WorldWideScience

Sample records for asian summer monsoon

  1. Relationship Between East Asian Winter Monsoon and Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    YAN Hongming; YANG Hui; YUAN Yuan; LI Chongyin

    2011-01-01

    Using National Centers for Environmental Prediction/National Centre for Atmospheric Research (NCEP/NCAR) reanalysis data and monthly Hadley Center sea surface temperature (SST) data,and selecting a representative East Asian winter monsoon (EAWM) index,this study investigated the relationship between EAWM and East Asian summer monsoon (EASM) using statistical analyses and numerical simulations.Some possible mechanisms regarding this relationship were also explored.Results indicate a close relationship between EAWM and EASM:a strong EAWM led to a strong EASM in the following summer,and a weak EAWM led to a weak EASM in the following summer.Anomalous EAWM has persistent impacts on the variation of SST in the tropical Indian Ocean and the South China Sea,and on the equatorial atmospheric thermal anomalies at both lower and upper levels.Through these impacts,the EAWM influences the land-sea thermal contrast in summer and the low-level atmospheric divergence and convergence over the Indo-Pacific region.It further affects the meridional monsoon circulation and other features of the EASM.Numerical simulations support the results of diagnostic analysis.The study provides useful information for predicting the EASM by analyzing the variations of preceding EAWM and tropical SST.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Reappraisal of Asian Summer Monsoon Indices and the Long-Term Variation of Monsoon

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Webster and Yang monsoon index (WYI)-the zonal wind shear between 850 and 200 hPa was calculated and modified on the basis of NCEP/NCAR reanalysis data. After analyzing the circulation and divergence fields of 150-100 and 200 hPa, however, we found that the 200-hPa level could not reflect the real change of the upper-tropospheric circulation of Asian summer monsoon, especially the characteristics and variation of the tropical easterly jet which is the most important feature of the upper-tropospheric circulation. The zonal wind shear U850-U(150+100) is much larger than U850-U200, and thus it can reflect the strength of monsoon more appropriately. In addition, divergence is the largest at 150 hPa rather than 200 hPa, so 150 hPa in the upper-troposphere can reflect the coupling of the monsoon system. Therefore,WYI is redefined as DHI, i.e., IDH=U*850 - U*(150+100), which is able to characterize the variability of not only the intensity of the center of zonal wind shear in Asia, but also the monsoon system in the upper and lower troposphere. DHI is superior to WYI in featuring the long-term variation of Asian summer monsoon as it indicates there is obvious interdecadal variation in the Asian summer monsoon and the climate abrupt change occurred in 1980. The Asian summer monsoon was stronger before 1980 and it weakened after then due to the weakening of the easterly in the layer of 150-100 hPa, while easterly at 200 hPa did not weaken significantly. After the climate jump year in general, easterly in the upper troposphere weakened in Asia, indicating the weakening of summer monsoon; the land-sea pressure difference and thermal difference reduced, resulting in the weakening of monsoon; the corresponding upper divergence as well as the water vapor transport decreased in Indian Peninsula, central Indo-China Peninsula, North China, and Northeast China, indicating the weakening of summer monsoon as well. The difference between NCEP/NCAR and ERA-40 reanalysis data in

  7. 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.

  8. 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.

  9. The onset and advance of the Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Based on the daily outgoing longwave radiation (OLR) data from National Oceanic and Atmospheric Administration (NOAA) satellites, the Climate Prediction Center's merged analysis of precipitation (CMAP) data and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis dataset, the mean intraseasonal variability of the Asian summer monsoon (ASM) is investigated by using power spectrum analysis, band-pass filter, and diagnostic analyses. The processes of the onset and advance of monsoon over the southern part of Indochina Peninsula, the east coast of Bay of Bengal, the South China Sea and the Indian subcontinent are explored. It is found that there is an abrupt change in OLR, precipitation and zonal wind during the onset and advance of the ASM. It is also indicated that the southern part of Indochina Peninsula and the adjacent Andaman Sea is the region where the earliest onset of the ASM occurs in the 2nd pentad of May.

  10. 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.

  11. Impact of irrigation on the South Asian summer monsoon

    Science.gov (United States)

    Saeed, Fahad; Hagemann, Stefan; Jacob, Daniela

    2009-10-01

    The Indian subcontinent is one of the most intensely irrigated regions of the world and state of the art climate models do not account for the representation of irrigation. Sensitivity studies with the regional climate model REMO show distinct feedbacks between the simulation of the monsoon circulation with and without irrigation processes. We find that the temperature and mean sea level pressure, where the standard REMO version without irrigation shows a significant bias over the areas of Indus basin, is highly sensitive to the water used for irrigation. In our sensitivity test we find that removal of this bias has caused less differential heating between land and sea masses. This in turns reduces the westerlies entering into land from Arabian Sea, hence creating conditions favorable for currents from Bay of Bengal to intrude deep into western India and Pakistan that have been unrealistically suppressed before. We conclude that the representation of irrigated water is unavoidable for realistic simulation of south Asian summer monsoon and its response under global warming.

  12. Response of Asian Summer Monsoon to CO2 Doubling

    Institute of Scientific and Technical Information of China (English)

    ZHENG Jian; LIU Qinyu; HUANG Fei

    2011-01-01

    Based on simulations of the IPCC 20C3M and SRES A1B experiments in ten coupled models,the Asian summer monsoon (ASM) response to CO2 doubling and the different responses among models are examined.Nine models show the similar results that the weakening of land-ocean thermal contrast caused by the CO2 doubling contributes to a weaker large-scale ASM circulation.Further analysis in this study also shows that the major ASM components,such as the Somali cross-equatorial flow,the low level India-South China Sea monsoon trough,and the upper level tropical easterly jet stream,weaken as CO2 doubles.However,the ASM rainfall increases as a result of the increased moisture from the warmer Indian Ocean and the South China Sea,and the enhanced northward moisture transport over the ASM region.For the response of enhanced northward moisture transport over South Asia,the positive contribution of moisture content increase in the Indian Ocean is dominant and the negative contribution of the weaker monsoon circulation is secondary at 850 hPa,but both have positive contribution to the total moisture transport along the East China coast.The paradox of the weaker ASM circulation and the increasing precipitation in CO2 doubling is confirmed.It is found that strengthening of northward moisture transport could intensify the precipitation and atmospheric heat source over the north Arabian Sea and East China,and result in enhanced southwesterly at 850hPa as global warming occurs.All ten models show significant enhanced southwesterly response over the north Arabian Sea,and six of them show enhanced southwesterly response along the East China coast.

  13. Land-sea heating contrast in an idealized Asian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Chou, C. [Environmental Change Research Project, Institute of Earth Sciences, Academia Sinica, Taipei, 115 (Taiwan)

    2003-07-01

    Mechanisms determining the tropospheric temperature gradient that is related to the intensity of the Asian summer monsoon are examined in an intermediate atmospheric model coupled with a mixed-layer ocean and a simple land surface model with an idealized Afro-Eurasian continent and no physical topography. These include processes involving in the influence of the Eurasian continent, thermal effects of the Tibetan Plateau and effects of sea surface temperature. The mechanical effect on the large-scale flow induced by the Plateau is not included in this study. The idealized land-sea geometry without topography induces a positive meridional tropospheric temperature gradient thus a weak Asian summer monsoon circulation. Higher prescribed heating and weaker surface albedo over Eurasia and the Tibetan Plateau, which mimic effects of different land surface processes and the thermal effect of the uplift of the Tibetan Plateau, strengthens the meridional temperature gradient, and so as cold tropical SST anomalies. The strengthened meridional temperature gradient enhances the Asian summer monsoon circulation and favors the strong convection. The corresponding monsoon rainbelt extends northward and northeastward and creates variations of the monsoon rainfall anomalies in different subregions. The surface albedo over the Tibetan Plateau has a relatively weak inverse relation with the intensity of the Asian summer monsoon. The longitudinal gradient of ENSO-like SST anomalies induces a more complicated pattern of the tropospheric temperature anomalies. First, the positive (negative) longitudinal gradient induced by the El Nino (La Nina)-like SST anomalies weakens (strengthens) the Walker circulation and the circulation between South Asia and northern Africa and therefore the intensity of the Asian summer monsoon, while the corresponding monsoon rainbelt extends northward (southward). The El Nino (La Nina)-like SST anomalies also induces colder (warmer) tropospheric temperature

  14. 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.

  15. 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.

  16. Dynamics of the Asian Summer Monsoon Onset and the Tibetan Plateau Impacts

    Science.gov (United States)

    Yimin, Liu; Guoxiong, Wu; Boqi, Liu; Suling, Ren; Yue, Guan

    2015-04-01

    The formation and development of the South Asian High (SAH) in early spring over South China Sea (SCS) provides upper tropospheric pumping over the Southeast Bay of Bengal (BOB) and leads to the BOB monsoon onset. The strong latent heat release of the BOB monsoon results in the northeastward unstable development of the SAH which contributes to the SCS monsoon onset. The zonal asymmetric unstable development of the SAH after the SCS monsoon onset leads to the Indian summer monsoon onset. In spring over South BOB, usually there is vortex development preceding the Asian summer monsoon onset. The rapid development of the BOB monsoon onset vortex is due to the local strong air-sea interaction, which is modulated by the Tibetan Plateau (TP) forcing and the land-sea thermal contrast across South Asia. Strong heating from BOB monsoon generates stationary Rossby-wave in lower troposphere, producing weak cold advection and convection over North SCS. Development of surface BOB cyclone provides Northeastward water vapor transport towards North SCS where convection develops. Before the Indian Summer Monsoon (ISM) onset, the North- South land- sea thermal contrast increases eastward remarkably on the southeast of Arabian Sea. Air traveling eastward along the near- surface tropical westerly jet gets northward accelerated, forcing a lower tropospheric convergence near and to the north of the jet stream. Such a forced convection development occurs intensively over the southeastern Arabian Sea and southwestern India, contributing to the ISM onset.

  17. See-saw relationship of the Holocene East Asian-Australian summer monsoon.

    Science.gov (United States)

    Eroglu, Deniz; McRobie, Fiona H; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F M; Marwan, Norbert; Kurths, Jürgen

    2016-09-26

    The East Asian-Indonesian-Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian-Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could 'lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see-saw relationship over the last 9,000 years-with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime.

  18. See-saw relationship of the Holocene East Asian-Australian summer monsoon

    Science.gov (United States)

    Eroglu, Deniz; McRobie, Fiona H.; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F. M.; Marwan, Norbert; Kurths, Jürgen

    2016-09-01

    The East Asian-Indonesian-Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian-Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could `lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see-saw relationship over the last 9,000 years--with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime.

  19. An improved south Asian summer monsoon index with Monte Carlo test

    Institute of Scientific and Technical Information of China (English)

    Shi Neng; Gu Jun-Qiang; Yi Yan-Ming; Lin Zhen-Min

    2005-01-01

    The Indian monsoon intensity index suggested by Webster and Yang (WY index) is optimized and improved in this paper. At first, the area (40°E-110°E, 0°-20°N) for calculating the zonal wind-shear between 850hPa and 200hPa in the WY index is optimized and adjusted according to the significance test of differences of wind fields. Then the regionally averaged zonal wind is computed over the optimized area. Finally, the optimal linear combination of the zonal winds at the two levels is performed using the regression method, thus defining a new broad-scale circulation index for the interannual variability of the south Asian summer monsoon, i.e. the improved south Asian summer monsoon index. Results indicate that the improved south Asian summer monsoon index has two advantages: its correlation with the All Indian Summer Monsoon Rainfall index is higher than that of WY index, and its computational domain of circulation is also larger than that of WY index. The computational results based on the 1948-98 NCAR/NCEP wind data indicate that the correlation of the improved SASM index with the All Indian Summer Monsoon Rainfall index is higher than that of WY index by 0.27.

  20. Lag influences of winter circulation conditions in the tropical western Pacific on South Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    By means of monthly mean NCEP/NCAR data analyses, this note investigates the lag influences of winter circulation conditions in the tropical western Pacific on South Asian summer monsoon through the methods of composite, correlation and statistical confident test. The results indicate clearly that winter climate variations in the equatorial western Pacific would produce significant influences on the following South Asian summer monsoon, and with the lapse of time the lag influences show clearly moving northward and extending westward features. When winter positive (negative) sea level pressure anomalies occupy the equatorial western Pacific, there is an anticyclonic (cyclonic) circulation anomaly appearing in the northwestern Pacific. With the lapse of time, the anticyclonic (cyclonic) circulation anomaly gradually moves to northeast, and its axis in the west-east directions also stretches, therefore, easterly (westerly) anomalies in the south part of the anticyclonic (cyclonic) circulation anomaly continuously expand westward to the peninsula of India. Undoubtedly, the South Asian summer monsoon is weak (strong)

  1. THE EAST ASIAN SUBTROPICAL SUMMER MONSOON INDEX AND ITS RELATION WITH THE CLIMATE ANOMALIES IN CHINA

    Institute of Scientific and Technical Information of China (English)

    LIU Xuan-fei; WANG-Jing

    2007-01-01

    A new East Asian subtropical summer monsoon circulation index is defined, where the barotropic and baroclinic components of circulation are included. Results show that this index can well indicate the interannual variability of summer precipitation and temperature anomalies in China. A strong monsoon is characterized by more rainfall in the Yellow River basin and northern China, less rainfall in the Yangtze River basin, and more rainfall in south and southeast China, in association with higher temperature in most areas of China. Furthermore, comparison is made between the index proposed in this paper and other monsoon indexes in representing climate anomalies in China.

  2. A possible impact of the North Atlantic Oscillation on the east Asian summer monsoon precipitation

    Science.gov (United States)

    Sung, Mi-Kyung; Kwon, Won-Tae; Baek, Hee-Jeong; Boo, Kyung-On; Lim, Gyu-Ho; Kug, Jong-Seong

    2006-11-01

    This letter reports on a possible delayed impact of the winter North Atlantic Oscillation (NAO) on the following east Asian summer monsoon precipitation. An analysis of weather station data shows significant correlations between the December NAO index and precipitation over Korea and China in the subsequent summer. It appears that the correlation may be related to a wave train pattern which originates from the North Atlantic. The east Asian branch of this wave train can affect large-scale circulation and the precipitation over east Asia in early summer. We also found a significant interdecadal change of this relationship, which is possibly linked to a climatological change of the east Asian jet stream.

  3. An East Asian Subtropical Summer Monsoon Index and Its Relationship to Summer Rainfall in China

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ping; ZHOU Zijiang

    2009-01-01

    Using the monthly mean NCEP/NCAR reanalysis data and the monthly rainfall observations at 160 rain gauge stations of China during 1961-1999, and based on major characteristics of the atmospheric circulation over East Asia and the western Pacific, a simple index for the East Asian subtropical summer monsoon (EASSM) is defined. The relationship between this index and summer rainfall in China and associated circulation features are examined. A comparison is made between this index and other monsoon indices. The results indicate that the index defined herein is reflective of variations of both the thermal low pressure centered in Siberia and the subtropical ridge over the western Pacific. It epitomizes the intensity of the EASSM and the variability of summer rainfall along the Yangtze River. Analysis shows that the Siberian low has a greater effect on the rainfall than the subtropical ridge, suggesting that the summer rainfall variability over the eastern parts of China is to a large extent affected by anomalies of the atmospheric circulation and cold air development in the midlatitudes. Taking into account of the effects of both the Siberian low and the subtropical ridge can better capture the summer rainfall anomalies of China. The index exhibits interannual and decadai variabilities, with high-index values occurring mainly in the 1960s and 1970s and low-index values in the 1980s and 1990s. When the EASSM index is low, the Siberian low and the subtropical ridge are weaker, and northerly wind anomalies appear at low levels over the midlatitudes and subtropics of East Asia, whereas southwesterly wind anomalies dominate in the upper troposphere over the tropics and subtropics of Asia and the western Pacific. The northerly wind anomalies bring about frequent cold air disturbances from the midlatitudes of East Asia, strengthening the convergence and ascending motions along the Meiyu front, and result in an increase of summer rainfall over the Yangtze River.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Impact of anthropogenic aerosols from global, East Asian, and non-East Asian sources on East Asian summer monsoon system

    Science.gov (United States)

    Wang, Qiuyan; Wang, Zhili; Zhang, Hua

    2017-01-01

    The impact of the total effects due to anthropogenic aerosols from global, East Asian, and non-East Asian sources on East Asian summer monsoon (EASM) system is studied using an aerosol-climate online model BCC_AGCM2.0.1_CUACE/Aero. The results show that the summer mean net all-sky shortwave fluxes averaged over East Asian monsoon region (EAMR) at the top of the atmosphere (TOA) and surface reduce by 4.8 and 5.0 W m- 2, respectively, due to the increases of global aerosol emissions in 2000 relative to 1850. Changes in radiations and their resulting changes in heat and water transport and cloud fraction contribute together to the surface cooling over EAMR in summer. The increases in global anthropogenic aerosols lead to a decrease of 2.1 K in summer mean surface temperature and an increase of 0.4 hPa in summer mean surface pressure averaged over EAMR, respectively. It is shown that the changes in surface temperature and pressure are significantly larger over land than ocean, thus decreasing the contrast of land-sea surface temperature and pressure. This results in the marked anomalies of north and northeast winds over eastern and southern China and the surrounding oceans in summer, thereby weakening the EASM. The summer mean precipitation averaged over the EAMR reduces by 12%. The changes in non-East Asian aerosol emissions play a more important role in inducing the changes of local temperature and pressure, and thus significantly exacerbate the weakness of the EASM circulation due to local aerosol changes. The weakening of circulation due to both is comparable, and even the effect of non-local aerosols is larger in individual regions. The changes of local and non-local aerosols contribute comparably to the reductions in precipitation over oceans, whereas cause opposite changes over eastern China. Our results highlight the importance of aerosol changes outside East Asia in the impact of the changes of anthropogenic aerosols on EASM.

  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. Vertical extension of the Tibetan high of the Asian summer monsoon

    OpenAIRE

    Krishnamurti, T. N.; Biswas, Mrinal K.; Bhaskar Rao, D. V.

    2008-01-01

    We illustrate the vast expanse and the connection of anticyclonic flows of the Tibetan high (at the 200 hPa level) to the pole centred hemispheric North Polar anticyclone at the 10 hPa level during 1988. This feature of clockwise flows appears in the form of a tilted cone that appears to connect the Asian summer monsoon to the 10 hPa high. The anticyclonic flow tapers down to the vortex of the cone near the 400 hPa level. The tropical easterly jet of the Asian summer season is found near 10°N...

  11. Clay mineralogical and geochemical proxies of the East Asian summer monsoon evolution in the South China Sea during Late Quaternary

    Science.gov (United States)

    Chen, Quan; Liu, Zhifei; Kissel, Catherine

    2017-01-01

    The East Asian summer monsoon controls the climatic regime of an extended region through temperature and precipitation changes. As the East Asian summer monsoon is primarily driven by the northern hemisphere summer insolation, such meteorological variables are expected to significantly change on the orbital timescale, influencing the composition of terrestrial sediments in terms of both mineralogy and geochemistry. Here we present clay mineralogy and major element composition of Core MD12-3432 retrieved from the northern South China Sea, and we investigate their relationship with the East Asian summer monsoon evolution over the last 400 ka. The variability of smectite/(illite + chlorite) ratio presents a predominant precession periodicity, synchronous with the northern hemisphere summer insolation changes and therefore with that of the East Asian summer monsoon. Variations in K2O/Al2O3 are characterized by eccentricity cycles, increasing during interglacials when the East Asian summer monsoon is enhanced. Based on the knowledge of sediment provenances, we suggest that these two proxies in the South China Sea are linked to the East Asian summer monsoon evolution with different mechanisms, which are (1) contemporaneous chemical weathering intensity in Luzon for smectite/(illite + chlorite) ratio and (2) river denudation intensity for K2O/Al2O3 ratio of bulk sediment. PMID:28176842

  12. 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

  13. INTERDECADAL VARIATIONS OF INTERACTION BETWEEN NORTH PACIFIC SSTA AND EAST ASIAN SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    李峰; 何金海

    2001-01-01

    Identification of key SST zones is essential in predicting the weather / climate systems in East Asia. With the SST data by the U.K. Meteorological Office and 40-year geopotential height and wind fields by NCAR / NCEP, the relationship between the East Asian summer monsoon and north Pacific SSTA is studied, which reveals their interactions are of interdecadal variation. Before mid-1970's, the north Pacific SSTA acts upon the summer monsoon in East Asia through a great circle wavetrain and results in more rainfall in the summer of the northern part of China. After 1976, the SSTA weakens the wavetrain and no longer influences the precipitation in North China due to loosened links with the East Asian summer monsoon. It can be drawn that the key SST zones having potential effects on the weather / climate systems in East Asia do not stay in one particular area of the ocean but rather shift elsewhere as governed by the interdecadal variations of the air-sea interactions. It is hoped that the study would help shed light on the prediction of drought / flood spans in China.

  14. 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

  15. 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.

  16. 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.

  17. The East Asian summer monsoon at mid-Holocene: results from PMIP3 simulations

    Directory of Open Access Journals (Sweden)

    W. Zheng

    2012-08-01

    Full Text Available Ten Coupled General Circulation Models (CGCMs participating the third phase of Paleoclimate Modeling Intercomparison project (PMIP3 are assessed for the simulations of East Asian Summer Monsoon (EASM at both the present climate and mid-Holocene. Results show that the PMIP3 model median well captures the characteristics of the EASM, including the two distinct features of the Meiyu Front and the stepwise meridional displacement of the monsoon rainbelt. At mid-Holocene, the enhanced EASM is simulated by the PMIP3 models. The model median shows that the changes of surface air temperature and precipitation are within the range as indicated by the proxy data over the eastern China. Both the changes of monsoonal circulation and the water vapor content favor the increasing of summer precipitation. Regional features can be identified between models because of their different simulations of the above changes. The model spread for the surface air temperature (TAS is relatively smaller when compared with that of PMIP2 models in both the Northern Hemisphere and the eastern China. However, the model spread of summer precipitation is larger among PMIP3 models, particularly in the lower reaches of Yangzi River. 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 for those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation.

  18. 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.

  19. Drought variability at the northern fringe of the Asian summer monsoon region over the past millennia

    Science.gov (United States)

    Yang, Bao; Kang, Shuyuan; Ljungqvist, Fredrik Charpentier; He, Minhui; Zhao, Yan; Qin, Chun

    2014-08-01

    The northern fringe of the Asian summer monsoon region (NASM) in China refers to the most northwestern extent of the Asian summer monsoon. Understanding the characteristics and underlying mechanisms of drought variability at long and short time-scales in the NASM region is of great importance, because present and future water shortages are of great concern. Here, we used newly developed and existing tree-ring, historical documentary and instrumental data available for the region to identify spatial and temporal patterns, and possible mechanisms of drought variability, over the past two millennia. We found that drought variations were roughly consistent in the western (the Qilian Mountains and Hexi Corridor) and eastern (the Great Bend of the Yellow River, referred to as GBYR) parts of the NASM on decadal to centennial timescales. We also identified the spatial extent of typical multi-decadal GBYR drought events based on historical dryness/wetness data and the Monsoon Asia Drought Atlas. It was found that the two periods of drought, in AD 1625-1644 and 1975-1999, exhibited similar patterns: specifically, a wet west and a dry east in the NASM. Spatial characteristics of wetness and dryness were also broadly similar over these two periods, such that when drought occurred in the Karakoram Mountains, western Tianshan Mountains, the Pamirs, Mongolia, most of East Asia, the eastern Himalayas and Southeast Asia, a wet climate dominated in most parts of the Indian subcontinent. We suggest that the warm temperature anomalies in the tropical Pacific might have been mainly responsible for the recent 1975-1999 drought. Possible causes of the drought of 1625-1644 were the combined effects of the weakened Asian summer monsoon and an associated southward shift of the Pacific Intertropical Convergence Zone. These changes occurred due to a combination of Tibetan Plateau cooling together with more general Northern Hemisphere cooling, rather than being solely due to changes in the sea

  20. 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

    2016-12-01

    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.

  1. 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.

  2. 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.

  3. 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

  4. The Leading Mode of Indian Ocean SST and Its Impacts on Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    YANG Mingzhu; DING Yihui; LI Weijing; MAO Hengqing; HUANG Changxing

    2008-01-01

    The Indian Ocean (IO) sea surface temperature (SST) was analyzed by using empirical orthogonal function (EOF), and the leading mode of Indian Ocean (LMIO) SST was extracted. The major spatial and temporal characters of LMIO were discussed, and the relationships between LMIO with Indian summer monsoon (ISM) and with China summer rainfalls (CSR) were investigated, then the impacts of LMIO on Asian summer monsoon (ASM) circulation were explored. Some notable results are obtained: The significant evolutional characters of LMIO are the consistent warming trend of almost the whole IO basin,the distinctive quasi-3- and quasi-ll-yr oscillations and remarkably interdecadal warming in 1976/1977 and1997/1998, respectively. The LMIO impaired the lower level circulation of ISM and was closely related with the climate trend of CSR. It was associated with the weakening of South Asian high, the easterly winds south of the Tibetan Plateau, and the cross-equatorial flows over 10°-20°N, 40°-110°E at the upper level; with the strengthening of Somali cross-equatorial jet but the weakening of the circulation of ISM in the sector of India, the strengthening of south wind over the middle and lower reaches of Yangtze River and South China but the weakening of southwesterly winds over North China at lower level and with the increasing of surface pressure over the Asian Continent. Changes in the moisture flux transports integrated vertically over the whole troposphere associated with LMIO are similar to those in the lower level circulation. To sum up, the significant SST increasing trend of IO basin was one of the important causes for weakening of the ASM circulation and the southwards shifting of China summer rainband.

  5. 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.

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

    Science.gov (United States)

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

    2016-07-01

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

  7. Sensitivity of Asian Summer Monsoon precipitation to tropical sea surface temperature anomalies

    Science.gov (United States)

    Fan, Lei; Shin, Sang-Ik; Liu, Zhengyu; Liu, Qinyu

    2016-10-01

    Sensitivity of Asian Summer Monsoon (ASM) precipitation to tropical sea surface temperature (SST) anomalies was estimated from ensemble simulations of two atmospheric general circulation models (GCMs) with an array of idealized SST anomaly patch prescriptions. Consistent sensitivity patterns were obtained in both models. Sensitivity of Indian Summer Monsoon (ISM) precipitation to cooling in the East Pacific was much weaker than to that of the same magnitude in the local Indian-western Pacific, over which a meridional pattern of warm north and cold south was most instrumental in increasing ISM precipitation. This indicates that the strength of the ENSO-ISM relationship is due to the large-amplitude East Pacific SST anomaly rather than its sensitivity value. Sensitivity of the East Asian Summer Monsoon (EASM), represented by the Yangtze-Huai River Valley (YHRV, also known as the meiyu-baiu front) precipitation, is non-uniform across the Indian Ocean basin. YHRV precipitation was most sensitive to warm SST anomalies over the northern Indian Ocean and the South China Sea, whereas the southern Indian Ocean had the opposite effect. This implies that the strengthened EASM in the post-Niño year is attributable mainly to warming of the northern Indian Ocean. The corresponding physical links between these SST anomaly patterns and ASM precipitation were also discussed. The relevance of sensitivity maps was justified by the high correlation between sensitivity-map-based reconstructed time series using observed SST anomaly patterns and actual precipitation series derived from ensemble-mean atmospheric GCM runs with time-varying global SST prescriptions during the same period. The correlation results indicated that sensitivity maps derived from patch experiments were far superior to those based on regression methods.

  8. 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

  9. Asian summer monsoon anomalies induced by aerosol direct forcing: the role of the Tibetan Plateau

    Energy Technology Data Exchange (ETDEWEB)

    Lau, K.M. [NASA Goddard Space Flight Center, Laboratory for Atmospheres, Greenbelt, MD (United States); Kim, M.K. [Kongju National University, Department of Atmospheric Science, Gongju (Korea); Kim, K.M. [Science Systems and Applications, Inc, Lanham, MD (United States)

    2006-06-15

    In this paper we present results of a numerical study using the NASA finite-volume GCM to elucidate a plausible mechanism for aerosol impact on the Asian summer monsoon involving interaction with physical processes over the Tibetan Plateau (TP). During the pre-monsoon season of March-April, dusts from the deserts of western China, Afghanistan/Pakistan, and the Middle East are transported into and stacked up against the northern and southern slopes of the TP. The absorption of solar radiation by dust heats up the elevated surface air over the slopes. On the southern slopes, the atmospheric heating is reinforced by black carbon from local emission. The heated air rises via dry convection, creating a positive temperature anomaly in the mid-to-upper troposphere over the TP relative to the region to the south. In May through early June in a manner akin to an ''elevated heat pump'', the rising hot air forced by the increasing heating in the upper troposphere, draws in warm and moist air over the Indian subcontinent, setting the stage for the onset of the South Asia summer monsoon. Our results suggest that increased dust loading coupled with black carbon emission from local sources in northern India during late spring may lead to an advance of the rainy periods and subsequently an intensification of the Indian summer monsoon. The enhanced rainfall over India is associated with the development of an aerosol-induced large-scale sea level pressure anomaly pattern, which causes the East Asia (Mei-yu) rain belt to shift northwestward, suppressing rainfall over East Asia and the adjacent oceanic regions. (orig.)

  10. 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

  11. 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

  12. 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

  13. 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.

  14. GENERAL SITUATION ABOUT ACTIVITY OF SUMMER MONSOON OVER SOUTH CHINA SEA IN 2004 ASIAN SUMMER MONSOON INDEX

    Institute of Scientific and Technical Information of China (English)

    LI Chun-hui; LIANG Jian-yin

    2006-01-01

    Based on daily NCEP reanalysis data, OLR and satellite rainfall data, the characteristic of the activities of South China Sea summer monsoon(SCSSM) in 2004 were analyzed. The results showed that the establishment of SCSSM was little later than normal and the intensity was stronger than normal. Influenced by the location of the northwest Pacific subtropical high, which was much northward and westward than normal,SCSSM was active mainly in the South China Sea areas. There existed obvious intraseasonal oscillation and two significant periods of SCSSM, one was about 20-30 days and the other about 40-50 days. The transportation of moisture was concentrated on the South China Sea and the northwest Pacific regions, reducing the northward transportation and resulting in drought in southern China.

  15. Interdecadal Variability of the East Asian Summer Monsoon and Associated Atmospheric Circulations

    Institute of Scientific and Technical Information of China (English)

    ZENG Gang; SUN Zhaobo; Wei-Chyung WANG; MIN Jinzhong

    2007-01-01

    Based on the National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis data from 1950-1999, interdecadal variability of the East Asian Summer Monsoon (EASM) and its associated atmospheric circulations are investigated. The EASM exhibits a distinct interdecadal variation, with stronger (weaker) summer monsoon maintained from 1950-1964 (1976-1997).In the former case, there is an enhanced Walker cell in the eastern Pacific and an anti-Walker cell in the western Pacific. The associated ascending motion resides in the central Pacific, which flows eastward and westward in the upper troposphere, descending in the eastern and western ends of the Pacific basin. At the same time, an anomalous East Asian Hadley Cell (EAHC) is found to connect the low-latitude and mid-latitude systems in East Asia, which strengthens the EASM. The descending branch of the EAHC lies in the west part of the anti-Walker cell, flowing northward in the lower troposphere and then ascending at the south of Lake Baikal (40°-50°N, 95°-115°E) before returning to low latitudes in the upper troposphere,thus strengthening the EASM.The relationship between the EASM and SST in the eastern tropical Pacific is also discussed. A possible mechanism is proposed to link interdecadal variation of the EASM with the eastern tropical Pacific SST. A warmer sea surface temperature anomaly (SSTA) therein induces anomalous ascending motion in the eastern Pacific, resulting in a weaker Walker cell, and at the same time inducing an anomalous Walker cell in the western Pacific and an enhanced EAHC, leading to a weaker EASM. Furthermore, the interdecadal variation of summer precipitation over North China is found to be strongly regulated by the velocity potential over the south of Lake Baikal through enhancing and reducing the regional vertical motions.

  16. 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)

    CHEN XiuLing; FANG XiaoMin; AN ZhiSheng; HAN WenXia; WANG Xin; BAI Yan; HONG Ye

    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.

  17. 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.

  18. Statistically related coupled modes of South Asian summer monsoon interannual variability in the tropics

    Science.gov (United States)

    Syed, Faisal S.; Kucharski, Fred

    2016-04-01

    Statistically coupled patterns of South Asian Summer Monsoon (SASM) interannual variability in the tropical oceans have been explored.Maximum covariance analysis (MCA) performed between global tropical sea surface temperature (SST) and SASM precipitation shows that El-Nino southern oscillation (ENSO) is the leading mode in the tropics, whereas the eastern pole of the Indian Ocean Dipole contributes to the second global mode and is the leading mode in the Indian Ocean. South tropical Atlantic SST variability is contributing to the second and third mode in the tropics and is the leading mode in the tropical Atlantic MCA coupled with SASM. The physical mechamism of the south tropical Atlantic-SASM teleconnection is analysed in more details.

  19. Simulation skill of APCC set of global climate models for Asian summer monsoon rainfall variability

    Science.gov (United States)

    Singh, U. K.; Singh, G. P.; Singh, Vikas

    2015-04-01

    The performance of 11 Asia-Pacific Economic Cooperation Climate Center (APCC) global climate models (coupled and uncoupled both) in simulating the seasonal summer (June-August) monsoon rainfall variability over Asia (especially over India and East Asia) has been evaluated in detail using hind-cast data (3 months advance) generated from APCC which provides the regional climate information product services based on multi-model ensemble dynamical seasonal prediction systems. The skill of each global climate model over Asia was tested separately in detail for the period of 21 years (1983-2003), and simulated Asian summer monsoon rainfall (ASMR) has been verified using various statistical measures for Indian and East Asian land masses separately. The analysis found a large variation in spatial ASMR simulated with uncoupled model compared to coupled models (like Predictive Ocean Atmosphere Model for Australia, National Centers for Environmental Prediction and Japan Meteorological Agency). The simulated ASMR in coupled model was closer to Climate Prediction Centre Merged Analysis of Precipitation (CMAP) compared to uncoupled models although the amount of ASMR was underestimated in both models. Analysis also found a high spread in simulated ASMR among the ensemble members (suggesting that the model's performance is highly dependent on its initial conditions). The correlation analysis between sea surface temperature (SST) and ASMR shows that that the coupled models are strongly associated with ASMR compared to the uncoupled models (suggesting that air-sea interaction is well cared in coupled models). The analysis of rainfall using various statistical measures suggests that the multi-model ensemble (MME) performed better compared to individual model and also separate study indicate that Indian and East Asian land masses are more useful compared to Asia monsoon rainfall as a whole. The results of various statistical measures like skill of multi-model ensemble, large spread

  20. Millennial-scale Asian summer monsoon variations in South China since the last deglaciation

    Science.gov (United States)

    Wang, Xisheng; Chu, Guoqiang; Sheng, Mei; Zhang, Shuqin; Li, Jinhua; Chen, Yun; Tang, Ling; Su, Youliang; Pei, Junling; Yang, Zhenyu

    2016-10-01

    Characterizing spatiotemporal variability of the Asian summer monsoon (ASM) is critical for full understanding of its behavior, dynamics, and future impacts. The present knowledge about ASM variations since the last glaciation in South China largely relies on several precisely-dated speleothem stable oxygen isotope (δ18 O) records. Although these speleothem δ18 O signals provide useful evidence for regional past environmental changes, their validity for denoting ASM intensity remains a great controversy. The Huguangyan Maar Lake (HML) provides one of the most complete archives of environmental and climatic changes in the tropical-subtropical South and East Asia since the last glaciation. Here we document a continuous centennial- to millennial-scale ASM record over the past 16 ky BP from the high-sedimentation-rate HML sediments. In contrast with the low-amplitude variations of Chinese speleothem-derived δ18 O signals and the Chinese loess-based monsoon precipitation proxy indexes, our multi-proxy records reveal a pattern of high-amplitude regional climatic fluctuations, including fine-scale oscillations during the Bølling-Allerød warming, the 8.2 ka cooling event, and an abrupt climate shift from 6.5-5.9 ka. The existence of Bond-like cold/dry events indicates a distinct influence of the North Atlantic circulation on low-latitude monsoon changes. The broad comparability between the HML paleo-proxies, Chinese speleothem δ18 O records, and the northern hemisphere summer insolation throughout the Holocene, suggests that solar insolation exerts a profound influence on ASM changes. These findings reinforce a model of combined insolation and glacial forcing of the ASM.

  1. The Influence of Regional SSTs on the Interdecadal Shift of the East Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    FU Jianjian; LI Shuanglin

    2013-01-01

    East Asia has experienced a significant interdecadal climate shift since the late 1970s.This shift was accompanied by a decadal change of global SST.Previous studies have suggested that the decadal shift of global SST background status played a substantial role in such a climatic shift.However,the individual roles of different regional SSTs remain unclear.In this study,we investigated these roles using ensemble experiments of an atmospheric general circulation model,GFDL (Geophysical Fluid Dynamics Laboratory) AM2.Two kinds of ensembles were performed.The first was a control ensemble in which the model was driven with the observed climatological SSTs.The second was an experimental ensemble in which the model was driven with the observed climatological SSTs plus interdecadal SST background shifts in separate ocean regions.The results suggest that the SST shift in the tropics exerted more important influence than those in the extratropics,although the latter contribute to the shift modestly.The variations of summer monsoonal circulation systems,including the South Asian High,the West Pacific Subtropical High,and the lower-level air flow,were analyzed.The results show that,in comparison with those induced by extratropical SSTs,the shifts induced by tropical SSTs bear more similarity to the observations and to the simulations with global SSTs prescribed.In particular,the observed SST shift in the tropical Pacific Ocean,rather than the Indian Ocean,contributed significantly to the shift of East Asian summer monsoon since the 1970s.

  2. 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.

  3. 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

  4. Assessment of seasonal prediction skill of East Asian summer monsoon in CMIP5

    Science.gov (United States)

    Huang, Bo; Kadow, Christopher; Cubasch, Ulrich

    2016-04-01

    The East Asian summer monsoon (EASM) is a strong monsoon system with a complicated internal variation. Its seasonal predictability is a long-standing issue in climate science. We analysed the seasonal prediction skill of EASM and the correlation between EASM and El Niño Southern Oscillation (ENSO). Our study is based on historical and decadal experiments of six prediction systems (i.e., BCC-CMS1.1, CanCM4, GFDL-CM2p1, HadCM3, MIROC5 and MPI-ESM-LR) from the Coupled Model Intercomparison Project phase 5 (CMIP5) in 1979-2005. We find that initialised simulations improve the prediction skill of EASM in CanCM4 and GFDL-CM2p1 model experiments, but lower it in the HadCM3 simulation, especially after the anomaly initialisation. The better predictability of EASM in the CanCM4 and GFDL-CM2p1 simulations due to their good performance in capturing the coupled ENSO-EASM mode, which is better than in the HadCM3 experiments. In predicting EASM, the coupled Southern Oscillation-EASM mode plays a more important role than the coupled El Niño-EASM mode.

  5. 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.

  6. Interdecadal Variability of the East Asian Summer Monsoon in an AGCM

    Institute of Scientific and Technical Information of China (English)

    HAN Jinping; WANG Huijun

    2007-01-01

    It is well known that significant interdecadal variation of the East Asian summer monsoon (EASM)occurred around the end of the 1970s. Whether these variations can be attributed to the evolution of global sea surface temperature (SST) and sea ice concentration distribution is investigated with an atmospheric general circulation model (AGCM). The model is forced with observed monthly global SST and sea ice evolution through 1958-1999. A total of four integrations starting from different initial conditions are carried out. It is found that only one of these reproduces the observed interdecadal changes of the EASM after the 1970s, including weakened low-level meridional wind, decreased surface air temperature and increased sea level pressure in central China, as well as the southwestward shift of the western Pacific subtropical high ridge and the strengthened 200-hPa westerlies. This discrepancy among these simulated results suggests that the interdecadal variation of the EASM cannot be accounted for by historical global SST and sea ice evolution. Thus, the possibility that the interdecadal timescale change of monsoon is a natural variability of the coupled climate system evolution cannot be excluded.

  7. 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.

  8. Effects of Intraseasonal Oscillation on the Anomalous East Asian Summer Monsoon During 1999

    Institute of Scientific and Technical Information of China (English)

    SUN Ying; DING Yihui

    2008-01-01

    The 1999 East Asian summer monsoon was very unusual for its weak northward advance and remarkably anomalous climate conditions.The monsoonal southwesterly airflow and related rain belt in East Asia were blocked south of the Yangtze River Valley.The monsoonal airflow and major moisture transport conduct shifted eastward and turned northward to Japan from the tropical western Pacific rather than to East China from the South China Sea(SCS)as in normal years.Severe and prolonged drought occurred over extensive areas of North China and heavy precipitation in South China and Japan.The investigation on the possible intrinsic mechanisms related to such an anomalous monsoon year has shown that the unique behavior of intraseasonal oscillation may play an essential role during this process.During this year,the northward propagation of 30-60-day anomalous low-level cyclone/anticyclone collapsed in the region around 20℃N and did not extend beyond the latitudes of the Yangtze River basin due to the barrier of strong cold air intrusion from the mid-latitudes.The southwesterly moisture flux on the northwestern flank of the anticyclonic moisture transport system in the western North Pacific,which was regulated by the northward shift of 30-60-day cyclonic/anticyclonic moisture transport.also did not reach the region north of 30℃N as well.Under this circumstance,the weak northward advance of the monsoon westerlies and associated northward moisture transport could not arrive in North China and led to the severe droughts there in 1999.The SCS and South China were mostly affected by the alrflow in the southern and northern flanks of the same 30-60-day cyclones or anticyclones.respectively,and thus controlled by the nearly reverse zonal wind and moisture convergent/divergent conditions.The rainfall in the SCS and South China showed out-of-phase oscillation through the transient local Hadley circulation.with the rainfall maximum occurring in the SCS (South China)when the 30-60-day

  9. 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.

  10. Influences of volcano eruptions on Asian Summer Monsoon over the last 110 years

    Science.gov (United States)

    Ning, Liang; Liu, Jian; Sun, Weiyi

    2017-02-01

    Asian summer monsoon (ASM) precipitation is the primary water resource for agriculture in many Asian countries that have experienced rapid economic growth in recent decades, thus implying the necessity for further investigations on both the internal variability of the ASM and the influence of external factors on the ASM. Using long-term high-resolution (0.5° × 0.5°) observed precipitation data, contrary to previous studies on inter-annual timescale, we showed that over the last 110 years, volcanic eruptions have influenced ASM variations on an inter-decadal timescale via teleconnections with the Atlantic Multi-decadal Oscillation (AMO). This relationship was also confirmed by Coupled Model Intercomparison Program Phase 5 (CMIP5) model simulations. During the active volcanic eruption periods (1901–1935 and 1963–1993), significantly lower ASM precipitation was observed compared with that during the inactive volcanic eruption period (1936–1962). We found that during active volcanic eruption periods, which correspond to a negative AMO state, there is an anomalously weakened Walker circulation over the tropical Pacific that transports less moisture to the ASM region and subsequently reduces ASM precipitation. This new finding may help improve decadal predictions of future changes in the ASM.

  11. Influences of volcano eruptions on Asian Summer Monsoon over the last 110 years.

    Science.gov (United States)

    Ning, Liang; Liu, Jian; Sun, Weiyi

    2017-02-16

    Asian summer monsoon (ASM) precipitation is the primary water resource for agriculture in many Asian countries that have experienced rapid economic growth in recent decades, thus implying the necessity for further investigations on both the internal variability of the ASM and the influence of external factors on the ASM. Using long-term high-resolution (0.5° × 0.5°) observed precipitation data, contrary to previous studies on inter-annual timescale, we showed that over the last 110 years, volcanic eruptions have influenced ASM variations on an inter-decadal timescale via teleconnections with the Atlantic Multi-decadal Oscillation (AMO). This relationship was also confirmed by Coupled Model Intercomparison Program Phase 5 (CMIP5) model simulations. During the active volcanic eruption periods (1901-1935 and 1963-1993), significantly lower ASM precipitation was observed compared with that during the inactive volcanic eruption period (1936-1962). We found that during active volcanic eruption periods, which correspond to a negative AMO state, there is an anomalously weakened Walker circulation over the tropical Pacific that transports less moisture to the ASM region and subsequently reduces ASM precipitation. This new finding may help improve decadal predictions of future changes in the ASM.

  12. 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.

  13. Sensitivity of the Asian summer monsoon to the horizontal resolution: differences between AMIP-type and coupled model experiments

    Energy Technology Data Exchange (ETDEWEB)

    Cherchi, Annalisa; Navarra, Antonio [Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy)

    2007-02-15

    A set of experiments forced with observed SST has been performed with the Echam4 atmospheric GCM at three different horizontal resolutions (T30, T42 and T106). These experiments have been used to study the sensitivity of the simulated Asian summer monsoon (ASM) to the horizontal resolution. The ASM is reasonably well simulated by the Echam4 model at all resolutions. In particular, the low-level westerly flow, that is the dominant manifestation of the Asian summer monsoon, is well captured by the model, and the precipitation is reasonably simulated in intensity and space appearance. The main improvements due to an higher resolution model are associated to regional aspects of the precipitation, for example the Western Ghats precipitation is better reproduced. The interannual variability of precipitation and wind fields in the Asian monsoon region appears to be less affected by an increase in the horizontal resolution than the mean climatology is. A possible reason is that the former is mainly SST-forced. Besides, the availability of experiments at different horizontal resolution realized with the Echam4 model coupled to a global oceanic model allows the possibility to compare these simulations with the experiments previously described. This analysis showed that the coupled model is able to reproduce a realistic monsoon, as the basic dynamics of the phenomenon is captured. The increase of the horizontal resolution of the atmospheric component influences the simulated monsoon with the same characteristics of the forced experiments. Some basic features of the Asian summer monsoon, as the interannual variability and the connection with ENSO, are further investigated. (orig.)

  14. Impact of the Asian Summer Monsoon on the Lower Stratosphere: Results from TACTS/ESMVal 2012

    Science.gov (United States)

    Hoor, Peter; Müller, Stefan; Vogel, Bärbel; Bozem, Heiko; Fischer, Horst; Bönisch, Harald; Engel, Andreas; Keber, Timo; Krämer, Martina; Riese, Martin; Gute, Ellen; Schlager, Hans; Ziereis, Helmut; Zahn, Andreas

    2016-04-01

    We present results from the German research aircraft HALO during the TACTS/ESMVal project (Transport and Composition in the UTLS and Earth System Model Validation). We focus on the distribution of CO, N2O and ozone as well as water vapour. The measurements took place in the extratropical UTLS (upper troposphere/lower stratosphere) region over Europe from August to September 2012. Here, we focus on the northern hemispheric trace gas composition above potential temperatures of 370 K. In this region we could for the first time identify mixing lines, which indicate mixing between stratospheric air masses of different origin. Introducing a new pair of correlation species (N2O-CO) we could identify air masses, which do not involve mixing directly at the tropopause. Based on a case study we show, that the atmospheric region between the extratropical tropopause and potential temperatures up to Θ = 405 K is affected by mixing of 'young' stratospheric air from the monsoon region with aged stratospheric air. Based on the distribution of CO and N2O we show that the lower stratosphere over Europe becomes more tropospheric from August to September with enhanced CO, N2O and water vapour as well as decreasing ozone. Using comprehensive trajectory calculations our results particularly indicate that the Asian summer monoon is the main contributor to this composition change and that mixing from the tropical tropopause layer becomes weaker over time. Therefore we conclude that the monsoon significantly contributes to the flushing of the extratropical UTLS during summer and autumn.

  15. The interactions between anthropogenic aerosols and the East Asian summer monsoon using RegCCMS

    Science.gov (United States)

    Wang, T. J.; Zhuang, B. L.; Li, S.; Liu, J.; Xie, M.; Yin, C. Q.; Zhang, Y.; Yuan, C.; Zhu, J. L.; Ji, L. Q.; Han, Y.

    2015-06-01

    An online coupled regional climate-chemistry model called RegCCMS is used to investigate the interactions between anthropogenic aerosols and the East Asian summer monsoon (EASM) over East Asia. The simulation results show that the mean aerosol loading and optical depth over the region are 17.87 mg/m2 and 0.25, respectively. Sulfate and black carbon (BC) account for approximately 61.2% and 7.8% of the total aerosols, respectively. The regional mean radiative forcing (RF) is approximately -3.64, -0.55, and +0.88 W/m2 at the top of the atmosphere for the total aerosol effect, the total aerosol direct effect, and the BC direct effect, respectively. The surface direct RF of BC accounts for approximately 31% of the total RF of all aerosols. Because of the total aerosol effect, both the energy budgets and air temperature are considerably reduced in the region with high aerosol loadings, leading to decreases in the land-ocean air temperature gradient in summer. The total column-absorbed solar radiation and surface air temperature decrease by 8.4 W/m2 and 0.31 K, respectively. This cooling effect weakens horizontal and vertical atmospheric circulations over East Asia. The wind speed at 850 hPa decreases by 0.18 m/s, and the precipitation decreases by 0.29 mm/d. The small responses of solar radiation, air temperature, and atmospheric circulations to the BC warming effect are opposite to those of the total aerosol effect. The BC-induced enhancement of atmospheric circulation can increase local floods in south China, while droughts in north China may worsen in response to the BC semidirect effect. The total aerosol effect is much more significant than the BC direct effect. The East Asian summer monsoon becomes weaker due to the total aerosol effect. However, this weakness could be partially offset by the BC warming effect. Sensitivity analyses further indicate that the influence of aerosols on the EASM might be more substantial in years when the southerlies or southwesterlies

  16. 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.

  17. C4 plant expansion since the late Miocene and the evolution of Asian summer monsoon

    Science.gov (United States)

    Wu, H.; Guo, Z.; Guiot, J.; Yu, Y.; Ge, J.; Zhang, Y.; Peng, S.

    2015-12-01

    A dramatic expansion of C4 plant distribution occurred in the South Asia during the late Miocene and in the East Asia during the Pliocene period, with broad spatial and temporal variations. Although the event is well documented, whether subsequent expansions were caused by a decreased atmospheric CO2 concentration or climate change is a contentious issue. In this study, we used an improved inverse vegetation modeling approach that accounts for the physiological responses of C3 and C4 plants to quantitatively reconstruct the paleoclimate in the Siwalik of South Asia and in the Loess Plateau of East Asia, based on pollen and carbon isotope data. We also studied the sensitivity of the C3 and C4 plants to changes in the climate and the atmospheric CO2 concentration. We suggest that the expansion of the C4 plant distribution since the late Miocene was unlikely caused by reduced CO2 levels alone. The expansion may have been primarily triggered by regional aridification, and seasonal analysis revealed that this climate shift mainly attributed to the summer rainfall decrease. Our findings suggest that this abrupt ecological shift mainly resulted from the weakening of the Asian summer monsoon, which may related to the decrease of SST in the tropic since the late Miocene.

  18. Impacts of Land Process on the Onset and Evolution of Asian Summer Monsoon in the NCEP Climate Forecast System

    Institute of Scientific and Technical Information of China (English)

    Song YANG; WEN Min; Rongqian YANG; Wayne HIGGINS; ZHANG Renhe

    2011-01-01

    Impacts of land models and initial land conditions (ICs) on the Asian summer monsoon,especially its onset,were investigated using the NCEP Climate Forecast System (CFS).Two land models,the Oregon State University (OSU) land model and the NCEP,OSU,Air Force,and Hydrologic Research Laboratory (Noah) land model,were used to get parallel experiments.The experiments also used land ICs from the NCEP/Department of Energy (DOE) Global Reanalysis 2 (GR2) and the Global Land Data Assimilation System (GLDAS).Previous studies have demonstrated that,a systematic weak bias appears in the modeled monsoon,and this bias may be related to a cold bias over the Asian land mass.Results of the current study show that replacement of the OSU land model by the Noah land model improved the model's cold bias and produced improved monsoon precipitation and circulation patterns.The CFS predicted monsoon with greater proficiency in El Ni(n)o years,compared to La Ni(n)a years,and the Noah model performed better than the OSU model in monsoon predictions for individual years.These improvements occurred not only in relation to monsoon onset in late spring but also to monsoon intensity in summer.Our analysis of the monsoon features over the India peninsula,the Indo-China peninsula,and the South Chinese Sea indicates different degrees of improvement.Furthermore,a change in the land models led to more remarkable improvement in monsoon prediction than did a change from the GR2 land ICs to the GLDAS land ICs.

  19. The influences of East Asian Monsoon on summer precipitation in Northeast China

    Science.gov (United States)

    Sun, Li; Shen, Baizhu; Sui, Bo; Huang, Bohua

    2017-03-01

    A unique dataset of 53-year (1961-2013) rainfall measurements from 104 stations uniformly distributed in the Northeast China, combined with the observation-based NCEP/NCAR atmospheric reanalysis, is used to analyze the precipitation anomalies in Northeast China during late boreal summer (July-August) and their relationship with the anomalous moisture transport associated with the fluctuations of the East Asian Summer Monsoon (EASM) circulation. Based on this analysis, a new EASM influence index ( I EASM ) is proposed to quantify the EASM effects on the Northeast China summer precipitation. The relationship between the IEASM variations and patterns of the anomalous regional atmospheric circulation is demonstrated. The characteristics of several precursors that lead to the major fluctuations of the I EASM index are also explored. The results show that the EASM influence index is closely linked to the anomalous rainfall in Northeast China and can be used as a major factor to measure the physical processes that affect the regional dry and wet conditions. The I EASM index responds to the large-scale anomalies of the atmospheric circulation sensitively. Specifically, the high I EASM values are associated with the intensified Mongolia cyclone, blocking developing near the Ural Mountains and a northwestward shift of subtropical high over the western Pacific. The low I EASM values are associated with a reversed pattern of these features. The I EASM anomalous fluctuation has some precursors. A major high (low) index during the summer is likely preceded with the pattern of the sea surface temperature anomalies of an El Niño (La Niña) event in the Pacific from the previous early fall to early winter.

  20. Seasonal Transitions and the Westerly Jet in the Holocene East Asian Summer Monsoon

    Science.gov (United States)

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

    2015-12-01

    The Holocene East Asian Summer Monsoon (EASM) was characterized by a trend to weaker monsoon intensity paced by orbital insolation. Here, we attribute the stronger EASM intensity in the early-mid Holocene to changes in the timing of the transition between the EASM seasonal stages - Spring, pre Mei- Yu, Mei-Yu, and Summer - during that time. Following the recent 'jet transition hypothesis' (Chiang et al., 2015), we explore the role of north-south displacement of the westerlies relative to the Tibetan Plateau that is hypothesized to control the downstream EASM seasonality changes across the Holocene. To this end, we analyze model simulations of the Holocene EASM, compare the simulated Holocene climate with the paleodata observations, and examine the role of atmospheric circulation and specifically the westerlies in modulating the East Asia summer climate. The PMIP3 climate model simulations suggest that, compared to the pre-industrial, the Mei-Yu onset and the transition from Mei-Yu to Summer rainfall occur earlier in the mid-Holocene. The advanced seasonal rainfall transition is accompanied by the weakened and northward-shifted upstream westerlies. In our atmospheric general circulation model (coupled to a slab ocean) simulations of various time periods across the Holocene (9ka, 6ka, 3ka, and pre-industrial), we quantitatively show that the timing and the length of each rainfall stage are closely related to the jet position over East Asia. We also show that the simulated changes in the maximum annual rainfall band and dust emission over East Asia largely agree with the paleo-proxy observations. In addition, we find that changes to the seasonal rainfall transitions, latitudinal westerly position, and stationary eddy activity over East Asia co-vary across the Holocene. In particular, we argue that the changes in the rainfall seasonal transitions are tied to an altered stationary wave pattern, resembling today's the so-called 'Silk Road Pattern', riding along the

  1. 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.

  2. 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...

  3. Hydrological Response of East China to the Variation of East Asian Summer Monsoon

    Directory of Open Access Journals (Sweden)

    Fuxing Li

    2016-01-01

    Full Text Available The sensitivity of hydrologic variables in East China, that is, runoff, precipitation, evapotranspiration, and soil moisture to the fluctuation of East Asian summer monsoon (EASM, is evaluated by the Mann-Kendall correlation analysis on a spatial resolution of 1/4° in the period of 1952–2012. The results indicate remarkable spatial disparities in the correlation between the hydrologic variables and EASM. The regions in East China susceptible to hydrological change due to EASM fluctuation are identified. When the standardized anomaly of intensity index of EASM (EASMI is above 1.00, the runoff of Haihe basin has increased by 49% on average, especially in the suburb of Beijing and Hebei province where the runoff has increased up to 105%. In contrast, the runoff in the basins of Haihe and Yellow River has decreased by about 27% and 17%, respectively, when the standardized anomaly of EASMI is below −1.00, which has brought severe drought to the areas since mid-1970s. The study can be beneficial for national or watershed agencies developing adaptive water management strategies in the face of global climate change.

  4. Effects of sulfate aerosol forcing on East Asian summer monsoon for 1985-2010

    Science.gov (United States)

    Kim, Minjoong J.; Yeh, Sang-Wook; Park, Rokjin J.

    2016-02-01

    We examine the effect of anthropogenic aerosol forcing on the East Asian summer monsoon (EASM) using the Community Atmosphere Model version 5.1.1. One control and two sensitivity model experiments were conducted in order to diagnose the separate roles played by sea surface temperature (SST) variations and anthropogenic sulfate aerosol forcing changes in East Asia. We find that the SST variation has been a major driver for the observed weakening of the EASM, whereas the effect of the anthropogenic aerosol forcing has been opposite and has slightly intensified the EASM over the recent decades. The reinforcement of the EASM results from radiative cooling by the sulfate aerosol forcing, which decelerates the jet stream around the jet's exit region. Subsequently, the secondary circulation induced by such a change in the jet stream leads to the increase in precipitation around 18-23°N. This result indicates that the increase in anthropogenic emissions over East Asia may play a role in compensating for the weakening of the EASM caused by the SST forcing.

  5. Natural interdecadal weak-ening of East Asian summer monsoon in the late 20th century

    Institute of Scientific and Technical Information of China (English)

    JIANG Dabang; WANG Huijun

    2005-01-01

    Based on the reanalysis data throughout 1948―2002 as derived from the United States National Centers for Environmental Prediction and National Center for Atmospheric Research, it is revealed that East Asian summer monsoon (EASM) intensity weakens on an interdecadal timescale since the mid-1960s, and twice interdecadal jumps are recorded in the EASM intensity index series in the late 20th century, respectively occurring in the mid-1960s and mid- to late 1970s. Six globally coupled atmosphere-ocean models' outputs under the SRES A2 greenhouse gas and aerosol emission scenario, provided by the IPCC Data Distribution Center and the Hadley Center for Climate Prediction and Research, are then systematically examined. It follows that the above EASM weakening is not closely related to synchronizing anthropogenic global warming, and, therefore, it should be qualitatively natural change process. Over the 21st century, the EASM intensity is likely increased slightly by continually intensified greenhouse effect relative to the late 20th century.

  6. 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.

  7. CMIP5 model-simulated onset, duration and intensity of the Asian summer monsoon in current and future climate

    Science.gov (United States)

    Dong, Guangtao; Zhang, H.; Moise, A.; Hanson, L.; Liang, P.; Ye, H.

    2016-01-01

    A number of significant weaknesses existed in our previous analysis of the changes in the Asian monsoon onset/retreat from coupled model intercomparison project phase 3 (CMIP3) models, including a lack of statistical significance tests, a small number of models analysed, and limited understanding of the causes of model uncertainties. Yet, the latest IPCC report acknowledges limited confidence for projected changes in monsoon onset/retreat. In this study we revisit the topic by expanding the analysis to a large number of CMIP5 models over much longer period and with more diagnoses. Daily 850 hPa wind, volumetric atmospheric precipitable water and rainfall data from 26 CMIP5 models over two sets of 50-year periods are used in this study. The overall model skill in reproducing the temporal and spatial patterns of the monsoon development is similar between CMIP3 and CMIP5 models. They are able to show distinct regional characteristics in the evolutions of Indian summer monsoon (ISM), East Asian summer monsoon (EASM) and West North Pacific summer monsoon (WNPSM). Nevertheless, the averaged onset dates vary significantly among the models. Large uncertainty exists in model-simulated changes in onset/retreat dates and the extent of uncertainty is comparable to that in CMIP3 models. Under global warming, a majority of the models tend to suggest delayed onset for the south Asian monsoon in the eastern part of tropical Indian Ocean and Indochina Peninsula and nearby region, primarily due to weakened tropical circulations and eastward shift of the Walker circulation. The earlier onset over the Arabian Sea and part of the Indian subcontinent in a number of the models are related to an enhanced southwesterly flow in the region. Weak changes in other domains are due to the offsetting results among the models, with some models showing earlier onsets but others showing delayed onsets. Different from the analysis of CMIP3 model results, this analysis highlights the importance of SST

  8. Uncertainties in the regional climate models simulations of South-Asian summer monsoon and climate change

    Science.gov (United States)

    Syed, F. S.; Iqbal, Waheed; Syed, Ahsan Ali Bukhari; Rasul, G.

    2014-04-01

    The uncertainties in the regional climate models (RCMs) are evaluated by analyzing the driving global data of ERA40 reanalysis and ECHAM5 general circulation models, and the downscaled data of two RCMs (RegCM4 and PRECIS) over South-Asia for the present day simulation (1971-2000) of South-Asian summer monsoon. The differences between the observational datasets over South-Asia are also analyzed. The spatial and the quantitative analysis over the selected climatic regions of South-Asia for the mean climate and the inter-annual variability of temperature, precipitation and circulation show that the RCMs have systematic biases which are independent from different driving datasets and seems to come from the physics parameterization of the RCMs. The spatial gradients and topographically-induced structure of climate are generally captured and simulated values are within a few degrees of the observed values. The biases in the RCMs are not consistent with the biases in the driving fields and the models show similar spatial patterns after downscaling different global datasets. The annual cycle of temperature and rainfall is well simulated by the RCMs, however the RCMs are not able to capture the inter-annual variability. ECHAM5 is also downscaled for the future (2071-2100) climate under A1B emission scenario. The climate change signal is consistent between ECHAM5 and RCMs. There is warming over all the regions of South-Asia associated with increasing greenhouse gas concentrations and the increase in summer mean surface air temperature by the end of the century ranges from 2.5 to 5 °C, with maximum warming over north western parts of the domain and 30 % increase in rainfall over north eastern India, Bangladesh and Myanmar.

  9. 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

  10. 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.

  11. Unraveling El Niño's impact on the East Asian Monsoon and Yangtze River summer flooding

    Science.gov (United States)

    Zhang, Wenjun; Jin, Fei-Fei; Stuecker, Malte F.; Wittenberg, Andrew T.; Timmermann, Axel; Ren, Hong-Li; Kug, Jong-Seong; Cai, Wenju; Cane, Mark

    2016-11-01

    Strong El Niño events are followed by massive summer monsoon flooding over the Yangtze River basin (YRB), home to about a third of the population in China. Although the El Niño-Southern Oscillation (ENSO) provides the main source of seasonal climate predictability for many parts of the Earth, the mechanisms of its connection to the East Asian monsoon remain largely elusive. For instance, the traditional Niño3.4 ENSO index only captures precipitation anomalies over East Asia in boreal winter but not during the summer. Here we show that there exists a robust year-round and predictable relationship between ENSO and the Asian monsoon. This connection is revealed by combining equatorial (Niño3.4) and off-equatorial Pacific sea surface temperature anomalies (Niño-A index) into a new metric that captures ENSO's various aspects, such as its interaction with the annual cycle and its different flavors. This extended view of ENSO complexity improves predictability of YRB summer flooding events.

  12. 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

  13. Late Cenozoic genus Fupingopollenites development and its implications for the Asian summer monsoon (ASM) evolution

    Science.gov (United States)

    Miao, Y.; Song, C.; Fang, X.; Meng, Q.; Zhang, P.; Wu, F.; Yan, X.

    2015-12-01

    An extinct palynomorph, Fupingopollenites, was used as the basis for a discussion of the late Cenozoic Asian summer monsoon (ASM) evolution and its possible driving forces. Based on the spatial and temporal variations in its percentages across Inner and East Asia, we found that Fupingopollenites mainly occurred in East Asia, with boundaries to the NE of ca. 42°N, 135°E and NW of ca. 36°N, 103°E during the Early Miocene (ca. 23-17 Ma). This region enlarged westwards, reaching the eastern Qaidam Basin (ca. 36°N, 97.5°E) during the Middle Miocene (ca. 17-11 Ma), before noticeably retreating to a region bounded to the NW at ca. 33°N, 105°E during ca. 11-5.3 Ma. The region then shrank further in the Pliocene, with the NE boundary shrinking southwards to about 35°N, 120°E; the area then almost disappeared during the Pleistocene (2.6-0 Ma). The flourishing and subsequent extinction of Fupingopollenites is indicative of a narrow ecological amplitude with a critical dependence on habitat humidity and temperature (most likely mean annual precipitation (MAP) >1000 mm and mean annual temperature (MAT) >10°C). Therefore, the Fupingopollenites geographic distribution can indicate the humid ASM evolution during the late Cenozoic, revealing that the strongest ASM period occurred during the Middle Miocene Climate Optimum (MMCO, ~17-14 Ma), after which the ASM weakened coincident with global cooling. We argue that the global cooling played a critical role in the ASM evolution, while the Tibetan Plateau uplifts made a relatively small contribution. This result was supported by a Miocene pollen record at the Qaidam Basin, inner Asia and the contemporaneously compiled pollen records across the Eurasia.

  14. 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.

  15. Competing Atmospheric and Surface-Driven Impacts of Absorbing Aerosols on the East Asian Summer Monsoon

    Science.gov (United States)

    Persad, G.; Paynter, D.; Ming, Y.; Ramaswamy, V.

    2015-12-01

    Absorbing aerosols, by attenuating shortwave radiation within the atmosphere and reemitting it as longwave radiation, redistribute energy both vertically within the surface-atmosphere column and horizontally between polluted and unpolluted regions. East Asia has the largest concentrations of anthropogenic absorbing aerosols globally, and these, along with the region's scattering aerosols, have both reduced the amount of solar radiation reaching the Earth's surface regionally ("solar dimming") and increased shortwave absorption within the atmosphere, particularly during the peak months of the East Asian Summer Monsoon (EASM). We here analyze how atmospheric absorption and surface solar dimming compete in driving the response of EASM circulation to anthropogenic absorbing aerosols, which dominates, and why—issues of particular importance for predicting how the EASM will respond to projected changes in absorbing and scattering aerosol emissions in the future. We probe these questions in a state-of-the-art general circulation model (GCM) using a combination of realistic and idealized aerosol perturbations that allow us to analyze the relative influence of absorbing aerosols' atmospheric and surface-driven impacts on EASM circulation. In combination, our results make clear that, although absorption-driven dimming has a less detrimental effect on EASM circulation than purely scattering-driven dimming, aerosol absorption is still a net impairment to EASM strength when both its atmospheric and surface effects are considered. Because atmospheric heating is not efficiently conveyed to the surface, the surface dimming and associated cooling from even a pure absorber is sufficient to counteract its atmospheric heating, resulting in a net reduction in EASM strength. These findings elevate the current understanding of the impacts of aerosol absorption on the EASM, improving our ability to diagnose EASM responses to current and future regional changes in aerosol emissions.

  16. 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.

  17. Atmospheric Moisture Distribution and Transport over the Tibetan Plateau and the Impacts of the South Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    周立波; 朱金焕; 邹捍; 马舒坡; 李鹏; 张宇; 霍翠萍

    2013-01-01

    In this study, by using the ECMWF ERA-Interim reanalysis data from 1979 to 2010, the spatial distribu-tion and transport of total atmospheric moisture over the Tibetan Plateau (TP) are analyzed, together with the associated impacts of the South Asian summer monsoon (SASM). Acting as a moisture sink in summer, the TP has a net moisture flux of 2.59×107 kg s-1 during 1979-2010, with moisture supplies mainly from the southern boundary along the latitude belts over the Bay of Bengal and the Arabian Sea. The total atmospheric moisture over the TP exhibits significant differences in both spatial distribution and transport between the monsoon active and break periods and between strong and weak monsoon years. Large positive (negative) moisture anomalies occur over the southwest edge of the TP and the Arabian Sea, mainly due to transport of easterly (westerly) anomalies during the monsoon active (break) period. For the whole TP region, the total moisture supply is more strengthened than the climatological mean during the monsoon active period, which is mainly contributed by the transport of moisture from the south edge of the TP. During the monsoon break period, however, the total moisture supply to the TP is slightly weakened. In addition, the TP moisture sink is also strengthened (weakened) in the strong (weak) monsoon years, mainly attributed by the moisture transport in the west-east directions. Our results suggest that the SASM has exerted great impacts on the total atmospheric moisture and its transport over the TP through adjusting the moisture spatial distribution.

  18. 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

  19. A Modeling Study of the Effects of Anomalous Snow Cover over the Tibetan Plateau upon the South Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    刘华强; 孙照渤; 王举; 闵锦忠

    2004-01-01

    The effect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo effect, which is compensated by weaker upward sensible heat flux associated with colder surface temperature, whereas the effects of snow melting and evaporation are relatively smaller.The anomalies of surface heat fluxes can last until June and become unobvions in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May.The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this influence is only obvious in early summer and almost disappears in later stages.

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

    Science.gov (United States)

    Zheng, Jiayu; Li, Jianping; Feng, Juan

    2014-07-01

    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.

  1. Impact of the quasi-biweekly oscillation over the western North Pacific on East Asian subtropical monsoon during early summer

    Science.gov (United States)

    Jia, Xiaolong; Yang, Song

    2013-05-01

    The impact of quasi-biweekly oscillation (QBWO) over the western North Pacific on East Asian summer monsoon (EASM) is investigated. The life cycle of QBWO is divided into eight phases defined by the two leading principal components (PC1 and PC2) of an empirical orthogonal function analysis. Subtropical rainfall shows significant changes, with a northwestward propagation of convection from equatorial regions to the South China Sea (SCS). The most significant variations occur in QBWO phases 3 and 4 (enhanced convection over SCS) and phases 7 and 8 (reduced convection over SCS). The East Asia Mei-yu significantly decreases in QBWO phases 3 and 4 but increases in phases 7 and 8. The QBWO influences EASM through modulating the subtropical monsoon flow and extratropical circulation. The response of lower tropospheric atmosphere to QBWO shows a northwestward propagation and a downstream wave train that extends northward into the western North Pacific, modulating the SCS monsoon trough and the EASM flow associated with moisture transportation. The mid-tropospheric extratropical circulation and the western Pacific subtropical high also show obvious changes accompanying QBWO evolution, resulting in circulation patterns associated with cold air activity. Moreover, changes with QBWO are found in the upper tropospheric East Asian westerly jet stream and the South Asian high, and these changes contribute to upper level divergence over subtropical East Asia.

  2. Transport pathways of carbon monoxide in the Asian summer monsoon diagnosed from Model of Ozone and Related Tracers (MOZART)

    Science.gov (United States)

    Park, Mijeong; Randel, William J.; Emmons, Louisa K.; Livesey, Nathaniel J.

    2009-04-01

    Satellite observations of tropospheric chemical constituents (such as carbon monoxide, CO) reveal a persistent maximum in the upper troposphere-lower stratosphere (UTLS) associated with the Asian summer monsoon anticyclone. Diagnostic studies suggest that the strong anticyclonic circulation acts to confine air masses, but the sources of pollution and transport pathways to altitudes near the tropopause are the subject of debate. Here we use the Model for Ozone and Related Tracers 4 (MOZART-4) global chemistry transport model, driven by analyzed meteorological fields, to study the source and transport of CO in the Asian monsoon circulation. A MOZART-4 simulation for one summer is performed, and results are compared with satellite observations of CO from the Aura Microwave Limb Sounder and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer. Overall, good agreement is found between the modeled and observed CO in the UTLS, promoting confidence in the model simulation. The model results are then analyzed to understand the sources and transport pathways of CO in the Asian monsoon region, and within the anticyclone in particular. The results show that CO is transported upward by monsoon deep convection, with the main surface sources from India and Southeast Asia. The uppermost altitude of the convective transport is ˜12 km, near the level of main deep convective outflow, and much of the CO is then advected in the upper troposphere northeastward across the Pacific Ocean and southwestward with the cross-equatorial Hadley flow. However, some of the CO is also advected vertically to altitudes near the tropopause (˜16 km) by the large-scale upward circulation on the eastern side of the anticyclone, and this air then becomes trapped within the anticyclone (to the west of the convection, extending to the Middle East). Within the anticyclone, the modeled CO shows a relative maximum near 15 km, in good agreement with observations.

  3. 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.

  4. 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.

  5. Projected response of East Asian summer monsoon system to future reductions in emissions of anthropogenic aerosols and their precursors

    Science.gov (United States)

    Wang, Zhili; Zhang, Hua; Zhang, Xiaoye

    2016-09-01

    The response of the East Asian summer monsoon (EASM) system to reductions in emissions of anthropogenic aerosols and their precursors at the end of the twenty-first century projected by Representative Concentration Pathway 4.5 is studied using an aerosol-climate model with aerosol direct, semi-direct, and indirect effects included. Our results show that the global annual mean aerosol effective radiative forcing at the top of the atmosphere (TOA) is +1.45 W m-2 from 2000 to 2100. The summer mean net all-sky shortwave fluxes averaged over the East Asian monsoon region (EAMR) at the TOA and surface increased by +3.9 and +4.0 W m-2, respectively, due to the reductions of aerosols in 2100 relative to 2000. Changes in radiations affect local thermodynamic and dynamic processes and the hydrological cycle. The summer mean surface temperature and pressure averaged over the EAMR are shown to increase by 1.7 K and decreased by 0.3 hPa, respectively, due to the reduced aerosols. The magnitudes of these changes are larger over land than ocean, causing a marked increase in the contrast of land-sea surface temperature and pressure in the EAMR, thus strengthening the EASM. The summer mean southwest and south winds at 850 hPa are enhanced over eastern and southern China and the surrounding oceans, and the East Asian subtropical jet shifted northward due to the decreases of aerosols. These factors also indicate enhanced EASM circulation, which in turn causes a 10 % increase in summer mean precipitation averaged over the EAMR.

  6. Numerical Modeling of Topography-Modulated Dust Aerosol Distribution and Its Influence on the Onset of East Asian Summer Monsoon

    Directory of Open Access Journals (Sweden)

    Hui Sun

    2016-01-01

    Full Text Available A regional climate model coupled with a dust module was used to simulate dust aerosol distribution and its effects on the atmospheric heat source over the TP, East Asian summer monsoon onset, and precipitation in East Asia modulated by the uplift of the northern TP. We carried out four experiments, including a modern (i.e., high-mountain experiment with (HMD and without (HM the major deserts in Northwest China and a low-mountain experiment with (LMD and without (LM the deserts. The results show that dust greatly increases in the Taklamakan Desert accompanied with the uplift of the northern TP, and the increase exceeds 150 µg kg−1 in spring. A strong cyclone in the Tarim Basin produced by the uplifted northern TP enhances dust emissions in the Taklamakan Desert in summer. Meanwhile, the dust loading over the TP also increases induced by the uplift of the northern TP, causing the heat source over the TP decreased. Under the condition of the northern TP uplift to present altitude, dust delays the East Asia summer monsoon onset by two pentads and one pentad, respectively, in the southern and northern monsoon regions and greatly suppresses precipitation in East Asia compared with results in the low terrain experiments.

  7. Change in the tilting of the ridgeline surface of the subtropical anticyclone and the predictability of the onset of the Asian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    MAO Jiangyu; DUAN Anmin; LIU Yimin; WU Guoxiong

    2003-01-01

    The NCEP/NCAR reanalysis data are used to study the relationships among the change in the tilting of the ridgeline surface of the subtropical anticyclone, the establishment of the so-called "seasonal transition axis (STA)" and the onset of the Asian summer monsoon. It is shown that the monsoon onset is characterized by the overturning of the meridional temperature gradient (MTG) in the vicinity of the ridgeline surface. A MTG index is then constructed to investigate the predictability of the Asian summer monsoon onset conceptually. Data diagnoses show that if the initial MTG is known and the meridional gradient across the ridgeline surface of the local temperature tendency can be estimated, a late or early onset of the summer monsoon can be qualitatively predicted in advance.

  8. 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.

  9. East China Sea δ18O Record Detects Millennial-Scale Changes in the East Asian Summer Monsoon

    Science.gov (United States)

    Gleeman, E.; Clemens, S. C.; Lawman, A. E.; Kubota, Y.; Holbourn, A. E.; Martin, A.

    2015-12-01

    The East Asian Summer Monsoon (EASM) brings heavy summer rainfall to some of Asia's most densely-populated areas, impacting agricultural production and water resources. Sediment cores were recovered from International Ocean Drilling Program Site U1429 in the East China Sea (31° 37.04' N, 128° 59.50' E, 732 mbsl). This location receives runoff from the Yangtze River, which serves as a major drainage system for monsoon-induced precipitation. Hence, the δ18O record of planktonic foraminifera at Site U1429 reflects changes in regional, monsoon-driven salinity. The top 100 meters of core at Site U1429 were sampled at a preliminary resolution of 15 cm and processed to isolate the planktonic foraminifer Globigerinoides ruber for δ18O mass spectrometry analyses. Abrupt, millennial-scale regional climate variability in the EASM and its linkage to orbital forcings have been reconstructed using stratigraphic analysis of δ18O. The sub-orbital scale structure of the δ18O record over the past 400 kyr matches the structures of both the composite speleothem δ18O from eastern China (Sanbao and Hulu caves) and the planktonic δ18O record from northern South China Sea Site 1146. The similarities between these δ18O records indicate a strong regional response to monsoon forcing. Removal of the temperature component of the δ18O signal by using Mg/Ca (G. ruber) paleothermometry will provide a record of changes in the δ18O composition of seawater in response to Yangtze River runoff.

  10. Antarctic link with East Asian summer monsoon variability during the Heinrich Stadial-Bølling interstadial transition

    Science.gov (United States)

    Zhang, Hongbin; Griffiths, Michael L.; Huang, Junhua; Cai, Yanjun; Wang, Canfa; Zhang, Fan; Cheng, Hai; Ning, Youfeng; Hu, Chaoyong; Xie, Shucheng

    2016-11-01

    Previous research has shown a strong persistence for direct teleconnections between the East Asian summer monsoon (EASM) and high northern latitude climate variability during the last glacial and deglaciation, in particular between monsoon weakening and a reduced Atlantic meridional overturning circulation (AMOC). However, less attention has been paid to EASM strengthening as the AMOC was reinvigorated following peak Northern Hemisphere (NH) cooling. Moreover, climate model simulations have suggested a strong role for Antarctic meltwater discharge in modulating northward heat transport and hence NH warming, yet the degree to which Southern Hemisphere (SH) climate anomalies impacted the Asian monsoon region is still unclear. Here we present a new stalagmite oxygen-isotope record from the EASM affected region of central China, which documents two prominent stages of increased 18O-depleted moisture delivery to the region through the transition from Heinrich Stadial 1 (HS1) to the Bølling-Allerød (B-A) interstadial; this is in general agreement with the other monsoonal records from both NH and SH mid to low latitudes. Through novel comparisons with a recent iceberg-rafted debris (IRD) record from the Southern Ocean, we propose that the two-stage EASM intensification observed in our speleothem records were linked with two massive Antarctic icesheet discharge (AID) events at ∼16.0 ka and ∼14.7 ka, immediately following the peak HS1 stadial event. Notably, the large increase in EASM intensity at the beginning of the HS1/B-A transition (∼16 ka) is relatively muted in the NH higher latitudes, and better aligns with the changes observed in the SH, indicating the Antarctic and Southern Ocean perturbations could have an active role in driving the initial EASM strengthening at this time. Indeed, Antarctic freshwater input to the Southern Ocean during these AID events would have cooled the surrounding surface waters and caused an expansion of sea ice, restricting the

  11. Decreasing Asian summer monsoon intensity after 1860 AD in the global warming epoch

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Hai [Institute of Earth Environment, Chinese Academy of Sciences, State Key Laboratory of Loess and Quaternary Geology, Xi' an, Shaanxi Province (China); Hong, Yetang; Hong, Bin [Institute of Geochemistry, Chinese Academy of Sciences, State Key Laboratory of Environmental Geochemistry, Guiyang (China)

    2012-10-15

    The trend of the Indian summer monsoon (ISM) intensity and its nature during the past 100 and 200 years still remain unclear. In this study we reconstructed the ISM intensity during the past 270 years from tree ring {delta}{sup 18}O at Hongyuan, eastern edge of the Tibet Plateau. The monsoon failures inferred from {delta}{sup 18}O{sub tree} {sub ring} correlate well with those recorded in ice cores, speleothem, and historical literature sources. 22.6, 59.0, and 110.9-years frequency components in the Hongyuan {delta}{sup 18}O{sub tree} {sub ring} series, which may be the responses to solar activities, synchronize well with those recorded in other ISM indices. A notable feature of the reconstructed ISM intensity is the gradually decreasing trend from about 1860 to the present, which is inversely related to the increasing temperature trend contemporaneously. Such ''decreasing ISM intensity-increasing temperature'' tendency can also be supported by ice core records and meteorological records over a wide geographic extension. The decrease in sea surface temperature gradient between tropical and north Indian Ocean, and the decrease in land-sea thermal contrast between tropical Indian Ocean and ''Indian sub-continent-western Himalaya'' are possibly responsible for the observed decreasing ISM trend. (orig.)

  12. Association of the East Asian subtropical westerly jet with the Southwest Asian summer monsoon: A diagnostic analysis on heavy rain events in Yunnan province, China

    Science.gov (United States)

    Chen, Jie

    2016-04-01

    Yunnan province, China is a typical area that is influenced by Southwest Asian summer monsoon (SASM) during boreal summer. Although the interannual variation of summer precipitation in Yunnan Province is closely related to that of the SASM, the East Asian subtropical westerly jet (EASWJ) may have an important role in heavy rainfall events in Yunnan Province during boreal summer. By using daily observations and the NACAR/NCEP data during 1960-2011, a diagnostic analysis is performed to investigate the association of the EASWJ with the SASM on heavy rain events in Yunnan Province during boreal summer. The analysis shows an anomalous divergence circulation pattern at upper level (200 hPa) over Eurasian continent that corresponds well to the negative anomaly of EASWJ during heavy rain events in boreal summer in Yunnan Province. At the same time, a low-level jet stream with abundant water vapor originated from the Arabian Sea and Bengal gulf provides necessarily dynamic and water conditions for heavy rain mechanism. The study further shows that the weakening of the EASWJ during heavy rain events in Yunnan Province is associated with the decrease in the meridional temperature gradient in northern mid-latitude (30o-40o N).

  13. Tropospheric ozone variability during the East Asian summer monsoon as observed by satellite (IASI), aircraft (MOZAIC) and ground stations

    Science.gov (United States)

    Safieddine, Sarah; Boynard, Anne; Hao, Nan; Huang, Fuxiang; Wang, Lili; Ji, Dongsheng; Barret, Brice; Ghude, Sachin D.; Coheur, Pierre-François; Hurtmans, Daniel; Clerbaux, Cathy

    2016-08-01

    Satellite measurements from the thermal Infrared Atmospheric Sounding Interferometer (IASI), aircraft data from the MOZAIC/IAGOS project, 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 seen 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. The year-to-year variability is found to be mainly dependent on meteorology. 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/IAGOS project for the EASM of 2008-2013 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 0.73 (12 %) between the 0-6 km O3 column derived from IASI and aircraft data. IASI captures very well the inter-annual variation of tropospheric O3 observed by the aircraft data over the studied domain. Analysis of vertical profiles of the aircraft data shows a decrease in the tropospheric O3 that is more important in the free troposphere than in the boundary layer and at 10-20° N than elsewhere. Ground station data at different locations in India and China show a spatiotemporal dependence on meteorology during the monsoon, with a decrease up to 22 ppbv in Hyderabad, and up to 5 ppbv in the North China Plain.

  14. 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.

  15. 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

    2016-10-01

    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

  16. Mesoscale convection system and occurrence of extreme low tropopause temperatures. Observations over Asian summer monsoon region

    Energy Technology Data Exchange (ETDEWEB)

    Jain, A.R.; Mandal, T.K.; Gautam, R. [National Physical Laboratory, New Delhi (India). Radio and Atmospheric Div.; Panwar, V. [National Physical Laboratory, New Delhi (India). Radio and Atmospheric Div.; Delhi Univ. (India). Dept. of Physics and Astrophysics; Rao, V.R. [India Meteorology Dept., New Delhi (India). Satellite Meteorology Div.; Goel, A. [Delhi Univ. (India). Dept. of Physics and Astrophysics; Das, S.S. [Vikram Sarabhai Space Center, Trivandrum (India). Space Physics Lab.; Dhaka, S.K. [Delhi Univ., New Delhi (India). Dept. of Physics and Electronics

    2010-07-01

    The present study examines the process of how tropospheric air enters the stratosphere, particularly in association with tropical mesoscale convective systems (TMCS) which are considered to be one of the causative mechanisms for the observation of extremely low tropopause temperature over the tropics. The association between the phenomena of convection and the observation of extreme low tropopause temperature events is, therefore, examined over the Asian monsoon region using data from multiple platforms. Satellite observations show that the area of low outgoing long wave radiation (OLR), which is a proxy for the enhanced convection, is embedded with high altitude clouds top temperatures ({<=}193 K). A detailed analysis of OLR and 100 hPa temperature shows that both are modulated by westward propagating Rossby waves with a period of {proportional_to}15 days, indicating a close linkage between them. The process by which the tropospheric air enters the stratosphere may, in turn, be determined by how the areas of convection and low tropopause temperature (LTT) i.e. T {<=}191K are spatially located. In this context, the relative spatial distribution of low OLR and LTT areas is examined. Though, the locations of low OLR and LTT are noticed in the same broad area, the two do not always overlap, except for partial overlap in some cases. When there are multiple low OLR areas, the LTT area generally appears in between the low OLR areas. Implications of these observations are also discussed. The present analysis also shows that the horizontal mean winds have a role in the spatial distribution of low OLR and LTT. (orig.)

  17. Transport of aerosol pollution in the UTLS during Asian summer monsoon as simulated by ECHAM5-HAMMOZ model

    Directory of Open Access Journals (Sweden)

    S. Fadnavis

    2012-11-01

    Full Text Available An eight member ensemble of ECHAM5-HAMMOZ simulations for the year 2003 is analyzed to study the transport of aerosols in the Upper Troposphere and Lower Stratosphere (UTLS during the Asian Summer Monsoon (ASM. Simulations show persistent maxima in black carbon, organic carbon, sulfate, and mineral dust aerosols within the anticyclone in the UTLS throughout the ASM (period from July to September when convective activity over the Indian subcontinent is highest. Model simulations indicate boundary layer aerosol pollution as the source of this UTLS aerosol layer and identify ASM convection as the dominant transport process. Evidence of ASM transport of aerosols into the stratosphere is observed in HALogen Occultation Experiment (HALOE and Stratospheric Aerosol and Gas Experiment (SAGE II aerosol extinction. The impact of aerosols in the UTLS region is analyzed by evaluating the differences between simulations with (CTRL and without aerosol (HAM-off loading. The transport of anthropogenic aerosols in the UTLS increases cloud ice, water vapour and temperature, indicating that aerosols play an important role in enhancement of cloud ice in the Upper-Troposphere (UT. Aerosol induced circulation changes include a weakening of the main branch of the Hadley circulation and increased vertical transport around the southern flank of the Himalayas and reduction in monsoon precipitation over the India region.

  18. The effect of Arabian Sea optical properties on SST biases and the South Asian summer monsoon in a coupled GCM

    Energy Technology Data Exchange (ETDEWEB)

    Turner, A.G.; Joshi, M.; Robertson, E.S.; Woolnough, S.J. [University of Reading, NCAS-Climate, Walker Institute for Climate System Research, Department of Meteorology, Reading (United Kingdom)

    2012-08-15

    This study examines the effect of seasonally varying chlorophyll on the climate of the Arabian Sea and South Asian monsoon. The effect of such seasonality on the radiative properties of the upper ocean is often a missing process in coupled general circulation models and its large amplitude in the region makes it a pertinent choice for study to determine any impact on systematic biases in the mean and seasonality of the Arabian Sea. In this study we examine the effects of incorporating a seasonal cycle in chlorophyll due to phytoplankton blooms in the UK Met Office coupled atmosphere-ocean GCM HadCM3. This is achieved by performing experiments in which the optical properties of water in the Arabian Sea - a key signal of the semi-annual cycle of phytoplankton blooms in the region - are calculated from a chlorophyll climatology derived from Sea-viewing Wide Field-of-View Sensor (SeaWiFS) data. The SeaWiFS chlorophyll is prescribed in annual mean and seasonally-varying experiments. In response to the chlorophyll bloom in late spring, biases in mixed layer depth are reduced by up to 50% and the surface is warmed, leading to increases in monsoon rainfall during the onset period. However when the monsoons are fully established in boreal winter and summer and there are strong surface winds and a deep mixed layer, biases in the mixed layer depth are reduced but the surface undergoes cooling. The seasonality of the response of SST to chlorophyll is found to depend on the relative depth of the mixed layer to that of the anomalous penetration depth of solar fluxes. Thus the inclusion of the effects of chlorophyll on radiative properties of the upper ocean acts to reduce biases in mixed layer depth and increase seasonality in SST. (orig.)

  19. EVOLUTION OF TROPOSPHERIC TEMPERATURE FIELDS AND CORRESPONDING THERMAL MECHANISMS BEFORE/AFTER ONSET PERIODS OF ASIAN SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The evolution of the tropospheric temperature fields over Indian and South China Sea monsoon areas and their thermal mechanisms are compared and analyzed during the period from March to June, 1996. The results show that the onsets of the Indian and South China Sea summer monsoons are closely associated with the seasonal warming in the troposphere over the zonal belt of 10° N ~ 30° N in these areas, which leads to the inversion of meridional temperature gradient. During the pre-onset period, the warming over the South China Sea monsoon region is mainly due to the warm horizontal advection and diabatic (latent) heating processes. Meanwhile, the warming is suppressed by the vertical adiabatic process (cooling). In spring over the Indian monsoon region, the significant adiabatic heating due to the subsidence motion, which compensates the cooling due to the strong cold advection and diabatic cooling processes, results in a larger warming rate than over the South China Sea monsoon region. However, the meridional temperature gradient over the Indian monsoon region is so large during the late winter and early spring that it takes longer time to warm the troposphere to have the reversion of meridional temperature gradient than it does over the South China Sea monsoon region. It results in the phenomenon that the South China Sea summer monsoon generally breaks out earlier than the Indian summer monsoon.

  20. 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.

  1. Tracing the boundary layer sources of carbon monoxide in the Asian summer monsoon anticyclone using WRF-Chem

    Science.gov (United States)

    Yan, Renchang; Bian, Jianchun

    2015-07-01

    The Asian summer monsoon (ASM) anticyclone is a dominant feature of the circulation in the upper troposphere-lower stratosphere (UTLS) during boreal summer, which is found to have persistent maxima in carbon monoxide (CO). This enhancement is due to the upward transport of air with high CO from the planetary boundary layer (PBL), and confinement within the anticyclonic circulation. With rapid urbanization and industrialization, CO surface emissions are relatively high in the ASM region, especially in India and East China. To reveal the transport pathway of CO surface emissions over these two regions, and investigate the contribution of these to the CO distribution within the ASM anticyclone, a source sensitivity experiment was performed using the Weather Research and Forecasting (WRF) with chemistry model (WRF-Chem). According to the experiment results, the CO within the ASM anticyclone mostly comes from India, while the contribution from East China is insignificant. The result ismainly caused by the different transportation mechanisms. In India, CO transportation is primarily affected by convection. The surface air with high CO over India is directly transported to the upper troposphere, and then confined within the ASM anticyclone, leading to a maximum value in the UTLS region. The CO transportation over East China is affected by deep convection and large-scale circulation, resulting mainly in transportation to Korea, Japan, and the North Pacific Ocean, with little upward transport to the anticyclone, leading to a high CO value at 215 hPa over these regions.

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

    Institute of Scientific and Technical Information of China (English)

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

    2011-01-01

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

  3. Composition of the Asian summer monsoon anticyclone: Climatology and variability from 10 years of Aura Microwave Limb Sounder measurements

    Science.gov (United States)

    Santee, Michelle; Manney, Gloria; Livesey, Nathaniel; Neu, Jessica; Schwartz, Michael; Read, William

    2016-04-01

    Satellite measurements are invaluable for investigating the composition of the upper troposphere / lower stratosphere (UTLS) in the region of the Asian summer monsoon anticyclone, which has been sparsely sampled by other means. The Microwave Limb Sounder (MLS), launched as part of NASA's Aura mission in July 2004, makes simultaneous co-located measurements of trace gases and cloud ice water content (IWC, a proxy for deep convection) in the UTLS on a daily basis. Here we exploit the dense spatial and temporal coverage, long-term data record, and extensive measurement suite of Aura MLS to characterize the climatological composition of the ASM anticyclone and quantify its considerable spatial, seasonal, and interannual variability. We relate the observed trace gas behavior to various meteorological quantities, such as the size and strength of the ASM anticyclone, the extent and intensity of deep convection, and variations in the tropopause and the upper tropospheric jets in that region. Multiple species of both tropospheric and stratospheric origin are examined to help assess whether the observed variability arises from variations in transport processes or changes in the strength or location of surface emissions.

  4. Decadal shifts of East Asian summer monsoon in a climate model free of explicit GHGs and aerosols

    Science.gov (United States)

    Lin, Renping; Zhu, Jiang; Zheng, Fei

    2016-12-01

    The East Asian summer monsoon (EASM) experienced decadal transitions over the past few decades, and the associated "wetter-South-drier-North" shifts in rainfall patterns in China significantly affected the social and economic development in China. Two viewpoints stand out to explain these decadal shifts, regarding the shifts either a result of internal variability of climate system or that of external forcings (e.g. greenhouse gases (GHGs) and anthropogenic aerosols). However, most climate models, for example, the Atmospheric Model Intercomparison Project (AMIP)-type simulations and the Coupled Model Intercomparison Project (CMIP)-type simulations, fail to simulate the variation patterns, leaving the mechanisms responsible for these shifts still open to dispute. In this study, we conducted a successful simulation of these decadal transitions in a coupled model where we applied ocean data assimilation in the model free of explicit aerosols and GHGs forcing. The associated decadal shifts of the three-dimensional spatial structure in the 1990s, including the eastward retreat, the northward shift of the western Pacific subtropical high (WPSH), and the south-cool-north-warm pattern of the upper-level tropospheric temperature, were all well captured. Our simulation supports the argument that the variations of the oceanic fields are the dominant factor responsible for the EASM decadal transitions.

  5. The sharp decline of East Asian summer monsoon at mid-Holocene indicated by the lake-wetland transition in the Sanjiang Plain, northeastern China

    Directory of Open Access Journals (Sweden)

    Z. Q. Zhang

    2014-12-01

    Full Text Available The timing of the waxing and wining of the East Asian summer monsoon during the Holocene is still under debate. In present study, we present the high-resolution grain-size and LOI records from a well-dated mud/peat profile to reveal the lake-wetland transition in the Sanjiang Plain and discuss its significance to Holocene monsoon evolutions. The results show that the shallow-water lakes have developed in low-lying areas of the plain before 4600 yr BP, corresponding to the Holocene monsoon maximum. Thereafter, the wetlands began to initiate with the extinction of the paleolakes, marking a lake-shrinking stage with the relative dry climate. Considering the prevalent monsoon climate in the Sanjiang Plain, we suggest the lake-wetland transition at 4600 yr BP indicate a sharp decline of the summer monsoon rather than the basin infilling process. Such a remarkable monsoon weakening event has been widely documented in northern China, and we associated it with the ocean–atmosphere interacting processes in low-latitude regions.

  6. An interdecadal change in the relationship between the western North Pacific Ocean and the East Asian summer monsoon

    Science.gov (United States)

    Yu, Peilong; Zhang, Lifeng; Zhong, Quanjia

    2016-09-01

    This study reveals that the relationship between the western North Pacific Ocean (WNPO; 0-55°N, 100-165°E) and the East Asian summer monsoon (EASM) experiences a well-defined interdecadal change in the late 1980s and early 1990s. The EASM-related WNPO sea surface temperature anomaly (SSTA) pattern changes from the dipole pattern [WNPO dipole (WNPOD)] that develops over the period between 1968 and 1987 (P1) to a tripole pattern [WNPO tripole (WNPOT)] between 1991 and 2010 (P2). The positive (negative) phase of the WNPOD is characterized by warm (cold) SSTAs in the Japan Sea and Kuroshio-Oyashio Extension region, and cold (warm) SSTAs in the subtropical WNPO, whereas the positive (negative) phase of the WNPOT shows warming (cooling) in the Kuroshio Extension region (KER), and cooling (warming) in the south of Kamchatka Peninsula (SKP) and Philippine Sea (PS). During P1 (P2), the WNPOD (WNPOT) can be regarded as the first (second) leading mode of summer WNPO SST variability, and its positive phase is associated with a weakened WNPO subtropical high and thereby the deficient summer rainfall in the Yangtze River valley, together with a strong EASM, and vice versa. The change in the WNPO-EASM relationship may be caused by interdecadal changes in the relationship of the equatorial central Pacific (ECP) with the WNPO and EASM, and an increase in summer KER SST variability. During P2, because the ECP warming-induced cyclonic anomalies move northwestwards and intensify, summertime ECP warming is able to generate a strong EASM and significant cooling over the two poles of the WNPOT (SKP and PS). These strengthened impacts of the ECP on the WNPOT and EASM contribute to the strengthened WNPOT-EASM relationship during P2. In addition, summer KER SST variability increases between 1991 and 2010, and this may have enhanced the impact of the KER on the EASM during P2. These two factors probably cause the EASM-related WNPO SSTA pattern to change from the WNPOD in P1 to the WNPOT in

  7. Dispersion of the Nabro volcanic plume and its relation to the Asian summer monsoon

    OpenAIRE

    Fairlie, T. D.; Vernier, J.-P.; M. Natarajan; Bedka, K M

    2014-01-01

    We use nighttime measurements from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, together with a Lagrangian trajectory model, to study the initial dispersion of volcanic aerosol from the eruption of Mt. Nabro (Ethiopia/Eritrea) in June 2011. The Nabro eruption reached the upper troposphere and lower stratosphere (UTLS) directly, and the plume was initially entrained by the flow surrounding the Asian anticyclone, which prevails in ...

  8. Droughts in the East Asian summer monsoon margin during the last 6 kyrs: Link to the North Atlantic cooling events

    Science.gov (United States)

    Fan, Jiawei; Xiao, Jule; Wen, Ruilin; Zhang, Shengrui; Wang, Xu; Cui, Linlin; Li, He; Xue, Dingshuai; Yamagata, Hideki

    2016-11-01

    Teleconnections to the high latitudes, forcing by the tropical oceans and solar variability have all been suggested as dominant factors in the sub-millennial global climate changes, yet there is little consensus as to the relative importance of these factors for the East Asian summer monsoon (EASM) variability. This study presents the results of high-resolution analyses of Ca and Mg concentrations, Mg/Ca ratio, δ18O and δ13C values of endogenic calcites from a sediment core from Dali Lake in the EASM margin, in order to investigate the sub-millennial EASM variability and its possible driving forces during the last 6 kyrs. Increases in these chemical proxy data were interpreted as drought events in the region due to the intensive evaporation losses overwhelming the water input to the lake. The chemical proxy data in this study combined with multi-proxy indicators including grain size component and total organic carbon concentrations from the same sediment core imply that declines in the EASM intensity may have played a dominant role in triggering the drought events during the last 6 kyrs. The results indicate that the EASM intensity significantly declined at the intervals of 5.8-4.75, 3.2-2.8, 1.65-1.15 and 0.65-0.2 kyrs BP. Large declines in the EASM intensity during the last 6 kyrs correspond in time to occurrences of ice-rafted debris in the North Atlantic, indicating that millennial-to-centennial scale changes in the EASM intensity were mainly controlled by climatic processes occurring in the northern high latitudes. These data imply that persistent global warming may be favorable for the strengthening of the EASM circulation and for the transportation of more rainfall to the semi-arid regions of northern China on sub-millennial scales.

  9. 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

    2016-09-01

    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.

  10. 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

  11. 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.

  12. Orbital forcing of the East Asian summer monsoon based on quantitative paleorainfall records from Chinese Loess using 10Be

    Science.gov (United States)

    Beck, W.; White, L.; Cheng, L.; Wu, Z.; zhou, W.; Kong, X.

    2013-12-01

    Here we outline a method for deriving quantitative records of paleoprecipitation using meteoric 10Be flux as recorded in Quaternary loess sediments, and apply this method to derive a ~500ka rainfall record from Chinese loess. The method involves measuring loess 10Be concentration by AMS, then applying corrections for radioactive decay, recycled 10Be in reaerosolized dust, and for variations in geomagnetic field to correct for atmospheric 10Be production rate variations. 10Be flux is calculated by multiplying the corrected 10Be concentrations with loess accumulation rate, where the later is derived from a (non-orbitally tuned) timescale determined from correlating variations in loess magnetic susceptibility with U/Th dated Chinese speleothem δ18O records. The dependence of 10Be flux on rainfall rate is determined using modern observations of 7Be flux in rainfall, and atmospheric 10Be/7Be cosmogenic nuclide production ratios. Modern rainfall on the Chinese Loess Plateau has been shown to be primarily a function of East Asian Summer Monsoon (EASM) intensity. Our 10Be rainfall proxy shows that glacial to peak interglacial rainfall rates in this region have varied by about a factor of two over the last 0.5 Ma. Our results suggests EASM intensity during interglacials MIS11, MIS 9c and MIS13 were all comparable (~850 mm/yr), but slightly less (by ~8%) than for MIS1, and about 15% less than for MIS5e, which is similar to the high latitude ice volume pattern of response except for MIS11. We note that the 10Be rainfall record of MIS13 differs from typical Chinese loess magnetic susceptibility records that suggest MIS13 was the strongest EASM of the last 6 interglacials. Our record instead indicates a relative subdued MIS13 EASM, more consistent with the Antarctic EPICA ice core deuterium or marine δ18O records. We correlate our results with orbital forced solar insolation variations at high and low latitudes as well as with interhemispheric insolation gradients. We find

  13. The influence of dynamic vegetation on the present-day simulation and future projections of the South Asian summer monsoon in the HadGEM2 family

    Science.gov (United States)

    Martin, G. M.; Levine, R. C.

    2012-11-01

    Various studies have shown the importance of Earth System feedbacks in the climate system and the necessity of including these in models used for making climate change projections. The HadGEM2 family of Met Office Unified Model configurations combines model components which facilitate the representation of many different processes within the climate system, including atmosphere, ocean and sea ice, and Earth System components including the terrestrial and oceanic carbon cycle and tropospheric chemistry. We examine the climatology of the Asian summer monsoon in present-day simulations and in idealised climate change experiments. Members of the HadGEM2 family are used, with a common physical framework (one of which includes tropospheric chemistry and an interactive terrestrial and oceanic carbon cycle), to investigate whether such components affect the way in which the monsoon changes. We focus particularly on the role of interactive vegetation in the simulations from these model configurations. Using an atmosphere-only HadGEM2 configuration, we investigate how the changes in land cover which result from the interaction between the dynamic vegetation and the model systematic rainfall biases affect the Asian summer monsoon, both in the present-day and in future climate projections. We demonstrate that the response of the dynamic vegetation to biases in regional climate, such as lack of rainfall over tropical dust-producing regions, can affect both the present-day simulation and the response to climate change forcing scenarios.

  14. 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

  15. Holocene moisture and East Asian summer monsoon evolution in the northeastern Tibetan Plateau recorded by Lake Qinghai and its environs: A review of conflicting proxies

    Science.gov (United States)

    Chen, Fahu; Wu, Duo; Chen, Jianhui; Zhou, Aifeng; Yu, Junqing; Shen, Ji; Wang, Sumin; Huang, Xiaozhong

    2016-12-01

    Climatic and environmental changes in the northeastern Tibetan Plateau are controlled by the Asian summer monsoon (ASM) and the westerlies, two key circulation components of the global climate system which directly affect a large human population and associated ecosystems in eastern Asia. During the past few decades, a series of Holocene palaeoclimatic records have been obtained from sediment cores from Lake Qinghai and from various other geological archives in the surrounding area of the northeastern Tibetan Plateau. However, because of uncertainties regarding the sediment chronologies and the climatic significance of the proxies used, the nature of Holocene climatic changes in the region remains unclear and even controversial. Here we review all major classes of the published data from drilled cores from Lake Qinghai, as well as other evidence from lakes and aeolian deposits from surrounding areas, in order to reconstruct changes in moisture patterns and possible summer monsoon evolution in the area during the Holocene. Combining the results of moisture and precipitation proxies such as vegetation history, pollen-based precipitation reconstruction, aeolian activity, lake water depth/lake level changes, salinity and sediment redness, we conclude that moisture and precipitation began to increase in the early Holocene, reached their maximum during the middle Holocene, and decreased during the late Holocene - similar to the pattern of the East Asian summer monsoon (EASM) in northern China. It is clear that the region experienced a relatively dry climate and weak EASM during the early Holocene, as indicated by relatively low tree pollen percentages and fluctuating pollen concentrations; generally low lake levels of Lake Qinghai and the adjacent Lake Hurleg and Lake Toson in the Qaidam Basin; and widely distributed aeolian sand deposition in the Lake Qinghai Basin and the nearby Gonghe Basin to the south, and in the eastern Qaidam Basin to the west. We argue that the

  16. Natural and human-induced changes in summer climate over the East Asian monsoon region in the last half century: A review

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Ren-He

    2015-01-01

    In the last half century,a significant warming trend occurred in summer over eastern China in the East Asian monsoon region.However,there were no consistent trends with respect to the intensity of the East Asian summer monsoon(EASM) or the amount of summer rainfall averaged over eastern China.Both of the EASM and summer rainfall exhibited clear decadal variations.Obvious decadal shifts of EASM occurred around the mid- and late 1970 s,the late 1980 s and the early 1990 s,and the late 1990 s and early 2000 s,respectively.Summer rainfall over eastern China exhibited a change in spatial distribution in the decadal timescale,in response to the decadal shifts of EASM.From the mid- and late 1970 s to the late 1980 s and the early 1990 s,there was a meridional tri-polar rainfall distribution anomaly with more rainfall over the Yangtze River valley and less rainfall in North and South China; but in the period from the early 1990 s to the late 1990 s and the early 2000 s the tri-polar distribution changed to a dipolar one,with more rainfall appearing over southern China south to the Yangtze River valley and less rainfall in North China.However,from the early 2000 s to the late 2000 s,the Yangtze River valley received less rainfall.The decadal changes in EASM and summer rainfall over eastern China in the last half century are closely related to natural internal forcing factors such as Eurasian snow cover,Arctic sea ice,sea surface temperatures in tropical Pacific and Indian Ocean,oceaneatmospheric coupled systems of the Pacific Decadal Oscillation(PDO) and AsianePacific Oscillation(APO),and uneven thermal forcing over the Asian continent.Up to now,the roles of anthropogenic factors,such as greenhouse gases,aerosols,and land usage/cover changes,on existing decadal variations of EASM and summer rainfall in this region remain uncertain.

  17. Impact of ice sheet induced North Atlantic oscillation on East Asian summer monsoon during an interglacial 500,000 years ago

    Science.gov (United States)

    Sundaram, S.; Yin, Q. Z.; Berger, A.; Muri, H.

    2012-09-01

    Marine Isotope Stage (MIS) 13, an interglacial about 500,000 years ago, is unique due to an exceptionally strong East Asia summer monsoon (EASM) occurring in a relatively cool climate with low greenhouse gas concentrations (GHG). This paper attempts to find one of the possible mechanisms for this seeming paradox. Simulations with an Earth System model LOVECLIM show that the presence of ice sheets over North America and Eurasia during MIS-13 induces a positive phase of the winter North Atlantic Oscillation (NAO) like feature. The ocean having a longer memory than the atmosphere, the oceanic anomalies associated with NAO persists until summer. The signals of summer NAO are transmitted to East Asia to reinforce the monsoon there through the stationary waves excited at the Asian Jet entrance. The geopotential height shows clearly a mid-latitude wave train with positive anomalies over the eastern Mediterranean/Caspian Sea and the Okhotsk Sea and a negative anomaly over Lake Baikal. This reinforces the effect of the high-latitude wave train induced independently by the Eurasian ice sheet topography as shown in previous study. These features reinforce the Meiyu front and enhance the precipitation over East Asia. The results obtained from LOVECLIM are further confirmed by an atmospheric general circulation model, ARPEGE.

  18. An Assessment on the Performance of IPCC AR4 Climate Models in Simulating Interdecadal Variations of the East Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    SUN Ying; DING Yihui

    2008-01-01

    Observations from several data centers together with a categorization method are used to evaluate the IPCC AR4 (Intergovernmental Panel on Climate Change, the Fourth Assessment Report) climate models' performance in simulating the interdecadal variations of summer precipitation and monsoon circulation in East Asia. Out of 19 models under examination, 9 models can relatively well reproduce the 1979-1999 mean June-July-August (JJA) precipitation in East Asia, but only 3 models (Category-1 models) can capture the interdecadal variation of precipitation in East Asia. These 3 models are: GFDL-CM2.0, MIROC3.2 (hires), and MIROC3.2 (medres), among which the GFDL-CM2.0 gives the best performance. The reason for the poor performance of most models in simulating the East Asian summer monsoon interdecadal variation lies in that the key dynamic and thermal-dynamic mechanisms behind the East Asian monsoon change are missed by the models, e.g., the large-scale tropospheric cooling and drying over East Asia. In contrast, the Category-1 models relatively well reproduce the variations in vertical velocity and water vapor over East Asia and thus show a better agreement with observations in simulating the pattern of "wet south and dry north" in China in the past 20 years.It is assessed that a single model's performance in simulating a particular variable has great impacts on the ensemble results. More realistic outputs can be obtained when the multi-model ensemble is carried out using a suite of well-performing models for a specific variable, rather than using all available models. This indicates that although a multi-model ensemble is in general better than a single model, the best ensemble mean cannot be achieved without looking into each member model's performance.

  19. East Asian monsoon climate simulated in the PlioMIP

    Directory of Open Access Journals (Sweden)

    R. Zhang

    2013-02-01

    Full Text Available Based on the simulations with fifteen 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 wind (EASW largely strengthens in monsoon China, and the East Asian winter wind (EAWW strengthens in south monsoon China but slightly weakens in north monsoon China in mid-Pliocene. The MMM of all models also illustrates a warmer and wetter mid-Pliocene climate in China. The simulated weakened mid-Pliocene EAWW in north monsoon China and intensified EASW in monsoon China agree well with geological reconstructions. However, the model-model discrepancy in simulating mid-Pliocene East Asian monsoon climate, in particular EAWW, should be further addressed in the future work of PlioMIP.

  20. 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.

  1. An exceptionally strensthened East Asian summer monsoon event between 19.9 and 1 7.1 ka BP recorded in a Hulu stalagmite

    Institute of Scientific and Technical Information of China (English)

    WU JiangYing; WANG YongJin; CHENG Hai; L.R.EDWARDS

    2009-01-01

    A stalagmite-based isotope record (No.H82)from Nanjing Hulu Cave,spanning from 16.5 to 10.3 ka BP,provided strong evidence for a coherence relation between the East Asian summer monsoon (EASM) and the North Atlantic climates on millennial time scales.Here we extend the high-resolution δ18O time series back to 22.1 ka BP with additional 7 230 Th dates and 573 stable isotope measurements on the lower part of that sample.The new record with a decadal resolution,piecing together with the previous data,provides a detailed,complete Last Glacial Maximum (LGM)/deglacial history of the EASM.Two centennial-scale weak monsoon events are detected within the analogue H1 event,and can be correlated to corresponding Greenland temperature shifts.This suggests a rapid re-organization of atmospheric and oceanic circulations during the ice-rafted debris (IRD) event in North Atlantic.A strengthened EASM event spanning from 19.9 to 17.1 ka BP,firstly reported here,reaches on average a half of the monsoon intensity of B(Φ)iling warming with its peak close to the full level.Taking all available evidence from continental and oceanic sediments into consideration,we suggest that a forcing mechanism behind the event would be a positive feedback of the tropical Pacific Super-ENSO cycles in response to precessional changes in solar irradiation.

  2. An exceptionally strengthened East Asian summer monsoon event between 19.9 and 17.1 ka BP recorded in a Hulu stalagmite

    Institute of Scientific and Technical Information of China (English)

    L.; R.; EDWARDS

    2009-01-01

    A stalagmite-based isotope record (No. H82) from Nanjing Hulu Cave, spanning from 16.5 to 10.3 ka BP, provided strong evidence for a coherence relation between the East Asian summer monsoon (EASM) and the North Atlantic climates on millennial time scales. Here we extend the high-resolution δ 18O time series back to 22.1 ka BP with additional 7 230Th dates and 573 stable isotope measurements on the lower part of that sample. The new record with a decadal resolution, piecing together with the previous data, provides a detailed, complete Last Glacial Maximum (LGM)/deglacial history of the EASM. Two centennial-scale weak monsoon events are detected within the analogue H1 event, and can be corre- lated to corresponding Greenland temperature shifts. This suggests a rapid re-organization of atmos- pheric and oceanic circulations during the ice-rafted debris (IRD) event in North Atlantic. A strength- ened EASM event spanning from 19.9 to 17.1 ka BP, firstly reported here, reaches on average a half of the monsoon intensity of B?lling warming with its peak close to the full level. Taking all available evi- dence from continental and oceanic sediments into consideration, we suggest that a forcing mecha- nism behind the event would be a positive feedback of the tropical Pacific Super-ENSO cycles in re- sponse to precessional changes in solar irradiation.

  3. 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).

  4. Warm Indian Ocean, Weak Asian Monsoon

    Science.gov (United States)

    Koll Roxy, Mathew; Ritika, Kapoor; Terray, Pascal; Murtugudde, Raghu; Ashok, Karumuri; Nath Goswami, Buphendra

    2015-04-01

    There are large uncertainties looming over the status and fate of the South Asian monsoon in a changing climate. Observations and climate models have suggested that anthropogenic warming in the past century has increased the moisture availability and the land-sea thermal contrast in the tropics, favoring an increase in monsoon rainfall. In contrast, we notice that South Asian subcontinent experienced a relatively subdued warming during this period. At the same time, the tropical Indian Ocean experienced a nearly monotonic warming, at a rate faster than the other tropical oceans. Using long-term observations and coupled model experiments, we suggest that the enhanced Indian Ocean warming along with the suppressed warming of the subcontinent weaken the land-sea thermal contrast throughout the troposphere, dampen the monsoon Hadley circulation, and reduce the rainfall over South Asia. As a result, the summer monsoon rainfall during 1901-2012 shows a significant weakening trend over South Asia, extending from Pakistan through central India to Bangladesh.

  5. A Diagnostic Study of Heavy Rainfall in Karachi Due to Merging of a Mesoscale Low and a Diffused Tropical Depression during South Asian Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    Ghulam RASUL; Qamar-uz-Zaman CHAUDHRY; ZHAO Sixiong; ZENG Qingcun; QI Linlin; ZHANG Gaoying

    2005-01-01

    This paper presents the results of a diagnostic study of a typical case of very heavy rainfall during the South Asian summer monsoon when a mesoscale low in a desert climate merged with a diffused tropical depression. The former low was located over Pakistan's desert region and the latter depression originated over the Bay of Bengal. Surface and NCEP reanalysis data supported by satellite and radar images were incorporated in the diagnosis. The relationship between the heavy precipitation process and large-scale circulations such as monsoon trough, subtropical high, westerly jet, low level jet and water vapor transport were investigated to further understand the mechanism of this peculiar interaction. It was found that: (1)the mesoscale low developed as a result of cold air advection aloft from northern latitudes and strong convection over the region of humidity convergence on 24 July 2003 over the Indian Rajistan area. (2) On the same day, a low that formed over the Bay of Bengal was transformed into a monsoon depression and moved westward to the mesoscale low which existed over southwest India and the adjoining southeastern parts of Pakistan. (3) Initially, the mesoscale low received moisture supply from both the Bay of Bengal as well as the Arabian Sea, whereas the Bay of Bengal maintained the continuous supply of moisture to the monsoon depression. (4) After the depression crossed central India, the Bay's moisture supply was cut off and the Arabian Sea became the only source of moisture to both the closely located systems. On 27July, both of the systems merged together and the merger resulted in a heavy downpour in the Karachi metropolitan and in its surroundings. (5) With the intensification as well as the southeastward extension of the subtropical high and the shift of the monsoon trough axis from southwest-west to northeast-east,the monsoon depression moved southwestward. In this situation, there existed a very favourable condition for a merger of the two

  6. Characterization of Asian Summer Monsoon Transport from the Boundary Layer to Lower Stratosphere: Recent Progress from Model Studies and New Observations

    Science.gov (United States)

    Pan, Laura; Honomichl, Shawn; Kinnison, Doug; Bian, Jianchun

    2016-04-01

    The Asian Summer Monsoon (ASM) system is a significant driver for transport between the boundary layer and the upper troposphere/lower stratosphere (UT/LS). Satellite observations, although provide clear evidence of its global impact on seasonal scales, are unable to resolve the details of the transport process. This work summarizes recent progress in characterizing the transport behavior using global chemistry-climate models (CCMs) and in situ observations. NCAR Whole Atmosphere Community Climate Model run in specified dynamics mode (WACCM-SD) is used to characterize the sub-seasonal scale dynamical variability of the monsoon system and the impact on transport of boundary layer tracers into lower stratosphere. The analysis focuses on three elements of the transport: uplifting from the boundary layer, transport to the regions outside of ASM at the UTLS level, and transport into stratosphere in association with the Brewer-Dobson circulation. In situ measurements from six years of sounding studies over the Tibetan plateau are analyzed to complement the model analyses. The profiles of ozone, water vapor, cirrus clouds, together with temperature from the soundings provide important insight into the ASM transport behaviors.

  7. 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.

  8. Modeling sensitivity study of the possible impact of snow and glaciers developing over Tibetan Plateau on Holocene African-Asian summer monsoon climate

    Directory of Open Access Journals (Sweden)

    L. Jin

    2008-12-01

    Full Text Available The impacts of various scenarios of snow and glaciers developing over the Tibetan Plateau on climate change in Afro-Asian monsoon region and other regions during the Holocene (9 kyr BP–0 kyr BP are studied by using the coupled climate model of intermediate complexity, CLIMBER-2. The simulations show that the imposed snow and glaciers over the Tibetan Plateau in the mid-Holocene induce global summer temperature decreases, especially in the northern parts of Europe, Asia, and North America. At the same time, with the imposed snow and glaciers, summer precipitation decreases strongly in North Africa and South Asia as well as northeastern China, while it increases in Southeast Asia and the Mediterranean. For the whole period of Holocene (9 kyr BP–0 kyr BP, the response of vegetation cover to the imposed snow and glaciers cover over the Tibetan Plateau is not synchronous in South Asia and in North Africa, showing an earlier and a more rapid decrease in vegetation cover in North Africa from 9 to 6 kyr BP while it has only minor influence on that in South Asia until 5 kyr BP. Imposed gradually increased snow and glacier cover over the Tibetan Plateau causes temperature increases in South Asia and it decreases in North Africa and Southeast Asia during 6 kyr BP to 0 kyr BP. The precipitation decreases rapidly in North Africa and South Asia while it decreases slowly or unchanged during 6 kyr BP to 0 kyr BP with imposed snow and glacier cover over the Tibetan Plateau. The different scenarios of snow and glacier developing over the Tibetan Plateau would result in differences in variation of temperature, precipitation and vegetation cover in North Africa, South Asia and Southeast Asia. The model results show that the response of climate change in African-Asian monsoon region to snow and glacier cover over the Tibetan Plateau is in the way that the snow and glaciers amplify the effect of vegetation feedback and, hence, further amplify orbital forcing.

  9. An East Asian Monsoon in the Mid-Pliocene

    Institute of Scientific and Technical Information of China (English)

    YAN Qing; ZHANG Zhong-Shi; GAO Yong-Qi

    2012-01-01

    In this study, the authors simulate the East Asian climate changes in the mid-Pliocene (~3.3 to 3.0 Ma BP) with the Community Atmosphere Model version 3.1 (CAM3.1) and compare the simulated East Asian monsoon with paleoclimate data. The simulations show an obvious warming pattern in East Asia in the mid-Pliocene compared with the pre-industrial climate, with surface air temperature increasing by 0.5 4.0°C. In the warm mid-Pliocene simulation, the East Asian Summer Monsoon (EASM) becomes stronger, while the East Asian Winter Monsoon (EAWM) is similar relative to the pre-industrial climate. Compared with the paleoclimate data, our simulations depict the intensified EASM well but cannot reproduce the weakened EAWM. This model-data discrepancy may be attributed to the uncertainty in the reconstructed mid-Pliocene sea surface temperature.

  10. 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.

  11. 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.

  12. Climatological perspectives of air transport from atmospheric boundary layer to tropopause layer over Asian monsoon regions during boreal summer inferred from Lagrangian approach

    Directory of Open Access Journals (Sweden)

    B. Chen

    2012-02-01

    Full Text Available The Asian Summer Monsoon (ASM region has been recognized as a key region that plays a vital role in troposphere-to-stratosphere transport (TST, which can significantly impact the budget of global atmospheric constituents and climate change. However, the details of transport from the boundary layer (BL to tropopause layer (TL over this region, particularly from a climatological perspective, remains an issue of uncertainty. In this study, we present the climatological properties of BL-to-TL transport over the ASM region during boreal summer season (June-July-August from 2001 to 2009. A comprehensive tracking analysis is conducted based on a large ensemble of TST-trajectories departing from the atmospheric BL and arriving at TL. Driven by the winds fields from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research Global Forecast System, all TST-trajectories are selected from the high resolution datasets generated by the Lagrangian particle transport model FLEXPART using a domain-filling technique. Three key atmospheric boundary layer sources for BL-to-TL transport are identified with their contributions: (i 38% from the region between tropical Western Pacific region and South China Seas (WP, (ii 21% from Bay of Bengal and South Asian subcontinent (BOB, and (iii 12% from the Tibetan Plateau, which includes the South Slope of the Himalayas (TIB. Controlled by the different patterns of atmospheric circulation, the air masses originating from these three source regions are transported along the different tracks into the TL. The spatial distributions of these three source regions remain similarly from year to year. The timescales of transport from BL to TL by the large-scale ascents range from 1 to 7 weeks, contributing up to 60–70% of the overall TST; whereas the transport governed by the deep convection overshooting becomes faster, with timescales of 1–2 days and contributions of 20–30%. These

  13. Climatological perspectives of air transport from atmospheric boundary layer to tropopause layer over Asian monsoon regions during boreal summer inferred from Lagrangian approach

    Directory of Open Access Journals (Sweden)

    B. Chen

    2012-07-01

    Full Text Available The Asian Summer Monsoon (ASM region has been recognized as a key region that plays a vital role in troposphere-to-stratosphere transport (TST, which can significant impact the budget of global atmospheric constituents and climate change. However, the details of transport from the boundary layer (BL to tropopause layer (TL over these regions, particularly from a climatological perspective, remain an issue of uncertainty. In this study, we present the climatological properties of BL-to-TL transport over the ASM region during boreal summer season (June-July-August from 2001 to 2009. A comprehensive tracking analysis is conducted based on a large ensemble of TST-trajectories departing from the atmospheric BL and arriving at TL. Driven by the winds fields from NCEP/NCAR Global Forecast System, all the TST-trajectories are selected from the high resolution datasets generated by the Lagrangian particle transport model FLEXPART using a domain-filling technique. Three key atmospheric boundary layer sources for BL-to-TL transport are identified with their contributions: (i 38% from the region between tropical Western Pacific region and South China Seas (WP (ii 21% from Bay of Bengal and South Asian subcontinent (BOB, and (iii 12% from the Tibetan Plateau, which includes the South Slope of the Himalayas (TIB. Controlled by the different patterns of atmospheric circulation, the air masses originated from these three source regions are transported along the different tracks into the TL. The spatial distributions of three source regions keep similarly from year to year. The timescales of transport from BL to TL by the large-scale ascents r-range from 1 to 7 weeks contributing up to 60–70% of the overall TST, whereas the transport governed by the deep convection overshooting become faster on a timescales of 1–2 days with the contributions of 20–30%. These results provide clear policy implications for the control of very short lived substances

  14. Understanding the Asian summer monsoon response to greenhouse warming: the relative roles of direct radiative forcing and sea surface temperature change

    Science.gov (United States)

    Li, Xiaoqiong; Ting, Mingfang

    2016-12-01

    Future hydroclimate projections from state-of-the-art climate models show large uncertainty and model spread, particularly in the tropics and over the monsoon regions. The precipitation and circulation responses to rising greenhouse gases involve a fast component associated with direct radiative forcing and a slow component associated with sea surface temperature (SST) warming; the relative importance of the two may contribute to model discrepancies. In this study, regional hydroclimate responses to greenhouse warming are assessed using output from coupled general circulation models in the Coupled Model Intercomparison Project-Phase 5 (CMIP5) and idealized atmospheric general circulation model experiments from the Atmosphere Model Intercomparison Project. The thermodynamic and dynamic mechanisms causing the rainfall changes are examined using moisture budget analysis. Results show that direct radiative forcing and SST change exert significantly different responses both over land and ocean. For most part of the Asian monsoon region, the summertime rainfall changes are dominated by the direct CO2 radiative effect through enhanced monsoon circulation. The response to SST warming shows a larger model spread compared to direct radiative forcing, possibly due to the cancellation between the thermodynamical and dynamical components. While the thermodynamical response of the Asian monsoon is robust across the models, there is a lack of consensus for the dynamical response among the models and weak multi-model mean responses in the CMIP5 ensemble, which may be related to the multiple physical processes evolving on different time scales.

  15. 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.

  16. ON THE PROCESS OF SUMMER MONSOON ONSET OVER EAST ASIA

    Institute of Scientific and Technical Information of China (English)

    陈隆勋; 李薇; 赵平; 陶诗言

    2001-01-01

    Using daily observational rainfall data covered 194 stations of China from 1961 to 1995 and NCEP model analyzed pentad precipitation data of global grid point from 1979 to 1997, the distribution of onset date of rainy season over Asian area from spring to summer is studied in this paper. The analyzed results show that there exist two stages of rainy season onset over East Asian region from spring to summer rainy season onset accompanying subtropical monsoon and tropical monsoon respectively. The former rain belt is mainly formed by the convergence of cold air and the recurved southwesterly flow from western part of subtropical high and westerly flow from the so-called western trough of subtropical region occurring during winter to spring over South Asia. The latter is formed in the process of subtropical monsoon rain belt over inshore regions of South China Sea originally coming from south of Changjiang (Yangtze) River Basin advancing with northward shift of subtropical high after the onset of tropical monsoon over South China Sea. The pre-flood rainy season over South China region then came into mature period and the second peak of rainfall appeared. Meiyu, the rainy season over Changjiang-Huaihe River Basin and North China then formed consequently. The process of summer tropical monsoon onset over South China Sea in 1998 is also discussed in this paper. It indicated that the monsoon during summer tropical monsoon onset over South China Sea is the result of the westerly flow over middle part of South China Sea,which is from the new generated cyclone formed in north subtropical high entering into South China Sea, converged with the tropical southwesterly flow recurved by the intensified cross-equatorial flow.

  17. Asian summer monsoon precipitation recorded by stalagmite oxygen isotopic composition in the western Loess Plateau during AD1875-2003 and its linkage with ocean-atmosphere system

    Institute of Scientific and Technical Information of China (English)

    LIU JingHua; SANG WenCui; Kathleen R.JOHNSON; ZHANG PingZhong; CHENG Hai; CHEN FaHu; YANG XunLin; ZHANG DeZhong; ZHOU Jing; JIA JiHong; AN ChunLei

    2008-01-01

    Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave,Wudu,Gansu,variation of monsoonal precipita- tion in the modern Asian Monsoon (AM) marginal zone over the past 100 years was reconstructed.Comparison of the speleothem δ18O record with instrumental precipitation data at Wudu in the past 50 years indicates a high parallelism between the two curves,suggesting that the speleothem δ18O is a good proxy for the AM strength and associated precipitation,controlled by "amount effect" of the pre-cipitation.Variation of the monsoonal precipitation during the past 100 years can be divided into three stages,increasing from AD 1875 to 1900,then decreasing from AD 1901 to 1946,and increasing again thereafter.This variation is quite similar to that of the Drought/Flooding index archived from Chinese historical documents.This speleothem-derived AM record shows a close association with the Pacific Decadal Oscillation (PDO) between AD 1875 and 1977,with higher monsoonal precipitation corre-sponding to cold PDO phase and vice versa at decadal timescale.The monsoonal precipitation varia- tion is out of phase with the PDO after AD 1977,probably resulting from the decadal climate jump in the north Pacific occurring at around AD 1976/77.These results demonstrate a strong linkage between the AM and associated precipitation and the Pacific Ocean via ocean/atmosphere interaction.This rela-tionship will aid to forecast future hydrological cycle for the AM monsoon region,and to improve forecasting potential of climatic model with observation data from cave.

  18. Asian monsoon variability, cyclicities, and forcing mechanisms

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    and the radiolarian Actinomma spp. (upwelling indicators) show that the evolution of the Asian monsoon started in the late Miocene, at about 9.5Ma (million years ago). Between 9.5 and 5Ma the monsoon increased noticeably in strength, with smaller fluctuations... 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...

  19. Revisiting Asian monsoon formation and change associated with Tibetan Plateau forcing: I. Formation

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Guoxiong; Liu, Yimin; Duan, Anmin; Bao, Qing [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing (China); Dong, Buwen [University of Reading, Department of Meteorology, National Centre for Atmospheric Science, Reading (United Kingdom); Liang, Xiaoyun [China Meteorological Administration, National Climate Center, Beijing (China); Yu, Jingjing [China Meteorological Administration, National Meteorological Information Center, Beijing (China)

    2012-09-15

    Numerical experiments with different idealized land and mountain distributions are carried out to study the formation of the Asian monsoon and related coupling processes. Results demonstrate that when there is only extratropical continent located between 0 and 120 E and between 20/30 N and the North Pole, a rather weak monsoon rainband appears along the southern border of the continent, coexisting with an intense intertropical convergence zone (ITCZ). The continuous ITCZ surrounds the whole globe, prohibits the development of near-surface cross-equatorial flow, and collects water vapor from tropical oceans, resulting in very weak monsoon rainfall. When tropical lands are integrated, the ITCZ over the longitude domain where the extratropical continent exists disappears as a consequence of the development of a strong surface cross-equatorial flow from the winter hemisphere to the summer hemisphere. In addition, an intense interaction between the two hemispheres develops, tropical water vapor is transported to the subtropics by the enhanced poleward flow, and a prototype of the Asian monsoon appears. The Tibetan Plateau acts to enhance the coupling between the lower and upper tropospheric circulations and between the subtropical and tropical monsoon circulations, resulting in an intensification of the East Asian summer monsoon and a weakening of the South Asian summer monsoon. Linking the Iranian Plateau to the Tibetan Plateau substantially reduces the precipitation over Africa and increases the precipitation over the Arabian Sea and the northern Indian subcontinent, effectively contributing to the development of the South Asian summer monsoon. (orig.)

  20. Natural and human-induced changes in summer climate over the East Asian monsoon region in the last half century: A review

    Directory of Open Access Journals (Sweden)

    Ren-He Zhang

    2015-06-01

    The decadal changes in EASM and summer rainfall over eastern China in the last half century are closely related to natural internal forcing factors such as Eurasian snow cover, Arctic sea ice, sea surface temperatures in tropical Pacific and Indian Ocean, ocean–atmospheric coupled systems of the Pacific Decadal Oscillation (PDO and Asian–Pacific Oscillation (APO, and uneven thermal forcing over the Asian continent. Up to now, the roles of anthropogenic factors, such as greenhouse gases, aerosols, and land usage/cover changes, on existing decadal variations of EASM and summer rainfall in this region remain uncertain.

  1. A Study of the Teleconnections in the Asian-Pacific Monsoon Region

    Institute of Scientific and Technical Information of China (English)

    DING Yihui; LIU Yunyun

    2008-01-01

    The interactions among the Asian-Pacific monsoon subsystems have significant impacts on the climatic regimes in the monsoon region and even the whole world. Based on the domestic and foreign related research, an analysis is made of four different teleconnection modes found in the Asian-Pacific monsoon region, which reveal clearly the interactions among the Indian summer monsoon (ISM), the East Asian summer monsoon (EASM), and the western North Pacific summer monsoon (WNPSM). The results show that: (1) In the period of the Asian monsoon onset, the date of ISM onset is two weeks earlier than the beginning of the Meiyu over the Yangtze River Basin, and a teleconnection mode is set up from the southwestern India via the Bay of Bengal (BOB) to the Yangtze River Basin and southern Japan, I.e., the "southern" teleconnection of the Asian summer monsoon. (2) In the Asian monsoon culmination period, the precipitation of the Yangtze River Basin is influenced significantly by the WNPSM through their teleconnection relationship, and is negatively related to the WNPSM rainfall, that is, when the WNPSM is weaker than normal, the precipitation of the Yangtze River Basin is too.re than normal. (3) In contrast to the rainfall over the Yangtze River Basin, the precipitation of northern China (from the 4th pentad of July to the 3rd pentad of August) is positively related to the WNPSM. When the WNPSM is stronger than normal, the position of the western Pacific subtropical high (WPSH) becomes farther northeast than normal, the anomalous northeastward water vapor transport along the southwestern flank of WPSH is converged over northern China, providing adequate moisture for more rainfalls than normal there. (4) The summer rainfall in northern China has also a positive correlation with the ISM. During the peak period of ISM, a teleconnection pattern is formed from Northwest India via the Tibetan Plateau to northern China, I.e., the "northern" teleconnection of the Asian summer monsoon

  2. Trace gas transport out of the Indian Summer Monsoon

    Science.gov (United States)

    Tomsche, Laura; Pozzer, Andrea; Zimmermann, Peter; Parchatka, Uwe; Fischer, Horst

    2016-04-01

    The trace gas transport out of the Indian summer monsoon was investigated during the aircraft campaign OMO (Oxidation Mechanism Observations) with the German research aircraft HALO (High Altitude and Long Range Research Aircraft) in July/August 2015. HALO was based at Paphos/Cyprus and also on Gan/Maledives. Flights took place over the Mediterranean Sea, the Arabian Peninsula and the Arabian Sea. In this work the focus is on the distribution of carbon monoxide (CO) and methane (CH4) in the upper troposphere. They were measured with the laser absorption spectrometer TRISTAR on board of HALO. During the Indian summer monsoon strong convection takes place over India and the Bay of Bengal. In this area the population is high accompanied by many emission sources e.g. wetlands and cultivation of rice. Consequently the boundary layer is polluted containing high concentrations of trace gases like methane and carbon monoxide. Due to vertical transport these polluted air masses are lifted to the upper troposphere. Here they circulate with the so called Asian monsoon anticyclone. In the upper troposphere polluted air masses lead to a change in the chemical composition thus influence the chemical processes. Furthermore the anticyclone spreads the polluted air masses over a larger area. Thus the outflow of the anticyclone in the upper troposphere leads to higher concentrations of trace gases over the Arabian Sea, the Arabian Peninsula and also over the eastern part of North Africa and the eastern part of the Mediterranean Sea. During OMO higher concentrations of methane and carbon monoxide were detected at altitudes between 11km and 15km. The highest measured concentrations of carbon monoxide and methane were observed over Oman. The CO concentration in the outflow of the monsoon exceeds background levels by 10-15ppb. However the enhancement in the concentration is not obviously connected to the monsoon due to the natural variability in the troposphere. The enhancement in the

  3. 亚洲夏季风的年际和年代际变化及其未来预测%Interdecadal and Interannual Variabilities of the Asian Summer Monsoon and Its Projection of Future Change

    Institute of Scientific and Technical Information of China (English)

    丁一汇; 孙颖; 刘芸芸; 司东; 王遵娅; 朱玉祥; 柳艳菊; 宋亚芳; 张锦

    2013-01-01

    响,未来的亚洲夏季风活动是人类排放的CO2引起的全球变暖与自然变化(海洋和陆面过程(积雪))共同作用的结果.%The present paper presents a concise summary of our studies on interdecadal and interannual variabilities of the Asian summer monsoon and its projection for recent five years, which can be summarized in the following three aspects: 1) A significant interdecadal weakening of the Asian summer monsoon was identified on the basis of our analysis of a 123-year precipitation dataset in China and studies made by Indian investigators. This variability has caused significant changes in summer precipitation patterns in both East and South Asia. In East Asia, the main monsoon precipitation belt has continuously retreated southward, leading to a precipitation pattern of droughts in North China and floods in South China. The interdecadal change in the preceding winter and spring over the Tibetan Plateau and the sea surface temperature anomaly (SSTA) of the tropical central and eastern Pacific, in addition to the resulting land-sea thermal contrast, are the main drivers for the weakening of the Asian summer monsoon. In the future, the responses of the South and East Asian summer monsoons to a warmer climate will differ, with a continuous weakening in the former and enhanced circulation and precipitation fields in the latter. 2) The interannual variability is mainly characterized by biennial and four-seven-year oscillations. The present paper focuses on formative processes, mechanisms and influences of tropospheric biennial oscillation (TBO) on precipitation in East Asia. The formation and cycle processes of two particular TBO modes, the Yangtze River Valley (YRV) and the Huaihe River Valley (HRV) modes, have been examined. 3) On the basis of previous studies of teleconnection modes in the Asian monsoon region, we suggest the occurrence of low-level teleconnection types propagating along a strong monsoonal airflow belt from South Asia or

  4. An Assessment of the South Asian Summer Monsoon Variability for Present and Future Climatologies Using a High Resolution Regional Climate Model (RegCM4.3 under the AR5 Scenarios

    Directory of Open Access Journals (Sweden)

    Mujtaba Hassan

    2015-11-01

    Full Text Available We assessed the present and future climatologies of mean summer monsoon over South Asia using a high resolution regional climate model (RegCM4 with a 25 km horizontal resolution. In order to evaluate the performance of the RegCM4 for the reference period (1976–2005 and for the far future (2070–2099, climate change projections under two greenhouse gas representative concentration pathways (RCP4.5 and RCP8.5 were made, the lateral boundary conditions being provided by the geophysical fluid dynamic laboratory global model (GFDL-ESM2M. The regional climate model (RCM improves the simulation of seasonal mean temperature and precipitation patterns compared to driving global climate model (GCM during present-day climate conditions. The regional characteristic features of South Asian summer monsoon (SASM, like the low level jet stream and westerly flow over the northern the Arabian Sea, are well captured by the RegCM4. In spite of some discrepancies, the RegCM4 could simulate the Tibetan anticyclone and the direction of the tropical easterly jet reasonably well at 200 hPa. The projected temperature changes in 2070–2099 relative to 1976–2005 for GFDL-ESM2M show increased warming compared to RegCM4. The projected patterns at the end of 21st century shows an increase in precipitation over the Indian Peninsula and the Western Ghats. The possibilities of excessive precipitation include increased southwesterly flow in the wet period and the effect of model bias on climate change. However, the spatial patterns of precipitation are decreased in intensity and magnitude as the monsoon approaches the foothills of the Himalayas. The RegCM4-projected dry conditions over northeastern India are possibly related to the anomalous anticyclonic circulations in both scenarios.

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

    OpenAIRE

    Zhang, R.; Yan, Q.; Z. S. Zhang; Jiang, D.; B. L. Otto-Bliesner; A. M. Haywood; D. J. Hill; Dolan, A. M.; Stepanek, C.; Lohmann, G.; Contoux, C.; F. Bragg; Chan, W.-L.; Chandler, M. A.; A. Jost

    2013-01-01

    Based on the simulations with fifteen 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 wind (EASW) largely strengthens in monsoon China, and the East Asian winter wind (EAWW) strengthens in south monsoon China but slightly weakens in north monsoon China i...

  6. 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.

  7. Transport pathways from the Asian monsoon anticyclone to the stratosphere

    Science.gov (United States)

    Garny, Hella; Randel, William

    2016-04-01

    The upper tropospheric Asian monsoon anticyclone emerges in response to persistent deep convection over India and southeast Asia in northern summer. The monsoon circulation is associated with rapid transport from the surface to the upper troposphere within convective updrafts, leading to tracer anomalies within the anticyclone. Possibly air is transported further into the stratosphere, but the exact pathways of air from the upper tropospheric anticyclone to the stratosphere are currently under debate. While air is thought to be confined to the anticyclone by its surrounding wind jets, large variability in the anticyclone results in shedding of air from the anticyclone to its surrounding, and possibly air might reach the extratropical lower stratosphere by isentropic mixing. On the other hand, positive vertical velocities in the anticyclone region suggests upward transport of air into the tropical lower stratosphere. In this study, we investigate transport pathways of air originating in the upper tropospheric Asian monsoon anticyclone based on isentropic and three-dimensional trajectories. Trajectories are driven by ERA-Interim reanalysis data, and three-dimensional results are based both on kinematic and diabatic transport calculations. Isentropic calculations show that air parcels are typically confined within the anticyclone for 10-20 days, and spread over the tropical belt within a month of their initialization. However, only few parcels (3 % at 360 K, 8 % at 380 K) reach the extratropical stratosphere by isentropic transport. When considering vertical transport we find that 31 % (48 %) of the trajectories reach the stratosphere within 60 days when using vertical velocities or diabatic heating rates to calculate vertical transport, respectively. In both cases, most parcels that reach the stratosphere are transported upward within the anticyclone and enter the stratosphere in the tropics, typically 10-20 days after their initialization at 360 K. This suggests

  8. The South Asian Monsoon Circulation in Moist Isentropic coordinates

    Science.gov (United States)

    Thazhe Purayil, Sabin; Pauluis, Olivier

    2016-04-01

    The atmospheric circulation and thermodynamic structure during the South Asian Summer Monsoon season is analyzed in isentropic coordinates through the mass transport represented in terms of the potential temperature and equivalent potential temperature. This approach, originally developed to analyze the global meridional circulation, makes it possible to identify the thermodynamic properties of the inflow and outflow of different air mass. To understand the thermodynamic properties of air mass in south Asian monsoon region, we have used three diagnostics; a) the joint distribution of the mass transport as a function of dry and moist entropy, b) the vertical mass flux over the monsoon domain and c) the mass transport and isentropic thickness for different moist ventilation range of tropical atmosphere. The thermodynamic properties of the various air masses, such as the inflow of warm moist air in the boundary layer, upper tropospheric outflow, and midlatitude dry air intrusion are being systematically identified. The isentropic distribution of the vertical mass flux transport in terms of equivalent potential temperature is used to explain the characteristics of ascending and descending air parcels over the Indian subcontinent. Diagnosis based on the isentropic thickness reveals that the regional monsoon circulation and associated precipitation features can be systematically explained by this method. This technique is used to study the evolution of the monsoon flow in the seasonal scale. We used the data from AMIP-type simulations carried out with prescribed Sea Surface Temperature and sea ice for a 25 year period (1981-2005) from the GFDL High-resolution atmospheric model (HiRAM) with an average grid spacing of ~25km over the globe.

  9. 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.

  10. Effects of the East Asian Summer Monsoon on Tropical Cyclone Genesis over the South China Sea on an Interdecadal Time Scale

    Institute of Scientific and Technical Information of China (English)

    WANG Xin; ZHOU Wen; LI Chongyin; WANG Dongxiao

    2012-01-01

    Tropical cyclone (TC) genesis over the South China Sea (SCS) during 1965-2004 was analyzed.The locations of TC genesis display evident seasonal changes,with the mean position of formation situated north of 15°N in summer (June-July-August) and south of 15°N in autumn (September-October November).The TC genesis in summer underwent dramatic interdecadal variations,with more and less TC frequency during 1965-1974/1995-2004 and 1979-1993,respectively.In contrast,a significant interannual variation of TC genesis with a period of ~4 years was observed in autumn.This study investigated the relationship of SCS TC genesis to the East Asian jet stream (EAJS) and the western North Pacific subtropical high (WNPSH) on an interdecadal time scale.Analysis and comparison of the impacts of the EAJS and the WNPSH on vertical wind shear changes indicate that changes in the WNPSH and EAJS intensity rather than EAJS meridional location are responsible for changes in TC genesis on an interdecadal time scale.Corresponding to a weaker EAJS,anomalous Rossby wave energy at upper levels displays equatorward propagation at midlatitudes and poleward propagation in the subtropics.This induces anomalous convergence and divergence of wave activity fluxes in East Asia around 30°N and the SCS,respectively.The anomalous divergence of wave activity fluxes reduces easterlies at upper levels over the SCS,which is favorable to TC genesis.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

    The summer monsoon rainfall over the Indian subcontinent shows 1 large inter-annual variability in three important aspects, namely, the onset date, quantum of monsoon rainfall and the monsoon activity within the monsoon (June - September) period...

  16. See–saw relationship of the Holocene East Asian–Australian summer monsoon

    Science.gov (United States)

    Eroglu, Deniz; McRobie, Fiona H.; Ozken, Ibrahim; Stemler, Thomas; Wyrwoll, Karl-Heinz; Breitenbach, Sebastian F. M.; Marwan, Norbert; Kurths, Jürgen

    2016-01-01

    The East Asian–Indonesian–Australian summer monsoon (EAIASM) links the Earth's hemispheres and provides a heat source that drives global circulation. At seasonal and inter-seasonal timescales, the summer monsoon of one hemisphere is linked via outflows from the winter monsoon of the opposing hemisphere. Long-term phase relationships between the East Asian summer monsoon (EASM) and the Indonesian–Australian summer monsoon (IASM) are poorly understood, raising questions of long-term adjustments to future greenhouse-triggered climate change and whether these changes could ‘lock in' possible IASM and EASM phase relationships in a region dependent on monsoonal rainfall. Here we show that a newly developed nonlinear time series analysis technique allows confident identification of strong versus weak monsoon phases at millennial to sub-centennial timescales. We find a see–saw relationship over the last 9,000 years—with strong and weak monsoons opposingly phased and triggered by solar variations. Our results provide insights into centennial- to millennial-scale relationships within the wider EAIASM regime. PMID:27666662

  17. 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.

    The present paper presents a diagnostic study of two recent monsoon years, of which one is dry monsoon year (2009) and the other is wet monsoon year (2010). The study utilized the IMD gridded rainfall data set in addition to the Reynolds SST, NCEP...

  18. Asian Monsoon Failure and Megadrought During the Last Millennium

    Science.gov (United States)

    Cook, Edward R.; Anchukaitis, Kevin J.; Buckley, Brendan M.; D'Arrigo, Rosanne D.; Jacoby, Gordon C.; Wright, William E.

    2010-04-01

    The Asian monsoon system affects more than half of humanity worldwide, yet the dynamical processes that govern its complex spatiotemporal variability are not sufficiently understood to model and predict its behavior, due in part to inadequate long-term climate observations. Here we present the Monsoon Asia Drought Atlas (MADA), a seasonally resolved gridded spatial reconstruction of Asian monsoon drought and pluvials over the past millennium, derived from a network of tree-ring chronologies. MADA provides the spatiotemporal details of known historic monsoon failures and reveals the occurrence, severity, and fingerprint of previously unknown monsoon megadroughts and their close linkages to large-scale patterns of tropical Indo-Pacific sea surface temperatures. MADA thus provides a long-term context for recent monsoon variability that is critically needed for climate modeling, prediction, and attribution.

  19. Interannual variation of East Asian summer monsoon and its impacts on general circulation and precipitation%东亚夏季风的年际变化及其对环流和降水的影响

    Institute of Scientific and Technical Information of China (English)

    于淑秋; 施晓晖; 林学椿

    2009-01-01

    Using NCEP/NCAR reanalysis geopotential height (GHT) and wind at 850 hPa,GHT at 500 hPa, precipitation rate, sea level pressure (SLP) and precipitation observations from more than 600 stations nationwide in June-August from 1951 to 2006, and focusing on the East Asia-West Pacific region (10Q-80QN, 70Q-180QE), interannual variation of East Asian summer monsoon (EASM) and its correlations with general circulation and precipitation patterns are studied by using statistical diagnostic methods such as 9-point high pass filtering,empirical orthogonal function (EOF) analysis, composite analysis and other statistical diagnosis, etc. It is concluded as follows: (1) EOF analysis of SLP in the East Asia-West Pacific region shows the existence of the zonal dipole oscillation mode (APD) between the Mongolia depression and the West Pacific high, and APD index can be used as an intensity index of EASM. (2) EOF analysis of GHT anomalies at 500 hPa in the East Asia-West Pacific region shows that the first EOF mode is characterized with an obvious meridional East Asian pattern (EAP), and EAP index can also be used as an EASM intensity index. (3) The composite analysis of high/low APD index years reveals the close correlation of APD index with EAP at 500 hPa (or 850 hPa). The study shows an obvious opposite correlation exists between APD index and EAP index with a correlation coefficient of -0.23, which passes the confidence test at 0.10 level. (4) Both APD and EAP indexes are closely correlated with precipitation during flood-prone season in China and precipitation rate over the East Asia-West Pacific region.The significant correlation area at 5% confidence level is mainly located from the southern area of the Yangtze River valley to the ocean around southern Japan, and the former is a positive correlation and the latter is a negative one.

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

    Directory of Open Access Journals (Sweden)

    H. Tang

    2011-08-01

    Full Text Available The Late Miocene (11.6–5.3 Ma is a crucial period in the history of the Asian monsoon. Significant changes in the Asian climate regime have been documented for this period, which saw the formation of the modern Asian monsoon system. However, the spatiotemporal structure of these changes is still ambiguous, and the associated mechanisms are debated. Here, we present a simulation of the average state of the Asian monsoon climate for 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 regional Tortonian run shows a stronger-than-present East Asian winter monsoon wind as a result of the enhanced mid-latitude westerly wind of our global forcing and the lowered present-day 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. Precipitation decreases in northern China and northern India, but increases in southern China, the western coast and the southern tip of India. This can be attributed to the changes in both the regional topography (e.g. the lower northern Tibetan Plateau and the global climate conditions (e.g. the higher sea surface temperature. The spread of dry summer conditions over northern China and northern Pakistan in our Tortonian run further implies that the monsoonal climate may not have been fully established in these regions in the Tortonian. Compared with the global model, the high resolution regional model highlights the spatial differences of the Asian monsoon climate in the Tortonian, and better

  1. 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.

  2. 中国年降水量的时空变化特征及其与东亚夏季风的关系%SPATIO-TEMPORAL VARIATION OF ANNUAL PRECIPITATION IN CHINA AND ITS RELATIONSHIP WITH THE EAST ASIAN SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    陆龙骅; 张德二

    2013-01-01

    利用中国1951~2010年652站年降水资料和7种东亚夏季风和1种冬季风指数,通过多项数学统计诊断分析,来研究中国年降水量的时空变化特征及其与东亚夏季风指数的关系.结果表明,这60年间全国总平均年降水量未呈现显著的时间变化趋势,但区域间的差异大.聚类分析可提供较客观的降水分区,据554站无缺测降水资料的聚类结果,将全国分成14个主要降水区,各区之间降水变化的差异显著.由7种夏季风指数与14个区的平均年降水量(1951~2010年)的相关系数可见,其中4种夏季风指数与14个区的年降水量之间没有显著相关,有3种指数只与14区中的2~3个区有显著负相关,它们并不能指示其他区域的或整个中国东部的降水变化.中国东部地区的夏季降水分布与东亚夏季风强度变化关系十分复杂,不能仅由降水的多少来认定夏季风的强弱,更不能用任意单个地点的降水记录来表示整个中国东部的干湿状况和夏季风的强度变化.%Variation of annual precipitation in China is one of the basic problems of climate change research, its relations with the East Asian summer monsoon is the important basis for inference of the ancient East Asian monsoon evolution. Issues of whether precipitation series in a single location can be representative of precipitation change in eastern China,as well as the possibility of using precipitation series in a single location as indices for East Asian summer monsoon, are in need of comprehensive analysis and discussion based on systematically collected meteorological observations and records and a variety of summer monsoon index series. In this paper,the authors use the annual precipitation data from 652 stations over 1951 -2010 in China and 7 East Asian summer monsoon indices and the 1 East Asian winter monsoon index to conduct a number of mathematical and statistical diagnosis and analysis. After discounting the effects of

  3. 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

  4. 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.

  5. 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.

  6. The East Asian Subtropical Summer Monsoon:Recent Progress

    Institute of Scientific and Technical Information of China (English)

    何金海; 刘伯奇

    2016-01-01

    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 fi rstly 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 Pro ject), 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 eff ect of the seasonal transition of the zonal land–sea thermal contrast and the infl uences from the Tibetan Plateau and midlatitudes. In addition, we reveal a possible reason for the subtropical climate diff erence between East Asia and East America. Finally, the multi-scale variability of the EASSM and its infl uential factors are summarized to uncover possible reasons for the intraseasonal, interannual, and interdecadal variability of the EASSM and their importance in climate prediction.

  7. Teleconnections associated with Northern Hemisphere summer monsoon intraseasonal oscillation

    Science.gov (United States)

    Moon, Ja-Yeon; Wang, Bin; Ha, Kyung-Ja; Lee, June-Yi

    2013-06-01

    The boreal summer intraseasonal oscillation (BSISO) has strong convective activity centers in Indian (I), Western North Pacific (WNP), and North American (NA) summer monsoon (SM) regions. The present study attempts to reveal BSISO teleconnection patterns associated with these dominant intraseasonal variability centers. During the active phase of ISM, a zonally elongated band of enhanced convection extends from India via the Bay of Bengal and Philippine Sea to tropical central Pacific with suppressed convection over the eastern Pacific near Mexico. The corresponding extratropical circulation anomalies occur along the waveguides generated by the North African-Asian jet and North Atlantic-North European jet. When the tropical convection strengthens over the WNPSM sector, a distinct great circle-like Rossby wave train emanates from the WNP to the western coast of United States (US) with an eastward shift of enhanced meridional circulation. In the active phase of NASM, large anticyclonic anomalies anchor over the western coast of US and eastern Canada and the global teleconnection pattern is similar to that during a break phase of the ISM. Examination of the evolution of the BSISO teleconnection reveals quasi-stationary patterns with preferred centers of teleconnection located at Europe, Russia, central Asia, East Asia, western US, and eastern US and Canada, respectively. Most centers are embedded in the waveguide along the westerly jet stream, but the centers at Europe and Russia occur to the north of the jet-induced waveguide. Eastward propagation of the ISO teleconnection is evident over the Pacific-North America sector. The rainfall anomalies over the elongated band near the monsoon domain over the Indo-western Pacific sector have an opposite tendency with that over the central and southern China, Mexico and southern US, providing a source of intraseasonal predictability to extratropical regions. The BSISO teleconnection along and to the north of the subtropical jet

  8. 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.

  9. Precipitation top heights of orographic heavy rainfall in the Asian monsoon regions

    Science.gov (United States)

    Shige, Shoichi; Kummerow, Christian

    2016-04-01

    In contrast to the dominant view that heavy rainfall results from deep clouds, the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) frequently observed heavy, but shallow orographic rainfall over coastal mountain ranges of the Asian monsoon regions. The low-level horizontal winds, leading to topographic forced upward motion on the windward slopes, are dynamically important for its occurrence. This paper focuses on the thermodynamic character of the atmospheric environment associated with shallow orographic heavy rainfall. The precipitation-top heights of orographic heavy rainfall generally decrease with low- and mid-level relative humidity especially for coastal mesoscale mountain ranges during summer monsoon. This differs from what has been observed for convection over the tropical ocean in previous studies, but is consistent with abundant shallow convection during the moist summer monsoon season. In contrast, the precipitation-top heights over Annam Cordillera during the transition phase from boreal summer to winter monsoon seasons, facing the prevailing northeasterly, increase with low-level and mid-level relative humidity, demonstrating that convection depth is not a simple function of humidity. The precipitation-top heights of orographic heavy rainfall decrease with the low-level stability for all regions considered in this study as well as Annam Cordillera during the transition phase from boreal summer to winter monsoon seasons. Therefore, low-level static stability, which inhibits cloud growth and promotes cloud detrainment, is inferred to be an equally important parameter in determining the precipitation-top heights.

  10. 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

  11. 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.

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

    Science.gov (United States)

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

    2016-06-01

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

  13. 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

  14. 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

  15. 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.

  16. Understanding land surface response to changing South Asian monsoon in a warming climate

    Directory of Open Access Journals (Sweden)

    M. V. S. Ramarao

    2015-05-01

    Full Text Available Recent studies have drawn attention to a significant weakening trend of the South Asian monsoon circulation and an associated decrease in regional rainfall during the last few decades. While surface temperatures over the region have steadily risen during this period, most of the CMIP (Coupled Model Intercomparison Project global climate models have difficulties in capturing the observed decrease of monsoon precipitation, thus limiting our understanding of the regional land surface response to monsoonal changes. This problem is investigated by performing two long-term simulation experiments, with and without anthropogenic forcing, using a variable resolution global climate model having high-resolution zooming over the South Asian region. The present results indicate that anthropogenic effects have considerably influenced the recent weakening of the monsoon circulation and decline of precipitation. It is seen that the simulated increase of surface temperature over the Indian region during the post-1950s is accompanied by a significant decrease of monsoon precipitation and soil moisture. Our analysis further reveals that the land surface response to decrease of soil moisture is associated with significant reduction in evapotranspiration over the Indian land region. A future projection, based on the representative concentration pathway 4.5 (RCP4.5 scenario of the Intergovernmental panel on Climate Change (IPCC, using the same high-resolution model indicates the possibility for detecting the summer-time soil drying signal over the Indian region during the 21st century, in response to climate change. While these monsoon hydrological changes have profound socioeconomic implications, the robustness of the high-resolution simulations provides deeper insights and enhances our understanding of the regional land surface response to the changing South Asian monsoon.

  17. Impact of Ocean-Continent Distribution over Southern Asia on the Formation of Summer Monsoon

    Institute of Scientific and Technical Information of China (English)

    JIN Qihua; HE Jinhai; CHEN Longxun; ZHU Congwen

    2006-01-01

    Using the CCM3/NCAR, a series of numerical experiments are designed to explore the effect of ocean-land interlaced distributions of Africa-Arabian Sea-India Peninsula-Bay of Bengal (BOB)-Indo-China PeninsulaSouth China Sea on the formation of the Asian summer monsoon circulation (ASMC). The results show that the thermal difference between African or Indian Subcontinent and nearby areas including the Indian Ocean,Arabian Sea, and part of BOB is the primary mechanism that maintains the Indian monsoon circulation.In the experiment getting rid of these two continents, the Indian monsoon system (IMS) members, i.e., the Somali cross-equatorial jet (40°E) and the southwesterly monsoon over the Arabian Sea and BOB, almost disappear. Moreover, the Hadley circulation weakens dominantly. It also proves that Africa has greater effect than Indian Subcontinent on the IMS.However, the existence of Indo-China Peninsula and Australia strengthens the East Asian monsoon system (EAMS). The thermal contrast between Indo-China Peninsula and SCS, Australia and western Pacific Ocean plays an important role in the formation of the tropical monsoon to the south of the EAMS. When the Indo-China Peninsula is masked in the experiment, the cross-equatorial flow (105°E and 125°E) vanishes,so does the southwesterly monsoon usually found over East Asia, and EAMS is enfeebled significantly. In addition, the impacts of these thermal contrasts on the distribution of the summer precipitation and surface temperature are investigated.

  18. 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.

  19. 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.

  20. 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.

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

    Science.gov (United States)

    Dallmeyer, A.; Claussen, M.

    2011-06-01

    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 in 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.

  2. The Influence of Sea Surface Temperature Anomaly on the East Asian Summer Monsoon Strength and Its Precursor%海温异常对东亚夏季风强度先兆信号的影响

    Institute of Scientific and Technical Information of China (English)

    柯宗建; 华丽娟; 钟霖浩; 杜良敏

    2015-01-01

    利用 ERA-Interim 再分析资料、NOAA 海温资料、CMAP 格点降水资料和中国气象站降水资料,通过合成、相关和回归分析等方法研究了1979—2012年东亚夏季风强度与其先兆信号的关系,并分析了热带海温异常的可能影响。研究表明:东亚夏季风先兆指数反映了2月200 hPa 纬向风距平的主要模态特征(EOF1),前冬热带中东太平洋海温偏低(高),2月亚洲地区西风急流位置偏北(偏南),东亚夏季风先兆指数偏强(弱)。前期热带海温异常对东亚夏季风强度有明显影响,前冬热带中东太平洋海温偏低(高)有利于东亚夏季风偏强(弱)。2月亚洲中纬度地区纬向风异常特征在春季不能持续,先兆信号与东亚夏季风强度的联系主要源自热带海洋。%The strength of the East Asian Summer Monsoon (EASM)is closely connected to the summer main rainfall belt in China.The precursor index defined by the difference of zonal wind anomaly at 200 hPa be-tween the middle latitude in Asia and eastern Pacific in February is well indicative to the strength of EASM,which is an important predicting factors in flood season.The potential mechanism of precursor signal influencing the EASM is proposed by changing the surface characteristics in South Asia continent, but it is unclear whether the atmospheric circulation anomaly in February persists in the following seasons over middle latitude region.In addition,a further investigation is needed about the surface anomaly varia-tion over South Asia in winter-spring seasons.ERA-Interim reanalysis data,NOAA sea surface data, gridded CMAP precipitation data and precipitation observations over China are used.By composite,corre-lation and regression analysis approaches,the difference of wind in middle latitude over Eurasia,sea sur-face temperature (SST)in tropics and thermal condition in South Asia continent in previous winter-spring seasons in various strength

  3. A study of the dynamic effect of the South Asian high on the upper troposphere water vapor abnormal distribution over the Asian monsoon region in boreal summer%南亚高压对亚洲季风区夏季对流层上层水汽异常分布的动力效应

    Institute of Scientific and Technical Information of China (English)

    陈斌; 徐祥德; 施晓晖

    2011-01-01

    Proper recognition of the water vapor distribution and formation mechanism in the upper troposphere (UT) over the Asian monsoon region is of great significance for understanding of global climate change. Based on the latest Earth Observing System Microwave Limb Sounder (EOS-MLS) satellite retrievals product, the study firstly presented a qualitative analysis of the anomaly characteristics of the upper troposphere water vapor distribution. Then we studied the air particles horizontal transport characters in the upper troposphere layer over the Tibetan Plateau and its adjoint areas using the National Centers for Environmental Prediction (NCEP) reanalysis data of 2005 and a particle dispersion model FLEXPART. Also the dynamical effects of the south Asian high, which are able to trap the constituents in its core, in determining and maintaining the water vapor distribution are investigated quantitatively.The analysis of the EOS-MLS satellite retrieval products shows that the Asian monsoon region is an area of particular interest, as it is characterized by a persistent maximum of water vapor in the upper troposphere. The location of maximum water vapor on 215 hPa coincides with the deep convection. However, the water vapor maximum at 147 hPa does not spatially correspond to the maximum of convective activity, but is located inside the South Asian high. The distribution of carbon monoxide over this area shows the same characteristic as the water vapor. This result suggests an important role of the South Asian high in determining and maintaining the water vapor distribution. For every numerical simulation, 10000 forward parcels trajectories were calculated for the summer of 2005. The result of idealized ensemble numerical simulations (total 66 groups) indicates that the South Asian high circulation acts as a horizontal transport barrier in the upper troposphere and low stratosphere during the boreal summer. The effects of the South Asian high are mostly in the height

  4. 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

  5. Investigation of summer monsoon rainfall variability in Pakistan

    Science.gov (United States)

    Hussain, Mian Sabir; Lee, Seungho

    2016-08-01

    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.

  6. 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.

  7. 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.

  8. 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.

  9. Role of Anomalous States of Upper Tropospheric Circulation on Extremely Dry and Wet Summer Monsoon Events

    Science.gov (United States)

    Ahmad, S.; Koike, T.; Nishii, K.; Shrestha, M.

    2011-12-01

    Seasonal changes in wind pattern, monsoon, sometimes result in severe droughts and intense flooding in many parts of the world including South Asian countries like Pakistan. The livelihood of a vast population in Pakistan depends on agriculture and land use is strongly influenced by water-based ecosystems that depend on the monsoon rains. Furthermore, climate change studies undertaken so far reveal that action is essential in order to prevent long term damage to water cycle and thus of great concern to the community and stakeholders. Pakistan Summer Monsoon (PSM) is affected by both the disturbances from the tropical and the extratropical regions; however there is lack of understanding of physical mechanisms of PSM compared to other regional studies i.e. Indian Summer Monsoon (ISM) and South-East Asian Monsoon (SEAM). In our study, we applied heat and vorticity budgets, and wave train analysis to reveal the mechanisms of the extremely dry and wet PSM events associated with the anomalous upper tropospheric conditions. We found that the extremely dry (wet) PSM events were closely related with the anomalous cyclonic (anticyclonic) upper-tropospheric circulation around northwest of Pakistan, and mid-upper tropospheric cooling (warming) anomaly around Pakistan and to its north/northwest. We also found in addition to Rossby wave response due to the suppressed (enhanced) convective activities around monsoon regions, the midlatitude wave energy propagation emanating around cyclonic/anticyclonic anomaly around northwestern Atlantic, northeastern Atlantic, Europe or Mediterranean regions induced/reinforced/maintained the anomalous upper tropospheric cyclonic (anticyclonic) circulation around northwest of Pakistan during extremely dry (wet) PSM events. Therefore, devastating drought (flood) events over the PSM region resulting from weak (strong) convection anomalies are induced by both the tropical and extratropical processes.

  10. Instability characteristics of the East Asian Monsoon recorded by high-resolution loess sections from the last interglacial (MIS5)

    Institute of Scientific and Technical Information of China (English)

    GUAN QingYu; PAN BaoTian; GAO HongShan; LI BingYuan; WANG JunPing; SU Huai

    2007-01-01

    The selection of high-resolution loess sections is needed in order to determine the climatic variability of the East Asian Monsoon during the last interglacial. Two sequences of S1 on the eastern and western sides of the Liupan Mountain were both composed of five paleosol layers and four loess layers, indicating that there were five strong summer monsoon events and four strong winter monsoon events in MIS5. This corresponds with other records of the East Asian Monsoon, along with NGRIP and the North Atlantic records, implying that the climate of the Northern Hemisphere was very instable during the last interglacial. Two layers of paleosols and one layer of loess had developed during MIS5a and MIS5c. Compared with MIS5e, the climate in MIS5a and MIS5c fluctuated more intensively on a millennial scale, whereas the climate was relatively stable in MIS5e.

  11. Onset of Indian Summer Monsoon: a retrospective analysis

    Science.gov (United States)

    Sruthi, S.; Mrudula, G.

    2016-05-01

    The monsoon onset over Kerala is considered as the beginning of rain fall over India and it is the end of hot summer. Different criteria have been used to define the monsoon onset over Kerala, with the one given by India Meteorological Department taken as the standard criteria. The analysis of the past 20 years of observations shows that the variables during the monsoon onset do not behave in the same way always. The purpose of this paper is to analyses the monsoon onset phases and to find possible reasons behind the variable nature of the monsoon onset. Different meteorological parameters like precipitation, outgoing long wave radiation (OLR), winds, air temperature, and specific humidity at different levels are analyzed for the same. Research has been done on various distinct features of monsoon such as Low Level Jet (LLJ), Tropical Easterly Jet (TEJ), monsoon trough, and depressions etc., during the onset phase. The analysis showed that in some years the strength of LLJ is lesser compared to the normal years. It is also seen that in some years the wind flow pattern is different from that observed during a standard onset year. The results of these analyses will be presented in detail in the paper.

  12. Current Progresses in Study of Impacts of the Tibetan Plateau on Asian Summer Climate

    Institute of Scientific and Technical Information of China (English)

    WU Guoxiong; MAO Jiangyu; DUAN Anmin; ZHANG Qiong

    2006-01-01

    The current progresses in the study of impacts of the Tibetan Plateau on Asian summer climate in the last decade are reviewed. By analyzing evolution of the transitional zone between westerly to the north and easterly to the south (WEB), it is shown that due to the strong heating over the Tibetan Plateau in spring, the overturning in the prevailing wind direction from easterly in winter to westerly in summer occurs firstly over the eastern Bay of Bengal (BOB), accompanied with vigorous convective precipitation to its east. The area between eastern BOB and western Indo-China Peninsula thus becomes the area with the earliest onset of Asian monsoon, which may be referred as BOB monsoon in short. It is shown that the summertime circulations triggered by the thermal forcing of the Iranian Plateau and the Tibetan Plateau are embedded in phase with the continental-scale circulation forced by the diabatic heating over the Eurasian Continent. As a result, the East Asian summer monsoon is intensified and the drought climate over the western and central Asian areas is enhanced. Together with perturbations triggered by the Tibetan Plateau,the above scenarios and the associated heating have important influences on the climate patterns over Asia.Furthermore, the characteristics of the Tibetan mode of the summertime South Asian high are compared with those of Iranian mode. Results demonstrate that corresponding to each of the bimodality of the South Asian high, the rainfall anomaly distributions over Asia exhibit different patterns.

  13. 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...

  14. Revisiting Asian monsoon formation and change associated with Tibetan Plateau forcing: II. Change

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yimin; Wu, Guoxiong; Duan, Anmin; Bao, Qing [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing (China); Hong, Jieli; Zhou, Linjiong [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Dong, Buwen [University of Reading, Department of Meteorology, National Centre for Atmospheric Science, Reading (United Kingdom)

    2012-09-15

    Data analysis based on station observations reveals that many meteorological variables averaged over the Tibetan Plateau (TP) are closely correlated, and their trends during the past decades are well correlated with the rainfall trend of the Asian summer monsoon. However, such correlation does not necessarily imply causality. Further diagnosis confirms the existence of a weakening trend in TP thermal forcing, characterized by weakened surface sensible heat flux in spring and summer during the past decades. This weakening trend is associated with decreasing summer precipitation over northern South Asia and North China and increasing precipitation over northwestern China, South China, and Korea. An atmospheric general circulation model, the HadAM3, is employed to elucidate the causality between the weakening TP forcing and the change in the Asian summer monsoon rainfall. Results demonstrate that a weakening in surface sensible heating over the TP results in reduced summer precipitation in the plateau region and a reduction in the associated latent heat release in summer. These changes in turn result in the weakening of the near-surface cyclonic circulation surrounding the plateau and the subtropical anticyclone over the subtropical western North Pacific, similar to the results obtained from the idealized TP experiment in Part I of this study. The southerly that normally dominates East Asia, ranging from the South China Sea to North China, weakens, resulting in a weaker equilibrated Sverdrup balance between positive vorticity generation and latent heat release. Consequently, the convergence of water vapor transport is confined to South China, forming a unique anomaly pattern in monsoon rainfall, the so-called ''south wet and north dry.'' Because the weakening trend in TP thermal forcing is associated with global warming, the present results provide an effective means for assessing projections of regional climate over Asia in the context of global

  15. The CLIVAR C20C project: which components of the Asian-Australian monsoon circulation variations are forced and reproducible?

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Tianjun; Li, Lijuan [Chinese Academy of Sciences, LASG, Institute of Atmospheric Physics, Beijing (China); Wu, Bo [Chinese Academy of Sciences, LASG, Institute of Atmospheric Physics, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Scaife, A.A.; Fereday, D.; Folland, C.K.; Knight, J.R. [Met Office Hadley Centre, Exeter (United Kingdom); Broennimann, S.; Fischer, A.M. [ETH, Institute for Atmospheric and Climate Science, Zurich (Switzerland); Cherchi, A.; Navarra, A. [Centro Euromediterraneo per i Cambiamenti Climatici, Istituto Nazionale di Geofisica e Vulcanologia, Bologna (Italy); Jin, K.E.; Kinter, J. [Centre for Ocean-Land-Atmosphere Studies, Calverton (United States); Kucharski, F. [Abdus Salam International Center for Theoretical Physics, Trieste (Italy); Kusunoki, S.; Nakaegawa, T. [Japan Meteorological Agency, Meteorological Research Institute, Tsukuba (Japan); Lau, N.C.; Nath, M.J. [NOAA, Geophysical Fluid Dynamics Laboratory, Princeton (United States); Pegion, P.; Schubert, S. [NASA Goddard Space Flight Center, Greenbelt (United States); Rozanov, E. [ETH, Institute for Atmospheric and Climate Science, Zurich (Switzerland); World Radiation Center, Physical-Meteorological Observatory, Davos (Switzerland); Sporyshev, P. [Voeikov Main Geophysical Observatory, St Petersburg (Russian Federation); Voldoire, A. [CNRM, Meteo France, Toulouse Cedex 1 (France); Wen, Xinyu [Chinese Academy of Sciences, LASG, Institute of Atmospheric Physics, Beijing (China); Beijing University, Department of Atmospheric Sciences, Beijing (China); Yoon, J.H.; Zeng, N. [University of Maryland, Baltimore (United States)

    2009-12-15

    A multi-model set of atmospheric simulations forced by historical sea surface temperature (SST) or SSTs plus Greenhouse gases and aerosol forcing agents for the period of 1950-1999 is studied to identify and understand which components of the Asian-Australian monsoon (A-AM) variability are forced and reproducible. The analysis focuses on the summertime monsoon circulations, comparing model results against the observations. The priority of different components of the A-AM circulations in terms of reproducibility is evaluated. Among the subsystems of the wide A-AM, the South Asian monsoon and the Australian monsoon circulations are better reproduced than the others, indicating they are forced and well modeled. The primary driving mechanism comes from the tropical Pacific. The western North Pacific monsoon circulation is also forced and well modeled except with a slightly lower reproducibility due to its delayed response to the eastern tropical Pacific forcing. The simultaneous driving comes from the western Pacific surrounding the maritime continent region. The Indian monsoon circulation has a moderate reproducibility, partly due to its weakened connection to June-July-August SSTs in the equatorial eastern Pacific in recent decades. Among the A-AM subsystems, the East Asian summer monsoon has the lowest reproducibility and is poorly modeled. This is mainly due to the failure of specifying historical SST in capturing the zonal land-sea thermal contrast change across the East Asia. The prescribed tropical Indian Ocean SST changes partly reproduce the meridional wind change over East Asia in several models. For all the A-AM subsystem circulation indices, generally the MME is always the best except for the Indian monsoon and East Asian monsoon circulation indices. (orig.)

  16. Impact of geographic variations of the convective and dehydration center on stratospheric water vapor over the Asian monsoon region

    Science.gov (United States)

    Zhang, Kai; Fu, Rong; Wang, Tao; Liu, Yimin

    2016-06-01

    The Asian monsoon region is the most prominent moisture center of water vapor in the lower stratosphere (LS) during boreal summer. Previous studies have suggested that the transport of water vapor to the Asian monsoon LS is controlled by dehydration temperatures and convection mainly over the Bay of Bengal and Southeast Asia. However, there is a clear geographic variation of convection associated with the seasonal and intra-seasonal variations of the Asian monsoon circulation, and the relative influence of such a geographic variation of convection vs. the variation of local dehydration temperatures on water vapor transport is still not clear. Using satellite observations from the Aura Microwave Limb Sounder (MLS) and a domain-filling forward trajectory model, we show that almost half of the seasonal water vapor increase in the Asian monsoon LS are attributable to geographic variations of convection and resultant variations of the dehydration center, of which the influence is comparable to the influence of the local dehydration temperature increase. In particular, dehydration temperatures are coldest over the southeast and warmest over the northwest Asian monsoon region. Although the convective center is located over Southeast Asia, an anomalous increase of convection over the northwest Asia monsoon region increases local diabatic heating in the tropopause layer and air masses entering the LS are dehydrated at relatively warmer temperatures. Due to warmer dehydration temperatures, anomalously moist air enters the LS and moves eastward along the northern flank of the monsoon anticyclonic flow, leading to wet anomalies in the LS over the Asian monsoon region. Likewise, when convection increases over the Southeast Asia monsoon region, dry anomalies appear in the LS. On a seasonal scale, this feature is associated with the monsoon circulation, convection and diabatic heating marching towards the northwest Asia monsoon region from June to August. The march of convection

  17. 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.

  18. 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)

    WANG RuJian; JIAN ZhiMin; XIAO WenShen; TIAN Jun; LI JianRu; CHEN RongHua; ZHENG YuLong; CHEN JianFang

    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 variability 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 (δ18O) 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 temporal variations.

  19. 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

  20. Late Quaternary clay minerals off Middle Vietnam in the western South China Sea: Implications for source analysis and East Asian monsoon evolution

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 450 ka during late Quaternary from Core MD05-2901 off Middle Vietnam in the western South China Sea are reported to reconstruct a history of East Asian monsoon evolution.Variations in Illite,chlorite,and kaolinite contents indicate a strong glacial-interglacial cyclicity,while changes in smectite content present a higher frequency cyclicity.The provenance analysis indicates a mixture of individual clay minerals from various sources surrounding the South China Sea.Smectite derived mainly from the Sunda shelf and its major source area of the Indonesian islands.Illite and chlorite originated mainly from the Mekong and Red rivers.Kaolinite was provided mainly by the Pearl River.Spectral analysis of the kaolinite/(illite+chlorite) ratio displays a strong eccentricity period of 100 ka,implying the ice sheet-forced winter monsoon evolution; whereas higher frequency changes in the smectite content show an ice sheet-forced obliquity period of 41 ka,and precession periods of 23 and 19 ka and a semi-precession period of 13 ka as well,implying the tropical-forced summer monsoon evolution.The winter monsoon evolution is generally in coherence with the glacial-interglacial cyclicity,with intensified winter monsoon winds during glacials and weakened winter monsoon winds during interglacials; whereas the summer monsoon evolution provides an almost linear response to the summer insolation of low latitude in the Northern Hemisphere,with strengthened summer monsoon during higher insolation and weakened summer monsoon during lower insolation.The result suggests that the high-latitude ice sheet and low-latitude tropical factor could drive the late Quaternary evolution of East Asian winter and summer monsoons,respectively,implying their diplex and self-contained forcing mechanism.

  1. 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

  2. Continued obliquity pacing of East Asian summer precipitation after the mid-Pleistocene transition

    Science.gov (United States)

    Li, Tao; Liu, Fei; Abels, Hemmo A.; You, Chen-Feng; Zhang, Zeke; Chen, Jun; Ji, Junfeng; Li, Laifeng; Li, Le; Liu, Hou-Chun; Ren, Chao; Xia, Renyuan; Zhao, Liang; Zhang, Wenfang; Li, Gaojun

    2017-01-01

    Records from natural archives show that the strength of the East Asian summer monsoon (EASM) strongly depends on the orbital configuration of the Earth. However, the dominant orbital cycles driving EASM have been found to be spatially different. Speleothem stable oxygen isotopic records from southern China, which are believed to reflect large-scale changes in the Asian monsoon system, are dominated by climatic precession cycles. Further north, on the Chinese Loess Plateau (CLP), loess-and-paleosol sequences, which are argued to be controlled by monsoon intensity, are in pace with global ice volume changes dominated by obliquity, and after the mid-Pleistocene transition by 100-kyr cycles. To understand these critical discrepancies, here we apply a novel proxy based on the trace metal compositions of pedogenic carbonate in the eolian deposits on the CLP to reconstruct summer precipitation over the last 1.5 million years. Our reconstructions show that summer precipitation on the CLP is dominantly forced by obliquity not in pace with the ice-volume-imprinted loess-paleosol sequences before and after the mid-Pleistocene transition or with the precession-paced speleothem oxygen isotopic records. Coupled with climate model results, we suggest that the obliquity-driven variations of summer precipitation may originate from the gradient of boreal insolation that modulates the thermal contrast between the Asian continent and surrounding oceans.

  3. 亚洲季风区过去700年来夏季极端干/湿事件多尺度变化特征分析%Multi-scale Analysis of the Extreme Dry/Wet Events in Asian Monsoon Region in Summer During Last 7 Centuries

    Institute of Scientific and Technical Information of China (English)

    杨萍; 侯威; 颜鹏程

    2016-01-01

    Monsoon failures,mega droughts,and extreme flooding events have repeatedly affected the agrari-an peoples of Asia over the past millennium.A scarcity of long-term instrumental climate data for many remote re-gions of Monsoon Asia impedes progress toward resolving these issues.To better elucidate the spatial complexity of the Asian monsoon,a large-scale,spatially explicit,long-term data set is needed.This context is provided here by our Monsoon Asia Drought Atlas (MADA).The MADA provides a seasonal-to centennial-scale window into the A-sian monsoon’s repeated tendency for extended dry and wet extremes with distinct spatial flavors of response.Re-cently,ensemble empirical mode decomposition (EEMD)method is developed for non-linear and non-stationary signal analysis.The EEMD method is instituted and utilized in several fields such as de-noising,ocean surface measurement,metrology,image processing and so on.The method can work on nature signals (non-linear and nonstationary signals)as well as reducing the speckle noise.The EEMD method is like as a filter bank that the sig-nal is decomposed into several intrinsic mode functions(IMFs)and the frequencies of IMFs are arranged in decrease order (high to low)after the EEMD processing.The scaling mode of the EEMD method is similar to wavelet trans-form,but the signal resolution at different frequency domain is not decrease by down-sampling.In this paper,we propose the EEMD method to extract the multi-scale characters of the variability of extreme dry/wet events in Asian monsoon area.Using the Palmer Drought Severity Index data of MADA from 504 stations in Asian monsoon area in summer from 1300-2005a and EEMD method,we get the series of the number of grids which is especially and seri-ous wet or dry in this region by an interval of 5 years,and analysis the variations of these series.Based the feature of nonlinear/nonstationarity and multi-scale in climatic system,applying EEMD to the series of the number of grids which is

  4. A STUDY ON THE RELATIONSHIP BETWEEN SPRING SOIL MOISTURE OVER CHINA AND EAST ASIA SUMMER MONSOON

    Institute of Scientific and Technical Information of China (English)

    LE Yi-long; LUO Yong; GUO Pin-wen

    2008-01-01

    The correlation analysis has been used to study the relationship between spring soil moisture over China and East Asian summer monsoon (EASM). It is shown that EASM has a strong positive correlation with spring soil moisture over southwest China and the Great Bend region of the Yellow River. A standard soil moisture index (SMI) has been defined using the observed soil moisture of the two regions. The results show that SMI has a strong correlation with EASM. The years of strong (weak) SMI are associated with stronger (weaker) summer monsoon circulation. In the years of strong SMI, the west Pacific subtropical high is much northward in position and weaker in intensity; the westerlies zone is also more to the north. All of these make EASM circulation move northward and cause the rainfall belt to relocate to North China and Northeast China. SMI can reflect the variation of the summer rainfall anomaly over eastern China. In the years of strong SMI, the rainfall belt is mainly located over the northem part of China.However, during the weak years, the summer rainfall belt is largely located over the mid- and lower- reaches of the Yangtze River. Additionally, the SMI has obvious oscillations of quasi 4-6 years and quasi 2 years. Moreover, negative SMI predicts EASM better than positive SMI.

  5. Quaternary clay mineralogy in the northern South China Sea (ODP Site 1146)--Implications for oceanic current transport and East Asian monsoon evolution

    Institute of Scientific and Technical Information of China (English)

    LIU Zhifei(刘志飞); Alain Trentesaux; Steven C. Clemens; WANG Pinxian(汪品先)

    2003-01-01

    Measurement of clay mineralogy at ODP Site 1146 in the northern South China Sea (SCS) indicates that illite, chlorite, and kaolinite contents increased during glacials and smectite content increased during interglacials. The smectite/(illite+chlorite) ratio and the smectite abundance were determined as mineralogical indicators for the East Asian monsoon evolution. At a 10 ka timescale, prevailing southeasterly surface oceanic currents during interglacials transported more smectite from the south and east areas to the north, showing a strengthened summer monsoon circulation, whereas dominated counter-clockwise surface currents during glacials carried more illite and chlorite from Taiwan as well as from the Yangtze River via the Luzon Strait to the northern SCS, indicating a strongly intensified winter monsoon. Based on a 100 ka timescale, a linear correlation between the smectite/(illite+chlorite) ratio and the sedimentation rate reflects that the winter monsoon has prevailed in the northern SCS in the intervals 2000-1200 ka and 400-0 ka and the summer monsoon did the same in the interval 1200-400 ka. The evolution of the summer monsoon provides an almost linear response to the summer insolation of Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.

  6. Eastward propagating MJO during boreal summer and Indian monsoon droughts

    Science.gov (United States)

    Joseph, Susmitha; Sahai, A. K.; Goswami, B. N.

    2009-06-01

    Improved understanding of underlying mechanism responsible for Indian summer monsoon (ISM) droughts is important due to their profound socio-economic impact over the region. While some droughts are associated with ‘external forcing’ such as the El-Niño and Southern Oscillation (ENSO), many ISM droughts are not related to any known ‘external forcing’. Here, we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics. We show that most ISM droughts are associated with at least one very long break (VLB; breaks with duration of more than 10 days) and that the processes responsible for VLBs may also be the mechanism responsible for ISM droughts. Our analysis also reveals that all extended monsoon breaks (whether co-occurred with El-Niño or not) are associated with an eastward propagating Madden-Julian Oscillation (MJO) in the equatorial Indian Ocean and western Pacific extending to the dateline and westward propagating Rossby waves between 10° and 25°N. The divergent Rossby wave associated with the dry phase of equatorial convection propagates westward towards Indian land, couple with the northward propagating dry phase and leads to the sustenance of breaks. Thus, the propensity of eastward propagating MJO during boreal summer is largely the cause of monsoon droughts. While short breaks are not accompanied by westerly wind events (WWE) over equatorial western Pacific favorable for initiating air-sea interaction, all VLBs are accompanied by sustained WWE. The WWEs associated with all VLB during 1975-2005 initiate air-sea interaction on intraseasonal time scale, extend the warm pool eastward allowing the convectively coupled MJO to propagate further eastward and thereby sustaining the divergent circulation over India and the monsoon break. The ocean-atmosphere coupling on interannual time scale (such as El-Niño) can also produce VLB, but not necessary.

  7. Eastward propagating MJO during boreal summer and Indian monsoon droughts

    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)

    2009-06-15

    Improved understanding of underlying mechanism responsible for Indian summer monsoon (ISM) droughts is important due to their profound socio-economic impact over the region. While some droughts are associated with 'external forcing' such as the El-Nino and Southern Oscillation (ENSO), many ISM droughts are not related to any known 'external forcing'. Here, we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics. We show that most ISM droughts are associated with at least one very long break (VLB; breaks with duration of more than 10 days) and that the processes responsible for VLBs may also be the mechanism responsible for ISM droughts. Our analysis also reveals that all extended monsoon breaks (whether co-occurred with El-Nino or not) are associated with an eastward propagating Madden-Julian Oscillation (MJO) in the equatorial Indian Ocean and western Pacific extending to the dateline and westward propagating Rossby waves between 10 and 25 N. The divergent Rossby wave associated with the dry phase of equatorial convection propagates westward towards Indian land, couple with the northward propagating dry phase and leads to the sustenance of breaks. Thus, the propensity of eastward propagating MJO during boreal summer is largely the cause of monsoon droughts. While short breaks are not accompanied by westerly wind events (WWE) over equatorial western Pacific favorable for initiating air-sea interaction, all VLBs are accompanied by sustained WWE. The WWEs associated with all VLB during 1975-2005 initiate air-sea interaction on intraseasonal time scale, extend the warm pool eastward allowing the convectively coupled MJO to propagate further eastward and thereby sustaining the divergent circulation over India and the monsoon break. The ocean-atmosphere coupling on interannual time scale (such as El-Nino) can also produce VLB, but not necessary. (orig.)

  8. 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

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

    Institute of Scientific and Technical Information of China (English)

    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 telecon- nection mode which is from the northwest of India via the Tibetan Plateau to northern China. The for- mer mode is defined as the "south" teleconnection of the Asian summer monsoon, forming in the pe- riod 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 ver- tically over east Asia, while the Yangtze River Valley happens to locate in the ascending

  10. 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

  11. Evolution and variability of the Asian monsoon and its potential linkage with uplift of the Himalaya and Tibetan Plateau

    Science.gov (United States)

    Tada, Ryuji; Zheng, Hongbo; Clift, Peter D.

    2016-12-01

    Uplift of the Himalaya and Tibetan Plateau (HTP) and its linkage with the evolution of the Asian monsoon has been regarded as a typical example of a tectonic-climate linkage. Although this linkage remains unproven because of insufficient data, our understanding has greatly advanced in the past decade. It is thus timely to summarize our knowledge of the uplift history of the HTP, the results of relevant climate simulations, and spatiotemporal changes in the Indian and East Asian monsoons since the late Eocene. Three major pulses of the HTP uplift have become evident: (1) uplift of the southern and central Tibetan Plateau (TP) at ca. 40-35 Ma, (2) uplift of the northern TP at ca. 25-20 Ma, and (3) uplift of the northeastern to eastern TP at ca. 15-10 Ma. Modeling predictions suggest that (i) uplift of the southern and central TP should have intensified the Indian summer monsoon (ISM) and the Somali Jet at 40-35 Ma; (ii) uplift of the northern TP should have intensified the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM), as well as the desertification of inland Asia at 25-20 Ma; and (iii) uplift of the northeastern and eastern TP should have further intensified the EASM and EAWM at 15-10 Ma. We tested these predictions by comparing them with paleoclimate data for the time intervals of interest. There are insufficient paleoclimate data to test whether the ISM and Somali Jet intensified with the uplift of the southern and central TP at 40-35 Ma, but it is possible that such uplift enhanced erosion and weathering that drew down atmospheric CO2 and resulted in global cooling. There is good evidence that the EASM and EAWM intensified, and desertification started in inland Asia at 25-20 Ma in association with the uplift of the northern TP. The impact of the uplift of the northeastern and eastern TP on the Asian monsoon at 15-10 Ma is difficult to evaluate because that interval was also a time of global cooling and Antarctic glaciation that might also

  12. Cloud Radiative Forcing in Asian Monsoon Region Simulated by IPCC AR4 AMIP Models

    Institute of Scientific and Technical Information of China (English)

    LI Jiandong; LIU Yimin; WU Guoxiong

    2009-01-01

    This study examines cloud radiative forcing (CRF) in the Asian monsoon region (0°-50°N,60°-150°E)simulated by Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) AMIP models.During boreal winter,no model realistically reproduces the larger long-wave cloud radiative forcing (LWCF) over the Tibet Plateau (TP) and only a couple of models reasonably capture the larger short-wave CRF (SWCF) to the east of the TP.During boreal summer,there are larger biases for central location and intensity of simulated CRF in active convective regions.The CRF biases are closely related to the rainfall biases in the models.Quantitative analysis further indicates that the correlation between simulated CRF and observations are not high,and that the biases and diversity in SWCF are larger than that in LWCF.The annual cycle of simulated CRF over East Asia (0°-50°N,100°-145°E) is also examined.Though many models capture the basic annual cycle in tropics,strong LWCF and SWCF to the east of the TP beginning in early spring are underestimated by most models.As a whole,GFDL-CM2.1,MPI-ECHAM5,UKMO-HadGAM1,and MIROC3.2 (medres) perform well for CRF simulation in the Asian monsoon region,and the multi-model ensemble (MME) has improved results over the individual simulations. It is suggested that strengthening the physical parameterizations involved over the TP,and improving cumulus convection processes and model experiment design are crucial to CRF simulation in the Asian monsoon region.

  13. A composite study of onset of the Australian summer monsoon

    Science.gov (United States)

    Hendon, Harry H.; Liebmann, Brant

    1990-01-01

    The circulation changes that accompany an onset (defined as the first occurrence of wet 850-mb westerly winds at Darwin, Australia) of the Australian summer monsoon are documented by a composite study for the years 1957-1987. Composites of atmospheric fields at stations in and about the Australian tropics are constructed relative to the onset data at Darwin. It is shown that the composite onset is dominated by a slow eastward migration of a deep-baroclinic convective circulation displaced south of the equator. This propagating anomaly exhibited many features of the so-called 40-50 day oscillation, including an upper level anticyclone that accompanies the convective anomaly.

  14. Forcing mechanism of the Pleistocene east Asian monsoon variations in a phase perspective

    Institute of Scientific and Technical Information of China (English)

    TIAN; Jun; WANG; Pinxian; CHENG; Xinrong; WANG; Rujian; SU

    2005-01-01

    The deep sea records from the ODP Sites 1143 and 1144 in the northern and southern South China Sea (SCS), including foraminiferal δ18O and δ13C, Opal% and pollen percentage, reveal that the variations of the east Asian monsoon have been closely correlated with the variations of the Earth's orbital parameters (eccentricity, obliquity and precession) and the global ice volume on orbital scale. All the monsoonal proxies show strong 100 ka, 41 ka and 23 ka cycles. Although G. ruber δ13C of Site 1143 is coherent with the ETP (ETP= normalized (eccentricity + obliquity-precession) at eccentricity, obliquity and precession bands, most of the coherent relationship focuses on the precession band, and the other monsoonal proxies are coherent with the ETP only at the precession band, which indicate that precession dominates the Pleistocene tropical climate changes. The phase relationship of the monsoonal proxies with the foraminiferal δ18O implies that the global ice volume changes have played a significant role in modulating the east Asian monsoon climate, at least dominating the winter monsoon. This forcing mechanism of the east Asian monsoon is apparently different from that of the Indian ocean monsoon. The variations of the east Asian monsoon at the precession band, at least that of the winter monsoon, have been controlled not only by the sensible heating but also by the latent heating of the surface water in the South China Sea.

  15. Multi-year simulation of the East Asian Monsoon and Precipitation in China using a Regional Climate Model and Evaluation

    Institute of Scientific and Technical Information of China (English)

    LI Qiaoping; DING Yihui

    2005-01-01

    By using the regional climate model (RegCM_NCC), East Asian monsoon and precipitation over China during 1998 to 2002 are simulated. Results show that the model can well reproduce the seasonal patterns of mean circulation as well as the intensity and seasonal march of the East Asian monsoon. The simulated onset or retreat time of the West Pacific subtropical high, and the intensity and location of the South Asian high are consistent with the fact. The spatial distribution and transport of moisture in lower layer are also well simulated. The seasonal variations of regional rainfall and temperature are reproduced in the model, with three northward shift time and intensity of the rain belts over the sub-regions (such as Mid-Lower Yangtze basins and South China) well corresponding to the observation. However, the simulated summer monsoon is stronger compared with NCEP reanalysis fields, with the location of subtropical high being further north by 2-3 degrees than normal. Error evaluation shows that there is a discernible systematic bias in the simulated mean circulation pattern, with air temperature bias being positive over the land and negative over the ocean in the lower troposphere in summer. The systematic bias exaggerates the summer temperature difference between the land and ocean, which may be a main responsible factor for the stronger simulated summer monsoon, thus resulting in the overestimated rainfall in North China and it can not reflect well the abnormal rainfall distribution in these 5 years. The deficiency may be mainly contributed to the complex topography and cloud-radiation parameterization scheme. The analyses also indicate that it is difficult to simulate the persistent abnormal precipitation pattern over China. It is necessary to improve the model's capability further.

  16. Spatio-temporal Distribution of Latent Heating in the Southeast Asian Monsoon Region

    Science.gov (United States)

    Zuluaga, M. D.; Hoyos, C. D.; Webster, P. J.

    2007-12-01

    The Latent Heat (LH), released as a result of deep convection, plays an important role in the vertical distribution of the diabatic energy budget from the surface to the atmosphere: the motor which drives the global atmospheric circulation, including the Southeast Asian Monsoon. In particular, knowing the spatio-temporal structure of the LH during the wet monsoon season could be a key factor to understand the interaction between seasonal features of the monsoon with the summer manifestation of the intra-seasonal oscillation in the Indian Ocean basin, and hence the distribution of the precipitation. Several studies have investigated how the structure of heating in the tropics has a direct influence in the dynamical response of the atmosphere to the large-scale dynamical forcing associated with tropical precipitating systems. However, these studies assume a uniform geographically distribution of the vertical diabatic heating profiles across the Tropics. The major objective of this study is to produce and to examine three-dimensional latent heating structures over the Indian Monsoon region for the three summer seasons of 1998-2000 period using TRMM-2A12 (GPROF algorithm) and TRMM-CSH (CSH algorithm) data. A specific goal in this work is to explore the differences in the distribution of the latent heating throughout the intraseasonal cycle. This intra- seasonal cycle not only generates wet and dry spells over the South-East Asian continent but also determines the spatial distribution of the climatological JJAS rainfall in the Indian Monsoon Region. Results show spatial distribution differences between the LH profiles during the suppressed and active phases of the oscillation as well as differences in the vertical. During an active phase of the oscillation over the Indian Ocean, the released latent heat is concentrated predominantly near the equator while during the suppressed phased the heating is concentrated in the Bay of Bengal and the continental South East Asia

  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. Strengthened African summer monsoon in the mid-Piacenzian

    Science.gov (United States)

    Zhang, Ran; Zhang, Zhongshi; Jiang, Dabang; Yan, Qing; Zhou, Xin; Cheng, Zhigang

    2016-09-01

    Using model results from the first phase of the Pliocene Model Intercomparison Project (PlioMIP) and four experiments with CAM4, the intensified African summer monsoon (ASM) in the mid-Piacenzian and corresponding mechanisms are analyzed. The results from PlioMIP show that the ASM intensified and summer precipitation increased in North Africa during the mid-Piacenzian, which can be explained by the increased net energy in the atmospheric column above North Africa. Further experiments with CAM4 indicated that the combined changes in the mid-Piacenzian of atmospheric CO2 concentration and SST, as well as the vegetation change, could have substantially increased the net energy in the atmospheric column over North Africa and further intensified the ASM. The experiments also demonstrated that topography change had a weak effect. Overall, the combined changes of atmospheric CO2 concentration and SST were the most important factor that brought about the intensified ASM in the mid-Piacenzian.

  19. 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’.

  20. Precipitation variability over the South Asian monsoon heat low and associated teleconnections

    Science.gov (United States)

    Saeed, Sajjad; Müller, Wolfgang A.; Hagemann, Stefan; Jacob, Daniela; Mujumdar, M.; Krishnan, R.

    2011-04-01

    The present study examines the precipitation variability over the South Asian monsoon heat low region and associated teleconnections using high resolution (T106L31) climate simulations performed with the ECHAM5 model. It is found that an intensification of the heat low in response to enhanced precipitation/convection over northwestern India-Pakistan (NWIP) can induce large-scale circulation anomalies that resemble the northern summer circumglobal teleconnection (CGT) wave-like pattern extending well into the Asian monsoon region. Accordingly the wave-like response to rainfall increase over the heat low region is associated with anomalous ascent over northern China and descent over the South China Sea. Additionally, small but statistically significant lead-lag correlations between the heat low and precipitation over northern China further suggest that the detected signal pertains to the true features of the process. On the other hand, suppressed convection and rainfall over the heat low region do not reveal any significant large-scale circulation anomalies.

  1. Heterodynes dominate precipitation isotopes in the East Asian monsoon region, reflecting interaction of multiple climate factors

    Science.gov (United States)

    Thomas, Elizabeth K.; Clemens, Steven C.; Sun, Youbin; Prell, Warren L.; Huang, Yongsong; Gao, Li; Loomis, Shannon; Chen, Guangshan; Liu, Zhengyu

    2016-12-01

    For the past decade, East Asian monsoon history has been interpreted in the context of an exceptionally well-dated, high-resolution composite record of speleothem oxygen isotopes (δ18Ocave) from the Yangtze River Valley. This record is characterized by a unique spectral response, with variance concentrated predominantly within the precession band and an enigmatic lack of variance at the eccentricity and obliquity bands. Here we examine the spectral characteristics of all existing >250-kyr-long terrestrial water isotope records in Asia, including a new water isotope record using leaf wax hydrogen isotope ratios from the Chinese Loess Plateau. There exist profound differences in spectral characteristics among all orbital-scale Asian water isotope records. We demonstrate that these differences result from latitudinal gradients in the influence of the winter and summer monsoons, both of which impact climate and water isotopes throughout East Asia. Water isotope records therefore do not reflect precipitation during a single season or from a single circulation system. Rather, water isotope records in East Asia reflect the complex interplay of oceanic and continental moisture sources, operating at multiple Earth-orbital periods. These non-linear interactions are reflected in water isotope spectra by the presence of heterodynes. Although complex, we submit that water isotope records, when paired with rapidly developing isotope-enabled model simulations, will have the potential to elucidate mechanisms causing seasonal precipitation variability and moisture source variability in East Asia.

  2. Twenty-first century projected summer mean climate in the Mediterranean interpreted through the monsoon-desert mechanism

    Science.gov (United States)

    Cherchi, Annalisa; Annamalai, H.; Masina, Simona; Navarra, Antonio; Alessandri, Andrea

    2016-10-01

    The term "monsoon-desert mechanism" indicates the relationship between the diabatic heating associated with the South Asian summer monsoon rainfall and the remote response in the western sub-tropics where long Rossby waves anchor strong descent with high subsidence. In CMIP5 twenty-first century climate scenarios, the precipitation over South Asia is projected to increase. This study investigates how this change could affect the summer climate projections in the Mediterranean region. In a linear framework the monsoon-desert mechanism in the context of climate change would imply that the change in subsidence over the Mediterranean should be strongly linked with the changes in South Asian monsoon precipitation. The steady-state solution from a linear model forced with CMIP5 model projected precipitation change over South Asia shows a broad region of descent in the Mediterranean, while the results from CMIP5 projections differ having increased descent mostly in the western sector but also decreased descent in parts of the eastern sector. Local changes in circulation, particularly the meridional wind, promote cold air advection that anchors the descent but the barotropic Rossby wave nature of the wind anomalies consisting of alternating northerlies/southerlies favors alternating descent/ascent locations. In fact, the local mid-tropospheric meridional wind changes have the strongest correlation with the regions where the difference in subsidence is largest. There decreased rainfall is mostly balanced by changes in moisture, omega and in the horizontal advection of moisture.

  3. Asian Monsoon Variability from the Monsoon Asia Drought Atlas (MADA) and Links to Indo-Pacific Climate

    Science.gov (United States)

    Ummenhofer, Caroline; D'Arrigo, Rosanne; Anchukaitis, Kevin; Hernandez, Manuel; Buckley, Brendan; Cook, Edward

    2014-05-01

    Drought patterns across monsoon and temperate Asia over the period 1877-2005 are linked to Indo-Pacific climate variability associated with the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Using the Monsoon Asia Drought Atlas (MADA) composed of a high-resolution network of hydroclimatically sensitive tree-ring records with a focus on the June-August months, spatial drought patterns during El Niño and IOD events are assessed as to their agreement with an instrumental drought index and consistency in the drought response amongst ENSO/IOD events. Spatial characteristics in drought patterns are related to regional climate anomalies over the Indo-Pacific basin, using reanalysis products, including changes in the Asian monsoon systems, zonal Walker circulation, moisture fluxes, and precipitation. A weakening of the monsoon circulation over the Indian subcontinent and Southeast Asia during El Niño events, along with anomalous subsidence over monsoon Asia and reduced moisture flux, is reflected in anomalous drought conditions over India, Southeast Asia and Indonesia. When an IOD event co-occurs with an El Niño, severe drought conditions identified in the MADA for Southeast Asia, Indonesia, eastern China and central Asia are associated with a weakened South Asian monsoon, reduced moisture flux over China, and anomalous divergent flow and subsidence over Indonesia. Variations in the strength of the South Asian monsoon can also be linked to the Strange Parallels Drought (1756-1768) affecting much of Southeast Asia and the Indian subcontinent in the mid-18th Century. Large-scale climate anomalies across the wider region during years with an anomalously strengthened/weakened South Asian monsoon are discussed with implications for severe droughts prior to the instrumental period. Insights into the relative influences of Pacific and Indian Ocean variability for Asian monsoon climate on interannual to decadal and longer timescales, as recorded in the

  4. 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

  5. Cloud-radiation-precipitation associations over the Asian monsoon region: an observational analysis

    Science.gov (United States)

    Li, Jiandong; Wang, Wei-Chyung; Dong, Xiquan; Mao, Jiangyu

    2017-01-01

    This study uses 2001-2014 satellite observations and reanalyses to investigate the seasonal characteristics of Cloud Radiative Effects (CREs) and their associations with cloud fraction (CF) and precipitation over the Asian monsoon region (AMR) covering Eastern China (EC) and South Asia (SA). The CREs exhibit strong seasonal variations but show distinctly different relationships with CFs and precipitation over the two regions. For EC, the CREs is dominated by shortwave (SW) cooling, with an annual mean value of - 40 W m- 2 for net CRE, and peak in summer while the presence of extensive and opaque low-level clouds contributes to large Top-Of-Atmosphere (TOA) albedo (>0.5) in winter. For SA, a weak net CRE exists throughout the year due to in-phase compensation of SWCRE by longwave (LW) CRE associated with the frequent occurrence of high clouds. For the entire AMR, SWCRE strongly correlates with the dominant types of CFs, although the cloud vertical structure plays important role particularly in summer. The relationships between CREs and precipitation are stronger in SA than in EC, indicating the dominant effect of monsoon circulation in the former region. SWCRE over EC is only partly related to precipitation and shows distinctive regional variations. Further studies need to pay more attention to vertical distributions of cloud micro- and macro-physical properties, and associated precipitation systems over the AMR.

  6. 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.

  7. Observations of barrier layer formation in the Bay of Bengal during summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Vinayachandran, P.N.; Murty, V.S.N.; RameshBabu, V.

    monsoon, J. Geophys. Res., 107(C12), 8018, doi:10.1029/2001JC000831, 2002. 1. Introduction [2] Several monsoon lows and depressions, that contrib- ute substantially to the summer monsoon rainfall of the Indian subcontinent, form over the Bay of Bengal... August–September, 1990,Murtyetal.[1996]foundthatthemixedlayerbasedon a temperature criterion is deeper than that using density. The regionwithrelativelyfreshwaterwithhighSSTappearstobe an excellent breeding ground for the formation of monsoon depressions...

  8. Amplification of the solar signal in the summer monsoon rainband in China by synergistic actions of different dynamical responses

    Science.gov (United States)

    Zhao, Liang; Wang, Jingsong; Liu, Haiwen; Xiao, Ziniu

    2017-02-01

    A rainband meridional shift index (RMSI) is defined and used to statistically prove that the East Asian summer monsoon rainband is usually significantly more northward in the early summer of solar maximum years than that of solar minimum years. By applying continuous wavelet transform, cross wavelet transform, and wavelet coherence, it is found that throughout most of the 20th century, the significant decadal oscillations of sunspot number (SSN) and the RMSI are phase-locked and since the 1960s, the SSN has led the RMSI slightly by approximately 1.4 yr. Wind and Eliassen-Palm (EP) flux analysis shows that the decadal meridional oscillation of the June rainband likely results from both a stronger or earlier onset of the tropical monsoon and poleward shift of the subtropical westerly jet in high-solar months of May and June. The dynamical responses of the lower tropical monsoon and the upper subtropical westerly jet to the 11-yr solar cycle transmit bottom-up and top-down solar signals, respectively, and the synergistic actions between the monsoon and the jet likely amplify the solar signal at the northern boundary of the monsoon to some extent.

  9. Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

    Science.gov (United States)

    Miriyala, Pavan; Sukumaran, N. P.; Nath, B. Nagender; Ramamurty, P. B.; Sijinkumar, A. V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, Tyson

    2017-03-01

    Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change.

  10. Increased chemical weathering during the deglacial to mid-Holocene summer monsoon intensification

    Science.gov (United States)

    Miriyala, Pavan; Sukumaran, N. P.; Nath, B. Nagender; Ramamurty, P. B.; Sijinkumar, A. V.; Vijayagopal, B.; Ramaswamy, V.; Sebastian, Tyson

    2017-01-01

    Chemical weathering and the ensuing atmospheric carbon dioxide consumption has long been considered to work on geological time periods until recently when some modelling and natural records have shown that the weathering-related CO2 consumption can change at century to glacial-interglacial time scale. Last glacial to interglacial transition period is a best test case to understand the interplay between Pco2-temperature-chemical weathering when a pulse of rapid chemical weathering was initiated. Here we show, from a high resolution 54 ka record from the Andaman Sea in the northern Indian Ocean, that the chemical weathering responds to deglacial to mid-Holocene summer monsoon intensification in the Myanmar watersheds. The multi-proxy data (Al/K, CIA, Rb/Sr, 87Sr/86Sr for degree of weathering and 143Nd/144Nd for provenance) reveal an increase in silicate weathering with initiation of interglacial warm climate at ~17.7 ka followed by a major change at 15.5 ka. Inferred changes in chemical weathering have varied in tandem with the regional monsoonal proxies (δ18Osw-salinity changes of Northern Indian Ocean, effective Asian moisture content and δ18O records of Chinese caves) and are synchronous with changes in summer insolation at 30°N and δ18O of GISP2 implying that chemical weathering was not a later amplifier but worked in tandem with global climate change. PMID:28303943

  11. Model Projections of East Asian Summer Climate under the'Free Arctic'Scenario

    Institute of Scientific and Technical Information of China (English)

    WANG Hui-Jun; ZHANG Ying

    2010-01-01

    This paper addresses the'ice-free Arctic'issue under the future global warming scenario.Four coupled climate models used in the third phase of the Coupled Model Intercomparison Project(CMIP3)were selected to project summer climate conditions over East Asia once the Arctic becomes ice-free.The models project that an ice-free Arctic summer will begin in the 2060s under the SRESA I B(according to IPCC Special Reports on Emissions Scenarios)simulations.Our results show that the East Asian summer monsoons will tend to be stronger and that the water vapor transport to central northern China will be strengthened,leading to increased summer precipitation in central northern China.The models also project an intensified Antarctic Oscillation,a condition which favors increased precipitation in South China's Yangtze River Valley.The overall precipitation in Northwest China is projected to increase under ice-free Arctic summer conditions.

  12. 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.

  13. South American Summer Monsoon history recorded in Brazilian speleothems

    Science.gov (United States)

    Wang, X.; Auler, A. S.; Edwards, R. L.; Cheng, H.

    2008-12-01

    We have obtained three high-resolution oxygen isotopic records of cave calcites from Caverna Botuverá, southern Brazil, Gruta do Padre, central Brazil, and Caverna Paraíso, Amazonian Brazil. All three records have chronologies determined by U-Th dates and span the last 90, 20 and 50 thousand years, respectively. Tests for equilibrium conditions show that their oxygen isotopic variations are primarily caused by climate change. The three records thus can provide information about precipitation history and fluctuations of the South American Summer Monsoon along a latitudinal transect from 28° S to 4° S. During the last glacial period, the three oxygen isotopic profiles show abrupt millennial-scale variations, which are anti- correlated with the Chinese speleothem monsoon records and northern high-latitude ice core records. This is likely related to the displacement of the mean position of the intertropical convergence zone and associated asymmetry of Hadley cells, consistent with an oceanic meridional overturning circulation mechanism for driving the abrupt climate events. However, the three records show distinct isotopic patterns in Holocene epoch. The δ18O values in the Botuvera record decrease steadily throughout Holocene, while in the Padre record, the δ18O drops slightly until ~6-7 thousand years ago and then gradually increases until the present. The Paraiso Holocene record is similar to the Padre one, but with a much greater amplitude. Together with Andean ice core and lake records, our observations suggest asynchronous changes in Holocene monsoonal precipitation in South America, possibly related to strengthened zonal tropical air-sea interactions after the melting of the large northern ice sheets.

  14. Influence of Soil Moisture on the Asian and African Monsoons. Part II: Interannual Variability.

    Science.gov (United States)

    Douville, H.

    2002-04-01

    The relevance of soil moisture (SM) for simulating the interannual climate variability has not been much investigated until recently. Much more attention has been paid on SST anomalies, especially in the Tropics where the El Niño-Southern Oscillation represents the main mode of variability. In the present study, ensembles of atmospheric integrations based on the Action de Recherche Petit Echelle Grande Echelle (ARPEGE) climate model have been performed for two summer seasons: 1987 and 1988, respectively. The aim is to compare the relative impacts of using realistic boundary conditions of SST and SM on the simulated variability of the Asian and African monsoons. Besides control runs with interactive SM, sensitivity tests have been done in which SM is relaxed toward a state-of-the-art SM climatology, either globally or regionally over the monsoon domain. The simulations indicate that the variations of the Asian monsoon between 1987 and 1988 are mainly driven by SST anomalies. This result might be explained by the strong teleconnection with the ENSO and by a weak SM-precipitation feedback over south Asia (Part I of the study). The influence of SM is more obvious over Africa. The model needs both realistic SST and SM boundary conditions to simulate the observed variability of the Sahelian monsoon rainfall. The positive impact of the SM relaxation is not only due to a local mechanism whereby larger surface evaporation leads to larger precipitation. The best results are obtained when the relaxation is applied globally, suggesting that remote SM impacts also contribute to the improved simulation of the precipitation variability. A relationship between the Sahelian rainfall anomalies and the meridional wind anomalies over North Africa points out the possible influence of the Northern Hemisphere midlatitudes. The comparison of the low- and midtropospheric anomalies in the various pairs of experiments indicates that SM anomalies can trigger stationary waves over Europe, and

  15. 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.

  16. 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.

  17. 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

  18. 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.

  19. An Indian Ocean precursor for Indian summer monsoon rainfall variability

    Science.gov (United States)

    Sreejith, O. P.; Panickal, S.; Pai, S.; Rajeevan, M.

    2015-11-01

    The Indian summer monsoon rainfall (ISMR) depicts large interannual variability strongly linked with El Niño-Southern Oscillation (ENSO). However, many of the El Niño years were not accompanied by deficient ISMR. The results from the study reveal the significant role of coupled air-sea interaction over the tropical Indian Ocean (IO) in modifying the ENSO-ISMR association. The IO warm water volume (WWV), a measure of heat content variations in the equatorial IO has strong influence on ISMR. A deepening (shoaling) of thermocline in the eastern equatorial IO (EEIO) during late boreal spring (April-May) accompanied by increase (decrease) in WWV anomalies weaken (enhance) the ISMR by enhancing (suppressing) the convection over EEIO resulting in the below (above) normal ISMR. Thus, the changes in the WWV anomalies in the EEIO along with ENSO conditions during boreal spring can be considered as a precursor for the performance of subsequent ISMR.

  20. 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.

  1. Impacts of intraseasonal oscillation on the onset and interannual variation of the Indian summer monsoon

    Institute of Scientific and Technical Information of China (English)

    QI YanJun; ZHANG RenHe; LI Tim; WEN Min

    2009-01-01

    The role of the intraseasonal oscillation (ISO) on the seasonal and interannual variations of the Indian summer monsoon is investigated based on the analysis of observational data. It is shown that the ISO significantly contributes to the establishment of low-level westerlies during the monsoon onset and developing periods. The effect of the ISO on the annual cycle of the monsoon is through nonlinear eddy momentum transport. On the interannual timescale, the Indian summer monsoon rainfall exhibits a significant out-of-phase relationship with the ISO intensity over the Indian monsoon region. In strong ISO years it appears the weak monsoon when there is an abnormal high over the India subcontinent in the lower troposphere. In weak ISO years there exists an abnormal low and the strong monsoon ap-pears.

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

    Science.gov (United States)

    Bouarar, I.; Law, K. S.; Pham, M.; Liousse, C.; Schlager, H.; Hamburger, T.; Reeves, C. E.; Cammas, J.-P.; Nédéléc, P.; Szopa, S.; Ravegnani, F.; Viciani, S.; D'Amato, F.; Ulanovsky, A.; Richter, A.

    2011-12-01

    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 growth in Asian emissions compared to African emissions

  3. Recent Progresses in Impacts of Indo-Western Pacific Ocean on East Asian Monsoon

    Science.gov (United States)

    Li, Jianping

    2016-04-01

    Some progresses in impacts of Western Pacific Ocean (WPO) on East Asian monsoon and stratosphere climate are reviewed from the following aspects. (1) Impact of the IPOD (a cross-basin dipole pattern of SSTA variability between the Indo-Pacific warm pool (IPWP) and North Pacific Ocean) on the East Asian summer monsoon (EASM).The IPOD exhibits a considerable correlation with the EASM. In summers with a positive IPOD phase, the western Pacific subtropical high (WPSH) weakens and shrinks with WPSH ridge moving northwards, which favours an intensified EASM and a decrease in summer rainfall in the Yangtze River valley, and vice versa. (2) TheIndo-Western Pacific convection oscillation (IPCO),which is an out-of-phase fluctuation in convection anomalies between the north Indian Ocean and the western North Pacific region,is closely related to the EASM.Negative IPCO phases, which exhibit an enhanced convection over the north Indian Ocean and a suppressed convection over the western North Pacific, favor a weakened EASM and an increase of summer rainfall in the Yangtze River valley with the joint actions of the stronger than normal Ural and Okhotsk blocking highs and the subtropical western Pacific high, and vice versa.(3) Asymmetric influence of the two types of ENSO on summer rainfall in China. The two types of ENSO have asymmetric impacts on summer rainfall over the Yangtze River Valley. The relation between summer rainfall over this valley and the cold tongue (CT) El Niño is significantly positive, while the relation with the CT La Niña is not significant. The negative phase of the warm pool (WP) ENSO has a significant positive influence, whereas no significant relation with the positive phase. They indicated that this asymmetric response of the EASM is likely to be linked to the different spatial patterns of the two types of ENSO.(4) Linkage between recent winter precipitation increase in the middle-lower Yangtze River valley (MLY) since the late 1970s andwarming in the

  4. 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.

  5. The abrupt onset of the modern South Asian Monsoon winds

    Science.gov (United States)

    Betzler, Christian; Eberli, Gregor P.; Kroon, Dick; Wright, James D.; Swart, Peter K.; Nath, Bejugam Nagender; Alvarez-Zarikian, Carlos A.; Alonso-García, Montserrat; Bialik, Or M.; Blättler, Clara L.; Guo, Junhua Adam; Haffen, Sébastien; Horozal, Senay; Inoue, Mayuri; Jovane, Luigi; Lanci, Luca; Laya, Juan Carlos; Mee, Anna Ling Hui; Lüdmann, Thomas; Nakakuni, Masatoshi; Niino, Kaoru; Petruny, Loren M.; Pratiwi, Santi D.; Reijmer, John J. G.; Reolid, Jesús; Slagle, Angela L.; Sloss, Craig R.; Su, Xiang; Yao, Zhengquan; Young, Jeremy R.

    2016-07-01

    The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

  6. 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

  7. 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.

  8. Chemical isolation in the Asian monsoon anticyclone observed in Atmospheric Chemistry Experiment (ACE-FTS data

    Directory of Open Access Journals (Sweden)

    M. Park

    2008-02-01

    Full Text Available Evidence of chemical isolation in the Asian monsoon anticyclone is presented using chemical constituents obtained from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer instrument during summer (June–August of 2004–2006. Carbon monoxide (CO shows a broad maximum over the monsoon anticyclone region in the upper troposphere and lower stratosphere (UTLS; these enhanced CO values are associated with air pollution transported upward by convection, and confined by the strong anticyclonic circulation. Profiles inside the anticyclone show enhancement of tropospheric tracers CO, HCN, C2H6, and C2H2 between ~12 to 20 km, with maxima near 13–15 km. Strong correlations are observed among constituents, consistent with sources from near-surface pollution and biomass burning. Stratospheric tracers (O3, HNO3 and HCl exhibit decreased values inside the anticyclone between ~12–20 km. These observations are further evidence of transport of lower tropospheric air into the UTLS region, and isolation of air within the anticyclone. The relative enhancements of tropospheric species inside the anticyclone are closely related to the photochemical lifetime of the species, with strongest enhancement for shorter lived species. Vertical profiles of the ratio of C2H2/CO (used to measure the relative age of air suggest relatively rapid transport of fresh emissions up to the tropopause level inside the anticyclone.

  9. Chemical Isolation in the Asian monsoon anticyclone observed in Atmospheric Chemistry Experiment (ACE-FTS data

    Directory of Open Access Journals (Sweden)

    M. Park

    2007-09-01

    Full Text Available Evidence of chemical isolation in the Asian monsoon anticyclone is presented using chemical constituents obtained from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer instrument during summer (June–August of 2004–2006. Carbon monoxide (CO shows a broad maximum over the monsoon anticyclone region in the upper troposphere and lower stratosphere (UTLS; these enhanced CO values are associated with air pollution transported upward by convection, and confined by the strong anticyclonic circulation. Profiles inside the anticyclone show enhancement of tropospheric tracers CO, HCN, C2H6, and C2H2 between ~12 to 20 km, with maxima near 13–15 km. Strong correlations are observed among constituents, consistent with sources from near-surface pollution and biomass burning. Stratospheric tracers (O3, HNO3 and HCl exhibit decreased values inside the anticyclone between ~12–20 km. These observations are further evidence of transport of lower tropospheric air into the UTLS region, and isolation of air within the anticyclone. The relative enhancements of tropospheric species inside the anticyclone are closely related to the photochemical lifetime of the species, with strongest enhancement for shorter lived species. Vertical profiles of the ratio of C2H2/CO (used to measure the relative age of air suggest relatively rapid transport of fresh emissions up to tropopause level inside the anticyclone.

  10. A Possible Impact of Cooling over the Tibetan Plateau on the Mid-Holocene East Asian Monsoon Climate

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    By using a 9-level global atmospheric general circulation model developed at the Institute of Atmospheric Physics (IAP9L-AGCM) under the Chinese Academy of Sciences, the authors investigated the response of the East Asian monsoon climate to changes both in orbital forcing and the snow and glaciers over the Tibetan Plateau at the mid-Holocene, about 6000 calendar years before the present (6kyr BP). With the Earth's orbital parameters appropriate for the mid-Holocene, the IAP9L-AGCM computed warmer and wetter conditions in boreal summer than for the present day. Under the precondition of continental snow and glacier cover existing over part of the Tibetan Plateau at the mid-Holocene, the authors examined the regional climate response to the Tibetan Plateau cooling. The simulations indicated that climate changes in South Asia and parts of central Asia as well as in East Asia are sensitive to the Tibetan Plateau cooling at the mid-Holocene, showing a significant decrease in precipitation in northern India, northern China and southern Mongolia and an increase in Southeast Asia during boreal summer.The latter seems to correspond to the weakening, southeastward shift of the Asian summer monsoon system resulting from reduced heat contrast between the Eurasian continent and the Pacific and Indian Oceans when a cooling over the Tibetan Plateau was imposed. The simulation results suggest that the snow and glacier environment over the Tibetan Plateau is an important factor for mid-Holocene climate change in the areas highly influenced by the Asian monsoon.

  11. 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.

  12. A Study on Extremely Dry and Wet Summer Monsoon in Pakistan by Focusing on the Anomalous States of the Upper Troposphere

    Science.gov (United States)

    Ahmad, S.; Koike, T.; Nishii, K.

    2012-04-01

    Seasonally-changes in wind pattern, monsoon, sometimes results in severe droughts and intense flooding in many parts of the world including South Asian countries like Pakistan. The livelihood of a vast population in Pakistan depends on agriculture and land use is strongly influenced by water-based ecosystems that depend on the monsoon rains. Furthermore, climate change studies undertaken so far reveal that action is essential in order to prevent long term damage to water cycle and thus of great concern to the community and stakeholders. Pakistan Summer Monsoon (PSM) is generally affected by both the disturbances from the tropical and the extratropical regions; however there is lack of understanding of physical mechanisms of PSM compared to other regional studies i.e. Indian Summer Monsoon (ISM) and South-East Asian Monsoon (SEAM). In our study, we applied heat and vorticity budgets and wave train analysis to reveal the mechanisms of the extremely dry and wet PSM events associated with the anomalous upper tropospheric circulation. We found that the extremely dry (wet) PSM events are closely related with the strengthening(weakening) of the upper-tropospheric central Asian high. We also found that in addition to Rossby-wave (Matsuno-Gill) type atmospheric response, the Rossby wave train along the Asian Jet originating from northwestern Europe or North Atlantic Ocean strengthened(weakened) the upper-tropospheric central Asian high. Therefore strong convection anomalies resulting in severe flooding (drought) events over the PSM region are induced by both the tropical and extratropical processes. Key Words: Pakistan, Extremes Monsoon Events, Physical Processes, Heat Budget, Vorticity, Wave Train

  13. 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

    2017-01-01

    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

  14. 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

  15. Variations in swells along Eastern Arabian Sea during the summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Johnson, G.; SanilKumar, V.; Sanjiv, P.C.; Singh, J.; Pednekar, P.S.; AshokKumar, K.; Dora, G.U.; Gowthaman, R.

    Science, 2012, 2, 43-50 doi:10.4236/ojms.2012.22006 Published Online April 2012 (http://www.SciRP.org/journal/ojms) Variations in Swells along Eastern Arabian Sea during the Summer Monsoon Glejin Johnson, V. Sanil Kumar, Sajiv Philip Chempalayil, Jai... [2] and in shallow water location in the north Indian Ocean during the summer monsoon [3] were mainly swells ar- riving from south and south-west direction. The waves in the north Indian Ocean will be high dur- ing summer monsoon period (June...

  16. 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.

  17. Extratropical influences on the inter-annual variability of South-Asian monsoon

    Science.gov (United States)

    Syed, F. S.; Yoo, J. H.; Körnich, H.; Kucharski, F.

    2012-04-01

    The effects of extratropical dynamics on the interannual variations in South-Asian Monsoon (SAM) are examined. Based on NCEP/NCAR reanalysis and CRU precipitation data, a conditional maximum covariance analysis is performed on sea level pressure, 200 hPa geopotential heights and the SAM rainfall by removing the linear effects of El-Niño Southern Oscillation from the fields. It is found that two modes provide a strong connection between the upper-level circulation in the Atlantic/European region and SAM rainfall: the Circumglobal Teleconnection (CGT) and the Summer North Atlantic Oscillation (SNAO). The structures in the 200 hPa heights of both modes in the Atlantic region are similar in the Atlantic region, and their southeastward extension to South Asia (SA) also corresponds to upper-level ridges (in their positive phases) in slightly different positions. Nevertheless, the influence of both modes on SAM rainfall is distinct. Whereas a positive CGT is related to a widespread increase of rainfall in SAM, a positive SNAO is related to a precipitation dipole with its positive phase over Pakistan and the negative phase over northern India. The physical mechanisms for the influence of CGT and SNAO on SAM are related to the upper-level geopotential anomaly which affects the amplitude and position of the low-level convergence. The small displacements of the centers of these responses and the low level cold advection from the north east of SA in case of SNAO explain the differences in the corresponding SAM rainfall distributions. These findings are confirmed with the relatively high-resolution coupled climate model EC-Earth, which gives confidence in the physical basis and robustness of these extratropical variability modes and their influence on the South-Asian monsoon rainfall.

  18. 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.

  19. 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.

  20. Predictor-Year Subspace Clustering Based Ensemble Prediction of Indian Summer Monsoon

    Directory of Open Access Journals (Sweden)

    Moumita Saha

    2016-01-01

    Full Text Available Forecasting the Indian summer monsoon is a challenging task due to its complex and nonlinear behavior. A large number of global climatic variables with varying interaction patterns over years influence monsoon. Various statistical and neural prediction models have been proposed for forecasting monsoon, but many of them fail to capture variability over years. The skill of predictor variables of monsoon also evolves over time. In this article, we propose a joint-clustering of monsoon years and predictors for understanding and predicting the monsoon. This is achieved by subspace clustering algorithm. It groups the years based on prevailing global climatic condition using statistical clustering technique and subsequently for each such group it identifies significant climatic predictor variables which assist in better prediction. Prediction model is designed to frame individual cluster using random forest of regression tree. Prediction of aggregate and regional monsoon is attempted. Mean absolute error of 5.2% is obtained for forecasting aggregate Indian summer monsoon. Errors in predicting the regional monsoons are also comparable in comparison to the high variation of regional precipitation. Proposed joint-clustering based ensemble model is observed to be superior to existing monsoon prediction models and it also surpasses general nonclustering based prediction models.

  1. 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

  2. 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.

    The summer monsoon contributes to about 75 % of mean annual rainfall over the various meteorological subdivisions of India. The role of ocean–atmosphere phenomena such as Indian Ocean Dipole (IOD) and El Nino-Southern Oscillation (ENSO...

  3. 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...

  4. 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...

  5. Linkage between the second uplifting of the Qinghai-Xizang (Tibetan) Plateau and the initiation of the Asian monsoon system

    Institute of Scientific and Technical Information of China (English)

    施雅风; 汤懋苍; 马玉贞

    1999-01-01

    During the period from 25 to 17 Ma BP, when the second plateau uplifting, i.e. the second phase of the Himalaya movement, occurred, the Qinghai-Xizang Plateau reached an altitude high enough to change the situation of the general circulation. Such an effect of the plateau on the atmospheric circulation was accompanied by the warming of the tropical ocean, the enhancement of the cross equatorial current, the enlargement of the marginal sea basins in the cast-southeastern Asia, the westward extending of the Asian continent and the regression of the Paratethys Sea. As a result, the thermal difference was enlarged, and the air currents were enhanced between continents and oceans; finally the Asian monsoon system, mainly the summer monsoon, was initiated. The former planet wind system was then substituted by the monsoon system, and this caused the important environmental changes, such as the large shrinkage of the dry steppe in Central Asia, and the extension of the humid forest zone in East Asia. Those chan

  6. Natural and anthropogenic impacts on the Asian monsoon precipitation during the 20th century

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The increase in the global average temperature during the last century is considered an integrated result of anthropogenic and natural forcing, but different views remain about the anthropogenic impacts on the Asian monsoon precipitation. Based on the ~2000-year records of stalagmite δ18O from the Dongge Cave (Guizhou Province) and Wanxiang Cave (Gansu Province), we address the possible anthropogenic impacts on the southwest and southeast Asian monsoon from 1900-2000 AD, using the method of Singular Spectrum Analysis (SSA). The results show that the monsoon precipitation trends in the last 100 years at both sites can be obtained through SSA prediction using the data prior to 1900 AD. These suggest that human activity has not significantly affected the trends of monsoon precipitation despite of its impact on the global temperature.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Possible role of warm SST bias in the simulation of boreal summer monsoon in SINTEX-F2 coupled model

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, Susmitha; Sahai, A.K.; Goswami, B.N. [Indian Institute of Tropical Meteorology, Pune (India); Terray, Pascal; Masson, Sebastian [LOCEAN, Paris (France); Luo, J.J. [RIGC, Yokohama (Japan)

    2012-04-15

    Reasonably realistic climatology of atmospheric and oceanic parameters over the Asian monsoon region is a pre-requisite for models used for monsoon studies. The biases in representing these features lead to problems in representing the strength and variability of Indian summer monsoon (ISM). This study attempts to unravel the ability of a state-of-the-art coupled model, SINTEX-F2, in simulating these characteristics of ISM. The coupled model reproduces the precipitation and circulation climatology reasonably well. However, the mean ISM is weaker than observed, as evident from various monsoon indices. A wavenumber-frequency spectrum analysis reveals that the model intraseasonal oscillations are also weaker-than-observed. One possible reason for the weaker-than-observed ISM arises from the warm bias, over the tropical oceans, especially over the equatorial western Indian Ocean, inherent in the model. This warm bias is not only confined to the surface layers, but also extends through most of the troposphere. As a result of this warm bias, the coupled model has too weak meridional tropospheric temperature gradient to drive a realistic monsoon circulation. This in turn leads to a weakening of the moisture gradient as well as the vertical shear of easterlies required for sustained northward propagation of rain band, resulting in weak monsoon circulation. It is also noted that the recently documented interaction between the interannual and intraseasonal variabilities of ISM through very long breaks (VLBs) is poor in the model. This seems to be related to the inability of the model in simulating the eastward propagating Madden-Julian oscillation during VLBs. (orig.)

  12. Eurasian Snow Conditions and Summer Monsoon Rainfall over South and Southeast Asia:Assessment and Comparison

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    This study reveals the complex nature of the connection between Eurasian snow and the following summer season's monsoon rainfall by using four different indicators of snow conditions and correlating each of them to summer monsoon rainfall. Using 46 years of historical records of mean winter snow depth,maximum snow depth, and snow starting dates, and 27 years of snow area coverage from remote sensing observations over Eurasia, the authors found diverse correlation patterns between snow conditions and the following warm season's rainfall over South and Southeast Asia. Some of the results contradict the well-known inverse relationships between snow and the summer monsoon. This study provides an easy comparison of results in that it shows the connections between Eurasian snow and monsoon rainfall by using different Eurasian snow indicators based on the best available historical records without discrimination of regional variations in snow conditions.

  13. Shifting covariability of North American summer monsoon precipitation with antecedent winter precipitation

    Science.gov (United States)

    McCabe, G.J.; Clark, M.P.

    2006-01-01

    Previous research has suggested that a general inverse relation exists between winter precipitation in the southwestern United states (US) and summer monsoon precipitation. In addition, it has been suggested that this inverse relation between winter precipitation and the magnitude of the southwestern US monsoon breaks down under certain climatic conditions that override the regional winter/monsoon precipitation relations. Results from this new study indicate that the winter/monsoon precipitation relations do not break down, but rather shift location through time. The strength of winter/monsoon precipitation relations, as indexed by 20-year moving correlations between winter precipitation and monsoon precipitation, decreased in Arizona after about 1970, but increased in New Mexico. The changes in these correlations appear to be related to an eastward shift in the location of monsoon precipitation in the southwestern US. This eastward shift in monsoon precipitation and the changes in correlations with winter precipitation also appear to be related to an eastward shift in July/August atmospheric circulation over the southwestern US that resulted in increased monsoon precipitation in New Mexico. Results also indicate that decreases in sea-surface temperatures (SSTs) in the central North Pacific Ocean also may be associated with th changes in correlations between winter and monsoon precipitation. Copyright ?? 2006 Royal Meteorological Society.

  14. 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.

  15. 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

  16. Long-term trend and abrupt events of the Holocene Asian monsoon inferred from a stalagmite δ18O record from Shennongjia in Central China

    Institute of Scientific and Technical Information of China (English)

    SHAO Xiaohua; WANG Yongjin; CHENG Hai; KONG Xinggong; WU Jiangying; EDWARDS R. Lawrence

    2006-01-01

    A high-resolution oxygen-isotope record from a thorium-uranium-dated stalagmite from Shanbao Cave at Shennongjia reflects variations in the amount of monsoon precipitation for the period from 11.5 to 2.1 ka (1 ka = 1000 cal aBP). Between 11.5 and 9.3 ka, a sharp decrease in δ18O indicates a rapid increase in monsoon precipitation. An interval of generally high monsoon precipitation is observed between 9.3 and 4.4 ka. An arid period has prevailed between 4.4 and 2.1 ka. The long-term trend of Shanbao record appears to follow summer insolation at 33°N latitude. An abrupt decrease in monsoon precipitation around 4.3 ka is synchronous with the collapse of Neolithic culture in central China. This abrupt change could have resulted from the amplification of the gradually decreased summer insolation by the positive vegetation-atmosphere-aerosol feedback. The weakened Asian monsoon events were in concert with decreased Greenland temperature during the early Holocene, centered at 8.2, 8.6, 9.3, 10.2 and 11.0 ka. This correlation suggests that changes in low-latitude monsoon are connected with climate change in high-latitude polar region.

  17. 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

  18. Bifurcations in a Nonlinear Dynamical Model between Western Pacific Subtropical High Ridge Line Index and Its Summer Monsoon Impact Factors

    Directory of Open Access Journals (Sweden)

    Mei Hong

    2014-01-01

    Full Text Available The western Pacific subtropical high (WPSH is closely related to Asian climate. Previous studies have shown that a precise dynamical model focusing on the interaction between WPSH and other summer monsoon factors has not been developed. Based on the concept of dynamical model reconstruction, this paper reconstructs a nonlinear dynamical model of subtropical high ridge line (SHRL and summer monsoon factors from recent 20 years data. Then, using genetic algorithm (GA, model inversion and model parameter optimization are carried out. Based on the reconstructed dynamical model, dynamical characteristics of SHRL are analyzed and an aberrance mechanism is developed, in which the external forcings resulting in the WPSH anomalies are explored. Results show that the configuration and diversification of the SHRL equilibriums have better represented the abnormal activities of the SHRL in short and medium term. Change of SHRL brought by the combination of equilibriums is more complex than that brought by mutation. The mutation behavior from high-value to low-value equilibriums of the SHRL in summer corresponds with the southward drop of the SHRL. The combination behavior of the two steady equilibriums corresponds with disappearance of the “double-ridge” phenomenon of WPSH. Dynamical mechanisms of these phenomena are explained.

  19. Low-Frequency Vortex Pair over the Tropical Eastern Indian Ocean and the South China Sea Summer Monsoon Onset

    Institute of Scientific and Technical Information of China (English)

    PAN Jing; LI Chong-Yin

    2011-01-01

    In this paper, the relationship between a pair of low-frequency vortexes over the equatorial Indian Ocean and the South China Sea (SCS) summer monsoon onset is studied based on a multi-year (1980-2003) analysis. A pair of vortexes symmetric about the equator is an important feature prior to the SCS summer monsoon onset. A composite analysis shows that the life cycle of the pair of vortexes is closely associated with the SCS summer monsoon onset. The westerly between the twin cyclones is an important factor to the SCS summer monsoon onset process.

  20. 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.

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

    Science.gov (United States)

    Mölg, T.; Maussion, F.; Yang, W.; Scherer, D.

    2012-12-01

    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, once the monsoon is in full swing, regional atmospheric variability prevails on the Tibetan Plateau in summer.

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

    Directory of Open Access Journals (Sweden)

    T. Mölg

    2012-08-01

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

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

    Directory of Open Access Journals (Sweden)

    T. Mölg

    2012-12-01

    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, once the monsoon is in full swing, regional atmospheric variability prevails on the Tibetan Plateau in summer.

  4. Observations of PAN and its confinement in the Asian Monsoon Anticyclone in high spatial resolution

    Science.gov (United States)

    Ungermann, Joern; Ploeger, Felix; Spang, Reinhold; Riese, Martin

    2016-04-01

    This talk presents a set of observations by the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) infrared limb sounder on the SPAS platform in low-earth orbit. The spatially highly resolved trace gas measurements of six days in August 1997 allow a close look on the confinement of air masses within the Asian Summer Monsoon (ASM) anticyclone. Peroxyacetyl nitrate (PAN) is a secondary pollutant without sources in the stratosphere and acts as a tropospheric tracer. In combination with ozone as a stratospheric tracer, an eddy-shedding event of the ASM could be observed. The measured PAN volume mixing ratios (VMR) correlate well with potential vorticity (PV) derived from ECMWF ERA-Interim model data. Computing the gradient of PAN over PV on isentropes reveals that PAN VMR exhibit the strongest decrease at each isentrope for an increasing value of PV, which may be used to identify the extent of the ASM on that isentrope. CRISTA measurements also provide the temperature of measured air parcels and thus allow to derive the location of the thermal tropopause. We find that the thermal tropopause coincides with the border of the positive PAN anomaly both horizontally and vertically within the ASM anticyclone. In contrast, the shed eddy exhibits enhanced PAN VMRs for 1 to 2 km above the thermal tropopause. The amount of mixing may also be characterised by projecting the derived air parcels into tracer-tracer space using PAN and ozone as tropospheric and stratospheric tracer, respectively. This reveals that the anticyclone contains few mixed parcels in contrast to the region between the anticyclone and the shed eddy. 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 time scale of only a few days.

  5. 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

  6. Examining Impact of Global warming on the summer monsoon system using regional Climate Model (PRECIS)

    Science.gov (United States)

    Patwardhan, S. K.; Kundeti, K.; Krishna Kumar, K.

    2011-12-01

    Every year, southwest monsoon arrives over Indian region with remarkable regularity. It hits the southern state of Kerala first by the end of May or the early June. More than 70% of the annual precipitation is received during the four monsoon months viz. June to September. This monsoon rainfall is vital for the agriculture as well as for the yearly needs of Indian population. The performance of the monsoon depends on the timely onset over southern tip of India and its progress along the entire country. This northward progression of monsoon to cover the entire Indian landmass, many times, is associated with the formation of synoptic scale system in the Bay of Bengal region and their movement along the monsoon trough region. The analysis of the observed cyclonic disturbances show that their frequency has reduced in recent decades. It is, therefore, necessary to assess the effect of global warming on the monsoon climate of India. A state-of-art regional climate modelling system, known as PRECIS (Providing REgional Climates for Impacts Studies) developed by the Hadley Centre for Climate Prediction and Research, U.K. is applied over the South Asian domain to investigate the impact of global warming on the cyclonic disturbances. The PRECIS simulations at 50 km x 50 km horizontal resolution are made for two time slices, present (1961-1990) and the future (2071-2100), for two socio-economic scenarios A2 and B2. The model skills are evaluated using observed precipitation and surface air temperature. The model has shown reasonably good skill in simulating seasonal monsoon rainfall, whereas cold bias is seen in surface air temperature especially in post-monsoon months. The typical monsoon features like monsoon trough, precipitation maxima over west coast and northeast India are well simulated by the model. The model simulations under the scenarios of increasing greenhouse gas concentrations and sulphate aerosols are analysed to study the likely changes in the quasi

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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...

  12. 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.

  13. Mechanism of ENSO influence on the South Asian monsoon rainfall in global model simulations

    Science.gov (United States)

    Joshi, Sneh; Kar, Sarat C.

    2017-02-01

    Coupled ocean atmosphere global climate models are increasingly being used for seasonal scale simulation of the South Asian monsoon. In these models, sea surface temperatures (SSTs) evolve as coupled air-sea interaction process. However, sensitivity experiments with various SST forcing can only be done in an atmosphere-only model. In this study, the Global Forecast System (GFS) model at T126 horizontal resolution has been used to examine the mechanism of El Niño-Southern Oscillation (ENSO) forcing on the monsoon circulation and rainfall. The model has been integrated (ensemble) with observed, climatological and ENSO SST forcing to document the mechanism on how the South Asian monsoon responds to basin-wide SST variations in the Indian and Pacific Oceans. The model simulations indicate that the internal variability gets modulated by the SSTs with warming in the Pacific enhancing the ensemble spread over the monsoon region as compared to cooling conditions. Anomalous easterly wind anomalies cover the Indian region both at 850 and 200 hPa levels during El Niño years. The locations and intensity of Walker and Hadley circulations are altered due to ENSO SST forcing. These lead to reduction of monsoon rainfall over most parts of India during El Niño events compared to La Niña conditions. However, internally generated variability is a major source of uncertainty in the model-simulated climate.

  14. Potential modulations of pre-monsoon aerosols during El Niño: impact on Indian summer monsoon

    Science.gov (United States)

    Fadnavis, S.; Roy, Chaitri; Sabin, T. P.; Ayantika, D. C.; Ashok, K.

    2016-11-01

    The potential role of aerosol loading on the Indian summer monsoon rainfall during the El Niño years are examined using satellite-derived observations and a state of the art fully interactive aerosol-chemistry-climate model. The Aerosol Index (AI) from TOMS (1978-2005) and Aerosol Optical Depth (AOD) from MISR spectroradiometer (2000-2010) indicate a higher-than-normal aerosol loading over the Indo-Gangetic plain (IGP) during the pre-monsoon season with a concurrent El Niño. Sensitivity experiments using ECHAM5-HAMMOZ climate model suggests that this enhanced loading of pre-monsoon absorbing aerosols over the Indo-Gangetic plain can reduce the drought during El Niño years by invoking the `Elevated-Heat-Pump' mechanism through an anomalous aerosol-induced warm core in the atmospheric column. This anomalous heating upshot the relative strengthening of the cross-equatorial moisture inflow associated with the monsoon and eventually reduces the severity of drought during El Niño years. The findings are subject to the usual limitations such as the uncertainties in observations, and limited number of El Niño years (during the study period).

  15. Role of the tropical Pacific Ocean in strengthening the East Asian Monsoon: Climate model study of MIS-13

    Science.gov (United States)

    Karami, M.; Herold, N.; Yin, Q.; Berger, A.

    2012-12-01

    Studying past climates is a valuable approach to improve our understanding of the present and future climate systems. Among the significant events in the history of climate, the interglacial periods are good candidates for representation of the future climate because of their astronomical characteristics and their similarity to predicted anthropogenic warming. Moreover, some interglacials exhibited significant changes in atmospheric and oceanic properties due to only small changes in their climatic forcing (greenhouse gases and solar insolation) which also make them a good case for investigating past climates. For instance, the interglacial stage of around 0.5 Ma identified as Marine Isotopic stage 13 (MIS-13), the focus of this study, was characterized by extremely strong East Asian and Indian summer monsoons while the CO2 and CH4 levels were lower and seasonal radiation energy could reach up to 50 Wm-2 higher than today. The extreme monsoon precipitation is quite unexpected for a climate with such forcing. To understand the physics-based mechanism that enhances the East Asian Summer Monsoon (EASM) during MIS-13, we used two fully coupled general circulation models, the HadCM3 and CCSM3. In MIS-13 experiments, concentrations of greenhouse gases were prescribed lower than in pre-industrial and seasonal insolation characterised by Northern-Hemisphere (NH) summer occurring at perihelion instead of aphelion as it does today. Results of both models confirm increased summer precipitation in the monsoon regions. We find that the tropical Pacific Ocean plays a major role in strengthening the EASM in MIS-13. Simulations of MIS-13 show stronger easterly surface winds along the equatorial Pacific and a subsequent increase in the mean thermocline tilt, in addition to a westward shift of the cold tongue. These changes alter the background climatic state of the equatorial Pacific towards a La Niña-type state. The interannual variability around the La Niña-like background

  16. 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.

  17. Circumglobal wave train and the summer monsoon over South Asia: The explicit role of the surface heat low

    Science.gov (United States)

    Saeed, Sajjad; Müller, Wolfgang A.; Hagemann, Stefan; Jacob, Daniela

    2010-05-01

    This study examines the influence of mid-latitude circulation on the surface heat low and associated monsoon rainfall over South Asia using the ERA40 data. A heat low index is defined to depict the surface heat low which forms over Pakistan and adjoining areas of India, Iran and Afghanistan during the summer season. The heat low divulges significant correlations with the upper level 200 hPa geopotential height anomalies over western central Asia and East Asian region and acts as a bridge connecting the mid-latitude wave train to the Indian summer monsoon. During the positive phase of the mid-latitude circumglobal wave train, anomalous upper level high pressure develops over western central Asia. The subsidence associated with the anomalous high reduces the surface pressure in the heat low by raising the mean air temperature and anomalous uplift in the middle and lower troposphere. The increasing middle tropospheric temperature creates an inversion between the lower and upper troposphere which consequently restricts the middle and low level cloud formation above the heat low. Further, the upper level subsidence also minimizes the high cloud cover above the heat low region and hence favors more solar radiation to this area. The accruing surface heating reduces the surface pressure, resulting in further intensification of the heat low and associated monsoon circulation. Moreover, the westward accruing surface air temperature shifts the anomalous core of the heat low to the West over Iran. The westward shift in the anomalous core of the intensified heat low 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, where convective heating and orographic lifting expedites the convection and hence the precipitation. Composite analysis reveals a dipole teleconnection pattern

  18. Impacts of the East Asian Monsoon on springtime dust concentrations over China: IMPACTS OF MONSOON ON DUST

    Energy Technology Data Exchange (ETDEWEB)

    Lou, Sijia [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Now at Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland Washington USA; Russell, Lynn M. [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Yang, Yang [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Now at Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland Washington USA; Xu, Li [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Lamjiri, Maryam A. [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; DeFlorio, Michael J. [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Miller, Arthur J. [Scripps Institution of Oceanography, University of California, San Diego, La Jolla California USA; Ghan, Steven J. [Now at Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland Washington USA; Liu, Ying [Now at Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland Washington USA; Singh, Balwinder [Now at Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland Washington USA

    2016-07-12

    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, MAMdust 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 3Wm2 at the surface, compared to 2.4 and +1.2Wm2 at the top of the atmosphere over eastern and western China, respectively.

  19. Reduction of uncertainty associated with future changes in Indian summer monsoon projected by climate models and assessment of monsoon teleconnections

    Science.gov (United States)

    Rajendran, Kavirajan; Surendran, Sajani; Kitoh, Akio; Varghese, Stella Jes

    2016-05-01

    Coupled Model Intercomparison Project phase 5 (CMIP5) coupled global climate model (CGCM) Representative Concentration Pathway (RCP) simulations project clear future temperature increase but diverse changes in Indian summer monsoon rainfall (ISMR) with substantial inter-model spread. Robust signals of projected changes are derived based on objective criteria and the physically consistent simulations with the highest reliability suggest future reduction in the frequency of light rainfall but increase in high to extreme rainfall. The role of equatorial Indian and Pacific Oceans on the projected changes in monsoon rainfall is investigated. The results of coupled model projections are also compared with the corresponding projections from high resolution AGCM time-slice, multi-physics and multi-forcing ensemble experiments.

  20. 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 Zuhui

    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.

  1. Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October-December) season

    Science.gov (United States)

    Sadhuram, Y.; Maneesha, K.

    2016-09-01

    In this study, an attempt has been made to examine the relationship between summer monsoon rainfall (June-September) and the total number of depressions, cyclones and severe cyclones (TNDC) over Bay of Bengal during the post-monsoon (October-December) season. The seasonal rainfall of the subdivisions (located in south India) (referred as rainfall index - RI), is positively and significantly correlated (r=0.59; significant at >99% level) with the TNDC during the period, 1984-2013. By using the first differences (current season minus previous season), the correlations are enhanced and a remarkably high correlation of 0.87 is observed between TNDC and RI for the recent period, 1993-2013. The average seasonal genesis potential parameter (GPP) showed a very high correlation of 0.84 with the TNDC. A very high correlation of 0.83 is observed between GPP and RI for the period, 1993-2013. The relative vorticity and mid-tropospheric relative humidity are found to be the dominant terms in GPP. The GPP was 3.5 times higher in above (below) normal RI in which TNDC was 4 (2). It is inferred that RI is playing a key role in TNDC by modulating the environmental conditions (low level vorticity and relative humidity) over Bay of Bengal during post-monsoon season which could be seen from the very high correlation of 0.87 (which explains 76% variability in TNDC). For the first time, we show that RI is a precursor for the TNDC over Bay of Bengal during post-monsoon season. Strong westerlies after the SW monsoon season transport moisture over the subdivisions towards Bay of Bengal due to cyclonic circulation. This circulation favours upward motion and hence transport moisture vertically to mid-troposphere which causes convective instability and this in turn favour more number of TNDC, under above-normal RI year.

  2. Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October–December) season

    Indian Academy of Sciences (India)

    Y Sadhuram; K Maneesha

    2016-10-01

    In this study, an attempt has been made to examine the relationship between summer monsoon rainfall (June–September) and the total number of depressions, cyclones and severe cyclones (TNDC) over Bay of Bengal during the post-monsoon (October–December) season. The seasonal rainfall of the subdivisions (located in south India) (referred as rainfall index – RI), is positively and significantly correlated(r = 0.59; significant at >99% level) with the TNDC during the period, 1984–2013. By using the first differences (current season minus previous season), the correlations are enhanced and a remarkably high correlation of 0.87 is observed between TNDC and RI for the recent period, 1993–2013. The average seasonalgenesis potential parameter (GPP) showed a very high correlation of 0.84 with the TNDC. A very high correlation of 0.83 is observed between GPP and RI for the period, 1993–2013. The relative vorticity and mid-tropospheric relative humidity are found to be the dominant terms in GPP. The GPP was 3.5 times higher in above (below) normal RI in which TNDC was 4 (2). It is inferred that RI is playing a keyrole in TNDC by modulating the environmental conditions (low level vorticity and relative humidity) over Bay of Bengal during post-monsoon season which could be seen from the very high correlation of 0.87 (which explains 76% variability in TNDC). For the first time, we show that RI is a precursor for the TNDC over Bay of Bengal during post-monsoon season. Strong westerlies after the SW monsoon seasontransport moisture over the subdivisions towards Bay of Bengal due to cyclonic circulation. This circulation favours upward motion and hence transport moisture vertically to mid-troposphere which causes convective instability and this in turn favour more number of TNDC, under above-normal RI year.

  3. Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October-December) season

    Science.gov (United States)

    Sadhuram, Y.; Maneesha, K.

    2016-10-01

    In this study, an attempt has been made to examine the relationship between summer monsoon rainfall (June-September) and the total number of depressions, cyclones and severe cyclones (TNDC) over Bay of Bengal during the post-monsoon (October-December) season. The seasonal rainfall of the subdivisions (located in south India) (referred as rainfall index - RI), is positively and significantly correlated ( r=0.59; significant at >99% level) with the TNDC during the period, 1984-2013. By using the first differences (current season minus previous season), the correlations are enhanced and a remarkably high correlation of 0.87 is observed between TNDC and RI for the recent period, 1993-2013. The average seasonal genesis potential parameter (GPP) showed a very high correlation of 0.84 with the TNDC. A very high correlation of 0.83 is observed between GPP and RI for the period, 1993-2013. The relative vorticity and mid-tropospheric relative humidity are found to be the dominant terms in GPP. The GPP was 3.5 times higher in above (below) normal RI in which TNDC was 4 (2). It is inferred that RI is playing a key role in TNDC by modulating the environmental conditions (low level vorticity and relative humidity) over Bay of Bengal during post-monsoon season which could be seen from the very high correlation of 0.87 (which explains 76% variability in TNDC). For the first time, we show that RI is a precursor for the TNDC over Bay of Bengal during post-monsoon season. Strong westerlies after the SW monsoon season transport moisture over the subdivisions towards Bay of Bengal due to cyclonic circulation. This circulation favours upward motion and hence transport moisture vertically to mid-troposphere which causes convective instability and this in turn favour more number of TNDC, under above-normal RI year.

  4. Mid-Pleistocene vermiculated red soils in southern China as an indication of unusually strengthened East Asian monsoon

    Institute of Scientific and Technical Information of China (English)

    YIN Qiuzhen; GUO Zhengtang

    2006-01-01

    The mid-Pleistocene vermiculated red soils (VRS) from Xuancheng (Anhui Province) and Bose (Guangxi) are studied through soil micromorphological, mineralogical and chemical approaches. The results indicate a polygenetic nature of the VRS, having experienced multiple soil-forming stages. Three main stages have been recognized, attributable to distinct climate regimes. They include the formation of the homogeneous matrix of a red soil (stage 1), development of the white veins within the soil profile (stage 2), and formation of juxtaposed textural features (stage 3). The white veins, resulting from iron-depletion in the groundmass of the homogeneous matrix of a red soil, required abundant rainfall without significant seasonal desiccations. The geographically widely spread VRS south of the Yangtze River in China implies a Mid-Pleistocene extreme East Asian summer monsoon. This climate extreme might be closely linked with the changes in the strength of NADW.

  5. The link between Tibetan Plateau monsoon and Indian summer precipitation: a linear diagnostic perspective

    Science.gov (United States)

    Ge, Fei; Sielmann, Frank; Zhu, Xiuhua; Fraedrich, Klaus; Zhi, Xiefei; Peng, Ting; Wang, Lei

    2017-03-01

    The thermal forcing of the Tibetan Plateau (TP) is analyzed to investigate the formation and variability of Tibetan Plateau Summer Monsoon (TPSM), which affects the climates of the surrounding regions, in particular the Indian summer monsoon precipitation. Dynamic composites and statistical analyses indicate that the Indian summer monsoon precipitation is less/greater than normal during the strong/weak TPSM. Strong (weak) TPSM is associated with an anomalous near surface cyclone (anticyclone) over the western part of the Tibetan Plateau, enhancing (reducing) the westerly flow along its southern flank, suppressing (favoring) the meridional flow of warm and moist air from the Indian ocean and thus cutting (providing) moisture supply for the northern part of India and its monsoonal rainfall. These results are complemented by a dynamic and thermodynamic analysis: (i) A linear thermal vorticity forcing primarily describes the influence of the asymmetric heating of TP generating an anomalous stationary wave flux. Composite analysis of anomalous stationary wave flux activity (after Plumb in J Atmos Sci 42:217-229, 1985) strongly indicate that non-orographic effects (diabatic heating and/or interaction with transient eddies) of the Tibetan Plateau contribute to the generation of an anomalous cyclone (anti-cyclone) over the western TP. (ii) Anomalous TPSM generation shows that strong TPSM years are related to the positive surface sensible heating anomalies over the eastern TP favoring the strong diabatic heating in summer. While negative TPSM years are associated with the atmospheric circulation anomalies during the preceding spring, enhancing northerly dry-cold air intrusions into TP, which may weaken the condensational heat release in the middle and upper troposphere, leading to a weaker than normal summer monsoon over the TP in summer.

  6. Paleoclimate and Asian monsoon variability inferred from n-alkanes and their stable isotopes at lake Donggi Cona, NE Tibetan Plateau

    Science.gov (United States)

    Saini, Jeetendra; Guenther, Franziska; Mäusbacher, Roland; Gleixner, Gerd

    2015-04-01

    The Tibetan Plateau is one of the most extensive and sensitive region of elevated topography affecting global climate. The interplay between the Asian summer monsoon and the westerlies greatly influences the lake systems at the Tibetan Plateau. Despite a considerable number of research efforts in last decade, possible environmental reactions to change in monsoon dynamics are still not well understood. Here we present results from a sediment core of lake Donggi Cona, which dates back to late glacial period. Distinct organic geochemical proxies and stable isotopes are used to study the paleoenvironmental and hydrological changes in late glacial and Holocene period. Sedimentary n-alkanes of lake Donggi Cona are used as a proxy for paleoclimatic and monsoonal reconstruction. The hydrogen (δD) and carbon (δ13C) isotopes of n-alkanes are used as proxy for hydrological and phytoplankton productivity, respectively . Qualitative and quantitative analysis were performed for n-alkanes over the sediment core. δD proxy for sedimentary n-alkanes is used to infer lake water and rainfall signal. δD of (n-alkane C23) records the signal of the lake water, whereas δD of (n-alkane C29) record the precipitation signal, hence act as an appropriate proxy to track Asian monsoon. Long chain n-alkanes dominate over the sediment core while unsaturated mid chain n-alkenes have high abundance in some samples. From 18.4-13.8 cal ka BP, sample shows low organic productivity due to cold and arid climate. After 13.8-11.8 cal ka BP, slight increase in phytoplankton productivity indicate onset of weaker monsoon. From 11.8-6.8 cal ka BP, high content of organic matter indicates rise in productivity and strong monsoon with high inflow. After 6.8 cal ka BP, decrease in phytoplankton productivity indicating cooler climate and show terrestrial signal. Our results provide new insight into the variability of east Asian monsoon and changes in phytoplankton productivity for last 18.4 ka. Keywords: n

  7. 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...

  8. 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...

  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.

    Waves at 15 m water depth in the northern Arabian Sea are measured during the summer monsoon for a period of 45 days and the characteristics are described. The significant wave height varied from 1.1 to 4.5 m with an average value of 2.5m. 75...

  10. Why is the Bay of Bengal less productive during summer monsoon compared to the Arabian Sea?

    Digital Repository Service at National Institute of Oceanography (India)

    PrasannaKumar, S; Muraleedharan, P.M.; Prasad; Gauns, M.; Ramaiah, N.; DeSouza, S; Sardessai, S; Madhupratap, M.

    The Bay of Bengal is traditionally considered to be a less productive basin compared to the Arabian Sea. We explore the reasons for this in the central Bay during summer when both are subjected to strong monsoon forcing. Copious rainfall and river...

  11. Model Interpretation of Climate Signals: Application to the Asian Monsoon Climate

    Science.gov (United States)

    Lau, William K. M.

    2002-01-01

    This is an invited review paper intended to be published as a Chapter in a book entitled "The Global Climate System: Patterns, Processes and Teleconnections" Cambridge University Press. The author begins with an introduction followed by a primer of climate models, including a description of various modeling strategies and methodologies used for climate diagnostics and predictability studies. Results from the CLIVAR Monsoon Model Intercomparison Project (MMIP) were used to illustrate the application of the strategies to modeling the Asian monsoon. It is shown that state-of-the art atmospheric GCMs have reasonable capability in simulating the seasonal mean large scale monsoon circulation, and response to El Nino. However, most models fail to capture the climatological as well as interannual anomalies of regional scale features of the Asian monsoon. These include in general over-estimating the intensity and/or misplacing the locations of the monsoon convection over the Bay of Bengal, and the zones of heavy rainfall near steep topography of the Indian subcontinent, Indonesia, and Indo-China and the Philippines. The intensity of convection in the equatorial Indian Ocean is generally weaker in models compared to observations. Most important, an endemic problem in all models is the weakness and the lack of definition of the Mei-yu rainbelt of the East Asia, in particular the part of the Mei-yu rainbelt over the East China Sea and southern Japan are under-represented. All models seem to possess certain amount of intraseasonal variability, but the monsoon transitions, such as the onset and breaks are less defined compared with the observed. Evidences are provided that a better simulation of the annual cycle and intraseasonal variability is a pre-requisite for better simulation and better prediction of interannual anomalies.

  12. Investigation of the "Elevated Heat Pump" hypothesis of the Asian monsoon using satellite observations

    OpenAIRE

    M. M. Wonsick; Pinker, R.T.; Ma, Y.

    2013-01-01

    In recent years, the "Elevated Heat Pump" (EHP) hypothesis has been a topic of intensive research and controversy. It postulates that aerosol-induced anomalous mid- and upper-tropospheric warming above the Tibetan Plateau leads to an early onset and intensification of Asian monsoon rainfall. The finding is primarily based on results from a NASA Finite-Volume General Circulation Model run with and without radiative forcing from different types of aerosols. In particular, black carbon emissions...

  13. Investigation of the "elevated heat pump" hypothesis of the Asian monsoon using satellite observations

    OpenAIRE

    M. M. Wonsick; Pinker, R.T.; Ma, Y.

    2014-01-01

    The "elevated heat pump" (EHP) hypothesis has been a topic of intensive research and controversy. It postulates that aerosol-induced anomalous mid- and upper-tropospheric warming in the Himalayan foothills and above the Tibetan Plateau leads to an early onset and intensification of Asian monsoon rainfall. This finding is primarily based on results from a NASA finite-volume general circulation model run with and without radiative forcing from different types of aerosols. In p...

  14. Investigation of the "Elevated Heat Pump" hypothesis of the Asian monsoon using satellite observations

    Directory of Open Access Journals (Sweden)

    M. M. Wonsick

    2013-04-01

    Full Text Available In recent years, the "Elevated Heat Pump" (EHP hypothesis has been a topic of intensive research and controversy. It postulates that aerosol-induced anomalous mid- and upper-tropospheric warming above the Tibetan Plateau leads to an early onset and intensification of Asian monsoon rainfall. The finding is primarily based on results from a NASA Finite-Volume General Circulation Model run with and without radiative forcing from different types of aerosols. In particular, black carbon emissions from sources in Northern India and dust from Western China, Afghanistan, Pakistan, and Southwest Asia affected the modeled anomalous heating. Since the initial discussion of the EHP hypothesis in 2006, the aerosol-monsoon relationship has been addressed using various modeling and observational techniques. The current study takes an observational approach to detect signatures of the "Elevated Heat Pump" effect in the cloud cover and cloud type distributions as derived from Meteosat-5 observations over the Asian Monsoon region, supplemented with temperature data from the NCEP/NCAR Reanalysis and precipitation data from the Global Precipitation Climatology Project (GPCP. Cloud, convection, precipitation, and temperature features for the highest-aerosol years are compared with lower-aerosol content years during the period 2000–2005. Predicted precipitation features in China and Korea are found to be consistent with the hypothesis, but the early onset and intensification of monsoon rainfall over India are not observed. It is proposed that model inaccuracies and/or indirect aerosol effects caused the disagreement between observed and hypothesized behavior.

  15. 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.

  16. Interactive Aspects of the Indian and the African Summer Monsoon Systems

    Science.gov (United States)

    Sanjeeva Rao, P.; Sikka, D. R.

    2007-09-01

    This study addresses an understanding of the possible mutual interactions of sub-seasonal variability of the two neighboring regional monsoon systems through data analysis. The NCEP/NCAR re-analysis and OLR data for three years was used to reveal the large-scale organization of convective episodes on synoptic (~5 days) and low frequency (15 50 day) scales. It is found that synoptic scale organization over both the sectors is influenced by the eastward migration of large-scale convective episodes associated with the Madden Julian Oscillation (MJO) on the low frequency scale. The organization of convection associated with the African monsoon on the synoptic scale is influenced by the pulsatory character of lower mid-troposphere and upper troposphere wind regimes moving westward over the African sector. Over the Indian region formation of low pressure areas and depressions in the monsoon trough occur in an overlapping manner under an envelope of low frequency seasonal oscillation. We have also found some correspondence between the summer monsoon rainfall over tropical North Africa and India on a decadal basis, which would suggest a common mode of multi-decadal variability in the two monsoon systems. The study points out the need to organize simultaneous field campaigns over the Indian and the African monsoon regions so as to bring out observational features of possible interactions between the two neighboring systems, which could then be validated through modeling studies.

  17. Contribution of Monthly and Regional Rainfall to the Strength of Indian Summer Monsoon

    Science.gov (United States)

    Zheng, Y.; Ali, M.; Bourassa, M. A.

    2015-12-01

    Indian Summer Monsoon Rainfall (ISMR: June-September) has both temporal and spatial variability causing floods/droughts in different seasons/locations leading to a strong or weak monsoon. Here, we present the contribution of all-India monthly, seasonal and regional rainfall to the ISMR, with special reference to the strong and weak monsoons. For this purpose, rainfall data provided by the India Meteorological Department (IMD: http://www.imd.gov.in/section/nhac/dynamic/Monsoon_frame.htm) for 1901-2013 have been used. The IMD divided the Indian sub-continent into four homogeneous regions of northwest India (NWI), northeast India (NEI), central India (CI), and south peninsula India (SPIN). Rainfall during July-August contributes the most to the total seasonal rainfall, whether it is a strong or weak monsoon. Although the NEI has the maximum area-weighted rainfall, its contribution is the least toward a strong or weak monsoon. The rainfall in the remaining three regions (NWI, CI, and SPIN) controls whether an ISMR is strong or weak. Compared to the monthly rainfall, the regional rainfall dominates the strong or weak rainfall periods.

  18. Trends in Peroxyacetyl Nitrate (PAN in the upper troposphere and lower stratosphere over Southern Asia during the summer monsoon season: regional impacts

    Directory of Open Access Journals (Sweden)

    S. Fadnavis

    2014-07-01

    Full Text Available We analyze temporal trends of Peroxyacetyl Nitrate (PAN retrievals from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS during 2002–2011 in the altitude range 8–23 km over the Asian summer monsoon (ASM region. The greatest enhancements of PAN mixing ratios in the upper troposphere and lower stratosphere (UTLS are seen during the summer monsoon season from June to September. During the monsoon season, the mole fractions of PAN show statistically significant (at 2 sigma level positive trends from 0.2 ± 0.05 to 4.6 ± 3.1 ppt year−1 (except between 12–14 km which is higher than the annual mean trends of 0.1 ± 0.05 to 2.7 ± 0.8 ppt year−1. These rising concentrations point to increasing NOx (=NO+NO2 and volatile organic compound (VOC emissions from developing nations in Asia, notably India and China. We analyze the influence of monsoon convection on the distribution of PAN in UTLS with simulations using the global chemistry-climate model ECHAM5-HAMMOZ. During the monsoon, transport into the UTLS over the Asian region primarily occurs from two convective zones, one extending from the Bay of Bengal to the South China Sea and the other over the southern flank of the Himalayas. India and China are NOx limited regions, and thus we use the model to evaluate the contributions from enhanced NOx emissions to the changes in PAN, HNO3 and O3 concentrations in the UTLS. From a set of sensitivity experiments with emission changes in particular regions it can be concluded that Chinese emissions have a greater impact on the concentrations of these species than Indian emissions. NOx emissions increases over India are about half of those over China.

  19. Multiscale characteristics of the rainy season rainfall and interdecadal decaying of summer monsoon in North China

    Institute of Scientific and Technical Information of China (English)

    DAI Xingang; WANG Ping; CHOU Jifan

    2003-01-01

    This paper focuses on the rainfall spectrum and its evolution of North China in rainy season with summer monsoon decaying in interdecadal time scale. The interannual component of the rainfall is the dominant part, accounting for 85% of the total variance, and has been changed significantly during the last 30 years. According to wavelet analysis its 5a periodic spectrum suddenly disappeared in the late 1960s, and its biennial oscillation gradually become weaker and weaker since 1970, accompanied by the summer monsoon decaying. Contrarily, the interdecadal component is principal in the summer monsoon over North China and is very similar to the counterpart of the rainfall. Their interdecadal parts are significantly correlated, and the correlation coefficient is nearly equal to the one of the original sequences. Besides, the dry and wet climate alternated with the monsoon abrupt changes in the 1960s and the 1970s over East Asia, apart from North China, climate drifted from a light drought to a severe drought during the past 30 years.

  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. East Asian monsoon variation and climate changes in Jeju Island, Korea, during the latest Pleistocene to early Holocene

    Science.gov (United States)

    Lee, Seung Hyoun; Lee, Yong Il; Yoon, Ho Il; Yoo, Kyu-Cheul

    2008-09-01

    A 4.96-m-long sediment core from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the paleoclimatic change and East Asian monsoon variations during the latest Pleistocene to early Holocene (23,000-9000 cal yr BP). High-resolution TOC content, magnetic susceptibility, and major element composition data indicate that Jeju Island experienced the coldest climate around 18,000 cal yr BP, which corresponds to the last glacial maximum (LGM). Further, these multi-proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14,000 cal yr BP, which represents the commencement of the last major deglaciation. After the last major deglaciation, the TOC content decreased from 13,300 to 12,000 cal yr BP and from 11,500 to 9800 cal yr BP, thereby reflecting the weakening of the summer monsoon. The LGM in Jeju Island occurred later in comparison with the Chinese Loess Plateau. Such a disparity in climatic change events between central China and Jeju Island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central China and by the buffering effect of the Pacific Ocean.

  3. 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

  4. A comparative study of the Indian summer monsoon hydroclimate and its variations in three reanalyses

    Energy Technology Data Exchange (ETDEWEB)

    Misra, Vasubandhu [Florida State University, Department of Earth, Ocean and Atmospheric Science, Tallahassee, FL (United States); Florida State University, Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL (United States); Pantina, P. [Science Systems and Application, Inc., Lanham, MD (United States); NASA/GSFC, Cloud and Radiation Laboratory, Greenbelt, MD (United States); Chan, S.C. [Newcastle University, School of Civil Engineering and Geosciences, Newcastle upon Tyne (United Kingdom); Met Office Hadley Center, Exeter (United Kingdom); DiNapoli, S. [Florida State University, Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL (United States)

    2012-09-15

    This study examines the Indian summer monsoon hydroclimate in the National Centers for Environmental Prediction (NCEP)-Department of Energy (DOE) Reanalysis (R2), the Climate Forecast System Reanalysis (CFSR), and the Modern Era Retrospective-Analysis for Research and Applications (MERRA). The three reanalyses show significant differences in the climatology of evaporation, low-level winds, and precipitable water fields over India. For example, the continental evaporation is significantly less in CFSR compared to R2 and MERRA. Likewise the mean boreal summer 925 hPa westerly winds in the northern Indian Ocean are stronger in R2. Similarly the continental precipitable water in R2 is much less while it is higher and comparable in MERRA and CFSR. Despite these climatological differences between the reanalyses, the climatological evaporative sources for rain events over central India show some qualitative similarities. Major differences however appear when interannual variations of the Indian summer monsoon are analyzed. The anomalous oceanic sources of moisture from the adjacent Bay of Bengal and Arabian Sea play a significant role in determining the wet or dry year of the Indian monsoon in CFSR. However in R2 the local evaporative sources from the continental region play a more significant role. We also find that the interannual variability of the evaporative sources in the break spells of the intraseasonal variations of the Indian monsoon is stronger than in the wet spells. We therefore claim that instead of rainfall, evaporative sources may be a more appropriate metric to observe the relationship between the seasonal monsoon strength and intraseasonal activity. These findings are consistent across the reanalyses and provide a basis to improve the predictability of intraseasonal variability of the Indian monsoon. This study also has a bearing on improving weather prediction for tropical cyclones in that we suggest targeting enhanced observations in the Bay of Bengal

  5. 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.

  6. Evaluating the influence of summer monsoon intensity on the runoff of the middle Yellow River Basin

    Science.gov (United States)

    Chen, D.; Lv, M.

    2012-12-01

    Continental monsoon climate controls the runoff in Central and Southeastern China, especially the drainage between Lanzhou and Huanyuankou, i.e. the middle Yellow River Basin. To analyze the influence of summer monsoon intensity on the runoff of the region, this paper evaluates the temporal variation and power spectrum of summer monsoon indices (Ism) of 139 years (1873-2011) and natural runoff of the middle Yellow River Basin of 93 years (1919-2011) by using continuous wavelet transform (CWT). The CWT of Ism indicates that ~80a and ~40a periodicities persist over the whole period, while the higher frequency oscillation (i.e. 2-8a) decreases after 1970 during which both the ENSO influence and continental monsoon intensity are being weak. The attenuating of 2-8a oscillation is also found in the CWT of natural runoff in the drainage area between Hekouzhen and Longmen, which might lead to a good correlation between Ism and natural runoff in the region. However, the 2-8a oscillation in the CWT of natural runoff is more consistent over the whole period of 1919-2000 in downstream areas, i.e. drainage area between Longmen and Huangyuankou, which indicates strong influence from other climatic factors such as ENSO.

  7. COMPOSITE ANALYSIS OF SUMMER MONSOON ONSET PROCESS OVER SOUTH CHINA SEA

    Institute of Scientific and Technical Information of China (English)

    徐海明; 何金海; 周兵

    2001-01-01

    Based on the method of composite analysis, the onset process and preceding signs of summer monsoon over the South China Sea (SCS) is investigated. The result indicates that convection activities appear first over the Indo-China Peninsula prior to the onset of the monsoon, then around the Philippines just at the point of onset, implying that the convection activities around the Philippines serve as one of the reasons leading to the SCS monsoon onset. Before the SCS monsoon onset, the equatorial westerly over the Indian Ocean (75°E ~ 95°E ) experiences noticeable enhancement and plays an important role on the SCS monsoon onset. It propagates eastward rapidly and causes the establishment and strengthening of equatorial westerly in the southern SCS, on the one hand, it results in the migration southward of the westerly on south side of the south-China stationary front by means of shift northeastward of the westerly and convection over the Bay of Bengal, on the other. Further study also shows that the intensification of equatorial westerly in the Indian Ocean (75°E ~ 95°E) and the southern SCS is closely related to the reinforcement of the Southern-Hemisphere Mascarene high and Australian high, and cross-equatorial flow northward around Somali, at 85°E and 105°E, respectively.

  8. Relationship between East Asian winter monsoon, warm pool situation and ENSO cycle

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Based on the observational data analyses and numerical simulations with the air-sea coupled model (CGCM), a new perspective on the occurrence mechanism of ENSO is advanced in this paper. The continuous strong (weak) East Asian winter monsoon will lead to continuous westerly (easterly) wind anomalies over the equatorial western Pacific region. The anomalous equatorial westerly (easterly) winds can cause eastward propagation of the subsurface ocean temperature anomalies (SOTA) in the warm pool region, the positive (negative) SOTA have been in the warm pool region for quite a long time. The eastward propagating of positive (negative) SOTA along the thermocline will lead to positive (negative) SSTA in the equatorial eastern Pacific and the occurrence of El Ni(n)o (La Ni(n)a) event. After the occurrence of ENSO, the winter monsoon in East Asia will be weak (strong) due to the influence of El Ni(n)o (La Ni(n)a).

  9. Structure of the marine boundary layer over north western Indian Ocean during 1983 summer monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Sadhuram, Y.; Michael, G.S.; Rao, L.V.G.

    STRUCTURE OF THE MARINE BOUNDARY LAYER OVER NORTH WESTERN INDIAN OCEAN DURING 1983 SUMMER MONSOON (Research Note) M. R. RAMESH KUMAR, Y. SADHURAM, G. S. MICHAEL and L. V. GANGADHARA RAO Physical Oceanography Division, National Institute of Oceanography..., Dona Paula, Goa - 403 004, India (Received 7 August, 1989) Abstract. The spatial variability of the structure of the lower troposphere over the northwestern Indian Ocean for the period 12th July to 2nd September, 1983 has been studied using upper...

  10. Generation of near-inertial oscillations by summer monsoon onset over the South China Sea in 1998 and 1999

    Science.gov (United States)

    Shu, Yeqiang; Pan, Jiayi; Wang, Dongxiao; Chen, Gengxin; Sun, Lu; Yao, Jinglong

    2016-12-01

    The summer monsoon onset over the South China Sea (SCS) is an abrupt event in May or early June every year. After the summer monsoon onset in 1998 and 1999, strong near-inertial oscillations (NIOs) in the central SCS were observed with Acoustic Doppler Current Profilers (ADCP) mooring data. The near-inertial current speed reached 0.25 ms-1, comparable to that induced by tropical storms (TS) in the same area, although the wind speed ( 10 ms-1) of the monsoon onset was much lower than what is typical of TSs. Further analyses suggest that the shallow mixed-layer (speed and direction resulting from the summer monsoon onset were responsible for developing the near-inertial current. The generated NIOs could be enhanced by a warm eddy appearing during the monsoon onset in the central SCS. The strong NIOs appeared in the middle of the SCS in May when the SCS summer monsoon starts to prevail, which implies that the beginning of the SCS summer monsoon may be a vital factor for generation of the strong NIOs in May.

  11. 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.

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

    Science.gov (United States)

    Miller, G. H.; Magee, J. W.; Fogel, M. L.; Gagan, M. K.

    2007-08-01

    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. We also suggest that altered climate feedbacks linked to changes

  14. 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.

  15. A prominent pattern of year-to-year variability in Indian Summer Monsoon Rainfall.

    Science.gov (United States)

    Mishra, Vimal; Smoliak, Brian V; Lettenmaier, Dennis P; Wallace, John M

    2012-05-08

    The dominant patterns of Indian Summer Monsoon Rainfall (ISMR) and their relationships with the sea surface temperature and 850-hPa wind fields are examined using gridded datasets from 1900 on. The two leading empirical orthogonal functions (EOFs) of ISMR over India are used as basis functions for elucidating these relationships. EOF1 is highly correlated with all India rainfall and El Niño-Southern Oscillation indices. EOF2 involves rainfall anomalies of opposing polarity over the Gangetic Plain and peninsular India. The spatial pattern of the trends in ISMR from 1950 on shows drying over the Gangetic Plain projects onto EOF2, with an expansion coefficient that exhibits a pronounced trend during this period. EOF2 is coupled with the dominant pattern of sea surface temperature variability over the Indian Ocean sector, which involves in-phase fluctuations over the Arabian Sea, the Bay of Bengal, and the South China Sea, and it is correlated with the previous winter's El Niño-Southern Oscillation indices. The circulation anomalies observed in association with fluctuations in the time-varying indices of EOF1 and EOF2 both involve distortions of the low-level monsoon flow. EOF1 in its positive polarity represents a southward deflection of moist, westerly monsoon flow from the Arabian Sea across India, resulting in a smaller flux of moisture to the Himalayas. EOF2 in its positive polarity represents a weakening of the monsoon trough over northeastern India and the westerly monsoon flow across southern India, reminiscent of the circulation anomalies observed during break periods within the monsoon season.

  16. Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006

    Directory of Open Access Journals (Sweden)

    S. Janicot

    2008-09-01

    Full Text Available The AMMA (African Monsoon Multidisciplinary Analysis program is dedicated to providing a better understanding of the West African monsoon and its influence on the physical, chemical and biological environment regionally and globally, as well as relating variability of this monsoon system to issues of health, water resources, food security and demography for West African nations. Within this framework, an intensive field campaign took place during the summer of 2006 to better document specific processes and weather systems at various key stages of this monsoon season. This campaign was embedded within a longer observation period that documented the annual cycle of surface and atmospheric conditions between 2005 and 2007. The present paper provides a large and regional scale overview of the 2006 summer monsoon season, that includes consideration of of the convective activity, mean atmospheric circulation and synoptic/intraseasonal weather systems, oceanic and land surface conditions, continental hydrology, dust concentration and ozone distribution. The 2006 African summer monsoon was a near-normal rainy season except for a large-scale rainfall excess north of 15° N. This monsoon season was also characterized by a 10-day delayed onset compared to climatology, with convection becoming developed only after 10 July. This onset delay impacted the continental hydrology, soil moisture and vegetation dynamics as well as dust emission. More details of some less-well-known atmospheric features in the African monsoon at intraseasonal and synoptic scales are provided in order to promote future research in these areas.

  17. Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006

    Science.gov (United States)

    Janicot, S.; Thorncroft, C. D.; Ali, A.; Asencio, N.; Berry, G.; Bock, O.; Bourles, B.; Caniaux, G.; Chauvin, F.; Deme, A.; Kergoat, L.; Lafore, J.-P.; Lavaysse, C.; Lebel, T.; Marticorena, B.; Mounier, F.; Nedelec, P.; Redelsperger, J.-L.; Ravegnani, F.; Reeves, C. E.; Roca, R.; de Rosnay, P.; Schlager, H.; Sultan, B.; Tomasini, M.; Ulanovsky, A.; Acmad Forecasters Team

    2008-09-01

    The AMMA (African Monsoon Multidisciplinary Analysis) program is dedicated to providing a better understanding of the West African monsoon and its influence on the physical, chemical and biological environment regionally and globally, as well as relating variability of this monsoon system to issues of health, water resources, food security and demography for West African nations. Within this framework, an intensive field campaign took place during the summer of 2006 to better document specific processes and weather systems at various key stages of this monsoon season. This campaign was embedded within a longer observation period that documented the annual cycle of surface and atmospheric conditions between 2005 and 2007. The present paper provides a large and regional scale overview of the 2006 summer monsoon season, that includes consideration of of the convective activity, mean atmospheric circulation and synoptic/intraseasonal weather systems, oceanic and land surface conditions, continental hydrology, dust concentration and ozone distribution. The 2006 African summer monsoon was a near-normal rainy season except for a large-scale rainfall excess north of 15° N. This monsoon season was also characterized by a 10-day delayed onset compared to climatology, with convection becoming developed only after 10 July. This onset delay impacted the continental hydrology, soil moisture and vegetation dynamics as well as dust emission. More details of some less-well-known atmospheric features in the African monsoon at intraseasonal and synoptic scales are provided in order to promote future research in these areas.

  18. 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.

  19. 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

  20. All India summer monsoon rainfall prediction using an artificial neural network

    Energy Technology Data Exchange (ETDEWEB)

    Sahai, A.K.; Soman, M.K.; Satyan, V. [Indian Inst. of Tropical Meteorol., Pune (India). Climate and Global Modelling Div.

    2000-04-01

    The prediction of Indian summer monsoon rainfall (ISMR) on a seasonal time scales has been attempted by various research groups using different techniques including artificial neural networks. The prediction of ISMR on monthly and seasonal time scales is not only scientifically challenging but is also important for planning and devising agricultural strategies. This article describes the artificial neural network (ANN) technique with error- back-propagation algorithm to provide prediction (hindcast) of ISMR on monthly and seasonal time scales. The ANN technique is applied to the five time series of June, July, August, September monthly means and seasonal mean (June+July+August+September) rainfall from 1871 to 1994 based on Parthasarathy data set. The previous five years values from all the five time-series were used to train the ANN to predict for the next year. The details of the models used are discussed. Various statistics are calculated to examine the performance of the models and it is found that the models could be used as a forecasting tool on seasonal and monthly time scales. It is observed by various researchers that with the passage of time the relationships between various predictors and Indian monsoon are changing, leading to changes in monsoon predictability. This issue is discussed and it is found that the monsoon system inherently has a decadal scale variation in predictability. (orig.)

  1. 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.

  2. 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.

  3. 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.

  4. 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

    2016-09-01

    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 230Th-dated stalagmite δ18O 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 δ18O 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.

  5. 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

  6. Asian monsoon modulation of nonsteady state diagenesis in hemipelagic marine sediments offshore of Japan

    Science.gov (United States)

    Chang, Liao; Bolton, Clara T.; Dekkers, Mark J.; Hayashida, Akira; Heslop, David; Krijgsman, Wout; Kodama, Kazuto; Paterson, Greig A.; Roberts, Andrew P.; Rohling, Eelco J.; Yamamoto, Yuhji; Zhao, Xiang

    2016-11-01

    We have identified millennial-scale variations in magnetic mineral diagenesis from Pacific Ocean sediments offshore of Japan that we correlate with changes in organic carbon burial that were likely driven by Asian monsoon fluctuations. The correlation was determined by identifying offsets between the positions of fossil diagenetic fronts and climatically induced variations in organic carbon burial inferred from magnetic and geochemical analyses. Episodes of intense monsoon activity and attendant sediment magnetic mineral diagenesis also appear to correlate with Heinrich events, which supports the existence of climatic telecommunications between Asia and the North Atlantic region. Several lines of evidence support our conclusions: (1) fluctuations in down-core magnetic properties and diagenetic pyrite precipitation are approximately coeval; (2) localized stratigraphic intervals with relatively stronger magnetic mineral dissolution are linked to enhanced sedimentary organic carbon contents that gave rise to nonsteady state diagenesis; (3) down-core variations in elemental S content provide a proxy for nonsteady state diagenesis that correlate with key records of Asian monsoon variations; and (4) relict titanomagnetite that is preserved as inclusions within silicate particles, rather than secondary authigenic phases (e.g., greigite), dominates the strongly diagenetically altered sediment intervals and are protected against sulfidic dissolution. We suggest that such millennial-scale environmental modulation of nonsteady state diagenesis (that creates a temporal diagenetic filter and relict magnetic mineral signatures) is likely to be common in organic-rich hemipelagic sedimentary settings with rapidly varying depositional conditions. Our work also demonstrates the usefulness of magnetic mineral inclusions for recording important environmental magnetic signals.

  7. Prediction model for peninsular Indian summer monsoon rainfall using data mining and statistical approaches

    Science.gov (United States)

    Vathsala, H.; Koolagudi, Shashidhar G.

    2017-01-01

    In this paper we discuss a data mining application for predicting peninsular Indian summer monsoon rainfall, and propose an algorithm that combine data mining and statistical techniques. We select likely predictors based on association rules that have the highest confidence levels. We then cluster the selected predictors to reduce their dimensions and use cluster membership values for classification. We derive the predictors from local conditions in southern India, including mean sea level pressure, wind speed, and maximum and minimum temperatures. The global condition variables include southern oscillation and Indian Ocean dipole conditions. The algorithm predicts rainfall in five categories: Flood, Excess, Normal, Deficit and Drought. We use closed itemset mining, cluster membership calculations and a multilayer perceptron function in the algorithm to predict monsoon rainfall in peninsular India. Using Indian Institute of Tropical Meteorology data, we found the prediction accuracy of our proposed approach to be exceptionally good.

  8. Theoretical aspects of the onset of Indian Summer Monsoon from perturbed orography simulations in a GCM

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, A. [Florida State Univ., Tallahassee, FL (United States). Dept. of Meteorology; Nanjundiah, R.S.; Srinivasan, J. [Indian Institute of Science, Bangalore (India). Centre for Atmospheric and Oceanic Sciences

    2006-07-01

    A theory is proposed to determine the onset of the Indian Summer Monsoon (ISM) in an Atmospheric General Circulation Model (AGCM). The onset of ISM is delayed substantially in the absence of global orography. The impact of orography over different parts of the Earth on the onset of ISM has also been investigated using five additional perturbed simulations. The large difference in the date of onset of ISM in these simulations has been explained by a new theory based on the Surface Moist Static Energy (SMSE) and vertical velocity at the mid-troposphere. It is found that onset occurs only after SMSE crosses a threshold value and the large-scale vertical motion in the middle troposphere becomes upward. This study shows that both dynamics and thermodynamics play profound roles in the onset of the monsoon. (orig.)

  9. Dynamic control on 8rain-size distribution of terri-genous sediments in the western South China Sea:Implication for East Asian monsoon evolution

    Institute of Scientific and Technical Information of China (English)

    CHEN GuoCheng; ZHENG HongBo; LI JianRu; XIE Xin; MEI Xi

    2008-01-01

    High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China Sea (SCS), was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density, fractional porosity and lithogenic content of the sedi-ments, terrigenous mass accumulation rate (TMAR) was obtained, which is 4.9-6.0 g cm-2 ka-1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9-5.0 g cm-2 ka-1, which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis of grain size distribution of all the samples, two main control factors (F1 and F2) were obtained, which are responsible for about 80% variance of granularity. The contents of grain size population 1.26-2.66 μm% and 10.8-14.3 μm% which are sensible to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15° N. They exhibit a dis-tinct cyclicity with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24-7.42 μm% and 30.1-43.7 μm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations of surface cur-rent forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer monsoon has fluctuated with high frequency and been forced by changes in solar in-solation in low latitude associated with precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing.

  10. Quantifying the sectoral contribution of pollution transport from South Asia during summer and winter monsoon seasons in support of HTAP-2 experiment

    Science.gov (United States)

    Surendran, Divya E.; Ghude, Sachin D.; Beig, G.; Jena, Chinmay; Chate, D. M.

    2016-11-01

    This study examines the contribution of 20% reduction in anthropogenic emissions from the energy, industry and transport sectors in South Asia to global distribution of ozone (O3) during summer and winter monsoon seasons. We used Model for Ozone and Related chemical Tracers (MOZART-4) and Hemispheric Transport of Air Pollution version-2 (HTAP-v2) emission inventory to simulate global O3 for five different sensitivity simulations. Contribution from different emission sectors is identified on the basis of the differences between model calculations with unperturbed emissions (Base-case) and the emissions reduced by 20% by different sectors over South Asia. During the summer season, 20% reduction in emissions from transportation sector contributes maximum decrease in O3 of the order of 0.8 ppb in the center of Asian Summer Monsoons (ASM) anticyclone at 200 hPa. Response to Extra Regional Emission Reduction (RERER) is found to vary between 0.4 and 0.7 inside the ASM, indicating that 40-70% of O3 trapped inside the anticyclone is influenced by the emission from non-Asian emissions, and the remaining O3 is influenced by South-Asian emissions. During winter, 20% reduction in emissions from transport sector contributes decrease in O3 at surface up to 0.5 ppb over South Asia and outflow region (the Arabian Sea and the Bay of Bengal). RERER values vary between 0 and 0.2 over South Asia indicating the predominant impact of local emissions reduction on surface O3 concentration than reduction in foreign emissions. We have also examined the health benefits of reduction in regional, global and sectoral emissions in terms of decrease in excess number of COPD (Chronic Obstructive Pulmonary Disease) cases due to O3 exposure. We find that more health benefits can be achieved if global emissions are decreased by 20%.

  11. Abrupt Holocene changes of the Asian monsoon at millen-nial- and centennial-scales:Evidence from lake sediment document in Minqin Basin,NW China

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Considerable research is now focusing on abrupt Holocene changes at millennial- and centennial-scales all over the world. This study shows that the changes in the Holocene summer monsoon can be divided into two main periods, based on climatic proxy records of lake sediments from the Sanjiaocheng section located at the NW boundary of the summer monsoon, Gansu Province. The early and middle Holocene was humid with stronger summer monsoon, while the late Holocene is dry with weak summer monsoon. Detailed results also show a series of millennial- and centennial-scale changes in the intensity of the summer monsoon, with a periodicity of 1600 years during the whole Holocene, and with a periodicity of 800 years during the early Holocene. Ten dry events during the Holocene are associated with the weakening of the summer monsoon. These rapid climatic changes may be representative of a global climatic change pattern during the Holocene.

  12. 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.

  13. 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

  14. Variations in temperature and precipitation during Indian summer monsoon simulated by RegCM3

    Science.gov (United States)

    Dash, S. K.; Mamgain, A.; Pattnayak, K. C.; Giorgi, F.

    2012-04-01

    Variations in temperature and precipitation due to global changes have large societal impact in sectors such as agriculture and health. It is therefore very important to examine their temporal and spatial variations at the regional level in order to access the impact of climate change. In India, the most important quasi-periodic system to affect the weather and climate is the Indian summer monsoon. The local changes in the temperature and precipitation can be well examined by a regional model. RegCM3 is one such model best suited for the Indian region. This model has been integrated in the ensemble mode at 55km resolution over India for the summer monsoon season during the years 1982-2009. The model simulations are compared with observed values in detail. Comparison with observations shows that RegCM3 has slightly underestimated summer monsoon precipitation over the Central and Northeast India. Nevertheless, over these regions, RegCM3 simulated rainfall is closer to the observations when compared to other regions where rainfall is highly overestimated. The model simulated mid-tropospheric temperature shows a warm bias over the Himalayan and Tibetan regions that gives leads to the low pressure in the region. Thus the position of the monsoon trough as simulated by the model lies to the north of its original position. This is similar to the usual monsoon break condition leading to less rainfall over Central India. RegCM3 simulated surface maximum temperature shows large negative bias over the country while the surface minimum temperature is close to the observation. Nevertheless, there is a strong correlation between the all India weighted average surface temperature simulated by RegCM3 and IMD observations. At the regional level, in the Central India, both rainfall and temperature show the best correlation with the respective observed values. While examining the extreme condition in Central India, it is found that RegCM3 simulated frequencies of very wet and

  15. Precise dating of abrupt shifts in the Asian Monsoon during the last deglaciation based on stalagmite data from Yamen Cave, Guizhou Province, China

    Institute of Scientific and Technical Information of China (English)

    EDWARDS; R.; Lawrence

    2010-01-01

    Based on 33 U/Th dates and 1020 oxygen isotopic data from stalagmite Y1 from Yamen Cave, Guizhou Province, China, a record of the Asian Summer Monsoon (ASM) was established. The record covers the last deglaciation and the early Holocene (from 16.2 to 7.3 ka BP) with an average oxygen isotope resolution of 9 years. The main millennial-scale deglacial events first identified in Greenland (Greenland Interstadial Events: GIS 1e through GIS 1a) and later in China are clearly present in the Y1 record. By analogy to earlier work, we refer to these as Chinese Interstadials (CIS): CIS A.1e to CIS A.1a. The onset of these events in Y1 δ18O records are nominally dated at: 14750±50, 14100±60, 13870±80, 13370±80, and 12990±80 a BP. The end of CIS A.1a or the beginning of the Younger Dryas (YD) event is nominally at 12850±50 a BP and the end of the YD dates to 11500±40 a BP. The δ18O values shift by close to 3‰ during the transition into the Bφlling-Allerφd (BA, the onset of CIS A.1e) and at the end of the YD. Comparisons of Y1 to previously published early Holocene records show no significant phase differences. Thus, the East Asia Monsoon and the Indian Monsoon do not appear to have been out of phase during this interval. The Y1 record confirms earlier work that suggested that solar insolation and North Atlantic climate both affect the Asian Monsoon.

  16. Regional integrated environmental model system and its simulation of East Asia summer monsoon

    Institute of Scientific and Technical Information of China (English)

    XIONG Zhe; FU CongBin; YAN XiaoDong

    2009-01-01

    A continuous 22-year simulation in Asia for the period of 1 January 1979 to 31 December 2000 was conducted using the Regional Integrated Environmental Model System (RIEMS 2.0) with NCEP Reanalysis Ⅱ data as the driving fields.The model processes include surface physics state package (BATS le),a Grell cumulus parameterization,and a modified radiation package (CCM3) with the focus on the ability of the model to simulate the summer monsoon over East Asia.The analysis results show that (1)RIEMS reproduces well the spatial pattern and the seasonal cycle of surface temperature.When regionally averaged,the summer mean temperature biases are within 1-2℃.(2) For precipitation,the model reproduces well the spatial pattern,and temporal evolution of the East Asia summer monsoon rain belt,with steady phases separated by more rapid transitions,is reproduced.The rain belt simulated by RIEMS 2.0 is closer to observation than by RIEMS 1.0.(3) RIEMS 2.0 can reasonably reproduce the large-scale circulation.

  17. Response of the South China Sea summer monsoon onset to air-sea heat fluxes over the Indian Ocean

    Institute of Scientific and Technical Information of China (English)

    CHEN Jinnian; ZUO Tao; WANG Hongna

    2012-01-01

    We objectively define the onset date of the South China Sea (SCS) summer monsoon,after having evaluated previous studies and considered various factors.Then,interannual and interdecadal characteristics of the SCS summer monsoon onset are analyzed.In addition,we calculate air-sea heat fluxes over the Indian Ocean using the advanced method of CORARE3.0,based on satellite remote sensing data.The onset variation cycle has remarkable interdecadal variability with cycles of 16 a and 28 a.Correlation analysis between air-sea heat fluxes in the Indian Ocean and the SCS summer monsoon indicates that there is a remarkable lag correlation between them.This result has important implications for prediction of the SCS summer monsoon,and provides a scientific basis for further study of the onset process of this monsoon and its prediction.Based on these results,a linear regression equation is obtained to predict the onset date of the monsoon in 2011 and 2012.The forecast is that the onset date of 2011 will be normal or 1 pentad earlier than the normal year,while the onset date in 2012 will be 1-2 pentads later.

  18. An Index of East Asian Winter Monsoon Applied to the Description of China's Mainland Winter Temperature Changes

    Institute of Scientific and Technical Information of China (English)

    ZHU Yanfeng

    2008-01-01

    Using the NCEP/NCAR reanalysis data (Version 1.0) and the observation data of China from January 1951 to February 2007, a new index of East Asian winter monsoon circulation (IEAWM) was defined based on the comparison of previous different winter monsoon indices and circulation factors influencing the winter climate over China. Its relationships with winter temperature over China and large-scale circulation were analyzed. Results show that IEAWM can successfully describe the variation of China's mainland winter temperature and the East Asian winter monsoon (EAWM) system. This index reflects the integrated effect of the circulations over high and low latitudes and the thermal difference between the continent and the ocean. While in the previous studies, most monsoon indices only describe the single monsoon member. The IEAWM is a good indicator of the intensity of the EAWM. Positive values of IEAWM correspond to the strong EAWM, the stronger Siberian high and East Asian trough than normal, and the strengthening of the meridional shear of 500-hPa zonal wind between high and low latitudes over East Asia, and therefore, the southward cold advection becomes stronger and leads to the decrease in surface temperature over China; and vice versa. The IEAWM inter decadal change is obviously positive before the mid-1980s, but negative since the mid-1980s, in good agreement with the fact of the winter warming in China after 1985.

  19. Prediction of seasonal summer monsoon rainfall over homogenous regions of India using dynamical prediction system

    Science.gov (United States)

    Ramu, Dandi A.; Rao, Suryachadra A.; Pillai, Prasanth A.; Pradhan, M.; George, G.; Rao, D. Nagarguna; Mahapatra, S.; Pai, D. S.; Rajeevan, M.

    2017-03-01

    Seasonal prediction of Indian summer monsoon rainfall is a challenging task for the modeling community and predicting seasonal mean rainfall at smaller regional scale is much more difficult than predicting all India averaged seasonal mean rainfall. The regional scale prediction of summer monsoon mean rainfall at longer lead time (e.g., predicting 3-4 months in advance) can play a vital role in planning of hydrological and agriculture aspects of the society. Previous attempts for predicting seasonal mean rainfall at regional level (over 5 Homogeneous regions) have resulted with limited success (anomaly correlation coefficient is low, ACC ≈ 0.1-0.4, even at a short lead time of one month). The high resolution Climate Forecast System, version 2 (CFSv2) model, with spectral resolution of T382 (∼38 km), can predict the Indian summer monsoon rainfall (ISMR) at lead time of 3-4 months, with a reasonably good prediction skill (ACC ≈ 0.55). In the present study, we have investigated whether the seasonal mean rainfall over different homogenous regions is predictable using the same model, at 3-4 months lead time? Out of five homogeneous regions of India three regions have shown moderate prediction skill, even at 3 months lead time. Compared to lower resolution model, high resolution model has good skill for all the regions except south peninsular India. High resolution model is able to capture the extreme events and also the teleconnections associated with large scale features at four months lead time and hence shows better skill (ACC ≈ 0.45) in predicting the seasonal mean rainfall over homogeneous regions.

  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. 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).

  2. 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.

  3. Fingerprinting the Impacts of Aerosols on Long-Term Trends of the Indian Summer Monsoon Regional Rainfall

    Science.gov (United States)

    Laul, K. M.; Kim, K. M.

    2010-01-01

    In this paper, we present corroborative observational evidences from satellites, in-situ observations, and re-analysis data showing possible impacts of absorbing aerosols (black carbon and dust) on subseasonal and regional summer monsoon rainfall over India. We find that increased absorbing aerosols in the Indo-Gangetic Plain in recent decades may have lead to long-term warming of the upper troposphere over northern India and the Tibetan Plateau, enhanced rainfall in northern India and the Himalayas foothill regions in the early part (may-June) of the monsoon season, followed by diminished rainfall over central and southern India in the latter part (July-August) of the monsoon season. These signals which are consistent with current theories of atmospheric heating and solar dimming by aerosol and induced cloudiness in modulating the Indian monsoon, would have been masked by conventional method of using al-India rainfall averaged over the entire monsoon season.

  4. Southern Indian Ocean SST as a modulator for the progression of Indian summer monsoon

    Science.gov (United States)

    Shahi, Namendra Kumar; Rai, Shailendra; Mishra, Nishant

    2016-11-01

    This study explores the possibility of southern Indian Ocean (SIO) sea surface temperature (SST) as a modulator for the early phase of Indian summer monsoon and its possible physical mechanism. A dipole-like structure is obtained from the empirical orthogonal function (EOF) analysis which is similar to an Indian Ocean subtropical dipole (IOSD) found earlier. A subtropical dipole index (SDI) is defined based on the SST anomaly over the positive and negative poles. The regression map of rainfall over India in the month of June corresponding to the SDI during 1983-2013 shows negative patterns along the Western Ghats and Central India. However, the regression pattern is insignificant during 1952-1982. The multiple linear regression models and partial correlation analysis also indicate that the SDI acts as a dominant factor to influence the rainfall over India in the month of June during 1983-2013. The similar result is also obtained with the help of composite rainfall over the land points of India in the month of June for positive (negative) SDI events. It is also observed that the positive (negative) SDI delays (early) the onset dates of Indian monsoon over Kerala during the time domain of our study. The study is further extended to identify the physical mechanism of this impact, and it is found that the heating (cooling) in the region covering SDI changes the circulation pattern in the SIO and hence impacts the progression of monsoon in India.

  5. Impact of Climate Change on the Characteristics of Indian Summer Monsoon Onset

    Directory of Open Access Journals (Sweden)

    Savita Patwardhan

    2014-01-01

    Full Text Available A high resolution regional climate modeling system, known as PRECIS (Providing REgional Climate for Impact Studies, developed by Hadley Centre for Climate Prediction and Research, UK, is applied for Indian subcontinent to assess the impact of climate change on the summer monsoon onset characteristics. The present day simulation (1961–1990 with PRECIS is evaluated for the characteristics of onset over Kerala, southernmost part of India, where the monsoon sets in over Indian landmass. The meteorological parameters like precipitation, outgoing long wave radiation (OLR, and low level winds are analysed to study the monsoon onset over Kerala. The model is able to capture the sudden and sharp increase of rainfall associated with the onset. The rapid built-up of convective activity over the southeastern Arabian Sea and Bay of Bengal is well represented by the model. PRECIS simulations, under scenarios of increasing greenhouse gas concentrations and sulphate aerosols, are analysed to study the likely changes in the onset characteristics in future, towards the end of present century (2071–2100. The analysis does not indicate significant difference in the mean onset dates in A2 and B2 scenarios. However, the variability of onset date is likely to be more towards the end of the 21st century especially in A2 scenario.

  6. 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.)

  7. High-resolution peat records for Holocene monsoon history in the eastern Tibetan Plateau

    Institute of Scientific and Technical Information of China (English)

    YU; Xuefeng; ZHOU; Weijian; Lars; G.Franzen; XIAN; Feng; CHENG; Peng; A.J.; Tim; Jull

    2006-01-01

    The variations of summer and winter monsoons during the Holocene in the eastern Tibetan Plateau are shown to follow two basic models based on the reliable dating and high-resolution monsoon proxies determinations, one being a synchronous model in that both summer and winter monsoons are strengthening or decreasing, and the other to form a complementary pattern. These two different patterns evenly interact with each other on different time scales and together compose a complicated monsoon climatic model in this region. The climatic condition integrated by winter and summer monsoons is synchronous to the global pattern, which also shows the instability of the Holocene climate on centennial-millennial timescale. The abrupt monsoon event in about 6.2 ka cal.BP is much more severe than that in ca. 8.0 ka cal. BP, which indicates the regional character of the Asian monsoon and that the Asian monsoon climate is indeed a window on the global climate system.

  8. A projection of future changes in summer precipitation and monsoon in East Asia

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The future potential changes in precipitation and monsoon circulation in the summer in East Asia are projected using the latest generation of coupled climate models under Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A1B scenario (a medium emission scenario).The multi-model ensemble means show that during the period of 2010-2099,the summer precipitation in East Asia will increase and experience a prominent change around the 2040s,with a small increase (~1%) before the end of the 2040s and a large increase (~9%) afterward.This kind of two-stage evolution characteristic of precipitation change can be seen most clearly in North China,and then in South China and in the mid and lower Yangtze River Valley.In 2010-2099,the projected precipitation pattern will be dominated by a pattern of "wet East China" that explains 33.6% of EOF total variance.The corresponded time coefficient will markedly increase after the 2040s,indicating a great contribution from this mode to the enhanced precipitation across all East China.Other precipitation patterns that prevail in the current climate only contribute a small proportion to the total variance,with no prominent liner trend in the future.By the late 21st century,the monsoon circulation will be stronger in East Asia.At low level,this is due to the intensification of southwesterly airflow north of the anticyclone over the western Pacific and the SCS,and at high level,it is caused by the increased northeasterly airflow east of the anticyclone over South Asia.The enhanced monsoon circulation will also experience a two-stage evolution in 2010-2099,with a prominent increase (by ~0.6 m s-1) after the 2040s.The atmospheric water vapor content over East Asia will greatly increase (by ~9%) at the end of 21st century.The water vapor transported northward into East China will be intensified and display a prominent increase around the 2040s similar to other examined variables.These indicate

  9. 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

  10. The Coupled Model Predictability of the Western North Pacific Summer Monsoon with Different Leading Times

    Institute of Scientific and Technical Information of China (English)

    LU Ri-Yu; LI Chao-Fan; Se-Hwan YANG; Buwen DONG

    2012-01-01

    Leading time length is an important issue for modeling seasonal forecasts. In this study, a comparison of the interannual predictability of the Western North Pacific (WNP) summer monsoon between different leading months was performed by using one-, four-, and sevenmonth lead retrospective forecasts (hindcasts) of four coupled models from Ensembles-Based Predictions of Climate Changes and Their Impacts (ENSEMBLES) for the period of 1960 2005. It is found that the WNP summer anomalies, including lower-tropospheric circulation and precipitation anomalies, can be well predicted for all these leading months. The accuracy of the four-month lead prediction is only slightly weaker than that of the one-month lead prediction, although the skill decreases with the increase of leading months.

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

    Directory of Open Access Journals (Sweden)

    Subimal Ghosh

    Full Text Available 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.

  12. 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.

  13. A potential vorticity-based index for the East Asian winter monsoon

    Science.gov (United States)

    Huang, Wenyu; Wang, Bin; Wright, Jonathon S.

    2016-08-01

    A novel dynamically based index that reflects the strength of the regional potential vorticity (PV) intrusion on the 300 K isentropic surface is proposed as a reliable measure of East Asian winter monsoon (EAWM) intensity. The index captures essential aspects of the EAWM, including its climatic influences on East Asia, its continuous weakening trend since the 1980s, and its close relationships with the Siberian high, Arctic Oscillation, and El Niño. The use of a potential vorticity framework enables the definition of a new metric called continuous PV intrusion duration (CPVID), which can be used to monitor and explain wintertime weather extremes like the extreme snowfall event that occurred in south China during January 2008. The CPVID of March is comparable to that of December, indicating that data from this month should be included in estimates of the strength of the EAWM.

  14. Investigation of the "elevated heat pump" hypothesis of the Asian monsoon using satellite observations

    Science.gov (United States)

    Wonsick, M. M.; Pinker, R. T.; Ma, Y.

    2014-08-01

    The "elevated heat pump" (EHP) hypothesis has been a topic of intensive research and controversy. It postulates that aerosol-induced anomalous mid- and upper-tropospheric warming in the Himalayan foothills and above the Tibetan Plateau leads to an early onset and intensification of Asian monsoon rainfall. This finding is primarily based on results from a NASA finite-volume general circulation model run with and without radiative forcing from different types of aerosols. In particular, black carbon emissions from sources in northern India and dust from Western China, Afghanistan, Pakistan, the Thar Desert, and the Arabian Peninsula drive the modeled anomalous heating. Since the initial discussion of the EHP hypothesis in 2006, the aerosol-monsoon relationship has been investigated using various modeling and observational techniques. The current study takes a novel observational approach to detect signatures of the "elevated heat pump" effect on convection, precipitation, and temperature for contrasting aerosol content years during the period of 2000-2012. The analysis benefits from unique high-resolution convection information inferred from Meteosat-5 observations as available through 2005. Additional data sources include temperature data from the NCEP/NCAR Reanalysis and the European Reanalysis (ERA-Interim) precipitation data from the Global Precipitation Climatology Project (GPCP), aerosol optical depth from the Multi-angle Imaging Spectroradiometer (MISR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), and aerosol optical properties from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) aerosol reanalysis. Anomalous upper-tropospheric warming and the early onset and intensification of the Indian monsoon were not consistently observed during the years with high loads of absorbing aerosols. Possibly, model assumptions and/or unaccounted semi-direct aerosol effects caused the disagreement between observed and hypothesized

  15. 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.

  16. Intraseasonal Variability of the Indian Summer Monsoon in the Regional Climate Model COSMO-CLM

    Science.gov (United States)

    Befort, Daniel J.; Leckebusch, Gregor C.; Cubasch, Ulrich

    2015-04-01

    The regional climate model COSMO-CLM driven by ERA-Interim reanalysis data with a spatial resolution of 55km is used to simulate 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 monsoon intraseasonal oscillations. We find, that the temporal evolution of this oscillation between model and observation is in good agreement, but the strength is less well simulated. Additionally, the models 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, but we find a higher ability for dry compared to wet events. We hypothesize this is related to differences in the atmospheric circulation during dry and wet events. Analyses show, that dry events are characterized by a cyclonic vortex over India as well as an anti-cyclonic vortex over Pakistan region in 500hPa, whereas wet events are characterized by an anti-cyclonic vortex over India, only. It is found that COSMO-CLM has a higher ability to simulate the observed anomalous circulation over Pakistan region compared to observed anomalous circulation patterns over India. Overall, this study shows that the current configuration of COSMO-CLM is able to simulate key features of the intraseasonal variability of the Indian summer monsoon. Thus, under consideration of its limitations, COSMO-CLM is suitable to investigate possible changes of the intraseasonal variability of ISM under changed climate conditions.

  17. Correcting the Science Record: Direct Stratospheric Injection vs. Asian Monsoon and the Solar Escalator

    Science.gov (United States)

    Fromm, M. D.; Nedoluha, G. E.; Kablick, G. P.

    2012-12-01

    Two entries in the literature in 2012 make provocative but unsupportable claims regarding pollutant pathways from the Earth to the stratosphere. One claims the 13 June 2011 Nabro volcano (Eritrea) emitted gases and particles into the troposphere, and these constituents reached the stratosphere in great abundance via the Asian Monsoon circulation [Bourassa et al., 2012]. The other claims that smoke from the Black Saturday fire storms (Australia) was emitted into the troposphere, and was lofted ~15 km into the stratosphere by solar-induced diabatic heating [de Laat et al., 2012]. In both cases the stratospheric plumes attributed to these events spread around the globe and lasted for months. We will show that in both cases the postulated pathways are incorrect; the correct pathway is a direct convective injection by volcanic eruption and pyrocumulonimbus (pyroCb), respectively. We will present satellite data that will unambiguously reveal multiple, distinct stratospheric volcano-convection columns from Nabro connected to height-resolved volcanic SO2 and sulfate particles. In the case of Black Saturday we will characterize the pyroCb columns with ground-based radar and satellite imagery. The young pyroCb plume in the stratosphere will be characterized with a synergistic analysis of several NASA A-Train passive and active remote sensors. We will discuss the implications of our findings with respect to how satellite-based data are best used for tracking and characterizing point source injection plumes in the stratosphere. Bourassa et al. (2012), Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport, Science, 337, 78, DOI: 10:1126/Science.1219371 de Laat, et al. (2012), A solar escalator: Observational evidence of the self-lifting of smoke and aerosols by absorption of solar radiation in the February 2009 Australian Black Saturday plume, J. Geophys. Res., 117, D04204, doi:10.1029/2011JD017016.

  18. Remote response of the East Asian winter monsoon to tropical forcing related to El Niño-Southern Oscillation

    Science.gov (United States)

    Sakai, Kumi; Kawamura, Ryuichi

    2009-03-01

    The mechanism of the East Asian winter monsoon variability in response to El Niño-Southern Oscillation (ENSO)-related tropical forcing is investigated using Japanese long-term reanalysis project data, additionally aided by the Japan Meteorological Agency climate data assimilation system. There are at least two different responses, zonally symmetric and asymmetric, of the Asian jet over South Asia to the ENSO-related tropical convective forcing during the Northern Hemisphere winter. The zonally symmetric response, induced by zonally extended anomalous convection from the Philippine Sea through southern India and Sri Lanka, is pronounced at the mature phase of ENSO. The zonally asymmetric response is intimately associated with anomalous convection localized in the vicinity of the Philippine and South China seas, accompanied by an anomalous Walker circulation cell between the Maritime Continent and tropical Indian Ocean. When this asymmetric response is prominent, ENSO-related anomalous convection can give rise to a change in the East Asian winter monsoon system through stationary Rossby wave propagation along the South Asian waveguide. The North Atlantic Oscillation (NAO)-related extratropical forcing is also a crucial factor and contributes not only to the downstream development of subpolar teleconnections across northern Eurasia but also to the reinforcement of the zonally asymmetric pattern of the Asian jet over South Asia, resulting in a significant effect on the East Asian winter monsoon circulation. A combination of the ENSO- and NAO-related forcing plays a vital role in triggering the occurrence of extraordinary anomalous monsoon circulations, such as extremely heavy snowfall in the 2005/2006 winter in Japan.

  19. 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

  20. Inverse relation between summer and winter monsoon strength during late Holocene: continental molecular isotopic record from the Indian subcontinent

    Science.gov (United States)

    Sanyal, P.; Basu, S.; Pillai, A.; Singh, P.; Ratnam, J.; Sankaran, M.; Amibili, A.

    2015-12-01

    The Indian monsoon shapes the livelihood of ca. 40% of world's population. Despite dedicated efforts, comprehensive picture of monsoon variability has proved elusive largely due to the absence of long-term qualitative high-resolution record from key climatic zones and variability of monsoon with respect to various forcing mechanisms (e.g., solar insolation) and teleconnections (e.g., El Niño-Southern Oscillation, Indian Ocean Dipole). In this study, high-resolution molecular (n-alkane) isotopic (δD and δ13C ratios) reconstruction of mid-late Holocene (~5.0 cal ka) climate has been undertaken using lacustrine sediments from two climatically sensitive regions; (i) Arid Banni grasslands, western India with dominant moisture source derived from Indian summer monsoon (June-September) and (ii) Semi-arid Ennamangalam lake, south India with significant fraction of rainfall received during winter period (October to December) from Northeast (NE) monsoon. The climate reconstruction from western India based on δDn-alkane values shows prevalence of intensified monsoon until ca. 3 cal ka followed by gradual decrease in the precipitation. In contrast, climate reconstruction from south India is characterized by more negative δDn-alkane (intensified precipitation) values during late Holocene (~2.5 cal ka). The compilation of paleoclimate records shows that the precipitation pattern in Banni region responded linearly to gradually changing insolation and additionally amplified by climate systems like ENSO. However, intensified monsoon in South India shows strengthened NE monsoonal precipitation during late Holocene. The spatial inhomogeneity in the palaeohydrological record can be attributed to the persistence of inverse relationship between summer and winter monsoon. In addition, strong positive correlation between δDn-alkane and δ13Cn-alkane values from both region shows that the relative abundance of C3-C4 plants in the contemporary ecosystems are governed by rainfall

  1. Relationship of the South Asian Monsoon and Regional Drought with Distinct Equatorial Pacific SST Patterns on Interannual and Decadal Timescales

    Science.gov (United States)

    Hernandez, M.; Ummenhofer, C.; Anchukaitis, K. J.

    2014-12-01

    The Asian monsoon system influences the lives of over 60% of the planet's population, with widespread socioeconomic effects resulting from weakening or failure of monsoon rains. Spatially broad and temporally extended drought episodes have been known to dramatically influence human history, including the Strange Parallels Drought in the mid-18th century. Here, we explore the dynamics of sustained monsoon failure using the Monsoon Asia Drought Atlas - a high-resolution network of hydro-climatically sensitive tree-ring records - and a 1300-year pre-industrial control run of the Community Earth System Model (CESM). Spatial drought patterns in the instrumental and model-based Palmer Drought Severity Index (PDSI) during years with extremely weakened South Asian monsoon are similar to those reconstructed during the Strange Parallels Drought in the MADA. We further explore how the large-scale Indo-Pacific climate during weakened South Asian monsoon differs between interannual and decadal timescales. The Strange Parallels Drought pattern is observed during March-April-May primarily over Southeast Asia, with decreased precipitation and reduced moisture fluxes, while anomalies in June-July-August are confined to the Indian subcontinent during both individual and decadal events. Individual years with anomalous drying exhibit canonical El Niño conditions over the eastern equatorial Pacific and associated shifts in the Walker circulation, while decadal events appear to be related to anomalous warming around the dateline in the equatorial Pacific, typical of El Niño Modoki events. The results suggest different dynamical processes influence drought at different time scales through distinct remote ocean influences.

  2. 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Pai, D.S.; Sreejith, O.P.; Hatwar, H.R. [India Meteorological Department, Pune (India); Bhate, Jyoti [National Atmospheric Research Laboratory, Gadnki (India)

    2011-01-15

    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

  4. Meso-scale distribution of summer monsoon rainfall near the Western Ghats (India)

    Science.gov (United States)

    Patwardhan, S. K.; Asnani, G. C.

    2000-04-01

    The spatial distribution of southwest monsoon rainfall is studied over Maharashtra State (India), which includes part of the well-known Western Ghats mountain range, near its western boundary, running almost from north to south, perpendicular to the summer monsoon current in the lower troposphere. Meso-scale analysis of daily rainfall is performed for Maharashtra State, including the Western Ghats, for the two mid-monsoon months of July and August, during the 10-year period of 1971-1980. Strong and weak monsoon days were identified for the 5-year period of 1976-1980. The meso-scale pattern of average daily rainfall is obtained separately for strong and for weak monsoon conditions.All these average patterns show the following features: (i) the rainfall increases rapidly from the Arabian Sea coast close to the line of maximum height of the Western Ghats; (ii) there are two rainfall maxima corresponding to the two mountain peaks parallel to the coast line; (iii) between the two mountain peaks, there is a valley which is narrow at the western end (upwind end), broadening towards the east (on the downwind side). Ground contour height of the valley rises eastwards and ends as a part of the Deccan Plateau east of the Ghats. Here the valley opens out like a funnel with higher mountains flanking its two sides. In the valley, the rainfall increases from the coast up to the line of maximum height of the Ghats, and then decreases eastwards towards the plateau. The rainfall isopleths also take a funnel-shaped configuration. An interesting feature is that near the wider section of the valley funnel, there is a rainfall minimum and then the rainfall increases further eastwards on the downwind side. This feature of rainfall minimum is somewhat similar to the rainfall minimum reported by Asnani and Kinuthia (personal communication); Asnani (Asnani GC. 1993. Tropical Meteorology, Vol. I. Prof. G.C. Asnani: Pune, India; 603) attributed the rainfall minimum to the Bernoulli effect. A

  5. 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

  6. Transport of aerosols into the UTLS and their impact on the Asian monsoon region as seen in a global model simulation

    Directory of Open Access Journals (Sweden)

    S. Fadnavis

    2013-09-01

    Full Text Available An eight-member ensemble of ECHAM5-HAMMOZ simulations for a boreal summer season is analysed to study the transport of aerosols in the upper troposphere and lower stratosphere (UTLS during the Asian summer monsoon (ASM. The simulations show persistent maxima in black carbon, organic carbon, sulfate, and mineral dust aerosols within the anticyclone in the UTLS throughout the ASM (period from July to September, when convective activity over the Indian subcontinent is highest, indicating that boundary layer aerosol pollution is the source of this UTLS aerosol layer. The simulations identify deep convection and the associated heat-driven circulation over the southern flanks of the Himalayas as the dominant transport pathway of aerosols and water vapour into the tropical tropopause layer (TTL. Comparison of model simulations with and without aerosols indicates that anthropogenic aerosols are central to the formation of this transport pathway. Aerosols act to increase cloud ice, water vapour, and temperature in the model UTLS. Evidence of ASM transport of aerosols into the stratosphere is also found, in agreement with aerosol extinction measurements from the Halogen Occultation Experiment (HALOE and Stratospheric Aerosol and Gas Experiment (SAGE II. As suggested by the observations, aerosols are transported into the Southern Hemisphere around the tropical tropopause by large-scale mixing processes. Aerosol-induced circulation changes also include a weakening of the main branch of the Hadley circulation and a reduction of monsoon precipitation over India.

  7. 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.

  8. 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 converg