is used to run numerical experiments, which verify that the anomalous summer precipitation in simulations is similar to that of diagnosis analysis based on the anomalous summer atmospheric heating forcing. Similarly, the atmospheric heating rate in March can force summer rainfall anomalies in the simulations just as observed in the data.

  20. Indian summer monsoon and winter hydrographic variations over past millennia resolved by clay sedimentation

    Science.gov (United States)

    Chauhan, Onkar S.; Dayal, A. M.; Basavaiah, Nathani; Kader, U. Syed Abdul

    2010-09-01

    Reconstruction of century-scale Indian monsoon and winter hydrography is made from an AMS-dated core located in the unique region of the southeast Arabian Sea which lies in the pathways of the low-salinity Bay of Bengal Waters, advecting during winter northeast monsoon (NEM). Based upon clay mineral analyses in seawaters, we identify chlorite and kaolinite as specific clays supplied by the Bay of Bengal Waters and local fluvial flux (by the southwest monsoon (SWM) precipitation from the Peninsular India), respectively, along the southwest continental margin of India. An evaluation of clay flux and δ18O in G. ruber portrays century-scale weaker SWM precipitation events during ˜450-650 yr, ˜1000 yr, and 1800-2200 cal yr BP. Kaolinite wt % and flux were found to be low during all these events, though chlorite had a persistent or enhanced flux. From the enhanced flux of chlorite and reduced kaolinite/chlorite ratio, during weaker phases of SWM, we deduce a stronger NEM (winter hydrography), implying an inverse coupling between the summer and the winter monsoon.

  1. The Indian summer monsoon rainfall: interplay of coupled dynamics, radiation and cloud microphysics

    Directory of Open Access Journals (Sweden)

    P. K. Patra

    2005-05-01

    Full Text Available The Indian summer monsoon rainfall (ISMR, which has a strong connection to agricultural food production, has been less predictable by conventional models in recent times. Two distinct years 2002 and 2003 with lower and higher July rainfall, respectively, are selected to help understand the natural and anthropogenic influences on ISMR. We show that heating gradients along the meridional monsoon circulation are reduced due to aerosol radiative forcing and the Indian Ocean Dipole in 2002. An increase in the dust and biomass-burning component of the aerosols through the zonal monsoon circulation resulted in reduction of cloud droplet growth in July 2002. These conditions were opposite to those in July 2003 which led to an above average ISMR. In this study, we have utilized NCEP/NCAR reanalyses for meteorological data (e.g. sea-surface temperature, horizontal winds, and precipitable water, NOAA interpolated outgoing long-wave radiation, IITM constructed all-India rainfall amounts, aerosol parameters as observed from the TOMS and MODIS satellites, and ATSR fire count maps. Based on this analysis, we suggest that monsoon rainfall prediction models should include synoptic as well as interannual variability in both atmospheric dynamics and chemical composition.

  2. Variability in AIRS CO2 during active and break phases of Indian summer monsoon.

    Science.gov (United States)

    Revadekar, J V; Ravi Kumar, K; Tiwari, Yogesh K; Valsala, Vinu

    2016-01-15

    Due to human activities, the atmospheric concentration of Carbon Dioxide (CO2) has been rising extensively since the Industrial Revolution. Indian summer monsoon (ISM) has a dominant westerly component from ocean to land with a strong tendency to ascend and hence may have role in CO2 distribution in lower and middle troposphere over Indian sub-continent. A substantial component of ISM variability arises from the fluctuations on the intra-seasonal scale between active and break phases which correspond to strong and weak monsoon circulation. In view of the above, an attempt is made in this study to examine the AIRS/AQUA satellite retrieved CO2 distribution in response to atmospheric circulation with focus on active and break phase. Correlation analysis indicates the increase in AIRS CO2 linked with strong monsoon circulation. Study also reveals that anomalous circulation pattern during active and break phase show resemblance with high and low values of AIRS CO2. Homogeneous monsoon regions of India show substantial increase in CO2 levels during active phase. Hilly regions of India show strong contrast in CO2 and vertical velocity during active and break phases. PMID:26476061

  3. 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

  4. EAST ASIA SUMMER MONSOON ONSET DATE CALCULATED FROM OBSERVED, REANALYZED AND COMBINED DAILY RAINFALL

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper, the East Asia summer monsoon onset date lines in East China are calculated by the definition similar to the traditional one, with the ECMWF reanalyzed 850 hPa daily wind and observed, reanalyzed and combined daily rainfall during 1980 ~ 1993. To make the onset date line as close as possible to the previous work, the earliest onset date limits have to be applied for the regions with different latitude and the daily mean datasets have to be smoothed by space before calculation, therefore their space-resolution is reduced to about 3° longitude ×1° latitude. The results show that the multiyear mean summer monsoon onset date lines are quite similar to each other. Compared with the one from the reanalysis, the 14-year average onset date line form combination is obviously improved in the southern Sichuan Basin and the correlation between observed and combined onset date is also slightly higher over the Huaihe valley and Northeast China. Since daily rainfall combination also improved the long term daily mean and standard deviation through the pentad CMAP, if no better daily dataset is available, such a kind of daily rainfall combination can be used to get reasonable result in the Indian monsoon region without sufficient observatories or over the North Pacific without any ground observation at all in future study.

  5. Direct radiative effects of anthropogenic aerosols on Indian summer monsoon circulation

    Science.gov (United States)

    Das, Sushant; Dey, Sagnik; Dash, S. K.

    2016-05-01

    The direct radiative impacts of anthropogenic aerosols on the dynamics of Indian summer monsoon circulation are examined using the regional climate model version 4.1 (RegCM4.1). High anthropogenic aerosol optical depth (AAOD >0.1) and surface shortwave cooling (0.2 °C due to the dimming effect of anthropogenic aerosols. The aerosol-induced cooling leads to an increase in surface pressure over the local hotspots in the Indian landmass, which reduces the land-sea pressure contrast resulting in weakening of summer monsoon circulation. The simulated surface pressure anomaly also inhibits moisture transport from the BoB towards Indian landmass thereby enhancing precipitation over the BoB and parts of the east coast of India. The impacts are interpreted as conservative estimates because of the underestimation of AAOD by the model due to uncertainties in emission inventory and biases in simulated meteorology. Our results demonstrate the direct radiative impacts of anthropogenic aerosols on the Indian monsoon circulation and call for future studies combining the dynamical and microphysical impacts, which are not considered in this study.

  6. Summer monsoon intraseasonal oscillation over eastern Arabian Sea – as revealed by TRMM microwave imager products

    Indian Academy of Sciences (India)

    S H Rahman; B Simon

    2006-10-01

    The time evolution of atmospheric parameters on intraseasonal time scale in the eastern Arabian Sea (EAS) is studied during the summer monsoon seasons of 1998–2003 using Tropical Rainfall Measuring Mission Microwave Imager (TMI) data. This is done using the spectral and wavelet analysis. Analysis shows that over EAS, total precipitable water vapour (TWV) and sea surface wind speed (SWS) have a periodicity of 8–15 days, 15–30 days and 30–60 days during the monsoon season. Significant power is seen in the 8–15-day time scale in TWV during onset and retreat of the summer monsoon. Analysis indicates that the timings of the intensification of 8–15, 15–30, and 30–60 days oscillations have a profound effect on the evolution of the daily rainfall over west coast of India. The positive and negative phases of these oscillations are directly related to the active and dry spells of rainfall along the west coast of India. The spectral analysis shows interannual variation of TWV and SWS. Heavy rainfall events generally occur over the west coast of India when positive phases of both 30–60 days and 15–30 days modes of TWV and SWS are simultaneously present.

  7. Has influence of extratropical waves in modulating Indian summer monsoon rainfall (ISMR) increased?

    Indian Academy of Sciences (India)

    A K Srivastava; Somenath Dutta; S R Kshirsagar; Kavita Srivastava

    2014-04-01

    In the paper, influence of extratropical circulation features on Indian Summer Monsoon Rainfall (ISMR) is examined. Energetics of extra tropics, north of Indian subcontinent for deficient and nondeficient ISMR years, during two periods 1951–1978 and 1979–2005, are calculated and critically analyzed. It is observed that for the period 1951–1978, only two out of the 10 energetic parameters, viz., the zonal available potential energy (high) and conversion of zonal available potential with kinetic energy to eddy kinetic energy (low) differed significantly in JJA months of the deficient years from that of the nondeficient years. However, during the 1979–2005 period, as many as six out of the 10 energetic parameters, viz., eddy available potential energy, zonal available potential energy, eddy kinetic energy, generation of zonal available potential energy, conversion of zonal available potential energy to zonal kinetic energy and conversion of zonal kinetic energy to eddy kinetic energy differed significantly in JJA months of the deficient years from that of the nondeficient years. These results confirm growing influence of the transient stationary waves in deficient years after the climate shift year, 1979. Analysis of energetic parameters of the pre-monsoon season of the two periods also reveals similar results. This suggests that forcings apparently responsible for energetics in JJA months of the deficient years of the later period were present even before the advent of Indian summer monsoon season.

  8. Predictability and Prediction of Early- and Peak-summer East Asian rainfall

    Science.gov (United States)

    Yim, S. Y.; Wang, B.; Xing, W.; Kim, H. K.

    2015-12-01

    East Asian summer monsoon (EASM) rainfall has a profound influence on the lives of billions of people. The seasonal prediction of the EASM rainfall, however, has long been an outstanding challenge in climate science. Traditional seasonal forecast of EASM deals with JJA mean rainfall anomalies, which may not be the best strategy because the EASM rainy season is typically from May to August and pronounced differences exist between early summer (May-June, MJ) and peak summer (July-August, JA): both climatological mean states and the principal modes of interannual variability exhibit distinct spatial and temporal structures. The present study explores the sources and limit of the predictability of the early and peak summer rainfall over the East Asian (EA) region. Since the climate models' seasonal forecasts have rather limited skills, it is important to find the causes of the low skills, to improve seasonal prediction, and to better estimate the predictability of EASM rainfall. We address this issue by applying predictable mode analysis method. Four empirical modes of variability for peak summer rainfall are identified: (a) an equatorial western Pacific-EA teleconnection mode, (b) a western Pacific subtropical high-dipole feedback mode, (c) a central Pacific-ENSO mode, and (d) a Eurasian wave train mode. These modes are named according to the major sources of predictability. Based on the understanding of predictability sources for each mode, a suite of physical-empirical (P-E) models is established to predict the four leading principal components (PCs). All four modes can be predicted with significant cross-validated correlation skills(0.59-0.65). Using the predicted PCs and the corresponding observed spatial patterns, a 35-year cross-validated hindcast over the EA yields a domain-averaged TCC skill is 0.37, which is higher than the MME hind cast skill (0.13). The estimated potential attainable pattern correlation coefficient skill averaged over the entire domain is

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

    Science.gov (United States)

    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

  10. 春季北大西洋涛动与东亚夏季风年际关系的转变及其可能成因分析%Change of the relationship between spring NAO and East Asian summer monsoon and its possible mechanism

    Institute of Scientific and Technical Information of China (English)

    左金清; 李维京; 任宏利; 陈丽娟

    2012-01-01

    The relationship between East Asian Summer Monsoon (EASM) and North Atlantic Oscillation (NAO) was examined by using correlation analysis for the period from 1948 to 2009. It was showed that the EASM was well correlated with the previous spring (April-May) NAO on annual timescale. But their relationship was characterized by large decadal variations, with change of sign from positive to negative in the 1970s. Composite analysis revealed that this change was closely related to the spring and pre-winter (December-March) ocean-scale atmosphere-ocean coupling mode, I. E. The NAO-SSTA (sea surface temperature anomaly) tripolepattern, over the North Atlantic Ocean. The effect of spring NAO on the annual variability of EASM depends on the persistence of SSTA tripole pattern induced by the spring NAO itself. However, this pattern was not only controlled by the spring NAO, but also influenced by the pre-winter NAO-SSTA tripole coupling mode, the effect of which was decadal unstationary. Before the 1970s, the effect of pre-winter NAO-SSTA tripole coupling mode on the spring NAO is asymmetric, I. E. The former only has a significant weakening effect on the positive phase of the latter. After the 1970s, the effect of the former on both the positive and negative phases of the latter was negligible. Therefore, the symmetric effect of spring NAO combined with the asymmetric effect of pre-winter NAO-SSTA tripole coupling mode caused the decadal unstationary relationship between the spring NAO and SSTA tripole pattern, resulting in change of the NAO-EASM relationship in the 1970s.%本文的相关分析表明,在1948~2009年期间东亚夏季风(EASM)与前期春季(4~5月)北大西洋涛动(NAO)之间存在显著的年际相关关系,但这种关系具有明显的年代际变化特征,即在1970s发生了由正相关到负相关的转变.进一步的合成分析指出,春季NAO与EASM之间年际相关关系的转变,与春季和前期冬季(12~3月)北大西洋海盆尺度

  11. Impact of the Desert dust on the summer monsoon system over Southwestern North America

    Directory of Open Access Journals (Sweden)

    C. Zhao

    2012-04-01

    Full Text Available The radiative forcing of dust emitted from the Southwest United States (US deserts and its impact on monsoon circulation and precipitation over the North America monsoon (NAM region are simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem for 15 years (1995–2009. During the monsoon season, dust has a cooling effect (−0.90 W m−2 at the surface, a warming effect (0.40 W m−2 in the atmosphere, and a negative top-of-the-atmosphere (TOA forcing (−0.50 W m−2 over the deserts on 24-h average. Most of the dust emitted from the deserts concentrates below 800 hPa and accumulates over the western slope of the Rocky Mountains and Mexican Plateau. The absorption of shortwave radiation by dust heats the lower atmosphere by up to 0.5 K day−1 over the western slope of the Mountains. Model sensitivity simulations with and without dust for 15 summers (June-July-August show that dust heating of the lower atmosphere over the deserts strengthens the low-level southerly moisture fluxes on both sides of the Sierra Madre Occidental. It also results in an eastward migration of NAM-driven moisture convergence over the western slope of the Mountains. These monsoonal circulation changes lead to a statistically significant increase of precipitation by up to ~40 % over the eastern slope of the Mountains (Arizona-New~Mexico-Texas regions. This study highlights the interaction between dust and the NAM system and motivates further investigation of possible dust feedback on monsoon precipitation under climate change and the mega-drought conditions projected for the future.

  12. Detailed Analysis of Indian Summer Monsoon Rainfall Processes with Modern/High-Quality Satellite Observations

    Science.gov (United States)

    Smith, Eric A.; Kuo, Kwo-Sen; Mehta, Amita V.; Yang, Song

    2007-01-01

    We examine, in detail, Indian Summer Monsoon rainfall processes using modernhigh quality satellite precipitation measurements. The focus here is on measurements derived from three NASA cloud and precipitation satellite missionslinstruments (TRMM/PR&TMI, AQUNAMSRE, and CLOUDSATICPR), and a fourth TRMM Project-generated multi-satellite precipitation measurement dataset (viz., TRMM standard algorithm 3b42) -- all from a period beginning in 1998 up to the present. It is emphasized that the 3b42 algorithm blends passive microwave (PMW) radiometer-based precipitation estimates from LEO satellites with infi-ared (IR) precipitation estimates from a world network of CEO satellites (representing -15% of the complete space-time coverage) All of these observations are first cross-calibrated to precipitation estimates taken from standard TRMM combined PR-TMI algorithm 2b31, and second adjusted at the large scale based on monthly-averaged rain-gage measurements. The blended approach takes advantage of direct estimates of precipitation from the PMW radiometerequipped LEO satellites -- but which suffer fi-om sampling limitations -- in combination with less accurate IR estimates from the optical-infrared imaging cameras on GEO satellites -- but which provide continuous diurnal sampling. The advantages of the current technologies are evident in the continuity and coverage properties inherent to the resultant precipitation datasets that have been an outgrowth of these stable measuring and retrieval technologies. There is a wealth of information contained in the current satellite measurements of precipitation regarding the salient precipitation properties of the Indian Summer Monsoon. Using different datasets obtained from the measuring systems noted above, we have analyzed the observations cast in the form of: (1) spatially distributed means and variances over the hierarchy of relevant time scales (hourly I diurnally, daily, monthly, seasonally I intra-seasonally, and inter

  13. 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.

  14. Predicting Indian Summer Monsoon onset through variations of surface air temperature and relative humidity

    Science.gov (United States)

    Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

    2015-04-01

    Indian Summer Monsoon (ISM) rainfall has an enormous effect on Indian agriculture, economy, and, as a consequence, life and prosperity of more than one billion people. Variability of the monsoonal rainfall and its onset have a huge influence on food production, agricultural planning and GDP of the country, which on 22% is determined by agriculture. Consequently, successful forecasting of the ISM onset is a big challenge and large efforts are being put into it. Here, we propose a novel approach for predictability of the ISM onset, based on critical transition theory. The ISM onset is defined as an abrupt transition from sporadious rainfall to spatially organized and temporally sustained rainfall. Taking this into account, we consider the ISM onset as is a critical transition from pre-monsoon to monsoon, which take place in time and also in space. It allows us to suggest that before the onset of ISM on the Indian subcontinent should be areas of critical behavior where indicators of the critical transitions can be detected through an analysis of observational data. First, we identify areas with such critical behavior. Second, we use detected areas as reference points for observation locations for the ISM onset prediction. Third, we derive a precursor for the ISM onset based on the analysis of surface air temperature and relative humidity variations in these reference points. Finally, we demonstrate the performance of this precursor on two observational data sets. The proposed approach allows to determine ISM onset in advance in 67% of all considered years. Our proposed approach is less effective during the anomalous years, which are associated with weak/strong monsoons, e.g. El-Nino, La-Nina or positive Indian Ocean Dipole events. The ISM onset is predicted for 23 out of 27 normal monsoon years (85%) during the past 6 decades. In the anomalous years, we show that time series analysis in both areas during the pre-monsoon period reveals indicators whether the

  15. 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...

  16. Long-range prediction of Indian summer monsoon rainfall using data mining and statistical approaches

    Science.gov (United States)

    H, Vathsala; Koolagudi, Shashidhar G.

    2016-07-01

    This paper presents a hybrid model to better predict Indian summer monsoon rainfall. The algorithm considers suitable techniques for processing dense datasets. The proposed three-step algorithm comprises closed itemset generation-based association rule mining for feature selection, cluster membership for dimensionality reduction, and simple logistic function for prediction. The application of predicting rainfall into flood, excess, normal, deficit, and drought based on 36 predictors consisting of land and ocean variables is presented. Results show good accuracy in the considered study period of 37years (1969-2005).

  17. Indian Summer Monsoon Drought 2009: Role of Aerosol and Cloud Microphysics

    Energy Technology Data Exchange (ETDEWEB)

    Hazra, Anupam; Taraphdar, Sourav; Halder, Madhuparna; Pokhrel, S.; Chaudhari, H. S.; Salunke, K.; Mukhopadhyay, P.; Rao, S. A.

    2013-07-01

    Cloud dynamics played a fundamental role in defining Indian summer monsoon (ISM) rainfall during drought in 2009. The anomalously negative precipitation was consistent with cloud properties. Although, aerosols inhibited the growth of cloud effective radius in the background of sparse water vapor, their role is secondary. The primary role, however, is played by the interactive feedback between cloud microphysics and dynamics owing to reduced efficient cloud droplet growth, lesser latent heating release and shortage of water content. Cloud microphysical processes were instrumental for the occurrence of ISM drought 2009.

  18. Observed anomalous upwelling in the Lakshadweep Sea during the summer monsoon season of 2005

    Digital Repository Service at National Institute of Oceanography (India)

    Gopalakrishna, V.V.; Rao, R.R.; Nisha, K.; GirishKumar, M.S.; Pankajakshan, T.; Ravichandran, M.; Johnson, Z.; Girish, K.; Aneeshkumar, N.; Srinath, M.; Rajesh, S.; Rajan, C.K.

    that the winds over the equatorial Indian Ocean play an impor- tant role in modulating the circulation features of the north Figure 6b. Daily march of Ekman pumping velocity (C210 C06 ms C01 ) derived from QuikSCAT in the coastal box during the summer monsoon... and traverse around the rim of Bay of Bengal (BoB) and enter the SEAS. In addition, the alongshore winds in the coastal BoB also trigger and modulate the propagating Kelvin waves. The signature of this wave propagation is examined utilizing the satellite...

  19. 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

  20. 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

  1. Boreal summer intraseasonal oscillations and seasonal Indian monsoon prediction in DEMETER coupled models

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, Susmitha; Sahai, A.K.; Goswami, B.N. [Indian Institute of Tropical Meteorology, Climate and Global Modeling Division, Pune (India)

    2010-09-15

    Even though multi-model prediction systems may have better skill in predicting the interannual variability (IAV) of Indian summer monsoon (ISM), the overall performance of the system is limited by the skill of individual models (single model ensembles). The DEMETER project aimed at seasonal-to-interannual prediction is not an exception to this case. The reasons for the poor skill of the DEMETER individual models in predicting the IAV of monsoon is examined in the context of the influence of external and internal components and the interaction between intraseasonal variability (ISV) and IAV. Recently it has been shown that the ISV influences the IAV through very long breaks (VLBs; breaks with duration of more than 10 days) by generating droughts. Further, all VLBs are associated with an eastward propagating Madden-Julian Oscillation (MJO) in the equatorial region, facilitated by air-sea interaction on intraseasonal timescales. This VLB-drought-MJO relationship is analyzed here in detail in the DEMETER models. Analyses indicate that the VLB-drought relationship is poorly captured by almost all the models. VLBs in observations are generated through air-sea interaction on intraseasonal time scale and the models' inability to simulate VLB-drought relationship is shown to be linked to the models' inability to represent the air-sea interaction on intraseasonal time scale. Identification of this particular deficiency of the models provides a direction for improvement of the model for monsoon prediction. (orig.)

  2. Variations in the summer monsoon rainbands across eastern China over the past 300 years

    Science.gov (United States)

    Hao, Zhixin; Zheng, Jingyun; Ge, Quansheng

    2009-07-01

    Based on reconstructions of precipitation events from the rain and snowfall archives of the Qing Dynasty (1736-1911), the drought/flood index data mainly derived from Chinese local gazettes from 1736-2000, and the observational data gathered since 1951, the spatial patterns of monsoon rainbands are analyzed at different time scales. Findings indicate that monsoon rainfall in northern China and the middle-lower reaches of the Yangtze River have significant inter-annual (e.g., 5-7-yr and 2-4-yr) as well as inter-decadal (e.g., 20-30-yr and quasi-10-yr) fluctuation signals. The spatial patterns in these areas also show significant cycles, such as on a 60-80-yr time scale, a reversal phase predominates the entire period from 1736-2000; on a quasi-30-yr time scale, a consistent phase was prevalent from 1736 to 2000; and on a 20-yr time scale, the summer monsoon rains show different spatial patterns before and after 1870.

  3. Indian summer monsoon rainfall: Dancing with the tunes of the sun

    Science.gov (United States)

    Hiremath, K. M.; Manjunath, Hegde; Soon, Willie

    2015-02-01

    There is strong statistical evidence that solar activity influences the Indian summer monsoon rainfall. To search for a physical link between the two, we consider the coupled cloud hydrodynamic equations, and derive an equation for the rate of precipitation that is similar to the equation of a forced harmonic oscillator, with cloud and rain water mixing ratios as forcing variables. Those internal forcing variables are parameterized in terms of the combined effect of external forcing as measured by sunspot and coronal hole activities with several well known solar periods (9, 13 and 27 days; 1.3, 5, 11 and 22 years). The equation is then numerically solved and the results show that the variability of the simulated rate of precipitation captures very well the actual variability of the Indian monsoon rainfall, yielding vital clues for a physical understanding that has so far eluded analyses based on statistical correlations alone. We also solved the precipitation equation by allowing for the effects of long-term variation of aerosols. We tentatively conclude that the net effects of aerosols variation are small, when compared to the solar factors, in terms of explaining the observed rainfall variability covering the full Indian monsoonal geographical domains.

  4. 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.

  5. Simulation of the Indian Summer Monsoon Using Comprehensive Atmosphere-land Interactions, in the Absence of Two-way Air-sea Interactions

    Science.gov (United States)

    Lim, Young-Kwon; Shin, D. W.; Cocke, Steven; Kang, Sung-Dae; Kim, Hae-Dong

    2011-01-01

    Community Land Model version 2 (CLM2) as a comprehensive land surface model and a simple land surface model (SLM) were coupled to an atmospheric climate model to investigate the role of land surface processes in the development and the persistence of the South Asian summer monsoon. Two-way air-sea interactions were not considered in order to identify the reproducibility of the monsoon evolution by the comprehensive land model, which includes more realistic vertical soil moisture structures, vegetation and 2-way atmosphere-land interactions at hourly intervals. In the monsoon development phase (May and June). comprehensive land-surface treatment improves the representation of atmospheric circulations and the resulting convergence/divergence through the improvements in differential heating patterns and surface energy fluxes. Coupling with CLM2 also improves the timing and spatial distribution of rainfall maxima, reducing the seasonal rainfall overestimation by approx.60 % (1.8 mm/d for SLM, 0.7 mm/dI for CLM2). As for the interannual variation of the simulated rainfall, correlation coefficients of the Indian seasonal rainfall with observation increased from 0.21 (SLM) to 0.45 (CLM2). However, in the mature monsoon phase (July to September), coupling with the CLM2 does not exhibit a clear improvement. In contrast to the development phase, latent heat flux is underestimated and sensible heat flux and surface temperature over India are markedly overestimated. In addition, the moisture fluxes do not correlate well with lower-level atmospheric convergence, yielding correlation coefficients and root mean square errors worse than those produced by coupling with the SLM. A more realistic representation of the surface temperature and energy fluxes is needed to achieve an improved simulation for the mature monsoon period.

  6. Summer monsoon onset-induced changes of autotrophic pico- and nanoplankton in the largest monsoonal estuary along the west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Mohan, A.P.; Jyothibabu, R.; Jagadeesan, L.; Lallu, K.R.; Karnan, C.

        Environ. Monit. Assess., vol.188; 2016; no.93 doi: 10.1007/s10661-016-5096-7 Summer Monsoon Onset -induced Changes of Autotrophic Pico - and Nano - plankton in the Largest Monsoonal Estuary along the West Coast of India Arya P. Mohan, Jyothibabu, R...: Phytoplankton, Synechococcus, Prochlorococcus, Picoeukaryotes, Cochin Backwaters  2    1. Introduction Smaller autotrophic plankton consist of pico - (0.2 - 2 μm) and nano - (2 - 20 μm) size ranges inhabiting the euphotic ocean surface layer. Earlier studies...

  7. Some characteristics of very heavy rainfall over Orissa during summer monsoon season

    Indian Academy of Sciences (India)

    M Mohapatra; U C Mohanty

    2005-02-01

    Orissa is one of the most flood prone states of India. The floods in Orissa mostly occur during monsoon season due to very heavy rainfall caused by synoptic scale monsoon disturbances. Hence a study is undertaken to find out the characteristic features of very heavy rainfall (24 hours rainfall ≥ 125mm) over Orissa during summer monsoon season (June-September) by analysing 20 years (1980-1999) daily rainfall data of different stations in Orissa. The principal objective of this study is to find out the role of synoptic scale monsoon disturbances in spatial and temporal variability of very heavy rainfall over Orissa. Most of the very heavy rainfall events occur in July and August. The region, extending from central part of coastal Orissa in the southeast towards Sambalpur district in the northwest, experiences higher frequency and higher intensity of very heavy rainfall with less interannual variability. It is due to the fact that most of the causative synoptic disturbances like low pressure systems (LPS) develop over northwest (NW) Bay of Bengal with minimum interannual variation and the monsoon trough extends in west-northwesterly direction from the centre of the system. The very heavy rainfall occurs more frequently with less interannual variability on the western side of Eastern Ghat during all the months and the season except September. It occurs more frequently with less interannual variability on the eastern side of Eastern Ghat during September. The NW Bay followed by Gangetic West Bengal/Orissa is the most favourable region of LPS to cause very heavy rainfall over different parts of Orissa except eastern side of Eastern Ghat. The NW Bay and west central (WC) Bay are equally favourable regions of LPS to cause very heavy rainfall over eastern side of Eastern Ghat. The frequency of very heavy rain-fall does not show any significant trend in recent years over Orissa except some places in north-east Orissa which exhibit significant rising trend in all the

  8. 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.

  9. Indian Summer Monsoon Rainfall: Implications of Contrasting Trends in the Spatial Variability of Means and Extremes

    Science.gov (United States)

    Ghosh, Subimal; Vittal, H.; Sharma, Tarul; Karmakar, Subhankar; Kasiviswanathan, K. S.; Dhanesh, Y.; Sudheer, K. P.; Gunthe, S. S.

    2016-01-01

    India’s agricultural output, economy, and societal well-being are strappingly dependent on the stability of summer monsoon rainfall, its variability and extremes. Spatial aggregate of intensity and frequency of extreme rainfall events over Central India are significantly increasing, while at local scale they are spatially non-uniform with increasing spatial variability. The reasons behind such increase in spatial variability of extremes are poorly understood and the trends in mean monsoon rainfall have been greatly overlooked. Here, by using multi-decadal gridded daily rainfall data over entire India, we show that the trend in spatial variability of mean monsoon rainfall is decreasing as exactly opposite to that of extremes. The spatial variability of extremes is attributed to the spatial variability of the convective rainfall component. Contrarily, the decrease in spatial variability of the mean rainfall over India poses a pertinent research question on the applicability of large scale inter-basin water transfer by river inter-linking to address the spatial variability of available water in India. We found a significant decrease in the monsoon rainfall over major water surplus river basins in India. Hydrological simulations using a Variable Infiltration Capacity (VIC) model also revealed that the water yield in surplus river basins is decreasing but it is increasing in deficit basins. These findings contradict the traditional notion of dry areas becoming drier and wet areas becoming wetter in response to climate change in India. This result also calls for a re-evaluation of planning for river inter-linking to supply water from surplus to deficit river basins. PMID:27463092

  10. A cold pool formation in the Lakshadweep Sea during Indian summer monsoon

    Science.gov (United States)

    Zacharia, Johnson; Rajan, Chungath Kuttan; Jayaram, Chiranjivi

    2012-06-01

    In Lakshadweep Sea, the distribution of observed sea surface temperature (SST) during summer monsoon season (June-September) shows the presence of a distinct cold pool (SST Mini Cold Pool. With the progress of the season, LCP intensifies, spread radially outwards and shows a westward spread during late July. Maximum intensity and radial spread are attained during July. By the end of August, LCP extends northward along the coast up to 13° N, and by September, it gets completely dissipated. Within the LCP, the thermocline exhibits pronounced shoaling compared to the adjacent regions. The intensity, duration, and spread of LCP showed annual variations in each summer monsoon during 1998-2005 and owes its origin to upwelling produced by uplift of poleward undercurrent induced by an elevated bathymetry in the presence of a seamount. The mechanism for the intensification is thought to be due to the combined action of Ekman pumping due to positive wind stress curl, eddy-induced upwelling due to the Lakshadweep low, and the intensification of the poleward undercurrent during the season. West- and northward spreads of LCP are attributed to the westward movement of Lakshadweep Low and the northerly spreading and intensification of positive wind stress curl, respectively. The mechanisms that govern this phenomenon are thoroughly examined.

  11. Role of distinct flavours of IOD events on Indian summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Anil, N.; RameshKumar, M.R.; Sajeev, R.; Saji, P.K.

    ) on the Indian monsoon activity is intriguing. The impacts of ENSO, IOD and Equatorial Indian Ocean Oscillation on monsoon are distinct. The ENSO (IOD) in general affects the monsoon negatively (positively). The present study aims to understand the role...

  12. 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.

  13. 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.

  14. 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)

  15. Impact of MJO on the intraseasonal variation of summer monsoon rainfall over India

    Science.gov (United States)

    Pai, D. S.; Bhate, Jyoti; Sreejith, O. P.; Hatwar, H. R.

    2011-01-01

    The summer monsoon rainfall over India exhibits strong intraseasonal variability. Earlier studies have identified Madden Julian Oscillation (MJO) as one of the most influencing factors of the intraseasonal variability of the monsoon rainfall. In this study, using India Meteorological Department (IMD) high resolution daily gridded rainfall data and Wheeler-Hendon MJO indices, the intra-seasonal variation of daily rainfall distribution over India associated with various Phases of eastward propagating MJO life cycle was examined to understand the mechanism linking the MJO to the intraseasonal variability. During MJO Phases of 1 and 2, formation of MJO associated positive convective anomaly over the equatorial Indian Ocean activated the oceanic tropical convergence zone (OTCZ) and the resultant changes in the monsoon circulation caused break monsoon type rainfall distribution. Associated with this, negative convective anomalies over monsoon trough zone region extended eastwards to date line indicating weaker than normal northern hemisphere inter tropical convergence zone (ITCZ). The positive convective anomalies over OTCZ and negative convective anomalies over ITCZ formed a dipole like pattern. Subsequently, as the MJO propagated eastwards to west equatorial Pacific through the maritime continent, a gradual northward shift of the OTCZ was observed and negative convective anomalies started appearing over equatorial Indian Ocean. During Phase 4, while the eastwards propagating MJO linked positive convective anomalies activated the eastern part of the ITCZ, the northward propagating OTCZ merged with monsoon trough (western part of the ITCZ) and induced positive convective anomalies over the region. During Phases 5 and 6, the dipole pattern in convective anomalies was reversed compared to that during Phases 1 and 2. This resulted active monsoon type rainfall distribution over India. During the subsequent Phases (7 and 8), the convective and lower tropospheric anomaly

  16. The Indian Summer Monsoon onset revisited: new approach based on the analysis of historical wind observations

    Science.gov (United States)

    Ordoñez, Paulina; Gallego, David; Ribera, Pedro; Peña-Ortiz, Cristina; Garcia-Herrera, Ricardo; Vega, Inmaculada; Gómez, Francisco de Paula

    2016-04-01

    The Indian Summer Monsoon onset is one of the meteorological events most anticipated in the world. Due to its relevance for the population, the India Meteorological Department has dated the onset over the southern tip of the Indian Peninsula (Kerala) since 1901. The traditional method to date the onset was based in the judgment of skilled meteorologist and because of this, the method was considered subjective and not adequate for the study of long-term changes in the onset. A new method for determining the monsoon onset based solely on objective criteria has been in use since 2006. Unfortunately, the new method relies -among other variables- on OLR measurements. This requirement impedes the construction of an objective onset series before the satellite era. An alternative approach to establish the onset by objective methods is the use of the wind field. During the last decade, some works have demonstrated that the changes in the wind direction in some areas of the Indian Ocean can be used to determine the monsoon onset rather precisely. However, this method requires precise wind observations over a large oceanic area which has limited the periods covered for such kind of indices to those of the reanalysis products. In this work we present a new approach to track the Indian monsoon onset based solely on historical wind direction measurements taken onboard ships. Our new series provides an objective record of the onset since the last decade of the 19th century and perhaps more importantly, it can incorporate any new historical wind record not yet known in order to extend the series length. The new series captures quite precisely the rapid precipitation increase associated to the monsoon onset, correlates well with previous approaches and it is robust against anomalous (bogus) onsets. Although no significant trends in the onset date were detected, a tendency to later than average onsets during the 1900-1925 and 1970-1990 periods and earlier than average onsets between

  17. 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

  18. 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.

  19. 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.

  20. Mean state and interannual variability of the Indian summer monsoon simulation by NCEP CFSv2

    Science.gov (United States)

    Shukla, Ravi P.; Huang, Bohua

    2016-06-01

    The capability of the National Centers for Environmental Prediction climate forecast system version 2 (CFSv2) in simulating the Indian summer monsoon (ISM) is evaluated in the context of the global monsoon in the Indo-Pacific domain and its variability. Although the CFSv2 captures the ISM spatial structure qualitatively, it demonstrates a severe dry bias over the Indian subcontinent. The weaker model monsoon may be related to an excessive surface convergence over the equatorial Indian Ocean, which reduces the moisture transport toward the Indian subcontinent. The excessively low equatorial pressure is in turn a part of a tropical-wise bias with the largest errors in the central and eastern equatorial Pacific associated with the cold sea surface temperature bias and an overly strong inter-tropical convergence zone. In this sense, the model bias in the tropical Pacific influences those in the Indian Ocean-ISM region substantially. The leading mode of the June-September averaged CFSv2 rainfall anomalies covering the ISM and its adjacent oceanic regions is qualitatively similar to that of the observations, characterized by a spatial pattern of strong anomalies over either side of the Indian peninsula as well as center of opposite sign over Myanmar. However, the model fails to reproduce the northward expansion of rainfall anomalies from Myanmar, leading to opposite anomalies over northeast India and Himalayas region. A substantial amount of the anomalous fluctuation is attributed to the El Niño and the Southern Oscillation (ENSO), although the model variability depends more strongly on ENSO. The active regional influences in the observations may contribute to its baroclinic vertical structure of the geopotential height anomalies in the ISM region, compared with the predominantly barotropic one in CFSv2. Model ENSO deficiencies also affects its ISM simulation significantly.

  1. A Primary Study of Interaction Between Monsoon and Sea Surface Temperature in the Neighborhood Sea Area in South Aisa

    Institute of Scientific and Technical Information of China (English)

    LIU Lihong; ZHENG Zuguang; XIA Youlong; WU Hong

    2005-01-01

    Using a coupled ocean-atmosphere model simplified, and the low spectrum method and the equilibria theory, we discussed the interaction of South Asian winter and summer monsoons with sea surface temperature(SST) seasonal variation in the neighbor sea area. The results indicate that, when the winter monsoon is strong, the winter SST is low, and the SST will also be low next summer;and vice versa. When the summer monsoon is strong, the summer SST is high;and vice versa. It is inconspicuous for SST in winter that summer monsoon is strong or weak. Ocean-atmosphere interaction reinforces winter and summer monsoons,while meridional SST gradient reinforces winter monsoon and weakens summer monsoon.

  2. Global effect of irrigation and its impact on the onset of the Indian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Guimberteau, Matthieu [Universite de Paris 6, Laboratoire de Meteorologie Dynamique, Paris Cedex 05 (France); Laval, Katia [Laboratoire de Meteorologie Dynamique, Paris (France); Perrier, Alain [UFR Physique de l' Environnement, AgroParisTech, Paris (France); Polcher, Jan [CNRS, Laboratoire de Meteorologie Dynamique, Paris (France)

    2012-09-15

    In a context of increased demand for food and of climate change, the water consumptions associated with the agricultural practice of irrigation focuses attention. In order to analyze the global influence of irrigation on the water cycle, the land surface model ORCHIDEE is coupled to the GCM LMDZ to simulate the impact of irrigation on climate. A 30-year simulation which takes into account irrigation is compared with a simulation which does not. Differences are usually not significant on average over all land surfaces but hydrological variables are significantly affected by irrigation over some of the main irrigated river basins. Significant impacts over the Mississippi river basin are shown to be contrasted between eastern and western regions. An increase in summer precipitation is simulated over the arid western region in association with enhanced evapotranspiration whereas a decrease in precipitation occurs over the wet eastern part of the basin. Over the Indian peninsula where irrigation is high during winter and spring, a delay of 6 days is found for the mean monsoon onset date when irrigation is activated, leading to a significant decrease in precipitation during May to July. Moreover, the higher decrease occurs in June when the water requirements by crops are maximum, exacerbating water scarcity in this region. A significant cooling of the land surfaces occurs during the period of high irrigation leading to a decrease of the land-sea heat contrast in June, which delays the monsoon onset. (orig.)

  3. Lack of Dependence of Indian Summer Monsoon Rainfall Extremes on Temperature: An Observational Evidence

    Science.gov (United States)

    Vittal, H.; Ghosh, Subimal; Karmakar, Subhankar; Pathak, Amey; Murtugudde, Raghu

    2016-08-01

    The intensification of precipitation extremes in a warming world has been reported on a global scale and is traditionally explained with the Clausius-Clapeyron (C-C) relation. The relationship is observed to be valid in mid-latitudes; however, the debate persists in tropical monsoon regions, with the extremes of the Indian Summer Monsoon Rainfall (ISMR) being a prime example. Here, we present a comprehensive study on the dependence of ISMR extremes on both the 2 m surface air temperature over India and on the sea surface temperature over the tropical Indian Ocean. Remarkably, the ISMR extremes exhibit no significant association with temperature at either spatial scale: neither aggregated over the entire India/Tropical Indian Ocean area nor at the grid levels. We find that the theoretical C-C relation overestimates the positive changes in precipitation extremes, which is also reflected in the Coupled Model Intercomparison Project 5 (CMIP5) simulations. We emphasize that the changing patterns of extremes over the Indian subcontinent need a scientific re-evaluation, which is possible due to availability of the unique long-term in-situ data. This can aid bias correction of model projections of extremes whose value for climate adaptation can hardly be overemphasized, especially for the developing tropical countries.

  4. Evaluation of Noah-LSM for soil hydrology parameters in the Indian summer monsoon conditions

    Science.gov (United States)

    Patil, M. N.; Kumar, Manoj; Waghmare, R. T.; Dharmaraj, T.; Mahanty, N. C.

    2014-10-01

    The micrometeorological observations, collected over a station in Ranchi (23°45'N, 85°30'E) which is under the monsoon trough region of India, were used in the Noah-LSM (NCEP, OSU, Air Force and Office of Hydrology Land Surface Model) to investigate the model performance in wet (2009 and 2011) and dry (2010) conditions during the south-west summer monsoon season. With this analysis, it is seen that the Noah-LSM has simulated the diurnal cycle of heat fluxes (sensible and ground) reasonably. The simulated heat fluxes were compared with its direct measurements by sonic anemometer and soil heat flux plate. The net radiation and sensible heat flux are simulated well by the model, but the simulation of ground heat flux was found to be poor in both dry as well as wet conditions. The soil temperature simulations were also found to be poor in 0-5- and 5-10-cm layers compared to other deeper layers. The observations were also correlated with the Modern Era Retrospective-analysis for Research and Applications (MERRA) data. The correlation between the observations and ground heat flux was better in MERRA dataset than that of the Noah-LSM simulation.

  5. Lack of Dependence of Indian Summer Monsoon Rainfall Extremes on Temperature: An Observational Evidence

    Science.gov (United States)

    Vittal, H.; Ghosh, Subimal; Karmakar, Subhankar; Pathak, Amey; Murtugudde, Raghu

    2016-01-01

    The intensification of precipitation extremes in a warming world has been reported on a global scale and is traditionally explained with the Clausius-Clapeyron (C-C) relation. The relationship is observed to be valid in mid-latitudes; however, the debate persists in tropical monsoon regions, with the extremes of the Indian Summer Monsoon Rainfall (ISMR) being a prime example. Here, we present a comprehensive study on the dependence of ISMR extremes on both the 2 m surface air temperature over India and on the sea surface temperature over the tropical Indian Ocean. Remarkably, the ISMR extremes exhibit no significant association with temperature at either spatial scale: neither aggregated over the entire India/Tropical Indian Ocean area nor at the grid levels. We find that the theoretical C-C relation overestimates the positive changes in precipitation extremes, which is also reflected in the Coupled Model Intercomparison Project 5 (CMIP5) simulations. We emphasize that the changing patterns of extremes over the Indian subcontinent need a scientific re-evaluation, which is possible due to availability of the unique long-term in-situ data. This can aid bias correction of model projections of extremes whose value for climate adaptation can hardly be overemphasized, especially for the developing tropical countries. PMID:27485661

  6. Evaluation of NCEP TIGGE short-range forecast for Indian summer monsoon intraseasonal oscillation

    Science.gov (United States)

    Tirkey, Snehlata; Mukhopadhyay, P.

    2016-04-01

    This study focuses on the short-range prediction of Monsoon Intraseasonal Oscillations (MISOs) using the National Centers for Environmental Prediction(NCEP) Ensemble Prediction System (EPS) data from The Observing System Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) archive. The Indian Summer Monsoon Rainfall (ISMR), which plays an important role in the socio-economic growth of the country, is highly variable and is mostly governed by the MISOs. In addition to this, deterministic forecasts of ISMR are not very reliable. Hence, a probabilistic approach at daily scale is required. Keeping this in mind, the present analysis is done by using daily forecast data for up to 7-day lead time and compared with observations. The analysis shows that the ensemble forecast well captures the variability as compared to observations even up to 7 days. The spatial characteristics and the northward propagation of MISO are observed thoroughly in the EPS. The evolution of dynamical and thermodynamical parameters such as specific humidity, moist static energy, moisture divergence, and vorticity is also captured well but show deviation from the observation from 96 h lead time onwards. The tropospheric temperature forecast captures the observed gradient but with certain bias in magnitude whereas the wind shear is simulated quite well both in pattern and magnitude. These analyses bring out the biases in TIGGE EPS forecast and also point out the possible moist processes which needs to be improved.

  7. Weakening of Indian Summer Monsoon Rainfall due to Changes in Land Use Land Cover.

    Science.gov (United States)

    Paul, Supantha; Ghosh, Subimal; Oglesby, Robert; Pathak, Amey; Chandrasekharan, Anita; Ramsankaran, Raaj

    2016-01-01

    Weakening of Indian summer monsoon rainfall (ISMR) is traditionally linked with large-scale perturbations and circulations. However, the impacts of local changes in land use and land cover (LULC) on ISMR have yet to be explored. Here, we analyzed this topic using the regional Weather Research and Forecasting model with European Center for Medium range Weather Forecast (ECMWF) reanalysis data for the years 2000-2010 as a boundary condition and with LULC data from 1987 and 2005. The differences in LULC between 1987 and 2005 showed deforestation with conversion of forest land to crop land, though the magnitude of such conversion is uncertain because of the coarse resolution of satellite images and use of differential sources and methods for data extraction. We performed a sensitivity analysis to understand the impacts of large-scale deforestation in India on monsoon precipitation and found such impacts are similar to the observed changes in terms of spatial patterns and magnitude. We found that deforestation results in weakening of the ISMR because of the decrease in evapotranspiration and subsequent decrease in the recycled component of precipitation. PMID:27553384

  8. Lack of Dependence of Indian Summer Monsoon Rainfall Extremes on Temperature: An Observational Evidence.

    Science.gov (United States)

    Vittal, H; Ghosh, Subimal; Karmakar, Subhankar; Pathak, Amey; Murtugudde, Raghu

    2016-01-01

    The intensification of precipitation extremes in a warming world has been reported on a global scale and is traditionally explained with the Clausius-Clapeyron (C-C) relation. The relationship is observed to be valid in mid-latitudes; however, the debate persists in tropical monsoon regions, with the extremes of the Indian Summer Monsoon Rainfall (ISMR) being a prime example. Here, we present a comprehensive study on the dependence of ISMR extremes on both the 2 m surface air temperature over India and on the sea surface temperature over the tropical Indian Ocean. Remarkably, the ISMR extremes exhibit no significant association with temperature at either spatial scale: neither aggregated over the entire India/Tropical Indian Ocean area nor at the grid levels. We find that the theoretical C-C relation overestimates the positive changes in precipitation extremes, which is also reflected in the Coupled Model Intercomparison Project 5 (CMIP5) simulations. We emphasize that the changing patterns of extremes over the Indian subcontinent need a scientific re-evaluation, which is possible due to availability of the unique long-term in-situ data. This can aid bias correction of model projections of extremes whose value for climate adaptation can hardly be overemphasized, especially for the developing tropical countries. PMID:27485661

  9. 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...

  10. Enhancement and depletion of lower/middle tropospheric ozone in Senegal during pre-monsoon and monsoon periods of summer 2008: observations and model results

    Directory of Open Access Journals (Sweden)

    G. S. Jenkins

    2011-10-01

    Full Text Available During the summer (8 June through 3 September of 2008, 9 ozonesondes are launched from Dakar, Senegal (14.75° N, 17.49° W to investigate ozone (O3 variability in the lower/middle troposphere during the pre-monsoon and monsoon periods. Results during June 2008 (pre-monsoon period show a reduction in O3 concentrations, especially in the 850–700 hPa layer with Saharan Air Layer (SAL events. However, O3 concentrations are increased in the 950–900 hPa layer where the peak of the inversion is found and presumably the highest dust concentrations. We also use the WRF-CHEM model to gain greater insights for observations of elevated/reduced O3 concentrations during the pre-monsoon/monsoon periods. In the transition period between 26 June and 2 July in the lower troposphere (925–600 hPa, a significant increase in O3 concentrations occur which we suggest is caused by enhanced biogenic NOx emissions from Sahelian soils following rain events on 28 June and 1 July. During July and August 2008 (monsoon period, with the exception of one SAL outbreak, vertical profiles of O3 are well mixed with concentrations not exceeding 55 ppb between the surface and 550 hPa. The results suggest that during the pre-monsoon period ozone concentrations in the lower troposphere are controlled by the SAL, which destroys ozone through heterogeneous processes. At the base of the SAL we also find elevated levels of ozone, which we attribute to biogenic sources of NOx from Saharan dust that are released in the presence of moist conditions. Once the monsoon period commences, wet and dry deposition become important sinks of ozone in the Sahel with episodes of ozone poor air that is horizontally transported from low latitudes into the Sahel. These results support aircraft chemical measurements and chemical modeling results from the African Monsoon Multidisciplinary Analysis (AMMA field

  11. High sensitivity of Indian summer monsoon to Middle East dust absorptive properties.

    Science.gov (United States)

    Jin, Qinjian; Yang, Zong-Liang; Wei, Jiangfeng

    2016-01-01

    The absorptive properties of dust aerosols largely determine the magnitude of their radiative impacts on the climate system. Currently, climate models use globally constant values of dust imaginary refractive index (IRI), a parameter describing the dust absorption efficiency of solar radiation, although it is highly variable. Here we show with model experiments that the dust-induced Indian summer monsoon (ISM) rainfall differences (with dust minus without dust) change from -9% to 23% of long-term climatology as the dust IRI is changed from zero to the highest values used in the current literature. A comparison of the model results with surface observations, satellite retrievals, and reanalysis data sets indicates that the dust IRI values used in most current climate models are too low, tending to significantly underestimate dust radiative impacts on the ISM system. This study highlights the necessity for developing a parameterization of dust IRI for climate studies. PMID:27465689

  12. 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.

  13. Intraseasonal variability of the Indian summer monsoon: wet and dry events in COSMO-CLM

    Science.gov (United States)

    Befort, Daniel J.; Leckebusch, G. C.; Cubasch, U.

    2016-02-01

    This study aims to validate the widely used regional climate model COSMO-CLM driven by ERA-Interim reanalysis data with a spatial resolution of 55 km with respect to observed features of the intraseasonal variability of the Indian summer monsoon (ISM) during the period 1979 until 2011. One of these features is the northward propagation of the ISM intraseasonal oscillations. We find, that the temporal evolution between model and observation is in good agreement, while less agreement with respect to the strength is found. Furthermore, the model's capability to simulate observed dry and wet events on a weekly time-scale is investigated using the standardized precipitation index. In general, the model is capable to simulate these events with a similar magnitude at the same time. Observational based analyses show, that the coupling between atmospheric circulation anomalies and rainfall anomalies over India on the intraseasonal time scale is well represented by the model. The most important circulation anomalies for dry events are a lower tropospheric anti-cyclonic vortex over India and partly an upper tropospheric cyclonic vortex over the Pakistan region and vice versa for wet events. The model shows a slightly higher ability to simulate dry compared to wet events. Overall, this study shows that the current configuration of COSMO-CLM is able to simulate the key features of the intraseasonal variability of the Indian summer monsoon. Being aware of its limitation, COSMO-CLM is suitable to investigate possible changes of the intraseasonal variability of ISM under changed climate conditions in the past or in the future.

  14. Interdecadal variation of the West African summer monsoon during 1979-2010 and associated variability

    Energy Technology Data Exchange (ETDEWEB)

    Li, Huanlian [Chinese Academy of Sciences, Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Chinese Academy of Sciences, Climate Change Research Center, Beijing (China); Wang, Huijun [Chinese Academy of Sciences, Nansen-Zhu International Research Centre, Institute of Atmospheric Physics, Beijing (China); Chinese Academy of Sciences, Climate Change Research Center, Beijing (China); Yin, Yizhou [Tsinghua University, Center for Earth System Science, Beijing (China)

    2012-12-15

    This paper addresses the interdecadal variation of the West African summer monsoon (WASM) along with its background of atmospheric circulation and possible physical mechanism over the past 32 years (1979-2010). It is indicated that the WASM starts to strengthen from 1998 as the rainfall begins to increase over western West Africa on the whole, which shows a new interdecadal variation. In this interdecadal variation, the strengthened ascending motion corresponding to enhanced divergence (convergence) movement on the upper (lower) troposphere is prone to develop the local circulation of the monsoon. Moreover, the strengthened southwestern (eastern) wind on the lower (upper) level leads to more moisture from the Atlantic and the Gulf of Guinea transported to the West African continent. In addition, the summer subtropical high over the north Atlantic and western West Africa is strong and northward, and the tropical east wind is also strong. Statistically, the weaker (stronger) the spring North Atlantic Oscillation (NAO) is, the stronger (weaker) the tropical easterly is, and then the WASM is also stronger. But the effect of the NAO on the decadal variation of the WASM is not so significant from the north Atlantic anomaly sensitivity simulation with a single model. This is also an indication that the relationship between the WASM and NAO is complicated in an interdecadal time scale and is needed further study. In terms of sea surface temperature (SST) variation, the tendency is toward warming in the subtropical north Pacific, the south Pacific and north Atlantic. Numerical simulation experiments and data analysis show that the SST variation in the north Pacific plays an important role in the latest interdecadal strengthening of the WASM during the past 32 years, while the influences of the south Pacific and the north Atlantic SST anomalies are not so significant to the associated atmospheric circulation changes. (orig.)

  15. 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

  16. 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...

  17. 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.

  18. 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

  19. 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.

  20. Summer Monsoon and Annual Variability of Sea Surface Slope and Their Effects on Alongshore Current near Qingdao

    Institute of Scientific and Technical Information of China (English)

    蒲书箴; 程军; 张义钧; 石强; 骆敬新; 范文静

    2004-01-01

    Based on the monthly mean sea level data obtained from 3 years′ (1999-2001) tide-gauge measurements, the annual variability of the sea level near Qingdao and Jiaozhou Bay is studied and discussed in this paper. Results show that the sea surface height at all the tide gauges becomes higher in summer than that in winter,with an obvious seasonal variability.Furthermore the sea surface height measured at a short distance outside the bay is lower than that in thebay, showing a sea surface slope downward from north to south. The reasons for the formation of the slope are explained as well, The dynamic action ofthe summer monsoon and the sea surface slope, and their effects on the monthly mean current are studied by means of dynamics principles. The importance of the summer monsoon and the pressure gradient generated by the sea surface slope, with their effects on the alongshore current, is pointed out and emphasized in this paper.

  1. Influence of Summer Monsoon on Asymmetric Bimodal Pattern of Tropical Cyclogenesis Frequency over the Bay of Bengal

    Institute of Scientific and Technical Information of China (English)

    XING Wen; HUANG Fei

    2013-01-01

    influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index.The annual cycle of cyclogenesis frequency over the BoB shows an asymmetric bimodal pattern with the maximum genesis number appearing in late October and the second largest in early May.The two peaks correspond to the withdrawal and onset of the BoB summer monsoon,respectively.The semimonthly GP index calculated without TC days over the BoB is consistent with TC genesis frequency,indicating that the index captures the monsoon-induced changes in the environment that are responsible for the seasonal variation of TC genesis frequency.Of the four environmental variables (i.e.,low-level vorticity,mid-level relative humidity,potential intensity,and vertical wind shear) that enter into the GP index,the potential intensity makes the largest contribution to the bimodal distribution,followed by vertical wind shear due to small wind speed during the summer monsoon onset and withdrawal.The difference in TC genesis frequency between autumn and late spring is mainly owing to the relative humidity difference because a divergence (convergence) of horizontal moisture flux associated with cold dry northerlies (warm wet westerlies) dominates the BoB in late spring (autumn).

  2. 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

  3. Role of low level flow on the summer monsoon rainfall over the Indian subcontinent during two contrasting monsoon years

    Digital Repository Service at National Institute of Oceanography (India)

    Swapna, P.; RameshKumar, M.R.

    . In the present study, we look into the role of the low level flow during two contrasting monsoon years, viz., 1987 (deficit) and 1988 (excess) using the daily data from the National Centre for Environmental Prediction (NCEP) Reanalysis and European Centre...

  4. Predictability of the Indian Summer Monsoon onset through an analysis of variations in surface air temperature and relative humidity during the pre-monsoon season

    Science.gov (United States)

    Stolbova, V.; Surovyatkina, E.; Bookhagen, B.; Kurths, J.

    2014-12-01

    The prediction of the Indian Summer monsoon (ISM) onset is one of the vital questions for the Indian subcontinent, as well as for areas directly or indirectly affected by the ISM. In previous studies, the areas used for ISM-onset prediction were often too large (or too small), or did not include all necessary information for the ISM-onset forecasting. Here, we present recent findings that suggest that a climate network approach may help to provide better definitions for areas used for ISM-onset prediction and an overall better ISM-onset prediction. Our analysis focuses on the following domains: North West Pakistan (NP) and the Eastern Ghats (EG) as they have been identified to include important pre-monsoon information for predicting ISM onset dates. Specifically, we focus on the analysis of surface air temperature and relative humidity in both areas that allows us to derive temporal trends and to estimate the ISM onset. We propose an approach, which allows to determine ISM onset in advance in 67% of all considered years. Our proposed approach is less effective during the anomalous years, which are associated with weak/strong monsoons, e.g. El-Nino, La-Nina or positive Indian Ocean Dipole events. ISM onset is predicted for 23 out of 27 normal monsoon years (85%) during the past 6 decades. In addition, we show that time series analysis in both areas during the pre-monsoon period reveals indicators whether the forthcoming ISM will be normal or weaker/stronger.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. Effects of spectral nudging on the 2010 East Asia summer monsoon using WRF model

    Institute of Scientific and Technical Information of China (English)

    SHAN Haixia; GUAN Yuping; HUANG Jianping

    2012-01-01

    The performance of spectral nudging in an investigation of the 2010 East Asia summer monsoon was assessed using the Weather Research and Forecasting (WRF) model,forced by 1-degree NCEP Global Final Analysis (FNL).Two pairs of experiments were made,spectral nudging (SP) and non-spectral nudging (NOSP),with five members in each group.The members were distinguished by different initial times,and the analysis was based on the ensemble mean of the two simulation pairs.The SP was able to constrain error growth in large-scale circulation in upper-level,during simulation,and generate realistic regional scale patterns.The main focus was the model ability to simulate precipitation.The Tropical Rainfall Measuring Mission (TRMM) 3B42 product was used for precipitation verification.Mean precipitation magnitude was generally overestimated by WRF.Nevertheless,SP simulations suppressed overestimation relative to the NOSP experiments.Compared to TRMM,SP also improved model simulation of precipitation in spatial and temporal distributions,with the ability to reproduce movement ofrainbands.However,extreme precipitation events were suppressed in the SP simulations.

  13. TRMM observations of latent heat distribution over the Indian summer monsoon region and associated dynamics

    Science.gov (United States)

    Subrahmanyam, Kandula V.; Kishore Kumar, Karanam

    2016-05-01

    The latent heat released/absorbed in the Earth's atmosphere due to phase change of water molecule plays a vital role in various atmospheric processes. It is now well established that the latent heat released in the clouds is the secondary source of energy for driving the atmosphere, the Sun being the primary. In this context, studies on latent heat released in the atmosphere become important to understand the some of the physical processes taking place in the atmosphere. One of the important implications of latent heat release is its role in driving the circulations on various temporal and spatial scales. Realizing the importance of latent heat released in the clouds, a comprehensive study is carried out to understand its role in driving the mesoscale circulation. As Indian summer monsoon (ISM) serves as natural laboratory for studying the clouds and their microphysics, an attempt is made to explore the latent heat distribution over this region using 13 years of Tropical Rainfall Measuring Mission (TRMM) observations. The observed profiles of latent heating over ISM region showed large spatial and temporal variability in the magnitude thus reflecting the presence of organization of convection on mesoscale. The latent profiles in convective and stratiform regions are segregated to study the differences in their interaction with large-scale environment. Various re-analysis dataset were used to examine the role of latent heating distribution on the mesoscale circulation. The significance of the present study lies in establishing the vertical distribution of latent heating and their impact on the background circulation.

  14. Discrepancies in Different Precipitation Data Products in the Bay of Bengal during Summer Monsoon Season

    Directory of Open Access Journals (Sweden)

    Li Qi

    2015-01-01

    Full Text Available In the east Bay of Bengal (BoB, the precipitation maximum always lies near the eastern coast on the windward side of Mountain Araka Yoma in the summer monsoon season. In this study, different precipitation products are compared in terms of their representation of the offshore rainfall maximum feature in this region. Climatologically, all products examined present similar rainfall distribution except for the CMAP. Significant discrepancies among different products are found in the interannual variation, as illustrated by the contrast features between 2002 and 2005. Based on the TRMM products (except for 3B42RT and GPCP V1.2, the precipitation maximum occurred near the coast in 2002, while it was about 100–200 km offshore in 2005. However, this difference is not obvious in the GPCP V2.2 and TRMM 3B42RT products. Larger easterly vertical wind shear and warmer SST were present in 2005. Both favor stronger orographically-forced convective systems to propagate offshore, leading to the offshore rainfall maximum in 2005. Therefore, it is suggested that the TRMM 3B40RT, which is mainly based on passive microwave estimates, may be more reliable among different precipitation products in reflecting the precipitation feature in the coastal region of the east BoB.

  15. 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...

  16. Biogeochemistry of the Bay of Bengal: Physical, chemical and primary productivity characteristics of the central and western Bay of Bengal during summer monsoon 2001

    Digital Repository Service at National Institute of Oceanography (India)

    Madhupratap, M.; Gauns, M.; Ramaiah, N.; PrasannaKumar, S.; Muraleedharan, P.M.; DeSousa, S.N.; Sardessai, S.; Muraleedharan, U.D.

    Reliable data on biological characteristics from the Bay of Bengal are elusive. In this paper, we present results on physics, chemistry and biology simultaneously measured during the summer monsoon, 2001 from open ocean and coastal areas...

  17. Evaluation of cloud properties in the NCEP CFSv2 model and its linkage with Indian summer monsoon

    Science.gov (United States)

    Hazra, Anupam; Chaudhari, Hemantkumar S.; Dhakate, Ashish

    2016-04-01

    Cloud fraction, which varies greatly among general circulation models, plays a crucial role in simulation of Indian summer monsoon rainfall (ISMR). The NCEP Climate Forecast System version 2 (CFSv2) model is evaluated in terms of its simulation of cloud fraction, cloud condensate, outgoing longwave radiation (OLR), and tropospheric temperature (TT). Biases in these simulated quantities are computed using observations from CALIPSO and reanalysis data from MERRA. It is shown that CFSv2 underestimates (overestimates) high- (mid-) level clouds. The cloud condensate is also examined to see its impact on different types of clouds. The upper-level cloud condensate is underestimated, particularly during the summer monsoon period, which leads to a cold TT and a dry precipitation bias. The unrealistically weak TT gradient between ocean and land is responsible for the underestimation of ISMR. The model-simulated OLR is overestimated which depicts the weaker convective activity. A large underestimate of precipitable water is also seen along the cross-equatorial flow and particularly over the Indian land region collocated with a dry precipitation bias. The linkages among cloud microphysical, thermodynamical, and dynamical processes are identified here. Thus, this study highlights the importance of cloud properties, a major cause of uncertainty in CFSv2, and also proposes a pathway for improvements in its simulation of the Indian summer monsoon.

  18. Variability of Indian summer monsoon over the past 252 kyr revealed by stalagmite record in Southwest China

    Science.gov (United States)

    Cai, Y.; Fung, I. Y.; Edwards, R.; An, Z.; Cheng, H.; Lee, J.

    2013-12-01

    Multiple proxies obtained from Arabian Sea sediments have revealed the variability of Indian summer Monsoon (ISM) on time scale of 100-105 years. These proxies mainly capture summertime winds over the Arabian Sea and our understanding of Indian summer monsoon precipitation variability; and the relationship between paleo-ISM and paleo East Asia summer monsoon (EASM) lacks precise articulation, however, due to the scarcity of high-resolution precipitation records spanning a glacial-interglacial cycle. Here, we present an absolutely-dated oxygen isotope record from stalagmites in Xiaobailong (XBL) cave, southwestern China, that documents the variability in local precipitation and the ISM for the past 252,000 years. This record is dominated by 23-kyr precessional cycles punctuated by prominent millennial-scale oscillations that are synchronous with Heinrich events in the North Atlantic. It also shows clear glacial-interglacial variations that are consistent with marine and other terrestrial proxies. The distinct glacial-interglacial range in XBL δ18O is larger than that of speleothem records from eastern China. Corroborated with results from an isotope-enabled global climate model, we hypothesize that these dissimilarities may reflect the different responses of ISM and EASM to changes in global circulation and moisture source, in particular those caused by glacial-interglacial sea-land configuration changes as manifested by notable coastline shifts in the Western Pacific and Maritime Continent.

  19. 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.

  20. 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.

  1. Interdecadal change of the controlling mechanisms for East Asian early summer rainfall variation around the mid-1990s

    Science.gov (United States)

    Yim, So-Young; Wang, Bin; Kwon, MinHo

    2014-03-01

    East Asian (EA) summer monsoon shows considerable differences in the mean state and principal modes of interannual variation between early summer (May-June, MJ) and late summer (July-August, JA). The present study focuses on the early summer (MJ) precipitation variability. We find that the interannual variation of the MJ precipitation and the processes controlling the variation have been changed abruptly around the mid-1990s. The rainfall anomaly represented by the leading empirical orthogonal function has changed from a dipole-like pattern in pre-95 epoch (1979-1994) to a tripole-like pattern in post-95 epoch (1995-2010); the prevailing period of the corresponding principal component has also changed from 3-5 to 2-3 years. These changes are concurrent with the changes of the corresponding El Nino-Southern Oscillation (ENSO) evolutions. During the pre-95 epoch, the MJ EA rainfall anomaly is coupled to a slow decay of canonical ENSO events signified by an eastern Pacific warming, which induces a dipole rainfall feature over EA. On the other hand, during the post-95 epoch the anomalous MJ EA rainfall is significantly linked to a rapid decay of a central Pacific warming and a distinct tripolar sea surface temperature (SST) in North Atlantic. The central Pacific warming-induced Philippine Sea anticyclone induces an increased rainfall in southern China and decreased rainfall in central eastern China. The North Atlantic Oscillation-related tripolar North Atlantic SST anomaly induces a wave train that is responsible for the increase northern EA rainfall. Those two impacts form the tripole-like rainfall pattern over EA. Understanding such changes is important for improving seasonal to decadal predictions and long-term climate change in EA.

  2. Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

    KAUST Repository

    Jin, Q.

    2015-09-02

    © Author(s) 2015. The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust-ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day-1 (∼10 % of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan

  3. Simulation of the Indian summer monsoon onset-phase rainfall using a regional model

    KAUST Repository

    Srinivas, C. V.

    2015-09-11

    This study examines the ability of the Advanced Research WRF (ARW) regional model to simulate Indian summer monsoon (ISM) rainfall climatology in different climate zones during the monsoon onset phase in the decade 2000–2009. The initial and boundary conditions for ARW are provided from the NCEP/NCAR Reanalysis Project (NNRP) global reanalysis. Seasonal onset-phase rainfall is compared with corresponding values from 0.25° IMD (India Meteorological Department) rainfall and NNRP precipitation data over seven climate zones (perhumid, humid, dry/moist, subhumid, dry/moist, semiarid and arid) of India to see whether dynamical downscaling using a regional model yields advantages over just using large-scale model predictions. Results show that the model could simulate the onset phase in terms of progression and distribution of rainfall in most zones (except over the northeast) with good correlations and low error metrics. The observed mean onset dates and their variability over different zones are well reproduced by the regional model over most climate zones. It has been found that the ARW performed similarly to the reanalysis in most zones and improves the onset time by 1 to 3 days in zones 4 and 7, in which the NNRP shows a delayed onset compared to the actual IMD onset times. The variations in the onset-phase rainfall during the below-normal onset (June negative) and above-normal onset (June positive) phases are well simulated. The slight underestimation of onset-phase rainfall in the northeast zone could be due to failure in resolving the wide extent of topographic variations and the associated multiscale interactions in that zone. Spatial comparisons showed improvement of pentad rainfall in both space and quantity in ARW simulations over NNRP data, as evident from a wider eastward distribution of pentad rainfall over the Western Ghats, central and eastern India, as in IMD observations. While NNRP under-represented the high pentad rainfall over northeast, east and

  4. Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

    KAUST Repository

    Jin, Q.

    2015-06-11

    The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust–ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44mmday1 ( 10% of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan Plateau. This study demonstrates

  5. Consistent response of Indian summer monsoon to Middle East dust in observations and simulations

    Science.gov (United States)

    Jin, Q.; Wei, J.; Yang, Z.-L.; Pu, B.; Huang, J.

    2015-09-01

    The response of the Indian summer monsoon (ISM) circulation and precipitation to Middle East dust aerosols on sub-seasonal timescales is studied using observations and the Weather Research and Forecasting model coupled with online chemistry (WRF-Chem). Satellite data show that the ISM rainfall in coastal southwest India, central and northern India, and Pakistan is closely associated with the Middle East dust aerosols. The physical mechanism behind this dust-ISM rainfall connection is examined through ensemble simulations with and without dust emissions. Each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. Experiments show that dust aerosols increase rainfall by about 0.44 mm day-1 (~10 % of the climatology) in coastal southwest India, central and northern India, and north Pakistan, a pattern consistent with the observed relationship. The ensemble mean rainfall response over India shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. The largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. In WRF-Chem, the dust aerosol optical depth (AOD) over the Middle East shows the strongest correlation with the ISM rainfall response when dust AOD leads rainfall response by about 11 days. Further analyses show that increased ISM rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the Arabian Sea to the Indian subcontinent, which are associated with the development of an anomalous low-pressure system over the Arabian Sea, the southern Arabian Peninsula, and the Iranian Plateau due to dust-induced heating in the troposphere. The dust-induced heating in the mid-upper troposphere is mainly located in the Iranian Plateau rather than the Tibetan Plateau. This study

  6. CHARACTERISTICS OF ATMOSPHERIC HEAT SOURCE ASSOCIATED WITH THE SUMMER MONSOON ONSET OVER THE SOUTH CHINA SEA AND THE POSSIBLE MECHANISM RESPONSIBLE FOR ITS LATE OR EARLY ONSET

    Institute of Scientific and Technical Information of China (English)

    蓝光东; 温之平; 贺海晏

    2004-01-01

    The characteristics of atmospheric heat source associated with the summer monsoon onset in the South China Sea (SCS) are studied using ECMWF reanalysis data from 1979 to 1993. A criterion of the SCS summer monsoon onset is defined by the atmospheric heat source. Applying this criterion to the 15-year (1979 - 1993) mean field, the onset of the SCS summer monsoon is found to occur in the fourth pentad of May. And this criterion can also give reasonable results for the onset time of the SCS summer monsoon on a year-to-year basis. In addition, pretty high correlation has been found between the onset time of the SCS summer monsoon and the zonal mean vertically integrated heat source at 40(S in April. The causes for the late or early onset of the SCS summer monsoon and the close relationship between the onset time and the zonal mean vertically integrated heat source at 40 (S in April might be explained by the variations in intensity of the Hadley circulation.

  7. The value of C sub(e) for the Arabian Sea during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, A.S.; Sadhuram, Y.; Krishna, V.V.G.

    We estimate, from the moisture budget the bulk aerodynamic coefficient for latent heat flux (C sub(e)) during the monsoon season over the central Arabian Sea. The average value of C sub(e) under active monsoon conditions was found to be 2.25 x 10...

  8. 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.

  9. Seasonal prediction of Indian summer monsoon rainfall in NCEP CFSv2: forecast and predictability error

    Science.gov (United States)

    Pokhrel, Samir; Saha, Subodh Kumar; Dhakate, Ashish; Rahman, Hasibur; Chaudhari, Hemantkumar S.; Salunke, Kiran; Hazra, Anupam; Sujith, K.; Sikka, D. R.

    2016-04-01

    A detailed analysis of sensitivity to the initial condition for the simulation of the Indian summer monsoon using retrospective forecast by the latest version of the Climate Forecast System version-2 (CFSv2) is carried out. This study primarily focuses on the tropical region of Indian and Pacific Ocean basin, with special emphasis on the Indian land region. The simulated seasonal mean and the inter-annual standard deviations of rainfall, upper and lower level atmospheric circulations and Sea Surface Temperature (SST) tend to be more skillful as the lead forecast time decreases (5 month lead to 0 month lead time i.e. L5-L0). In general spatial correlation (bias) increases (decreases) as forecast lead time decreases. This is further substantiated by their averaged value over the selected study regions over the Indian and Pacific Ocean basins. The tendency of increase (decrease) of model bias with increasing (decreasing) forecast lead time also indicates the dynamical drift of the model. Large scale lower level circulation (850 hPa) shows enhancement of anomalous westerlies (easterlies) over the tropical region of the Indian Ocean (Western Pacific Ocean), which indicates the enhancement of model error with the decrease in lead time. At the upper level circulation (200 hPa) biases in both tropical easterly jet and subtropical westerlies jet tend to decrease as the lead time decreases. Despite enhancement of the prediction skill, mean SST bias seems to be insensitive to the initialization. All these biases are significant and together they make CFSv2 vulnerable to seasonal uncertainties in all the lead times. Overall the zeroth lead (L0) seems to have the best skill, however, in case of Indian summer monsoon rainfall (ISMR), the 3 month lead forecast time (L3) has the maximum ISMR prediction skill. This is valid using different independent datasets, wherein these maximum skill scores are 0.64, 0.42 and 0.57 with respect to the Global Precipitation Climatology Project

  10. Empirical prediction of the onset dates of South China Sea summer monsoon

    Science.gov (United States)

    Zhu, Zhiwei; Li, Tim

    2016-05-01

    The onset of South China Sea summer monsoon (SCSSM) signifies the commencement of the wet season over East Asia. Predicting the SCSSM onset date is of significant importance. In this study, we establish two different statistical models, namely the physical-empirical model (PEM) and the spatial-temporal projection model (STPM) to predict the SCSSM onset. The PEM is constructed from the seasonal prediction perspective. Observational diagnoses reveal that the early onset of the SCSSM is preceded by (a) a warming tendency in middle and lower troposphere (850-500 hPa) over central Siberia from January to March, (b) a La Niña-like zonal dipole sea surface temperature pattern over the tropical Pacific in March, and (c) a dipole sea level pressure pattern with negative center in subtropics and positive center over high latitude of Southern Hemisphere in January. The PEM built on these predictors achieves a cross-validated reforecast temporal correlation coefficient (TCC) skill of 0.84 for the period of 1979-2004, and an independent forecast TCC skill of 0.72 for the period 2005-2014. The STPM is built on the extended-range forecast perspective. Pentad data are used to predict a zonal wind index over the South China Sea region. Similar to PEM, the STPM is constructed using 1979-2004 data. Based on the forecasted zonal wind index, the independent forecast of the SCSSM onset dates achieves a TCC skill of 0.90 for 2005-2014. The STPM provides more detailed information for the intraseasonal evolution during the period of the SCSSM onset (pentad 25-35). The two models proposed herein are expected to facilitate the real-time prediction of the SCSSM onset.

  11. The role of low-frequency intraseasonal oscillations in the anomalous Indian summer monsoon rainfall of 2002

    Indian Academy of Sciences (India)

    S Sajani; S Naseema Beegum; K Krishna Moorthy

    2007-04-01

    We analyze the dynamical features and responsible factors of the low-frequency intraseasonal time scales which influenced the nature of onset, intensity and duration of active/break phases and withdrawal of the monsoon during the anomalous Indian summer monsoon of 2002 – the most severe drought recorded in recent times. During that season, persistent warm sea surface temperature anomalies over the equatorial Indian Ocean played a significant role in modulating the strength of the monsoon Hadley circulation. This in turn affected the onset and intense break spells especially the long break during the peak monsoon month of July. Strong low-frequency intraseasonal modulations with significant impact on the onset and active/break phases occurred in 2002 which were manifested as a good association between low-frequency intraseasonal oscillations and the onset and active/break spells. Further, SST anomalies over the equatorial Indo-Pacific region on low-frequency intraseasonal time scales were found to affect the equatorial eastward and thereby off-equatorial northward propagations of enhanced convection over the Indian region. These propagations in turn modulated the active/break cycle deciding the consequent severity of the 2002 drought.

  12. 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.

  13. 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

  14. The Relationship of Land-Ocean Thermal Anomaly Difference with Mei-yu and South China Sea Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    WANG Zhifu; QIAN Yongfu

    2009-01-01

    Based on the NCEP/NCAR reanalysis data for the period of 1948-2004 and the monthly rainfall data at 160 stations in China from 1951 to 2004, the relationships among the land-ocean temperature anomaly difference in the mid-lower troposphere in spring (April-May), the mei-yu rainfall in the Yangtze River-Huaihe River basin, and the activities of the South China Sea summer monsoon (SCSSM) are analyzed by using correlation and composite analyses. Results show that a significant positive correlation exists between mei-yu rainfall and air temperature in the middle latitudes above the western Pacific, while a significant negative correlation is located to the southwest of the Baikal Lake. When the land-ocean thermal anomaly difference is stronger in spring, the western Pacific subtropical high (WPSH) will be weaker and retreat eastward in summer (June-July), and the SCSSM will be stronger and advance further north, resulting in deficient moisture along the mei-yu front and below-normal precipitation in the mid and lower reaches of the Yangtze River, and vice versa for the weaker difference case. The effects and relative importance of the land and ocean anomalous heating on monsoon variability is also compared. It is found that the land and ocean thermal anomalies are both closely related to the summer circulation and mei-yu rainfall and SCSSM intensity, whereas the land heating anomaly is more important than ocean heating in changing the land-ocean thermal contrast and hence the summer monsoon intensity.

  15. Carbon dioxide and water vapour characteristics on the west coast of Arabian Sea during Indian summer monsoon

    Indian Academy of Sciences (India)

    T Dharmaraj; M N Patil; R T Waghmare; P Ernest Raj

    2012-08-01

    Carbon dioxide, water vapour, air temperature and wind measurements at 10 Hz sampling rate were carried out over the coast of Arabian Sea, Goa (15°21′N, 73° 51′E) in India. These observations were collected, in association with the surface layer turbulent parameters for the Arabian Sea Monsoon Experiment (ARMEX). In the summer monsoon period, concentration of CO2 was in the range of 550–790 mg m−3 whereas the water vapour was in the range of 17.5–24.5 g m−3. The Fast Fourier Transform (FFT) analysis has been performed on these observations to investigate the spectral behaviour of CO2 and water vapour. The relation between CO2 and water vapour on various atmospheric scales has been proposed. CO2 and water vapour observations confirmed the existence of periodicities of large (11, 8 days), meso (5 days) and micrometeorological (20 min) scales.

  16. Carbon dioxide and water vapour characteristics on the west coast of Arabian Sea during Indian summer monsoon

    Science.gov (United States)

    Dharmaraj, T.; Patil, M. N.; Waghmare, R. T.; Ernest Raj, P.

    2012-08-01

    Carbon dioxide, water vapour, air temperature and wind measurements at 10 Hz sampling rate were carried out over the coast of Arabian Sea, Goa (15°21'N, 73°51'E) in India. These observations were collected, in association with the surface layer turbulent parameters for the Arabian Sea Monsoon Experiment (ARMEX). In the summer monsoon period, concentration of CO2 was in the range of 550-790 mg m - 3 whereas the water vapour was in the range of 17.5-24.5 g m - 3. The Fast Fourier Transform (FFT) analysis has been performed on these observations to investigate the spectral behaviour of CO2 and water vapour. The relation between CO2 and water vapour on various atmospheric scales has been proposed. CO2 and water vapour observations confirmed the existence of periodicities of large (11, 8 days), meso (5 days) and micrometeorological (20 min) scales.

  17. 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.

  18. Enhancement and depletion of lower/middle tropospheric ozone in Senegal during pre-monsoon and monsoon periods of summer 2008: observations and model results

    Directory of Open Access Journals (Sweden)

    G. S. Jenkins

    2011-03-01

    Full Text Available During the summer (8 June through 3 September of 2008, nine ozonesondes are launched from Dakar, Senegal (14.75° N, 17.49° W to investigate the impact of the Saharan Dust Layer (SAL on ozone (O3 concentrations in the lower troposphere. Results during June (pre-monsoon period show a reduction in O3, especially in the 850–700 hPa layer with SAL events. However, O3 concentrations are increased in the 950–900 hPa layer where the peak of the inversion is found and presumably the highest dust concentrations. We use the WRF-CHEM model to explore the causes of elevated O3 concentrations that appear to have a stratospheric contribution. During July and August (monsoon period, with the exception of one SAL outbreak, vertical profiles of O3 are well mixed with concentrations not exceeding 55 ppb between the surface and 550 hPa. In the transition period between 26 June and 2 July lower tropospheric (925–600 hPa O3 concentrations are likely enhanced by enhanced biogenic NOx emissions from the Saharan desert and Sahelian soils following several rain events on 28 June and 1 July.

  19. Uncertainty in CMIP5 model-projected changes in the onset/retreat of the Australian summer monsoon

    Science.gov (United States)

    Zhang, Huqiang; Dong, Guangtao; Moise, A.; Colman, R.; Hanson, L.; Ye, H.

    2016-04-01

    This study addresses several significant drawbacks in our previous analyses of how Australian summer monsoon onset/retreat may respond to global warming in CMIP3 model simulations. We have analysed daily 850 hPa wind, volumetric precipitable water, precipitation and temperature data from 26 CMIP5 models over a pair of 55-year simulations. Firstly, the CMIP5 models do not show significant improvement in capturing observed features of the monsoon onset/retreat in the region, despite of a slightly reduced bias in multi-model ensemble results. We show that wind-rainfall relationship varies with models and rainfall-based wet season onsets may not adequately represent the monsoon development. Under global warming, although 26-model averages show delayed onset and shortened duration, significant uncertainty exists: 10 models simulated delayed onset but it became earlier in another group of 7 models. Similar model discrepancies are seen in the modelled changes in retreat dates. The range of uncertainty in the projected changes is similar in CMIP3 and CMIP5 models and further analysis re-affirms previously proposed reasons: one is the different influence of a number of drivers in these models and the other is the different changes in these drivers themselves in future climate. Overall, most of the models showed impacts of ENSO and the Indian Ocean on the Australian summer monsoon onset/retreat, but the models differed quite significantly in the magnitude of such impacts. Another factor is different warming patterns and magnitudes in the tropical Pacific and Indian Oceans. When combined, the two provide a better explanation of the scatter among the 26 CMIP5 model results.

  20. Evaluation of the impact of AIRS profiles on prediction of Indian summer monsoon using WRF variational data assimilation system

    Science.gov (United States)

    Raju, Attada; Parekh, Anant; Kumar, Prashant; Gnanaseelan, C.

    2015-08-01

    This study investigates the impact of temperature and moisture profiles from Atmospheric Infrared Sounder (AIRS) on the prediction of the Indian summer monsoon, using the variational data assimilation system annexed to the Weather Research and Forecasting model. In this study, three numerical experiments are carried out. The first is the control and includes no assimilation; in the second, named Conv, assimilation of conventional Global Telecommunication System data is performed. The third one, named ConvAIRS, is identical to the Conv except that it also includes assimilation of AIRS profiles. The initial fields of tropospheric temperature and water vapor mixing ratio showed significant improvement over the model domain. Assimilation of AIRS profiles has significant impact on predicting the seasonal mean monsoon characteristics such as tropospheric temperature, low-level moisture distribution, easterly wind shear, and precipitation. The vertical structure of the root-mean-square error is substantially affected by the assimilation of AIRS profiles, with smaller errors in temperature, humidity, and wind magnitude. The consequent improved representation of moisture convergence in the boundary layer (deep convection as well) causes an increase in precipitation forecast skill. The fact that the monsoonal circulation is better captured, thanks to an improved representation of thermal gradients, which in turn leads to more realistic moisture transport, is particularly noteworthy. Several previous data impact studies with AIRS and other sensors have focused on the short or medium range of the forecast. The demonstrated improvement in all the predicted fields associated with the Indian summer monsoon, consequent to the month long assimilation of AIRS profiles, is an innovative finding with large implications to the operational seasonal forecasting capabilities over the Indian subcontinent.

  1. Circumglobal wave train and the summer monsoon over northwestern India and Pakistan: the explicit role of the surface heat low

    Energy Technology Data Exchange (ETDEWEB)

    Saeed, Sajjad [Max Planck Institute for Meteorology, Hamburg (Germany); International Max Planck Research School on Earth System Modeling, Hamburg (Germany); Pakistan Meteorological Department, Islamabad (Pakistan); Mueller, Wolfgang A.; Hagemann, Stefan; Jacob, Daniela [Max Planck Institute for Meteorology, Hamburg (Germany)

    2011-09-15

    This study examines the influence of the mid-latitude circulation on the surface heat low (HL) and associated monsoon rainfall over northwestern India and Pakistan using the ERA40 data and high resolution (T106L31) climate model ECHAM5 simulation. Special emphasis is given to the surface HL which forms over Pakistan and adjoining areas of India, Iran and Afghanistan during the summer season. A heat low index (HLI) is defined to depict the surface HL. The HLI displays significant correlations with the upper level mid-latitude circulation over western central Asia and low level monsoon circulation over Arabian Sea and acts as a bridge connecting the mid-latitude wave train to the Indian summer monsoon. A time-lagged singular value decomposition analysis reveals that the eastward propagation of the mid-latitude circumglobal wave train (CGT) influences the surface pressure anomalies over the Indian domain. The largest low (negative) pressure anomalies over the western parts of the HL region (i.e., Iran and Afghanistan) occur in conjunction with the upper level anomalous high that develops over western-central Asia during the positive phase of the CGT. The composite analysis also reveals a significant increase in the low pressure anomalies over Iran and Afghanistan during the positive phase of CGT. The westward increasing low pressure anomalies with its north-south orientation provokes enormous north-south pressure gradient (lower pressure over land than over sea). This in turn enables the moist southerly flow from the Arabian Sea to penetrate farther northward over northwestern India and Pakistan. A monsoon trough like conditions develops over northwestern India and Pakistan where the moist southwesterly flow from the Arabian Sea and the Persian Gulf converge. The convergence in association with the orographic uplifting expedites convection and associated precipitation over northwestern India and Pakistan. The high resolution climate model ECHAM5 simulation also

  2. Driving forces of Indian summer monsoon on Milankovitch and sub-Milankovitch time scales: A review

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    A scientific consensus exists that tectonic evolution of Himalaya is the main cause of monsoon initiation and evolution in southeast Asia. Several forcing factors such as tectonic, solar insolation, latent heat transport, albedo of the earth surface...

  3. 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...

  4. Stable isotopes of summer monsoonal precipitation in southern China and the moisture sources evidence from δ18O signature%中国南部夏季季风降水水汽来源的稳定同位素证据

    Institute of Scientific and Technical Information of China (English)

    柳鉴容; 宋献方; 袁国富; 孙晓敏; 刘鑫; 王仕琴; 王志民

    2008-01-01

    Summer monsoons (South Asian monsoon, South China Sea monsoon and Sub-tropical monsoon) are prominent features of summertime climate over southern China. Dif-ferent monsoons carry different inflow moisture into China and control the temporal and spa-tial distributions of precipitation. Analyses of meteorological data, particularly wind, tempera-ture and pressure anomalies are traditional methods of characterizing moisture sources and transport patterns. Here, we try to utilize the evidence from stable isotopes signatures to trace summer monsoons over southern China. Based on seven CHNIP (Chinese Network of Iso-topes in Precipitation) observatory stations located in southern China, monthly composite precipitation samples have been collected and analyzed for the composition of δ18O during July, 2005. The results indicated that the spatial distributions of δ18O in precipitation could properly portray the moisture sources together with their transport pathways. Moreover, the amount effect, altitude effect, temperature effect and the correlation between δ18O vs. relative humidity were discussed.

  5. Orbital forcing of the late Pleistocene boreal summer monsoon: Links to North Atlantic cold events and El Nino; Southern Oscillation. Geologica Ultraiectina (313)

    NARCIS (Netherlands)

    Ziegler, M.

    2009-01-01

    This thesis revolves about the timing of precession-related variations in the boreal summer monsoon and the impact of North Atlantic cold events and the El Nino Southern Oscillation on this timing. Transient climate modelling experiments indicate that the intensity of the Northern Hemisphere summer

  6. Decadal variability in snow depth anomaly over Eurasia and its association with all India summer monsoon rainfall and seasonal circulations

    International Nuclear Information System (INIS)

    The Historical Soviet Daily Snow Depth (HSDSD) version II data set has been used in the computation of winter and spring snow depth anomalies over west (25 deg. E to 70 deg. E, 35 deg. N to 65 deg. N) and east (70 deg. E to 160 deg. E, 35 deg. N to 65 deg. N) Eurasia. It is noticed that winter snow depth anomaly over east Eurasia is positively correlated while west Eurasia is negatively correlated with subsequent Indian summer monsoon rainfall (ISMR). The DJF snow depth anomaly shows highest and inverse correlation coefficient (CC) with ISMR over a large area of west Eurasia in a recent period of study i.e. 1975-1995. On the basis of standardised winter (mean of December, January and February) snow depth anomaly over west Eurasia, the years 1966, 1968, 1979 and 1986 are identified as high snow years and the years 1961 and 1975 as low snow years. The characteristics of seasonal monsoon circulation features have been studied in detail during contrasting years of less (more) snow depth in winter/spring seasons followed by excess (deficient) rainfall over India using National Center for Environmental Prediction (NCEP) / National Center for Atmospheric Research (NCAR) reanylised data for the period 1948-1995. The composite difference of temperature, wind, stream function and velocity potential during the years of high and low snow years at upper and lower levels have been studied in detail. The temperature at lower level shows maximum cooling up to 6 deg. C during DJF and this cooling persists up to 500hPa by 2 deg. C which gives rise to anomalous cyclonic circulation over the Caspian Sea and this may be one of the causes of the weakening of the summer monsoon circulation over Indian sub-continent. The stream function difference fields show westerly dominated over Arabian Sea at upper level in weak monsoon years. Velocity potential difference field shows complete phase reversal in the dipole structure from the deficient to excess Indian summer monsoon rainfall. (author)

  7. Interannual Meridional Displacement of the East Asian Upper-tropospheric Jet Stream in Summer

    Institute of Scientific and Technical Information of China (English)

    LIN Zhongda; LU Riyu

    2005-01-01

    On the interannual timescale, the meridional displacement of the East Asian upper-tropospheric jet stream (EAJS) is significantly associated with the rainfall anomalies in East Asia in summer. In this study, using the data from the National Centers for Environmental Prediction-Department of Energy (NCEP/DOE) reanalysis-2 from 1979 to 2002, the authors investigate the interannual variations of the EAJS's meridional displacement in summer and their associations with the variations of the South Asian high (SAH) and the western North Pacific subtropical high (WNPSH), which are dominant circulation features in the upper and lower troposhere, respectively. The result from an EOF analysis shows that the meridional displacement is the most remarkable feature of the interannual variations of the EAJS in each month of summer and in summer as a whole. A composite analysis indicates that the summer (June-JulyAugust, JJA) EAJS index, which is intended to depict the interannual meridional displacement of the EAJS, is not appropriate because the anomalies of the zonal wind at 200 hPa (U200) in July and August only, rather than in June, significantly contribute to the summer EAJS index. Thus, the index for each month in summer is defined according to the location of the EAJS core in each month. Composite analyses based on the monthly indexes show that corresponding to the monthly equatorward displacement of the EAJS, the South Asian high (SAH) extends southeastward clearly in July and August, and the western North Pacific subtropical high (WNPSH) withdraws southward in June and August.

  8. 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