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Sample records for holocene asian monsoon

  1. Late Holocene anti-phase change in the East Asian summer and winter monsoons

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    Kang, Shugang; Wang, Xulong; Roberts, Helen M.; Duller, Geoff A. T.; Cheng, Peng; Lu, Yanchou; An, Zhisheng

    2018-05-01

    Changes in East Asian summer and winter monsoon intensity have played a pivotal role in the prosperity and decline of society in the past, and will be important for future climate scenarios. However, the phasing of changes in the intensity of East Asian summer and winter monsoons on millennial and centennial timescales during the Holocene is unclear, limiting our ability to understand the factors driving past and future changes in the monsoon system. Here, we present a high resolution (up to multidecadal) loess record for the last 3.3 ka from the southern Chinese Loess Plateau that clearly demonstrates the relationship between changes in the intensity of the East Asian summer and winter monsoons, particularly at multicentennial scales. At multimillennial scales, the East Asian summer monsoon shows a steady weakening, while the East Asian winter monsoon intensifies continuously. At multicentennial scales, a prominent ∼700-800 yr cycle in the East Asian summer and winter monsoon intensity is observed, and here too the two monsoons are anti-phase. We conclude that multimillennial changes are driven by Northern Hemisphere summer insolation, while multicentennial changes can be correlated with solar activity and changing strength of the Atlantic meridional overturning circulation.

  2. Holocene climatic fluctuations and periodic changes in the Asian southwest monsoon region

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    Zhang, Wenxiang; Niu, Jie; Ming, Qingzhong; Shi, Zhengtao; Lei, Guoliang; Huang, Linpei; Long, Xian'e.; Chang, Fengqin

    2018-05-01

    Climatic changes in the Asian southwest monsoon (ASWM) during the Holocene have become a topic of recent studies. It is important to understand the patterns and causes of Holocene climatic changes and their relationship with global changes. Based on the climate proxies and wavelet analysis of Lugu Lake in the ASWM region, the climatic fluctuations and periodic changes in the ASWM region during the Holocene have been reconstructed with a high-precision chronology. The results indicate the intensification of ASWM began to increase with Northern Hemisphere low-latitude solar insolation (LSI) and solar activity during the early Holocene, and gradually decreased during the late Holocene, exhibiting an apparent synchrony with numerous records of ASWM region. Meanwhile, an apparent 1000-a quasi-periodic signal is present in the environment proxies, and it demonstrates that the environmental change in the ASWM region has been driven mainly by LSI and solar activity.

  3. Variability of East Asian summer monsoon precipitation during the Holocene and possible forcing mechanisms

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    Lu, Fuzhi; Ma, Chunmei; Zhu, Cheng; Lu, Huayu; Zhang, Xiaojian; Huang, Kangyou; Guo, Tianhong; Li, Kaifeng; Li, Lan; Li, Bing; Zhang, Wenqing

    2018-03-01

    Projecting how the East Asian summer monsoon (EASM) rainfall will change with global warming is essential for human sustainability. Reconstructing Holocene climate can provide critical insight into its forcing and future variability. However, quantitative reconstructions of Holocene summer precipitation are lacking for tropical and subtropical China, which is the core region of the EASM influence. Here we present high-resolution annual and summer rainfall reconstructions covering the whole Holocene based on the pollen record at Xinjie site from the lower Yangtze region. Summer rainfall was less seasonal and 30% higher than modern values at 10-6 cal kyr BP and gradually declined thereafter, which broadly followed the Northern Hemisphere summer insolation. Over the last two millennia, however, the summer rainfall has deviated from the downward trend of summer insolation. We argue that greenhouse gas forcing might have offset summer insolation forcing and contributed to the late Holocene rainfall anomaly, which is supported by the TraCE-21 ka transient simulation. Besides, tropical sea-surface temperatures could modulate summer rainfall by affecting evaporation of seawater. The rainfall pattern concurs with stalagmite and other proxy records from southern China but differs from mid-Holocene rainfall maximum recorded in arid/semiarid northern China. Summer rainfall in northern China was strongly suppressed by high-northern-latitude ice volume forcing during the early Holocene in spite of high summer insolation. In addition, the El Niño/Southern Oscillation might be responsible for droughts of northern China and floods of southern China during the late Holocene. Furthermore, quantitative rainfall reconstructions indicate that the Paleoclimate Modeling Intercomparison Project (PMIP) simulations underestimate the magnitude of Holocene precipitation changes. Our results highlight the spatial and temporal variability of the Holocene EASM precipitation and potential forcing

  4. Non-linear regime shifts in Holocene Asian monsoon variability: potential impacts on cultural change and migratory patterns

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    Donges, J. F.; Donner, R. V.; Marwan, N.; Breitenbach, S. F. M.; Rehfeld, K.; Kurths, J.

    2015-05-01

    The Asian monsoon system is an important tipping element in Earth's climate with a large impact on human societies in the past and present. In light of the potentially severe impacts of present and future anthropogenic climate change on Asian hydrology, it is vital to understand the forcing mechanisms of past climatic regime shifts in the Asian monsoon domain. Here we use novel recurrence network analysis techniques for detecting episodes with pronounced non-linear changes in Holocene Asian monsoon dynamics recorded in speleothems from caves distributed throughout the major branches of the Asian monsoon system. A newly developed multi-proxy methodology explicitly considers dating uncertainties with the COPRA (COnstructing Proxy Records from Age models) approach and allows for detection of continental-scale regime shifts in the complexity of monsoon dynamics. Several epochs are characterised by non-linear regime shifts in Asian monsoon variability, including the periods around 8.5-7.9, 5.7-5.0, 4.1-3.7, and 3.0-2.4 ka BP. The timing of these regime shifts is consistent with known episodes of Holocene rapid climate change (RCC) and high-latitude Bond events. Additionally, we observe a previously rarely reported non-linear regime shift around 7.3 ka BP, a timing that matches the typical 1.0-1.5 ky return intervals of Bond events. A detailed review of previously suggested links between Holocene climatic changes in the Asian monsoon domain and the archaeological record indicates that, in addition to previously considered longer-term changes in mean monsoon intensity and other climatic parameters, regime shifts in monsoon complexity might have played an important role as drivers of migration, pronounced cultural changes, and the collapse of ancient human societies.

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

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    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.

  6. Middle Holocene Organic Carbon and Biomarker Records from the South Yellow Sea: Relationship to the East Asian Monsoon

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    Zou, Liang; Hu, Bangqi; Li, Jun; Dou, Yanguang; Xie, Luhua; Dong, Liang

    2018-03-01

    The East Asian monsoon system influences the sedimentation and transport of organic matter in East Asian marginal seas that is derived from both terrestrial and marine sources. In this study, we determined organic carbon (OC) isotope values, concentrations of marine biomarkers, and levels of OC and total nitrogen (TN) in core YSC-1 from the central South Yellow Sea (SYS). Our objectives were to trace the sources of OC and variations in palaeoproductivity since the middle Holocene, and their relationships with the East Asian monsoon system. The relative contributions of terrestrial versus marine organic matter in core sediments were estimated using a two-end-member mixing model of OC isotopes. Results show that marine organic matter has been the main sediment constituent since the middle Holocene. The variation of terrestrial organic carbon concentration (OCter) is similar to the EASM history. However, the variation of marine organic carbon concentration (OCmar) is opposite to that of the EASM curve, suggesting OCmar is distinctly influenced by terrestrial material input. Inputs of terrestrial nutrients into the SYS occur in the form of fluvial and aeolian dust, while concentrations of nutrients in surface water are derived mainly from bottom water via the Yellow Sea circulation system, which is controlled by the East Asian winter monsoon (EAWM). Variations in palaeoproductivity represented by marine organic matter and biomarker records are, in general, consistent with the recent EAWM intensity studies, thus, compared with EASM, EAWM may play the main role to control the marine productivity variations in the SYS.

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

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

    2016-04-01

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

  8. Reconstructing Holocene hematite and goethite variations in the Indus Canyon to trace changes in the Asian monsoon system

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    Koehler, Cornelia; Clift, Peter; Pressling, Nicola; Limmer, David; Giosan, Liviu; Tabrez, Ali

    2010-05-01

    In order to study Holocene Asian monsoon variations, we reconstructed changes in chemical weathering by examining sediments from the Indus Canyon. During the late Holocene, the Asian monsoon system had periods of high and low intensities that influenced the civilisations living in its realm. For example, the demise of the Harappan civilisation has been linked to a weakened monsoon system around 4 ka. The sediments in the Indus Canyon, which originate from the River Indus and its Himalayan tributaries, provide an ideal, natural environmental archive of the South Asian monsoon system. In order to investigate the alternation between arid and humid monsoonal climatic conditions, variations are traced using the magnetic minerals hematite and goethite, which form under distinct environmental conditions: goethite is stable under humid conditions, whereas hematite forms from the dehydration of goethite under arid conditions. The two minerals are characterised and quantified using environmental magnetic measurements, as well as diffuse reflectance spectrometry. Combining both approaches will enable us to reconstruct variations in chemical weathering over time. Furthermore, because this is governed by temperature and the availability of moisture, our weathering record will allow us to understand monsoon variability during the Holocene and test whether summer rain intensity has been decreasing in SW Asia since 8 ka. In addition, the multi-component analysis of colour reflectance spectra identifies different mineral components including hematite/goethite, clay mineral mixtures, calcite and organics. We will present our results from the multi-sensor core logger equipped with a Minolta spectrometer, measuring both magnetic susceptibility and the optical properties of the split sediment cores. Initial results indicate the presence of hematite and goethite in the sediment. There is an increasing hematite content up the cores, indicating an aridification trend during the Holocene

  9. The 9.2 ka event in Asian summer monsoon area: the strongest millennial scale collapse of the monsoon during the Holocene

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    Zhang, Wenchao; Yan, Hong; Dodson, John; Cheng, Peng; Liu, Chengcheng; Li, Jianyong; Lu, Fengyan; Zhou, Weijian; An, Zhisheng

    2018-04-01

    Numerous Holocene paleo-proxy records exhibit a series of centennial-millennial scale rapid climatic events. Unlike the widely acknowledged 8.2 ka climate anomaly, the likelihood of a significant climate excursion at around 9.2 cal ka BP, which has been notably recognized in some studies, remains to be fully clarified in terms of its magnitude and intensity, as well as its characteristics and spatial distributions in a range of paleoclimatic records. In this study, a peat sediment profile from the Dajiuhu Basin in central China was collected with several geochemical proxies and a pollen analysis carried out to help improve understanding of the climate changes around 9.2 cal ka BP. The results show that the peat development was interrupted abruptly at around 9.2 cal ka BP, when the chemical weathering strength decreased and the tree-pollen declined. This suggests that a strong drier regional climatic event occurred at around 9.2 cal ka BP in central China, which was, in turn, probably connected to the rapid 9.2 ka climate event co-developing worldwide. In addition, based on the synthesis of our peat records and the other Holocene hydrological records from Asian summer monsoon (ASM) region, we further found that the 9.2 ka event probably constituted the strongest abrupt collapse of the Asian monsoon system during the full Holocene interval. The correlations between ASM and the atmospheric 14C production rate, the North Atlantic drift ice records and Greenland temperature indicated that the weakened ASM event at around 9.2 cal ka BP could be interpreted by the co-influence of external and internal factors, related to the changes of the solar activity and the Atlantic Meridional Overturning Circulation (AMOC).

  10. Seasonal and interannual variability of the Mid-Holocene East Asian monsoon in coral δ18O records from the South China Sea

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    Sun, Donghuai; Gagan, Michael K.; Cheng, Hai; Scott-Gagan, Heather; Dykoski, Carolyn A.; Edwards, R. Lawrence; Su, Ruixia

    2005-08-01

    Understanding the full range of past monsoon variability, with reference to specific monsoon seasons, is essential to test coupled climate models and improve their predictive capabilities. We present a 54-year long, high-resolution skeletal oxygen isotope (δ18O) record extracted from a well-preserved, massive Porites sp. coral at Hainan Island, South China Sea, to investigate East Asian monsoon variability during summer and winter ∼4400 calendar yr ago. Analysis of modern coral δ18O confirms that Porites from Hainan Island are well positioned to record winter monsoon forcing of sea surface temperature (SST), as well as the influence of summer monsoon rainfall on sea surface salinity (SSS). The coral record for ∼4400 yr ago shows ∼9% amplification of the annual cycle of δ18O, in good agreement with coupled ocean-atmosphere models showing higher summer rainfall (lower coral δ18O) and cooler winter SSTs (higher coral δ18O) in response to greater Northern Hemisphere insolation seasonality during the Middle Holocene. Mean SSTs in the South China Sea during the Mid-Holocene were within 0.5 °C of modern values, yet the mean δ18O for the fossil coral is ∼0.6‰ higher than that for the modern coral, suggesting that the δ18O of surface seawater was higher by at least ∼0.5‰, relative to modern values. The 18O-enrichment is likely to be driven by greater advection of moisture towards the Asian landmass, enhanced monsoon wind-induced evaporation and vertical mixing, and/or invigorated advection of saltier 18O-enriched Pacific water into the relatively fresh South China Sea. The 18O-enrichment of the northern South China Sea ∼4400 yr ago contributes to mounting evidence for recent freshening of the tropical Western Pacific. Today, winter SST and summer SSS variability in the South China Sea reflect the interannual influence of ENSO and the biennial variability inherent to monsoon precipitation. Spectral analysis of winter SSTs ∼4400 yr ago reveals a

  11. Holocene soil pH changes and East Asian summer monsoon evolution derived from loess brGDGTs in the northeastern Tibetan Plateau

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    Duan, Y.; Sun, Q.; Zhao, H.

    2017-12-01

    GDGTs-based proxies have been used successfully to reconstruct paleo-temperature from loess-paleosol sequences during the past few years. However, the pH variations of loess sediments derived from GDGTs covering the geological history remain poorly constrained. Here we present two pH records spanning the last 12 ka (1ka=1000years) based on the modified cyclization ratio index (CBT') of the branched GDGTs using regional CBT'-pH empirical relationship from two well-dated loess-paleosol sections (YWY14 and SHD09) in the northeastern Tibetan Plateau. The results indicate that a slightly alkaline condition occurred during 12 8.5 ka with pH values ranging from 6.98 to 7.24, then CBT'-derived pH decreased from 8.5 to 6.5 ka with values from 7.19 to 6.49 and gradually increased thereafter. The reconstructed pH values from topmost samples can be well compared with instrumental pH values of the surrounding surface soil. The lowest intervals of CBT'-derived pH values during the mid-Holocene in our records are consistent with the results of highest tree pollen percentage from the adjacent lake sediments and regional weakest aeolian activities, which reveals that the moisture maximum during that period, but conflicted with previous results of the wettest early-Holocene inferred from speleothem or ostracod shell oxygen isotope (δ18O) values. Taking together, we conclude that Holocene humidity evolution (wettest middle Holocene) in response to the East Asian summer monsoon (EASM) changes exerts important control on pH variations of loess deposits in northeastern Tibetan Plateau. CBT'-derived pH variations can be potentially used as an indicator of EASM evolution reconstructions. In addition, we argue that speleothem or ostracod shell δ18O records are essentially a signal of the isotopic composition of precipitations rather than EASM intensity.

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

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    L. Jin

    2009-08-01

    Full Text Available The impacts of various scenarios of a gradual 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 Earth system 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 over most of Eurasia but in the Southern Asia temperature response is opposite. 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 kyr BP to 6 kyr BP while it has only minor influence on that in South Asia until 5 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 suggest that the development of snow and ice cover over Tibetan Plateau represents an additional important climate feedback, which amplify orbital forcing and produces a significant synergy with the positive vegetation feedback.

  13. Transient coupling relationships of the Holocene Australian monsoon

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    McRobie, F. H.; Stemler, T.; Wyrwoll, K.-H.

    2015-08-01

    The northwest Australian summer monsoon owes a notable degree of its interannual variability to interactions with other regional monsoon systems. Therefore, changes in the nature of these relationships may contribute to variability in monsoon strength over longer time scales. Previous attempts to evaluate how proxy records from the Indonesian-Australian monsoon region correspond to other records from the Indian and East Asian monsoon regions, as well as to El Niño-related proxy records, have been qualitative, relying on 'curve-fitting' methods. Here, we seek a quantitative approach for identifying coupling relationships between paleoclimate proxy records, employing statistical techniques to compute the interdependence of two paleoclimate time series. We verify the use of complex networks to identify coupling relationships between modern climate indices. This method is then extended to a set of paleoclimate proxy records from the Asian, Australasian and South American regions spanning the past 9000 years. The resulting networks demonstrate the existence of coupling relationships between regional monsoon systems on millennial time scales, but also highlight the transient nature of teleconnections during this period. In the context of the northwest Australian summer monsoon, we recognise a shift in coupling relationships from strong interhemispheric links with East Asian and ITCZ-related proxy records in the mid-Holocene to significantly weaker coupling in the later Holocene. Although the identified links cannot explain the underlying physical processes leading to coupling between regional monsoon systems, this method provides a step towards understanding the role that changes in teleconnections play in millennial-to orbital-scale climate variability.

  14. A geochemical record of the link between chemical weathering and the East Asian summer monsoon during the late Holocene preserved in lacustrine sediments from Poyang Lake, central China

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    Huang, Chao; Wei, Gangjian; Li, Wuxian; Liu, Ying

    2018-04-01

    This paper presents relatively high-resolution geochemical records spanning the past 4000 cal yr BP obtained from the lacustrine sediments of Poyang Lake in central China. The variations in the intensity of the East Asian summer monsoon (EASM) are traced using the K/Na, Ti/Na, Al/K, kaolinite/illite and clay/feldspar ratios, together with the chemical index of alteration (CIA), as indicators of chemical weathering. During the last 4000 years, the proxy records of chemical weathering from Poyang Lake exhibit an overall enhanced trend, consistent with regional hydrological changes in previous independent records. Further comparisons and analyses demonstrate that regional moisture variations in central China is inversely correlated with the EASM intensity, with weak EASM generating high precipitation in central China. Our data reveal three intervals of dramatically dry climatic conditions (i.e., ca. 4000-3200 cal yr BP, ca. 2800-2400 cal yr BP, and ca. 500-200 cal yr BP). A period of weak chemical weathering, related to cold and dry climatic conditions, occurred during the Little Ice Age (LIA), whereas more intense chemical weathering, reflecting warm and humid climatic conditions, was recorded during the Medieval Warm Period (MWP). Besides, an intensification of chemical weathering in Poyang Lake during the late Holocene agrees well with strong ENSO activity, suggesting that moisture variations in central China may be predominantly driven by ENSO variability.

  15. Global monsoons in the mid-Holocene and oceanic feedback

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    Liu, Z.; Kutzbach, J. [Center for Climatic Research, University of Wisconsin-Madison, 1225 W. Dayton Street, Madison, WI 53706 (United States); Harrison, S.P. [Max Planck Institute for Biogeochemistry, P.O. Box 100164, 07701 Jena (Germany); Otto-Bliesner, B. [National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307 (United States)

    2004-03-01

    The response of the six major summer monsoon systems (the North American monsoon, the northern Africa monsoon, the Asia monsoon, the northern Australasian monsoon, the South America monsoon and the southern Africa monsoon) to mid-Holocene orbital forcing has been investigated using a coupled ocean-atmosphere general circulation model (FOAM), with the focus on the distinct roles of the direct insolation forcing and oceanic feedback. The simulation result is also found to compare well with the NCAR CSM. The direct effects of the change in insolation produce an enhancement of the Northern Hemisphere monsoons and a reduction of the Southern Hemisphere monsoons. Ocean feedbacks produce a further enhancement of the northern Africa monsoon and the North American monsoon. However, ocean feedbacks appear to weaken the Asia monsoon, although the overall effect (direct insolation forcing plus ocean feedback) remains a strengthened monsoon. The impact of ocean feedbacks on the South American and southern African monsoons is relatively small, and therefore these regions, especially the South America, experienced a reduced monsoon regime compared to present. However, there is a strong ocean feedback on the northern Australian monsoon that negates the direct effects of orbital changes and results in a strengthening of austral summer monsoon precipitation in this region. A new synthesis is made for mid-Holocene paleoenvironmental records and is compared with the model simulations. Overall, model simulations produce changes in regional climates that are generally consistent with paleoenvironmental observations. (orig.)

  16. Asian monsoon variability, cyclicities, and forcing mechanisms

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    in monsoonal intensity from 5 to 2Ma. Uplift of the Himalayas and the Tibetan Plateau occurred coeval with the increase in strength of the Asian Monsoon between 9.5 and 5Ma. Variability of monsoon on glacial and interglacial time scale Multi proxy based... in the Western Ghats of India 131 Fig. 3. Multi proxy monsoon reconstructions show that summer monsoon strength was stronger during interglacials (shaded intervals) as compared to glacials 0 2 4 6 8 10 12 14 16 18 20 0 100 200 300 400 0 50...

  17. Modelling the Asian summer monsoon using CCAM

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    Nguyen, Kim Chi; McGregor, John L. [CSIRO Marine and Atmospheric Research, Aspendale, VIC (Australia)

    2009-02-15

    A ten-year mean (1989-1998) climatology of the Asian summer monsoon is studied using the CSIRO Conformal-Cubic Atmospheric Model (CCAM) to downscale NCEP reanalyses. The aim of the current study is to validate the model results against previous work on this topic, in order to identify model strengths and weaknesses in simulating the Asian summer monsoon. The model results are compared with available observations and are presented in two parts. In the first part, the mean summer rainfall, maximum and minimum temperatures and winds are compared with the observations. The second part focuses on validation of the monsoon onset. The model captures the mean characteristics such as the cross-equatorial flow of low-level winds over the Indian Ocean and near the Somali coast, rainfall patterns, onset indices, northward movements, active-break and revival periods. (orig.)

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

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    Mohtadi, Mahyar; Oppo, Delia W.; Steinke, Stephan; Stuut, Jan-Berend W.; de Pol-Holz, Ricardo; Hebbeln, Dierk; Lückge, Andreas

    2011-08-01

    The Australian-Indonesian monsoon is an important component of the climate system in the tropical Indo-Pacific region. However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java. We show that glacial-interglacial variations in the Australian-Indonesian winter monsoon were in phase with the Indian summer monsoon system, consistent with their modern linkage through cross-equatorial surface winds. Likewise, millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea. On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive, we infer that (austral) summer monsoon rainfall was highest during the Bølling-Allerød period and the past 2,500 years. Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator. We suggest that the Australian-Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere.

  19. Indian monsoon variations during three contrasting climatic periods: the Holocene, Heinrich Stadial 2 and the last interglacial-glacial transition

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    Zorzi, Coralie; Fernanda Sanchez Goñi, Maria; Anupama, Krishnamurthy; Prasad, Srinivasan; Hanquiez, Vincent; Johnson, Joel; Giosan, Liviu

    2016-04-01

    In contrast to the East Asian and African monsoons the Indian monsoon is still poorly documented throughout the last climatic cycle (last 135,000 years). Pollen analysis from two marine sediment cores (NGHP-01-16A and NGHP-01-19B) collected from the offshore Godavari and Mahanadi basins, both located in the Core Monsoon Zone (CMZ) reveals changes in Indian summer monsoon variability and intensity during three contrasting climatic periods: the Holocene, the Heinrich Stadial (HS) 2 and the Marine Isotopic Stage (MIS) 5/4 during the ice sheet growth transition. During the first part of the Holocene between 11,300 and 4,200 cal years BP, characterized by high insolation (minimum precession, maximum obliquity), the maximum extension of the coastal forest and mangrove reflects high monsoon rainfall. This climatic regime contrasts with that of the second phase of the Holocene, from 4,200 cal years BP to the present, marked by the development of drier vegetation in a context of low insolation (maximum precession, minimum obliquity). The historical period in India is characterized by an alternation of strong and weak monsoon centennial phases that may reflect the Medieval Climate Anomaly and the Little Ice Age, respectively. During the HS 2, a period of low insolation and extensive iceberg discharge in the North Atlantic Ocean, vegetation was dominated by grassland and dry flora indicating pronounced aridity as the result of a weak Indian summer monsoon. The MIS 5/4 glaciation, also associated with low insolation but moderate freshwater fluxes, was characterized by a weaker reduction of the Indian summer monsoon and a decrease of seasonal contrast as recorded by the expansion of dry vegetation and the development of Artemisia, respectively. Our results support model predictions suggesting that insolation changes control the long term trend of the Indian monsoon precipitation, but its millennial scale variability and intensity are instead modulated by atmospheric

  20. Biomarker records of Holocene climate variations in Asian interior

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    Song, M.; Liu, Z.; Liu, W.; Zhao, C.; Li, S.; He, Y.

    2012-12-01

    Understanding Holocene climate fluctuation may provide clues to projection of future climate change. Lake sediments in the arid central Asia (ACA), as an archive of past climate information, keep attracting considerable interest. We have retrieved several sediment cores from Lake Manas, an endorheic lake in Zunggar desert, Xinjiang Province, China. Biomarker proxies including alkenone Uk'37, %C37:4 and C37 concentration (C37 Conc), and physical proxies including density and magnetic susceptibility (MS) have been analyzed. We have found substantial climatic and environmental changes during the late Holocene. Density, MS and Uk'37 values are high during Medieval Warm Period (MWP) and C37 Conc is very low. During the Little Ice Age, density and MS decrease, Uk'37 values drop to near 0.1, C37 Conc is increased by 2 to 3 magnitude. Thus, warm and dry conditions dominated MWP while cold and wet conditions dominated LIA, a typical "Westerly" pattern which is opposite to the hydrological variation in Asian monsoonal regions. Biomarker records' correlation with solar irradiance (SI), the North Atlantic Oscillation (NAO), the 1000year ACA Moisture Index (ACAM), and the North Hemisphere Temperature (NHT) suggests SI as one of the forcing factor on temperature fluctuation and cold and wet LIA possibly resulting from westerly-jet shift, negative NAO oscillation and the lower evaporation induced by the decrease of temperature. Biomarker records for the whole Holocene will be also presented.

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

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    Yu Li

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

  2. Comparison of East Asian winter monsoon indices

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    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.

  3. Stalagmite-derived Last Glacial Maximum - Mid Holocene Indian Monsoon Record from Krem Mawmluh, Meghalaya, NE India

    Science.gov (United States)

    Lone, M. A.; Routh, J.; Kumar, V.; Mangini, A.; Rangarajan, R.; Ghosh, P.; Munnuru Singamshetty, K.; Shen, C. C.; Ahmad, S. M.; Mii, H. S.

    2016-12-01

    Seasonal reversals in monsoon winds strongly influence rainfall patterns on the Indian sub-continent regulating the socio-economy of south Asian region. High-resolution centennial-millennial scale records of climate change from the core zone of the monsoon impacted region are nonetheless very few. Here, we report Indian summer monsoon (ISM) variability record from an 87-cm long stalagmite (KM-1) from Krem Mawmluh in the Khasi Hills, Meghalaya. The absolute dated stalagmite record ranges from 22.7 (LGM) to 6.7 ka (Mid Holocene), revealing last glacial-interglacial paleoclimatic changes over the Indian sub-continent. A sharp change in δ18O ( 5‰) and growth rate post Younger Dryas (YD) is marked by continued rapid speleogenesis in KM-1 and coincides with monsoon intensification during the early Holocene. Prominent multi-centennial to millennial scale dry phases in ISM activity are observed from LGM to YD. During early to mid-Holocene, the record shows significant multi-decadal to centennial scale changes. The high frequency δ18O variations referring to abrupt changes in ISM activity are believed to be driven by changes in temperature and shifting of Inter-Tropical Convergence Zone.

  4. A Holocene Record of Monsoon Intensity From Speleothems in Flores, Indonesia

    Science.gov (United States)

    Griffiths, M. L.; Drysdale, R.; Gagan, M.; Ayliffe, L.; Zhao, J.; St. Pierre, E.; Hantoro, W.; Suwargadi, B.

    2007-12-01

    The Australasian monsoon is among the largest monsoon systems on Earth. The affected region experiences a marked seasonal cycle in winds and precipitation, similar to its Northern Hemisphere counterparts (e.g., Asian monsoons). The Australasian monsoon is the life blood of the millions of people of the Indonesian archipelago. Since the climate is the dominating factor controlling food production, it is of great significance and urgency that we gain a firmer grasp on the parameters that control variations in monsoon intensity. Precise uranium series dating of two actively growing speleothems measuring ~1.25 (LR06-B1) and ~1.61 (LR06-B3) meters in length from Liang Luar cave (Flores, eastern Indonesia), reveal basal ages of ~12,846±103 and 23,605±171 years respectively. In previous studies, stable isotope ratios (δ18O and δ13C) and trace element concentrations in speleothems have revealed past environmental change (e.g., Burns et al., 2001; Wang et al., 2001; Fleitmann et al., 2004; Drysdale et al., 2004).In monsoon-affected regions, the δ18O signal recorded in stalagmites seems to be dominated by the amount of precipitation (so-called `amount effect'), whereby more negative (positive) δ18O values indicate enhanced (diminished) precipitation. Preliminary results from LR06-B1 indicate that δ18O values show a general increase in monsoon intensity from the beginning of the record to ~2000 years BP: this more or less follows insolation changes over the Australian continent.Comparison of our record with D4 from Dongge Cave reveals an anticorrelation during the Holocene, further supporting the hypothesis that tropical monsoon intensity is largely controlled by changes in insolation in both the Northern and Southern Hemisphere. Examination of our δ13C record demonstrates a high-frequency signal superimposed on low- frequency variability which correlates with the reconstructed sunspot cycle: higher (lower) sunspot numbers, and hence increased solar activity

  5. Late holocene primary productivity and sea surface temperature variations in the northeastern Arabian Sea: Implications for winter monsoon variability.

    Digital Repository Service at National Institute of Oceanography (India)

    Boll, A.; Luckge, A.; Munz, P.; Forke, S.; Schulz, H.; Ramaswamy, V.; Rixen, T.; Gaye, B.; Emeis, K.-C.

    changes in winter monsoon strength with winds from the northeast that drive convective mixing and high surface ocean productivity in the northeastern Arabian Sea. To establish a high-resolution record of winter monsoon variability for the late Holocene, we...

  6. 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

  7. Monsoonal response to mid-holocene orbital forcing in a high resolution GCM

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    J. H. C. Bosmans

    2012-04-01

    Full Text Available In this study, we use a sophisticated high-resolution atmosphere-ocean coupled climate model, EC-Earth, to investigate the effect of Mid-Holocene orbital forcing on summer monsoons on both hemispheres. During the Mid-Holocene (6 ka, there was more summer insolation on the Northern Hemisphere than today, which intensified the meridional temperature and pressure gradients. Over North Africa, monsoonal precipitation is intensified through increased landward monsoon winds and moisture advection as well as decreased moisture convergence over the oceans and more convergence over land compared to the pre-industrial simulation. Precipitation also extends further north as the ITCZ shifts northward in response to the stronger poleward gradient of insolation. This increase and poleward extent is stronger than in most previous ocean-atmosphere GCM simulations. In north-westernmost Africa, precipitation extends up to 35° N. Over tropical Africa, internal feedbacks completely overcome the direct warming effect of increased insolation. We also find a weakened African Easterly Jet. Over Asia, monsoonal precipitation during the Mid-Holocene is increased as well, but the response is different than over North-Africa. There is more convection over land at the expense of convection over the ocean, but precipitation does not extend further northward, monsoon winds over the ocean are weaker and the surrounding ocean does not provide more moisture. On the Southern Hemisphere, summer insolation and the poleward insolation gradient were weaker during the Mid-Holocene, resulting in a reduced South American monsoon through decreased monsoon winds and less convection, as well as an equatorward shift in the ITCZ. This study corroborates the findings of paleodata research as well as previous model studies, while giving a more detailed account of Mid-Holocene monsoons.

  8. Dynamics and composition of the Asian summer monsoon anticyclone

    NARCIS (Netherlands)

    Gottschaldt, Klaus Dirk; Schlager, Hans; Baumann, Robert; Sinh Cai, Duy; Eyring, Veronika; Graf, Phoebe; Grewe, V.; Jöckel, Patrick; Jurkat-Witschas, Tina; Voigt, Christiane; Zahn, Andreas; Ziereis, Helmut

    2018-01-01

    This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth

  9. Late Holocene monsoon climate as evidenced by proxy records from a lacustrine sediment sequence in western Guangdong, South China

    Science.gov (United States)

    Zhong, Wei; Cao, jiayuan; Xue, Jibin; Ouyang, Jun; Tang, Xiaohong; Yin, Huanling; Liao, Congyun; Long, Kun

    2014-02-01

    The study of a 300-cm-thick exposed lacustrine sediment section in the Hedong village in Zhaoqing area which is located in sub-tropical west Guangdong Province in South China, demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of Asian monsoon climate. Multi-proxy records, including the humification intensity, total organic carbon, and grain size fractions, reveal a general trend towards dry and cold conditions in the late Holocene that this is because of a decrease in solar insolation on an orbital scale. Three intensified Asian summer monsoon (ASM) intervals (˜3300-3000 cal yr BP, ˜2600-1600 cal yr BP, and ˜900-600 cal yr BP), and three weakened ASM intervals (˜4000-3300 cal yr BP, ˜3000-2600 cal yr BP, and ˜1600-900 cal yr BP) are identified. Our humification record (HDcal) shows a good correlation on multi-centennial scale with the tree ring Δ14C record, a proxy of solar activity. A spectral analysis of HDcal reveals four significant cycles, i.e., ˜1250 yr, 300 yr, 110 yr, and 70 yr, and most of these cycles are related to the solar activity. Our findings indicate that solar output and oceanic-atmospheric circulation probably have influenced the late Holocene climate variability in the study region.

  10. A Stalagmite record of Holocene Indonesian-Australian summer monsoon variability from the Australian tropics

    Science.gov (United States)

    Denniston, Rhawn F.; Wyrwoll, Karl-Heinz; Polyak, Victor J.; Brown, Josephine R.; Asmerom, Yemane; Wanamaker, Alan D.; LaPointe, Zachary; Ellerbroek, Rebecca; Barthelmes, Michael; Cleary, Daniel; Cugley, John; Woods, David; Humphreys, William F.

    2013-10-01

    Oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave KNI-51, located in the eastern Kimberley region of tropical Western Australia, represent the first absolute-dated, high-resolution speleothem record of the Holocene Indonesian-Australian summer monsoon (IASM) from the Australian tropics. Stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic Holocene IASM which strengthened in the early Holocene, decreased in strength by 4 ka, with a further decrease from ˜2 to 1 ka, before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka. The relationships between the KNI-51 IASM reconstruction and those from published speleothem time series from Flores and Borneo, in combination with other data sets, appear largely inconsistent with changes in the position and/or organization of the Intertropical Convergence Zone (ITCZ). Instead, we argue that the El Niño/Southern Oscillation (ENSO) may have played a dominant role in driving IASM variability since at least the middle Holocene. Given the muted modern monsoon rainfall responses to most El Niño events in the Kimberley, an impact of ENSO on regional monsoon precipitation over northwestern Australia would suggest non-stationarity in the long-term relationship between ENSO forcing and IASM rainfall, possibly due to changes in the mean state of the tropical Pacific over the Holocene.

  11. Asian monsoons in a late Eocene greenhouse world.

    Science.gov (United States)

    Licht, A; van Cappelle, M; Abels, H A; Ladant, J-B; Trabucho-Alexandre, J; France-Lanord, C; Donnadieu, Y; Vandenberghe, J; Rigaudier, T; Lécuyer, C; Terry, D; Adriaens, R; Boura, A; Guo, Z; Soe, Aung Naing; Quade, J; Dupont-Nivet, G; Jaeger, J-J

    2014-09-25

    The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.

  12. 20th century intraseasonal Asian monsoon dynamics viewed from Isomap

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    A. Hannachi

    2013-10-01

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

  13. Cyclicity in the Late Holocene monsoonal changes from the western Bay of Bengal: Foraminiferal approach.

    Digital Repository Service at National Institute of Oceanography (India)

    Rana, S.S.; Nigam, R.

    .; Imbrie, J.; Hays, J.; Kukla, G.; Saltzman, B.. NATO ASI Ser. C: Math. Phys. Sci.; 126: 349-366. Sarkar, A., Ramesh, R., Somayajulu, B.L.K., Agnihotri, R., Jull, A.J.T., Burr, G.S. 2000. High resolution Holocene monsoon record from the eastern Arabian Sea...

  14. Early-Holocene decoupled summer temperature and monsoon precipitation in southwest China

    Science.gov (United States)

    Wu, D.; Chen, F.; Chen, X.; Lv, F.; Zhou, A.; Chen, J.; Abbott, M. B.; Yu, J.

    2017-12-01

    Proxy based reconstructions of Holocene temperature have shown that both the timing and magnitude of the thermal maximum vary substantially between different regions; the simulations results from climate models also show that summers were substantially cooler over regions directly influenced by the presence of the Laurentide ice sheet during the early Holocene, whereas other regions of the Northern Hemisphere were dominated by orbital forcing. However, for lack of summer temperature reconstruction in the low latitude regions like southwestern China dominated by the Indian summer monsoon, the Holocene summer temperature variations and it underlying forcing mechanism are ambiguous. Here we present a well-dated record of pollen-based quantitative summer temperature (mean July; MJT) over the last 14000 years from Xingyun Lake, Yunnan Province, southwest China. It was found that MJT decreased during the YD event, then increased slowly until 7400 yr BP, and decreased thereafter. The MJT shows a pattern with middle Holocene maximum of MJT, indicating a different changing pattern with the carbonate oxygen isotope record (d18O) from the same core during the early Holocene (11500-7400 yr BP), which has the similar variation with speleothem d18O record from Dongge cave, both indicate the variation of monsoon precipitation with the highest precipitation occurred during the early Holocene. Therefore, we propose that the variation of summer temperature and precipitation in southwest China was decoupled during the early Holocene. However, both MJT and monsoon precipitation decreased after the middle Holocene following the boreal summer insolation. We suggest that the high precipitation with strong summer monsoon and hence higher cloud cover may depress the temperature increasing forced by increasing summer insolation during the early Holocene; while melting ice-sheet in the high latitude regions had strongly influenced the summer temperature increase during the deglacial period

  15. 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

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

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    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.

  17. Atmospheric water budget over the South Asian summer monsoon region

    Science.gov (United States)

    Unnikrishnan, C. K.; Rajeevan, M.

    2018-04-01

    High resolution hybrid atmospheric water budget over the South Asian monsoon region is examined. The regional characteristics, variability, regional controlling factors and the interrelations of the atmospheric water budget components are investigated. The surface evapotranspiration was created using the High Resolution Land Data Assimilation System (HRLDAS) with the satellite-observed rainfall and vegetation fraction. HRLDAS evapotranspiration shows significant similarity with in situ observations and MODIS satellite-observed evapotranspiration. Result highlights the fundamental importance of evapotranspiration over northwest and southeast India on atmospheric water balance. The investigation shows that the surface net radiation controls the annual evapotranspiration over those regions, where the surface evapotranspiration is lower than 550 mm. The rainfall and evapotranspiration show a linear relation over the low-rainfall regions (forcing (like surface net radiation). The lead and lag correlation of water budget components show that the water budget anomalies are interrelated in the monsoon season even up to 4 months lead. These results show the important regional interrelation of water budget anomalies on south Asian monsoon.

  18. Dynamics and composition of the Asian summer monsoon anticyclone

    Science.gov (United States)

    Gottschaldt, Klaus-Dirk; Schlager, Hans; Baumann, Robert; Sinh Cai, Duy; Eyring, Veronika; Graf, Phoebe; Grewe, Volker; Jöckel, Patrick; Jurkat-Witschas, Tina; Voigt, Christiane; Zahn, Andreas; Ziereis, Helmut

    2018-04-01

    This study places HALO research aircraft observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) into the context of regional, intra-annual variability by hindcasts with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. The observations were obtained during the Earth System Model Validation (ESMVal) campaign in September 2012. Observed and simulated tracer-tracer relations reflect photochemical O3 production as well as in-mixing from the lower troposphere and the tropopause layer. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from those in the rest of the year, and the measurements reflect the main processes acting throughout the monsoon season. Net photochemical O3 production is significantly enhanced in the ASMA, where uplifted precursors meet increased NOx, mainly produced by lightning. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank and then transported in the southern fringe around the interior region. Radial transport barriers of the circulation are effectively overcome by subseasonal dynamical instabilities of the anticyclone, which occur quite frequently and are of paramount importance for the trace gas composition of the ASMA. Both the isentropic entrainment of O3-rich air and the photochemical conversion of uplifted O3-poor air tend to increase O3 in the ASMA outflow.

  19. The abrupt onset of the modern South Asian monsoon winds

    Digital Repository Service at National Institute of Oceanography (India)

    Betzler, C.; Eberli, G.P.; Kroon, D.; Wright, J.D.; Swart, P.K.; Nath, B.N.; Alvarez-Zarikian, C.A.; Alonso-Garcia, M.; Bialik, O.M.; Blattler, C.L.; Guo, J.; Haffen, S.; Horozal, S.; Inoue, M.; Jovane, L.; Lanci, L.; Laya, J.C.; Mee, A.L.H.; Ludmann, T.; Nakakuni, M.; Niino, K.; Petruny, L.M.; Pratiwi, S.D.; Reijmer, J.J.G.; Reolid, J.; Slagle, A.L.; Sloss, C.R.; Su, X.; Yao, Z.; Young, J.R.

    :29838 | DOI: 10.1038/srep29838 www.nature.com/scientificreports The abrupt onset of the modern South Asian Monsoon winds Christian Betzler1, Gregor P. Eberli2, Dick Kroon3, James D. Wright4, Peter K. Swart2, Bejugam Nagender Nath5, Carlos A. Alvarez....betzler@uni-hamburg.de) Received: 25 April 2016 accepted: 21 June 2016 Published: 20 July 2016 OPEN www.nature.com/scientificreports/ 2Scientific RepoRts | 6:29838 | DOI: 10.1038/srep29838 control, and we propose that the post Miocene Climate Optimum cooling, together...

  20. Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

    Directory of Open Access Journals (Sweden)

    L. Giosan

    2017-12-01

    Full Text Available Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.

  1. Short communication: Massive erosion in monsoonal central India linked to late Holocene land cover degradation

    Science.gov (United States)

    Giosan, Liviu; Ponton, Camilo; Usman, Muhammed; Blusztajn, Jerzy; Fuller, Dorian Q.; Galy, Valier; Haghipour, Negar; Johnson, Joel E.; McIntyre, Cameron; Wacker, Lukas; Eglinton, Timothy I.

    2017-12-01

    Soil erosion plays a crucial role in transferring sediment and carbon from land to sea, yet little is known about the rhythm and rates of soil erosion prior to the most recent few centuries. Here we reconstruct a Holocene erosional history from central India, as integrated by the Godavari River in a sediment core from the Bay of Bengal. We quantify terrigenous fluxes, fingerprint sources for the lithogenic fraction and assess the age of the exported terrigenous carbon. Taken together, our data show that the monsoon decline in the late Holocene significantly increased soil erosion and the age of exported organic carbon. This acceleration of natural erosion was later exacerbated by the Neolithic adoption and Iron Age extensification of agriculture on the Deccan Plateau. Despite a constantly elevated sea level since the middle Holocene, this erosion acceleration led to a rapid growth of the continental margin. We conclude that in monsoon conditions aridity boosts rather than suppresses sediment and carbon export, acting as a monsoon erosional pump modulated by land cover conditions.

  2. Dynamics and Composition of the Asian Summer Monsoon Anticyclone

    Science.gov (United States)

    Gottschaldt, K. D.; Schlager, H.; Baumann, R.; Bozem, H.; Cai, D. S.; Eyring, V.; Hoor, P. M.; Graf, P.; Joeckel, P.; Jurkat, T.; Voigt, C.; Grewe, V.; Zahn, A.; Ziereis, H.

    2017-12-01

    This study places trace gas observations in the upper-tropospheric Asian summer monsoon anticyclone (ASMA) obtained with the HALO research aircraft during the ESMVal campaign into the context of regional, intra-annual variability by hindcasts with the EMAC model. The simulations demonstrate that tropospheric trace gas profiles in the monsoon season are distinct from the rest of the year. Air uplifted from the lower troposphere to the tropopause layer dominates the eastern part of the ASMA's interior, while the western part is characterized by subsidence down to the mid-troposphere. Soluble compounds are being washed out when uplifted by convection in the eastern part, where lightning simultaneously replenishes reactive nitrogen in the upper troposphere. Net photochemical ozone production is significantly enhanced in the ASMA, contrasted by an ozone depleting regime in the mid-troposphere and more neutral conditions in autumn and winter. An analysis of multiple monsoon seasons in the simulation shows that stratospherically influenced tropopause layer air is regularly entrained at the eastern ASMA flank, and then transported in the southern fringe around the interior region. Observed and simulated tracer-tracer relations reflect photochemical O3 production, as well as in-mixing from the lower troposphere and the tropopause layer. The simulation additionally shows entrainment of clean air from the equatorial region by northerly winds at the western ASMA flank. Although the in situ measurements were performed towards the end of summer, the main ingredients needed for their interpretation are present throughout the monsoon season.Subseasonal dynamical instabilities of the ASMA effectively overcome horizontal transport barriers, occur quite frequently, and are of paramount importance for the trace gas composition of the ASMA and its outflow into regions around the world.

  3. Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales

    Science.gov (United States)

    Goldsmith, Yonaton; Broecker, Wallace S.; Xu, Hai; Polissar, Pratigya J.; deMenocal, Peter B.; Porat, Naomi; Lan, Jianghu; Cheng, Peng; Zhou, Weijian; An, Zhisheng

    2017-02-01

    The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene-Holocene EAM rainfall intensity is reconstructed using a well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early and middle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ˜400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall “intensity based” interpretations of these deposits as opposed to an alternative “water vapor sourcing” interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (˜35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.

  4. Northward extent of East Asian monsoon covaries with intensity on orbital and millennial timescales.

    Science.gov (United States)

    Goldsmith, Yonaton; Broecker, Wallace S; Xu, Hai; Polissar, Pratigya J; deMenocal, Peter B; Porat, Naomi; Lan, Jianghu; Cheng, Peng; Zhou, Weijian; An, Zhisheng

    2017-02-21

    The magnitude, rate, and extent of past and future East Asian monsoon (EAM) rainfall fluctuations remain unresolved. Here, late Pleistocene-Holocene EAM rainfall intensity is reconstructed using a well-dated northeastern China closed-basin lake area record located at the modern northwestern fringe of the EAM. The EAM intensity and northern extent alternated rapidly between wet and dry periods on time scales of centuries. Lake levels were 60 m higher than present during the early and middle Holocene, requiring a twofold increase in annual rainfall, which, based on modern rainfall distribution, requires a ∼400 km northward expansion/migration of the EAM. The lake record is highly correlated with both northern and southern Chinese cave deposit isotope records, supporting rainfall "intensity based" interpretations of these deposits as opposed to an alternative "water vapor sourcing" interpretation. These results indicate that EAM intensity and the northward extent covary on orbital and millennial timescales. The termination of wet conditions at 5.5 ka BP (∼35 m lake drop) triggered a large cultural collapse of Early Neolithic cultures in north China, and possibly promoted the emergence of complex societies of the Late Neolithic.

  5. Study on coral annual banding for the investigation of Asian monsoon; Asian monsoon to sango nenrin kenkyu

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, A. [Geological Survey of Japan, Tsukuba (Japan); Kawabata, H. [Tohoku University, Sendai (Japan)

    1998-07-01

    A coral skeleton is sampled at Kenya`s Malindi National Marine Park situated west of the Seychelles, and it offers information about the Afro-Asian monsoon. An X-ray profile of the specimen discloses the seasonal variation in the density of the coral skeleton. The oxygen isotopic ratio, which is generally affected by the seawater oxygen isotopic ratio composition which is dependent on the surface layer water temperature and fresh water, is found dominated, in the coral skeleton, practically by the surface layer water temperature. Accordingly, the oxygen isotopic ratio represents the seasonal and annual variations in the surface layer water temperature. It is inferred that the emergence of Ba/Ca ratio peaks in December into January reflects the presence of Ba from rivers, and there are indications that the Somali current has transported water to the coral sampling area from the Galana River which is the greatest river in Kenya. Five of the Ba/Ca ratio peaks coincide with peaks in the UV fluorescent band, which is attributed to the presence of terrigenous organic matters. The ENSO and Asian monsoon phenomena are estimated on the basis of the findings described above. 11 refs., 6 figs.

  6. Vegetation Response and Landscape Dynamics of Indian Summer Monsoon Variations during Holocene: An Eco-Geomorphological Appraisal of Tropical Evergreen Forest Subfossil Logs

    Science.gov (United States)

    Kumaran, Navnith K. P.; Padmalal, Damodaran; Nair, Madhavan K.; Limaye, Ruta B.; Guleria, Jaswant S.; Srivastava, Rashmi; Shukla, Anumeha

    2014-01-01

    The high rainfall and low sea level during Early Holocene had a significant impact on the development and sustenance of dense forest and swamp-marsh cover along the southwest coast of India. This heavy rainfall flooded the coastal plains, forest flourishing in the abandoned river channels and other low-lying areas in midland.The coastline and other areas in lowland of southwestern India supply sufficient evidence of tree trunks of wet evergreen forests getting buried during the Holocene period under varying thickness of clay, silty-clay and even in sand sequences. This preserved subfossil log assemblage forms an excellent proxy for eco-geomorphological and palaeoclimate appraisal reported hitherto from Indian subcontinent, and complements the available palynological data. The bulk of the subfossil logs and partially carbonized wood remains have yielded age prior to the Holocene transgression of 6.5 k yrs BP, suggesting therein that flooding due to heavy rainfall drowned the forest cover, even extending to parts of the present shelf. These preserved logs represent a unique palaeoenvironmental database as they contain observable cellular structure. Some of them can even be compared to modern analogues. As these woods belong to the Late Pleistocene and Holocene, they form a valuable source of climate data that alleviates the lack of contemporaneous meteorological records. These palaeoforests along with pollen proxies depict the warmer environment in this region, which is consistent with a Mid Holocene Thermal Maximum often referred to as Holocene Climate Optimum. Thus, the subfossil logs of tropical evergreen forests constitute new indices of Asian palaeomonsoon, while their occurrence and preservation are attributed to eco-geomorphology and hydrological regimes associated with the intensified Asian Summer Monsoon, as recorded elsewhere. PMID:24727672

  7. The Preboreal-like Asian monsoon climate in the early last interglacial period recorded from the Dark Cave, Southwest China

    Science.gov (United States)

    Jiang, Xiuyang; He, Yaoqi; Wang, Xiaoyan; Sun, Xiaoshuang; Hong, Hui; Liu, Juan; Yu, Tsai-Luen; Li, Zhizhong; Shen, Chuan-Chou

    2017-08-01

    Transitions of glacial-interglacial cycles are critical periods for Quaternary climate shifts. Here, we present new, decadal resolution Asian summer monsoon (ASM) record from three stalagmites obtained from the Dark Cave in southwestern China over 130-114 thousand years ago (ka, before CE 1950). Chronology was anchored by 28 230Th dates with typical uncertainties of ±0.3-1.0 kyr, allowing an assessment of timing and transition of climate changes during the onset and end of the last interglacial. An agreement between this new and previous stalagmite δ18O records supports that summer insolation predominates orbital-scale ASM evolution. A 2-3 kyr-long gradually increasing ASM period, analogous to the classical Preboreal episode in the early Holocene, follows the termination of a weak monsoon interval at 129.0 ± 0.8 ka. This finding suggests a strong influence of high-latitude ice-sheet dynamics on Asian monsoonal conditions during the early interglacial period. An abrupt end of the marine isotope stage 5e at 118.8 ± 0.6 ka was probably caused by the internal climate system threshold effects.

  8. Holocene monsoon variability inferred from Targo Xian peat bog in the Tangra Yumco basin, central Tibetan Plateau

    Science.gov (United States)

    Henkel, Karoline; Haberzettl, Torsten; Miehe, Sabine; Frenzel, Peter; Daut, Gerhard; Dietze, Elisabeth; Kasper, Thomas; Ahlborn, Marieke; Mäusbacher, Roland

    2013-04-01

    The Tibetan Plateau is the greatest plateau on Earth with an average altitude of 4,500 m asl. Due to its high elevation, large area and significant role in the formation of the Asian Monsoon Systems (e.g., Indian Ocean and East-Asian Summer Monsoon) it is considered to react very sensitive to climate variations. The numerous lake systems on the Tibetan Plateau represent excellent archives reflecting variations in the strength of the monsoon system in terms of hydrological changes expressed in lake level fluctuations. For example, terraces and lacustrine deposits around the saline lake Tangra Yumco indicate lake level highstands up to ~215 m higher than the present lake level. To study Holocene lake level variations we investigated a 3.6 m long sediment core recovered from a peat bog (near the Targo Xian settlement, 30°46'N, 86°40'E) on a recessional lake level terrace ~150 m above the present shoreline of Tangra Yumco. In particular, our analyses of sedimentological (grain size), geochemical (CNS and ICP-OES) and mineralogical (XRD) data allow a detailed and high-resolution interpretation of the hydrological conditions during the Holocene. The existence of two carbonate layers in the Targo Xian record, separated by a sand layer and intercalated in peat sequences at the bottom and top of the core, provide evidence for two stable lake stages at the coring position. Peat at the bottom of the core, which is radiocarbon-dated to 11,130 +130/-345 cal BP, indicates wetland conditions similar to the Recent situation (Miehe et al., submitted). After a transition zone, a layer of pure aragonitic lake marl gives evidence for a lake stage. During this stage, high values of the total inorganic carbon (TIC) and Ca/Ti ratios as well as low C/N ratios point to a stable lake due to wet climatic conditions. This carbonate layer can be correlated with a 2-3 m thick carbonate layer found in outcrops around the present lake Tangra Yumco presenting a high lake level until approx. 2

  9. 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.)

  10. Recently studied sedimentary records from the eastern Arabian Sea: Implications to Holocene monsoonal variability

    Digital Repository Service at National Institute of Oceanography (India)

    Agnihotri, R.; Kurian, S.

    stream_size 72460 stream_content_type text/plain stream_name Earth_Sci_India_1_258.pdf.txt stream_source_info Earth_Sci_India_1_258.pdf.txt Content-Encoding UTF-8 Content-Type text/plain; charset=UTF-8 Agnihotri http://www....earthscienceindia.info/Agnihotri.htm 1 of 14 10/15/2008 9:41 AM Earth Science India Vol.1 (IV), October, 2008, pp. 258-287 http://www.earthscienceindia.info/ Recently studied sedimentary records from the eastern Arabian Sea: Implications to Holocene monsoonal variability Rajesh...

  11. Atmospheric circulation characteristics associated with the onset of Asian summer monsoon

    Science.gov (United States)

    Li, Chongyin; Pan, Jing

    2006-12-01

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

  12. Similar speleothem δ18O signals indicating diverging climate variations in inland central Asia and monsoonal south Asia during the Holocene

    Science.gov (United States)

    Jin, Liya; Zhang, Xiaojian

    2017-04-01

    High-resolution and precisely dated speleothem oxygen isotope (δ18O) records from Asia have provided key evidence for past monsoonal changes. It is found that δ18O records of stalagmites from Kesang Cave (42°52'N, 81°45'E, Xinjiang, China) in inland central Asia were very similar to those from Qunf Cave (17°10'N, 54°18'E, southern Oman) in South Asia, shifting from light to heavy throughout the Holocene, which was regarded as a signal that strong Asian summer monsoon (ASM) may have intruded into the Kesang Cave site and/or adjacent areas in inland central Asia to produce heavy rainfall during the high insolation times (e.g. the early Holocene). However, this is in contrast to conclusions based on other Holocene proxy records and modeling simulations, showing a persistent wetting trend in arid central Asia during the Holocene with a dryer condition in the early Holocene and the wettest condition in the late Holocene. With an analysis of model-proxy data comparison, we revealed a possible physical mechanism responsible for the Holocene evolution of moisture/precipitation in Asian summer monsoon (ASM)-dominated regions and that in the inland central Asia. It is revealed that a recurrent circumglobal teleconnection (CGT) pattern in the summertime mid-latitude circulation of the Northern Hemisphere was closely related to the ASM and the climate of inland central Asia, acting as a bridge linking the ASM to insolation, high-latitude forcing (North Atlantic sea surface temperature (SST)), and low-latitude forcing (tropical Ocean SST). Also, the CGT influence speleothem δ18O values in South Asia via its effect on the amount of precipitation. In addition, the moisture source from the Indian Ocean is associated with relatively high δ18O values compared with that from the North Atlantic Ocean, leading to increased precipitation δ18O values. Hence, the CGT has probably been the key factor responsible for the in-phase relationship in speleothem δ18O values (Kesang Cave

  13. Carbon sequestration in Southeast Asian tropical peatlands over the Holocene period: large-scale hydrological controls

    Science.gov (United States)

    Dommain, R.; Couwenberg, J.; Cobb, A.; Gandois, L.; Kai, F.; Su'ut, N.; Abu Salim, K.; Harvey, C. F.; Glaser, P. H.; Joosten, H.

    2012-12-01

    Tropical peatlands are recognized as a significant sink of carbon dioxide and an important source of methane. Low latitude peatlands contain an estimated pool of 90 Pg C, of which ca. 70 Pg C is stored in Southeast Asian peatlands. However, the Holocene development of this carbon reservoir is poorly established. Here we provide a synthesis of carbon uptake rates by tropical peatlands in Southeast Asia across millennial timescales for the past 11,000 years. Our reconstruction of the carbon accumulation history for Borneo, Sumatra and Peninsular Malaysia is based on a synthesis of radiocarbon dated peat profiles, modeling of peatland extent, and a new carbon accumulation record from Brunei (NW-Borneo). During the early Holocene the first peatlands formed in southern Borneo under the influence of a strong monsoon and rapid rise in sea-level. The carbon accumulation rate (CAR) in these peatlands was on average 60 g C m-2 yr-1 at this time. Peatlands started to spread across the coastal lowlands of Borneo, Sumatra and Peninsular Malaysia after 8000 cal BP only when the rate of rising sea-level decreased. The major phase of coastal peatland initiation lasted from 7000 to 4000 cal BP. This period was marked by a Holocene precipitation maximum, suppressed El Niño activity, and the Holocene maximum in sea-level on the Sunda Shelf. The mean CAR of coastal peatlands at this time was 80 g C m-2 yr-1, with a Holocene peak of ~100 g C m-2 yr-1 from 4900 to 4500 cal BP. Significantly, atmospheric CO2 concentrations measured in the Taylor Dome Antarctic ice core indicate a plateau during this period of otherwise rising CO2 concentrations. During the Late Holocene CAR declined both in coastal peatlands (ca. 70 g C m-2 yr-1) and in southern Borneo (ca. 20 g C m-2 yr-1) in response to falling sea-levels and increased El Niño frequency and intensity. In fact, several peatlands in southern Borneo have stopped accumulating peat-carbon under higher El Niño activity. These results

  14. South America Monsoon variability on millennial to multi-centennial time scale during the Holocene in central eastern Brazil

    Science.gov (United States)

    Strikis, N. M.; Cruz, F. W.; Cheng, H.; Karmann, I.; Vuille, M.; Edwards, R.; Wang, X.; Paula, M. S.; Novello, V. F.; Auler, A.

    2011-12-01

    A paleoprecipitation reconstruction based on high resolution and well-dated speleothem oxygen isotope records shows that the monsoon precipitation over central eastern Brazil underwent to strong variations on millennial to multi-centennial time-scales during the Holocene. This new record indicates that abrupt events of increase in monsoon precipitation are correlated to Bond events 6, 5 and 4 and also with 8.2 ky event during the early and mid-Holocene, with a mean amplitude of 1.5 % (PDB). The pacing and structure of such events are general consistent with variations in solar activity suggested by atmospheric Δ14 C records. In the late-Holocene, abrupt events of increase in monsoon precipitation peaking at 3.2, 2.7 and 2.3 ky B.P. are approximately synchronous with periods of low solar minima. In this regard, the most prominent event occurred during the late Holocene occurred at ~2.7 ky B.P. In addition, these positive anomalies of the precipitation recorded in central eastern Brazil are also in good agreement with variations in Titicaca lake level. The good correspondence between the speleothem and marine records imply that the variations in the north Atlantic sea surface temperature is the main forcing for abrupt millennial to multi-centennial precipitations variation within the region under influence of South American Monsoon.

  15. Investigating extreme flood response to Holocene palaeoclimate in the Chinese monsoonal zone: A palaeoflood case study from the Hanjiang River

    Science.gov (United States)

    Guo, Yongqiang; Huang, Chun Chang; Pang, Jiangli; Zha, Xiaochun; Zhou, Yali; Wang, Longsheng; Zhang, Yuzhu; Hu, Guiming

    2015-06-01

    Palaeoflood events recorded by slackwater deposits (SWDs) were investigated extensively by sedimentological criteria of palaeohydrology along the upper Hanjiang River valley. Modern flood SWDs were collected for comparison with palaeoflood SWD in the same reaches. Three typical palaeoflood SWDs were observed within Holocene loess-soil blanket on the first river terrace land. The grain size distributions of palaeoflood SWDs are similar to modern flood SWDs, whereas they are different from eolian loess and soil. Palaeoflood SWD lies in three major pedo-stratigraphic boundaries (TS/L0, L0/S0, and S0/Lt) in the Holocene loess-soil profiles. The chronology of three palaeoflood episodes was established by OSL dating and pedo-stratigraphic correlation with the well-dated Holocene loess-soil profiles in the upper Hanjiang River basin. Holocene palaeoflood events were dated to 9500-8500, 3200-2800, and 1800-1700 a B.P., respectively. Palaeoflood discharges were estimated by the palaeoflood model (i.e., slope-area method and step-backwater method). The highest discharges are 51,680-53,950 m3 s- 1 at the 11,500-time scale in the Xunyang reach of the upper Hanjiang River valley. Holocene extraordinary hydroclimatic events in the Hanjiang River often result from abnormal atmospheric circulations from Southwest monsoons in the Chinese monsoonal zone. These results provide a regional expression of extreme flood response to Holocene palaeoclimate to understand the effects of global climatic variations on the river system dynamics.

  16. Initial results from the StratoClim aircraft campaign in the Asian Monsoon in summer 2017

    Science.gov (United States)

    Rex, M.

    2017-12-01

    The Asian Monsoon System is one of the Earth's largest and most energetic weather systems. Monsoon rainfall is critical to feeding over a billion people in Asia and the monsoon circulation affects weather patterns over the entire northern hemisphere. The Monsoon also acts like an enormous elevator, pumping vast amounts of air and pollutants from the surface up to the tropopause region at levels above 16km altitude, from where air can ascend into the stratosphere, where it spreads globally. Thus the monsoon affects the chemical composition of the global tropopause region and the stratosphere, and hence plays a key role for the composition of the UTS. Dynamically the monsoon circulation leads to the formation of a large anticyclone at tropopause levels above South Asia - the Asian Monsoon Anticyclone (AMA). Satellite images show a large cloud of aerosols directly above the monsoon, the Asian Tropopause Aerosol Layer (ATAL). In July to August 2017 the international research project StratoClim carried out the first in-situ aircraft measurements in the AMA and the ATAL with the high altitude research aircraft M55-Geophysica. Around 8 scientific flights took place in the airspaces of Nepal, India and Bangladesh and have horizontally and vertically probed the AMA and have well characterized the ATAL along flight patterns that have been carefully designed by a theory, modelling and satellite data analysing team in the field. The aircraft campaign has been complemented by launches of research balloons from ground stations in Nepal, Bangladesh, China and Palau. The presentation will give an overview of the StratoClim project, the aircraft and balloon activities and initial results from the StratoClim Asian Monsoon campaign in summer 2017.

  17. Asian Summer Monsoon Rainfall associated with ENSO and its Predictability

    Science.gov (United States)

    Shin, C. S.; Huang, B.; Zhu, J.; Marx, L.; Kinter, J. L.; Shukla, J.

    2015-12-01

    The leading modes of the Asian summer monsoon (ASM) rainfall variability and their seasonal predictability are investigated using the CFSv2 hindcasts initialized from multiple ocean analyses over the period of 1979-2008 and observation-based analyses. It is shown that the two leading empirical orthogonal function (EOF) modes of the observed ASM rainfall anomalies, which together account for about 34% of total variance, largely correspond to the ASM responses to the ENSO influences during the summers of the developing and decaying years of a Pacific anomalous event, respectively. These two ASM modes are then designated as the contemporary and delayed ENSO responses, respectively. It is demonstrated that the CFSv2 is capable of predicting these two dominant ASM modes up to the lead of 5 months. More importantly, the predictability of the ASM rainfall are much higher with respect to the delayed ENSO mode than the contemporary one, with the predicted principal component time series of the former maintaining high correlation skill and small ensemble spread with all lead months whereas the latter shows significant degradation in both measures with lead-time. A composite analysis for the ASM rainfall anomalies of all warm ENSO events in this period substantiates the finding that the ASM is more predictable following an ENSO event. The enhanced predictability mainly comes from the evolution of the warm SST anomalies over the Indian Ocean in the spring of the ENSO maturing phases and the persistence of the anomalous high sea surface pressure over the western Pacific in the subsequent summer, which the hindcasts are able to capture reasonably well. The results also show that the ensemble initialization with multiple ocean analyses improves the CFSv2's prediction skill of both ENSO and ASM rainfall. In fact, the skills of the ensemble mean hindcasts initialized from the four different ocean analyses are always equivalent to the best ones initialized from any individual ocean

  18. Contributions of a Strengthened Early Holocene Monsoon and Sediment Loading to Present-Day Subsidence of the Ganges-Brahmaputra Delta

    Science.gov (United States)

    Karpytchev, M.; Ballu, V.; Krien, Y.; Becker, M.; Goodbred, S.; Spada, G.; Calmant, S.; Shum, C. K.; Khan, Z.

    2018-02-01

    The contribution of subsidence to relative sea level rise in the Ganges-Brahmaputra delta (GBD) is largely unknown and may considerably enhance exposure of the Bengal Basin populations to sea level rise and storm surges. This paper focuses on estimating the present-day subsidence induced by Holocene sediment in the Bengal Basin and by oceanic loading due to eustatic sea level rise over the past 18 kyr. Using a viscoelastic Earth model and sediment deposition history based on in situ measurements, results suggest that massive sediment influx initiated in the early Holocene under a strengthened South Asian monsoon may have contributed significantly to the present-day subsidence of the GBD. We estimate that the Holocene loading generates up to 1.6 mm/yr of the present-day subsidence along the GBD coast, depending on the rheological model of the Earth. This rate is close to the twentieth century global mean sea level rise (1.1-1.7 mm/yr). Thus, past climate change, by way of enhanced sedimentation, is impacting vulnerability of the GBD populations.

  19. The East Asian Atmospheric Water Cycle and Monsoon Circulation in the Met Office Unified Model

    Science.gov (United States)

    Rodríguez, José M.; Milton, Sean F.; Marzin, Charline

    2017-10-01

    In this study the low-level monsoon circulation and observed sources of moisture responsible for the maintenance and seasonal evolution of the East Asian monsoon are examined, studying the detailed water budget components. These observational estimates are contrasted with the Met Office Unified Model (MetUM) climate simulation performance in capturing the circulation and water cycle at a variety of model horizontal resolutions and in fully coupled ocean-atmosphere simulations. We study the role of large-scale circulation in determining the hydrological cycle by analyzing key systematic errors in the model simulations. MetUM climate simulations exhibit robust circulation errors, including a weakening of the summer west Pacific Subtropical High, which leads to an underestimation of the southwesterly monsoon flow over the region. Precipitation and implied diabatic heating biases in the South Asian monsoon and Maritime Continent region are shown, via nudging sensitivity experiments, to have an impact on the East Asian monsoon circulation. By inference, the improvement of these tropical biases with increased model horizontal resolution is hypothesized to be a factor in improvements seen over East Asia with increased resolution. Results from the annual cycle of the hydrological budget components in five domains show a good agreement between MetUM simulations and ERA-Interim reanalysis in northern and Tibetan domains. In simulations, the contribution from moisture convergence is larger than in reanalysis, and they display less precipitation recycling over land. The errors are closely linked to monsoon circulation biases.

  20. 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

  1. Indian summer monsoon variability during the Holocene as recorded in sediments of the Arabian Sea: Timing and implications

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Kawahata, H.; Rao, V.P.

    ., 2005). Recently a 11,000 yr reconstruction of sunspots using tree ring ∆ 14 C data revealed exceptional changes in sunspot activity within the Holocene (Solanki et al., 2004). Since sun is the principal source of energy, changes in solar energy output... seem to be stimulated by the sun, suggest- ing the importance of small changes in solar activity lead- ing to perceptible changes in monsoon conditions. Acknowledgements We thank the Directors of National Centre for Ant- arctic and Ocean Research (NCAOR...

  2. Lake Baikal isotope records of Holocene Central Asian precipitation

    Science.gov (United States)

    Swann, George E. A.; Mackay, Anson W.; Vologina, Elena; Jones, Matthew D.; Panizzo, Virginia N.; Leng, Melanie J.; Sloane, Hilary J.; Snelling, Andrea M.; Sturm, Michael

    2018-06-01

    Climate models currently provide conflicting predictions of future climate change across Central Asia. With concern over the potential for a change in water availability to impact communities and ecosystems across the region, an understanding of historical trends in precipitation is required to aid model development and assess the vulnerability of the region to future changes in the hydroclimate. Here we present a record from Lake Baikal, located in the southern Siberian region of central Asia close to the Mongolian border, which demonstrates a relationship between the oxygen isotope composition of diatom silica (δ18Odiatom) and precipitation to the region over the 20th and 21st Century. From this, we suggest that annual rates of precipitation in recent times are at their lowest for the past 10,000 years and identify significant long-term variations in precipitation throughout the early to late Holocene interval. Based on comparisons to other regional records, these trends are suggested to reflect conditions across the wider Central Asian region around Lake Baikal and highlight the potential for further changes in precipitation with future climate change.

  3. 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.

  4. Quantifying pollution transport from the Asian monsoon anticyclone into the lower stratosphere

    Directory of Open Access Journals (Sweden)

    F. Ploeger

    2017-06-01

    Full Text Available Pollution transport from the surface to the stratosphere within the Asian monsoon circulation may cause harmful effects on stratospheric chemistry and climate. Here, we investigate air mass transport from the monsoon anticyclone into the stratosphere using a Lagrangian chemistry transport model. We show how two main transport pathways from the anticyclone emerge: (i into the tropical stratosphere (tropical pipe, and (ii into the Northern Hemisphere (NH extratropical lower stratosphere. Maximum anticyclone air mass fractions reach around 5 % in the tropical pipe and 15 % in the extratropical lowermost stratosphere over the course of a year. The anticyclone air mass fraction correlates well with satellite hydrogen cyanide (HCN and carbon monoxide (CO observations, confirming that pollution is transported deep into the tropical stratosphere from the Asian monsoon anticyclone. Cross-tropopause transport occurs in a vertical chimney, but with the pollutants transported quasi-horizontally along isentropes above the tropopause into the tropics and NH.

  5. Interactions Between Asian Air Pollution and Monsoon System: South Asia (ROSES-2014 ACMAP)

    Science.gov (United States)

    Pan, Xiaohua; Chin, Mian; Tao, Zhining; Kim, Dongchul; Bian, Huisheng; Kucsera, Tom

    2018-01-01

    Asia's rapid economic growth over the past several decades has brought a remarkable increase in air pollution levels in that region. High concentrations of aerosols (also known as particulate matter or PM) from pollution sources pose major health hazards to half of the world population in Asia including South Asia. How do pollution and dust aerosols regulate the monsoon circulation and rainfall via scattering and absorbing solar radiation, changing the atmospheric heating rates, and modifying the cloud properties? We conducted a series of regional model experiments with NASA-Unified Weather Research and Forecast (NUWRF) regional model with coupled aerosol-chemistry-radiation-microphysics processes over South Asia for winter, pre-monsoon, and monsoon seasons to address this question. This study investigates the worsening air quality problem in South Asia by focusing on the interactions between pollution and South Asian monsoon, not merely focusing on the increase of pollutant emissions.

  6. Transport of regional pollutions to UTLS during Asian Summer Monsoon - A CTM study

    Science.gov (United States)

    Li, Qian; Bian, Jianchun; Lu, Daren

    2013-04-01

    We use a 3-D global Chemical Transport Model (CTM) GEOS-Chem to simulate the observed Asian Summer Monsoon transport of biomass burning tracers HCN and CO from local emissions to UTLS. By analyzing the satellite observations, we focus on the distribution and spatial-temporal variation of HCN and CO concentration in UTLS. The model simulations capture well the main features of distribution of HCN and CO compared with satellite observations. Recent studies (Li et al., 2009; Randel et al., 2010) indicated that regional emissions may play an important role controlling the distribution and variation of HCN in tropical UTLS during Asian Summer Monsoon seasons, mainly due to the local dynamical uplift of Asian Summer Monsoon. By using GEOS-Chem simulations, we will analyze the UTLS distribution and variation of HCN and CO from emissions of different regions including S.E. Asia, Boreal Asia, Indonesia and Australia, Africa, Europe, Northern America and Southern America. According to the amount and seasonal variability of emissions, the contribution of biomass burning and biofuel burning emissions of different regions to the highly concentrated HCN and CO in UTLS during Asian Summer Monsoon seasons will be discussed, individually.

  7. Impacts of half a degree additional warming on the Asian summer monsoon rainfall characteristics

    Science.gov (United States)

    Lee, Donghyun; Min, Seung-Ki; Fischer, Erich; Shiogama, Hideo; Bethke, Ingo; Lierhammer, Ludwig; Scinocca, John F.

    2018-04-01

    This study investigates the impacts of global warming of 1.5 °C and 2.0 °C above pre-industrial conditions (Paris Agreement target temperatures) on the South Asian and East Asian monsoon rainfall using five atmospheric global climate models participating in the ‘Half a degree Additional warming, Prognosis and Projected Impacts’ (HAPPI) project. Mean and extreme precipitation is projected to increase under warming over the two monsoon regions, more strongly in the 2.0 °C warmer world. Moisture budget analysis shows that increases in evaporation and atmospheric moisture lead to the additional increases in mean precipitation with good inter-model agreement. Analysis of daily precipitation characteristics reveals that more-extreme precipitation will have larger increase in intensity and frequency responding to the half a degree additional warming, which is more clearly seen over the South Asian monsoon region, indicating non-linear scaling of precipitation extremes with temperature. Strong inter-model relationship between temperature and precipitation intensity further demonstrates that the increased moisture with warming (Clausius-Clapeyron relation) plays a critical role in the stronger intensification of more-extreme rainfall with warming. Results from CMIP5 coupled global climate models under a transient warming scenario confirm that half a degree additional warming would bring more frequent and stronger heavy precipitation events, exerting devastating impacts on the human and natural system over the Asian monsoon region.

  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. Mid- to late Holocene Indian Ocean Monsoon variability recorded in four speleothems from Socotra Island, Yemen

    Science.gov (United States)

    Van Rampelbergh, Maïté; Fleitmann, Dominik; Verheyden, Sophie; Cheng, Hai; Edwards, Lawrence; De Geest, Peter; De Vleeschouwer, David; Burns, Stephen J.; Matter, Albert; Claeys, Philippe; Keppens, Eddy

    2013-04-01

    Four stalagmites covering the last 7.0 ka were sampled on Socotra, an island in the northern Indian Ocean to investigate the evolution of the northeast Indian Ocean Monsoon (IOM) since the mid Holocene. On Socotra, rain is delivered at the start of the southwest IOM in May-June and at the start of the northeast IOM from September to December. The Haggeher Mountains act as a barrier forcing precipitation brought by the northeast winds to fall preferentially on the eastern side of the island, where the studied caves are located. δ18O and δ13C and Mg/Ca and Sr/Ca signals in the stalagmites reflect precipitation amounts brought by the northeast winds. For stalagmite STM6, this amount effect is amplified by kinetic effects during calcite deposition. Combined interpretation of the stalagmites' signals suggest a weakening of the northeast precipitation between 6.0 and 3.8 ka. After 3.8 ka precipitation intensities remain constant with two superimposed drier periods, between 0 and 0.6 ka and from 2.2 to 3.8 ka. No link can be established with Greenland ice cores and with the summer IOM variability. In contrast to the stable northeast rainy season suggested by the records in this study, speleothem records from western Socotra indicate a wettening of the southwest rainy season on Socotra after 4.4 ka. The local wettening of western Socotra could relate to a more southerly path (more over the Indian Ocean) taken by the southwest winds. Stalagmite STM5, sampled at the fringe between both rain areas displays intermediate δ18O values. After 6.2 ka, similar precipitation changes are seen between eastern Socotra and northern Oman indicating that both regions are affected similarly by the monsoon. Different palaeoclimatologic records from the Arabian Peninsula currently located outside the ITCZ migration pathway display an abrupt drying around 6 ka due to their disconnection from the southwest rain influence. Records that are nowadays still receiving rain by the southwest winds

  10. Asian summer monsoon prediction in ECMWF System 4 and NCEP CFSv2 retrospective seasonal forecasts

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hye-Mi; Webster, Peter J.; Curry, Judith A.; Toma, Violeta E. [Georgia Institute of Technology, School of Earth and Atmospheric Science, Atlanta, GA (United States)

    2012-12-15

    The seasonal prediction skill of the Asian summer monsoon is assessed using retrospective predictions (1982-2009) from the ECMWF System 4 (SYS4) and NCEP CFS version 2 (CFSv2) seasonal prediction systems. In both SYS4 and CFSv2, a cold bias of sea-surface temperature (SST) is found over the equatorial Pacific, North Atlantic, Indian Oceans and over a broad region in the Southern Hemisphere relative to observations. In contrast, a warm bias is found over the northern part of North Pacific and North Atlantic. Excessive precipitation is found along the ITCZ, equatorial Atlantic, equatorial Indian Ocean and the maritime continent. The southwest monsoon flow and the Somali Jet are stronger in SYS4, while the south-easterly trade winds over the tropical Indian Ocean, the Somali Jet and the subtropical northwestern Pacific high are weaker in CFSv2 relative to the reanalysis. In both systems, the prediction of SST, precipitation and low-level zonal wind has greatest skill in the tropical belt, especially over the central and eastern Pacific where the influence of El Nino-Southern Oscillation (ENSO) is dominant. Both modeling systems capture the global monsoon and the large-scale monsoon wind variability well, while at the same time performing poorly in simulating monsoon precipitation. The Asian monsoon prediction skill increases with the ENSO amplitude, although the models simulate an overly strong impact of ENSO on the monsoon. Overall, the monsoon predictive skill is lower than the ENSO skill in both modeling systems but both systems show greater predictive skill compared to persistence. (orig.)

  11. 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

  12. Tropospheric biennial oscillation and South Asian summer monsoon ...

    Indian Academy of Sciences (India)

    20

    suggested that the Indo-Pacific SST displays strong impact on TBO as compared to .... and model display clear biennial signals with above 95% confidence level .... Ascending motion and low level convergence over the monsoon core ..... Indian and western Pacific oceans during the northern winter as revealed by a self-.

  13. Air pollution episodes associated with East Asian winter monsoons

    Energy Technology Data Exchange (ETDEWEB)

    Hien, P.D., E-mail: pdhien@gmail.com [Vietnam Atomic Energy Agency, 59 Ly Thuong Kiet str. Hanoi (Viet Nam); Loc, P.D.; Dao, N.V. [National Hydro-Meteorological Center, 62-A2 Nguyen Chi Thanh str. Hanoi (Viet Nam)

    2011-11-01

    A dozen multi-day pollution episodes occur from October to February in Hanoi, Vietnam due to prolonged anticyclonic conditions established after the northeast monsoon surges (cold surges). These winter pollution episodes (WPEs) account for most of the 24-h PM{sub 10} exceedances and the highest concentrations of gaseous pollutants in Hanoi. In this study, WPEs were investigated using continuous air quality monitoring data and information on upper-air soundings and air mass trajectories. The 24-h pollutant concentrations are lowest during cold surges; concurrently rise thereafter reaching the highest levels toward the middle of a monsoon cycle, then decline ahead of the next cold surge. Each monsoon cycle usually proceeds through a dry phase and a humid phase as Asiatic continental cold air arrives in Hanoi through inland China then via the East China Sea. WPEs are associated with nighttime radiation temperature inversions (NRTIs) in the dry phase and subsidence temperature inversions (STIs) in the humid phase. In NRTI periods, the rush hour pollution peak is more pronounced in the evening than in the morning and the pollution level is about two times higher at night than in daytime. In STI periods, broad morning and evening traffic peaks are observed and pollution is as high at night as in daytime. The close association between pollution and winter monsoon meteorology found in this study for the winter 2003-04 may serve as a basis for advance warning of WPEs and for forecasting the 24-h pollutant concentrations. - Highlights: {yields} Dozen pollution episodes from Oct. to Feb in Hanoi associated with anticyclones after monsoon surges. {yields} 24-h concentrations of PM{sub 10}, SO{sub 2}, NO{sub 2}, CO rise after surge and decline ahead of the next. {yields} Episodes caused by nighttime radiation and subsidence inversions in dry and humid monsoon phases. {yields} Distinct diurnal variations of pollutant concentrations observed in the two periods. {yields} Close

  14. Diagnosis of the Asian summer monsoon variability and the climate prediction of monsoon precipitation via physical decomposition

    Science.gov (United States)

    Lim, Young-Kwon

    This study investigates the space-time evolution of the dominant modes that constitute the Asian summer monsoon (ASM), and, as an ultimate goal, the climate prediction of the ASM rainfall. Precipitation and other synoptic variables during the prominent life cycle of the ASM (May 21 to September 17) are used to show the detailed features of dominant modes, which are identified as the seasonal cycle, the ISO defined by the 40--50 day intraseasonal oscillation including the Madden-Julian oscillation, and the El Nino mode. The present study reveals that the ISO is the second largest component of the ASM rainfall variation. Correlation analysis indicates that ISO explains a larger fraction of the variance of the observed precipitation (without climatology) than the ENSO mode. The dominant ISO signal faithfully explains the northward propagation of the ISO toward the Asian continent causing intraseasonal active/break periods. The interannual variation of the ISO strength suggests that the ENSO exerts some influence on the ISO. The composite convective ISO anomaly and Kelvin-Rossby wave response over the Indian Ocean shows that the ISO tends to be stronger during the early stage of the ASM than normal in El Nino (La Nina) years, indicating greater (smaller) possibility of ISO-related extreme rainfall over India, Bangladesh, and the Bay of Bengal. The ENSO mode reveals that the following factors affect the evolution of the ASM system in El Nino (La Nina) years. (1) The anomalous sea surface temperature and sea level pressure over the Indian Ocean during the early stage of the ASM weaken (enhance) the meridional pressure gradient. (2) As a result, the westerly jet and the ensuing moisture transport toward India and the Bay of Bengal become weak (strong) and delayed (expedited), providing a less (more) favorable condition for regional monsoon onsets. (3) The Walker circulation anomaly results in an enhanced subsidence (ascent) and drought (flood) over the Maritime continent

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

    Science.gov (United States)

    Joshi, Sneh; Kar, Sarat C.

    2018-02-01

    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.

  16. Changes in the Asian monsoon climate during 1700-1850 induced by preindustrial cultivation.

    Science.gov (United States)

    Takata, Kumiko; Saito, Kazuyuki; Yasunari, Tetsuzo

    2009-06-16

    Preindustrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an atmospheric general circulation model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked and was consistent with the observational changes derived from examining the Himalayan ice cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/use change was the major source of disturbances to the climate during that period. This report will set forward quantitative examination of the actual impacts of land cover/use changes on Asian monsoons, relative to the impact of greenhouse gases and aerosols, viewed in the context of global warming on the interannual, decadal, and centennial time scales.

  17. Regional environment and hydrology changes documented by lake sediments from Lake Dalianhai, northeastern Tibetan Plateau since the last glacial maximum and their relationship with Asian summer monsoon variability

    Science.gov (United States)

    Wu, D.; Chen, F.; Zhou, A.; Abbott, M. B.

    2016-12-01

    Variability of the Asian summer monsoon (ASM) significantly affects environment and hydrology conditions within its area of influence, as well as economic and social development. Thus it is important to investigate the variability of the ASM on various time-scales and to explore its underlying forcing mechanisms, in order to improve our ability to predict the long-term trends of regional and global climate. Northeastern Tibetan Plateau, a margin area of modern ASM, is sensitive to summer monsoon changes. Existing paleoclimate records from this region contain conflicting evidence for the timing of summer monsoon advance into this region: an early arrival pre-Younger Dryas or a late arrival at the beginning of the Holocene. In addition, it is also debated that whether the Holocene ASM maximum in this region occurred during the early Holocene or the middle Holocene. Here we present a high-resolution record of a 52-m drilling core from Lake Dalianhai in this region. Multiply geochemistry indexes were obtained from the sediment core. 22 AMS 14C data from plant remains and bulk organic matters illustrate that the upper 52 m core covered the whole period since the last glacial maximum (LGM). The results generally indicate that the Lake Dalianhai was occupied by very shallow water body with eolian sand surrounding the lake from 20 to 15 ka BP (1ka=1000 cal yr). With the beginning of the B/A warm period, the sedimentary sequence changed to grey lacustrine clay abruptly. The sedimentary environment was relatively stable under a high lake level state during the B/A period which was marked with fine mean grain size, and high exogenous detrital element content (such as Al, K, Ti and Rb), but with low organic matter content. This perhaps was caused by the increasing of ASM precipitation. Increased contents of element Ca, Sr, and Br, as well as TOC and TN, highlight the increase of ASM during the Holocene. However, reddish lacustrine clay with lower magnetic susceptibility and

  18. Increases in aerosol concentrations over eastern China due to the decadal-scale weakening of the East Asian summer monsoon

    Science.gov (United States)

    Zhu, Jianlei; Liao, Hong; Li, Jianping

    2012-05-01

    China has been experiencing increased concentrations of aerosols, commonly attributed to the large increases in emissions associated with the rapid economic development. We show by using a chemical transport model driven by the assimilated meteorological fields that the observed decadal-scale weakening of the East Asian summer monsoon also contributed to the increases in aerosols in China. We find that the simulated aerosol concentrations have strong negative correlations with the strength of the East Asian Summer monsoon. Accounting for sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols, the summer surface-layer PM2.5 concentration averaged over eastern China (110°-125°E, 20°-45°N) can be 17.7% higher in the weakest monsoon years than in the strongest monsoon years. The weakening of the East Asian Summer monsoon increases aerosol concentrations mainly by the changes in atmospheric circulation (the convergence of air pollutants) in eastern China.

  19. High carbon dioxide uptake by subtropical forest ecosystems in the East Asian monsoon region

    Science.gov (United States)

    Yu, Guirui; Chen, Zhi; Piao, Shilong; Peng, Changhui; Ciais, Philippe; Wang, Qiufeng; Li, Xuanran; Zhu, Xianjin

    2014-01-01

    Temperate- and high-latitude forests have been shown to contribute a carbon sink in the Northern Hemisphere, but fewer studies have addressed the carbon balance of the subtropical forests. In the present study, we integrated eddy covariance observations established in the 1990s and 2000s to show that East Asian monsoon subtropical forests between 20°N and 40°N represent an average net ecosystem productivity (NEP) of 362 ± 39 g C m−2 yr−1 (mean ± 1 SE). This average forest NEP value is higher than that of Asian tropical and temperate forests and is also higher than that of forests at the same latitudes in Europe–Africa and North America. East Asian monsoon subtropical forests have comparable NEP to that of subtropical forests of the southeastern United States and intensively managed Western European forests. The total NEP of East Asian monsoon subtropical forests was estimated to be 0.72 ± 0.08 Pg C yr−1, which accounts for 8% of the global forest NEP. This result indicates that the role of subtropical forests in the current global carbon cycle cannot be ignored and that the regional distributions of the Northern Hemisphere's terrestrial carbon sinks are needed to be reevaluated. The young stand ages and high nitrogen deposition, coupled with sufficient and synchronous water and heat availability, may be the primary reasons for the high NEP of this region, and further studies are needed to quantify the contribution of each underlying factor. PMID:24639529

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

    Energy Technology Data Exchange (ETDEWEB)

    Annamalai, H. [Univ. of Hawaii, Honolulu, HI (United States)

    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

  1. 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.

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

    Science.gov (United States)

    Shinozaki, T.; Uchida, M.; Minoura, K.; Kondo, M.; Rella, S. F.; Shibata, Y.

    2011-06-01

    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 Japan. On the other hand, the 680 yr periodicity between 10.0 and 8.0 kyr is

  3. Possible teleconnections between East and South Asian summer monsoon precipitation in projected future climate change

    Science.gov (United States)

    Woo, Sumin; Singh, Gyan Prakash; Oh, Jai-Ho; Lee, Kyoung-Min

    2018-01-01

    The present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010-2039), mid-(2040-2069) and far-(2070-2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40 km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea-Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850 hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea-Japan, while precipitation variations over Korea-Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea-Japan and Southern China with the wind (at 850 hPa) and MSLP fields indicate that the major parts of the moisture over Korea-Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity.

  4. First detection of ammonia (NH3 in the Asian summer monsoon upper troposphere

    Directory of Open Access Journals (Sweden)

    M. Höpfner

    2016-11-01

    Full Text Available Ammonia (NH3 has been detected in the upper troposphere by the analysis of averaged MIPAS (Michelson Interferometer for Passive Atmospheric Sounding infrared limb-emission spectra. We have found enhanced amounts of NH3 within the region of the Asian summer monsoon at 12–15 km altitude. Three-monthly, 10° longitude  ×  10° latitude average profiles reaching maximum mixing ratios of around 30 pptv in this altitude range have been retrieved, with a vertical resolution of 3–8 km and estimated errors of about 5 pptv. These observations show that loss processes during transport from the boundary layer to the upper troposphere within the Asian monsoon do not deplete the air entirely of NH3. Thus, ammonia might contribute to the so-called Asian tropopause aerosol layer by the formation of ammonium aerosol particles. On a global scale, outside the monsoon area and during different seasons, we could not detect enhanced values of NH3 above the actual detection limit of about 3–5 pptv. This upper bound helps to constrain global model simulations.

  5. Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

    Science.gov (United States)

    Konda, Gopinadh; Chowdary, J. S.; Srinivas, G.; Gnanaseelan, C.; Parekh, Anant; Attada, Raju; Rama Krishna, S. S. V. S.

    2018-06-01

    In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

  6. Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

    KAUST Repository

    Konda, Gopinadh; Chowdary, Jasti S.; Srinivas, G; Gnanaseelan, C; Parekh, Anant; Attada, Raju; Rama Krishna, S S V S

    2018-01-01

    In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

  7. Tropospheric biennial oscillation and south Asian summer monsoon rainfall in a coupled model

    KAUST Repository

    Konda, Gopinadh

    2018-05-22

    In this study Tropospheric Biennial Oscillation (TBO) and south Asian summer monsoon rainfall are examined in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. High correlation between the observations and model TBO index suggests that the model is able to capture most of the TBO years. Spatial patterns of rainfall anomalies associated with positive TBO over the south Asian region are better represented in the model as in the observations. However, the model predicted rainfall anomaly patterns associated with negative TBO years are improper and magnitudes are underestimated compared to the observations. It is noted that positive (negative) TBO is associated with La Niña (El Niño) like Sea surface temperature (SST) anomalies in the model. This leads to the fact that model TBO is El Niño-Southern Oscillation (ENSO) driven, while in the observations Indian Ocean Dipole (IOD) also plays a role in the negative TBO phase. Detailed analysis suggests that the negative TBO rainfall anomaly pattern in the model is highly influenced by improper teleconnections allied to IOD. Unlike in the observations, rainfall anomalies over the south Asian region are anti-correlated with IOD index in CFSv2. Further, summer monsoon rainfall over south Asian region is highly correlated with IOD western pole than eastern pole in CFSv2 in contrast to the observations. Altogether, the present study highlights the importance of improving Indian Ocean SST teleconnections to south Asian summer rainfall in the model by enhancing the predictability of TBO. This in turn would improve monsoon rainfall prediction skill of the model.

  8. Interannual Variability, Global Teleconnection, and Potential Predictability Associated with the Asian Summer Monsoon

    Science.gov (United States)

    Lau, K. M.; Kim, K. M.; Li, J. Y.

    2001-01-01

    In this Chapter, aspects of global teleconnections associated with the interannual variability of the Asian summer monsoon (ASM) are discussed. The basic differences in the basic dynamics of the South Asian Monsoon and the East Asian monsoon, and their implications on global linkages are discussed. Two teleconnection modes linking ASM variability to summertime precipitation over the continental North America were identified. These modes link regional circulation and precipitation anomalies over East Asia and continental North America, via coupled atmosphere-ocean variations over the North Pacific. The first mode has a large zonally symmetrical component and appears to be associated with subtropical jetstream variability and the second mode with Rossby wave dispersion. Both modes possess strong sea surface temperature (SST) expressions in the North Pacific. Results show that the two teleconnection modes may have its origin in intrinsic modes of sea surface temperature variability in the extratropical oceans, which are forced in part by atmospheric variability and in part by air-sea interaction. The potential predictability of the ASM associated with SST variability in different ocean basins is explored using a new canonical ensemble correlation prediction scheme. It is found that SST anomalies in tropical Pacific, i.e., El Nino, is the most dominant forcing for the ASM, especially over the maritime continent and eastern Australia. SST anomalies in the India Ocean may trump the influence from El Nino in western Australia and western maritime continent. Both El Nino, and North Pacific SSTs contribute to monsoon precipitation anomalies over Japan, southern Korea, northern and central China. By optimizing SST variability signals from the world ocean basins using CEC, the overall predictability of ASM can be substantially improved.

  9. Impacts of interannual variation of the East Asian winter monsoon on aerosol concentrations over eastern China

    Science.gov (United States)

    Zhu, J.; Liao, H.; Li, J.; Feng, J.

    2012-04-01

    China has been experiencing increased concentrations of aerosols, commonly attributed to the large increases in emissions associated with the rapid economic development. We apply a global three-dimensional Goddard Earth Observing System chemical transport model (GEOS-Chem) driven by the NASA/GEOS-4 assimilated meteorological data to quantify the impacts of East Asian winter monsoon (EAWM) on the aerosol concentrations over eastern China. We found that the simulated aerosol concentrations over eastern China have strong interannual variation and negative correlations with the strength of EAWM. Model results show that, accounting for sulfate, nitrate, ammonium, black carbon, and organic carbon aerosols, the winter surface layer PM2.5 concentration averaged over eastern China (110°-125°E, 20°-45°N) can be 17.97% (4.78 µg m-3) higher in the weak monsoon years than that in the strong monsoon years. Regionally, the weakening of EAWM is shown to be able to increase PM2.5 concentration in the middle and lower reach of the Yellow River by 12 µg m-3. This point indicates that climate change associated with variation of EAWM has an essential influence on worsening air quality over eastern China. The possible causes of higher aerosol concentrations in the weak monsoon years may be attributed to the changing in wind fields and planetary boundary layer height between the weak and strong monsoon years. Sensitivity studies are performed to identify the role of chemical reaction associated with temperature and humidity on the higher aerosol concentrations in the weak monsoon years over eastern China.

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

    Directory of Open Access Journals (Sweden)

    B. Barret

    2016-07-01

    Full Text Available 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

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

    Directory of Open Access Journals (Sweden)

    K. Zhang

    2016-06-01

    Full Text Available 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

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

    Science.gov (United States)

    Ichoku, Charles; Petrenko, Maksym

    2012-01-01

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

  13. Impact of East Asian Summer Monsoon on Surface Ozone Pattern in China

    Science.gov (United States)

    Li, Shu; Wang, Tijian; Huang, Xing; Pu, Xi; Li, Mengmeng; Chen, Pulong; Yang, Xiu-Qun; Wang, Minghuai

    2018-01-01

    Tropospheric ozone plays a key role in regional and global atmospheric and climate systems. In East Asia, ozone can be affected both in concentration level and spatial pattern by typical monsoon climate. This paper uses three different indices to identify the strength of East Asian summer monsoon (EASM) and explores the possible impact of EASM intensity on the ozone pattern through synthetic and process analysis. The difference in ozone between three strong and three weak monsoon years was analyzed using the simulations from regional climate model RegCM4-Chem. It was found that EASM intensity can significantly influence the spatial distribution of ozone in the lower troposphere. When EASM is strong, ozone in the eastern part of China (28°N - 42° N) is reduced, but the inverse is detected in the north and south. The surface ozone difference ranges from -7 to 7 ppbv during the 3 months (June to August) of the EASM, with the most obvious difference in August. Difference of the 3 months' average ozone ranges from -3.5 to 4 ppbv. Process analysis shows that the uppermost factor controlling ozone level during summer monsoon seasons is the chemistry process. Interannual variability of EASM can impact the spatial distribution of ozone through wind in the lower troposphere, cloud cover, and downward shortwave radiation, which affect the transport and chemical formation of ozone. The phenomenon should be addressed when considering the interaction between ozone and the climate in East Asia region.

  14. Seasonal modulation of the Asian summer monsoon between the Medieval Warm Period and Little Ice Age: a multi model study

    Science.gov (United States)

    Kamae, Youichi; Kawana, Toshi; Oshiro, Megumi; Ueda, Hiroaki

    2017-12-01

    Instrumental and proxy records indicate remarkable global climate variability over the last millennium, influenced by solar irradiance, Earth's orbital parameters, volcanic eruptions and human activities. Numerical model simulations and proxy data suggest an enhanced Asian summer monsoon during the Medieval Warm Period (MWP) compared to the Little Ice Age (LIA). Using multiple climate model simulations, we show that anomalous seasonal insolation over the Northern Hemisphere due to a long cycle of orbital parameters results in a modulation of the Asian summer monsoon transition between the MWP and LIA. Ten climate model simulations prescribing historical radiative forcing that includes orbital parameters consistently reproduce an enhanced MWP Asian monsoon in late summer and a weakened monsoon in early summer. Weakened, then enhanced Northern Hemisphere insolation before and after June leads to a seasonally asymmetric temperature response over the Eurasian continent, resulting in a seasonal reversal of the signs of MWP-LIA anomalies in land-sea thermal contrast, atmospheric circulation, and rainfall from early to late summer. This seasonal asymmetry in monsoon response is consistently found among the different climate models and is reproduced by an idealized model simulation forced solely by orbital parameters. The results of this study indicate that slow variation in the Earth's orbital parameters contributes to centennial variability in the Asian monsoon transition.[Figure not available: see fulltext.

  15. Lower tropospheric ozone over India and its linkage to the South Asian monsoon

    Science.gov (United States)

    Lu, Xiao; Zhang, Lin; Liu, Xiong; Gao, Meng; Zhao, Yuanhong; Shao, Jingyuan

    2018-03-01

    Lower tropospheric (surface to 600 hPa) ozone over India poses serious risks to both human health and crops, and potentially affects global ozone distribution through frequent deep convection in tropical regions. Our current understanding of the processes controlling seasonal and long-term variations in lower tropospheric ozone over this region is rather limited due to spatially and temporally sparse observations. Here we present an integrated process analysis of the seasonal cycle, interannual variability, and long-term trends of lower tropospheric ozone over India and its linkage to the South Asian monsoon using the Ozone Monitoring Instrument (OMI) satellite observations for years 2006-2014 interpreted with a global chemical transport model (GEOS-Chem) simulation for 1990-2010. OMI observed lower tropospheric ozone over India averaged for 2006-2010, showing the highest concentrations (54.1 ppbv) in the pre-summer monsoon season (May) and the lowest concentrations (40.5 ppbv) in the summer monsoon season (August). Process analyses in GEOS-Chem show that hot and dry meteorological conditions and active biomass burning together contribute to 5.8 Tg more ozone being produced in the lower troposphere in India in May than January. The onset of the summer monsoon brings ozone-unfavorable meteorological conditions and strong upward transport, which all lead to large decreases in the lower tropospheric ozone burden. Interannually, we find that both OMI and GEOS-Chem indicate strong positive correlations (r = 0.55-0.58) between ozone and surface temperature in pre-summer monsoon seasons, with larger correlations found in high NOx emission regions reflecting NOx-limited production conditions. Summer monsoon seasonal mean ozone levels are strongly controlled by monsoon strengths. Lower ozone concentrations are found in stronger monsoon seasons mainly due to less ozone net chemical production. Furthermore, model simulations over 1990-2010 estimate a mean annual trend of 0

  16. Tibet, the Himalaya, Asian monsoons and biodiversity – In what ways are they related?

    Directory of Open Access Journals (Sweden)

    Robert A. Spicer

    2017-10-01

    Full Text Available Prevailing dogma asserts that the uplift of Tibet, the onset of the Asian monsoon system and high biodiversity in southern Asia are linked, and that all occurred after 23 million years ago in the Neogene. Here, spanning the last 60 million years of Earth history, the geological, climatological and palaeontological evidence for this linkage is reviewed. The principal conclusions are that: 1 A proto-Tibetan highland existed well before the Neogene and that an Andean type topography with surface elevations of at least 4.5 km existed at the start of the Eocene, before final closure of the Tethys Ocean that separated India from Eurasia. 2 The Himalaya were formed not at the start of the India–Eurasia collision, but after much of Tibet had achieved its present elevation. The Himalaya built against a pre-existing proto-Tibetan highland and only projected above the average height of the plateau after approximately 15 Ma. 3 Monsoon climates have existed across southern Asia for the whole of the Cenozoic, and probably for a lot longer, but that they were of the kind generated by seasonal migrations of the Inter-tropical Convergence Zone. 4 The projection of the High Himalaya above the Tibetan Plateau at about 15 Ma coincides with the development of the modern South Asia Monsoon. 5 The East Asia monsoon became established in its present form about the same time as a consequence of topographic changes in northern Tibet and elsewhere in Asia, the loss of moisture sources in the Asian interior and the development of a strong winter Siberian high as global temperatures declined. 6 New radiometric dates of palaeontological finds point to southern Asia's high biodiversity originating in the Paleogene, not the Neogene.

  17. Did the demise of Green Sahara play a role in the mid-to-late Holocene megadrought and `missing millennia' in southeast Asian societies?

    Science.gov (United States)

    Griffiths, M. L.; Johnson, K. R.; Pausata, F. S. R.; White, J.; Yang, H.; Henderson, G. M.; Conrad, C.

    2017-12-01

    The mid-to-late Holocene in eastern Africa and Eurasia was characterized by one of, if not the, largest climate anomalies of the past 10,000 years (i.e. the `4.2 ka event'), yet the cause of this event remains enigmatic. The nature and geographical extent of the event has been a topic of great interest because of its potential connections with societal upheavals in western Asia and northeastern Africa. However, while paleoclimate data from India and southern China show evidence for a large-scale megadrought during this period, there have hitherto been no high-resolution and well-dated records from mainland southeast Asia (MSEA) to document the regional footprint of this event. This is somewhat surprising given that this period also coincides with what has been termed the `missing millennia' in MSEA, which refers to the major gap in archeological evidence that may have some link with the broader Asian monsoon failure during this time. To help shed light on the potential connection between climate change and the missing millennia, we have compiled four new speleothem oxygen (δ18O) and carbon (δ13C) isotope records from Tham Doun Mai cave in northern Laos. The δ18O profiles show a general increasing trend through much of the Holocene which is interpreted to reflect an overall weakening of the Southeast Asian monsoon. This general trend is punctuated by a marked positive δ18O shift at 4-5 ka, signifying an overall reduction in monsoon strength that persisted until 3.5 ka. Interestingly, the onset of this anomaly coincides with the cessation in speleothem growth of three speleothems, and a 4 per mil increase in δ13C for the speleothem that continued to grow. We interpret this large and abrupt increase in δ13C to reflect enhanced CO2 degassing due to a much slower drip-rate (supported by a slower growth rate), and the hiatuses to reflect large groundwater deficits to those drip sites. The onset of this abrupt megadrought in northern Laos is consistent with abrupt

  18. Pleistocene Indian Monsoon Rainfall Variability

    Science.gov (United States)

    Yirgaw, D. G.; Hathorne, E. C.; Giosan, L.; Collett, T. S.; Sijingeo, A. V.; Nath, B. N.; Frank, M.

    2014-12-01

    The past variability of the Indian Monsoon is mostly known from records of wind strength over the Arabian Sea. Here we investigate proxies for fresh water input and runoff in a region of strong monsoon precipitation that is a major moisture source for the east Asian Monsoon. A sediment core obtained by the IODP vessel JOIDES Resolution and a gravity core from the Alcock Seamount complex in the Andaman Sea are used to examine the past monsoon variability on the Indian sub-continent and directly over the ocean. The current dataset covers the last glacial and deglacial but will eventually provide a Pleistocene record. We utilise the ecological habitats of G. sacculifer and N. dutertrei to investigate the freshwater-induced stratification with paired Mg/Ca and δ18O analyses to estimate seawater δ18O (δ18Osw). During the last 60 kyrs, Ba/Ca ratios and δ18Osw values generally agree well between the two cores and suggest the weakest surface runoff and monsoon during the LGM and strongest monsoon during the Holocene. The difference in δ18O between the species, interpreted as a proxy for upper ocean stratification, implies stratification developed around 37 ka and remained relatively constant during the LGM, deglacial and Holocene. To investigate monsoon variability for intervals in the past, single shell Mg/Ca and δ18O analyses have been conducted. Mg/Ca ratios from individual shells of N. dutertrei suggest relatively small changes in temperature. However, individual N. dutertrei δ18O differ greatly between the mid-Holocene and samples from the LGM and a nearby core top. The mid-Holocene individuals have a greater range and large skew towards negative values indicating greater fresh water influence.

  19. Objective spatiotemporal proxy-model comparisons of the Asian monsoon for the last millennium

    Science.gov (United States)

    Anchukaitis, K. J.; Cook, E. R.; Ammann, C. M.; Buckley, B. M.; D'Arrigo, R. D.; Jacoby, G.; Wright, W. E.; Davi, N.; Li, J.

    2008-12-01

    The Asian monsoon system can be studied using a complementary proxy/simulation approach which evaluates climate models using estimates of past precipitation and temperature, and which subsequently applies the best understanding of the physics of the climate system as captured in general circulation models to evaluate the broad-scale dynamics behind regional paleoclimate reconstructions. Here, we use a millennial-length climate field reconstruction of monsoon season summer (JJA) drought, developed from tree- ring proxies, with coupled climate simulations from NCAR CSM1.4 and CCSM3 to evaluate the cause of large- scale persistent droughts over the last one thousand years. Direct comparisons are made between the external forced response within the climate model and the spatiotemporal field reconstruction. In order to identify patterns of drought associated with internal variability in the climate system, we use a model/proxy analog technique which objectively selects epochs in the model that most closely reproduce those observed in the reconstructions. The concomitant ocean-atmosphere dynamics are then interpreted in order to identify and understand the internal climate system forcing of low frequency monsoon variability. We examine specific periods of extensive or intensive regional drought in the 15th, 17th, and 18th centuries, many of which are coincident with major cultural changes in the region.

  20. Efficient transport of tropospheric aerosol into the stratosphere via the Asian summer monsoon anticyclone

    Science.gov (United States)

    Yu, Pengfei; Rosenlof, Karen H.; Liu, Shang; Telg, Hagen; Thornberry, Troy D.; Rollins, Andrew W.; Portmann, Robert W.; Bai, Zhixuan; Ray, Eric A.; Duan, Yunjun; Pan, Laura L.; Toon, Owen B.; Bian, Jianchun; Gao, Ru-Shan

    2017-07-01

    An enhanced aerosol layer near the tropopause over Asia during the June-September period of the Asian summer monsoon (ASM) was recently identified using satellite observations. Its sources and climate impact are presently not well-characterized. To improve understanding of this phenomenon, we made in situ aerosol measurements during summer 2015 from Kunming, China, then followed with a modeling study to assess the global significance. The in situ measurements revealed a robust enhancement in aerosol concentration that extended up to 2 km above the tropopause. A climate model simulation demonstrates that the abundant anthropogenic aerosol precursor emissions from Asia coupled with rapid vertical transport associated with monsoon convection leads to significant particle formation in the upper troposphere within the ASM anticyclone. These particles subsequently spread throughout the entire Northern Hemispheric (NH) lower stratosphere and contribute significantly (˜15%) to the NH stratospheric column aerosol surface area on an annual basis. This contribution is comparable to that from the sum of small volcanic eruptions in the period between 2000 and 2015. Although the ASM contribution is smaller than that from tropical upwelling (˜35%), we find that this region is about three times as efficient per unit area and time in populating the NH stratosphere with aerosol. With a substantial amount of organic and sulfur emissions in Asia, the ASM anticyclone serves as an efficient smokestack venting aerosols to the upper troposphere and lower stratosphere. As economic growth continues in Asia, the relative importance of Asian emissions to stratospheric aerosol is likely to increase.

  1. Change in the tropical cyclone activity around Korea by the East Asian summer monsoon

    Science.gov (United States)

    Choi, Jae-Won; Cha, Yumi; Kim, Jeoung-Yun

    2017-12-01

    Correlation between the frequency of summer tropical cyclones (TCs) affecting Korea and the East Asian summer monsoon index (EASMI) was analyzed over the last 37 years. A clear positive correlation existed between the two variables, and this high positive correlation remained unchanged even when excluding El Niño-Southern Oscillation (ENSO) years. To investigate the causes of the positive correlation between the two variables in non-ENSO years, after the 8 years with the highest EASMI (high EASMI years) and the 8 years with the lowest EASMI (low EASMI years) were selected, and the average difference between the two phases was analyzed. In high EASMI years, in the difference between the two phases regarding 850 and 500 hPa streamline, anomalous cyclones were reinforced in the tropical and subtropical western North Pacific, while anomalous anticyclones were reinforced in mid-latitude East Asian areas. Due to these two anomalous pressure systems, anomalous southeasterlies developed near Korea, with these anomalous southeasterlies playing the role of anomalous steering flows making the TCs head toward areas near Korea. In addition, a monsoon trough strengthened more eastward, and TCs in high EASMI years occurred more in east ward over the western North Pacific.

  2. Origins of the Asian-Australian monsoons related to Cenozoic plate movement and Tibetan Plateau uplift - A modeling study

    Science.gov (United States)

    Liu, X.; Dong, B.; Yin, Z. Y.; Smith, R. S.; Guo, Q.

    2017-12-01

    The origin of monsoon is a subject that has attracted much attention in the scientific community and even today it is still controversial. According to geological records, there is conflicting evidence regarding the timings of establishment of the monsoon climates in South Asia, East Asia, and northern Australia. Additionally, different explanations for the monsoon origins have been derived from various numerical simulations. To further investigate the origin and evolution of the Asian and Australian monsoons, we designed a series of numerical experiments using a coupled atmospheric-oceanic general circulation model. Since the Indian-Australian plate has shifted its position significantly during the Cenozoic, together with the large-scale uplift of the Tibetan Plateau (TP), in these experiments we considered the configurations of ocean-land masses and large topographic features based on geological evidence of plate motion and TP uplift in 5 typical Cenozoic geological periods: mid-Paleocene ( 60Ma), late-Eocene ( 40Ma), late-Oligocene ( 25Ma), late-Miocene ( 10Ma), and present day. These experiments allowed us to examine the combined effects of the changes in the land-ocean configuration due to plate movement and TP uplift, they also provided insight into the effects of the high CO2 levels during the Eocene. The simulations revealed that during the Paleocene, the Indian Subcontinent was still positioned in the Southern Hemisphere (SH) and, therefore, its climate behaved as the SH tropical monsoon. By the late Eocene, it moved into the tropical Northern Hemisphere, which allowed the establishment of the South Asian monsoon. In contrast, the East Asian and Australian monsoon did not exist in the late Oligocene. These monsoon systems were established in the Miocene and then enhanced thereafter. Establishments of the low-latitude monsoons in South Asia and Australia were entirely determined by the position of the Indian-Australian plate and not related to the TP uplift

  3. 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

  4. The Abrupt Onset of the Modern South Asian Monsoon Winds (iodp Exp. 359)

    Science.gov (United States)

    Betzler, C.; Eberli, G. P.; Kroon, D.; Wright, J. D.; Swart, P. K.; Nath, B. N.; Reijmer, J.; Alvarez Zarikian, C. A.

    2016-12-01

    The South Asian Monson (SAM) is one of the most extreme features in Earth's climate system, yet its initiation and variations are not well established. The SAM is a seasonal reversal of winds accompanied by changes in precipitation with heavy rain during the summer monsoon. It is one of the most intense annually recurring climatic elements and of immense importance in supplying moisture to the Indian subcontinent thus affecting human population and vegetation, as well as marine biota in the surrounding seas. The seasonal precipitation change is one of the SAM elements most noticed on land, whereas the reversal of the wind regime is the dominating driver of circulation in the central and northern Indian Ocean realm. New data acquired during International Ocean Discovery Program Expedition 359 from the Inner Sea of the Maldives provide a previously unread archive that reveals an abrupt onset of the SAM-linked ocean circulation pattern and its relationship to the long term Neogene climate cooling. In particular it registers ocean current fluctuations and changes of intermediate water mass properties for the last 25 myrs that are directly related to the monsoon. Dating the deposits of SAM wind-driven currents 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 sedimentary 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.

  5. Equilibrium climate response of the East Asian summer monsoon to forcing of anthropogenic aerosol species

    Science.gov (United States)

    Wang, Zhili; Wang, Qiuyan; Zhang, Hua

    2017-12-01

    We used an online aerosol-climate model to study the equilibrium climate response of the East Asian summer monsoon (EASM) to increases in anthropogenic emissions of sulfate, organic carbon, and black carbon aerosols from 1850 to 2000. Our results show that each of these aerosol species has a different effect on the EASM as a result of changes in the local sea-land thermal contrast and atmospheric circulation. The increased emission of sulfate aerosol leads to a decrease in the thermal contrast between the land and ocean, a southward shift of the East Asian subtropical jet, and significant northerly wind anomalies at 850 hPa over eastern China and the ambient oceans, markedly dampening the EASM. An increase in organic carbon aerosol results in pronounced surface cooling and the formation of an anomalous anticyclone over the oceans north of 30°N. These effects cause a slight increase in the sea-land thermal contrast and southerly flow anomalies to the west of the anticyclonic center, strengthening the northern EASM. An increase in organic carbon emission decreases the sea-land thermal contrast over southern China, which weakens the southern EASM. The response of the summer 850-hPa winds and rainfall over the East Asian monsoon region to an increase in black carbon emission is generally consistent with the response to an increase in organic carbon. The increase in black carbon emission leads to a strengthening of the northern EASM north of 35°N and a slight weakening of the southern EASM south of 35°N. The simulated response of the EASM to the increase in black carbon emission is unchanged when the emission of black carbon is scaled up by five times its year 2000 levels, although the intensities of the response is enhanced. The increase in sulfate emission primarily weakens the EASM, whereas the increases in black carbon and organic carbon emissions mitigate weakening of the northern EASM.

  6. Divergent influences of the Greenland and Antarctica climates on the Asian monsoon during a stadial to interstadial cycle

    Science.gov (United States)

    Duan, Fucai; Wang, Yongjin; Liao, Zebo; Chen, Shitao; Zhang, Weihong; Shao, Qingfeng

    2018-06-01

    Despite the links of Asian monsoon with climates at high northern and southern latitudes, it remains unclear that at which time and to what extent the Asian monsoon variation is dominated by one of the two drivers throughout a Greenland Stadial (GS) to Greenland Interstadial (GI) cycle. Here we provide a Chinese stalagmite δ18O record to study their teleconnections throughout the GS-6 to GI-5.2 cycle. The resemblance between the stalagmite and Greenland records, in timing, duration and abruptness of GI-5.2, supports that the occurrence and termination of GIs are paced by the northern driving force. During the intervals of GI-5.2 and GS-6, however, the Asian monsoon fluctuated concomitantly with variation in temperature over Antarctica, instead of over Greenland. This covariation indicates dominant influences of the Antarctic climate during the climatically stable intervals of stadials and interstadials. This study updates our knowledge on mechanical dynamics of the Asian monsoon change and global climate change throughout a GS to GI cycle.

  7. Last Glacial Maximum to Holocene climate evolution controlled by sea-level change, Leeuwin Current, and Australian Monsoon in the Northwestern Australia

    Science.gov (United States)

    Ishiwa, T.; Yokoyama, Y.; McHugh, C.; Reuning, L.; Gallagher, S. J.

    2017-12-01

    The transition from cold to warm conditions during the last deglaciation influenced climate variability in the Indian Ocean and Pacific as a result of submerge of continental shelf and variations in the Indonesian Throughflow and Australian Monsoon. The shallow continental shelf (Program Expedition 356 Indonesian Throughflow drilled in the northwestern Australian shallow continental shelf and recovered an interval from the Last Glacial Maximum to Holocene in Site U1461. Radiocarbon dating on macrofossils, foraminifera, and bulk organic matter provided a precise age-depth model, leading to high-resolved paleoclimate reconstruction. X-ray elemental analysis results are interpreted as an indicator of sedimentary environmental changes. The upper 20-m part of Site U1461 apparently records the climate transition from the LGM to Holocene in the northwestern Australia, which could be associated with sea-level change, Leeuwin Current activity, and the Australian Monsoon.

  8. 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

  9. Response of the Asian summer monsoons to idealized precession and obliquity forcing in a set of GCMs

    Science.gov (United States)

    Bosmans, J. H. C.; Erb, M. P.; Dolan, A. M.; Drijfhout, S. S.; Tuenter, E.; Hilgen, F. J.; Edge, D.; Pope, J. O.; Lourens, L. J.

    2018-05-01

    We examine the response of the Indian and East Asian summer monsoons to separate precession and obliquity forcing, using a set of fully coupled high-resolution models for the first time: EC-Earth, GFDL CM2.1, CESM and HadCM3. We focus on the effect of insolation changes on monsoon precipitation and underlying circulation changes, and find strong model agreement despite a range of model physics, parameterization, and resolution. Our results show increased summer monsoon precipitation at times of increased summer insolation, i.e. minimum precession and maximum obliquity, accompanied by a redistribution of precipitation and convection from ocean to land. Southerly monsoon winds over East Asia are strengthened as a consequence of an intensified land-sea pressure gradient. The response of the Indian summer monsoon is less straightforward. Over south-east Asia low surface pressure is less pronounced and winds over the northern Indian Ocean are directed more westward. An Indian Ocean Dipole pattern emerges, with increased precipitation and convection over the western Indian Ocean. Increased temperatures occur during minimum precession over the Indian Ocean, but not during maximum obliquity when insolation is reduced over the tropics and southern hemisphere during northern hemisphere summer. Evaporation is reduced over the northern Indian Ocean, which together with increased precipitation over the western Indian Ocean dampens the increase of monsoonal precipitation over the continent. The southern tropical Indian Ocean as well as the western tropical Pacific (for precession) act as a moisture source for enhanced monsoonal precipitation. The models are in closest agreement for precession-induced changes, with more model spread for obliquity-induced changes, possibly related to a smaller insolation forcing. Our results indicate that a direct response of the Indian and East Asian summer monsoons to insolation forcing is possible, in line with speleothem records but in

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

    Directory of Open Access Journals (Sweden)

    A. K. Baker

    2011-01-01

    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 the upper troposphere over southwestern Asia. 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 a number of C2–C8 non-methane hydrocarbons. Non-methane hydrocarbons are relatively short-lived compounds and the large enhancements in their mixing ratios in the upper troposphere over southwestern Asia during the monsoon, 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 with 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 fossil fuels, 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 days in the south and 9–12 days in

  11. Overview of the StratoClim Asian Monsoon Aircraft Campaign: Strategy, Instrumentation and preliminary Results

    Science.gov (United States)

    Stroh, F.

    2017-12-01

    The StratoClim Aircraft Field Campaign employing the high-flying research aircraft M55 Geophysica was carried out from mid July to mid August of 2017 from Kathmandu, Nepal, covering the airspace of Nepal, India, Bangladesh and Myanmar in the frame of the EC FP7 funded StratoClim project (see the Rex. et al. overview in this session). In order to sample the first detailed data set on climate relevant processes of the Asian Summer Monsoon anticyclone a comprehensive chemical and aerosol payload of more than 2 metric tons consisting of 26 different instrumets was flown to altitudes in excess of 20km to measure remote sensing and in-situ data on dynamical, chemical, and micro-chemical processes governing this experimentally underresearched atmospheric domain. An overview of the instrumentation, observation strategies, and preliminary results on open challenges as the horizontal and vertical trace gas and aerosol structures, effects of convective events and the ATAL will be given.

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

    International Nuclear Information System (INIS)

    Guo, Zhun; Zhou, Tianjun; Wang, Minghuai; Qian, Yun

    2015-01-01

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

  13. Changing circulation structure and precipitation characteristics in Asian monsoon regions: greenhouse warming vs. aerosol effects

    Science.gov (United States)

    Lau, William K. M.; Kim, Kyu-Myong; Ruby Leung, L.

    2017-12-01

    Using model outputs from CMIP5 historical integrations, we have investigated the relative roles of anthropogenic emissions of greenhouse gases (GHG) and aerosols in changing the characteristics of the large-scale circulation and rainfall in Asian summer monsoon (ASM) regions. Under GHG warming, a strong positive trend in low-level moist static energy (MSE) is found over ASM regions, associated with increasing large-scale land-sea thermal contrast from 1870s to present. During the same period, a mid-tropospheric convective barrier (MCB) due to widespread reduction in relative humidity in the mid- and lower troposphere is strengthening over the ASM regions, in conjunction with expanding areas of anomalous subsidence associated with the Deep Tropical Squeeze (Lau and Kim in Proc Natl Acad Sci 12:3630-3635, 2015). The opposing effects of MSE and MCB lead to enhanced total ASM rainfall, but only a partial strengthening of the southern portion of the monsoon meridional circulation, coupled to anomalous multi-cellular overturning motions over ASM land. Including anthropogenic aerosol emissions strongly masks MSE but enhances MCB via increased stability in the lower troposphere, resulting in an overall weakened ASM circulation with suppressed rainfall. Analyses of rainfall characteristics indicate that under GHG, overall precipitation efficiency over the ASM region is reduced, manifesting in less moderate but more extreme heavy rain events. Under combined effects of GHG and aerosols, precipitation efficiency is unchanged, with more moderate, but less extreme rainfall.

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

    International Nuclear Information System (INIS)

    Zhou, Derong; Ding, Aijun; Mao, Huiting; Fu, Congbin; Ding, Ke; Zhang, Yang; Liu, Jane; Wang, Tao; Chan, L Y; Lu, An; Hao, Nan

    2013-01-01

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

  15. 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

    2017-11-01

    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.

  16. Analysis of the nonlinearity of Asian summer monsoon intraseasonal variability using spherical PDFs

    Science.gov (United States)

    Jajcay, Nikola; Hannachi, Abdel

    2013-04-01

    The Asian summer monsoon (ASM) is a high-dimensional and highly complex phenomenon affecting more than one fifth of the world population. The intraseasonal component of the ASM undergoes periods of active and break phases associated respectively with enhanced and reduced rainfall over the Indian subcontinent and surroundings. In this paper the nonlinear nature of the intraseasonal monsoon variability is investigated using the leading EOFs of ERA-40 sea level pressure reanalyses field over the ASM region. The probability density function is then computed in spherical coordinates using a Epaneshnikov kernel method. Three significant modes are identified. They represent respectively (i) East - West mode with above normal sea level pressure over East China sea and below normal pressure over Himalayas, (ii) mode with above normal sea level pressure over East China sea (without compensating centre of opposite sign as in (i)) and (iii) mode with below normal sea level pressure over East China sea (same as (ii) but with opposite sign). Relationship to large scale flow are also investigated and discussed.

  17. Projected change in East Asian summer monsoon by dynamic downscaling: Moisture budget analysis

    Science.gov (United States)

    Jung, Chun-Yong; Shin, Ho-Jeong; Jang, Chan Joo; Kim, Hyung-Jin

    2015-02-01

    The summer monsoon considerably affects water resource and natural hazards including flood and drought in East Asia, one of the world's most densely populated area. In this study, we investigate future changes in summer precipitation over East Asia induced by global warming through dynamical downscaling with the Weather Research and Forecast model. We have selected a global model from the Coupled Model Intercomparison Project Phase 5 based on an objective evaluation for East Asian summer monsoon and applied its climate change under Representative Concentration Pathway 4.5 scenario to a pseudo global warming method. Unlike the previous studies that focused on a qualitative description of projected precipitation changes over East Asia, this study tried to identify the physical causes of the precipitation changes by analyzing a local moisture budget. Projected changes in precipitation over the eastern foothills area of Tibetan Plateau including Sichuan Basin and Yangtze River displayed a contrasting pattern: a decrease in its northern area and an increase in its southern area. A local moisture budget analysis indicated the precipitation increase over the southern area can be mainly attributed to an increase in horizontal wind convergence and surface evaporation. On the other hand, the precipitation decrease over the northern area can be largely explained by horizontal advection of dry air from the northern continent and by divergent wind flow. Regional changes in future precipitation in East Asia are likely to be attributed to different mechanisms which can be better resolved by regional dynamical downscaling.

  18. Future changes in Asian summer monsoon precipitation extremes as inferred from 20-km AGCM simulations

    Science.gov (United States)

    Lui, Yuk Sing; Tam, Chi-Yung; Lau, Ngar-Cheung

    2018-04-01

    This study examines the impacts of climate change on precipitation extremes in the Asian monsoon region during boreal summer, based on simulations from the 20-km Meteorological Research Institute atmospheric general circulation model. The model can capture the summertime monsoon rainfall, with characteristics similar to those from Tropical Rainfall Measuring Mission and Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation. By comparing the 2075-2099 with the present-day climate simulations, there is a robust increase of the mean rainfall in many locations due to a warmer climate. Over southeastern China, the Baiu rainband, Bay of Bengal and central India, extreme precipitation rates are also enhanced in the future, which can be inferred from increases of the 95th percentile of daily precipitation, the maximum accumulated precipitation in 5 consecutive days, the simple daily precipitation intensity index, and the scale parameter of the fitted gamma distribution. In these regions, with the exception of the Baiu rainband, most of these metrics give a fractional change of extreme rainfall per degree increase of the lower-tropospheric temperature of 5 to 8.5% K-1, roughly consistent with the Clausius-Clapeyron relation. However, over the Baiu area extreme precipitation change scales as 3.5% K-1 only. We have also stratified the rainfall data into those associated with tropical cyclones (TC) and those with other weather systems. The AGCM gives an increase of the accumulated TC rainfall over southeastern China, and a decrease in southern Japan in the future climate. The latter can be attributed to suppressed TC occurrence in southern Japan, whereas increased accumulated rainfall over southeastern China is due to more intense TC rain rate under global warming. Overall, non-TC weather systems are the main contributor to enhanced precipitation extremes in various locations. In the future, TC activities over southeastern China tend to further

  19. Uncertainty Source of Modeled Ecosystem Productivity in East Asian Monsoon Region: A Traceability Analysis

    Science.gov (United States)

    Cui, E.; Xia, J.; Huang, K.; Ito, A.; Arain, M. A.; Jain, A. K.; Poulter, B.; Peng, C.; Hayes, D. J.; Ricciuto, D. M.; Huntzinger, D. N.; Tian, H.; Mao, J.; Fisher, J.; Schaefer, K. M.; Huang, M.; Peng, S.; Wang, W.

    2017-12-01

    East Asian monsoon region, benefits from sufficient water-heat availability and increasing nitrogen deposition, represents significantly higher net ecosystem productivity than the same latitudes of Europe-Africa and North America. A better understanding of major contributions to the uncertainties of terrestrial carbon cycle in this region is greatly important for evaluating the global carbon balance. This study analyzed the key carbon processes and parameters derived from a series of terrestrial biosphere models. A wide range of inter-model disagreement on GPP was found in China's subtropical regions. Then, this large difference was traced to a few traceable components included in terrestrial carbon cycle. The increase in ensemble mean GPP over 1901-2010 was predominantly resulted from increasing atmospheric CO2 concentration and nitrogen deposition, while high frequent land-use change over this region showed a slightly negative effect on GPP. However, inter-model differences of GPP were mainly attributed to the baseline simulations without changes in external forcing. According to the variance decomposition, the large spread in simulated GPP was well explained by the differences in leaf area index (LAI) and specific leaf area (SLA) among models. In addition, the underlying errors in simulated GPP propagate through the model and introduce some additional errors to the simulation of NPP and biomass. By comparing the simulations with satellite-derived, data-oriented and observation-based datasets, we further found that GPP, vegetation carbon turn-over time, aboveground biomass, LAI and SLA were all overestimated in most of the models while biomass distribution in leaves was significantly underestimated. The results of this study indicate that model performance on ecosystem productivity in East Asian monsoon region can be improved by a more realistic representation of leaf functional traits.

  20. The Holocene history of the North American Monsoon: 'known knowns' and 'known unknowns' in understanding its spatial and temporal complexity

    Science.gov (United States)

    Metcalfe, Sarah E.; Barron, John A.; Davies, Sarah J.

    2015-01-01

    Evidence for climatic change across the North American Monsoon (NAM) and adjacent areas is reviewed, drawing on continental and marine records and the application of climate models. Patterns of change at 12,000, 9000, 6000 and 4000 cal yr BP are presented to capture the nature of change from the Younger Dryas (YD) and through the mid-Holocene. At the YD, conditions were cooler overall, wetter in the north and drier in the south, while moving into the Holocene wetter conditions became established in the south and then spread north as the NAM strengthened. Until c. 8000 cal yr BP, the Laurentide Ice Sheet influenced precipitation in the north by pushing the Bermuda High further south. The peak extent of the NAM seems to have occurred around 6000 cal yr BP. 4000 cal yr BP marks the start of important changes across the NAM region, with drying in the north and the establishment of the clear differences between the summer-rain dominated south and central areas and the north, where winter rain is more important. This differentiation between south and north is crucial to understanding many climate responses across the NAM. This increasing variability is coincident with the declining influence of orbital forcing. 4000 cal yr BP also marks the onset of significant anthropogenic activity in many areas. For the last 2000 years, the focus is on higher temporal resolution change, with strong variations across the region. The Medieval Climate Anomaly (MCA) is characterised by centennial scale ‘megadrought’ across the southwest USA, associated with cooler tropical Pacific SSTs and persistent La Niña type conditions. Proxy data from southern Mexico, Central America and the Caribbean reveal generally wetter conditions, whereas records from the highlands of central Mexico and much of the Yucatan are typified by long -term drought. The Little Ice Age (LIA), in the north, was characterised by cooler, wetter winter conditions that have been linked with increased

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

    International Nuclear Information System (INIS)

    Molteni, Franco; Corti, Susanna; Ferranti, Laura; Slingo, Julia M.

    2003-07-01

    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. On the other hand, the second mode of variability, which again has a good correspondence with observed patterns, shows a clear relationship with the ENSO cycle. Since the mode related to ENSO accounts for only a small part of the total variance, the notion of a quasi-linear superposition of forced and unforced modes of variability may not provide an appropriate interpretation of monsoon interannual variability. Consequently, the possibility of a non-linear influence has been investigated by exploring the relationship between interannual and intraseasonal variability. As in other studies, a common mode of interannual and intraseasonal variability has been found, in this case describing the north-south transition of the TCZ associated with monsoon active/break cycles. Although seasonal-mean values of the Principal Component (PC) timeseries associated with the leading intraseasonal mode shows no significant correlation with ENSO, the 2-dimensional probability

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

    International Nuclear Information System (INIS)

    Molteni, F.; Corti, S.; Ferranti, L.; Slingo, J.M.

    2002-04-01

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

  3. The decadal-scale variation of the South Asian summer monsoon onset and its connection with the PDO

    Science.gov (United States)

    Watanabe, T.; Yamazaki, K.

    2013-12-01

    The summer Asian monsoon shows the abrupt increase of precipitation on the onset phase. It is an interesting and important problem when the summer monsoon onset occurs because natural resources, such as water and renewable energy agricultural product, are influenced by the variation of the summer Asian monsoon. Some researchers suggested the advance of the Asian summer monsoon onset in recent decades. We investigated the variation of the Asian monsoon onset using the long-term onset data over Kerala, a state in the southwest region of India, for 1948-2011. We discuss three main questions: 1) how is the variation of the monsoon onset date in the long-term period, 2) how the variation of the onset date is related to variations of atmospheric circulation and SST, and 3) what is the mechanism of such variation. Our main method is composite analysis using monthly-mean data. Though the onset date over Kerala shows the trend toward the early onset in recent three decades, such a trend is not observed in the whole period. It is noteworthy that the onset over Kerala shows the interannual variation on a multi-decadal scale. As regards the early onset years of Kerala, the summer monsoon onset is early over the following regions: the region from the southern Arabian Sea to southwestern India, the region from the southern Bay of Bengal to the Indochina Peninsula and the western North Pacific Ocean. On the other hand, the onset is late over southern China, Taiwan and the northern Philippine Sea. In early onset years of Kerala, the sea surface temperature over the northern Pacific Ocean is very similar to the negative PDO. The stationary wave train related with the negative PDO reaches into the Central Asia region, generates warm anomaly there and hence intensifies the land-sea thermal contrast there, which promotes the summer monsoon onset over South and Southeast Asia. Though the correlation between the onset over Kerala and the PDO is weak before 1976, it becomes high after

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

    Science.gov (United States)

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

    2016-04-01

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

  5. Condensation heating of the Asian summer monsoon and the subtropical anticyclone in the Eastern Hemisphere

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Y.M.; Wu, G.X.; Liu, H.; Liu, P. [Chinese Academy of Sciences, Beijing (China). Inst. of Atmospheric Physics

    2001-02-01

    The effects of condensation heating on the formation of the subtropical anticyclone in the Eastern Hemisphere (EH) are studied by means of theoretical analysis and numerical simulation. The complete vorticity equation is employed for the analysis. It is found that, due to the vertical gradient of strong condensation heating, the distribution of cyclone and anticyclone in the upper troposphere is out of phase with that in the middle and lower troposphere. This is confirmed by a series of numerical experiments. The horizontal gradient of the condensation heating also affects the configuration of the subtropical anticyclone. It is concluded that condensation heating is a key factor for the formation and location of the summer subtropical anticyclone in the EH. The latent heating released by the Asian monsoon rainfall contributes to the formation of the 200 hPa South Asian anticyclone on the western side of the heating center and the 500 hPa western Pacific subtropical anticyclone on the eastern side of the center. Such configurations are modified to some extent by surface sensible heating and orography. The circulation in mid-latitudes is also affected by the latent heating in the subtropical area through the propagation of Rossby waves. (orig.)

  6. Causes of early Holocene desertification in arid central Asia

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Liya [Lanzhou University, Key Laboratory of Western China' s Environmental System, Lanzhou, Gansu (China); University of Kiel, Institute of Geosciences, Kiel (Germany); Chen, Fahu [Lanzhou University, Key Laboratory of Western China' s Environmental System, Lanzhou, Gansu (China); Morrill, Carrie [University of Colorado, Cooperative Institute for Research in Environmental Sciences, Boulder, CO (United States); NOAA' s National Climatic Data Center, Paleoclimatology Branch, Boulder, CO (United States); Otto-Bliesner, Bette L.; Rosenbloom, Nan [National Center for Atmospheric Research, Climate and Global Dynamics Division, Boulder, CO (United States)

    2012-04-15

    Paleoclimate records of effective moisture (precipitation minus evaporation, or P-E) show a dry (low effective moisture) period in mid-latitude arid/semi-arid central Asia during the early Holocene (11,000-8,000 years ago) relative to the middle and late Holocene, in contrast to evidence for greater-than-present precipitation at the same time in the south and east Asian monsoonal areas. To investigate the spatial differences in climate response over mid-latitude central Asia and monsoonal Asia we conducted a series of simulations with the Community Climate System Model version 3 coupled climate model for the early, middle and late Holocene. The simulations test the climatic impact of all important forcings for the early Holocene, including changes in orbital parameters, the presence of the remnant Laurentide ice sheet and deglacial freshening of the North Atlantic. Model results clearly show the early Holocene patterns indicated by proxy records, including both the decreased effective moisture in arid central Asia, which occurs in the model primarily during the winter months, and the increase in summer monsoon precipitation in south and east Asia. The model results suggest that dry conditions in the early Holocene in central Asia are closely related to decreased water vapor advection due to reduced westerly wind speed and less evaporation upstream from the Mediterranean, Black, and Caspian Seas in boreal winter. As an extra forcing to the early Holocene climate system, the Laurentide ice sheet and meltwater fluxes have a substantial cooling effect over high latitudes, especially just over and downstream of the ice sheets, but contribute only to a small degree to the early Holocene aridity in central Asia. Instead, most of the effective moisture signal can be explained by orbital forcing decreasing the early Holocene latitudinal temperature gradient and wintertime surface temperature. We find little evidence for regional subsidence related to a stronger summer Asian

  7. Correlation and anti-correlation of the East Asian summer and winter monsoons during the last 21,000 years.

    Science.gov (United States)

    Wen, Xinyu; Liu, Zhengyu; Wang, Shaowu; Cheng, Jun; Zhu, Jiang

    2016-06-22

    Understanding the past significant changes of the East Asia Summer Monsoon (EASM) and Winter Monsoon (EAWM) is critical for improving the projections of future climate over East Asia. One key issue that has remained outstanding from the paleo-climatic records is whether the evolution of the EASM and EAWM are correlated. Here, using a set of long-term transient simulations of the climate evolution of the last 21,000 years, we show that the EASM and EAWM are positively correlated on the orbital timescale in response to the precessional forcing, but are anti-correlated on millennial timescales in response to North Atlantic melt water forcing. The relation between EASM and EAWM can differ dramatically for different timescales because of the different response mechanisms, highlighting the complex dynamics of the East Asian monsoon system and the challenges for future projection.

  8. 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

  9. Changes in the influence of the western Pacific subtropical high on Asian summer monsoon rainfall in the late 1990s

    Science.gov (United States)

    Huang, Yanyan; Wang, Bin; Li, Xiaofan; Wang, Huijun

    2017-10-01

    The Year-to-year variability of the western Pacific subtropical high (WPSH) is primarily controlled by atmosphere-ocean interaction (AOI) between the WPSH and the Indo-Pacific warm pool dipole SST anomalies (AOI mode) and the anomalous SST forcing from the equatorial central Pacific (the CP forcing mode). In this study, we show that the impacts of the WPSH variability on Asian summer monsoon rainfall have changed after the late 1990s. Before the late 1990s (the PRE epoch), the WPSH primarily affects East Asian summer monsoon (EASM) and had little influence on Indian summer monsoon (ISM), whereas after the late 1990s (the POST epoch), the WPSH has strengthened its linkage to the ISM while weakened its relationship with the EASM. This epochal change is associated with a change in the leading circulation mode in the Asia-WP region. During the PRE (POST) epoch the WPSH variation is mainly controlled by the AOI (CP forcing) that mainly affects EASM (ISM). The epochal change of the leading mode may be attributed to the change of the ENSO properties in late 1990s: the CP types of El Nino become a leading ENSO mode in the POST epoch. This work provides a new perspective for understanding decadal changes of the ENSO-monsoon relationship through subtropical dynamics.

  10. Do differences in future sulfate emission pathways matter for near-term climate? A case study for the Asian monsoon

    Science.gov (United States)

    Bartlett, Rachel E.; Bollasina, Massimo A.; Booth, Ben B. B.; Dunstone, Nick J.; Marenco, Franco; Messori, Gabriele; Bernie, Dan J.

    2018-03-01

    Anthropogenic aerosols could dominate over greenhouse gases in driving near-term hydroclimate change, especially in regions with high present-day aerosol loading such as Asia. Uncertainties in near-future aerosol emissions represent a potentially large, yet unexplored, source of ambiguity in climate projections for the coming decades. We investigated the near-term sensitivity of the Asian summer monsoon to aerosols by means of transient modelling experiments using HadGEM2-ES under two existing climate change mitigation scenarios selected to have similar greenhouse gas forcing, but to span a wide range of plausible global sulfur dioxide emissions. Increased sulfate aerosols, predominantly from East Asian sources, lead to large regional dimming through aerosol-radiation and aerosol-cloud interactions. This results in surface cooling and anomalous anticyclonic flow over land, while abating the western Pacific subtropical high. The East Asian monsoon circulation weakens and precipitation stagnates over Indochina, resembling the observed southern-flood-northern-drought pattern over China. Large-scale circulation adjustments drive suppression of the South Asian monsoon and a westward extension of the Maritime Continent convective region. Remote impacts across the Northern Hemisphere are also generated, including a northwestward shift of West African monsoon rainfall induced by the westward displacement of the Indian Ocean Walker cell, and temperature anomalies in northern midlatitudes linked to propagation of Rossby waves from East Asia. These results indicate that aerosol emissions are a key source of uncertainty in near-term projection of regional and global climate; a careful examination of the uncertainties associated with aerosol pathways in future climate assessments must be highly prioritised.

  11. How autumn Eurasian snow anomalies affect east asian winter monsoon: a numerical study

    Science.gov (United States)

    Luo, Xiao; Wang, Bin

    2018-03-01

    Previous studies have found that snow Eurasian anomalies in autumn can affect East Asian winter monsoon (EAWM), but the mechanisms remain controversial and not well understood. The possible mechanisms by which Eurasian autumn snow anomalies affect EAWM are investigated by numerical experiments with a coupled general circulation model and its atmospheric general circulation model component. The leading empirical orthogonal function mode of the October-November mean Eurasian snow cover is characterized by a uniform anomaly over a broad region of central Eurasia (40°N-65°N, 60°E-140°E). However, the results from a 150-ensemble mean simulation with snow depth anomaly specified in October and November reveal that the Mongolian Plateau and Vicinity (MPV, 40°-55°N, 80°-120°E) is the key region for autumn snow anomalies to affect EAWM. The excessive snow forcing can significantly enhance EAWM and the snowfall over the northwestern China and along the EAWM front zone stretching from the southeast China to Japan. The physical process involves a snow-monsoon feedback mechanism. The excessive autumn snow anomalies over the MPV region can persist into the following winter, and significantly enhance winter snow anomalies, which increase surface albedo, reduce incoming solar radiation and cool the boundary layer air, leading to an enhanced Mongolian High and a deepened East Asian trough. The latter, in turn, strengthen surface northwesterly winds, cooling East Asia and increasing snow accumulation over the MPV region and the southeastern China. The increased snow covers feedback to EAWM system through changing albedo, extending its influence southeastward. It is also found that the atmosphere-ocean coupling process can amplify the delayed influence of Eurasian snow mass anomaly on EAWM. The autumn surface albedo anomalies, however, do not have a lasting "memory" effect. Only if the albedo anomalies are artificially extended into December and January, will the EAWM be

  12. Quasi-biweekly oscillations of the South Asian monsoon and its co-evolution in the upper and lower troposphere

    Science.gov (United States)

    Ortega, Sebastián; Webster, Peter J.; Toma, Violeta; Chang, Hai-Ru

    2017-11-01

    The Upper Tropospheric Quasi-Biweekly Oscillation (UQBW) of the South Asian monsoon is studied using the potential vorticity field on the 370 K isentrope. The UQBW is shown to be a common occurrence in the upper troposphere during the monsoon, and its typical evolution is described. We suggest that the UQBW is a phenomenon of both the middle and tropical latitudes, owing its existence to the presence of the planetary-scale upper-tropospheric monsoon anticyclone. The UQBW is first identified as Rossby waves originating in the northern flank of the monsoon anticyclone. These Rossby waves break when reaching the Pacific Ocean, and their associated cyclonic PV anomalies move southward to the east of Asia and then westward across the Indian Ocean and Africa advected by the monsoon anticyclone. A strong correlation, or co-evolution, between the UQBW and quasi-biweekly oscillations in the lower troposphere (QBW) is also found. In particular, analysis of vertically-integrated horizontal moisture transport, 850 hPa geopotential, and outgoing long-wave radiation show that the UQBW is usually observed at the same time as, and co-evolves with, the lower tropospheric QBW over South Asia. We discuss the nature of the UQBW, and its possible physical link with the QBW.

  13. Mineralogical evidence of reduced East Asian summer monsoon rainfall on the Chinese loess plateau during the early Pleistocene interglacials

    Science.gov (United States)

    Meng, Xianqiang; Liu, Lianwen; Wang, Xingchen T.; Balsam, William; Chen, Jun; Ji, Junfeng

    2018-03-01

    The East Asian summer monsoon (EASM) is an important component of the global climate system. A better understanding of EASM rainfall variability in the past can help constrain climate models and better predict the response of EASM to ongoing global warming. The warm early Pleistocene, a potential analog of future climate, is an important period to study EASM dynamics. However, existing monsoon proxies for reconstruction of EASM rainfall during the early Pleistocene fail to disentangle monsoon rainfall changes from temperature variations, complicating the comparison of these monsoon records with climate models. Here, we present three 2.6 million-year-long EASM rainfall records from the Chinese Loess Plateau (CLP) based on carbonate dissolution, a novel proxy for rainfall intensity. These records show that the interglacial rainfall on the CLP was lower during the early Pleistocene and then gradually increased with global cooling during the middle and late Pleistocene. These results are contrary to previous suggestions that a warmer climate leads to higher monsoon rainfall on tectonic timescales. We propose that the lower interglacial EASM rainfall during the early Pleistocene was caused by reduced sea surface temperature gradients across the equatorial Pacific, providing a testable hypothesis for climate models.

  14. Role of cold surge and MJO on rainfall enhancement over indonesia during east asian winter monsoon

    Science.gov (United States)

    Fauzi, R. R.; Hidayat, R.

    2018-05-01

    Intensity of precipitation in Indonesia is influenced by convection and propagation of southwest wind. Objective of this study is to analyze the relationship between cold surge and the phenomenon of intra-seasonal climate variability Madden-julian Oscillation (MJO) for affecting precipitation in Indonesia. The data used for identifying the occurrence of cold surge are meridional wind speed data from the ERA-Interim. In addition, this study also used RMM1 and RMM2 index data from Bureau of Meteorology (BOM) for identifying MJO events. The results showed that during East Asian Winter Monsoon (EAWM) in 15 years (2000-2015), there are 362 cold surge events, 186 MJO events, and 113 cold surge events were associated with MJO events. The spread of cold surge can penetrate to equator and brought mass of water vapor that causes dominant precipitation in the Indonesian Sea up to 50-75% from climatological precipitation during EAWM. The MJO convection activity that moves from west to east also increases precipitation, but the distribution of rainfall is wider than cold surge, especially in Eastern Indonesia. MJO and cold surge simultaneously can increase rainfall over 100-150% in any Indonesian region that affected by MJO and cold surge events. The mechanism of heavy rainfall is illustrated by high activity of moisture transport in areas such as Java Sea and coastal areas of Indonesia.

  15. On the interannual variability of the Bonin high associated with the East Asian summer monsoon rain

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Kyung-Ja; Lee, Sun-Seon [Pusan National University, Department of Atmospheric Sciences, Busan (Korea)

    2007-01-15

    In order to assess how the Bonin high affects interannual variability of the East Asian summer monsoon (EASM) around the Korean Peninsula, the pulsation of the Bonin high and its association with teleconnection patterns was examined. The major factor for the interannual intensity of the EASM is the center position of the Bonin high rather than its center pressure. Up to 12 harmonics over time can be used to reconstruct the Bonin high, demonstrating its intraseasonal variation. The interannual variability of the Bonin high correlates with the Tibet high. This correlation is dominant for the EASM onset time, though not its retreat. The primary teleconnection pattern, reliant up on the interannual variability of the Bonin high, is the Western Pacific oscillation (WPO) in April. In relation to long-term variability, the correlation between the WPO and the Bonin high appears to contribute to the retreat stage of the EASM, which has itself increased since the mid-1970s. Furthermore, the WPO in May and the Tibet correlation has marked the onset rather than the retreat of the EASM since the 1970s. This highly correlated pattern since the mid-1970s may be the result of El Nino. (orig.)

  16. A tripolar pattern as an internal mode of the East Asian summer monsoon

    Science.gov (United States)

    Hirota, Nagio; Takahashi, Masaaki

    2012-11-01

    A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59 %, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area.

  17. A tripolar pattern as an internal mode of the East Asian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Hirota, Nagio; Takahashi, Masaaki [University of Tokyo, Atmosphere and Ocean Research Institute, Chiba (Japan)

    2012-11-15

    A tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59 %, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area. (orig.)

  18. 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...

  19. Inter-decadal change in potential predictability of the East Asian summer monsoon

    Science.gov (United States)

    Li, Jiao; Ding, Ruiqiang; Wu, Zhiwei; Zhong, Quanjia; Li, Baosheng; Li, Jianping

    2018-05-01

    The significant inter-decadal change in potential predictability of the East Asian summer monsoon (EASM) has been investigated using the signal-to-noise ratio method. The relatively low potential predictability appears from the early 1950s through the late 1970s and during the early 2000s, whereas the potential predictability is relatively high from the early 1980s through the late 1990s. The inter-decadal change in potential predictability of the EASM can be attributed mainly to variations in the external signal of the EASM. The latter is mostly caused by the El Niño-Southern Oscillation (ENSO) inter-decadal variability. As a major external signal of the EASM, the ENSO inter-decadal variability experiences phase transitions from negative to positive phases in the late 1970s, and to negative phases in the late 1990s. Additionally, ENSO is generally strong (weak) during a positive (negative) phase of the ENSO inter-decadal variability. The strong ENSO is expected to have a greater influence on the EASM, and vice versa. As a result, the potential predictability of the EASM tends to be high (low) during a positive (negative) phase of the ENSO inter-decadal variability. Furthermore, a suite of Pacific Pacemaker experiments suggests that the ENSO inter-decadal variability may be a key pacemaker of the inter-decadal change in potential predictability of the EASM.

  20. The response of East Asian Summer Monsoon to a Global Warming Scenario

    Science.gov (United States)

    Stan, C.; Jin, Y.

    2016-12-01

    The response of East Asian Summer Monsoon (EASM) to the abrupt quadrupling of atmospheric CO2 concentration is investigated using the Super-Parameterized Community Climate Model, version 4 (SP-CCSM4). The EASM precipitation and circulation intensify in response to global warming and these changes are related to the westward extension of the Western North Pacific Subtropical High (WNPSH). The displacement of WNPSH is caused by two mechanisms: i) the increase of sea surface temperature and ii) the reduction of latent heat flux over the South China Sea and adjacent western Pacific Ocean. The changes in the surface fluxes over the tropics induce a Gill-type anti-cyclonic circulation to the north of the heating anomaly and a Rossy wave train from the tropics into the midlatitude Pacific Ocean. The westerly anomalies on the northern side of the anticyclone strengthen the southwesterly flow on the western edge of WNPSH. This flow further affects the wind anomalies and moisture transport over East Asia.

  1. Asian monsoons and aridification response to Paleogene sea retreat and Neogene westerly shielding indicated by seasonality in Paratethys oysters

    Science.gov (United States)

    Bougeois, Laurie; Dupont-Nivet, Guillaume; de Rafélis, Marc; Tindall, Julia C.; Proust, Jean-Noël; Reichart, Gert-Jan; de Nooijer, Lennart J.; Guo, Zhaojie; Ormukov, Cholponbelk

    2018-03-01

    Asian climate patterns, characterised by highly seasonal monsoons and continentality, are thought to originate in the Eocene epoch (56 to 34 million years ago - Ma) in response to global climate, Tibetan Plateau uplift and the disappearance of the giant Proto-Paratethys sea formerly extending over Eurasia. The influence of this sea on Asian climate has hitherto not been constrained by proxy records despite being recognised as a major driver by climate models. We report here strongly seasonal records preserved in annual lamina of Eocene oysters from the Proto-Paratethys with sedimentological and numerical data showing that monsoons were not dampened by the sea and that aridification was modulated by westerly moisture sourced from the sea. Hot and arid summers despite the presence of the sea suggest a strong anticyclonic zone at Central Asian latitudes and an orographic effect from the emerging Tibetan Plateau. Westerly moisture precipitating during cold and wetter winters appear to have decreased in two steps. First in response to the late Eocene (34-37 Ma) sea retreat; second by the orogeny of the Tian Shan and Pamir ranges shielding the westerlies after 25 Ma. Paleogene sea retreat and Neogene westerly shielding thus provide two successive mechanisms forcing coeval Asian desertification and biotic crises.

  2. 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

  3. Simulation of the Onset of the Southeast Asian Monsoon during 1997 and 1998: The Impact of Surface Processes

    Science.gov (United States)

    Wang, Yansen; Tao, W.-K.; Lau, K.-M.; Wetzel, Peter J.

    2004-01-01

    The onset of the southeast Asian monsoon during 1997 and 1998 was simulated by coupling a mesoscale atmospheric model (MM5) and a detailed, land surface model, PLACE (the Parameterization for Land-Atmosphere-Cloud Exchange). The rainfall results from the simulations were compared with observed satellite data from the TRMM (Tropical Rainfall Measuring Mission) TMI (TRMM Microwave Imager) and GPCP (Global Precipitation Climatology Project). The control simulation with the PLACE land surface model and variable sea surface temperature captured the basic signatures of the monsoon onset processes and associated rainfall statistics. Sensitivity tests indicated that simulations were sigmficantly improved by including the PLACE land surface model. The mechanism by which the land surface processes affect the moisture transport and the convection during the onset of the southeast Asian monsoon were analyzed. The results indicated that land surface processes played an important role in modifying the low-level wind field over two major branches of the circulation: the southwest low-level flow over the Indo-china peninsula and the northern, cold frontal intrusion from southern China. The surface sensible and latent heat fluxes modified the low-level temperature distribution and gradient, and therefore the low-level wind due to the thermal wind effect. The more realistic forcing of the sensible and latent heat fluxes from the detailed, land surface model improved the low-level wind simulation apd associated moisture transport and convection.

  4. 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.

  5. On the recent warming in the subcloud layer entropy and vertically integrated moist static energy over South Asian Monsoon region.

    Science.gov (United States)

    Konduru, R.; Gupta, A.; Matsumoto, J.; Takahashi, H. G.

    2017-12-01

    In order to explain monsoon circulation, surface temperature gradients described as most traditional concept. However, it cannot explain certain important aspects of monsoon circulation. Later, convective quasi-equilibrium framework and vertically integrated atmospheric energy budget has become recognized theories to explain the monsoon circulation. In this article, same theories were analyzed and observed for the duration 1979-2010 over south Asian summer monsoon region. With the help of NCEP-R2, NOAA 20th Century, and Era-Interim reanalysis an important feature was noticed pertained to subcloud layer entropy and vertical moist static energy. In the last 32 years, subcloud layer entropy and vertically integrated moist static energy has shown significant seasonal warming all over the region with peak over the poleward flank of the cross-equatorial cell. The important reason related to the warming was found to be increase in surface enthalpy fluxes. Instead, other dynamical contributions pertained to the warming was also observed. Increase in positive anomalies of vertical advection of moist static energy over northern Bay of Bengal, Central India, Peninsular India, Eastern Arabian Sea, and Equatorial Indian Ocean was found to be an important dynamic factor contributing for warming of vertically integrated moist static energy. Along with it vertical moist stability has also supported the argument. Similar interpretations were perceived in the AMIP simulation of CCSM4 model. Further modeling experiments on this warming will be helpful to know the exact mechanism behind it.

  6. Orbital-scale nonlinear response of East Asian summer monsoon to its potential driving forces in the late Quaternary

    Science.gov (United States)

    Yi, Liang; Shi, Zhengguo; Tan, Liangcheng; Deng, Chenglong

    2018-03-01

    We conducted a statistical study to characterize the nonlinear response of the East Asian summer monsoon (EASM) to its potential forcing factors over the last 260 ka on orbital timescales. We find that both variation in solar insolation and global ice volume were responsible for the nonlinear forcing of orbital-scale monsoonal variations, accounting for 80% of the total variance. Specifically, EASM records with dominated precession variance exhibit a more sensitive response to changes in solar insolation during intervals of enhanced monsoon strength, but are less sensitive during intervals of reduced monsoon strength. In the case of global ice volume with 100-ka variance, this difference is not one of sensitivity but rather a difference in baseline conditions, such as the relative areas of land and sea which affected the land-sea thermal gradient. We therefore suggest that EASM records with dominated precession variance recorded the signal of a shift in the location of the Inter-tropical Convergence Zone, and the associated changes in the incidence of torrential rainfall; while for proxies with dominated 100-ka variance, it recorded changes in the land-sea thermal gradient via its effects on non-torrential precipitation.

  7. ENSO variability reflected in precipitation oxygen isotopes across the Asian Summer Monsoon region

    Science.gov (United States)

    Cai, Zhongyin; Tian, Lide; Bowen, Gabriel J.

    2017-10-01

    Oxygen isotope signals (δ18O) from paleo-archives are important proxies for past Asian Summer Monsoon (ASM) climate reconstruction. However, causes of interannual variation in the δ18O values of modern precipitation across the ASM region remain in argument. We report interannual δ18O variation in southern Tibetan Plateau precipitation based on long-term observations at Lhasa. These data, together with precipitation δ18O records from five Global Network of Isotopes in Precipitation (GNIP) stations and two ice core δ18O records, were used to define a regional metric of ASM precipitation δ18O (ASMOI). Back-trajectory analyses for rainy season precipitation events indicate that moisture sources vary little between years with relatively high and low δ18O values, a result that is consistent for the south (Lhasa), southeast (Bangkok), and east ASM regions (Hong Kong). In contrast, δ18O values at these three locations are significantly correlated with convection in the estimated source regions and along transport paths. These results suggest that upstream convection, rather than moisture source change, causes interannual variation in ASM precipitation δ18O values. Contrasting values of the ASMOI in El Niño and La Niña years reveal a positive isotope-El Niño Southern Oscillation (ENSO) response (e.g., high values corresponding to warm phases), which we interpret as a response to changes in regional convection. We show that the isotope-ENSO response is amplified at high elevation sites and during La Niña years. These findings should improve interpretations of paleo-δ18O data as a proxy for past ASM variation and provide new opportunities to use data from this region to study paleo-ENSO activity.

  8. Precipitation and ice core isotopes from the Asian Summer Monsoon region reflect coherent ENSO variability

    Science.gov (United States)

    Cai, Z.; Tian, L.; Bowen, G. J.

    2017-12-01

    Oxygen isotope signals (δ18O) from paleo-archives are important proxies for past Asian Summer Monsoon (ASM) climate reconstruction. However, causes of interannual variation in the δ18O values of modern precipitation across the ASM region remain in argument. We report interannual δ18O variation in southern Tibetan Plateau precipitation based on long-term observations at Lhasa. These data, together with precipitation δ18O records from five Global Network of Isotopes in Precipitation (GNIP) stations and two ice core δ18O records, were used to define a regional metric of ASM precipitation δ18O (ASMOI). Back-trajectory analyses for rainy season precipitation events indicate that moisture sources vary little between years with relatively high and low δ18O values, a result that is consistent for the south (Lhasa), southeast (Bangkok), and east ASM regions (Hong Kong). In contrast, δ18O values at these three locations are significantly correlated with convection in the estimated source regions and along transport paths. These results suggest that upstream convection, rather than moisture source change, causes interannual variation in ASM precipitation δ18O values. Contrasting values of the ASMOI in El Niño and La Niña years reveal a positive isotope-El Niño Southern Oscillation (ENSO) response (e.g., high values corresponding to warm phases), which we interpret as a response to changes in regional convection. We show that the isotope-ENSO response is amplified at high elevation sites and during La Niña years. These findings should improve interpretations of paleo-δ18O data as a proxy for past ASM variation and provide new opportunities to use data from this region to study paleo-ENSO activity.

  9. Terrestrial mollusk records from Chinese loess sequences and changes in the East Asian monsoonal environment

    Science.gov (United States)

    Wu, Naiqin; Li, Fengjiang; Rousseau, Denis-Didier

    2018-04-01

    The terrestrial mollusk fossils found in Chinese loess strata have been studied for over one hundred years. However, the greatest progress in these studies has been made only in the last two decades. In this paper, we review the advancements, advantages and limitations of terrestrial mollusk studies in Chinese loess deposits. Improvements in research methods and approaches have allowed the extraction of more detailed paleoenvironmental and paleoclimatic information from mollusk assemblages. The broadened research scope and content have yielded many new findings and results. The mollusk record has thus become one of the most important proxies in the paleoenvironmental and paleoclimatic reconstruction of loess-paleosol sequences in China. The greatest progress in the studies of terrestrial mollusks in Chinese loess sequences can be summarized as follows: (1) modern mollusk assemblages can be classified into four ecotypes, based on their temperature and humidity requirements, including eurytopic, semi-aridiphilous and sub-humidiphilous, cold-aridiphilous, and thermo-humidiphilous types; (2) Quaternary mollusk assemblages can be modified into the following three ecological types: glacial loess, interglacial paleosol, and interstadial weakly-developed paleosol assemblages; (3) mollusk records successfully reveal long-term climatic and environmental changes reflective of the history of East Asian monsoonal variations since the Late Cenozoic, and the succession of mollusk species also indicate short-term environmental changes such as millennial climate variability during Last Glacial Maximum and unstable climatic fluctuations during glacial and interglacial periods; and (4) more recently, new analytical approaches have offered increased research potential in areas such as paleotemperature reconstruction using the isotopic compositions of modern and fossil mollusk shells, combined with higher accuracy 14C dating of Quaternary loess deposits, which will greatly improve

  10. Performance of the Chicago Water Isotope Spectrometer in the UTLS during the Asian Monsoon

    Science.gov (United States)

    Gaeta, D. C.; Clouser, B.; Sarkozy, L.; Singer, C. E.; Moyer, E. J.

    2017-12-01

    The preferential condensation of water vapor isotopologues makes the isotopic composition of water vapor a useful tracer of the processes responsible for the distribution of water in the UTLS, but the UTLS also offers particular challenges for its measurement. We report here on the field performance of a new instrument designed for measurement of HDO and H2O in the UTLS region: the Chicago Water Isotope Spectrometer (Chi-WIS). Chi-WIS is a laser-based infrared absorption spectrometer at 2.65 μm that uses a high-reflectivity optical cavity to obtain 6 km of effective path length, allowing sensitive measurements of scarce molecules. During the 2017 StratoClim aircraft campaign in Kathmandu, Nepal, Chi-WIS flew aboard the M-55 Geophysica high-altitude research aircraft in a series of flights to probe the Asian Monsoon. Preliminary results show in-flight performance consistent with laboratory performance and the achievement of design targets necessary to reach UTLS science goals. Residual noise on spectra is stable across flights at 4-5x10-4 with 1 second averaging (i.e. absorption depth of .04-.05%); the instrument is robust in terms of alignment and shows no evidence of optical resonances. The resulting measurement precision is as expected from these characteristics. Because we use a relatively strong water line, the water vapor measurement is extremely precise: constant-altitude flight legs in the stratosphere at 4 ppm H2O show 1 s standard deviation 0.03 ppmv for 1 s averaging, and 0.08 ppbv for HDO with 10 s averaging. We show comparisons with other StratoClim instruments and examples of how these measurements resolve scientifically relevant atmospheric features.

  11. Decadal modulation of the ENSO-East Asian winter monsoon relationship by the Atlantic Multidecadal Oscillation

    Science.gov (United States)

    Geng, Xin; Zhang, Wenjun; Stuecker, Malte F.; Liu, Peng; Jin, Fei-Fei; Tan, Guirong

    2017-10-01

    This work investigates the decadal modulation of the El Niño-Southern Oscillation (ENSO)-East Asian winter monsoon (EAWM) relationship by the Atlantic Multidecadal Oscillation (AMO). A stable ENSO-EAWM relationship is found during the positive AMO phase but not during the negative phase. While the impact of El Niño events on the EAWM does not depend on the AMO phase, a different picture is observed for La Niña events. The La Niña boreal winter season coincides with a strengthened EAWM during a positive AMO phase and a weakened EAWM during a negative AMO phase. We suggest that the AMO's modulating effect mainly comprises two pathways that influence ENSO's impact on the EAWM. On one hand, when La Niña coincides with a positive AMO, the warm SST anomalies over the western North Pacific (WNP) are amplified both in intensity and spatial extent, which favors strengthened WNP cyclonic anomalies and an enhanced EAWM. During La Niña with a negative AMO, only very weak SST anomalies occur over the WNP with reduced WNP cyclonic anomalies that are confined to the tropics, thus having little effect on the EAWM. On the other hand, an eastward-propagating Rossby wavetrain across the mid-high latitudes of Eurasia during a warm AMO phase strengthens the Siberian high and thus leads to a strengthened EAWM, while during a cold AMO phase the Siberian high is weakened, leading to a reduced EAWM. In contrast, El Niño and its associated atmospheric responses are relatively strong and stable, independent of the AMO phase. These results carry important implications to the seasonal-to-interannual predictability associated with ENSO.

  12. East Asian winter monsoon forecasting schemes based on the NCEP's climate forecast system

    Science.gov (United States)

    Tian, Baoqiang; Fan, Ke; Yang, Hongqing

    2017-12-01

    The East Asian winter monsoon (EAWM) is the major climate system in the Northern Hemisphere during boreal winter. In this study, we developed two schemes to improve the forecasting skill of the interannual variability of the EAWM index (EAWMI) using the interannual increment prediction method, also known as the DY method. First, we found that version 2 of the NCEP's Climate Forecast System (CFSv2) showed higher skill in predicting the EAWMI in DY form than not. So, based on the advantage of the DY method, Scheme-I was obtained by adding the EAWMI DY predicted by CFSv2 to the observed EAWMI in the previous year. This scheme showed higher forecasting skill than CFSv2. Specifically, during 1983-2016, the temporal correlation coefficient between the Scheme-I-predicted and observed EAWMI was 0.47, exceeding the 99% significance level, with the root-mean-square error (RMSE) decreased by 12%. The autumn Arctic sea ice and North Pacific sea surface temperature (SST) are two important external forcing factors for the interannual variability of the EAWM. Therefore, a second (hybrid) prediction scheme, Scheme-II, was also developed. This scheme not only involved the EAWMI DY of CFSv2, but also the sea-ice concentration (SIC) observed the previous autumn in the Laptev and East Siberian seas and the temporal coefficients of the third mode of the North Pacific SST in DY form. We found that a negative SIC anomaly in the preceding autumn over the Laptev and the East Siberian seas could lead to a significant enhancement of the Aleutian low and East Asian westerly jet in the following winter. However, the intensity of the winter Siberian high was mainly affected by the third mode of the North Pacific autumn SST. Scheme-I and Scheme-II also showed higher predictive ability for the EAWMI in negative anomaly years compared to CFSv2. More importantly, the improvement in the prediction skill of the EAWMI by the new schemes, especially for Scheme-II, could enhance the forecasting skill of

  13. Assessing Covariation of Holocene Monsoon Intensity and Local Moisture Conditions in Eastern and Southwestern Amazon Basin Using Speleothem δ18O and 87Sr/86Sr Values

    Science.gov (United States)

    Ward, B. M.; Wong, C. I.; Novello, V. F.; Silva, L.; McGee, D.; Cheng, H.; Wang, X.; Edwards, R. L.; Cruz, F. W., Sr.; Santos, R. V.

    2017-12-01

    δ18O records from South America offer insight into past variability of the South American Monsoon System (SAMS). Potential, however, for understanding local moisture conditions is limited as precipitation δ18O is strongly influenced by regional climate dynamics. Here we create Holocene speleothem 87Sr/86Sr records at 200-yr resolution using TIMS methods in the Center for Isotope Geochemistry at Boston College to complement existing Holocene δ18O speleothem records and investigate local moisture conditions above caves located in the eastern Amazon Basin (PAR - 4°S, 55°W) and southwestern Brazil (JAR - 21°S, 56°W). Speleothem 87Sr/86Sr variability is interpreted to reflect differences in the extent of water-rock interaction due to differences in infiltration rates under wet and dry conditions. Drier conditions promote longer residence time, enhanced water-rock interaction, and greater evolution of dripwater 87Sr/86Sr values from an initial isotopic signature acquired from the soil to the signature of the cave host rock. PAR speleothem 87Sr/86Sr values range from 0.71024 to 0.71067 and are bracketed by soil (0.71710 to 0.70956) and bedrock (0.70852 to 0.70899) values. JAR speleothem 87Sr/86Sr values range from 0.71216 to 0.71539 and are greater than bedrock values (0.70825 to 0.71219), although some speleothem values exceed the single analysis conducted of the soil isotopic composition (0.71473). JAR speleothem 87Sr/86Sr values increase from the early to mid Holocene, consistent with increase in local moisture availability associated with intensification of the SAMS suggested by decreasing δ18O values in many records from the region. Speleothem 87Sr/86Sr values at JAR decrease from the mid to late Holocene, consistent with an increase in δ18O values at PAR that suggest a decline in monsoon intensity. 87Sr/86Sr variability at JAR, however, is positively correlated with the δ18O record. Preliminary 87Sr/86Sr results from PAR are only broadly consistent with

  14. Air-sea interaction and formation of the Asian summer monsoon onset vortex over the Bay of Bengal

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Guoxiong; Liu, Yimin; Mao, Jiangyu [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, P.O. Box 9804, Beijing (China); Guan, Yue [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, P.O. Box 9804, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Yan, Jinghui [China Meteorological Administration, National Climate Center, Beijing (China)

    2012-01-15

    In spring over the southern Bay of Bengal (BOB), a vortex commonly develops, followed by the Asian summer monsoon onset. An analysis of relevant data and a case study reveals that the BOB monsoon onset vortex is formed as a consequence of air-sea interaction over BOB, which is modulated by Tibetan Plateau forcing and the land-sea thermal contrast over the South Asian area during the spring season. Tibetan Plateau forcing in spring generates a prevailing cold northwesterly over India in the lower troposphere. Strong surface sensible heating is then released, forming a prominent surface cyclone with a strong southwesterly along the coastal ocean in northwestern BOB. This southwesterly induces a local offshore current and upwelling, resulting in cold sea surface temperatures (SSTs). The southwesterly, together with the near-equatorial westerly, also results in a surface anticyclone with descending air over most of BOB and a cyclone with ascending air over the southern part of BOB. In the eastern part of central BOB, where sky is clear, surface wind is weak, and ocean mixed layer is shallow, intense solar radiation and low energy loss due to weak surface latent and sensible heat fluxes act onto a thin ocean layer, resulting in the development of a unique BOB warm pool in spring. Near the surface, water vapor is transferred from northern BOB and other regions to southeastern BOB, where surface sensible heating is relatively high. The atmospheric available potential energy is generated and converted to kinetic energy, thereby resulting in vortex formation. The vortex then intensifies and moves northward, where SST is higher and surface sensible heating is stronger. Meanwhile, the zonal-mean kinetic energy is converted to eddy kinetic energy in the area east of the vortex, and the vortex turns eastward. Eventually, southwesterly sweeps over eastern BOB and merges with the subtropical westerly, leading to the onset of the Asian summer monsoon. (orig.)

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

    OpenAIRE

    T. Shinozaki; M. Uchida; K. Minoura; M. Kondo; S. F. Rella; Y. Shibata

    2011-01-01

    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 ...

  16. Interannual and Interdecadal Variations of the East Asian Summer Monsoon and Tropical Pacific SSTs. Part I: Roles of the Subtropical Ridge

    OpenAIRE

    Chang, C.-P.; Zhang, Yongsheng; Li, Tim

    2000-01-01

    The interannual relationship between the East Asian summer monsoon and the tropical Pacific SSTs is studied using rainfall data in the Yangtze River Valley and the NCEP reanalysis for 1951–96. The datasets are also partitioned into two periods, 1951–77 and 1978–96, to study the interdecadal variations of this relationship. A wet summer monsoon is preceded by a warm equatorial eastern Pacific in the previous winter and followed by a cold equatorial eastern Pacific in the following fa...

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

    Science.gov (United States)

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

    2011-12-01

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

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

    Science.gov (United States)

    Lim, Young-Kwon; Kim, Hae-Dong

    2014-01-01

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

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

    Directory of Open Access Journals (Sweden)

    Wang Li

    2012-11-01

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

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

    Science.gov (United States)

    Wang, Li; Schneider, Harald; Zhang, Xian-Chun; Xiang, Qiao-Ping

    2012-11-09

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

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

    Science.gov (United States)

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

    2015-08-01

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

  2. Reduced connection between the East Asian Summer Monsoon and Southern Hemisphere Circulation on interannual timescales under intense global warming

    Science.gov (United States)

    Yu, Tianlei; Guo, Pinwen; Cheng, Jun; Hu, Aixue; Lin, Pengfei; Yu, Yongqiang

    2018-03-01

    Previous studies show a close relationship between the East Asian Summer Monsoon (EASM) and Southern Hemisphere (SH) circulation on interannual timescales. In this study, we investigate whether this close relationship will change under intensive greenhouse-gas effect by analyzing simulations under two different climate background states: preindustrial era and Representative Concentration Pathway (RCP) 8.5 stabilization from the Community Climate System Model Version 4 (CCSM4). Results show a significantly reduced relationship under stabilized RCP8.5 climate state, such a less correlated EASM with the sea level pressure in the southern Indian Ocean and the SH branch of local Hadley Cell. Further analysis suggests that the collapse of the Atlantic Meridional Overturning Circulation (AMOC) due to this warming leads to a less vigorous northward meridional heat transport, a decreased intertropical temperature contrast in boreal summer, which produces a weaker cross-equatorial Hadley Cell in the monsoonal region and a reduced Interhemispheric Mass Exchange (IME). Since the monsoonal IME acts as a bridge connecting EASM and SH circulation, the reduced IME weakens this connection. By performing freshwater hosing experiment using the Flexible Global Ocean—Atmosphere—Land System model, Grid-point Version 2 (FGOALS-g2), we show a weakened relationship between the EASM and SH circulation as in CCSM4 when AMOC collapses. Our results suggest that a substantially weakened AMOC is the main driver leading to the EASM, which is less affected by SH circulation in the future warmer climate.

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

    Digital Repository Service at National Institute of Oceanography (India)

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

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

  4. A Centennial Episode of Weak East Asian Summer Monsoon in the Midst of the Medieval Warming

    Science.gov (United States)

    Jin, C.; Liu, J.; Wang, B.; Wang, Z.; Yan, M.

    2017-12-01

    Recent paleo-proxy evidences suggested that the East Asian summer monsoon (EASM) was generally strong (i.e., northern China wet and southern China dry) during the Medieval Warm Period (MWP, 9th to the mid-13th century), however, there was a centennial period (around 11th century) during which the EASM was weak. This study aims to explore the causes of this centennial weak EASM episode and in general, what controls the centennial variability of the EASM in the pre-industrial period of AD 501-1850. With the Community Earth System Model (CESM), a suit of control and forced experiments were conducted for the past 2000 years. The model run with all external forcings simulates a warm period of EA from AD 801-1250 with a generally increased summer mean precipitation over the northern EA; however, during the 11th century (roughly from AD 980 to AD 1100), the EASM is significantly weaker than the other periods during the MWP. We find that on the multi-decadal to centennial time scale, a strong EASM is associated with a La Nina-like Indo-Pacific warming and the opposite is also true. This sea surface temperature (SST) anomaly pattern represents the leading EOF mode of centennial SST variations, and it is primarily forced by the solar radiation and volcanic activity, whereas the land use/land cover and greenhouse gases as well as internal dynamics play a negligible role. During the MWP, the solar forcing plays a dominate role in supporting the SST variation as the volcanic activity is weak. The weakening of the EASM during the AD 980-1100 is attributed to the relatively low solar radiation, which leads to a prevailing El Nino-like Indo-Pacific cooling with strongest cooling occurring in the equatorial western Pacific. The suppressed convection over the equatorial western Pacific directly induces a Philippine Sea anticyclone anomaly, which increases southern China precipitation, meanwhile suppresses Philippine Sea precipitation, exciting a meridional teleconnection that

  5. Spring Arctic Oscillation-East Asian summer monsoon connection through circulation changes over the western North Pacific

    Energy Technology Data Exchange (ETDEWEB)

    Gong, Dao-Yi; Yang, Jing; Hu, Miao [Beijing Normal University, State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing (China); Kim, Seong-Joong [Korea Polar Research Institute, Incheon (Korea, Republic of); Gao, Yongqi [Nansen-Zhu International Research Center, IAP/CAS, Beijing (China); Nansen Environmental and Remote Sensing Center/Bjerknes Center for Climate Research, Bergen (Norway); Guo, Dong [Beijing Normal University, State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing (China); Nansen-Zhu International Research Center, IAP/CAS, Beijing (China); Zhou, Tianjun [State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), IAP/CAS, Beijing (China)

    2011-12-15

    In the present study the links between spring Arctic Oscillation (AO) and East Asian summer monsoon (EASM) was investigated with focus on the importance of the North Pacific atmospheric circulation and sea surface temperature (SST). To reduce the statistical uncertainty, we analyzed high-pass filtered data with the inter-annual time scales, and excluded the El Nino/Southern Oscillation signals in the climate fields using a linear fitting method. The significant relationship between spring AO and EASM are supported by the changes of multi-monsoon components, including monsoon indices, precipitation, and three-dimensional atmospheric circulations. Following a stronger positive spring AO, an anomalous cyclonic circulation at 850 hPa appears in southeastern Asia and the western North Pacific in summer, with the easterly anomalies spanning from the Pacific to Asian continent along 25 N-30 N and the westerly anomalies south of 15 N. At the same time, the summer western North Pacific subtropical high becomes weaker. Consistently, the positive precipitation anomalies are developed over a broad region south of 30 N stretching from southern China to the western Pacific and the negative precipitation anomalies appear in the lower valley of the Yangtze River and southern Japan. The anomalous cyclone in the western North Pacific persisting from spring to summer plays a key role in modulating EASM and monsoon precipitation by a positive air-sea feedback mechanism. During spring the AO-associated atmospheric circulation change produces warmer SSTs between 150 E-180 near the equator. The anomalous sensible and latent heating, in turn, intensifies the cyclone through a Gill-type response of the atmosphere. Through this positive feedback, the tropical atmosphere and SST patterns sustain their strength from spring to summer, that consequently modifies the monsoon trough and the western North Pacific subtropical high and eventually the EASM precipitation. Moreover, the SST response to

  6. Observed OH and HO2 concentrations in the upper troposphere inside and outside of Asian monsoon influenced air.

    Science.gov (United States)

    Marno, D. R.; Künstler, C.; Hens, K.; Tatum Ernest, C.; Broch, S.; Fuchs, H.; Martinez, M.; Bourtsoukidis, E.; Williams, J.; Holland, F.; Hofzumahaus, A.; Tomsche, L.; Fischer, H.; Klausner, T.; Schlager, H.; Eirenschmalz, L.; Stratmann, G.; Stock, P.; Ziereis, H.; Roiger, A.; Bohn, B.; Zahn, A.; Wahner, A.; Lelieveld, J.; Harder, H.

    2016-12-01

    The Asian monsoon convectively transports pollutants like volatile organic compounds (VOCs), NOx, and SO2 from the boundary layer over South Asia into the upper troposphere where they can potentially enter the stratosphere, or be dispersed globally. Therefore, it is crucial to understand the oxidizing capacity of this system regarding the rate of aerosol formation, and conversion of pollutants into compounds that have much shorter atmospheric lifetimes. OH plays a central role in this oxidation process. During the OMO-ASIA campaign in the summer of 2015, OH and HO2 were measured onboard the High Altitude Long-Range (HALO) Research Aircraft. Two laser-induced fluorescence instruments based on the fluorescence assay by gas expansion technique (LIF-FAGE) had been deployed, the AIR-LIF instrument from Forschungszentrum Jülich GmbH and the HORUS instrument from the Max Planck Institute for Chemistry, Mainz. To measure the chemical background of OH potentially produced inside the HORUS instrument from highly oxidized VOCs, atmospheric OH is scavenged by an Inlet Pre-injector (IPI) system. This was the first time an IPI system was implemented within an airborne LIF-FAGE instrument measuring OH and HO2. Throughout this campaign OH and HO2 were measured at 12 to 15km within the Asian monsoon anticyclone. These measurements have been contrasted by probing air outside the anticyclone in air masses influenced by North American emissions, and in very clean air masses originated from the southern hemisphere.

  7. Water vapor increase in the northern hemispheric lower stratosphere by the Asian monsoon anticyclone observed during TACTS campaign in 2012

    Science.gov (United States)

    Rolf, Christian; Vogel, Bärbel; Hoor, Peter; Günther, Gebhard; Krämer, Martina; Müller, Rolf; Müller, Stephan; Riese, Martin

    2017-04-01

    Water vapor plays a key role in determining the radiative balance in the upper troposphere and lower stratosphere (UTLS) and thus the climate of the Earth (Forster and Shine, 2002; Riese et al., 2012). Therefore a detailed knowledge about transport pathways and exchange processes between troposphere and stratosphere is required to understand the variability of water vapor in this region. The Asian monsoon anticyclone caused by deep convection over and India and east Asia is able to transport air masses from the troposphere into the nothern extra-tropical stratosphere (Müller et al. 2016, Vogel et al. 2016). These air masses contain pollution but also higher amounts of water vapor. An increase in water vapor of about 0.5 ppmv in the extra-tropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 by in-situ instrumentation above the European northern hemisphere during the HALO aircraft mission TACTS. Here, we investigated the origin of this water vapor increase with the help of the 3D Lagrangian chemistry transport model CLaMS (McKenna et al., 2002). We can assign an origin of the moist air masses in the Asian region (North and South India and East China) with the help of model origin tracers. Additionally, back trajectories of these air masses with enriched water vapor are used to differentiate between transport from the Asia monsoon anticyclone and the upwelling of moister air in the tropics particularly from the Pacific and Southeast Asia.

  8. Both temperature fluctuations and East Asian monsoons have driven plant diversification in the karst ecosystems from southern China.

    Science.gov (United States)

    Kong, Hanghui; Condamine, Fabien L; Harris, A J; Chen, Junlin; Pan, Bo; Möller, Michael; Hoang, Van Sam; Kang, Ming

    2017-11-01

    Karst ecosystems in southern China are species-rich and have high levels of endemism, yet little is known regarding the evolutionary processes responsible for the origin and diversification of karst biodiversity. The genus Primulina (Gesneriaceae) comprises ca. 170 species endemic to southern China with high levels of ecological (edaphic) specialization, providing an exceptional model to study the plant diversification in karsts. We used molecular data from nine chloroplast and 11 nuclear regions and macroevolutionary analyses to assess the origin and cause of species diversification due to palaeoenvironmental changes and edaphic specialization in Primulina. We found that speciation was positively associated with changes in past temperatures and East Asian monsoons through the evolutionary history of Primulina. Climatic change around the mid-Miocene triggered an early burst followed by a slowdown of diversification rate towards the present with the climate cooling. We detected different speciation rates among edaphic types, and transitions among soil types were infrequently and did not impact the overall speciation rate. Our findings suggest that both global temperature changes and East Asian monsoons have played crucial roles in floristic diversification within the karst ecosystems in southern China, such that speciation was higher when climate was warmer and wetter. This is the first study to directly demonstrate that past monsoon activity is positively correlated with speciation rate in East Asia. This case study could motivate further investigations to assess the impacts of past environmental changes on the origin and diversification of biodiversity in global karst ecosystems, most of which are under threat. © 2017 John Wiley & Sons Ltd.

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

    Directory of Open Access Journals (Sweden)

    A. Rauthe-Schöch

    2016-03-01

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

  10. Seasonal and Intraseasonal Variability of Mesoscale Convective Systems over the South Asian Monsoon Region

    Energy Technology Data Exchange (ETDEWEB)

    Virts, Katrina S.; Houze, Robert A.

    2016-12-01

    Seasonal and intraseasonal differences in mesoscale convective systems (MCSs) over South Asia are examined using A-Train satellites, a ground-based lightning network, and reanalysis fields. Pre-monsoon (April-May) MCSs occur primarily over Bangladesh and the eastern Bay of Bengal. During the monsoon (June-September), small MCSs occur over the Meghalaya Plateau and northeast Himalayan notch, while large and connected MCSs are most widespread over the Bay of Bengal. Monsoon MCSs produce less lightning and exhibit more extensive stratiform and anvil reflectivity structures in CloudSat observations than do pre-monsoon MCSs. During the monsoon season, Bay of Bengal and Meghalaya Plateau MCSs vary with the 30-60 day northward-propagating intraseasonal oscillation, while northeast Himalayan notch MCSs are associated with weak large-scale anomalies but locally enhanced CAPE. During intraseasonal active periods, a zone of enhanced large and connected MCSs, precipitation, and lightning extends from the northeastern Arabian Sea southeast over India and the Bay of Bengal, flanked by suppressed anomalies. Spatial variability is observed within this enhancement zone: lightning is most enhanced where MCSs are less enhanced, and vice versa. Reanalysis composites indicate that Bay of Bengal MCSs are associated with monsoon depressions, which are frequent during active monsoon periods, while Meghalaya Plateau MCSs are most frequent at the end of break periods, as anomalous southwesterly winds strengthen moist advection toward the terrain. Over both regions, MCSs exhibit more extensive stratiform and anvil regions and less lightning when the large-scale environment is moister, and vice versa.

  11. The Asian-Australian Monsoon and El Niño-Southern Oscillation in the NCAR Climate System Model*.

    Science.gov (United States)

    Meehl, Gerald A.; Arblaster, Julie M.

    1998-06-01

    Features associated with the Asian-Australian monsoon system and El Niño-Southern Oscillation (ENSO) are described in the National Center for Atmospheric Research (NCAR) global coupled Climate System Model (CSM). Simulation characteristics are compared with a version of the atmospheric component of the CSM, the NCAR CCM3, run with time-evolving SSTs from 1950 to 1994, and with observations. The CSM is shown to represent most major features of the monsoon system in terms of mean climatology, interannual variability, and connections to the tropical Pacific. This includes a representation of the Southern Oscillation links between strong Asian-Australian monsoons and associated negative SST anomalies in the eastern equatorial Pacific. The equatorial SST gradient across the Pacific in the CSM is shown to be similar to the observed with somewhat cooler mean SSTs across the entire Pacific by about 1°-2°C. The seasonal cycle of SSTs in the eastern equatorial Pacific has the characteristic signature seen in the observations of relatively warmer SSTs propagating westward in the first half of the year followed by the reestablishment of the cold tongue with relatively colder SSTs propagating westward in the second half of the year. Like other global coupled models, the propagation is similar to the observed but with the establishment of the relatively warmer water in the first half of the year occurring about 1-2 months later than observed. The seasonal cycle of precipitation in the tropical eastern Pacific is also similar to other global coupled models in that there is a tendency for a stronger-than-observed double ITCZ year round, particularly in northern spring, but with a well-reproduced annual maximum of ITCZ strength north of the equator in the second half of the year. Time series of area-averaged SSTs for the NINO3 region in the eastern equatorial Pacific show that the CSM is producing about 60% of the amplitude of the observed variability in that region, consistent

  12. Climatic differences and similarities between Indian and East Asian Monsoon regions of China over the last millennium: a perspective based mainly on stalagmite records.

    Directory of Open Access Journals (Sweden)

    Ming Tan

    2007-07-01

    Full Text Available Cave sediments, especially stalagmites, have been providing absolute dated climate records that can extend from the present to over 500,000 years ago. Based on the reconstructed temperature time series, a comprehensive overview of the climatic differences and similarities between the Indian and the East Asian Monsoon regions of China over the last millennium is presented. Evidence from accurately dated and high-resolution records including stalagmites, ice cores and tree rings show that there was a “Medieval Warm Period” (around 1000 to 1400 AD in north and east China where climate is dominated by the East Asian monsoon; whilst no such interval is evident in the records including stalagmites and ice cores from southwest China where climate is dominated by the Indian monsoon. However, both regions underwent a significant cooling during the Little Ice Age (around the mid 1500s to the 1800s. The result achieved here may allow a possibility of distinguishing the boundary between Indian monsoon and East Asian monsoon regions over the last millennium with increase of climate records, especially stalagmites that are mostly suitable for accurate U/Th dating and/or lamina counting.

  13. Water vapor increase in the lower stratosphere of the Northern Hemisphere due to the Asian monsoon anticyclone observed during the TACTS/ESMVal campaigns

    Science.gov (United States)

    Rolf, Christian; Vogel, Bärbel; Hoor, Peter; Afchine, Armin; Günther, Gebhard; Krämer, Martina; Müller, Rolf; Müller, Stefan; Spelten, Nicole; Riese, Martin

    2018-03-01

    The impact of air masses originating in Asia and influenced by the Asian monsoon anticyclone on the Northern Hemisphere stratosphere is investigated based on in situ measurements. A statistically significant increase in water vapor (H2O) of about 0.5 ppmv (11 %) and methane (CH4) of up to 20 ppbv (1.2 %) in the extratropical stratosphere above a potential temperature of 380 K was detected between August and September 2012 during the HALO aircraft missions Transport and Composition in the UT/LMS (TACTS) and Earth System Model Validation (ESMVal). We investigate the origin of the increased water vapor and methane using the three-dimensional Chemical Lagrangian Model of the Stratosphere (CLaMS). We assign the source of the moist air masses in the Asian region (northern and southern India, eastern China, southeast Asia, and the tropical Pacific) based on tracers of air mass origin used in CLaMS. The water vapor increase is correlated with an increase of the simulated Asian monsoon air mass contribution from about 10 % in August to about 20 % in September, which corresponds to a doubling of the influence from the Asian monsoon region. Additionally, back trajectories starting at the aircraft flight paths are used to differentiate transport from the Asian monsoon anticyclone and other source regions by calculating the Lagrangian cold point (LCP). The geographic location of the LCPs, which indicates the region where the set point of water vapor mixing ratio along these trajectories occurs, can be predominantly attributed to the Asian monsoon region.

  14. Coastal rainforest boundary dynamics during the late Holocene in monsoonal Australia: evidence from radiocarbon dates of abandoned nests of Orange-footed Scrubfowl

    Energy Technology Data Exchange (ETDEWEB)

    Bowman, D M.J.S.; Panton, W J [Parks and Wildlife Commission of the Northern Territory, Darwin, NT (Australia); Head, J [Australian National Univ, Canberra, ACT (Australia). Quaternary Dating Research Centre

    1998-12-31

    The late Holocene history of monsoon rainforest retreat was explored by radiocarbon dating abandoned Orange-footed Scrubfowl (Megapodius reinwardt Gaimard) nests in coastal savannas in the Northern Territory of Australia. Previous work has demonstrated that in savanna environments this rainforest bird can not build nor maintain the large heaps of soil and leaf litter that it uses for nests. Excavations of two earthen mounds in a savanna habitat verified that they were abandoned Scrubfowl nests, and not Aboriginal middens, given their lack of stratigraphy, non-sequential dating of charcoal in a vertical profile, and absence of archaeological material. Radiocarbon dates of material taken from the surface of abandoned nests were determined for three sites on the coast of the Northern Territory. These analyses revealed that for all three sites, rainforests have contracted within the last 1800 years BP. On Elcho Island an abandoned nest was found to contain the land snail Xanthomelon spheroidea Le Guillou (known to prefer rainforest habitat) with a modern radiocarbon age, suggesting recent contraction of rainforest. The results of this study further weaken the theory that Aboriginal burning was a major cause of rain forest fragmentation in the monsoon tropics, and possibly elsewhere in Australia.

  15. Coastal rainforest boundary dynamics during the late Holocene in monsoonal Australia: evidence from radiocarbon dates of abandoned nests of Orange-footed Scrubfowl

    Energy Technology Data Exchange (ETDEWEB)

    Bowman, D.M.J.S.; Panton, W.J. [Parks and Wildlife Commission of the Northern Territory, Darwin, NT (Australia); Head, J. [Australian National Univ, Canberra, ACT (Australia). Quaternary Dating Research Centre

    1997-12-31

    The late Holocene history of monsoon rainforest retreat was explored by radiocarbon dating abandoned Orange-footed Scrubfowl (Megapodius reinwardt Gaimard) nests in coastal savannas in the Northern Territory of Australia. Previous work has demonstrated that in savanna environments this rainforest bird can not build nor maintain the large heaps of soil and leaf litter that it uses for nests. Excavations of two earthen mounds in a savanna habitat verified that they were abandoned Scrubfowl nests, and not Aboriginal middens, given their lack of stratigraphy, non-sequential dating of charcoal in a vertical profile, and absence of archaeological material. Radiocarbon dates of material taken from the surface of abandoned nests were determined for three sites on the coast of the Northern Territory. These analyses revealed that for all three sites, rainforests have contracted within the last 1800 years BP. On Elcho Island an abandoned nest was found to contain the land snail Xanthomelon spheroidea Le Guillou (known to prefer rainforest habitat) with a modern radiocarbon age, suggesting recent contraction of rainforest. The results of this study further weaken the theory that Aboriginal burning was a major cause of rain forest fragmentation in the monsoon tropics, and possibly elsewhere in Australia.

  16. An updated astronomical time scale for the Plio-Pleistocene deposits from South China Sea and new insights into Asian monsoon evolution

    NARCIS (Netherlands)

    Ao, H.; Dekkers, M.J.; Qin, L.; Xiao, G.

    2011-01-01

    Here we present an improved astronomical timescale since 5 Ma as recorded in the ODP Site 1143 in the southern South China Sea, using a recently published Asian summer monsoon record (hematite to goethite content ratio, Hm/Gt) and a parallel benthic δ18O record. Correlation of the benthic δ18O

  17. Geochemical provenance of sediments from the northern East China Sea document a gradual migration of the Asian Monsoon belt over the past 400,000 years

    Science.gov (United States)

    Beny, François; Toucanne, Samuel; Skonieczny, Charlotte; Bayon, Germain; Ziegler, Martin

    2018-06-01

    The reconstruction of the long-term evolution of the East Asian Monsoon remains controversial. In this study, we aim to give a new outlook on this evolution by studying a 400 kyr long sediment record (U1429) from the northern East China Sea recovered during IODP Expedition 346. Neodymium isotopic ratios and rare earth element concentrations of different grain-size fractions reveal significant provenance changes of the sediments in the East China Sea between East Asian continental sources (mainly Yellow River) and sediment contributions from the Japanese Archipelago. These provenance changes are interpreted as the direct impact of sea level changes, due to the reorganization of East Asian river mouth locations and ocean circulation on the East China Sea shelf, and latitudinal shifts of the intertropical convergence zone (ITCZ) from the interior of Asia to the western North Pacific Ocean. Our data reveal the dominance of winter and summer monsoons during glacial and interglacial periods, respectively, except for glacial MIS 6d (∼150-180 ka) during which unexpected summer monsoon dominated conditions prevailed. Finally, our data suggests a possible strengthening of the interglacial summer monsoon rainfalls over the East Asian continent and Japan throughout the past 400 kyr, and between MIS 11 and MIS 5 in particular. This could result from a gradual northward migration of the ITCZ.

  18. Early-Holocene greening of the Afro-Asian dust belt changed sources of mineral dust in West Asia

    Science.gov (United States)

    Sharifi, Arash; Murphy, Lisa N.; Pourmand, Ali; Clement, Amy C.; Canuel, Elizabeth A.; Naderi Beni, Abdolmajid; Lahijani, Hamid A. K.; Delanghe, Doriane; Ahmady-Birgani, Hesam

    2018-01-01

    Production, transport and deposition of mineral dust have significant impacts on different components of the Earth systems through time and space. In modern times, dust plumes are associated with their source region(s) using satellite and land-based measurements and trajectory analysis of air masses through time. Reconstruction of past changes in the sources of mineral dust as related to changes in climate, however, must rely on the knowledge of the geochemical and mineralogical composition of modern and paleo-dust, and that of their potential source origins. In this contribution, we present a 13,000-yr record of variations in radiogenic Sr-Nd-Hf isotopes and Rare Earth Element (REE) anomalies as well as dust grain size from an ombrotrophic (rain fed) peat core in NW Iran as proxies of past changes in the sources of dust over the interior of West Asia. Our data shows that although the grain size of dust varies in a narrow range through the entire record, the geochemical fingerprint of dust particles deposited during the low-flux, early Holocene period (11,700-6,000 yr BP) is distinctly different from aerosols deposited during high dust flux periods of the Younger Dryas and the mid-late Holocene (6,000-present). Our findings indicate that the composition of mineral dust deposited at the study site changed as a function of prevailing atmospheric circulation regimes and land exposure throughout the last deglacial period and the Holocene. Simulations of atmospheric circulation over the region show the Northern Hemisphere Summer Westerly Jet was displaced poleward across the study area during the early Holocene when Northern Hemisphere insolation was higher due to the Earth's orbital configuration. This shift, coupled with lower dust emissions simulated based on greening of the Afro-Asian Dust Belt during the early Holocene likely led to potential sources in Central Asia dominating dust export to West Asia during this period. In contrast, the dominant western and

  19. Variation in the Asian monsoon intensity and dry-wet conditions since the Little Ice Age in central China revealed by an aragonite stalagmite

    Science.gov (United States)

    Yin, J.-J.; Yuan, D.-X.; Li, H.-C.; Cheng, H.; Li, T.-Y.; Edwards, R. L.; Lin, Y.-S.; Qin, J.-M.; Tang, W.; Zhao, Z.-Y.; Mii, H.-S.

    2014-10-01

    This paper focuses on the climate variability in central China since AD 1300, involving: (1) a well-dated, 1.5-year resolution stalagmite δ18O record from Lianhua Cave, central China (2) links of the δ18O record with regional dry-wet conditions, monsoon intensity, and temperature over eastern China (3) correlations among drought events in the Lianhua record, solar irradiation, and ENSO (El Niño-Southern Oscillation) variation. We present a highly precise, 230Th / U-dated, 1.5-year resolution δ18O record of an aragonite stalagmite (LHD1) collected from Lianhua Cave in the Wuling Mountain area of central China. The comparison of the δ18O record with the local instrumental record and historical documents indicates that (1) the stalagmite δ18O record reveals variations in the summer monsoon intensity and dry-wet conditions in the Wuling Mountain area. (2) A stronger East Asian summer monsoon (EASM) enhances the tropical monsoon trough controlled by ITCZ (Intertropical Convergence Zone), which produces higher spring quarter rainfall and isotopically light monsoonal moisture in the central China. (3) The summer quarter/spring quarter rainfall ratio in central China can be a potential indicator of the EASM strength: a lower ratio corresponds to stronger EASM and higher spring rainfall. The ratio changed from 1 after 1950, reflecting that the summer quarter rainfall of the study area became dominant under stronger influence of the Northwestern Pacific High. Eastern China temperatures varied with the solar activity, showing higher temperatures under stronger solar irradiation, which produced stronger summer monsoons. During Maunder, Dalton and 1900 sunspot minima, more severe drought events occurred, indicating a weakening of the summer monsoon when solar activity decreased on decadal timescales. On an interannual timescale, dry conditions in the study area prevailed under El Niño conditions, which is also supported by the spectrum analysis. Hence, our record

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

    Energy Technology Data Exchange (ETDEWEB)

    Qian, Yun; Flanner, M G; Leung, Lai-Yung R; Wang, Weiguo

    2011-03-02

    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 extensively at a speed faster than any other part of the world. In this study a series of experiments with a global climate model are designed to simulate black carbon (BC) and dust in snow and their radiative forcing and to assess the relative impacts of anthropogenic CO2 and carbonaceous particles in the atmosphere and snow, respectively, on the snowpack over the TP, as well as their subsequent impacts on the Asian monsoon climate and hydrological cycle. Results show a large BC content in snow over the TP, especially the southern slope, with concentration larger than 100 µk/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. 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 snowpack over the TP more than that induced by pre-industrial to present CO2 increase and carbonaceous particles in the atmosphere during spring. As a result, runoff increases during late winter and early spring but decreases during late spring and early summer (i.e. a trend toward earlier melt dates). The snowmelt efficacy, defined as the snowpack reduction per unit degree of warming induced by the forcing agent, is 1-4 times larger for BC-in-snow than CO2 increase during April-July, indicating that BC-in-snow more efficiently

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

    International Nuclear Information System (INIS)

    Zheng, Jiayu; Feng, Juan; Li, Jianping

    2014-01-01

    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. (letter)

  2. The Eocene climate of China, the early elevation of the Tibetan Plateau and the onset of the Asian Monsoon.

    Science.gov (United States)

    Wang, Qing; Spicer, Robert A; Yang, Jian; Wang, Yu-Fei; Li, Cheng-Sen

    2013-12-01

    Eocene palynological samples from 37 widely distributed sites across China were analysed using co-existence approach to determine trends in space and time for seven palaeoclimate variables: Mean annual temperature, mean annual precipitation, mean temperature of the warmest month, mean temperature of the coldest month, mean annual range of temperature, mean maximum monthly precipitation and mean minimum monthly precipitation. Present day distributions and observed climates within China of the nearest living relatives of the fossil forms were used to find the range of a given variable in which a maximum number of taxa can coexist. Isotherm and isohyet maps for the early, middle and late Eocene were constructed. These illustrate regional changing patterns in thermal and precipitational gradients that may be interpreted as the beginnings of the modern Asian Monsoon system, and suggest that the uplift of parts of the Tibetan Plateau appear to have taken place by the middle to late Eocene. © 2013 John Wiley & Sons Ltd.

  3. An upper tropospheric ‘ozone river’ from Africa to India during the 2008 Asian post-monsoon season

    Directory of Open Access Journals (Sweden)

    Flore Tocquer

    2015-03-01

    Full Text Available We have used ozone data from the Infrared Atmospheric Sounding Interferometer to follow an event of ozone-enriched air-masses in the upper troposphere from eastern Africa to northern India. The ozone transport (hereafter called ‘ozone river’ or O3R occurred during the Asian post-monsoon season in 2008 and was associated with Rossby wave propagation. The persistence of the O3R in a narrow channel was confirmed by MOZAIC airborne data over the northwestern Indian coast. The regions of origin of the O3R were identified by a transport analysis based on the Lagrangian model FLEXPART. The Lagrangian simulations combined with potential vorticity fields indicate that stratospheric intrusions are not likely to be the most important contributor to the observed O3 enhancements. A high-resolution Eulerian model, Meso-NH, with tagged tracers was used to discriminate between African biomass burning, lightnings and Indian anthropogenic pollution as potential sources of precursors for the O3R. Lightning NOx emissions, associated with convective clouds over Africa, were found to be the principal contributor to the ozone enhancement over the Indian Ocean taking advantage of a northeastward jet. This case study illustrates African lightning emissions as an important source for enhanced O3 in the upper troposphere over the Indian Ocean region during the post-monsoon season.

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

    Science.gov (United States)

    Annamalai, H.; Liu, P.

    2005-04-01

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

  5. Three-Dimensional modelling of the long-term variability of tracer transport in the Asian Summer Monsoon anticyclone

    Science.gov (United States)

    Taverna, Giorgio; Chipperfield, Martyn; Feng, Wuhu; Pope, Richard; Hossaini, Ryan; Forster, Piers

    2017-04-01

    The Asian Monsoon is an important region for the transport of gases from the troposphere to the stratosphere. Recent work by many groups has focused on quantifying processes which contribute to coupling in the upper troposphere - lower stratosphere (UTLS), including transport during the Asian Summer Monsoon (ASM). Troposphere-to-stratosphere transport in this region has been the focus of a number of recent campaigns, including the EU "StratoClim campaign" in Kalamata, Greece, 2016. Anthropogenic compounds such as CO Very Short-Lived Substances (VSLS), which destroy stratospheric ozone, and sulphur compounds, which maintain the stratospheric aerosol layer, are among the important species involved in large convective systems transport such as the ASM. An important question for halogenated VSLS is whether ASM-associated transport can take place on timescales which are short relative to their chemical lifetimes of days to months. This talk will present results of the TOMCAT/SLIMCAT off-line 3-D chemical transport model to investigate these issues using moderate-resolution simulations (2.8°x2.8°, 60 levels from surface to 60 km). The model is forced by ECMWF ERA-Interim reanalyses. A 1979-2016 simulation was run using artificial and idealized tracers with parametrized loss rates, lifetimes and emissions. These types of tracer have already been successfully used to study the transport of VSLS from surface through the TTL. The interannual variability of the transport inside and through the ASM anticyclone and related confinement will be shown and quantified. Comparisons will be made with in-situ and remote satellite data, where possible.

  6. Boreal summer sub-seasonal variability of the South Asian monsoon in the Met Office GloSea5 initialized coupled model

    Science.gov (United States)

    Jayakumar, A.; Turner, A. G.; Johnson, S. J.; Rajagopal, E. N.; Mohandas, Saji; Mitra, A. K.

    2017-09-01

    Boreal summer sub-seasonal variability in the Asian monsoon, otherwise known as the monsoon intra-seasonal oscillation (MISO), is one of the dominant modes of intraseasonal variability in the tropics, with large impacts on total monsoon rainfall and India's agricultural production. However, our understanding of the mechanisms involved in MISO is incomplete and its simulation in various numerical models is often flawed. In this study, we focus on the objective evaluation of the fidelity of MISO simulation in the Met Office Global Seasonal forecast system version 5 (GloSea5), an initialized coupled model. We analyze a series of nine-member hindcasts from GloSea5 over 1996-2009 during the peak monsoon period (July-August) over the South-Asian monsoon domain focusing on aspects of the time-mean background state and air-sea interaction processes pertinent to MISO. Dominant modes during this period are evident in power spectrum analysis, but propagation and evolution characteristics of the MISO are not realistic. We find that simulated air-sea interactions in the central Indian Ocean are not supportive of MISO initiation in that region, likely a result of the low surface wind variance there. As a consequence, the expected near-quadrature phase relationship between SST and convection is not represented properly over the central equatorial Indian Ocean, and northward propagation from the equator is poorly simulated. This may reinforce the equatorial rainfall mean state bias in GloSea5.

  7. Impact of atmospheric circulation types on southwest Asian dust and Indian summer monsoon rainfall

    Science.gov (United States)

    Kaskaoutis, D. G.; Houssos, E. E.; Solmon, F.; Legrand, M.; Rashki, A.; Dumka, U. C.; Francois, P.; Gautam, R.; Singh, R. P.

    2018-03-01

    This study examines the meteorological feedback on dust aerosols and rainfall over the Arabian Sea and India during the summer monsoon using satellite data, re-analysis and a regional climate model. Based on days with excess aerosol loading over the central Ganges basin during May - September, two distinct atmospheric circulation types (weather clusters) are identified, which are associated with different dust-aerosol and rainfall distributions over south Asia, highlighting the role of meteorology on dust emissions and monsoon rainfall. Each cluster is characterized by different patterns of mean sea level pressure (MSLP), geopotential height at 700 hPa (Z700) and wind fields at 1000 hPa and at 700 hPa, thus modulating changes in dust-aerosol loading over the Arabian Sea. One cluster is associated with deepening of the Indian/Pakistan thermal low leading to (i) increased cyclonicity and thermal convection over northwestern India and Arabian Peninsula, (ii) intensification of the southwest monsoon off the Horn of Africa, iii) increase in dust emissions from Rub-Al-Khali and Somalian deserts, (iv) excess dust accumulation over the Arabian Sea and, (v) strengthening of the convergence of humid air masses and larger precipitation over Indian landmass compared to the other cluster. The RegCM4.4 model simulations for dust-aerosol and precipitation distributions support the meteorological fields and satellite observations, while the precipitation over India is positively correlated with the aerosol loading over the Arabian Sea on daily basis for both weather clusters. This study highlights the key role of meteorology and atmospheric dynamics on dust life cycle and rainfall over the monsoon-influenced south Asia.

  8. An oxygen isotope record from Lake Xiarinur in Inner Mongolia since the last deglaciation and its implication for tropical monsoon change

    Science.gov (United States)

    Sun, Qing; Chu, Guoqiang; Xie, Manman; Zhu, Qingzeng; Su, Youliang; Wang, Xisheng

    2018-04-01

    We present a high-resolution oxygen isotope record from authigenic carbonate (δ18Ocarb) from Lake Xiarinur (Inner Mongolia) since the last deglaciation. The lake is located at the modern northern limit of the monsoon, and is therefore sensitive to the extension of the East Asian summer monsoon. Based on calibration against the instrumental record, the δ18Ocar variation has been interpreted as changes in atmospheric circulation pattern on decadal time scales. On longer time scales, the δ18Ocarb in lake sediments could be mainly regulated by the relative contribution of nearby (remote) water-vapor sources associated with subtropical (tropical) monsoon through changes in the distance from sources to the site of precipitation. Increased remote water vapors from tropical monsoon would lead to lighter isotope value in our study site. Through time the δ18Ocarb record in Lake Xiarinur indicate a notable weak tropical monsoon during the Younger Dryas, a gradual increasing monsoon from the early Holocene and weakening monsoon after the middle Holocene. Oxygen isotope records from lakes and stalagmite in the Asian monsoon region across different localities show a general similar temporal pattern since the last deglaciation, and highlight a fundamental role of the tropical monsoon.

  9. Difference in the influence of Indo-Pacific Ocean heat content on South Asian Summer Monsoon intensity before and after 1976/1977

    Science.gov (United States)

    Dong, Yujie; Feng, Junqiao; Hu, Dunxin

    2016-05-01

    Monthly ocean temperature from ORAS4 datasets and atmospheric data from NCEP/NCAR Reanalysis I/II were used to analyze the relationship between the intensity of the South Asian summer monsoon (SASM) and upper ocean heat content (HC) in the tropical Indo-Pacific Ocean. The monsoon was differentiated into a Southwest Asian Summer Monsoon (SWASM) (2.5°-20°N, 35°-70°E) and Southeast Asian Summer Monsoon (SEASM) (2.5°-20°N, 70°-110°E). Results show that before the 1976/77 climate shift, the SWASM was strongly related to HC in the southern Indian Ocean and tropical Pacific Ocean. The southern Indian Ocean affected SWASM by altering the pressure gradient between southern Africa and the northern Indian Ocean and by enhancing the Somali cross-equatorial flow. The tropical Pacific impacted the SWASM through the remote forcing of ENSO. After the 1976/77 shift, there was a close relationship between equatorial central Pacific HC and the SEASM. However, before that shift, their relationship was weak.

  10. Water Isotope Proxy-Proxy and Proxy-Model Convergence for Late Pleistocene East Asian Monsoon Rainfall Reconstructions

    Science.gov (United States)

    Clemens, S. C.; Holbourn, A.; Kubota, Y.; Lee, K. E.; Liu, Z.; Chen, G.

    2017-12-01

    Confidence in reconstruction of East Asian paleomonsoon rainfall using precipitation isotope proxies is a matter of considerable debate, largely due to the lack of correlation between precipitation amount and isotopic composition in the present climate. We present four new, very highly resolved records spanning the past 300,000 years ( 200 year sample spacing) from IODP Site U1429 in the East China Sea. We demonstrate that all the orbital- and millennial-scale variance in the onshore Yangtze River Valley speleothem δ18O record1 is also embedded in the offshore Site U1429 seawater δ18O record (derived from the planktonic foraminifer Globigerinoides ruber and sea surface temperature reconstructions). Signal replication in these two independent terrestrial and marine archives, both controlled by the same monsoon system, uniquely identifies δ18O of precipitation as the primary driver of the precession-band variance in both records. This proxy-proxy convergence also eliminates a wide array of other drivers that have been called upon as potential contaminants to the precipitation δ18O signal recorded by these proxies. We compare East Asian precipitation isotope proxy records to precipitation amount from a CCSM3 transient climate model simulation of the past 300,000 years using realistic insolation, ice volume, greenhouse gasses, and sea level boundary conditions. This model-proxy comparison suggests that both Yangtze River Valley precipitation isotope proxies (seawater and speleothem δ18O) track changes in summer-monsoon rainfall amount at orbital time scales, as do precipitation isotope records from the Pearl River Valley2 (leaf wax δ2H) and Borneo3 (speleothem δ18O). Notably, these proxy records all have significantly different spectral structure indicating strongly regional rainfall patterns that are also consistent with model results. Transient, isotope-enabled model simulations will be necessary to more thoroughly evaluate these promising results, and to

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

    Science.gov (United States)

    Prasanna, V.

    2016-06-01

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

  12. Reconstruction of Last Glacial to early Holocene monsoon variability from relict lake sediments of the Higher Central Himalaya, Uttrakhand, India

    DEFF Research Database (Denmark)

    Juyal, N.; Pant, R.K.; Basavaiah, N.

    2009-01-01

    .5 ka and after14.5–13 ka. The Last Glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of Holocene condition. Additionally, centennial scale fluctuations between 16.5 ka and 12.7 ka in the magnetic and geochemical data are seen. A close...... instability in higher northern latitudes. However, centennial scale abrupt changes are attributed to the result of albedo changes on the Himalaya and Tibetan plateau....

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

    Science.gov (United States)

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

    2012-04-01

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

  14. Factors controlling the interannual variation of 30-60-day boreal summer intraseasonal oscillation over the Asian summer monsoon region

    Science.gov (United States)

    Li, Jianying; Mao, Jiangyu

    2018-04-01

    The 30-60-day boreal summer intraseasonal oscillation (BSISO) is a dominant variability of the Asian summer monsoon (ASM), with its intensity being quantified by intraseasonal standard deviations based on OLR data. The spatial and interannual variations of the BSISO intensity are identified via empirical orthogonal function (EOF) analysis for the period 1981-2014. The first EOF mode (EOF1) shows a spatially coherent enhancement or suppression of BSISO activity over the entire ASM region, and the interannual variability of this mode is related to the sea surface temperature anomaly (SSTA) contrast between the central-eastern North Pacific (CNP) and tropical Indian Ocean. In contrast, the second mode (EOF2) exhibits a seesaw pattern between the southeastern equatorial Indian Ocean (EIO) and equatorial western Pacific (EWP), with the interannual fluctuation linked with developing ENSO events. During strong years of EOF1 mode, the enhanced low-level westerlies induced by the summer-mean SSTA contrast between the warmer CNP and cooler tropical Indian Ocean tend to form a wetter moisture background over the eastern EIO, which interacts with intraseasonal low-level convergent flows, leading to stronger equatorial eastward propagation. The intensified easterly shear favors stronger northward propagation over the South Asian and Eastern Asian/Western North Pacific sectors, respectively. Opposite situation is for weak years. For interannual variations of EOF2 mode, the seesaw patterns with enhanced BSISO activity over the southeastern EIO while weakened activity over the EWP mostly occur in the La Niña developing summers, but inverse patterns appear in the El Niño developing summers.

  15. 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.)

  16. Variation in the Asian monsoon intensity and dry-wet condition since the Little Ice Age in central China revealed by an aragonite stalagmite

    Science.gov (United States)

    Yin, J.-J.; Yuan, D.-X.; Li, H.-C.; Cheng, H.; Li, T.-Y.; Edwards, R. L.; Lin, Y.-S.; Qin, J.-M.; Tang, W.; Zhao, Z.-Y.; Mii, H.-S.

    2014-04-01

    Highlight: this paper focuses on the climate variability in central China since 1300 AD, involving: 1. A well-dated, 1.5 year resolution stalagmite δ18O record from Lianhua Cave, central China; 2. Links of the δ18O record with regional dry-wet condition, monsoon intensity, and temperature over eastern China; 3. Correlations among drought events in the Lianhua record, solar irradiation, and ENSO index. We present a highly precisely 230Th/U dated, 1.5 year resolution δ18O record of an aragonite stalagmite (LHD1) collected from Lianhua Cave in Wuling mountain area of central China. The comparison of the δ18O record with the local instrumental record and historical documents exhibits at least 15 drought events in the Wuling mountain and adjacent areas during the Little Ice Age, in which some of them were corresponding to megadrought events in the broad Asian monsoonal region of China. Thus, the stalagmite δ18O record reveals variations in the summer monsoon precipitation and dry-wet condition in Wuling mountain area. The eastern China temperature varied with the solar activity, showing higher temperature under stronger solar irradiation which produces stronger summer monsoon. During Maunder, Dalton and 1900 sunspot minima, more severe drought events occurred, indicating weakening of the summer monsoon when solar activity decreased on decadal time scales. On interannual time scale, dry conditions in the studying area were prevailing under El Niño condition, which is also supported by the spectrum analysis. Hence, our record illustrates the linkage of Asian summer monsoon precipitation to solar irradiation and ENSO: wetter condition under stronger summer monsoon during warm periods and vice versa; During cold periods, the Walker circulation will shift toward central Pacific under El Niño condition, resulting further weakening of Asian summer monsoon. However, the δ18O of LHD1 record is positively correlated with temperature after ~1940 AD which is opposite to the

  17. Disentangling sea-surface temperature and anthropogenic aerosol influences on recent trends in South Asian monsoon rainfall

    Science.gov (United States)

    Patil, Nitin; Venkataraman, Chandra; Muduchuru, Kaushik; Ghosh, Subimal; Mondal, Arpita

    2018-05-01

    Recent studies point to combined effects of changes in regional land-use, anthropogenic aerosol forcing and sea surface temperature (SST) gradient on declining trends in the South Asian monsoon (SAM). This study attempted disentangling the effects produced by changes in SST gradient from those by aerosol levels in an atmospheric general circulation model. Two pairs of transient ensemble simulations were made, for a 40-year period from 1971 to 2010, with evolving versus climatological SSTs and with anthropogenic aerosol emissions fixed at 1971 versus 2010, in each case with evolution of the other forcing element, as well as GHGs. Evolving SST was linked to a widespread feedback on increased surface temperature, reduced land-sea thermal contrast and a weakened Hadley circulation, with weakening of cross-equatorial transport of moisture transport towards South Asia. Increases in anthropogenic aerosol levels (1971 versus 2010), led to an intensification of drying in the peninsular Indian region, through several regional pathways. Aerosol forcing induced north-south asymmetries in temperature and sea-level pressure response, and a cyclonic circulation in the Bay of Bengal, leading to an easterly flow, which opposes the monsoon flow, suppressing moisture transport over peninsular India. Further, aerosol induced decreases in convection, vertically integrated moisture flux convergence, evaporation flux and cloud fraction, in the peninsular region, were spatially congruent with reduced convective and stratiform rainfall. Overall, evolution of SST acted through a weakening of cross-equatorial moisture flow, while increases in aerosol levels acted through suppression of Arabian Sea moisture transport, as well as, of convection and vertical moisture transport, to influence the suppression of SAM rainfall.

  18. A strengthened East Asian Summer Monsoon during Pliocene warmth: Evidence from 'red clay' sediments at Pianguan, northern China

    Science.gov (United States)

    Yang, Shiling; Ding, Zhongli; Feng, Shaohua; Jiang, Wenying; Huang, Xiaofang; Guo, Licheng

    2018-04-01

    The Pliocene epoch (5.3-2.6 Ma) is the most recent geological interval in which atmospheric CO2 levels were similar to those of the present day (∼400 ppmv). This epoch is therefore considered to be the best ancient analog for predicting a future anthropogenic greenhouse world. In order to determine the response of the East Asian Summer Monsoon (EASM) rainbelt during Pliocene warmth, a 71.9 m-thick aeolian 'red clay' sequence at Pianguan was investigated. Rock magnetic experiments suggest that magnetite of pseudo-single domain size is the dominant remanence carrier in the 'red clay' sequence. Magnetostratigraphic data, constrained by lithostratigraphy, show that the polarity zones of the 'red clay' section correlate with those between subchrons C2An.2r and C3An.2n of the geomagnetic polarity time scale (GPTS), yielding an age range of 6.9-2.9 Ma. The 'red clay' deposits exhibit enhanced weathering intensity over two time intervals, namely 5.23-4.3 Ma and 3.7-2.9 Ma, as evidenced by their well-developed pedogenic characteristics, as well as their high free to total Fe2O3 ratios and high redness (a∗) values, which in turn indicate an increased summer monsoon intensity during most of the Pliocene. Furthermore, the pedogenic characteristics of the well-weathered Pliocene soils were compared with those of paleosol unit S5 (one of the best-developed soil units found in Pleistocene loess) from the Yulin, Luochuan and Lantian sections, which constitute a north-south transect across the Chinese Loess Plateau (CLP). The Pliocene soils at Pianguan show a pedogenic development similar to the S5 (∼0.5 Ma) at Luochuan in the central Plateau, which is located some 3.7° latitude south of Pianguan, but this development is much stronger than that observed at Yulin in the north, and weaker than that seen at Lantian in the south. This may imply a more northerly penetration (∼400 km) of the monsoon rainbelt during Pliocene warmth compared with the Pleistocene interglacial

  19. Deficiencies and possibilities for long-lead coupled climate prediction of the Western North Pacific-East Asian summer monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sun-Seon; Ha, Kyung-Ja [Pusan National University, Division of Earth Environmental System, Busan (Korea, Republic of); Lee, June-Yi; Wang, Bin [University of Hawaii, Department of Meteorology and International Pacific Research Center, Honolulu, HI (United States); Schemm, Jae Kyung E. [Climate Prediction Center/NCEP, Camp Springs, MD (United States)

    2011-03-15

    Long-lead prediction of waxing and waning of the Western North Pacific (WNP)-East Asian (EA) summer monsoon (WNP-EASM) precipitation is a major challenge in seasonal time-scale climate prediction. In this study, deficiencies and potential for predicting the WNP-EASM precipitation and circulation one or two seasons ahead were examined using retrospective forecast data for the 26-year period of 1981-2006 from two operational couple models which are the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS) and the Bureau of Meteorology Research Center (BMRC) Predictive Ocean-Atmosphere Model for Australia (POAMA). While both coupled models have difficulty in predicting summer mean precipitation anomalies over the region of interest, even for a 0-month lead forecast, they are capable of predicting zonal wind anomalies at 850 hPa several months ahead and, consequently, satisfactorily predict summer monsoon circulation indices for the EA region (EASMI) and for the WNP region (WNPSMI). It should be noted that the two models' multi-model ensemble (MME) reaches 0.40 of the correlation skill for the EASMI with a January initial condition and 0.75 for the WNPSMI with a February initial condition. Further analysis indicates that prediction reliability of the EASMI is related not only to the preceding El Nino and Southern Oscillation (ENSO) but also to simultaneous local SST variability. On other hand, better prediction of the WNPSMI is accompanied by a more realistic simulation of lead-lag relationship between the index and ENSO. It should also be noted that current coupled models have difficulty in capturing the interannual variability component of the WNP-EASM system which is not correlated with typical ENSO variability. To improve the long-lead seasonal prediction of the WNP-EASM precipitation, a statistical postprocessing was developed based on the multiple linear regression method. The method utilizes the MME prediction of the EASMI and

  20. 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

    2017-10-01

    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.

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

    Science.gov (United States)

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

    2015-12-01

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

  2. South Asian summer monsoon variability during the last ~54 kyrs inferred from surface water salinity and river run off proxies

    Digital Repository Service at National Institute of Oceanography (India)

    Gebregiorgis, D.; Hathorne, E.C.; Sijinkumar, A.V.; Nath, B.N.; Nurnberg, D.; Frank, M.

    ; Viswambharan and Mohanakumar, 2014). Decadal to centennial scale variations in monsoon precipitation have been in phase with temperature fluctuations in northern high latitudes(Fleitmann et al., 2003). Monsoonal changes on millennial to longer time...

  3. Daily modes of South Asian summer monsoon variability in the NCEP climate forecast system

    Energy Technology Data Exchange (ETDEWEB)

    Achuthavarier, Deepthi; Krishnamurthy, V. [George Mason University, Department of Atmospheric, Oceanic and Earth Sciences, Fairfax, VA (United States); Institute of Global Environment and Society, Center for Ocean-Land-Atmosphere Studies, Calverton, MD (United States)

    2011-05-15

    The leading modes of daily variability of the Indian summer monsoon in the climate forecast system (CFS), a coupled general circulation model, of the National Centers for Environmental Predictions (NCEP) are examined. The space-time structures of the daily modes are obtained by applying multi-channel singular spectrum analysis (MSSA) on the daily anomalies of rainfall. Relations of the daily modes to intraseasonal and interannual variability of the monsoon are investigated. The CFS has three intraseasonal oscillations with periods around 106, 57 and 30 days with a combined variance of 7%. The 106-day mode has spatial structure and propagation features similar to the northeastward propagating 45-day mode in the observations except for its longer period. The 57-day mode, despite being in the same time scale as of the observations has poor eastward propagation. The 30-day mode is northwestward propagating and is similar to its observational counterpart. The 106-day mode is specific to the model and should not be mistaken for a new scale of variability in observations. The dominant interannual signal is related to El Nino-Southern Oscillation (ENSO), and, unlike in the observations, has maximum variance in the eastern equatorial Indian Ocean. Although the Indian Ocean Dipole (IOD) mode was not obtained as a separate mode in the rainfall, the ENSO signal has good correlations with the dipole variability, which, therefore, indicates the dominance of ENSO in the model. The interannual variability is largely determined by the ENSO signal over the regions where it has maximum variance. The interannual variability of the intraseasonal oscillations is smaller in comparison. (orig.)

  4. 8000-year monsoonal record from Himalaya revealing reinforcement of tropical and global climate systems since mid-Holocene.

    Science.gov (United States)

    Srivastava, Pradeep; Agnihotri, Rajesh; Sharma, Deepti; Meena, Narendra; Sundriyal, Y P; Saxena, Anju; Bhushan, Ravi; Sawlani, R; Banerji, Upasana S; Sharma, C; Bisht, P; Rana, N; Jayangondaperumal, R

    2017-11-06

    We provide the first continuous Indian Summer Monsoon (ISM) climate record for the higher Himalayas (Kedarnath, India) by analyzing a 14 C-dated peat sequence covering the last ~8000 years, with ~50 years temporal resolution. The ISM variability inferred using various proxies reveal striking similarity with the Greenland ice core (GISP2) temperature record and rapid denitrification changes recorded in the sediments off Peru. The Kedarnath record provides compelling evidence for a reorganization of the global climate system taking place at ~5.5 ka BP possibly after sea level stabilization and the advent of inter-annual climate variability governed by the modern ENSO phenomenon. The ISM record also captures warm-wet and cold-dry conditions during the Medieval Climate Anomaly and Little Ice Age, respectively.

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

    Directory of Open Access Journals (Sweden)

    Chaozhu Li

    2015-01-01

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

  6. The role of the Asian winter monsoon in the rapid propagation of abrupt climate changes during the last deglaciation

    Science.gov (United States)

    Chu, Guoqiang; Sun, Qing; Zhu, Qingzeng; Shan, Yabing; Shang, Wenyu; Ling, Yuan; Su, Youliang; Xie, Manman; Wang, Xishen; Liu, Jiaqi

    2017-12-01

    High-resolution temperature records spanning the last deglaciation from low latitudes are scarce; however, they are important for understanding the rapid propagation of abrupt climate events throughout the Northern Hemisphere and the tropics. Here, we present a branched GDGTs-based temperature reconstruction from the sediments of Maar Lake Huguangyan in tropical China. The record reveals that the mean temperature during the Oldest Dryas was 17.8 °C, which was followed by a two-step increase of 2-3 °C to the Bølling-Allerød, a decrease to 19.8 °C during the Younger Dryas, and a rapid warming at the onset of the Holocene. The Oldest Dryas was about 2 °C warmer than the Younger Dryas. The reconstructed temperature was weighted towards the wintertime since the lake is monomictic and the mixing process in winter supplies nutrients from the lake bottom to the entire water column, greatly promoting biological productivity. In addition, the winter-biased temperature changes observed in the study are more distinctive than the summer-biased temperature records from extra-tropical regions of East Asia. This implies that the temperature decreases during abrupt climatic events were mainly a winter phenomenon. Within the limits of the dating uncertainties, the broadly similar pattern of winter-weighted temperature change observed in both tropical Lake Huguangyan and in Greenland ice cores indicates the occurrence of tightly-coupled interactions between high latitude ice sheets and land areas in the tropics. We suggest that the winter monsoon (especially cold surges) could play an important role in the rapid transmission of the temperature signal from the Arctic to the tropics.

  7. Did opening of the South China Sea impact development of the Asian Monsoon? Results from Oligocene microfossils, IODP Site U1435, northern South China Sea

    Science.gov (United States)

    Kulhanek, Denise K.; Su, Xin; Li, Qianyu; Gregory, Mitch; Warny, Sophie; Clift, Peter D.

    2016-04-01

    Development of the Asian Monsoon is linked to uplift of the Himalayas and Tibetan Plateau in the Cenozoic, with good evidence for a strong monsoon system by the late Oligocene to early Miocene (e.g., Guo et al., 2002; Clift et al., 2008). However, Licht et al. (2014) suggested the presence of an Asian Monsoon in the late Eocene. Recent scientific ocean drilling in the Indian Ocean and surrounding marginal seas gives us the opportunity to test this hypothesis with newly recovered Paleogene sediment cores. International Ocean Discovery Program Expedition 349 to the South China Sea recovered a 30 m section of primarily lower Oligocene nannofossil-rich claystone at Site U1435, located near the northern continent/ocean boundary. A thick sandstone unit devoid of typical marine microfossils underlies the marine claystone. The sandstone is interpreted as a deltaic or restricted marine deposit and is dated to the Eocene based on the presence of organic-walled palynomorphs, suggesting that a hiatus of several million years likely separates the sandstone below from the Oligocene marine claystone. This hiatus is interpreted as the breakup unconformity, with paleodepths in the South China Sea increasing during the Oligocene. Thus, this claystone should record if opening of the South China Sea during the early Oligocene influenced development of the Asian Monsoon. Combined calcareous nannofossil and planktonic foraminifer biostratigraphy indicates that the 30 m section is primarily early Oligocene in age (~33.5-30 Ma) and was deposited on the middle slope, with paleodepths >500 m. Stable oxygen isotopes from planktonic foraminifers become heavier up-hole, suggestive of cooling/deepening in the region, whereas carbon isotopes record variable conditions with no distinct maxima or minima. Calcareous nannoplankton primarily live in the upper 50 m of the ocean and are sensitive to sea-surface temperature and nutrient conditions, thus making them useful recorders of paleoceanographic

  8. Quantitative Holocene climatic reconstructions for the lower Yangtze region of China

    Science.gov (United States)

    Li, Jianyong; Dodson, John; Yan, Hong; Wang, Weiming; Innes, James B.; Zong, Yongqiang; Zhang, Xiaojian; Xu, Qinghai; Ni, Jian; Lu, Fengyan

    2018-02-01

    Quantitative proxy-based and high-resolution palaeoclimatic datasets are scarce for the lower reaches of the Yangtze River (LYR) basin. This region is in a transitional vegetation zone which is climatologically sensitive; and as a birthplace for prehistorical civilization in China, it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region. We present a pollen-based and regionally-averaged Holocene climatic twin-dataset for mean total annual precipitation (PANN) and mean annual temperature (TANN) covering the last 10,000 years for the LYR region. This is based on the technique of weighted averaging-partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences. The pollen-based reconstructions generally show an early Holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions, and a declining pattern of both PANN and TANN values in the middle to late Holocene. The main driving forces behind the Holocene climatic changes in the LYR area are likely summer solar insolation associated with tropical or subtropical macro-scale climatic circulations such as the Intertropical Convergence Zone (ITCZ), Western Pacific Subtropical High (WPSH), and El Niño/Southern Oscillation (ENSO). Regional multi-proxy comparisons indicate that the Holocene variations in precipitation and temperature for the LYR region display an in-phase relationship with other related proxy records from southern monsoonal China and the Indian monsoon-influenced regions, but are inconsistent with the Holocene moisture or temperature records from northern monsoonal China and the westerly-dominated region in northwestern China. Overall, our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the Holocene Asian monsoonal evolution and for anticipating its future dynamics in eastern Asia.

  9. Impact of Land Use Land Cover Change on East Asian monsoon

    Science.gov (United States)

    Chilukoti, N.; Xue, Y.; Liu, Y.; Lee, J.

    2017-12-01

    Humans modify the Earth's terrestrial surface on a continental scale by removing natural vegetation for crops/grazing. The current rates, extents and intensities of Land Use and Land Cover Change (LULCC) are greater than ever in history. The earlier studies of Land-atmosphere interactions used specified land surface conditions without interannual variations. In this study using NCEP CFSv2 coupled with Simplified Simple Biosphere (SSiB) model, biogeophysical impacts of LULCC on climate variability, anomaly, and changes are investigated by using the LULCC map from the Hurtt et al. (2006, 2011), which covered 66 years from 1950-2015 with annual variability. We combined the changes in crop and pasture fractions and consider as LULCC. A methodology had been developed to convert the Hurtt LULCC change map with 1° resolution to the GCM grid points. Since the GCM has only one dominant type, when the crop and pasture frction value at one point was larger than the critical value, that grid was assigned as degraded. Comprehensive evaluation was conducted to ensure the consistence of the trend of land degradation in the Hurtt's map and in the GCM LULCC map. In the degraded point, trees were changed to low vegetation or grasses, and low vegetation to bare soil. A set of surface parameters such as leaf area index, vegetation height, roughness length, and soil parameters, associated with vegetation are changed to show the degradation effects. We integrated the model with the potential vegetation map and the map with LULCC from 1950 to 2015, and the results indicate the LULCC causes precipitation reduction globally, with the strongest signals over monsoon regions. For instance, the degradation in Mexico, West Africa, south and East Asia and South America produced significant precipitation anomalies, some of which are consistent with observed regional precipitation anomalies. Meanwhile, it has also found that the LULCC enhances the surface warming during the summer in monsoon

  10. Mid-Miocene C4 expansion on the Chinese Loess Plateau under an enhanced Asian summer monsoon

    Science.gov (United States)

    Dong, Jibao; Liu, Zhonghui; An, Zhisheng; Liu, Weiguo; Zhou, Weijian; Qiang, Xiaoke; Lu, Fengyan

    2018-06-01

    Atmospheric CO2 starvation, aridity, fire and warm season precipitation have all been proposed as major contributors to C4 plant expansion during the Late Miocene. However, the driving factors responsible for the distribution of C4 plants in the early and mid-Miocene still remain enigmatic. Here we report pedogenic carbon and oxygen isotope data (δ13Cpedo, δ18Opedo), along with magnetic susceptibility (MS) results, from the Zhuang Lang drilling core on the Chinese Loess Plateau (CLP). Elevated δ13Cpedo values (>-5‰) signal a prominent C4 expansion and substantially increased δ18Opedo and MS values indicate enhanced Asian summer monsoon (ASM) precipitation. Both of these conditions are observed during the Mid-Miocene Climatic Optimum (MMCO), 14.5-17 million years ago. The marked increase in C4 plants, associated with warm temperatures and increased precipitation, strongly suggests the control of an enhanced ASM on C4 expansion on the CLP during the MMCO. This finding contrasts with the late-Miocene C4 expansion associated with cooling and drying conditions observed in low latitudes and argues for regionally specific control of C4 plant distribution/expansion.

  11. Forced decadal changes in the East Asian summer monsoon: the roles of greenhouse gases and anthropogenic aerosols

    Science.gov (United States)

    Tian, Fangxing; Dong, Buwen; Robson, Jon; Sutton, Rowan

    2018-02-01

    Since the mid-1990s precipitation trends over eastern China display a dipole pattern, characterized by positive anomalies in the south and negative anomalies in the north, named as the Southern-Flood-Northern-Drought (SFND) pattern. This work investigates the drivers of decadal changes of the East Asian summer monsoon (EASM), and the dynamical mechanisms involved, by using a coupled climate model (specifically an atmospheric general circulation model coupled to an ocean mixed layer model) forced by changes in (1) anthropogenic greenhouse gases (GHG), (2) anthropogenic aerosol (AA) and (3) the combined effects of both GHG and AA (All Forcing) between two periods across the mid-1990s. The model experiment forced by changes in All Forcing shows a dipole pattern of response in precipitation over China that is similar to the observed SFND pattern across the mid-1990s, which suggests that anthropogenic forcing changes played an important role in the observed decadal changes. Furthermore, the experiments with separate forcings indicate that GHG and AA forcing dominate different parts of the SFND pattern. In particular, changes in GHG increase precipitation over southern China, whilst changes in AA dominate in the drought conditions over northern China. Increases in GHG cause increased moisture transport convergence over eastern China, which leads to increased precipitation. The AA forcing changes weaken the EASM, which lead to divergent wind anomalies over northern China and reduced precipitation.

  12. 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.

  13. Modeling biomass burning over the South, South East and East Asian Monsoon regions using a new, satellite constrained approach

    Science.gov (United States)

    Lan, R.; Cohen, J. B.

    2017-12-01

    Biomass burning over the South, South East and East Asian Monsoon regions, is a crucial contributor to the total local aerosol loading. Furthermore, the impact of the ITCZ, and Monsoonal circulation patterns coupled with complex topography also have a prominent impact on the aerosol loading throughout much of the Northern Hemisphere. However, at the present time, biomass burning emissions are highly underestimated over this region, in part due to under-reported emissions in space and time, and in part due to an incomplete understanding of the physics and chemistry of the aerosols emitted in fires and formed downwind from them. Hence, a better understanding of the four-dimensional source distribution, plume rise, and in-situ processing, in particular in regions with significant quantities of urban air pollutants, is essential to advance our knowledge of this problem. This work uses a new modeling methodology based on the simultaneous constraints of measured AOD and some trace gasses over the region. The results of the 4-D constrained emissions are further expanded upon using different fire plume height rise and in-situ processing assumptions. Comparisons between the results and additional ground-based and remotely sensed measurements, including AERONET, CALIOP, and NOAA and other ground networks are included. The end results reveal a trio of insights into the nonlinear processes most-important to understand the impacts of biomass burning in this part of the world. Model-measurement comparisons are found to be consistent during the typical burning years of 2016. First, the model performs better under the new emissions representations, than it does using any of the standard hotspot based approaches currently employed by the community. Second, long range transport and mixing between the boundary layer and free troposphere contribute to the spatial-temporal variations. Third, we indicate some source regions that are new, either because of increased urbanization, or of

  14. Delivery of halogenated very short-lived substances from the west Indian Ocean to the stratosphere during the Asian summer monsoon

    Directory of Open Access Journals (Sweden)

    A. Fiehn

    2017-06-01

    Full Text Available Halogenated very short-lived substances (VSLSs are naturally produced in the ocean and emitted to the atmosphere. When transported to the stratosphere, these compounds can have a significant influence on the ozone layer and climate. During a research cruise on RV Sonne in the subtropical and tropical west Indian Ocean in July and August 2014, we measured the VSLSs, methyl iodide (CH3I and for the first time bromoform (CHBr3 and dibromomethane (CH2Br2, in surface seawater and the marine atmosphere to derive their emission strengths. Using the Lagrangian particle dispersion model FLEXPART with ERA-Interim meteorological fields, we calculated the direct contribution of observed VSLS emissions to the stratospheric halogen burden during the Asian summer monsoon. Furthermore, we compare the in situ calculations with the interannual variability of transport from a larger area of the west Indian Ocean surface to the stratosphere for July 2000–2015. We found that the west Indian Ocean is a strong source for CHBr3 (910 pmol m−2 h−1, very strong source for CH2Br2 (930 pmol m−2 h−1, and an average source for CH3I (460 pmol m−2 h−1. The atmospheric transport from the tropical west Indian Ocean surface to the stratosphere experiences two main pathways. On very short timescales, especially relevant for the shortest-lived compound CH3I (3.5 days lifetime, convection above the Indian Ocean lifts oceanic air masses and VSLSs towards the tropopause. On a longer timescale, the Asian summer monsoon circulation transports oceanic VSLSs towards India and the Bay of Bengal, where they are lifted with the monsoon convection and reach stratospheric levels in the southeastern part of the Asian monsoon anticyclone. This transport pathway is more important for the longer-lived brominated compounds (17 and 150 days lifetime for CHBr3 and CH2Br2. The entrainment of CHBr3 and CH3I from the west Indian Ocean to the stratosphere during the

  15. Interdecadal variations of East Asian summer monsoon northward propagation and influences on summer precipitation over East China

    Science.gov (United States)

    Jiang, Z.; Yang, S.; He, J.; Li, J.; Liang, J.

    2008-08-01

    The interdecadal variation of northward propagation of the East Asian Summer Monsoon (EASM) and summer precipitation in East China have been investigated using daily surface rainfall from a dense rain gauge network in China for 1957 2001, National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, European Center for Medium-Range Weather Forecast (ECMWF) reanalysis, and Global Mean Sea Level Pressure Dataset (GMSLP2) from Climatic Research Unit (CRU). Results in general show a consistent agreement on the interdecadal variability of EASM northward propagations. However, it appears that the interdecadal variation is stronger in NCEP than in ECMWF and CRU datasets. A newly defined normalized precipitation index (NPI), a 5-day running mean rainfall normalized with its standard deviation, clearly depicts the characteristics of summer rainbelt activities in East China in terms of jumps and durations during its northward propagations. The EASM northward propagation shows a prominent interdecadal variation. EASM before late 1970s had a rapid northward advance and a northern edge beyond its normal position. As a result, more summer rainfall occurred for the North China rainy season, Huaihe-River Mei-Yu, and South China Mei-Yu. In contrast, EASM after late 1970s had a slow northward movement and a northern edge located south of its normal position. Less summer precipitation occurred in East China except in Yangtze River basin. The EASM northernmost position (ENP), northernmost intensity (ENI), and EASM have a complex and good relationship at interdecadal timescales. They have significant influences on interdecadal variation of the large-scale precipitation anomalies in East China.

  16. Evaluation of a multi-scale WRF-CAM5 simulation during the 2010 East Asian Summer Monsoon

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, Patrick; Zhang, Yang; Wang, Kai; Leung, Ruby; Fan, Jiwen; Zheng, Bo; Zhang, Qiang; He, Kebin

    2017-11-01

    The Weather Research and Forecasting model with Chemistry (WRF-Chem) with the physics package of the Community Atmosphere Model Version 5 (CAM5) has been applied at multiple scales over Eastern China (EC) and the Yangtze River Delta (YRD) to evaluate how increased horizontal resolution with physics designed for a coarser resolution climate model impacts aerosols and clouds, and the resulting precipitation characteristics and performance during the 2010 East Asian Summer Monsoon (EASM). Despite large underpredictions in surface aerosol concentrations and aerosol optical depth, there is good spatial agreement with surface observations of chemical predictions, and increasing spatial resolution tends to improve performance. Model bias and normalized root mean square values for precipitation predictions are relatively small, but there are significant differences when comparing modeled and observed probability density functions for precipitation in EC and YRD. Increasing model horizontal resolution tends to reduce model bias and error for precipitation predictions. The surface and column aerosol loading is maximized between about 32N and 42N in early to mid-May during the 2010 EASM, and then shifts north while decreasing in magnitude during July and August. Changing model resolution moderately changes the spatiotemporal relationships between aerosols, cloud properties, and precipitation during the EASM, thus demonstrating the importance of model grid resolution in simulating EASM circulation and rainfall patterns over EC and the YRD. Results from this work demonstrate the capability and limitations in the aerosol, cloud, and precipitation representation of WRF-CAM5 for regional-scale applications down to relatively fine horizontal resolutions. Further WRF-CAM5 model development and application in this area is needed.

  17. The multidecadal variations of the interannual relationship between the East Asian summer monsoon and ENSO in a coupled model

    Science.gov (United States)

    Liu, Bo; Huang, Gang; Hu, Kaiming; Wu, Renguang; Gong, Hainan; Wang, Pengfei; Zhao, Guijie

    2017-10-01

    This study investigates the multidecadal variations of the interannual relationship between the East Asian summer monsoon (EASM) and El Niño-Southern Oscillation (ENSO) in 1000-year simulation of a coupled climate model. The interannual relationship between ENSO and EASM has experienced pronounced changes throughout the 1000-year simulation. During the periods with significant ENSO-EASM relationship, the ENSO-related circulation anomalies show a Pacific-Japan (PJ)-like pattern with significant wave-activity flux propagating from the tropics to the north in lower troposphere and from the mid-latitudes to the south in upper troposphere. The resultant ENSO-related precipitation anomalies are more (less) than normal over the East Asia (western North Pacific) in the decaying summers of El Niño events. In contrast, the circulation and precipitation anomalies are weak over East Asia-western North Pacific during the periods with weak ENSO-EASM relationship. Based on the energy conversion analysis, the related anomalies achieve barotropic and baroclinic energy from the mean flow during the periods with strong ENSO-EASM relationship. On the contrary, during the low-correlation periods, the energy conversion is too weak to form the link between the tropics and mid-latitudes. The main reason for the multidecadal variations of ENSO-EASM relationship is the amplitude discrepancy of SST anomalies over the Indo-western Pacific Ocean which, in turn, leads to the intensity difference of the western North Pacific anomalous anticyclone (WPAC) and related climate anomalies.

  18. Projections of East Asian summer monsoon change at global warming of 1.5 and 2 °C

    Science.gov (United States)

    Liu, Jiawei; Xu, Haiming; Deng, Jiechun

    2018-04-01

    Much research is needed regarding the two long-term warming targets of the 2015 Paris Agreement, i.e., 1.5 and 2 °C above pre-industrial levels, especially from a regional perspective. The East Asian summer monsoon (EASM) intensity change and associated precipitation change under both warming targets are explored in this study. The multimodel ensemble mean projections by 19 CMIP5 models show small increases in EASM intensity and general increases in summer precipitation at 1.5 and 2 °C warming, but with large multimodel standard deviations. Thus, a novel multimodel ensemble pattern regression (EPR) method is applied to give more reliable projections based on the concept of emergent constraints, which is effective at tightening the range of multimodel diversity and harmonize the changes of different variables over the EASM region. Future changes projected by using the EPR method suggest decreased precipitation over the Meiyu belt and increased precipitation over the high latitudes of East Asia and Central China, together with a considerable weakening of EASM intensity. Furthermore, reduced precipitation appears over 30-40° N of East Asia in June and over the Meiyu belt in July, with enhanced precipitation at their north and south sides. These changes in early summer are attributed to a southeastward retreat of the western North Pacific subtropical high (WNPSH) and a southward shift of the East Asian subtropical jet (EASJ), which weaken the moisture transport via southerly wind at low levels and alter vertical motions over the EASM region. In August, precipitation would increase over the high latitudes of East Asia with more moisture from the wetter area over the ocean in the east and decrease over Japan with westward extension of WNPSH. These monthly precipitation changes would finally contribute to a tripolar pattern of EASM precipitation change at 1.5 and 2 °C warming. Corrected EASM intensity exhibits a slight difference between 1.5 and 2 °C, but a

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

    NARCIS (Netherlands)

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

    2012-01-01

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

  20. One year of continuous measurements of soil CH4 and CO2 fluxes in a Japanese cypress forest: Temporal and spatial variations associated with Asian monsoon rainfall

    OpenAIRE

    Sakabe, Ayaka; Kosugi, Yoshiko; Takahashi, Kenshi; Itoh, Masayuki; Kanazawa, Akito; Makita, Naoki; Ataka, Mioko

    2015-01-01

    We examined the effects of Asian monsoon rainfall on CH[4] absorption of water-unsaturated forest soil. We conducted a 1 year continuous measurement of soil CH[4] and CO[2] fluxes with automated chamber systems in three plots with different soil characteristics and water content to investigate how temporal variations in CH[4] fluxes vary with the soil environment. CH[4] absorption was reduced by the “Baiu” summer rainfall event and peaked during the subsequent hot, dry period. Although CH[4] ...

  1. Potential impact of carbonaceous aerosol on the upper troposphere and lower stratosphere (UTLS) and precipitation during Asian summer monsoon in a global model simulation

    KAUST Repository

    Fadnavis, Suvarna

    2017-09-28

    Recent satellite observations show efficient vertical transport of Asian pollutants from the surface to the upper-level anticyclone by deep monsoon convection. In this paper, we examine the transport of carbonaceous aerosols, including black carbon (BC) and organic carbon (OC), into the monsoon anticyclone using of ECHAM6-HAM, a global aerosol climate model. Further, we investigate impacts of enhanced (doubled) carbonaceous aerosol emissions on the upper troposphere and lower stratosphere (UTLS), underneath monsoon circulation and precipitation from sensitivity simulations. The model simulation shows that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay of Bengal, southern slopes of the Himalayas and the South China Sea. Doubling of emissions of both BC and OC aerosols over Southeast Asia (10° S–50° N, 65–155° E) shows that lofted aerosols produce significant warming (0.6–1 K) over the Tibetan Plateau (TP) near 400–200 hPa and instability in the middle/upper troposphere. These aerosols enhance radiative heating rates (0.02–0.03 K day−1) near the tropopause. The enhanced carbonaceous aerosols alter aerosol radiative forcing (RF) at the surface by −4.74 ± 1.42 W m−2, at the top of the atmosphere (TOA) by +0.37 ± 0.26 W m−2 and in the atmosphere by +5.11 ± 0.83 W m−2 over the TP and Indo-Gangetic Plain region (15–35° N, 80–110° E). Atmospheric warming increases vertical velocities and thereby cloud ice in the upper troposphere. Aerosol induced anomalous warming over the TP facilitates the relative strengthening of the monsoon Hadley circulation and increases moisture inflow by strengthening the cross-equatorial monsoon jet. This increases precipitation amounts over India (1–4 mm day−1) and eastern China (0.2–2 mm day−1). These results are significant at the 99 % confidence level.

  2. Trace gas composition in the Asian summer monsoon anticyclone: a case study based on aircraft observations and model simulations

    Science.gov (United States)

    Gottschaldt, Klaus-D.; Schlager, Hans; Baumann, Robert; Bozem, Heiko; Eyring, Veronika; Hoor, Peter; Jöckel, Patrick; Jurkat, Tina; Voigt, Christiane; Zahn, Andreas; Ziereis, Helmut

    2017-05-01

    We present in situ measurements of the trace gas composition of the upper tropospheric (UT) Asian summer monsoon anticyclone (ASMA) performed with the High Altitude and Long Range Research Aircraft (HALO) in the frame of the Earth System Model Validation (ESMVal) campaign. Air masses with enhanced O3 mixing ratios were encountered after entering the ASMA at its southern edge at about 150 hPa on 18 September 2012. This is in contrast to the presumption that the anticyclone's interior is dominated by recently uplifted air with low O3 in the monsoon season. We also observed enhanced CO and HCl in the ASMA, which are tracers for boundary layer pollution and tropopause layer (TL) air or stratospheric in-mixing respectively. In addition, reactive nitrogen was enhanced in the ASMA. Along the HALO flight track across the ASMA boundary, strong gradients of these tracers separate anticyclonic from outside air. Lagrangian trajectory calculations using HYSPLIT show that HALO sampled a filament of UT air three times, which included air masses uplifted from the lower or mid-troposphere north of the Bay of Bengal. The trace gas gradients between UT and uplifted air masses were preserved during transport within a belt of streamlines fringing the central part of the anticyclone (fringe), but are smaller than the gradients across the ASMA boundary. Our data represent the first in situ observations across the southern part and downstream of the eastern ASMA flank. Back-trajectories starting at the flight track furthermore indicate that HALO transected the ASMA where it was just splitting into a Tibetan and an Iranian part. The O3-rich filament is diverted from the fringe towards the interior of the original anticyclone, and is at least partially bound to become part of the new Iranian eddy. A simulation with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model is found to reproduce the observations reasonably well. It shows that O3-rich air is entrained by the outer streamlines of the

  3. Late Holocene (~ 2 ka) East Asian Monsoon variations inferred from river discharge and climate interrelationships in the Pearl River Estuary

    Digital Repository Service at National Institute of Oceanography (India)

    Nan, Q.; Li, T.; Chen, J.; Nigam, R.

    A sediment core from the Pearl River Estuary (PRE) was analyzed for grain size and organic geochemistry parameters (TOC and δ13Corg). The results showed that high mean grain-size value and increased sand content were correlated...

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

    International Nuclear Information System (INIS)

    Cristofanelli, P; Putero, D; Landi, T C; Marinoni, A; Duchi, R; Calzolari, F; Bonasoni, P; Adhikary, B; Stocchi, P; Verza, G; Vuillermoz, E; Laj, P; Kang, S; Ming, J

    2014-01-01

    Over the course of six years (2006–2011), equivalent black carbon (eqBC), coarse aerosol mass (PM 1–10 ), and surface ozone (O 3 ), observed during the monsoon onset period at the Nepal Climate Observatory–Pyramid WMO/GAW Global Station (NCO-P, 5079 m a.s.l.), were analyzed to investigate events characterized by a significant increase in these short-lived climate forcers/pollutants (SLCF/P). These events occurred during periods characterized by low (or nearly absent) rain precipitation in the central Himalayas, and they appeared to be related to weakening stages (or ‘breaking’) of the South Asian summer monsoon system. As revealed by the combined analysis of atmospheric circulation, air-mass three-dimensional back trajectories, and satellite measurements of atmospheric aerosol loading, surface open fire, and tropospheric NO x , the large amount of SLCF/P reaching the NCO-P appeared to be related to natural (mineral dust) and anthropogenic emissions occurring within the PBL of central Pakistan (i.e., Thar Desert), the Northwestern Indo-Gangetic plain, and the Himalayan foothills. The systematic occurrence of these events appeared to represent the most important source of SLCF/P inputs into the central Himalayas during the summer monsoon onset period, with possible important implications for the regional climate and for hydrological cycles. (letter)

  5. Preliminary global paleogeographic maps through the Greenhouse-Icehouse transition: forcing of the Drake Passage and Asian Monsoons.

    Science.gov (United States)

    Poblete, Fernando; Dupont-Nivet, Guillaume; Licht, Alexis; van Hinsbergen, Douwe; Roperch, Pierrick; Guillocheau, Francois; Baby, Guillaume; Baatsen, Michiel

    2017-04-01

    Paleogeographic maps are essential for understanding Earth dynamics. They provide the necessary boundary conditions for climate and geodynamic modeling, surface processes and biotic interactions. In particular, the opening and closing of ocean gateways and the growth of major mountain belts are major drivers of climate changes and biotic interchange. However, the timing and spatial extent of such events are highly controversial and regularly questioned by new data. As part of the ERC "MAGIC" project focusing on Asian Monsoons during the Icehouse to Greenhouse transition we thus produced a set of worldwide Cenozoic paleogeographic maps in the period time between 60 to 20 Ma, with a set of boundary conditions specific to the India-Asia collision zone and the Drake Passage. The creation of a paleogeographic map followed a rigorous and reproductively methodology that integrates paleobathymetric, paleoshoreline and paleotopographic data into a coherent plate tectonic model using the open source software GPlates. (1) We use the model provided by Seton et al. (2012) as a first order tectonic model modified to integrate the full restoration of five regions: the Andes, the Scotia Arc, Africa, The Mediterranean Sea and the Tibet-Himalayan collision zone. (2) The paleobathymetry was provided by Müller et al. (2008) using age-depth relationships and assuming symmetric ridge spreading. (3) Paleoshoreline maps were modified according to the fossil database from fossilworks.org and the geological record and were used to represent the boundary between terrestrial and marine paleo-environments. (4) To reconstruct paleoelevations, the most controversial task, we compiled a wide range of data including stable isotope, leaf physiognomy, and thermochronology combined with regional fossil and geological records (tectonic setting) and geomorphological data. Finally, we use the open source GMT software and a set of masks to modify the current Earth relief model (ETOPO) according to the

  6. 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

  7. The Interdecadal Variability of Summer Precipitation over the South of China and its Response to Asian Monsoon at the Turning Points of Global Warming

    Science.gov (United States)

    Wang, Huan; Li, Dongliang

    2017-04-01

    Under the background of global warming, decadal variability of the summer precipitation in the South of China and the Asian monsoon experienced mutations at around the end of 1970s, the beginning of 1990s and 21st century. We examined the external and internal forcings which may cause the mutations and diagnosed the mechanism. Human emission of CO2 has always been the fatal reason for global warming, and it is also the primary reason for the precipitation increasing over Yangtze-Huai river basin at the end of the 1970s. The Yangtze-Huai river basin and South China demonstrated more summer rainfall after 1993. This can be explained by the weakening of the Asian summer monsoon caused by the positive anomaly of summer SST over northwest Pacific Ocean and Indian Ocean. A significant trend in the enhancement of sensible heat over the TP has exerted some considerable influence on the reinforce of the EASM, accompanied by the northward migration of the summer precipitation belt shifting northward at the beginning of 21st century.

  8. Paired measurements of foraminiferal delta 18 O and Mg/Ca ratios of Indian monsoons reconstructed from Holocene to Last Glacial record

    Digital Repository Service at National Institute of Oceanography (India)

    Mahesh, B.; Banakar, V.K.; Burr, G.

    et al., 1993; Anderson and Prell, 1993; Clemens and Prell, 1990; Prell and Van Campo, 1986; Duplessy, 1982). The robust proxy to monitor monsoon intensity could be the variation in SS as it instantly responds to changes in evaporation- precipitation...

  9. Orbitally-paced variations of water availability in the SE Asian Monsoon region following the Miocene Climate Transition

    Science.gov (United States)

    Heitmann, Emma O.; Ji, Shunchuan; Nie, Junsheng; Breecker, Daniel O.

    2017-09-01

    Middle Miocene Earth had several boundary conditions similar to those predicted for future Earth including similar atmospheric pCO2 and substantial Antarctic ice cover but no northern hemisphere ice sheets. We describe a 12 m outcrop of the terrestrial Yanwan Section in the Tianshui Basin, Gansu, China, following the Miocene Climate Transition (13.9-13.7 Ma). It consists of ∼25 cm thick CaCO3-cemented horizons that overprint siltstones every ∼1 m. We suggest that stacked soils developed in siltstones under a seasonal climate with a fluctuating water table, evidenced by roots, clay films, mottling, presence of CaCO3 nodules, and stacked carbonate nodule δ13 C and δ18 O profiles that mimic modern soils. We suggest that the CaCO3-cemented horizons are capillary-fringe carbonates that formed in an arid climate with a steady water table and high potential evapotranspiration rates (PET), evidenced by sharp upper and basal contacts, micrite, sparite, and root-pore cements. The CaCO3 of the cemented horizons and the carbonate nodules have similar mean δ18 O and δ13 C values but the cements have significantly smaller variance in δ13 C and δ18 O values and a different δ18 O versus δ13 C slope, supporting the conclusion that these carbonates are from different populations. The magneto-stratigraphic age model indicates obliquity pacing of the arid conditions required to form the CaCO3-cemented horizons suggesting an orbital control on water availability. We suggest two possible drivers for the obliquity pacing of arid conditions: 1) variability in the cross-equatorial pressure gradient that controls summer monsoon (ASM) strength and is influenced by obliquity-paced variations of Antarctic ice volume and 2) variability in Western Pacific Ocean-East Asian continent pressure gradient controlled by the 25-45°N meridional insolation gradient. We also suggest that variations in aridity were influenced by variations in PET and sensible heating of the regional land

  10. Increasing persistent haze in Beijing: potential impacts of weakening East Asian winter monsoons associated with northwestern Pacific sea surface temperature trends

    Directory of Open Access Journals (Sweden)

    L. Pei

    2018-03-01

    Full Text Available Over the past decades, Beijing, the capital city of China, has encountered increasingly frequent persistent haze events (PHE. While the increased pollutant emissions are considered as the most important reason, changes in regional atmospheric circulations associated with large-scale climate warming also play a role. In this study, we find a significant positive trend of PHE in Beijing for the winters from 1980 to 2016 based on updated daily observations. This trend is closely related to an increasing frequency of extreme anomalous southerly episodes in North China, a weakened East Asian trough in the mid-troposphere and a northward shift of the East Asian jet stream in the upper troposphere. These conditions together depict a weakened East Asian winter monsoon (EAWM system, which is then found to be associated with an anomalous warm, high-pressure system in the middle–lower troposphere over the northwestern Pacific. A practical EAWM index is defined as the seasonal meridional wind anomaly at 850 hPa in winter over North China. Over the period 1900–2016, this EAWM index is positively correlated with the sea surface temperature anomalies over the northwestern Pacific, which indicates a wavy positive trend, with an enhanced positive phase since the mid-1980s. Our results suggest an observation-based mechanism linking the increase in PHE in Beijing with large-scale climatic warming through changes in the typical regional atmospheric circulation.

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

    Energy Technology Data Exchange (ETDEWEB)

    Sundaram, S.; Yin, Q.Z.; Berger, A.; Muri, H. [Universite Catholique de Louvain, Earth and Life Institute (ELI), Georges Lemaitre Centre for Earth and Climate Research (TECLIM), Louvain la Neuve (Belgium)

    2012-09-15

    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. (orig.)

  12. Impact of East Asian Winter and Australian Summer Monsoons on the Enhanced Surface Westerlies over the Western Tropical Pacific Ocean Preceding the El Niño Onset

    Science.gov (United States)

    Zheng, Y.; Zhang, R.; Bourassa, M. A.

    2014-12-01

    Composite analysis from NCEP-NCAR reanalysis datasets over the period 1948-2007 indicates that stronger East Asian winter monsoons (EAWM) and stronger Australian summer monsoons (ASM) generally co-exist in boreal winters preceding the onset of El Niño, although the EAWM tend to be weak after 1990, probably because of the decadal shift of EAWM and the change in El Niño events from cold-tongue type to warm-pool type. The anomalous EAWM and ASM enhance surface westerlies over the western tropical Pacific Ocean (WTP). It is proposed that the enhanced surface westerlies over the WTP prior to El Niño onset are generally associated with the concurrent anomalous EAWM and ASM. A simple analytical atmospheric model is constructed to test the hypothesis that the emergence of enhanced surface westerlies over the WTP can be linked to concurrent EAWM and ASM anomalies. Model results indicate that when anomalous northerlies from the EAWM converge with anomalous southerlies from the ASM, westerly anomalies over the WTP are enhanced. This result provides a possible explanation of the co-impact of the EAWM and the ASM on the onset of El Niño through enhancing the surface westerly over the WTP.

  13. Decoupling of monsoon activity across the northern and southern Indo-Pacific during the Late Glacial

    Science.gov (United States)

    Denniston, R. F.; Asmerom, Y.; Polyak, V. J.; Wanamaker, A. D.; Ummenhofer, C. C.; Humphreys, W. F.; Cugley, J.; Woods, D.; Lucker, S.

    2017-11-01

    Recent studies of stalagmites from the Southern Hemisphere tropics of Indonesia reveal two shifts in monsoon activity not apparent in records from the Northern Hemisphere sectors of the Austral-Asian monsoon system: an interval of enhanced rainfall at ∼19 ka, immediately prior to Heinrich Stadial 1, and a sharp increase in precipitation at ∼9 ka. Determining whether these events are site-specific or regional is important for understanding the full range of sensitivities of the Austral-Asian monsoon. We present a discontinuous 40 kyr carbon isotope record of stalagmites from two caves in the Kimberley region of the north-central Australian tropics. Heinrich stadials are represented by pronounced negative carbon isotopic anomalies, indicative of enhanced rainfall associated with a southward shift of the intertropical convergence zone and consistent with hydroclimatic changes observed across Asia and the Indo-Pacific. Between 20 and 8 ka, however, the Kimberley stalagmites, like the Indonesian record, reveal decoupling of monsoon behavior from Southeast Asia, including the early deglacial wet period (which we term the Late Glacial Pluvial) and the abrupt strengthening of early Holocene monsoon rainfall.

  14. A climate model study of an intense Asian Monsoon in a La Niña-like climate of MIS-13

    Science.gov (United States)

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

    2012-04-01

    Studying the paleo-monsoon during past interglacials is a valuable approach to improve our understanding of the monsoon system in present-day and future climates. We focus on Marine Isotopic stage 13 (MIS-13; ~0.5 Ma) which was a relatively cool interglacial, but with a paradoxically intense monsoonal precipitation over eastern and southern Asia. Our main goal is to understand the physics-based mechanism driving the intense monsoon, specifically the East Asian Summer Monsoon (EASM), during MIS-13. We applied both an intermediate complexity model (LOVECLIM) as well as fully coupled general circulation models (HadCM3 and CCSM3) to simulate pre-industrial and MIS-13 climates. The boundary conditions for MIS-13 were chosen for 506 ka with Northern-Hemisphere (NH) summer at perihelion and a CO2 concentration of 240 ppm. For pre-industrial, NH-winter occurring at perihelion and a CO2 concentration of 280 ppm were prescribed. Preliminary analysis of the model results shows different atmospheric and oceanic features in MIS-13 compared to the pre-industrial which could affect the EASM. The Northern Pacific Subtropical High (NPSH), which is an important factor in controlling the EASM, strengthened and extended to the northwest in MIS-13 partially due to cooling of the central Pacific Ocean. This in turn brought more moisture from the Central Pacific to the EASM-region and caused a northwestward shift and bending of the low-level jet along East Asia. The change in the low-level jet subsequently increased the meridional wind velocity at 850 mbar in the EASM-region providing more moisture from the tropical Pacific and Indian Oceans. In addition, higher sea-surface temperature in the Indian Ocean during MIS-13 further increased the source of moisture for the EASM. The Asian low, which is another component of the EASM-system, also shifted eastward moving the rain band northward. Moreover, it was found that MIS-13 had a dominant La Niña condition in the tropical Pacific. La Ni

  15. A comprehensive overview of the climatological composition of the Asian summer monsoon anticyclone based on 10 years of Aura Microwave Limb Sounder measurements

    Science.gov (United States)

    Santee, M. L.; Manney, G. L.; Livesey, N. J.; Schwartz, M. J.; Neu, J. L.; Read, W. G.

    2017-05-01

    Intense deep convection associated with the Asian summer monsoon (ASM) lofts surface pollutants to the upper troposphere/lower stratosphere (UTLS), where strong winds and long chemical lifetimes allow intercontinental transport, affecting atmospheric composition around the globe. The Aura Microwave Limb Sounder (MLS), launched in 2004, makes simultaneous colocated measurements of trace gases and cloud ice water content (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, extensive measurement suite, and insensitivity to aerosol and most clouds of Aura MLS to characterize the climatological (2005-2014) composition of the ASM anticyclone throughout its annual life cycle. We use version 4 MLS data to quantify spatial and temporal variations in both tropospheric (H2O, CO, CH3Cl, CH3CN, CH3OH) and stratospheric (O3, HNO3, HCl) tracers on four potential temperature surfaces (350-410 K). Inside the mature anticyclone, all species exhibit substantial changes, not only from their premonsoon distributions in the ASM region but also from their summertime distributions in the rest of the hemisphere. Different tracers exhibit dissimilar seasonal evolution, and the exact location and timing of their extreme values vary. Although individual aspects of the anticyclone have been described previously, we present a uniquely comprehensive overview of the climatological seasonal evolution of the ASM and its impact on UTLS composition. This work provides valuable context for planned in situ measurements as well as a benchmark for model evaluation and future investigations of interannual variability and long-term changes in monsoon processes.

  16. Projected Changes in the Asian-Australian Monsoon Region in 1.5°C and 2.0°C Global-Warming Scenarios

    Science.gov (United States)

    Chevuturi, Amulya; Klingaman, Nicholas P.; Turner, Andrew G.; Hannah, Shaun

    2018-03-01

    In light of the Paris Agreement, it is essential to identify regional impacts of half a degree additional global warming to inform climate adaptation and mitigation strategies. We investigate the effects of 1.5°C and 2.0°C global warming above preindustrial conditions, relative to present day (2006-2015), over the Asian-Australian monsoon region (AAMR) using five models from the Half a degree Additional warming, Prognosis and Projected Impacts (HAPPI) project. There is considerable intermodel variability in projected changes to mean climate and extreme events in 2.0°C and 1.5°C scenarios. There is high confidence in projected increases to mean and extreme surface temperatures over AAMR, as well as more-frequent persistent daily temperature extremes over East Asia, Australia, and northern India with an additional 0.5°C warming, which are likely to occur. Mean and extreme monsoon precipitation amplify over AAMR, except over Australia at 1.5°C where there is uncertainty in the sign of the change. Persistent daily extreme precipitation events are likely to become more frequent over parts of East Asia and India with an additional 0.5°C warming. There is lower confidence in projections of precipitation change than in projections of surface temperature change. These results highlight the benefits of limiting the global-mean temperature change to 1.5°C above preindustrial, as the severity of the above effects increases with an extra 0.5°C warming.

  17. Differential response of vegetation in Hulun Lake region at the northern margin of Asian summer monsoon to extreme cold events of the last deglaciation

    Science.gov (United States)

    Zhang, Shengrui; Xiao, Jule; Xu, Qinghai; Wen, Ruilin; Fan, Jiawei; Huang, Yun; Yamagata, Hideki

    2018-06-01

    The response of vegetation to extreme cold events during the last deglaciation is important for assessing the impact of possible extreme climatic events on terrestrial ecosystems under future global warming scenarios. Here, we present a detailed record of the development of regional vegetation in the northern margin of Asian summer monsoon during the last deglaciation (16,500-11,000 cal yr BP) based on a radiocarbon-dated high-resolution pollen record from Hulun Lake, northeast China. The results show that the regional vegetation changed from subalpine meadow-desert steppe to mixed coniferous and deciduous forest-typical steppe during the last deglaciation. However, its responses to the Heinrich event 1 (H1) and the Younger Dryas event (YD) were significantly different: during the H1 event, scattered sparse forest was present in the surrounding mountains, while within the lake catchment the vegetation cover was poor and was dominated by desert steppe. In contrast, during the YD event, deciduous forest developed and the proportion of coniferous forest increased in the mountains, the lake catchment was occupied by typical steppe. We suggest that changes in Northern Hemisphere summer insolation and land surface conditions (ice sheets and sea level) caused temperature and monsoonal precipitation variations that contributed to the contrasting vegetation response during the two cold events. We conclude that under future global warming scenarios, extreme climatic events may cause a deterioration of the ecological environment of the Hulun Lake region, resulting in increased coniferous forest and decreased total forest cover in the surrounding mountains, and a reduction in typical steppe in the lake catchment.

  18. Teleconnection among Asian Summer Monsoon, ENSO and PDO revealed by instrumental and historic records as well as an annual resolution stalagmite record from Lianhua Cave, northwestern Hunan, China

    Science.gov (United States)

    Li, H.; Yin, J.; Yuan, D.; Li, T.

    2013-12-01

    A 33-cm long aragonite stalagmite, LHN-1, from Lianhua Cave (29°09'N, 109°33'E , 459m a.s.l.) in NW Hunan Province of China has been dated by ICP-MS 230Th/U method. The 14 230Th/U dates with less than ×37 years uncertainties yield excellent chronology, showing that the stalagmite grew continuously over the past 3400 years. The 0.1-mm sampling interval for stable isotope analyses provides annual resolution δ18O and δ13C records of the LHN-1 stalagmite. Up-to-dated, a total of 887 measurements for δ18O and δ13C have been made, which reveal detailed monsoonal climatic changes during the past 1000 years. The average values of δ18O and δ13C are -5.83 (‰, PDB) and -3.29 (‰, PDB), respectively. For the youngest part of the δ18O record, we have compared with the instrumentally meteorological records and historical dryness/wetness indexes from the studying area, indicating that stalagmite δ18O on annual-to-decadal scales reflects mainly rainfall change in the monsoonal area, with lighter δ18O reflecting wetter condition. The comparison of the δ18O with the East Asian Summer Monsoon (EASM) index since AD 1850 adopted by IPCC (2007) illustrates that lighter stalagmite δ18O corresponds to stronger EASM. Taking the average δ18O value of the 1000-yr record as an average climatic condition, we have found that the δ18O values during AD 1050~1100, 1125~1225, 1300~1350, 1430~1630 and 1900~1960 are lighter than the average, reflecting stronger EASM and wetter condition. The δ18O values during AD 1100~1125, 1225~1300, 1350~1430, 1630~1900 and 1960 to the present are heavier than the average, indicating weak EASM and drier condition. On decadal-to-centennial scales, the δ13C variations generally follow that of δ18O which probably demonstrates that vegetation above the cave controls the δ13C variations. Further comparisons of the δ18O, EASM, ENSO and PDO show that a negative SOI (El Nino phase) correlates warm PDO phase and higher N. Pacific pressure, resulting

  19. Lakes or wetlands? A comment on 'The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons' by Enzel et al.

    Science.gov (United States)

    Engel, Max; Matter, Albert; Parker, Adrian G.; Parton, Ash; Petraglia, Michael D.; Preston, Gareth W.; Preusser, Frank

    2017-01-01

    Enzel et al. (2015) reassess sedimentary records of Early to Mid-Holocene lake sites in Arabia based on a reinterpretation of published multiproxy data and a qualitative analysis of satellite imagery. The authors conclude that these sites represent palaeo-wetland environments rather than palaeolakes and that the majority of the Arabian Peninsula experienced no or, if at all, only a very minor increase of rainfall at that time mainly due to eastward expansion of the East African Summer Monsoon. We disagree with their reassessment and identify several cases where unequivocal evidence for early Late Pleistocene and Early to Mid-Holocene perennial lake environments in Arabia, lasting for centuries to millennia, was neglected by Enzel et al. (2015). Here we summarize findings which indicate the presence of lakes from the sites of Jubbah, Tayma, Mundafan (all Saudi Arabia), Wahalah, Awafi (both UAE), and the Wahiba Sands (Oman), supported by evidence including occurrence of barnacle colonies in living position, remnant bioclastic shoreline deposits, undisturbed varve formation, shallowing-up lacustrine sequences, various aquatic freshwater, brackish and saline micro- and macrofossils, such as ichnofaunal remains, which are the result of prolonged field-based research. While the precise depth, hydrology and ecology of these water bodies is still not entirely resolved, their perennial nature is indicative of a markedly increased precipitation regime, which, in combination with more abundant groundwater and increased spring outflow in terminal basins fed by charged aquifers, was sufficient to overcome evaporative losses. The palaeolakes' influence on sustaining prehistoric populations is corroborated by the presence of rich archaeological evidence.

  20. A persistent Holocene wetting trend in arid central Asia, with wettest conditions in the late Holocene, revealed by multi-proxy analyses of loess-paleosol sequences in Xinjiang, China

    Science.gov (United States)

    Chen, Fahu; Jia, Jia; Chen, Jianhui; Li, Guoqiang; Zhang, Xiaojian; Xie, Haichao; Xia, Dunsheng; Huang, Wei; An, Chengbang

    2016-08-01

    There are significant differences in the interpretation of the moisture (precipitation) history of arid central Asia (ACA) during the Holocene, as inferred on one hand from speleothem oxygen isotope records, and on the other from lake sediments. Here we present the results of measurements of climatically-sensitive magnetic properties and soil color from four well-dated loess-paleosol sequences from the northern slopes of the Tienshan Mountains and the Yili River valley, Xinjiang, China, in the core area of ACA. Our results demonstrate that the characteristic Holocene paleosol, indicating relatively moist conditions, generally formed after ∼6 ka (1 ka = 1000 cal yr BP) in the study region, and that the accumulation of unweathered loess prevailed during the early Holocene, indicating a dry climate at that time. The magnetic proxies further reveal a trend of generally increasing moisture since the Last Glacial Maximum, with the wettest climate occurring during the late Holocene. This trend of increasing moisture during the Holocene is representative of the Xinjiang region and possibly of the whole of the core area of ACA, and is in marked contrast both to the mid-Holocene moisture maximum observed in the East Asian summer monsoon region and to the general decrease in the strength of the Indian summer monsoon since the early Holocene. Our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the Holocene in the core area of ACA, caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO).

  1. Late Holocene vegetation and climate change on the southeastern Tibetan Plateau: Implications for the Indian Summer Monsoon and links to the Indian Ocean Dipole

    Science.gov (United States)

    Li, Kai; Liu, Xingqi; Wang, Yongbo; Herzschuh, Ulrike; Ni, Jian; Liao, Mengna; Xiao, Xiayun

    2017-12-01

    The Indian Summer Monsoon (ISM) is one of the most important climate systems, whose variability and driving mechanisms are of broad interest for academic and societal communities. Here, we present a well-dated high-resolution pollen analysis from a 4.82-m long sediment core taken from Basomtso, in the southeastern Tibetan Plateau (TP), which depicts the regional climate changes of the past millennium. Our results show that subalpine coniferous forest was dominant around Basomtso from ca. 867 to ca. 750 cal. yr BP, indicating a warm and semi-humid climate. The timberline in the study area significantly decreased from ca. 750 to ca. 100 cal. yr BP, and a cold climate, corresponding to the Little Ice Age (LIA) prevailed. Since ca. 100 cal. yr BP, the vegetation type changed to forest-meadow with rising temperatures and moisture. Ordination analysis reveals that the migration of vegetation was dominated by regional temperatures and then by moisture. Further comparisons between the Basomtso pollen record and the regional temperature reconstructions underscore the relevance of the Basomtso record from the southeastern TP for regional and global climatologies. Our pollen based moisture reconstruction demonstrates the strong multicentennial-scale link to ISM variability, providing solid evidence for the increase of monsoonal strengths over the past four centuries. Spectral analysis indicates the potential influence of solar forcing. However, a closer relationship has been observed between multicentennial ISM variations and Indian Ocean sea surface temperature anomalies (SSTs), suggesting that the variations in monsoonal precipitation over the southeastern TP are probably driven by the Indian Ocean Dipole on the multicentennial scale.

  2. The chemical effects on the summertime ozone in the upper troposphere and lower stratosphere over the Tibetan Plateau and the South Asian monsoon region

    Science.gov (United States)

    Gu, Yixuan; Liao, Hong; Xu, Jianming; Zhou, Guangqiang

    2018-01-01

    We use the global three-dimensional Goddard Earth Observing System chemical transport model with the Universal tropospheric-stratospheric Chemistry eXtension mechanism to examine the contributions of the chemical processes to summertime O3 in the upper troposphere and lower stratosphere (UTLS) over the Tibetan Plateau and the South Asian monsoon region (TP/SASM). Simulated UTLS O3 concentrations are evaluated by comparisons with Microwave Limb Sounder products and net chemical production of O3 (NPO3) are evaluated by comparisons with model results in previous studies. Simulations show that the chemical processes lead to an increase in O3 concentration, which is opposite to the effect of O3 transport in the UTLS over the TP/SASM region throughout the boreal summer. NPO3 in UTLS over the TP/SASM region is the largest in summer. Elevated values (0.016-0.020 Tg year-1) of the seasonal mean NPO3 are simulated to locate at 100 hPa in the TP/SASM region, where the mixing ratios of O3 are low and those of O3 precursors (NO x , VOCs, and CO) are high. The high concentrations of O3 precursors (NO x , VOCs, and CO) together with the active photochemical reactions of NO2 in the UTLS over the TP/SASM region during summertime could be important reasons for the enhancement of {NP}_{{{O}3 }} over the studied region.

  3. Environmental status of the Jilantai Basin, North China, on the northwestern margin of the modern Asian summer monsoon domain during Marine Isotope Stage 3

    Science.gov (United States)

    Fan, Yuxin; Wang, Yongda; Mou, Xuesong; Zhao, Hui; Zhang, Fu; Zhang, Fan; Liu, Wenhao; Hui, Zhengchuang; Huang, Xiaozhong; Ma, Jun

    2017-10-01

    Two drill cores were obtained from the Jilantai sub-depression (JLT(d)) and the neighboring Dengkou sub-uplift (DK(u)), within a huge, former lake basin in northern China. From an analysis of the lithology and pollen assemblages, combined with radiocarbon dating of extracted pollen and OSL dating of extracted quartz, we concluded the following: JLT(d) was continuously occupied by lakes since 85 ka; however, DK(u), the neighboring sub-uplift, was covered by lakes during 80-74 ka, 50-44 ka, 32.5-27.5 ka and DK(u) during Marine Isotope Stage (MIS) 3. Evidence from shorelines, previously published cores, and the sedimentary and chronological evidence presented in this paper indicate the occurrence of a sub-humid environment, characterized by the occurrence of lakes separated by dunes, in the Jilantai Basin during MIS 3. However, further work is needed to understand the environmental significance of the co-existence of lakes and dunes during MIS 3, although a sub-humid climate background during MIS 3 is supported by well-dated geological archives along the western front of the present-day Asian Summer Monsoon domain and its eastern extensional area.

  4. Glacial-interglacial changes and Holocene variations in Arabian Sea denitrification

    Science.gov (United States)

    Gaye, Birgit; Böll, Anna; Segschneider, Joachim; Burdanowitz, Nicole; Emeis, Kay-Christian; Ramaswamy, Venkitasubramani; Lahajnar, Niko; Lückge, Andreas; Rixen, Tim

    2018-01-01

    At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST) and δ15N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ15N values of 4-7 ‰ during the last glacial maximum (LGM) and stadials (Younger Dryas and Heinrich events) suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs) had elevated δ15N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ15N values > 6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ15N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ15N values are lower during the mid-Holocene (4.2-8.2 ka BP) compared to the late Holocene ( ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ15N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position in the northeast was established during the middle and late Holocene. This was

  5. Role of the mid-Holocene environmental transition in the decline of late Neolithic cultures in the deserts of NE China

    Science.gov (United States)

    Guo, Licheng; Xiong, Shangfa; Ding, Zhongli; Jin, Guiyun; Wu, Jiabin; Ye, Wei

    2018-06-01

    The mid-Holocene environmental transition was characterised by global cooling and the abrupt weakening of the Northern Hemisphere monsoon systems. It is generally considered the key driver of the collapse of several mid-Holocene agricultural societies, on a global scale. However, only a few previous studies have tried to verify the climatic origin of the collapse of these societies, using the compilation of spatiotemporal data at a large scale. Especially, the nature of mid-Holocene human-environment interactions in the climatically-sensitive margin of the East Asian summer monsoon front remains to be thoroughly understood. However, a systematic compilation of archaeological data at a regional scale can be used to verify the role the mid-Holocene environmental transition played in the collapse of late Neolithic cultures in China. Here, we present a regional compilation of Holocene records from sub-aerial sedimentary deposits, lake sediments, and archaeological sites in the deserts of NE China and the adjacent regions to explore human-environment interactions during the mid-Holocene. Comparison of the records of Holocene climate change with the evolution of archaeological sites reveals that the mid-Holocene environmental transition resulted in ecosystem degradation in the deserts of NE China, rendering these areas much less habitable. Faced with substantially increased environmental pressures, the late Neolithic inhabitants used several subsistence strategies to adapt to the environmental transition, including change in agricultural practices and ultimately migration. Overall, our results support the view that a widespread mid-Holocene drought destroyed the rain-fed agricultural and/or plant-based subsistence economies, ultimately contributing to the collapse of late Neolithic cultures in NE China.

  6. Is precipitation a predictor of mortality in Bangladesh? A multi-stratified analysis in a South Asian monsoon climate.

    Science.gov (United States)

    Burkart, Katrin; Kinney, Patrick

    2016-05-15

    While numerous studies have assessed the association between temperature and mortality in various locations, few have addressed the relationship between precipitation and mortality. Given the high amounts of rainfall in many tropical monsoon areas and the often seasonally pronounced differences, there might be a potentially strong impact on health outcomes and death. In this study, we investigated the association between precipitation and daily death counts in Bangladesh from 2003 to 2007 using regression models with a quasipoisson distribution adjusting for long-term time and seasonal trends, day of the month, age and perceived temperature. Effects were assessed for all ages, the elderly and by gender. During the dry season a sharp increase in death risk was found at very high precipitation amounts which are most likely to be cyclone-related. This cyclone effect was most pronounced for females at the immediate day with an increase of 18.7% (3.8-35.6%) in non-external cause mortality per mm precipitation above 5mm. At longer lags we found a negative association between precipitation and mortality indicating some kind of dry effect which was more pronounced for the elderly with a mortality increase of 4.4% (2.6-6.2%) per mm decrease in precipitation. During the rainy season, we observed a protective effect of rainfall which was strongest during periods of seasonally high equivalent temperatures with a decrease in mortality of 4.0% (2.3-5.6%) per mm increase in precipitation on the immediate day. The observed associations between precipitation and mortality differed by season, age and gender. Generally, a strong short-term increase in mortality was associated with cyclonic activity during the dry season, while ongoing low rainfall seemed to have an adverse impact at higher lags. During the rainy season, precipitation seemed to mitigate heat effects. Copyright © 2016 Elsevier B.V. All rights reserved.

  7. Decoding the drivers of bank erosion on the Mekong river: The roles of the Asian monsoon, tropical storms, and snowmelt.

    Science.gov (United States)

    Darby, Stephen E; Leyland, Julian; Kummu, Matti; Räsänen, Timo A; Lauri, Hannu

    2013-04-01

    We evaluate links between climate and simulated river bank erosion for one of the world's largest rivers, the Mekong. We employ a process-based model to reconstruct multidecadal time series of bank erosion at study sites within the Mekong's two main hydrological response zones, defining a new parameter, accumulated excess runoff (AER), pertinent to bank erosion. We employ a hydrological model to isolate how snowmelt, tropical storms and monsoon precipitation each contribute to AER and thus modeled bank erosion. Our results show that melt (23.9% at the upstream study site, declining to 11.1% downstream) and tropical cyclones (17.5% and 26.4% at the upstream and downstream sites, respectively) both force significant fractions of bank erosion on the Mekong. We also show (i) small, but significant, declines in AER and hence assumed bank erosion during the 20th century, and; (ii) that significant correlations exist between AER and the Indian Ocean Dipole (IOD) and El Niño Southern Oscillation (ENSO). Of these modes of climate variability, we find that IOD events exert a greater control on simulated bank erosion than ENSO events; but the influences of both ENSO and IOD when averaged over several decades are found to be relatively weak. However, importantly, relationships between ENSO, IOD, and AER and hence inferred river bank erosion are not time invariant. Specifically, we show that there is an intense and prolonged epoch of strong coherence between ENSO and AER from the early 1980s to present, such that in recent decades derived Mekong River bank erosion has been more strongly affected by ENSO.

  8. An aircraft gas chromatograph–mass spectrometer System for Organic Fast Identification Analysis (SOFIA: design, performance and a case study of Asian monsoon pollution outflow

    Directory of Open Access Journals (Sweden)

    E. Bourtsoukidis

    2017-12-01

    Full Text Available Volatile organic compounds (VOCs are important for global air quality and oxidation processes in the troposphere. In addition to ground-based measurements, the chemical evolution of such species during transport can be studied by performing in situ airborne measurements. Generally, aircraft instrumentation needs to be sensitive, robust and sample at higher frequency than ground-based systems while their construction must comply with rigorous mechanical and electrical safety standards. Here, we present a new System for Organic Fast Identification Analysis (SOFIA, which is a custom-built fast gas chromatography–mass spectrometry (GC-MS system with a time resolution of 2–3 min and the ability to quantify atmospheric mixing ratios of halocarbons (e.g. chloromethanes, hydrocarbons (e.g isoprene, oxygenated VOCs (acetone, propanal, butanone and aromatics (e.g. benzene, toluene from sub-ppt to ppb levels. The relatively high time resolution is the result of a novel cryogenic pre-concentration unit which rapidly cools (∼ 6 °C s−1 the sample enrichment traps to −140 °C, and a new chromatographic oven designed for rapid cooling rates (∼ 30 °C s−1 and subsequent thermal stabilization. SOFIA was installed in the High Altitude and Long Range Research Aircraft (HALO for the Oxidation Mechanism Observations (OMO campaign in August 2015, aimed at investigating the Asian monsoon pollution outflow in the tropical upper troposphere. In addition to a comprehensive instrument characterization we present an example monsoon plume crossing flight as a case study to demonstrate the instrument capability. Hydrocarbon, halocarbon and oxygenated VOC data from SOFIA are compared with mixing ratios of carbon monoxide (CO and methane (CH4, used to define the pollution plume. By using excess (ExMR and normalized excess mixing ratios (NEMRs the pollution could be attributed to two air masses of distinctly different origin, identified by back

  9. An aircraft gas chromatograph-mass spectrometer System for Organic Fast Identification Analysis (SOFIA): design, performance and a case study of Asian monsoon pollution outflow

    Science.gov (United States)

    Bourtsoukidis, Efstratios; Helleis, Frank; Tomsche, Laura; Fischer, Horst; Hofmann, Rolf; Lelieveld, Jos; Williams, Jonathan

    2017-12-01

    Volatile organic compounds (VOCs) are important for global air quality and oxidation processes in the troposphere. In addition to ground-based measurements, the chemical evolution of such species during transport can be studied by performing in situ airborne measurements. Generally, aircraft instrumentation needs to be sensitive, robust and sample at higher frequency than ground-based systems while their construction must comply with rigorous mechanical and electrical safety standards. Here, we present a new System for Organic Fast Identification Analysis (SOFIA), which is a custom-built fast gas chromatography-mass spectrometry (GC-MS) system with a time resolution of 2-3 min and the ability to quantify atmospheric mixing ratios of halocarbons (e.g. chloromethanes), hydrocarbons (e.g isoprene), oxygenated VOCs (acetone, propanal, butanone) and aromatics (e.g. benzene, toluene) from sub-ppt to ppb levels. The relatively high time resolution is the result of a novel cryogenic pre-concentration unit which rapidly cools (˜ 6 °C s-1) the sample enrichment traps to -140 °C, and a new chromatographic oven designed for rapid cooling rates (˜ 30 °C s-1) and subsequent thermal stabilization. SOFIA was installed in the High Altitude and Long Range Research Aircraft (HALO) for the Oxidation Mechanism Observations (OMO) campaign in August 2015, aimed at investigating the Asian monsoon pollution outflow in the tropical upper troposphere. In addition to a comprehensive instrument characterization we present an example monsoon plume crossing flight as a case study to demonstrate the instrument capability. Hydrocarbon, halocarbon and oxygenated VOC data from SOFIA are compared with mixing ratios of carbon monoxide (CO) and methane (CH4), used to define the pollution plume. By using excess (ExMR) and normalized excess mixing ratios (NEMRs) the pollution could be attributed to two air masses of distinctly different origin, identified by back-trajectory analysis. This work

  10. SEACIONS During the 2012 Asian Monsoon: A Strategic Approach to Determining Convective Impacts on Tropospheric Ozone and TTL Gravity Waves

    Science.gov (United States)

    Thompson, Anne M. (Principal Investigator); Young, George S. (Principal Investigator); Morris, Gary; Johnson, Bryan; Oltmans, Samuel; Selkirk, Henry B.

    2016-01-01

    Purpose of making ozone and water vapor profiles measurements in SEAC4RS is to give consistent coverage of the vertical structure at fixed sites to (1) complement 2 campaign aircraft sampling; (2) ground-truth satellite measurements of H O and ozone; (3) provide profiles for model evaluation; (4) study processes responsible for day-to-day variability at each site. Revised objective for 2013, due to cancellation of the 2012 and 2013 plans to operate in Southeast Asia: rapidly re-configure the original "SEACIONS," Southeast Asian Consortium for Intensive Ozonesonde Network Study, to a SouthEast American plan (SEACIONS) for collecting daily ozonesonde data during DC-8 and ER-2 flights throughout the southeastern US. As in previous IONS (2004, 2006, 2008), students were trained at St Louis, Tallahassee, Houston, Penn State, Huntsville, Socorro. Images of the soundings and related flight-planning products were posted each day at NASA and Penn State (PSU) websites. With the aircraft based at Ellington Field (Houston), water CFH (cryogenic frost-point hygrometer) sondes in addition to ozonesondes, were to be taken launched at that site.

  11. The resolution sensitivity of the Asian summer monsoon and its inter-model comparison between MRI-AGCM and MetUM

    Science.gov (United States)

    Ogata, Tomomichi; Johnson, Stephanie J.; Schiemann, Reinhard; Demory, Marie-Estelle; Mizuta, Ryo; Yoshida, Kohei; Osamu Arakawa

    2017-11-01

    In this study, we compare the resolution sensitivity of the Asian Summer Monsoon (ASM) in two Atmospheric General Circulation Models (AGCMs): the MRI-AGCM and the MetUM. We analyze the MetUM at three different resolutions, N96 (approximately 200-km mesh on the equator), N216 (90-km mesh) and N512 (40-km mesh), and the MRI-AGCM at TL95 (approximately 180-km mesh on the equator), TL319 (60-km mesh), and TL959 (20-km mesh). The MRI-AGCM and the MetUM both show decreasing precipitation over the western Pacific with increasing resolution, but their precipitation responses differ over the Indian Ocean. In MRI-AGCM, a large precipitation increase appears off the equator (5-20°N). In MetUM, this off-equatorial precipitation increase is less significant and precipitation decreases over the equator. Moisture budget analysis demonstrates that a changing in moisture flux convergence at higher resolution is related to the precipitation response. Orographic effects, intra-seasonal variability and the representation of the meridional thermal gradient are explored as possible causes of the resolution sensitivity. Both high-resolution AGCMs (TL959 and N512) can represent steep topography, which anchors the rainfall pattern over south Asia and the Maritime Continent. In MRI-AGCM, representation of low pressure systems in TL959 also contributes to the rainfall pattern. Furthermore, the seasonal evolution of the meridional thermal gradient appears to be more accurate at higher resolution, particularly in the MRI-AGCM. These findings emphasize that the impact of resolution is only robust across the two AGCMs for some features of the ASM, and highlights the importance of multi-model studies of GCM resolution sensitivity.

  12. Aerosol and Cloud Properties during the Cloud Cheju ABC Plume -Asian Monsoon Experiment (CAPMEX) 2008: Linking between Ground-based and UAV Measurements

    Science.gov (United States)

    Kim, S.; Yoon, S.; Venkata Ramana, M.; Ramanathan, V.; Nguyen, H.; Park, S.; Kim, M.

    2009-12-01

    Cheju Atmospheric Brown Cloud (ABC) Plume-Monsoon Experiment (CAPMEX), comprehsensive ground-based measurements and a series of data-gathering flights by specially equipped autonomous unmanned aerial vehicles (AUAVs) for aerosol and cloud, had conducted at Jeju (formerly, Cheju), South Korea during August-September 2008, to improve our understanding of how the reduction of anthropogenic emissions in China (so-called “great shutdown” ) during and after the Summer Beijing Olympic Games 2008 effcts on the air quliaty and radiation budgets and how atmospheric brown clouds (ABCs) influences solar radiation budget off Asian continent. Large numbers of in-situ and remote sensing instruments at the Gosan ABC observatory and miniaturized instruments on the aircraft measure a range of properties such as the quantity of soot, size-segregated aerosol particle numbers, total particle numbers, size-segregated cloud droplet numbers (only AUAV), aerosol scattering properties (only ground), aerosol vertical distribution, column-integrated aerosol properties, and meteorological variables. By integrating ground-level and high-elevation AUAV measurements with NASA-satellite observations (e.g., MODIS, CALIPSO), we investigate the long range transport of aerosols, the impact of ABCs on clouds, and the role of biogenic and anthropogenic aerosols on cloud condensation nuclei (CCN). In this talk, we will present the results from CAPMEX focusing on: (1) the characteristics of aerosol optical, physical and chemical properties at Gosan observatory, (2) aerosol solar heating calculated from the ground-based micro-pulse lidar and AERONET sun/sky radiometer synergy, and comparison with direct measurements from UAV, and (3) aerosol-cloud interactions in conjunction with measurements by satellites and Gosan observatory.

  13. Methyl chloride in the upper troposphere observed by the CARIBIC passenger aircraft observatory: Large-scale distributions and Asian summer monsoon outflow

    Science.gov (United States)

    Umezawa, T.; Baker, A. K.; Oram, D.; Sauvage, C.; O'Sullivan, D.; Rauthe-Schöch, A.; Montzka, S. A.; Zahn, A.; Brenninkmeijer, C. A. M.

    2014-05-01

    We present spatial and temporal variations of methyl chloride (CH3Cl) in the upper troposphere (UT) observed mainly by the Civil Aircraft for Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) passenger aircraft for the years 2005-2011. The CH3Cl mixing ratio in the UT over Europe was higher than that observed at a European surface baseline station throughout the year, indicative of a persistent positive vertical gradient at Northern Hemisphere midlatitudes. A series of flights over Africa and South Asia show that CH3Cl mixing ratios increase toward tropical latitudes, and the observed UT CH3Cl level over these two regions and the Atlantic was higher than that measured at remote surface sites. Strong emissions of CH3Cl in the tropics combined with meridional air transport through the UT may explain such vertical and latitudinal gradients. Comparisons with carbon monoxide (CO) data indicate that noncombustion sources in the tropics dominantly contribute to forming the latitudinal gradient of CH3Cl in the UT. We also observed elevated mixing ratios of CH3Cl and CO in air influenced by biomass burning in South America and Africa, and the enhancement ratios derived for CH3Cl to CO in those regions agree with previous observations. In contrast, correlations indicate a high CH3Cl to CO ratio of 2.9 ± 0.5 ppt ppb-1 in the Asian summer monsoon anticyclone and domestic biofuel emissions in South Asia are inferred to be responsible. We estimated the CH3Cl emission in South Asia to be 134 ± 23 Gg Cl yr-1, which is higher than a previous estimate due to the higher CH3Cl to CO ratio observed in this study.

  14. Low-high latitude interaction forcing on the evolution of the 400 kyr cycle in East Asian winter monsoon records during the last 2.8 Myr

    Science.gov (United States)

    Li, Dawei; Zhao, Meixun; Tian, Jun

    2017-09-01

    Variability of the East Asian winter monsoon (EAWM), stronger during glacials and weaker during interglacials, has been tightly linked to the wax and wane of the Northern Hemisphere ice sheets (NHIS) via the Siberian High over the last 2.8 million years (Myr). However, the long eccentricity cycle (ca. 400 kyr) in the EAWM record from the late Pliocene to early-Pleistocene (2.8-1.2 Ma) could not be linked to NHIS changes, which lacked the long eccentricity cycle in the Pleistocene. Here, we present the first low latitude EAWM record of the last 2.8 Myr using surface and subsurface temperature difference from the northern South China Sea to evaluate interactions between tropical ocean and EAWM changes. The results show that the EAWM variability displayed significant 400 kyr cycle between 2.8 Ma and 1.2 Ma, with weak (strong) EAWM during high (low) earth orbital eccentricity state. A super El Niño-Southern Oscillation (ENSO) proxy record, calculated using west-east equatorial Pacific sea surface temperature differences, revealed 400 kyr cycles throughout the last 2.8 Myr with warm phase during high eccentricity state. Thus, we propose that super ENSO mean state strongly modulated the EAWM strength through remote forcing to generate the 400 kyr cycle between 2.8 Ma and 1.2 Ma, while low NHIS volume was not sufficient to dominate the EAWM variation as it did over the last 0.9 Myr with 100 kyr cycles in dominance.

  15. Projections of East Asian summer monsoon change at global warming of 1.5 and 2 °C

    Directory of Open Access Journals (Sweden)

    J. Liu

    2018-04-01

    Full Text Available Much research is needed regarding the two long-term warming targets of the 2015 Paris Agreement, i.e., 1.5 and 2 °C above pre-industrial levels, especially from a regional perspective. The East Asian summer monsoon (EASM intensity change and associated precipitation change under both warming targets are explored in this study. The multimodel ensemble mean projections by 19 CMIP5 models show small increases in EASM intensity and general increases in summer precipitation at 1.5 and 2 °C warming, but with large multimodel standard deviations. Thus, a novel multimodel ensemble pattern regression (EPR method is applied to give more reliable projections based on the concept of emergent constraints, which is effective at tightening the range of multimodel diversity and harmonize the changes of different variables over the EASM region. Future changes projected by using the EPR method suggest decreased precipitation over the Meiyu belt and increased precipitation over the high latitudes of East Asia and Central China, together with a considerable weakening of EASM intensity. Furthermore, reduced precipitation appears over 30–40° N of East Asia in June and over the Meiyu belt in July, with enhanced precipitation at their north and south sides. These changes in early summer are attributed to a southeastward retreat of the western North Pacific subtropical high (WNPSH and a southward shift of the East Asian subtropical jet (EASJ, which weaken the moisture transport via southerly wind at low levels and alter vertical motions over the EASM region. In August, precipitation would increase over the high latitudes of East Asia with more moisture from the wetter area over the ocean in the east and decrease over Japan with westward extension of WNPSH. These monthly precipitation changes would finally contribute to a tripolar pattern of EASM precipitation change at 1.5 and 2 °C warming. Corrected EASM intensity exhibits a slight difference

  16. Holocene environmental change and archaeology, Yangtze River Valley, China: Review and prospects

    Directory of Open Access Journals (Sweden)

    Li Wu

    2012-11-01

    Full Text Available Holocene environmental change and environmental archaeology are important components of an international project studying the human-earth interaction system. This paper reviews the progress of Holocene environmental change and environmental archaeology research in the Yangtze River Valley over the last three decades, that includes the evolution of large freshwater lakes, Holocene transgression and sea-level changes, Holocene climate change and East Asian monsoon variation, relationship between the rise and fall of primitive civilizations and environmental changes, cultural interruptions and palaeoflood events, as well as relationship between the origin of agriculture and climate change. These research components are underpinned by the dating of lacustrine sediments, stalagmites and peat to establish a chronology of regional environmental and cultural evolution. Interdisciplinary and other environment proxy indicators need to be used in comparative studies of archaeological site formation and natural sedimentary environment in the upper, middle and lower reaches of the Yangtze River Valley. Modern technology such as remote sensing, molecular bioarchaeology, and virtual reality, should be integrated with currently used dating, geochemical, sedimentological, and palaeobotanical methods of analysis in environmental archaeology macro- and micro-studies, so as to provide a greater comprehensive insight into Holocene environmental and cultural interaction and change in the Yangtze River Valley area.

  17. Holocene moisture variations over the arid central Asia revealed by a comprehensive sand-dune record from the central Tian Shan, NW China

    Science.gov (United States)

    Long, Hao; Shen, Ji; Chen, Jianhui; Tsukamoto, Sumiko; Yang, Linhai; Cheng, Hongyi; Frechen, Manfred

    2017-10-01

    Arid central Asia (ACA) is one of the largest arid (desert) areas in the world, and its climate is dominated by the westerlies. In this study, we examined sand dune evolution from the Bayanbulak Basin in the Tian Shan (Xinjiang, NW China), aiming to infer the Holocene moisture history of the ACA. Combined with stratigraphic observation and environmental proxies analysis (grain size, magnetic susceptibility and total organic content), large numbers of luminescence ages from multiple sites (eight sections, 79 samples) were applied to reconstruct the evolution of the sand dune accumulation in the study basin. The overall results imply very dry conditions characterized by sand dune accumulation at ∼12-6.5 ka, a wet interval between ∼6.5 and 0.8 ka when soil formation occurred, and decreased moisture during the last 0.8 ka. This moisture variation pattern is generally consistent with that inferred from many lacustrine records in the core zone of ACA, suggesting a widespread dry period in the early-to-middle Holocene and relatively wet middle-to-late Holocene. Thus, the moisture history derived from the current sand dune system contrasts with that in Asian monsoon areas, which are characterized by a strong monsoon (high precipitation) in the early and mid-Holocene and a weak monsoon (low precipitation and dry climate) during the late Holocene. Our results strongly suggest that the winter solar insolation and the external boundary conditions such as atmospheric CO2 concentration, ice sheets, and meltwater fluxes, have been major influential factors triggering the Holocene moisture evolution in the core zone of ACA.

  18. Holocene aridification of India

    Science.gov (United States)

    Ponton, C.; Giosan, L.; Eglinton, T.I.; Fuller, D.Q.; Johnson, J.E.; Kumar, P.; Collett, T.S.

    2012-01-01

    Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long-term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity-adapted vegetation from ???4,000 until 1,700 years ago followed by the persistence of aridity-adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub-millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ???4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water-conservation technology in south India. Copyright 2012 by the American Geophysical Union.

  19. Equatorward dispersion of a high-latitude volcanic plume and its relation to the Asian summer monsoon: a case study of the Sarychev eruption in 2009

    Science.gov (United States)

    Wu, Xue; Griessbach, Sabine; Hoffmann, Lars

    2017-11-01

    Tropical volcanic eruptions have been widely studied for their significant contribution to stratospheric aerosol loading and global climate impacts, but the impact of high-latitude volcanic eruptions on the stratospheric aerosol layer is not clear and the pathway of transporting aerosol from high latitudes to the tropical stratosphere is not well understood. In this work, we focus on the high-latitude volcano Sarychev (48.1° N, 153.2° E), which erupted in June 2009, and the influence of the Asian summer monsoon (ASM) on the equatorward dispersion of the volcanic plume. First, the sulfur dioxide (SO2) emission time series and plume height of the Sarychev eruption are estimated with SO2 observations of the Atmospheric Infrared Sounder (AIRS) and a backward trajectory approach using the Lagrangian particle dispersion model Massive-Parallel Trajectory Calculations (MPTRAC). Then, the transport and dispersion of the plume are simulated using the derived SO2 emission time series. The transport simulations are compared with SO2 observations from AIRS and validated with aerosol observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). The MPTRAC simulations show that about 4 % of the sulfur emissions were transported to the tropical stratosphere within 50 days after the beginning of the eruption, and the plume dispersed towards the tropical tropopause layer (TTL) through isentropic transport above the subtropical jet. The MPTRAC simulations and MIPAS aerosol data both show that between the potential temperature levels of 360 and 400 K, the equatorward transport was primarily driven by anticyclonic Rossby wave breaking enhanced by the ASM in boreal summer. The volcanic plume was entrained along the anticyclone flows and reached the TTL as it was transported southwestwards into the deep tropics downstream of the anticyclone. Further, the ASM anticyclone influenced the pathway of aerosols by isolating an aerosol hole inside of the ASM, which

  20. Coral Geochemical Proxy Records Of The East Asian Winter Monsoon And Hydrological Conditions In The Central Vietnam From 1978-2004 AD

    Science.gov (United States)

    Chang, C.; Shen, C.; Chen, Y.; Chiang, H.; Lam, D. D.; Ngai, N.

    2007-12-01

    Monthly-resolution geochemical proxies, including δ18O, δ13C, Sr/Ca, and Ba/Ca, in a living Porites coral head, collected from Son Tra Island, a near-shore island located at the north tip of Vung Da Nang Bay, central Vietnam (16°12'59.4", 108°1'57.1"), was used to quantitatively reconstruct records of sea surface temperature (SST), sea surface salinity (SSS), seasonality of rainfall, and regional terrestrial input during a period of 1978-2004 AD. By comparing the 1/4-century geochemical data, five features are exhibited. (1) The coral Sr/Ca-inferred summer SSTs correspond well with the 1°x1° instrumental data to suggest that the regional SST record can be retrieved from this local coral head. (2) Interannual variation of coral winter SST data does not follow regional instrumental values. The harmonic phenomenon between coral inferred winter SST dynamic and the surface pressure difference, between the southern South China Sea (SCS) (0-10°N, 105-115°E) and the northern SCS (22.5-32.5°N, 112-122°E), indicating that the cold local SST induced by East Asian winter monsoon was addressed in the Son Tra coral. (3) 1‰ seasonal anomaly of δ18O residual (Δδ18O) suggests a 2-4-psu seasonal salinity change between dry and wet seasons. (4) The synchronous intra-annual changes of δ18O and Ba/Ca data suggest that the rainy season is from late summer to winter, which is consistent with the meteorological record. (5) The high Ba/Ca background level of 10 μmol/mol in 1992-2004, 2-3 times larger than the averaged value of 4 μmol/mol in 1978-1992, indicates an enhanced terrestrial sediment discharge into the bay over the past 10 years. Ba records probably reflect an impact of human activity on hydrological change since the Vietnam War.

  1. Methyl chloride in the UT/LS observed by CARIBIC: global distribution, Asian summer monsoon outflow, and use as a tracer for tropical air

    Science.gov (United States)

    Baker, A. K.; Umezawa, T.; Oram, D.; Sauvage, C.; Rauthe-Schoech, A.; Montzka, S. A.; Zahn, A.; Brenninkmeijer, C. A. M.

    2014-12-01

    We present spatiotemporal variations of methyl chloride (CH3Cl) in the UT/LS observed mainly by the CARIBIC passenger aircraft for the years 2005-2011. The CH3Cl mixing ratio in the UT over Europe was higher than that observed at a European surface baseline station year-round, indicative of a persistent positive vertical gradient at NH mid latitudes. A series of flights over Africa and South Asia show that CH3Cl mixing ratios increase toward tropical latitudes, and the observed UT CH3Cl level over these two regions and the Atlantic was higher than that measured at remote surface sites. Strong emissions of CH3Cl in the tropics combined with meridional transport through the UT may explain such vertical and latitudinal gradients. Comparisons with CO data indicate that non-combustion sources in the tropics dominantly contribute to forming the latitudinal gradient of CH3Cl in the UT. We also observed elevated CH3Cl and CO in air influenced by biomass burning in South America and Africa, and the enhancement ratios derived for CH3Cl to CO in those regions agree with previous observations. In contrast, correlations indicate a high CH3Cl to CO ratio of 2.9±0.5 ppt ppb-1 in the Asian summer monsoon anticyclone and domestic biofuel emissions in South Asia are inferred to be responsible. We estimated CH3Cl emissions from South Asia to be 134±23 Gg Cl yr-1, which is higher than a previous estimate due to the higher CH3Cl to CO ratio observed in this study. We also examine the use of CH3Cl as a tracer of tropical tropospheric air in the LMS, where we identified air masses with elevated CH3Cl that were however stratospheric in terms of N2O. Back trajectories suggest recent low-latitude origins of such air masses in early summer. In this season, high CH3Cl LMS air shows a clear branch connecting stratospheric and tropical tropospheric air on N2O-CH3Cl scatterplots. This distinct feature vanishes in late summer when the LMS is ventilated by tropospheric air.

  2. Fluvial incision by the Qingyijiang River on the northern fringe of Mt. Huangshan, eastern China: Responses to weakening of the East Asian summer monsoon

    Science.gov (United States)

    Hu, Chunsheng; Liu, Shaochen; Hu, Chenqi; Xu, Guanglai; Zhou, Yingqiu

    2017-12-01

    This paper focuses on climatic and tectonic controls to determine their relative importance to the Quaternary fluvial incision by the Qingyijiang River, eastern China. The Qingyijiang, which is one of longest tributaries of the lower Yangtze River, drains the northern piedmont of Mt. Huangshan. A field survey focused on three natural sections of the Qingyijiang in the Jingxian basin, where a well-preserved sequence of one alluvial platform (P) and three fluvial terraces (T3, T2, and T1) is presented. The heights of the platform and the terraces above river level are 65, 40, 20, and 7 m respectively. In this study, electron spin resonance (ESR), optical stimulated luminescence (OSL), and palaeomagnetic dating were applied to reconstruct the fluvial incision history of the Qingyijiang and evaluate the possible influence of tectonic uplift and/or climate change on the fluvial incision. The main results show that (1) the ages of P, T3, T2, and T1 were determined to be ∼ 1300, ∼ 900, ∼ 600, and ∼ 1.5 ka respectively, corresponding to four incision events in the Qingyijiang; (2) the East Asian summer monsoon (EASM) experienced four significant weakening events at 1300, 900, 600, and ∼ 1.5 ka, according to previous research. Correspondingly, we propose that four significant increased periods of regional precipitation occurred at 1300, 900, 600, and ∼ 1.5 ka in the study area because of the negative correlation between the intensity of the EASM and regional precipitation from 1960 to 2012; and (3) fluvial incision by the Qingyijiang arose as a result of the weakening of the EASM in combination with tectonic uplift, determined by matching fluvial incision history of the Qingyijiang with tectonic movement and EASM change. In addition, the weakening of the EASM climatically triggered fluvial incision by the Qingyijiang. This study supports the conclusion that major fluvial incision has been climatically triggered; however, it also suggests that the mechanism of

  3. Human Remains from the Pleistocene-Holocene Transition of Southwest China Suggest a Complex Evolutionary History for East Asians

    Science.gov (United States)

    Curnoe, Darren; Xueping, Ji; Herries, Andy I. R.; Kanning, Bai; Taçon, Paul S. C.; Zhende, Bao; Fink, David; Yunsheng, Zhu; Hellstrom, John; Yun, Luo; Cassis, Gerasimos; Bing, Su; Wroe, Stephen; Shi, Hong; Parr, William C. H.; Shengmin, Huang; Rogers, Natalie

    2012-01-01

    Background Later Pleistocene human evolution in East Asia remains poorly understood owing to a scarcity of well described, reliably classified and accurately dated fossils. Southwest China has been identified from genetic research as a hotspot of human diversity, containing ancient mtDNA and Y-DNA lineages, and has yielded a number of human remains thought to derive from Pleistocene deposits. We have prepared, reconstructed, described and dated a new partial skull from a consolidated sediment block collected in 1979 from the site of Longlin Cave (Guangxi Province). We also undertook new excavations at Maludong (Yunnan Province) to clarify the stratigraphy and dating of a large sample of mostly undescribed human remains from the site. Methodology/Principal Findings We undertook a detailed comparison of cranial, including a virtual endocast for the Maludong calotte, mandibular and dental remains from these two localities. Both samples probably derive from the same population, exhibiting an unusual mixture of modern human traits, characters probably plesiomorphic for later Homo, and some unusual features. We dated charcoal with AMS radiocarbon dating and speleothem with the Uranium-series technique and the results show both samples to be from the Pleistocene-Holocene transition: ∼14.3-11.5 ka. Conclusions/Significance Our analysis suggests two plausible explanations for the morphology sampled at Longlin Cave and Maludong. First, it may represent a late-surviving archaic population, perhaps paralleling the situation seen in North Africa as indicated by remains from Dar-es-Soltane and Temara, and maybe also in southern China at Zhirendong. Alternatively, East Asia may have been colonised during multiple waves during the Pleistocene, with the Longlin-Maludong morphology possibly reflecting deep population substructure in Africa prior to modern humans dispersing into Eurasia. PMID:22431968

  4. Little Ice Age wetting of interior Asian deserts and the rise of the Mongol Empire

    Science.gov (United States)

    Putnam, Aaron E.; Putnam, David E.; Andreu-Hayles, Laia; Cook, Edward R.; Palmer, Jonathan G.; Clark, Elizabeth H.; Wang, Chunzeng; Chen, Feng; Denton, George H.; Boyle, Douglas P.; Bassett, Scott D.; Birkel, Sean D.; Martin-Fernandez, Javier; Hajdas, Irka; Southon, John; Garner, Christopher B.; Cheng, Hai; Broecker, Wallace S.

    2016-01-01

    The degree to which warming of the planet will alter Asia's water resources is an important question for food, energy, and economic security. Here we present geological evidence, underpinned by radiometric dating and dendrochronology, and bolstered by hydrological modeling, indicating that wetter-than-present conditions characterized the core of the inner Asian desert belt during the Little Ice Age, the last major Northern Hemispheric cold spell of the Holocene. These wetter conditions accompanied northern mid-latitude cooling, glacier expansion, a strengthened/southward-shifted boreal jet, and weakened south Asian monsoons. We suggest that southward migration of grasslands in response to these wetter conditions aided the spread of Mongol Empire steppe pastoralists across Asian drylands. Conversely, net drying over the 20th century has led to drought that is unprecedented for the past ∼830 years, and that could intensify with further heating of the Asian continent.

  5. Centennial- to decadal-scale monsoon precipitation variations in the upper Hanjiang River region, China over the past 6650 years

    Science.gov (United States)

    Tan, Liangcheng; Cai, Yanjun; Cheng, Hai; Edwards, Lawrence R.; Gao, Yongli; Xu, Hai; Zhang, Haiwei; An, Zhisheng

    2018-01-01

    The upper Hanjiang River region is the recharge area of the middle route of South-to-North Water Transfer Project. The region is under construction of the Hanjiang-Weihe River Water Transfer Project in China. Monsoon precipitation variations in this region are critical to water resource and security of China. In this study, high-resolution monsoon precipitation variations were reconstructed in the upper Hanjiang River region over the past 6650 years from δ18O and δ13C records of four stalagmites in Xianglong cave. The long term increasing trend of stalagmite δ18O record since the middle Holocene is consistent with other speleothem records from monsoonal China. This trend follows the gradually decreasing Northern Hemisphere summer insolation, which indicates that solar insolation may control the orbital-scale East Asian summer monsoon (EASM) variations. Despite the declined EASM intensity since the middle Holocene, local precipitation may not have decreased remarkably, as revealed by the δ13C records. A series of centennial- to decadal-scale cyclicity was observed, with quasi-millennium-, quasi-century-, 57-, 36- and 22-year cycles by removing the long-term trend of stalagmite δ18O record. Increased monsoon precipitation during periods of 4390-3800 a BP, 3590-2960 a BP, 2050-1670 a BP and 1110-790 a BP had caused four super-floods in the upper reach of Hanjiang River. Dramatically dry climate existed in this region during the 5.0 ka and 2.8 ka events, coinciding with notable droughts in other regions of monsoonal China. Remarkably intensified and southward Westerly jet, together with weakened summer monsoon, may delay the onset of rainy seasons, resulting in synchronous decreasing of monsoon precipitation in China during the two events. During the 4.2 ka event and the Little Ice Age, the upper Hanjiang River region was wet, which was similar to the climate conditions in central and southern China, but was the opposite of drought observed in northern China. We

  6. OSL dating of fine-grained quartz from Holocene Yangtze delta sediments

    DEFF Research Database (Denmark)

    Sugisaki, Saiko; Buylaert, Jan-Pieter; Murray, Andrew

    2015-01-01

    Holocene flood events in the Yangtze River are associated with variations in East Asian Summer Monsoon (EASM) precipitation, and so Yangtze delta sediments may preserve information about the frequency and magnitude of EASM precipitation. These flood/drought cycles of the EASM directly affect...... the living standards of East Asian population. However, despite its importance, little chronological control is available for the Yangtze Delta sediments; because biogenic carbonate only occurs sporadically, it has proved the difficulty to discuss sedimentation mechanisms and rates in any detail. In 2013 two...... sediment cores (YD13-G3 and H1) were taken from the Yangtze subaqueous delta to investigate precipitation history. In this study, we investigate the potential of quartz OSL dating of the fine silt fraction (fine-grained quartz; 4-11 μm) from these cores to estimate the depositional age of the sediments. We...

  7. Evidence of Suess solar-cycle bursts in Holocene speleothem d18O records

    DEFF Research Database (Denmark)

    Knudsen, Mads Faurschou; Jacobsen, B. H.; Riisager, Peter

    2012-01-01

    Several studies indicate that changes in solar activity may have driven Holocene subtropical monsoon variability on decadal and centennial timescales, but the strength and nature of this link remains debated. In this study, we combine a recent mapping of the Holocene solar-cycle activity with four...... in driving centennial-scale changes in the hydrological cycle in the subtropics during the Holocene....

  8. Aerosol and monsoon climate interactions over Asia: AEROSOL AND MONSOON CLIMATE INTERACTIONS

    Energy Technology Data Exchange (ETDEWEB)

    Li, Zhanqing [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Lau, W. K. -M. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Ramanathan, V. [Department of Atmospheric and Climate Sciences, University of California, San Diego California USA; Wu, G. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Ding, Y. [National Climate Center, China Meteorological Administration, Beijing China; Manoj, M. G. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Liu, J. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Qian, Y. [Pacific Northwest National Laboratory, Richland Washington USA; Li, J. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Zhou, T. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Fan, J. [Pacific Northwest National Laboratory, Richland Washington USA; Rosenfeld, D. [Institute of Earth Sciences, Hebrew University, Jerusalem Israel; Ming, Y. [Geophysical Fluid Dynamic Laboratory, NOAA, Princeton New Jersey USA; Wang, Y. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena California USA; Huang, J. [College of Atmospheric Sciences, Lanzhou University, Lanzhou China; Wang, B. [Department of Atmospheric Sciences, University of Hawaii, Honolulu Hawaii USA; School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing China; Xu, X. [Chinese Academy of Meteorological Sciences, Beijing China; Lee, S. -S. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Cribb, M. [Department of Atmospheric and Oceanic Science and ESSIC, University of Maryland, College Park Maryland USA; Zhang, F. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Yang, X. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Zhao, C. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Takemura, T. [Research Institute for Applied Mechanics, Kyushu University, Fukuoka Japan; Wang, K. [State Key Laboratory of Earth Surface Processes and Resource Ecology and College of Global Change and Earth System Science, Beijing Normal University, Beijing China; Xia, X. [Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing China; Yin, Y. [School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing China; Zhang, H. [National Climate Center, China Meteorological Administration, Beijing China; Guo, J. [Chinese Academy of Meteorological Sciences, Beijing China; Zhai, P. M. [Chinese Academy of Meteorological Sciences, Beijing China; Sugimoto, N. [National Institute for Environmental Studies, Tsukuba Japan; Babu, S. S. [Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram India; Brasseur, G. P. [Max Planck Institute for Meteorology, Hamburg Germany

    2016-11-15

    Asian monsoons and aerosols have been studied extensively which are intertwined in influencing the climate of Asia. This paper provides a comprehensive review of ample studies on Asian aerosol, monsoon and their interactions. The region is the primary source of aerosol emissions of varies species, influenced by distinct weather and climatic regimes. On continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulation. The atmospheric thermodynamic state may also be altered by the aerosol serving as cloud condensation nuclei or ice nuclei. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of numerous monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcings of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

  9. Possible connection between the East Asian summer monsoon and a swing of the haze-fog-prone area in eastern China

    Science.gov (United States)

    Liu, Qian; Cao, Ziqi; Sheng, Lifang; Diao, Yina; Wang, Wencai; Zhou, Yang; Qiu, Jingyi

    2018-05-01

    The summer monsoon has recently been hypothesized to influence haze-fog events over China, but the detailed processes involved have yet to be determined. In the present study, we found that the haze-fog-prone area swings over eastern China during boreal summer (May to September), coinciding with the movement of the subtropical monsoon convergence belt (hereinafter referred to simply as the "convergence belt"). Further investigation showed that the convergence belt modulates the spatial distribution of the haze-fog-prone area by altering the regional atmospheric conditions. When the warm and wet summer monsoon air mass pushes northwards and meets with cold air, a frontal zone (namely, the convergence belt) forms. The ascent of warm and wet air along the front strengthens the atmospheric stability ahead of the frontal zone, while the descent of cold and dry air weakens the vertical diffusion at the same place. These processes result in an asymmetric distribution of haze-fog along the convergence belt. Based on the criterion of absolute stability and downdraft, these atmospheric conditions favorable for haze-fog are able to identify 57-79% of haze-fog-prone stations, and the anticipation accuracy is 61-71%. After considering the influence of air pollutants on haze-fog occurrence, the anticipation accuracy rises to 78-79%. Our study reveals a connection between local haze-fog weather phenomena and regional atmospheric conditions and large-scale circulation, and demonstrates one possible mechanism for how the summer monsoon influences the distribution of haze-fog in eastern China.

  10. Potential impact of carbonaceous aerosol on the upper troposphere and lower stratosphere (UTLS) and precipitation during Asian summer monsoon in a global model simulation

    KAUST Repository

    Fadnavis, Suvarna; Kalita, Gayatry; Kumar, K. Ravi; Gasparini, Blaž; Li, Jui-Lin Frank

    2017-01-01

    The model simulation shows that boundary layer aerosols are transported into the monsoon anticyclone by the strong monsoon convection from the Bay of Bengal, southern slopes of the Himalayas and the South China Sea. Doubling of emissions of both BC and OC aerosols over Southeast Asia (10° S–50° N, 65–155° E) shows that lofted aerosols produce significant warming (0.6–1 K) over the Tibetan Plateau (TP) near 400–200 hPa and instability in the middle/upper troposphere. These aerosols enhance radiative heating rates (0.02–0.03 K day−1) near the tropopause. The enhanced carbonaceous aerosols alter aerosol radiative forcing (RF) at the surface by −4.74 ± 1.42 W m−2, at the top of the atmosphere (TOA) by +0.37 ± 0.26 W m−2 and in the atmosphere by +5.11 ± 0.83 W m−2 over the TP and Indo-Gangetic Plain region (15–35° N, 80–110° E). Atmospheric warming increases vertical velocities and thereby cloud ice in the upper troposphere. Aerosol induced anomalous warming over the TP facilitates the relative strengthening of the monsoon Hadley circulation and increases moisture inflow by strengthening the cross-equatorial monsoon jet. This increases precipitation amounts over India (1–4 mm day−1) and eastern China (0.2–2 mm day−1). These results are significant at the 99 % confidence level.

  11. Aeolian processes during the Holocene in Gannan Region, Eastern Tibetan Plateau

    Science.gov (United States)

    Yang, S.; Cheng, T.; Li, S.; Liang, M.

    2016-12-01

    Aeolian desertification occurring in the Tibetan Plateau has received attention recently for it has become a severe environmental problem by accelerating the grassland degradation and eco-environment damage. The Gannan Region is located in the northeastern Tibetan Plateau with a mean altitude of 3500m. It is highly sensitive to global environmental change and human disturbance. Serious soil erosion and desertification and extensive land degradation have caused heavy eco-environmental impacts. To investigate the evolution of the desertification in Holocene in the Plateau is of great importance for understanding the desertification trend under the global changes in the Tibetan Plateau. Loess and aeolian sands is a key geological archive related to desertification processes and the past environment changes. In this study a typical 8.5m-thick loess-sands profile named MQQ, was selected at the Maqu city. It is situated on the first terrace (T1) of the Yellow River. Detailed accelerator mass spectrometry (AMS) 14C dating of bulk organic matter content has shown the Aeolian sediments of the MQQ section occurring since the early Holocene. the mass-specific frequency-dependent magnetic susceptibility (χfd) and grainsize records show a clear upward increase in the contents of superparamagnetic grains and fine fractions in grain size, which indicates a gradual wetting trend during the Holocene.The sediment rates change from very high in the early Holocene to low values after 8.2 ka. The wetting process can be divided into three steps: 10.0-8.2 ka, 8.2-3.0 ka and 3.0-present. It indicates that the climate in the eastern Tibetan Plateau was dry during the early Holocene. After that the climate was getting wet gradually. The variations of the westerlies and the Asian monsoon may cause the environmental change in this region.

  12. Seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in the southern South China Sea under the influence of the East Asian monsoon

    Science.gov (United States)

    Zhou, L.; Tan, Y.; Huang, L.; Hu, Z.; Ke, Z.

    2015-11-01

    To examine seasonal and size-dependent variations in the phytoplankton growth and microzooplankton grazing in oligotrophic tropical waters under the influence of seasonal reversing monsoon, dilution experiments were conducted during the summer of 2009 (21 May to 9 June) and winter 2010 (9 to 18 November) in the southern South China Sea (SSCS). The results showed that environmental variables, phytoplankton biomass, phytoplankton growth rate (μ), microzooplankton grazing rate (m), and correlationship (coupling) between the μ and m, rather than the microzooplankton grazing impact on phytoplankton (m/μ) significantly varied between the two seasons. Higher relative preference index (RPI) for the larger-sized (> 3 μm) phytoplankton than pico-phytoplankton (intermittent arrivals of the northeast winter monsoon could lead to the low μ and m, and the decoupling between the μ and m in the SSCS, through influencing nutrient supply to the surface water, and inducing surface seawater salinity decrease. The low m/μ (waters such as that of the SSCS.

  13. Changes in the Indian summer monsoon intensity in Sri Lanka during the last 30 ky - A multiproxy record from a marine sediment core.

    Science.gov (United States)

    Ranasinghage, P. N.; Nanayakkara, N. U.; Kodithuwakku, S.; Siriwardana, S.; Luo, C.; Fenghua, Z.

    2016-12-01

    Indian monsoon plays a vital role in determining climate events happening in the Asian region. There is no sufficient work in Sri Lanka to fully understand how the summer monsoonal variability affected Sri Lanka during the quaternary. Sri Lanka is situated at an ideal location with a unique geography to isolate Indian summer monsoon record from iris counterpart, Indian winter monsoon. Therefore, this study was carried out to investigate its variability and understand the forcing factors. For this purpose a 1.82 m long gravity core, extracted from western continental shelf off Colombo, Sri Lanka by Shiyan 1 research vessel, was used. Particle size, chemical composition and colour reflectance were measured using laser particle size analyzer at 2 cm resolution, X-Ray Fluorescence spectrometer (XRF) at 2 cm resolution, and color spectrophotometer at 1 cm resolution respectively. Radio carbon dating of foraminifera tests by gas bench technique yielded the sediment age. Finally, principal component analysis (PCA) of XRF and color reflectance (DSR) data was performed to identify groups of correlating elements and mineralogical composition of sediments. Particle size results indicate that Increasing temperature and strengthening monsoonal rainfall after around 18000 yrs BP, at the end of last glacial period, enhanced chemical weathering over physical weathering. Proxies for terrestrial influx (XRF PC1, DSR PC1) and upwelling and nutrient supply driven marine productivity (XRF PC3 and DSR PC2) indicate that strengthening of summer monsoon started around 15000 yrs BP and maximized around 8000-10000 yrs BP after a short period of weakening during Younger Dryas (around 11000 yrs BP). The 8.2 cold event was recorded as a period of low terrestrial influx indicating weakening of rainfall. After that terrestrial input was low till around 2000 yrs BP indicating decrease in rainfall. However, marine productivity remained increasing throughout the Holocene indicating an increase in

  14. Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification

    Directory of Open Access Journals (Sweden)

    B. Gaye

    2018-01-01

    Full Text Available At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST and δ15N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ15N values of 4–7 ‰ during the last glacial maximum (LGM and stadials (Younger Dryas and Heinrich events suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs had elevated δ15N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ15N values  >  6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ15N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ15N values are lower during the mid-Holocene (4.2–8.2 ka BP compared to the late Holocene ( <  4.2 ka BP due to stronger ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ15N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position

  15. The asymmetric effects of El Niño and La Niña on the East Asian winter monsoon and their simulation by CMIP5 atmospheric models

    Science.gov (United States)

    Guo, Zhun; Zhou, Tianjun; Wu, Bo

    2017-02-01

    El Niño-Southern Oscillation (ENSO) events significantly affect the year-by-year variations of the East Asian winter monsoon (EAWM). However, the effect of La Niña events on the EAWM is not a mirror image of that of El Niño events. Although the EAWM becomes generally weaker during El Niño events and stronger during La Niña winters, the enhanced precipitation over the southeastern China and warmer surface air temperature along the East Asian coastline during El Niño years are more significant. These asymmetric effects are caused by the asymmetric longitudinal positions of the western North Pacific (WNP) anticyclone during El Niño events and the WNP cyclone during La Niña events; specifically, the center of the WNP cyclone during La Niña events is westward-shifted relative to its El Niño counterpart. This central-position shift results from the longitudinal shift of remote El Niño and La Niña anomalous heating, and asymmetry in the amplitude of local sea surface temperature anomalies over the WNP. However, such asymmetric effects of ENSO on the EAWM are barely reproduced by the atmospheric models of Phase 5 of the Coupled Model Intercomparison Project (CMIP5), although the spatial patterns of anomalous circulations are reasonably reproduced. The major limitation of the CMIP5 models is an overestimation of the anomalous WNP anticyclone/cyclone, which leads to stronger EAWM rainfall responses. The overestimated latent heat flux anomalies near the South China Sea and the northern WNP might be a key factor behind the overestimated anomalous circulations.

  16. On the Holocene evolution of the Ayeyawady megadelta

    Directory of Open Access Journals (Sweden)

    L. Giosan

    2018-06-01

    Full Text Available The Ayeyawady delta is the last Asian megadelta whose evolution has remained essentially unexplored so far. Unlike most other deltas across the world, the Ayeyawady has not yet been affected by dam construction, providing a unique view on largely natural deltaic processes benefiting from abundant sediment loads affected by tectonics and monsoon hydroclimate. To alleviate the information gap and provide a baseline for future work, here we provide a first model for the Holocene development of this megadelta based on drill core sediments collected in 2016 and 2017, dated with radiocarbon and optically stimulated luminescence, together with a reevaluation of published maps, charts and scientific literature. Altogether, these data indicate that Ayeyawady is a mud-dominated delta with tidal and wave influences. The sediment-rich Ayeyawady River built meander belt alluvial ridges with avulsive characters. A more advanced coast in the western half of the delta (i.e., the Pathein lobe was probably favored by the more western location of the early course of the river. Radiogenic isotopic fingerprinting of the sediment suggests that the Pathein lobe coast does not receive significant sediment from neighboring rivers. However, the eastern region of the delta (i.e., Yangon lobe is offset inland and extends east into the mudflats of the Sittaung estuary. Wave-built beach ridge construction during the late Holocene, similar to several other deltas across the Indian monsoon domain, suggests a common climatic control on monsoonal delta morphodynamics through variability in discharge, changes in wave climate or both. Correlation of the delta morphological and stratigraphic architecture information on land with the shelf bathymetry, as well as its tectonic, sedimentary and hydrodynamic characteristics, provides insight on the peculiar growth style of the Ayeyawady delta. The offset between the western Pathein lobe and the eastern deltaic coast appears to be driven

  17. Fluctuations in the East Asian monsoon recorded by pollen assemblages in sediments from the Japan Sea off the southwestern coast of Hokkaido, Japan, from 4.3 Ma to the present

    Science.gov (United States)

    Igarashi, Yaeko; Irino, Tomohisa; Sawada, Ken; Song, Lu; Furota, Satoshi

    2018-04-01

    We reconstructed fluctuations in the East Asian monsoon and vegetation in the Japan Sea region since the middle Pliocene based on pollen data obtained from sediments collected by the Integrated Ocean Drilling Program off the southwestern coast of northern Japan. Taxodiaceae conifers Metasequoia and Cryptomeria and Sciadopityacere conifer Sciadopitys are excellent indicators of a humid climate during the monsoon. The pollen temperature index (Tp) can be used as a proxy for relative air temperature. Based on changes in vegetation and reconstructed climate over a period of 4.3 Ma, we classified the sediment sequence into six pollen zones. From 4.3 to 3.8 Ma (Zone 1), the climate fluctuated between cool/moist and warm/moist climatic conditions. Vegetation changed between warm temperate mixed forest and cool temperate conifer forest. The Neogene type tree Carya recovered under a warm/moist climate. The period from 3.8 to 2.5 Ma (Zone 2) was characterized by increased Metasequoia pollen concentration. Warm temperate mixed forest vegetation developed under a cool/moist climate. The period from 2.5 to 2.2 Ma (Zone 3) was characterized by an abrupt increase in Metasequoia and/or Cryptomeria pollen and a decrease in warm broadleaf tree pollen, indicating a cool/humid climate. The Zone 4 period (2.2-1.7 Ma) was characterized by a decrease in Metasequoia and/or Cryptomeria pollen and an increase in cool temperate conifer Picea and Tsuga pollen, indicating a cool/moist climate. The period from 1.7 to 0.3 Ma (Zone 5) was characterized by orbital-scale climate fluctuations. Cycles of abrupt increases and decreases in Cryptomeria and Picea pollen and in Tp values indicated changes between warm/humid and cold/dry climates. The alpine fern Selaginella selaginoides appeared as of 1.6 Ma. Vegetation alternated among warm mixed, cool mixed, and cool temperate conifer forests. Zone 6 (0.3 Ma to present) was characterized by a decrease in Cryptomeria pollen. The warm temperate broadleaf

  18. Observed variability of summer precipitation pattern and extreme events in East China associated with variations of the East Asian summer monsoon: VARIABILITY OF SUMMER PRECIPITATION AND EXTREME EVENT IN EAST CHINA

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lei [School of Atmospheric Sciences, Nanjing University, China; Pacific Northwest National Laboratory, Richland WA USA; Qian, Yun [Pacific Northwest National Laboratory, Richland WA USA; Zhang, Yaocun [School of Atmospheric Sciences, Nanjing University, China; Zhao, Chun [Pacific Northwest National Laboratory, Richland WA USA; Leung, L. Ruby [Pacific Northwest National Laboratory, Richland WA USA; Huang, Anning [School of Atmospheric Sciences, Nanjing University, China; Xiao, Chuliang [Cooperative Institute for Limnology and Ecosystems Research, School of Natural Resources and Environment, University of Michigan, Ann Arbor MI USA

    2015-11-09

    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.

  19. The Indian Monsoon

    Indian Academy of Sciences (India)

    The word 'monsoon' is derived from the Arabic word 'mausam' for season and the distinguishing attribute of ... lance, the word monsoon is used for the rainfall in the rainy season. In this article, I discuss the ..... [1] C S Ramage, Monsoon meteorology, International Geophysics Series,. Academic Press, San Diego, California ...

  20. AMS 14 C dating controlled records of monsoon and Indonesian throughflow variability from the eastern Indian Ocean of the past 32,000 years

    Science.gov (United States)

    Li, Z. Y.; Chen, M. T.; Shi, X.; Liu, S.; Wang, H.

    2015-12-01

    Zi-Ye Li a, Min-Te Chen b, Hou-Jie Wang a, Sheng-Fa Liu c, Xue-Fa Shi ca College of Marine Geosciences, Ocean University of China, Qingdao 266100, P.R. Chinab Institute of Applied Geosciences, National Taiwan Ocean University, Keelung, Taiwan 20224, ROCc First Institute of Oceanography, SOA, Qingdao 266100, P.R. China Indonesian throughflow (ITF) is one of the most important currents responsible for transporting heat and moisture from the western Pacific to the Indian Oceans. The ITF is also well-known as effectively in modulating the global climate change with the interactions among ENSO and Asian monsoons. Here we present an AMS 14C dating controlled sea surface temperature (SST) record from core SO184-10043 (07°18.57'S, 105°03.53'E), which was retrieved from 2171m water depth at a north-south depression located at the southeastern offshore area of Sumatera in the eastern Indian Ocean. Based on our high-resolution SST using Mg/Ca analyses based on planktonic foraminifera shells of Globigerinoides ruber and alkenone index, U k'37-SST, oxygen isotope stratigraphy, and AMC 14C age-controls, our records show that, during the past 32,000 years, the SSTs were decreased which imply weaker ITF during Marine Isotope Stage (MIS) 2 and 3. The weaker UTF may respond to strengthened northeast monsoon during the boreal winter. During 21 to 15ka, the southeast monsoon had been stronger and the northeast monsoon was relatively weaker. During 15 to 8ka, rapid sea level rising may allow the opening of the gateways in the Makassar Strait and Lombok Strait that may have further strengthened the ITF. During the early Holocene, the northeast and southeast monsoons seem to be both strengthened. We will discuss the implications of the hydrographic variability and their age uncertainties in this paper during the meeting.

  1. Dirtier Air from a Weaker Monsoon

    Science.gov (United States)

    Chin, Mian

    2012-01-01

    The level of air pollution in China has much increased in the past decades, causing serious health problems. Among the main pollutants are aerosols, also known as particulate matter: tiny, invisible particles that are suspended in the air. These particles contribute substantially to premature mortality associated with cardiopulmonary diseases and lung cancer1. The increase of the aerosol level in China has been commonly attributed to the fast rise in pollutant emissions from the rapid economic development in the region. However, writing in Geophysical Research Letters, Jianlei Zhu and colleagues2 tell a different side of the story: using a chemical transport model and observation data, they show that the decadal scale weakening of the East Asian summer monsoon has also contributed to the increase of aerosol concentrations in China. The life cycle of atmospheric aerosols starts with its emission or formation in the atmosphere. Some aerosol components such as dust, soot and sea salt are emitted directly as particles to the atmosphere, but others are formed there by way of photochemical reactions. For example, sulphate and nitrate aerosols are produced from their respective precursor gases, sulphur dioxide and nitrogen oxides. Aerosol particles can be transported away from their source locations by winds or vertical motion of the air. Eventually, they are removed from the atmosphere by means of dry deposition and wet scavenging by precipitation. Measurements generally show that aerosol concentrations over Asia are lowest during the summer monsoon season3, because intense rainfall efficiently removes them from the air. The East Asian summer monsoon extends over subtropics and mid-latitudes. Its rainfall tends to concentrate in rain belts that stretch out for many thousands of kilometres and affect China, Korea, Japan and the surrounding area. Observations suggest that the East Asian summer monsoon circulation and precipitation have been in decline since the 1970s4. In

  2. South Asian high and Asian-Pacific-American climate teleconnection

    Science.gov (United States)

    Zhang, Peiqun; Song, Yang; Kousky, Vernon E.

    2005-11-01

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

  3. Holocene climate variability in arid Central Asia as revealed from high-resolution sedimentological and geochemical analyses of laminated sediments from Lake Chatyr Kol (Central Tian Shan, Kyrgyzstan)

    Science.gov (United States)

    Lauterbach, S.; Plessen, B.; Dulski, P.; Mingram, J.; Prasad, S.

    2013-12-01

    A pronounced trend from a predominantly wet climate during the early Holocene towards significantly drier conditions since the mid-Holocene, mainly attributed to the weakening of the Asian summer monsoon (ASM), is documented in numerous palaeoclimate records from the monsoon-influenced parts of Asia, e.g. the Tibetan Plateau and north- and southeastern China. In contrast, climate in the adjacent regions of mid-latitude arid Central Asia, located north and northwest of the Tibetan Plateau, is supposed to have been characterized by pronounced dry conditions during the early Holocene, wet conditions during the mid-Holocene and a rather moderate drying during the late Holocene, which is mainly attributed to the complex interplay between the mid-latitude Westerlies and the ASM. However, although mid-latitude Central Asia thus might represent a key region for the understanding of teleconnections between the ASM system and the Westerlies, knowledge about past climate development in this region is still ambiguous due to the limited number of high-resolution palaeoclimate records. Hence, new well-dated and highly resolved palaeoclimate records from this region are expected to provide important information about spatio-temporal changes in the regional interplay between Westerlies and ASM and thus aid the understanding of global climate teleconnections. As a part of the project CADY (Central Asian Climate Dynamics), aiming at reconstructing past climatic and hydrological variability in Central Asia, a sediment core of about 6.25 m length has been recovered from alpine Lake Chatyr Kol (40°36' N, 75°14' E, 3530 m a. s. l., surface area ~170 km2, maximum depth ~20 m), located in the Central Tian Shan of Kyrgyzstan. Sediment microfacies analysis on large-scale petrographic thin sections reveals continuously sub-mm scale laminated sediments throughout the record except for the uppermost ca. 60 cm. Microsedimentological characterization of these laminae, which are most probably

  4. Palaeoenvironmental implications of a Holocene sequence of lacustrine-peat sediments from the desert-loess transitional zone in Northern China

    Science.gov (United States)

    Jia, Feifei; Lu, Ruijie; Liu, Xiaokang; Zhao, Chao; Lv, Zhiqiang; Gao, Shangyu

    2018-05-01

    A high-resolution lacustrine-peat record from the desert-loess transitional zone in Northern China was obtained to reconstruct Holocene environmental change in the region. AMS 14C dates are used to provide a chronology. The results indicate that the site was a desert environment before 12.2 cal kyr BP, and was then occupied by a paleolake which started to shrink, with a wetland occurring from 6.2 to 3.0 cal kyr BP. Subsequently, the site became a seasonally water-filled depression. Based on the lithology and measurements of grain size and total organic carbon content, the climate changed from arid to humid at 12.2 cal kyr BP, and became more humid after 8.3 cal kyr BP. From 6.2 to 3.0 cal kyr BP, precipitation decreased but the climate remained at an optimum. After 3.0 cal kyr BP, the climate was dry overall but with several humid intervals. A comparison of paleoclimatic records from lacustrine and aeolian deposits from the region reveals a discrepancy about the nature of the early Holocene climate, and we conclude that this is because lacustrine sediments responded more sensitively to precipitation than aeolian deposits when the temperature was low. The environmental evolution of the region was synchronous with changes in the Asian summer monsoon (ASM), but temperature also played a key role in the early Holocene.

  5. Foraminiferal production and monsoonal upwelling in the Arabian sea: evidence from sediment traps

    Digital Repository Service at National Institute of Oceanography (India)

    Curry, W.B.; Ostermann, D.R.; Guptha, M.V.S.; Ittekkot, V.

    Planktonic foraminifera collected in sediment traps in the Arabian Sea during 1986 and 1987 responded to the southern Asian monsoon with changes in productivity, relative abundance of species and isotopic shell chemistry. Most species...

  6. The Aerosol-Monsoon Climate System of Asia

    Science.gov (United States)

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

    2012-01-01

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

  7. The Indian Monsoon

    Indian Academy of Sciences (India)

    user

    and led to the expectation that the impact of the monsoon on the ... a lead time of 10 days to a month for rainfall, temperature, etc., ... trying to predict, such as clouds or a monsoon depression (in ... occur because (i) the models are not perfect (involving many ... ally at many centres in the world, long-range predictions are.

  8. The Indian Monsoon

    Indian Academy of Sciences (India)

    Pacific Oceans, on subseasonal scales of a few days and on an interannual scale. ... over the Indian monsoon zone2 (Figure 3) during the summer monsoon .... each 500 km ×500 km grid over the equatorial Indian Ocean, Bay of Bengal and ...

  9. Large-Scale Control of the Arabian Sea Summer Monsoon Inversion and Low Clouds: A New Perspective

    Science.gov (United States)

    Wu, C. H.; Wang, S. Y.; Hsu, H. H.; Hsu, P. C.

    2016-12-01

    The Arabian Sea undergoes a so-called summer monsoon inversion that reaches the maximum intensity in August associated with a large amount of low-level clouds. The formation of inversion and low clouds was generally thought to be a local system influenced by the India-Pakistan monsoon advancement. New empirical and numerical evidence suggests that, rather than being a mere byproduct of the nearby monsoon, the Arabian Sea monsoon inversion is coupled with a broad-scale monsoon evolution connected across the Africa Sahel, South Asia, and the East Asia-western North Pacific (WNP). Several subseasonal variations occur in tandem: The eastward expansion of the Asian-Pacific monsoonal heating likely suppresses the India-Pakistan monsoon while enhancing low-level thermal inversion of Arabian Sea; the upper-tropospheric anticyclone in South Asia weakens in August smoothing zonal contrast in geopotential heights (10°N-30°N); the subtropical WNP monsoon trough in the lower troposphere that signals the revival of East Asian summer monsoon matures in August; the Sahel rainfall peaks in August accompanied by an intensified tropical easterly jet. The occurrence of the latter two processes enhances upper-level anticyclones over Africa and WNP and this, in turn, induces subsidence in between over the Arabian Sea. Numerical experiments demonstrate the combined effect of the African and WNP monsoonal heating on the enhancement of the Arabian Sea monsoon inversion. Connection is further found in the interannual and decadal variations between the East Asian-WNP monsoon and the Arabian Sea monsoon inversion. In years with reduced low clouds of Arabian Sea, the East Asian midlatitude jet stream remains strong in August while the WNP monsoon trough appears to be weakened. The Arabian Sea inversion (ridge) and WNP trough pattern which forms a dipole structure, is also found to have intensified since the 21st century.

  10. Sediment records of Yellow River channel migration and Holocene environmental evolution of the Hetao Plain, northern China

    Science.gov (United States)

    Wang, Jingzhong; Wu, Jinglu; Pan, Baotian; Jia, Hongjuan; Li, Xiao; Wei, Hao

    2018-05-01

    The origin and evolution of lakes in the Hetao Plain, northern China, were influenced by climate variation, channel migration, and human activity. We analyzed a suite of sediment cores from the region to investigate Yellow River channel migration and environmental change in this region over the Holocene. Short sediment cores show that environmental indicators changed markedly around CE 1850, a time that corresponds to flood events, when large amounts of river water accumulated in the western part of the Hetao Plain, giving rise to abundant small lakes. Multiple sediment variables (environmental proxies) from two long cores collected in the Tushenze Paleolake area show that sediments deposited between 12.0 and 9.0 cal ka BP were yellow clay, indicative of fluvial deposition and channel migration. From 9.0 to 7.5 cal ka BP, sand was deposited, reflecting a desert environment. From 7.5 to 2.2 cal ka BP, however, the sediments were blue-gray clay that represents lacustrine facies of Lake Tushenze, which owes its origin to an increase in strength of the East Asian monsoon. At about 2.2 cal ka BP, the north branch of the Yellow River was flooded, and the Tushenze Paleolake developed further. Around 2.0 cal ka BP, the paleolake shrank and eolian sedimentation was recorded. The analyzed sediment records are consistent with the written history from the region, which documents channel migration and environmental changes in the Hetao Plain over the Holocene.

  11. Validation of the HIRHAM-Simulated Indian Summer Monsoon Circulation

    Directory of Open Access Journals (Sweden)

    Stefan Polanski

    2010-01-01

    Full Text Available The regional climate model HIRHAM has been applied over the Asian continent to simulate the Indian monsoon circulation under present-day conditions. The model is driven at the lateral and lower boundaries by European reanalysis (ERA40 data for the period from 1958 to 2001. Simulations with a horizontal resolution of 50 km are carried out to analyze the regional monsoon patterns. The focus in this paper is on the validation of the long-term summer monsoon climatology and its variability concerning circulation, temperature, and precipitation. Additionally, the monsoonal behavior in simulations for wet and dry years has been investigated and compared against several observational data sets. The results successfully reproduce the observations due to a realistic reproduction of topographic features. The simulated precipitation shows a better agreement with a high-resolution gridded precipitation data set over the central land areas of India and in the higher elevated Tibetan and Himalayan regions than ERA40.

  12. Large-scale control of the Arabian Sea monsoon inversion in August

    Science.gov (United States)

    Wu, Chi-Hua; Wang, S.-Y. Simon; Hsu, Huang-Hsiung

    2017-12-01

    The summer monsoon inversion in the Arabian Sea is characterized by a large amount of low clouds and August as the peak season. Atmospheric stratification associated with the monsoon inversion has been considered a local system influenced by the advancement of the India-Pakistan monsoon. Empirical and numerical evidence from this study suggests that the Arabian Sea monsoon inversion is linked to a broader-scale monsoon evolution across the African Sahel, South Asia, and East Asia-Western North Pacific (WNP), rather than being a mere byproduct of the India-Pakistan monsoon progression. In August, the upper-tropospheric anticyclone in South Asia extends sideways corresponding with the enhanced precipitation in the subtropical WNP, equatorial Indian Ocean, and African Sahel while the middle part of this anticyclone weakens over the Arabian Sea. The increased heating in the adjacent monsoon systems creates a suppression effect on the Arabian Sea, suggesting an apparent competition among the Africa-Asia-WNP monsoon subsystems. The peak Sahel rainfall in August, together with enhanced heating in the equatorial Indian Ocean, produces a critical effect on strengthening the Arabian Sea thermal inversion. By contrast, the WNP monsoon onset which signifies the eastward expansion of the subtropical Asian monsoon heating might play a secondary or opposite role in the Arabian Sea monsoon inversion.

  13. Reconstruction of the vegetation distribution of different topographic units of the Chinese Loess Plateau during the Holocene

    Science.gov (United States)

    Sun, Aizhi; Guo, Zhengtang; Wu, Haibin; Li, Qin; Yu, Yanyan; Luo, Yunli; Jiang, Wenying; Li, Xiaoqiang

    2017-10-01

    Soil erosion and related ecological restoration present a tremendous challenge to the socioeconomic development of the Chinese Loess Plateau (CLP). Although the Chinese government has addressed the problem of soil erosion via an afforestation programme, there have been several negative outcomes. One of the reasons for this is our incomplete understanding of the past natural vegetation distribution in the various topographic units of the CLP under different climate scenarios. Consequently, we used fossil pollen data from 41 sites from different topographic units, together with the biomization method, to reconstruct the Holocene vegetation distribution of the CLP. The results demonstrate significant differences in vegetation types between different topographic units: forest was distributed in mountainous areas, steppe was dominant in Yuan areas, and desert vegetation was distributed in the transition zone between loess and desert. The vegetation in the gully areas exhibited significant spatial differences during the mid-Holocene. In addition, the vegetation on the various topographic units was well-developed during the interval from 9 to 4 ka B.P., when regional moisture levels reached a maximum. This suggests that the East Asian Summer Monsoon was one of the main factors controlling the evolution of vegetation patterns during the Holocene. In addition, our results confirm that both topography and human activity were fundamental factors determining the vegetation distribution of the region. Against a background of ongoing global warming, we advocate a program of vegetation restoration including planting trees and shrubs in the mountainous areas, and promoting the growth of grasses in the Yuan areas and in the transitional zone between loess and desert. In the gully areas, the planting of trees and shrubs is appropriate for reducing soil erosion caused by human activities.

  14. Effects of large-scale deforestation on precipitation in the monsoon regions: remote versus local effects.

    Science.gov (United States)

    Devaraju, N; Bala, Govindasamy; Modak, Angshuman

    2015-03-17

    In this paper, using idealized climate model simulations, we investigate the biogeophysical effects of large-scale deforestation on monsoon regions. We find that the remote forcing from large-scale deforestation in the northern middle and high latitudes shifts the Intertropical Convergence Zone southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, and South Asia) and moderate precipitation increases in the Southern Hemisphere monsoon regions (South Africa, South America, and Australia). The magnitude of the monsoonal precipitation changes depends on the location of deforestation, with remote effects showing a larger influence than local effects. The South Asian Monsoon region is affected the most, with 18% decline in precipitation over India. Our results indicate that any comprehensive assessment of afforestation/reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation alongside the large local impacts on temperatures.

  15. Energetics and monsoon bifurcations

    Science.gov (United States)

    Seshadri, Ashwin K.

    2017-01-01

    Monsoons involve increases in dry static energy (DSE), with primary contributions from increased shortwave radiation and condensation of water vapor, compensated by DSE export via horizontal fluxes in monsoonal circulations. We introduce a simple box-model characterizing evolution of the DSE budget to study nonlinear dynamics of steady-state monsoons. Horizontal fluxes of DSE are stabilizing during monsoons, exporting DSE and hence weakening the monsoonal circulation. By contrast latent heat addition (LHA) due to condensation of water vapor destabilizes, by increasing the DSE budget. These two factors, horizontal DSE fluxes and LHA, are most strongly dependent on the contrast in tropospheric mean temperature between land and ocean. For the steady-state DSE in the box-model to be stable, the DSE flux should depend more strongly on the temperature contrast than LHA; stronger circulation then reduces DSE and thereby restores equilibrium. We present conditions for this to occur. The main focus of the paper is describing conditions for bifurcation behavior of simple models. Previous authors presented a minimal model of abrupt monsoon transitions and argued that such behavior can be related to a positive feedback called the `moisture advection feedback'. However, by accounting for the effect of vertical lapse rate of temperature on the DSE flux, we show that bifurcations are not a generic property of such models despite these fluxes being nonlinear in the temperature contrast. We explain the origin of this behavior and describe conditions for a bifurcation to occur. This is illustrated for the case of the July-mean monsoon over India. The default model with mean parameter estimates does not contain a bifurcation, but the model admits bifurcation as parameters are varied.

  16. Indian monsoon variability on millennial-orbital timescales.

    Science.gov (United States)

    Kathayat, Gayatri; Cheng, Hai; Sinha, Ashish; Spötl, Christoph; Edwards, R Lawrence; Zhang, Haiwei; Li, Xianglei; Yi, Liang; Ning, Youfeng; Cai, Yanjun; Lui, Weiguo Lui; Breitenbach, Sebastian F M

    2016-04-13

    The Indian summer monsoon (ISM) monsoon is critical to billions of people living in the region. Yet, significant debates remain on primary ISM drivers on millennial-orbital timescales. Here, we use speleothem oxygen isotope (δ(18)O) data from Bittoo cave, Northern India to reconstruct ISM variability over the past 280,000 years. We find strong coherence between North Indian and Chinese speleothem δ(18)O records from the East Asian monsoon domain, suggesting that both Asian monsoon subsystems exhibit a coupled response to changes in Northern Hemisphere summer insolation (NHSI) without significant temporal lags, supporting the view that the tropical-subtropical monsoon variability is driven directly by precession-induced changes in NHSI. Comparisons of the North Indian record with both Antarctic ice core and sea-surface temperature records from the southern Indian Ocean over the last glacial period do not suggest a dominant role of Southern Hemisphere climate processes in regulating the ISM variability on millennial-orbital timescales.

  17. A Temperature and Monsoon Record Derived from Environmental Tracers in the Groundwater of Northwest India

    Energy Technology Data Exchange (ETDEWEB)

    Wieser, M.; Aeschbach-Hertig, W.; Schneider, T. [Institute of Environmental Physics, University of Heidelberg, Heidelberg (Germany); Deshpande, R. D.; Gupta, S. K. [Physical Research Laboratory, Ahmedabad (India)

    2013-07-15

    A quantitative palaeoclimate record was derived from the aquifer system of the cambay Basin, gujarat, India, a region characterised by a semi arid, monsoon dominated climate. Stable isotopes generally increase with flow distance and {sup 14}C age, whereas noble gas temperatures (NGTs) show a decline with age, amounting to a difference of {approx}3.5{sup o}C between Holocene and last glacial samples. The paper focuses on the Holocene covariation of the climate proxies. Stable isotopes and excess air show consistent variations, confirming their interpretation as proxies for palaeohumidity. A group of early to mid Holocene samples depleted in stable isotopes and enriched in excess air indicates a phase of strong monsoon during the Holocene climate optimum. This is followed by a drying trend in the second half of the Holocene, and more humid conditions in the youngest part of the record. A temporary rise of NGT in the dry late Holocene may reflect a change in the soil temperature-air temperature relationship. (author)

  18. Monsoon onset over Kerala and pre monsoon rainfall peak

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Shenoi, S.S.C.; Shankar, D.

    and the monsoon onset date over Kerala was found to be 0.72, which was statistically significant. Thus, as is felt that the pre monsoon rainfall estimate from the satellite data can be used for predicting the monsoon onset over Kerala coast. The results...

  19. Causal evidence between monsoon and evolution of rhizomyine rodents.

    Science.gov (United States)

    López-Antoñanzas, Raquel; Knoll, Fabien; Wan, Shiming; Flynn, Lawrence J

    2015-03-11

    The modern Asian monsoonal systems are currently believed to have originated around the end of the Oligocene following a crucial step of uplift of the Tibetan-Himalayan highlands. Although monsoon possibly drove the evolution of many mammal lineages during the Neogene, no evidence thereof has been provided so far. We examined the evolutionary history of a clade of rodents, the Rhizomyinae, in conjunction with our current knowledge of monsoon fluctuations over time. The macroevolutionary dynamics of rhizomyines were analyzed within a well-constrained phylogenetic framework coupled with biogeographic and evolutionary rate studies. The evolutionary novelties developed by these rodents were surveyed in parallel with the fluctuations of the Indian monsoon so as to evaluate synchroneity and postulate causal relationships. We showed the existence of three drops in biodiversity during the evolution of rhizomyines, all of which reflected elevated extinction rates. Our results demonstrated linkage of monsoon variations with the evolution and biogeography of rhizomyines. Paradoxically, the evolution of rhizomyines was accelerated during the phases of weakening of the monsoons, not of strengthening, most probably because at those intervals forest habitats declined, which triggered extinction and progressive specialization toward a burrowing existence.

  20. Mid- to Late Holocene climate development in Central Asia as revealed from multi-proxy analyses of sediments from Lake Son Kol (Kyrgyzstan)

    Science.gov (United States)

    Lauterbach, Stefan; Dulski, Peter; Gleixner, Gerd; Hettler-Riedel, Sabine; Mingram, Jens; Plessen, Birgit; Prasad, Sushma; Schwalb, Antje; Schwarz, Anja; Stebich, Martina; Witt, Roman

    2013-04-01

    A mid-Holocene shift from predominantly wet to significantly drier climate conditions, attributed to the weakening of the Asian summer monsoon (ASM), is documented in numerous palaeoclimate records from the monsoon-influenced parts of Asia, e.g. the Tibetan Plateau and north- and southeastern China. In contrast, Holocene climate development in the arid regions of mid-latitude Central Asia, located north and northwest of the Tibetan Plateau, is less well-constrained but supposed to have been influenced by a complex interaction between the mid-latitude Westerlies and the ASM. Hence, well-dated and highly resolved palaeoclimate records from Central Asia might provide important information about spatio-temporal changes in the regional interplay between Westerlies and ASM and thus aid the understanding of global climate teleconnections. As a part of the project CADY (Central Asian Climate Dynamics), aiming at reconstructing past climatic and hydrological variability in Central Asia, several sediment cores were recovered from alpine Lake Son Kol (41° 48'N, 75° 12'E, 3016 m a. s. l.) in the Central Tian Shan of Kyrgyzstan. A radiocarbon-dated sediment sequence of 154.5 cm length, covering approximately the last 6000 years, was investigated by using a multi-proxy approach, including sedimentological, (bio)geochemical, isotopic and micropalaeontological analyses. Preliminary proxy data indicate hydrologically variable but predominantly wet conditions until ca. 5100 cal. a BP, characterized by the deposition of finely laminated organic-carbonatic sediments. In contrast to monsoonal Asia, where a distinct trend towards drier conditions is observed since the mid-Holocene, the hydrologically variable interval at Lake Son Kol was apparently followed by an only short-term dry episode between ca. 5100 and 4200 cal. a BP. This is characterized by a higher δD of the C29 n-alkanes, probably reflecting increased evapotranspiration. Also pollen, diatom and ostracod data point

  1. Simulation of the Holocene climate evolution in Nothern Africa: the termination of the African Humid Period.

    NARCIS (Netherlands)

    Renssen, H.; Brovkin, V.; Fichefet, T.; Goosse, H.

    2006-01-01

    The Holocene climate evolution in Northern Africa is studied in a 9000-yr-long transient simulation with a coupled atmosphere-ocean-vegetation model forced by changes in insolation and atmospheric greenhouse gas concentrations. The model simulates in the monsoonal domains a significant decrease in

  2. Measuring the monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Nair, R.R.

    that are constant enough to be used for navigation. But the monsoon also acts as a sign of the climatic times. Although its timing is remarkably regular, the intensity of its effects varies considerably from year to year. On top of natural variations in the strength...

  3. Tropical and Monsoonal Studies.

    Science.gov (United States)

    1988-01-01

    Duiing the cold surge event the balance of the 200 mb zonal momentum budget is between the zonal advecton of momentum and the coriolis, aceration ...over the South China Sea in the Malaysia ACKNOWLEDGEMENTS region during the winter monsoon, December 1973. Pure AppL Geophys., 115, 1303-1334. We wish

  4. The Indian Monsoon

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 13; Issue 3. The Indian Monsoon - Links to Cloud systems over the Tropical Oceans. Sulochana Gadgil. Series Article Volume 13 Issue 3 March 2008 pp 218-235. Fulltext. Click here to view fulltext PDF. Permanent link:

  5. Foretelling the Monsoon

    Indian Academy of Sciences (India)

    Relation between the continental TCZ and the TCZ over Equatorial Indian Ocean · Understanding year-to year (interannual) variation of the monsoon · Slide 40 · IMPACT OF EL NINO/LA NINA · Slide 42 · Variation of ISMR anomalies ( i.e. difference from the average value) normalized by std. deviation from 1979-2004.

  6. A humid early Holocene in Yemen interpreted from palaeoecology and taxonomy of freshwater ostracods

    Science.gov (United States)

    Mohammed, Munef; Frenzel, Peter; Keyser, Dietmar; Hussain, Fadhl; Abood, Abdulkareem; Sha'af, Abdulmajed; Alzara'e, Sadham; Alammari, Sakher

    2018-01-01

    Lake or marsh sediments in the Qa'a Jahran-Dhamār area indicate a period of higher moisture availability in the early Holocene of the highlands of Yemen. Forty-two marl-peat sediment samples from eight stratigraphic sections of that area have been collected and are examined for the first time for their ostracod associations. Eight species belonging to seven genera and four families are reported. Their ecological tolerances and preferences are used to investigate the climatic and environmental changes in the early to mid-Holocene. Our data are compared and correlated with previous archaeological results, particularly from the region of Qa'a Jahran (Dhamār) in the vicinity of the village of Beyt Nahmi. We conclude that the wettest period of the Holocene was from about 7900 to 7400 cal yr BP, when northwards incursion of the Indian Ocean Monsoon caused intensified monsoon precipitation over southern Arabia.

  7. The Monsoon Erosion Pump and the Indian Monsoon since Eocene

    Science.gov (United States)

    Giosan, L.

    2017-12-01

    Lack of consensus on the Neogene establishment and evolution of the Indian Monsoon is remarkable after half a century of research. Conflicting interpretations point toward the possibility of periodic decoupling between monsoon winds and monsoon precipitation. Here I introduce the concept of a monsoon erosion pump based on terrestrial and oceanic records reconstructed from recent NGHP and IODP drilling and spanning the last 34 million years in the Bay of Bengal, Arabian and Andaman Seas. From millennial to orbital to tectonic timescales, these records suggest that vegetation land cover interacts and modulates the regime of erosion and weathering under perennial but variable monsoonal rain conditions. Under this new proposed paradigm the Indian monsoon exhibits two distinct flavours during the Neogene that can be largely explained by its heartbeat, or astronomical forcing, mediated by the global glacial state and interacting with the paleogeography of South Asia.

  8. Holocene evolution of a wave-dominated fan-delta: Godavari delta, India

    Science.gov (United States)

    Saito, Y.; Nageswara Rao, K.; Nagakumar, K.; Demudu, G.; Rajawat, A.; Kubo, S.; Li, Z.

    2013-12-01

    The Godavari delta is one of the world's largest wave-dominated deltas. The Godavari River arises in the Western Ghats near the west coast of India and drains an area of about 3.1x10^5 km^2, flowing about 1465 km southeast across the Indian peninsula to the Bay of Bengal. The Godavari delta consists of a gentle seaward slope from its apex (12 m elevation) at Rajahmundry and a coastal beach-ridge plain over a distance of about 75 km and covers ~5200 km^2 as a delta plain. The river splits into two major distributary channels, the Gautami and the Vasishta, at a barrage constructed in the mid-1800s. The coastal environment of the deltaic coast is microtidal (~1 m mean tidal range) and wave-dominated (~1.5 m mean wave height in the June-September SW monsoon season, ~0.8 m in the NE monsoon season). Models of the Holocene evolution of the Godavari delta have changed from a zonal progradation model (e.g. Nageswara Rao & Sadakata, 1993) to a truncated cuspate delta model (Nageswara Rao et al., 2005, 2012). Twelve borehole cores (340 m total length), taken in the coastal delta plain during 2010-2013, yielded more than 100 C-14 dates. Sediment facies and C-14 dates from these and previous cores and remote-sensing data support a new delta evolution model. The Holocene coastal delta plain is divided into two parts by a set of linear beach ridges 12-14 km landward from the present shoreline in the central part of the delta. The location of the main depocenter (lobe) has shifted during the Holocene from 1) the center to 2) the west, 3) east, 4) center, 5) west, and 6) east. The linear beach ridges separate the first three from the last three stages. These lobe shifts are controlled by river channel shifts near the apex. Just as the current linear shoreline of the central part of the delta and the concave-up nearshore topography are the result of coastal erosion of a cuspate delta, the linear beach ridges indicate a former eroded shoreline. An unconformity within the deltaic

  9. Glacial-interglacial water cycle, global monsoon and atmospheric methane changes

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Zhengtang; Wu, Haibin [Chinese Academy of Sciences, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Beijing (China); Zhou, Xin [Chinese Academy of Sciences, Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Beijing (China); University of Science and Technology of China, School of Earth and Space Sciences and Institute of Polar Environment, Hefei (China)

    2012-09-15

    The causes of atmospheric methane (CH{sub 4}) changes are still a major contention, in particular with regards to the relative contributions of glacial-interglacial cycles, monsoons in both hemispheres and the late Holocene human intervention. Here, we explore the CH{sub 4} signals in the Antarctic EPICA Dome C and Vostok ice records using the methods of timeseries analyses and correlate them with insolation and geological records to address these issues. The results parse out three distinct groups of CH{sub 4} signals attributable to different drivers. The first group ({proportional_to}80% variance), well tracking the marine {delta}{sup 18}O record, is attributable to glacial-interglacial modulation on the global water cycle with the effects shared by wetlands at all latitudes, from monsoonal and non-monsoonal regions in both hemispheres. The second group ({proportional_to}15% variance), centered at the {proportional_to}10-kyr semi-precession frequency, is linkable with insolation-driven tropical monsoon changes in both hemispheres. The third group ({proportional_to}5% variance), marked by millennial frequencies, is seemingly related with the combined effect of ice-volume and bi-hemispheric insolation changes at the precession bands. These results indicate that bi-hemispheric monsoon changes have been a constant driver of atmospheric CH{sub 4}. This mechanism also partially explains the Holocene CH{sub 4} reversal since {proportional_to}5 kyr BP besides the human intervention. In the light of these results, we propose that global monsoon can be regarded as a system consisting of two main integrated components, one primarily driven by the oscillations of Inter-Tropical Convergence Zone (ITCZ) in response to the low-latitude summer insolation changes, anti-phase between the two hemispheres (i.e. the ITCZ monsoon component); and another modulated by the glacial-interglacial cycles, mostly synchronous at the global scale (i.e. the glacial-interglacial monsoon

  10. Cyclone trends constrain monsoon variability during late Oligocene sea level highstands (Kachchh Basin, NW India)

    Science.gov (United States)

    Reuter, M.; Piller, W. E.; Harzhauser, M.; Kroh, A.

    2013-09-01

    Climate change has an unknown impact on tropical cyclones and the Asian monsoon. Herein we present a sequence of fossil shell beds from the shallow-marine Maniyara Fort Formation (Kachcch Basin) as a recorder of tropical cyclone activity along the NW Indian coast during the late Oligocene warming period (~ 27-24 Ma). Proxy data providing information about the atmospheric circulation dynamics over the Indian subcontinent at this time are important since it corresponds to a major climate reorganization in Asia that ends up with the establishment of the modern Asian monsoon system at the Oligocene-Miocene boundary. The vast shell concentrations are comprised of a mixture of parautochthonous and allochthonous assemblages indicating storm-generated sediment transport from deeper to shallow water during third-order sea level highstands. Three distinct skeletal assemblages were distinguished, each recording a relative storm wave base. (1) A shallow storm wave base is shown by nearshore molluscs, reef corals and Clypeaster echinoids; (2) an intermediate storm wave base depth is indicated by lepidocyclinid foraminifers, Eupatagus echinoids and corallinacean algae; and (3) a deep storm wave base is represented by an Amussiopecten bivalve-Schizaster echinoid assemblage. These wave base depth estimates were used for the reconstruction of long-term tropical storm intensity during the late Oligocene. The development and intensification of cyclones over the recent Arabian Sea is primarily limited by the atmospheric monsoon circulation and strength of the associated vertical wind shear. Therefore, since the topographic boundary conditions for the Indian monsoon already existed in the late Oligocene, the reconstructed long-term cyclone trends were interpreted to reflect monsoon variability during the initiation of the Asian monsoon system. Our results imply an active monsoon over the Eastern Tethys at ~ 26 Ma followed by a period of monsoon weakening during the peak of the late

  11. Holocene fire, vegetation, and climate dynamics inferred from charcoal and pollen record in the eastern Tibetan Plateau

    Science.gov (United States)

    Zhao, Wenwei; Zhao, Yan; Qin, Feng

    2017-10-01

    Understanding fire history and its driving mechanisms can provide valuable insights into present fire regime (intensity, severity and frequency), the interplay between vegetation and fire, and trigger of fire activities. Here we reconstruct the Holocene fire history in the Zoige Basin on the eastern Tibetan Plateau, on the basis of sedimentary micro-charcoal record over the last 10.0 ka (1 ka = 1000 cal yr BP) and discuss the influences of vegetation and climate on fire dynamics. Our results show that regional fire was active at 10.0-3.3 ka and a significant decrease in fire activity characterized the period after 3.3 ka. The high regional fire frequency at 10.0-3.3 ka is consistent with the forested landscape suggested by high affinity scores of cool mixed forest biome (mainly consisted of spruce), implying that fire dynamics during this period was generally controlled by the variations of arboreal biomass and summer temperature. During 6.3-4.6 ka the prevailing Asian summer monsoon provided increased moisture to this region and thus suppressed fire activities to an extent, despite the availability of abundant biomass. Declined tree biomass after 3.3 ka probably accounted for the decreased fire activities. In addition, two successive fire events at ca. 3.5-3.3 ka were likely responsible for the subsequent abrupt decline of forest components in the landscape.

  12. Volcanic influence on centennial to millennial Holocene Greenland temperature change.

    Science.gov (United States)

    Kobashi, Takuro; Menviel, Laurie; Jeltsch-Thömmes, Aurich; Vinther, Bo M; Box, Jason E; Muscheler, Raimund; Nakaegawa, Toshiyuki; Pfister, Patrik L; Döring, Michael; Leuenberger, Markus; Wanner, Heinz; Ohmura, Atsumu

    2017-05-03

    Solar variability has been hypothesized to be a major driver of North Atlantic millennial-scale climate variations through the Holocene along with orbitally induced insolation change. However, another important climate driver, volcanic forcing has generally been underestimated prior to the past 2,500 years partly owing to the lack of proper proxy temperature records. Here, we reconstruct seasonally unbiased and physically constrained Greenland Summit temperatures over the Holocene using argon and nitrogen isotopes within trapped air in a Greenland ice core (GISP2). We show that a series of volcanic eruptions through the Holocene played an important role in driving centennial to millennial-scale temperature changes in Greenland. The reconstructed Greenland temperature exhibits significant millennial correlations with K + and Na + ions in the GISP2 ice core (proxies for atmospheric circulation patterns), and δ 18 O of Oman and Chinese Dongge cave stalagmites (proxies for monsoon activity), indicating that the reconstructed temperature contains hemispheric signals. Climate model simulations forced with the volcanic forcing further suggest that a series of large volcanic eruptions induced hemispheric-wide centennial to millennial-scale variability through ocean/sea-ice feedbacks. Therefore, we conclude that volcanic activity played a critical role in driving centennial to millennial-scale Holocene temperature variability in Greenland and likely beyond.

  13. Monsoon Convection during the South China Sea Monsoon Experiment Observed from Shipboard Radar and the TRMM Satellite

    Science.gov (United States)

    Rickenbach, Tom; Cifelli, Rob; Halverson, Jeff; Kucera, Paul; Atkinson, Lester; Fisher, Brad; Gerlach, John; Harris, Kathy; Kaufman, Cristina; Liu, Ching-Hwang; hide

    1999-01-01

    A main goal of the recent South China Sea Monsoon Experiment (SCSMEX) was to study convective processes associated with the onset of the Southeast Asian summer monsoon. The NASA TOGA C-band scanning radar was deployed on the Chinese research vessel Shi Yan #3 for two 20 day cruises, collecting dual-Doppler measurements in conjunction with the BMRC C-Pol dual-polarimetric radar on Dongsha Island. Soundings and surface meteorological data were also collected with an NCAR Integrated Sounding System (ISS). This experiment was the first major tropical field campaign following the launch of the Tropical Rainfall Measuring Mission (TRMM) satellite. These observations of tropical oceanic convection provided an opportunity to make comparisons between surface radar measurements and the Precipitation Radar (PR) aboard the TRMM satellite in an oceanic environment. Nearly continuous radar operations were conducted during two Intensive Observing Periods (IOPS) straddling the onset of the monsoon (5-25 May 1998 and 5-25 June 1998). Mesoscale lines of convection with widespread regions of both trailing and forward stratiform precipitation were observed during the active monsoon periods in a southwesterly flow regime. Several examples of mesoscale convection will be shown from ship-based and spacebome radar reflectivity data during times of TRMM satellite overpasses. Further examples of pre-monsoon convection, characterized by isolated cumulonimbus and shallow, precipitating congestus clouds, will be discussed. A strong waterspout was observed very near the ship from an isolated cell in the pre-monsoon period, and was well documented with photography, radar, sounding, and sounding data.

  14. Decoupled warming and monsoon precipitation in East Asia over the last deglaciation

    NARCIS (Netherlands)

    Peterse, F.; Prins, M.A.; Beets, C.J.; Troelstra, S.R.; Zheng, H.B.; Gu, Z.Y.; Schouten, S.; Sinninghe Damsté, J.S.

    2011-01-01

    Our understanding of the continental climate development in East Asia is mainly based on loess-paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes (delta O-18) of stalagmites from several Chinese caves. Based on these records, it is thought that East Asian

  15. 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

  16. Winter/Summer Monsoon Experiment

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Winter/Summer Monsoon Experiment (MONEX) was conducted during the First Global GARP (Global Atmospheric Research Program) Experiment (FGGE). An international...

  17. Holocene precipitation changes in the deep tropics recorded by Speleothems (Invited)

    Science.gov (United States)

    Wang, X.; Auler, A. S.; Edwards, R.; Kong, X.; Cheng, H.; Cruz, F. W.; Wang, Y.; Broecker, W. S.

    2010-12-01

    We have obtained a high-resolution oxygen isotope (δ18O) record of cave calcite from Paraiso Cave, eastern Amazon, which covers most of the Holocene. Its chronology was determined by U-Th ages from three column-shaped stalagmites. Their δ18O profiles replicate among their contemporaneous growth periods. Therefore, the samples were likely precipitated under equilibrium conditions and their oxygen isotopic variations are primarily caused by climate change. We find that the δ18O decreases steadily from ~11.0 to 5.0 thousand years ago, with a growth gap between ~8.4 to 6.3 thousand years ago, and then gradually increases until the present. The large amplitude of the δ18O change (up to 4 per mil) suggests that the variation in δ18O value is dominated by meteoric precipitation change at this equatorial site. In order to investigate the interactions between the Intertropical Convergence Zone (ITCZ), monsoons and El Niño-Southern Oscillation (ENSO) activity during the Holocene, we compare the Paraiso record to speleothem records from other locations in the deep tropics, namely, cave sites from Flores, Borneo and Peru. We find that all these speleothem records are consistent, with a progressive δ18O decrease (rainfall increase) during the early Holocene, probably in response to the southward retreat of the ITCZ from its northernmost location in the early Holocene. This is evident from the strong anti-correlation between the speleothem monsoonal records from China and southern Brazil. However, our record is distinct from the others during the last 4 thousand years, when it switches to a continuous δ18O increase (rainfall decrease) trend, while the others flatten out. We propose that, during the late Holocene, the strengthened South American Summer Monsoon may override the ENSO influence and cause the discrepancy in precipitation between eastern Amazon and other deep tropical cave sites.

  18. Monsoon Convective During the South China Sea Monsoon Experiment: Observations from Ground-Based Radar and the TRMM Satellite

    Science.gov (United States)

    Cifelli, Rob; Rickenbach, Tom; Halverson, Jeff; Keenan, Tom; Kucera, Paul; Atkinson, Lester; Fisher, Brad; Gerlach, John; Harris, Kathy; Kaufman, Cristina

    1999-01-01

    A main goal of the recent South China Sea Monsoon Experiment (SCSMEX) was to study convective processes associated with the onset of the Southeast Asian summer monsoon. The NASA TOGA C-band scanning radar was deployed on the Chinese research vessel Shi Yan #3 for two 20 day cruises, collecting dual-Doppler measurements in conjunction with the BMRC C-Pol dual-polarimetric radar on Dongsha Island. Soundings and surface meteorological data were also collected with an NCAR Integrated Sounding System (ISS). This experiment was the first major tropical field campaign following the launch of the Tropical Rainfall Measuring Mission (TRMM) satellite. These observations of tropical oceanic convection provided an opportunity to make comparisons between surface radar measurements and the Precipitation Radar (PR) aboard the TRMM satellite in an oceanic environment. Nearly continuous radar operations were conducted during two Intensive Observing Periods (IOPS) straddling the onset of the monsoon (5-25 May 1998 and 5-25 June 1998). Mesoscale lines of convection with widespread regions of both trailing and forward stratiform precipitation were observed following the onset of the active monsoon in the northern South China Sea region. The vertical structure of the convection during periods of strong westerly flow and relatively moist environmental conditions in the lower to mid-troposphere contrasted sharply with convection observed during periods of low level easterlies, weak shear, and relatively dry conditions in the mid to upper troposphere. Several examples of mesoscale convection will be shown from the ground (ship)-based and spaceborne radar data during times of TRMM satellite overpasses. Examples of pre-monsoon convection, characterized by isolated cumulonimbus and shallow, precipitating congestus clouds, will also be discussed.

  19. Sediment Buffering and Transport in the Holocene Indus River System

    Science.gov (United States)

    Clift, P. D.; Giosan, L.; Henstock, T.; Tabrez, A. R.; Vanlaningham, S.; Alizai, A. H.; Limmer, D. R.; Danish, M.

    2009-12-01

    Submarine fans are the largest sediment bodies on Earth and potentially hold records of erosion that could be used to assess the response of continents to changing climate in terms of both physical erosion and chemical weathering. However, buffering between the mountain sources and the abyssal plain may make detailed correlation of climate and erosion records difficult. We investigated the nature of sediment transport in the Indus drainage in SW Asia. Through trenching in the flood plain, drilling in the delta and new seismic and coring data from the shelf and canyon we can now constrain sediment transport from source to sink since the Last Glacial Maximum (LGM). The Indus was affected by intensification of the summer monsoon during the Early Holocene and subsequent weakening since ca. 8 ka. Sediment delivery to the delta was very rapid at 12-8 ka, but slowed along with the weakening monsoon. At the LGM erosion in the Karakoram dominated the supply of sandy material, while the proportion of Lesser Himalayan flux increased with strengthening summer rainfall after 12 ka. Total load also increased at that time. Since 5 ka incision of rivers into the upper parts of the flood plain has reworked Lower Holocene sediments, although the total flux slowed. Coring in the Indus canyon shows that sediment has not reached the lower canyon since ca. 7 ka, but that sedimentation has recently been very rapid in the head of the canyon. We conclude that variations in sealevel and terrestrial climate have introduced a lag of at least 7 k.y. into the deep sea fan record and that monsoon strength is a primary control on whether sediment is stored or released in the flood plain.

  20. Circulation characteristics of a monsoon depression during ...

    Indian Academy of Sciences (India)

    M. Senthilkumar (Newgen Imaging) 1461 1996 Oct 15 13:05:22

    ciated with organized convective processes in a monsoon depression. The objective is to ..... the errors are large and the performance of the high-resolution ... Ramage C S 1971 Monsoon meteorology (London: Academic. Press) 45–46.

  1. On breaks of the Indian monsoon

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    quadrapole is a basic feature of weak spells of the intraseasonal variation over the Asia-west Pacific region. ... (Earth Planet. Sci.), 112 .... be useful to define the break monsoon (and active ... monsoon zone, different scientists have used the.

  2. Meteorological results of monsoon-88 Expedition (pre-monsoon period)

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y.; Krishnamurthy, L.; Babu, M.T.

    Mean atmospheric circulation, moisture budget and net heat exchange were studied during a pre-monsoon period (18th March to 3rd May, 1988), making use of the data collected on board "Akademik Korolev" in the central equatorial and southern Arabian...

  3. Molecular records of continental air temperature and monsoon precipitation variability in East Asia spanning the past 130,000 years

    NARCIS (Netherlands)

    Peterse, F.; Martínez-García, A.; Zhou, B.; Beets, C.J.; Prins, M.A.; Zheng, H.; Eglinton, T.I.

    2014-01-01

    Our current understanding of past changes in East Asian summer monsoon (EASM) precipitation intensity derives from several loess–paleosol sequences and oxygen isotope (δ18O) records of well-dated stalagmites. Although temperature is generally presumed to have had minimal impact on EASM records, past

  4. Importance of monsoon rainfall in mass fluxes of filtered and unfiltered mercury in Gwangyang Bay, Korea

    International Nuclear Information System (INIS)

    Jang, Jiyi; Han, Seunghee

    2011-01-01

    We investigated the effects of the East Asian Summer Monsoon (EASM), which brings approximately half of Korea's annual rainfall in July, on the concentration and particle-water partitioning, and sources of Hg in coastal waters. Surface seawater samples were collected from eight sites in Gwangyang Bay, Korea, during the monsoon (July, 2009) and non-monsoon dry (April and November, 2009) seasons and the concentrations of suspended particulate matter, chlorophyll-a, and unfiltered and filtered Hg were determined. We found significant (p 0.05) between the monsoon (459 ± 141 pmol g -1 ) and the dry season (346 ± 30 pmol g -1 ), which resulted in decreased particle-water partition coefficients of Hg in the monsoon season compared to the values in the dry season: 5.7 ± 0.1 in April, 5.3 ± 0.1 in July, and 5.8 ± 0.1 in November. The annual Hg input to Gwangyang Bay was estimated at 64 ± 6.6 mol yr -1 and 27 ± 1.9 mol yr -1 for unfiltered and filtered Hg, respectively. The Hg discharged from rivers was a major source of Hg in Gwangyang Bay: the river input contributed 83 ± 13% of total input of unfiltered and 73 ± 6.0% of filtered Hg. On a monthly basis, unfiltered Hg input was 17 ± 11 mol month -1 in the monsoon season and 3.2 ± 0.70 mol month -1 in the dry season, while filtered Hg input was 7.1 ± 4.1 mol month -1 in the monsoon and 1.3 ± 0.26 mol month -1 in the dry. Consequently, the EASM resulted in an unfiltered Hg input 5.3 times greater than the mean dry month input and a filtered Hg input 5.5 times greater than the mean dry month input, which is mainly attributable to enhanced river water discharge during the monsoon season. - Research Highlights: → Filtered mercury concentration increased in the monsoon month in coastal water. → The monsoon rain increased unfiltered Hg input 5.5 times greater than the dry month. → The monsoon rain increased filtered Hg input 5.3 times greater than the dry month.

  5. Distribution of mountain wetlands and their response to Holocene climate change in the Hachimantai Volcanic Groups, northeastern Japan

    Science.gov (United States)

    Sasaki, N.; Sugai, T.

    2017-12-01

    Mountain wetlands, natural peatlands or lakes, with narrow catchment areas need abundant water supply and topography retaining water because of unstable water condition. This study examines wetland distribution with a focus on topography and snow accumulation, and discuss wetland evolution responding to Holocene climate change in the Hachimantai Volcanic Group, northeastern Japan, where the East Asian winter monsoon brings heavier snow and where has many wetlands of varied origin: crater lakes and wetlands in nivation hollows on original volcanic surfaces, and wetlands in depressions formed by landslides. We identified and classified wetlands using aerial photographs and 5-m and 10-m digital elevation models. Wetlands on the original volcanic surfaces tend to be concentrated under the small scarps with much snow or on saddles of the mountain ridge where snowmelt from surrounding slopes maintains a moist environment. More lake type wetlands are formed in the saddle than in the snowdrifts. That may represent that the saddles can correct more recharge water and may be a more suitable topographic condition for wetland formation and endurance. On the contrary, wetlands on landslides lie at the foot of the scarps where spring water can be abundantly supplied, regardless of snow accumulation. We used lithological analysis, 14C dating, tephra age data, and carbon contents of wetland cores to compare the evolution of wetlands, one (the Oyachi wetland) within a huge landslide and three (the Appi Highland wetlands) outside of a landslide area. We suggest that the evolution of the wetland in the landslide is primarily influenced by landslide movements and stream dissection rather than climate change. In the Appi Highland wetlands, peatlands appeared much later and at the almost same time in the Medieval Warm Period. We suggest that the development of mountain wetlands outside of landslide areas is primarily related to climate changes. Responsiveness of mountain wetlands to

  6. Influence of cloud radiative effects on tropical circulation and hydrological cycle in the Mid-Holocene

    Science.gov (United States)

    Izumi, Kenji; Kageyama, Masa; Bony, Sandrine; Braconnot, Pascale

    2016-04-01

    Paleoenvironmental data in particular, vegetation and lake-status at mid-Holocene (6,000 years ago) in Sahara shows that African monsoon extended much further north than today. Much of this change results from the changes in insolation driven by precession of the Earth's orbit, but in the state-of-the-art climate models, this factor alone is insufficient to explain the magnitude of the change. Previous studies showed that ocean and vegetation feedbacks affect the mid-Holocene monsoon and that the incorporation of these feedbacks in models improves the simulation of the hydrological cycle. However, it is not sufficient to reduce the discrepancies between simulated and reconstructed surface climates. In this study, we investigate the extent to which the simulation of cloud-radiative effects matters for the simulation of paleo-climatic changes, and past changes in the position and strength of the tropical rain belts in particular. This is done by running a general circulation model with and without clouds-radiation interactions using the IPSL model. The impact of cloud -radiative effects, which prevents the precipitation band to move north, on the tropical circulation and precipitation changes in mid-Holocene experiments will be discussed. Additionally, we will show the simulated effects of land cover change over Sahara.

  7. The role of potential vorticity anomalies in the Somali Jet on Indian Summer Monsoon Intraseasonal Variability

    Science.gov (United States)

    Rai, P.; Joshi, M.; Dimri, A. P.; Turner, A. G.

    2018-06-01

    The climate of the Indian subcontinent is dominated by rainfall arising from the Indian summer monsoon (ISM) during June to September. Intraseasonal variability during the monsoon is characterized by periods of heavy rainfall interspersed by drier periods, known as active and break events respectively. Understanding and predicting such events is of vital importance for forecasting human impacts such as water resources. The Somali Jet is a key regional feature of the monsoon circulation. In the present study, we find that the spatial structure of Somali Jet potential vorticity (PV) anomalies varies considerably during active and break periods. Analysis of these anomalies shows a mechanism whereby sea surface temperature (SST) anomalies propagate north/northwestwards through the Arabian Sea, caused by a positive feedback loop joining anomalies in SST, convection, modification of PV by diabatic heating and mixing in the atmospheric boundary layer, wind-stress curl, and ocean upwelling processes. The feedback mechanism is consistent with observed variability in the coupled ocean-atmosphere system on timescales of approximately 20 days. This research suggests that better understanding and prediction of monsoon intraseasonal variability in the South Asian monsoon may be gained by analysis of the day-to-day dynamical evolution of PV in the Somali Jet.

  8. On the shortening of Indian summer monsoon season in a warming scenario

    Science.gov (United States)

    Sabeerali, C. T.; Ajayamohan, R. S.

    2018-03-01

    Assessing the future projections of the length of rainy season (LRS) has paramount societal impact considering its potential to alter the seasonal mean rainfall over the Indian subcontinent. Here, we explored the projections of LRS using both historical and Representative Concentration Pathways 8.5 (RCP8.5) simulations of the Coupled Model Intercomparison Project Phase5 (CMIP5). RCP8.5 simulations project shortening of the LRS of Indian summer monsoon by altering the timing of onset and withdrawal dates. Most CMIP5 RCP8.5 model simulations indicate a faster warming rate over the western tropical Indian Ocean compared to other regions of the Indian Ocean. It is found that the pronounced western Indian Ocean warming and associated increase in convection results in warmer upper troposphere over the Indian Ocean compared to the Indian subcontinent, reducing the meridional gradient in upper tropospheric temperature (UTT) over the Asian summer monsoon (ASM) domain. The weakening of the meridional gradient in UTT induces weakening of easterly vertical wind shear over the ASM domain during first and last phase of monsoon, facilitate delayed (advanced) monsoon onset (withdrawal) dates, ensues the shortening of LRS of the Indian summer monsoon in a warming scenario.

  9. Prediction of a thermodynamic wave train from the monsoon to the Arctic following extreme rainfall events

    Science.gov (United States)

    Krishnamurti, T. N.; Kumar, Vinay

    2017-04-01

    This study addresses numerical prediction of atmospheric wave trains that provide a monsoonal link to the Arctic ice melt. The monsoonal link is one of several ways that heat is conveyed to the Arctic region. This study follows a detailed observational study on thermodynamic wave trains that are initiated by extreme rain events of the northern summer south Asian monsoon. These wave trains carry large values of heat content anomalies, heat transports and convergence of flux of heat. These features seem to be important candidates for the rapid melt scenario. This present study addresses numerical simulation of the extreme rains, over India and Pakistan, and the generation of thermodynamic wave trains, simulations of large heat content anomalies, heat transports along pathways and heat flux convergences, potential vorticity and the diabatic generation of potential vorticity. We compare model based simulation of many features such as precipitation, divergence and the divergent wind with those evaluated from the reanalysis fields. We have also examined the snow and ice cover data sets during and after these events. This modeling study supports our recent observational findings on the monsoonal link to the rapid Arctic ice melt of the Canadian Arctic. This numerical modeling suggests ways to interpret some recent episodes of rapid ice melts that may require a well-coordinated field experiment among atmosphere, ocean, ice and snow cover scientists. Such a well-coordinated study would sharpen our understanding of this one component of the ice melt, i.e. the monsoonal link, which appears to be fairly robust.

  10. The role of potential vorticity anomalies in the Somali Jet on Indian Summer Monsoon Intraseasonal Variability

    Science.gov (United States)

    Rai, P.; Joshi, M.; Dimri, A. P.; Turner, A. G.

    2017-08-01

    The climate of the Indian subcontinent is dominated by rainfall arising from the Indian summer monsoon (ISM) during June to September. Intraseasonal variability during the monsoon is characterized by periods of heavy rainfall interspersed by drier periods, known as active and break events respectively. Understanding and predicting such events is of vital importance for forecasting human impacts such as water resources. The Somali Jet is a key regional feature of the monsoon circulation. In the present study, we find that the spatial structure of Somali Jet potential vorticity (PV) anomalies varies considerably during active and break periods. Analysis of these anomalies shows a mechanism whereby sea surface temperature (SST) anomalies propagate north/northwestwards through the Arabian Sea, caused by a positive feedback loop joining anomalies in SST, convection, modification of PV by diabatic heating and mixing in the atmospheric boundary layer, wind-stress curl, and ocean upwelling processes. The feedback mechanism is consistent with observed variability in the coupled ocean-atmosphere system on timescales of approximately 20 days. This research suggests that better understanding and prediction of monsoon intraseasonal variability in the South Asian monsoon may be gained by analysis of the day-to-day dynamical evolution of PV in the Somali Jet.

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

    Science.gov (United States)

    Stolbova, Veronika; Surovyatkina, Elena; Kurths, Jurgen

    2015-04-01

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

  12. Clouds vertical properties over the Northern Hemisphere monsoon regions from CloudSat-CALIPSO measurements

    Science.gov (United States)

    Das, Subrata Kumar; Golhait, R. B.; Uma, K. N.

    2017-01-01

    The CloudSat spaceborne radar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) space-borne lidar measurements, provide opportunities to understand the intriguing behavior of the vertical structure of monsoon clouds. The combined CloudSat-CALIPSO data products have been used for the summer season (June-August) of 2006-2010 to present the statistics of cloud macrophysical (such as cloud occurrence frequency, distribution of cloud top and base heights, geometrical thickness and cloud types base on occurrence height), and microphysical (such as ice water content, ice water path, and ice effective radius) properties of the Northern Hemisphere (NH) monsoon region. The monsoon regions considered in this work are the North American (NAM), North African (NAF), Indian (IND), East Asian (EAS), and Western North Pacific (WNP). The total cloud fraction over the IND (mostly multiple-layered cloud) appeared to be more frequent as compared to the other monsoon regions. Three distinctive modes of cloud top height distribution are observed over all the monsoon regions. The high-level cloud fraction is comparatively high over the WNP and IND. The ice water content and ice water path over the IND are maximum compared to the other monsoon regions. We found that the ice water content has little variations over the NAM, NAF, IND, and WNP as compared to their macrophysical properties and thus give an impression that the regional differences in dynamics and thermodynamics properties primarily cause changes in the cloud frequency or coverage and only secondary in the cloud ice properties. The background atmospheric dynamics using wind and relative humidity from the ERA-Interim reanalysis data have also been investigated which helps in understanding the variability of the cloud properties over the different monsoon regions.

  13. Understanding the Unusual 2017 Monsoon and Floods in South Asia

    Science.gov (United States)

    Akanda, A. S.; Palash, W.; Hasan, M. A.; Nusrat, F.

    2017-12-01

    Driven primarily by the South Asian Monsoon, the Ganges-Brahmaputra-Meghna (GBM) river basin system collectively drains intense precipitation for an area of more than 1.5 million square kilometers during the wet summer season. Bangladesh, being the lowest riparian country in the system, experiences recurrent floods and immense suffering to its population. The 2017 monsoon season was quite unusual in terms of the characteristics of the precipitation received in the basin. The monsoon was spread out over a much larger time span (April-October) compared to the average monsoon season (June-September). Although the monsoon does not typically start until June in Bangladesh, the 2017 season started much earlier in April with unusually heavy precipitation in the Meghna basin region and caused major damage to agriculture in northeastern Bangladesh. The rainfall continued in several record-breaking pulses, compared to the typical one or two large waves. One of the largest pulses occurred in early August with very high in intensity and volume, causing ECMWF to issue a major warning about widespread flooding in Bangladesh, Northern India, and Eastern Nepal. This record flood event impacted over 40 million people in the above regions, causing major damage to life and infrastructure. Although the Brahmaputra rose above the danger level several times this season, the Ganges was unusually low, thus sparing downstream areas from disastrous floods. However, heavy precipitation continued until October, causing urban flooding in Dhaka and Chittagong - and worsening sanitation and public health conditions in southern Bangladesh - currently undergoing a terrible humanitarian crisis involving Rohingya refugees from the Myanmar. Despite marked improvement in flood forecasting systems in recent years, the 2017 floods identified critical gaps in our understanding of the flooding phenomena and limitations of dissemination in these regions. In this study, we investigate 1) the unusual

  14. Holocene sea-level fluctuation in the southern hemisphere

    Science.gov (United States)

    Isla, Federico Ignacio

    If rising sea levels dominate in the northern hemisphere (NH), falling or fluctuating sea levels predominate in the southern hemisphere (SH). Endogenic processes (tectonics, isostasy or geoidal changes) could explain local or regional mean sea level (MSL) fluctuations but not an hemispherical one. Evidence from South America, Africa, Antarctica, Australia and the Pacific and Indian Oceans suggest that the Holocene transgression rose above the present MSL, in higher latitudes before the tropics. By plotting latitude against the age of MSL arrival at present coasts, good correlation is observed. Oceanic salinity mixing has been already proposed to explain this mid-Holocene sea-level fluctuation. Climate could be the only factor responsible for this hemisphere-wide behavior of MSL. It has been suggested previously that the climate of the SH precedes that of the NH by 3000 years. The climatic optimum, or maximum warmth, occurred predominantly about 6000 BP in the NH, but about 10-9000 BP in the SH. Short-term climatic effects on the sea level (monsoons, southern oscillation/El Niño phenomena) should have significant occurrences during the past in the windiest oceanic hemisphere. This latitudinal trend in former MSL should be considered when using shorelines as reference points for measuring vertical crustal movements.

  15. Carbon dioxide emissions from Indian monsoonal estuaries

    Science.gov (United States)

    Sarma Vedula, VSS

    2012-07-01

    The oceans act as a net sink for atmospheric CO2, however, the role of coastal bodies on global CO2 fluxes remains unclear due to lack of data. The estimated absorption of CO2 from the continental shelves, with limited data, is 0.22 to 1.0 PgC/y, and of CO2 emission by estuaries to the atmosphere is 0.27 PgC/y. The estimates from the estuaries suffer from large uncertainties due to large variability and lack of systematic data collection. It is especially true for Southeast Asian estuaries as the biogeochemical cycling of material are different due to high atmospheric temperature, seasonality driven by monsoons, seasonal discharge etc. In order to quantify CO2 emissions from the Indian estuaries, samples were collected at 27 estuaries all along the Indian coast during discharge wet and dry periods. The emissions of CO2 to the atmosphere from Indian estuaries were 4-5 times higher during wet than dry period. The pCO2 ranged between ~300 and 18492 microatm which were within the range of world estuaries. The mean pCO2 and particulate organic carbon (POC) showed positive relation with rate of discharge suggesting availability of high quantities of organic matter that led to enhanced microbial decomposition. The annual CO2 fluxes from the Indian estuaries, together with dry period data available in the literature, amounts to 1.92 TgC which is >10 times less than that from the European estuaries. The low CO2 fluxes from the Indian estuaries are attributed to low flushing rates and less human settlements along the banks of the Indian estuaries.

  16. Asian Ginseng

    Science.gov (United States)

    ... care provider before using Asian ginseng. Keep in Mind Tell all your health care providers about any ... Privacy and Policies Accessibility en Español FOIA Site Map Contact Us U.S. Department of Health & Human Services , ...

  17. The Summer Monsoon of 1987.

    Science.gov (United States)

    Krishnamurti, T. N.; Bedi, H. S.; Subramaniam, M.

    1989-04-01

    In this paper we have examined the evolution of a number of parameters we believe were important for our understanding of the drought over India during the summer of 1987. The list of parameters includes monthly means or anomalies of the following fields: sea surface temperatures, divergent circulations, outgoing longwave radiation, streamfunction of the lower and upper troposphere, and monthly precipitation (expressed as a percentage departure from a long-term mean). The El Niño related warm sea surface temperature anomaly and a weaker warm sea surface temperature anomaly over the equatorial Indian Ocean provide sustained convection, as reflected by the negative values of the outgoing longwave radiation. With the seasonal heating, a pronounced planetary-scale divergent circulation evolved with a center along the western Pacific Ocean. The monsoonal divergent circulation merged with that related to the El Niño, maintaining most of the heavy rainfall activity between the equatorial Pacific Ocean and east Asia. Persistent convective activity continued south of India during the entire monsoon season. Strong Hadley type overturnings with rising motions over these warm SST anomaly regions and descent roughly near 20° to 25°S was evident as early as April 1987. The subtropical high pressure areas near 20° to 25°S showed stronger than normal circulations. This was revealed by the presence of a counterclockwise streamfunction anomaly at 850 mb during April 1987. With the seasonal heating, this anomaly moved northwards and was located over the Arabian Sea and India. This countermonsoon circulation anomaly at the low levels was associated with a weaker than normal Somali jet and Arabian Sea circulation throughout this summer. The monsoon remained active along northeast India, Bangladesh, northern lndochina, and central China during the summer monsoon season. This was related to the eastward shift of the divergent circulation. An eastward shift of the upper tropospheric

  18. Mass accumulation rate and monsoon records from Xifeng, Chinese Loess Plateau, based on a luminescence age model

    DEFF Research Database (Denmark)

    Stevens, Thomas; Buylaert, Jan-Pieter; Lu, Huayu

    2016-01-01

    common than previously realized. MARs from undisturbed portions of Xifeng vary dramatically, with peaks potentially matching the timing of Heinrich events. The last glacial maximum peak MAR (22–27 ka) matches the Pacific and Greenland dust flux records, although appears earlier than peak MARs seen...... in many other OSL‐dated Loess Plateau sites. East Asian monsoon grain‐size and magnetic susceptibility records also show several differences between independently dated loess sites. This complicates our understanding of any lag between insolation forcing and monsoon response. Nevertheless, the Xifeng...

  19. Glacial to Holocene fluctuations in hydrography and productivity along the southwestern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.; Schneider, R.R.; Grootes, P.M.

    was highly reduced (S.W.A. Naqvi, personal communication). during 13–6 ka BP, when the intensity of summer Secondly, the dynamics of the upwelling system monsoon is expected to be high. We suggest that along the southwest coast of India oVers an past changes...: S0031-0182(00)00156-5 114 M. Thamban et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 165 (2001) 113–127 during the early to mid-Holocene period, following and Malmgren, 1996; Naqvi and Fairbanks, 1996; Overpeck et al., 1996; Zonneveld et...

  20. Characteristics of monsoon low level jet (MLLJ)

    Indian Academy of Sciences (India)

    Temperature and wind data are used to describe variation in the strength of the Monsoon Low Level Jet (MLLJ) from an active phase of the monsoon to a break phase. Also estimated are the characteristics of turbulence above and below MLLJ.

  1. Sensible climates in monsoon Asia.

    Science.gov (United States)

    Ono, H S; Kawamura, T

    1991-06-01

    This study identifies characteristics of the geographical distribution of sensible climates and their diurnal and annual variations, and presents a classification of bioclimates in monsoon Asia by using Kawamura's discomfort index formula. During the hottest month, tropical areas and areas in central and South China are uncomfortable for humans throughout the day and night, and temperate zones in lowlands are uncomfortable during the daytime. Tropical zones are uncomfortable all year long and temperate zones in lowlands are uncomfortable during summer. Four climatic types were distinguished in monsoon Asia. Climatic type I, hyperthermal throughout the year, occurs in the tropics south of latitude 20 degrees N. Climatic type II, hyperthermal in the hottest month and comfortable in the coldest month, extends over latitudes from 20 degrees to 30 degrees N except in the highlands. Climatic type III, hyperthermal in the hottest month and hypothermal in the coldest month, encompasses temperate zones of East Asia and subtropical arid areas of northwestern India. Climatic type V, comfortable in the hottest month and hypothermal in coldest month, occurs near the southeast coast of the Soviet Union and in the highlands of the Himalayas.

  2. Profile: Asian Americans

    Science.gov (United States)

    ... and Data > Minority Population Profiles > Asian American Profile: Asian Americans Asian American Profile (Map of the US with the top 10 states displaying the largest Asian American population according to the Census Bureau) CA - ...

  3. Insolation driven biomagnetic response to the Holocene Warm Period in semi-arid East Asia

    OpenAIRE

    Liu, Suzhen; Deng, Chenglong; Xiao, Jule; Li, Jinhua; Paterson, Greig A.; Chang, Liao; Yi, Liang; Qin, Huafeng; Pan, Yongxin; Zhu, Rixiang

    2015-01-01

    The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior. The pronounced increase of magnetofossil concentrations at ~9.8?ka and decrease at ~5.9?ka in Dali Lake coincided respectively wit...

  4. Plant-pollinator interactions in tropical monsoon forests in Southeast Asia.

    Science.gov (United States)

    Kato, Makoto; Kosaka, Yasuyuki; Kawakita, Atsushi; Okuyama, Yudai; Kobayashi, Chisato; Phimminith, Thavy; Thongphan, Daovorn

    2008-11-01

    Forests with different flora and vegetation types harbor different assemblages of flower visitors, and plant-pollinator interactions vary among forests. In monsoon-dominated East and Southeast Asia, there is a characteristic gradient in climate along latitude, creating a broad spectrum of forest types with potentially diverse pollinator communities. To detect a geographical pattern of plant-pollinator interactions, we investigated flowering phenology and pollinator assemblages in the least-studied forest type, i.e., tropical monsoon forest, in the Vientiane plain in Laos. Throughout the 5-year study, we observed 171 plant species blooming and detected flower visitors on 145 species. Flowering occurred throughout the year, although the number of flowering plant species peaked at the end of dry season. The dominant canopy trees, including Dipterocarpaceae, bloomed annually, in contrast to the supra-annual general flowering that occurs in Southeast Asian tropical rain forests. Among the 134 native plant species, 68 were pollinated by hymenopterans and others by lepidopterans, beetles, flies, or diverse insects. Among the observed bees, Xylocopa, megachilids, and honeybees mainly contributed to the pollination of canopy trees, whereas long-tongued Amegilla bees pollinated diverse perennials with long corolla tubes. This is the first community-level study of plant-pollinator interactions in an Asian tropical monsoon forest ecosystem.

  5. Observational Analysis of Two Contrasting Monsoon Years

    Science.gov (United States)

    Karri, S.; Ahmad, R.; Sujata, P.; Jose, S.; Sreenivas, G.; Maurya, D. K.

    2014-11-01

    The Indian summer monsoon rainfall contributes about 75 % of the total annual rainfall and exhibits considerable interannual variations. The agricultural economy of the country depends mainly on the monsoon rainfall. The long-range forecast of the monsoon rainfall is, therefore of significant importance in agricultural planning and other economic activities of the country. There are various parameters which influence the amount of rainfall received during the monsoon. Some of the important parameters considered by the Indian Meteorological Department (IMD) for the study of monsoon are Outgoing Longwave Radiation (OLR), moisture content of the atmosphere, zonal wind speed, low level vorticity, pressure gradient etc. Compared to the Long Period Average (LPA) value of rain fall, the country as a whole received higher amount of rainfall in June, 2013 (34 % more than LPA). The same month showed considerable decrease next year as the amount of rainfall received was around 43 % less compared to LPA. This drastic difference of monsoon prompted to study the behaviour of some of the monsoon relevant parameters. In this study we have considered five atmospheric parameters as the indicators of monsoon behaviour namely vertical relative humidity, OLR, aerosol optical depth (AOD), wind at 850 hPa and mean sea level pressure (MSLP). In the initial analysis of weekly OLR difference for year 2013 and 2014 shows positive values in the month of May over north-western parts of India (region of heat low). This should result in a weaker monsoon in 2014. This is substantiated by the rainfall data received for various stations over India. Inference made based on the analysis of RH profiles coupled with AOD values is in agreement with the rainfall over the corresponding stations.

  6. Pollen record of the mid- to late-Holocene centennial climate change on the East coast of South Korea and its influential factors

    Science.gov (United States)

    Song, Bing; Yi, Sangheon; Jia, Hongjuan; Nahm, Wook-Hyun; Kim, Jin-Cheul; Lim, Jaesoo; Lee, Jin-Young; Sha, Longbin; Mao, Limi; Yang, Zhongyong; Nakanishi, Toshimichi; Hong, Wan; Li, Zhen

    2018-01-01

    To understand historical climate change in western Pacific coastal areas, a sediment core (SOJ-2) from the stable sedimentary environment of the Songjiho Lagoon on the east coast of South Korea was obtained for centennial-resolution palynological analysis. The ages of the SOJ-2 core is well controlled by carbon 14 dating with high-resolution accelerator mass spectrometry (AMS), and the results indicated a general warm to cold climate trend from the mid-Holocene to the present, which can be divided into two different stages: a warmer stage between 6842 and 1297 cal yr BP and a colder stage from 1297 cal yr BP to the present, with fluctuations during these stages. The climate was wetter from 6842 to 6227 cal yr BP and 4520 to 1297 cal yr BP and was drier from 6227 to 4520 cal yr BP. The climate changed to cold and dry during the period from 1297-425 cal yr BP. The impact of human activity on the climate began at approximately 1297 cal yr BP and became pronounced starting in 425 cal yr BP. The general cooling trend may represent a response to decreasing solar insolation; however, the relative dryness or wetness of the climate may have been co-determined by westerlies and the East Asian summer monsoon (EASM). The climate had a teleconnection with the North Atlantic region, resulting from changes in solar activity. Nevertheless, EI Niño-Southern Oscillation (ENSO) activity played an important role in impacting the EASM changes in western Pacific coastal areas.

  7. Time-slice analysis of the Australian summer monsoon during the late Quaternary using the Fast Ocean Atmosphere Model

    Science.gov (United States)

    Marshall, A. G.; Lynch, A. H.

    2006-10-01

    We use the Fast Ocean Atmosphere Model (FOAM) to investigate the variation in the Australian summer monsoon over the last 55 000 years. A synthesis of palaeoenvironmental observations is used to constrain the model for six time slices: 55, 35, 21, 11, 6 and 0 ka. Both inter-hemispheric forcing and the seasonal timing of local insolation changes play key, and interacting, roles on the evolution and intensity of the monsoon.During the onset to the monsoon, a heat low develops to the west of Australia over the Indian Ocean in all time slices, but with varying strengths. Divergent outflow from Asia converges with the cyclonic flow to bring increased rainfall to northern Australia and the maritime continent. The relative importance of a low pressure pull and the high pressure push varies according to the strength of the pressure anomalies. Only in the middle Holocene is the low pressure pull the dominant forcing mechanism. At 21 ka, the climate shift to colder mean temperatures determines the large-scale dynamics of the monsoon.The general picture that emerges from these results is consistent with available palaeodata but highlights the importance of a broad regional perspective to ascribe the driving mechanisms at different times. Copyright

  8. Mid-Holocene to Present Climate Transition in Tropical South America

    Science.gov (United States)

    Turcq, B.; Cordeiro, R.; Sifeddine, A.; Braconnot, P.; Dias, P. S.; Costa, R.; Jorgetti, T.

    2008-12-01

    The classical illustration of Holocene climate changes in tropical South America is the huge rising of Titicaca lake level from 4400 to 4000 cal BP. Because the Amazon basin is the source of Andean rainfalls we have explored Amazonian data of climate changes during the Holocene to better understand the cause of this abrupt transition. Amazonian data confirm the existence of mid-Holocene dryness: (1) lacustrine level studies show a lower precipitation/evaporation budget than present, with the lowest lake levels between 8500 and 6800 cal BP; (2) although the dominant Holocene vegetation has always been the rainforest in the heart of Amazonia, this forest expanded towards the northwestern and southwestern regions from 6800 to 1550 cal BP, moreover, pioneer elements of the rainforest developed during the mid-Holocene and the best example is those of Cecropia, between 9000 and 5000 cal BP. (3) soil d13C indicates a forest expansion over savannas areas in Roraima (north), Mato Grosso and Rondonia (southwest), during the Holocene. (4) the mid-Holocene (8000- 4000 cal BP) is characterized by repeated occurrences of forest fires, marked by the presence of charcoals in soils and lacustrine sediments. However these different records are not characterized by abrupt transitions at the end of the Middle Holocene in Amazonia. In the Andean records there is a clear north-south shift in the timing of the transition. Analysis of coupled Ocean Atmosphere Model simulations suggest that convection in Amazon basin is directly controlled by insolation leading to an almost linear response of local climate to the global forcing. Differently, in the eastern and south-western regions where the rain is brought by the South American Monsoon, the climate transition appears more abrupt. It may be because the involved climate mechanisms are more complex and depend on Ocean/Atmosphere/Vegetation coupled process (ITCZ position, ZCAS formation, etc.). Tectonic movements or threshold links to

  9. Relationship between summer monsoon rainfall and cyclogenesis ...

    Indian Academy of Sciences (India)

    relationship between Indian Ocean Dipole Mode. Index (IODMI) and the ... 2013) in the cyclogenesis over north Indian Ocean ..... Indian summer monsoon; J. Climate 17 3141–3155. ... Murakami H, Wang B and Kitoh A 2011 Future change.

  10. Aridity of Central Asia through the Holocene

    Science.gov (United States)

    Aizen, E. M.; Aizen, V. B.; Mayewski, P. A.; Zhou, H.; Rodda, C.; Joswiak, D.; Takeuchi, N.; Fujita, K.; Kurbatov, A.; Grigholm, B. O.

    2017-12-01

    The dynamics of aridity in Central Asia for over the past 12,000 years has been analyzed using deep ice core records recovered from the Siberian Altai, Tien Shan and Pamir glaciers. An analysis of aridity in the 20-21 centuries based on the long-term meteorological observations complements the paleo- climate reconstruction. The goal of our research is to examine an aridity (at low and high temperatures) in Central Asia as a complex of characteristics including air temperature-precipitation relationship (Koppen, 1918, Geiger, 1961, Mezencev, 1973), intensity of dust loading and biomass burning. The stable isotope ratio, soluble ionic and insoluble particulate geochemical components and oxalate preserved in ice were considered in relation to climatic and environmental changes; and to determine the main aerosol sources using ground- and upper-level meteorological data. Multivariate statistical methods were employed for examination of the main geo-chemical components responsible for the preserved aridity variability. Insoluble particle concentrations preserved in the ice core were affected mainly by precipitation regimes and wind speed. Concentration of all size particles was found to be negatively correlated with monthly temperatures indicating low temperatures during the dry particle deposition. Two abrupt depletions in stable isotope records, i.e., Younger Dryas and Centurial Sever Drought (CSD), occurred during cold, dry, windy periods of intensified dust storms in large desert areas. When climate became colder and drier, the Central Asian deserts extended, wind speeds increased loading mineral dust to atmosphere, which formed inversion while the convection processes and precipitation occurrence were limited. Warmer and wetter conditions are associated with less dust loading that occurred during the Holocene climate optimum, medieval warm and modern warm periods. The sudden climate transitions are accompanied by the most intensifying mineral dust loading. From the

  11. Holocene fire dynamics in Fennoscandia

    Science.gov (United States)

    Clear, Jennifer; Seppa, Heikki; Kuosmanen, Niina; Molinari, Chiara; Lehsten, Veiko; Allen, Katherine; Bradshaw, Richard

    2015-04-01

    Prescribed burning is advocated in Fennoscandia to promote regeneration and to encourage biodiversity. This method of forest management is based on the perception that fire was much more frequent in the recent past and over a century of active fire suppression has created a boreal forest ecosystem almost free of natural fire. The absence of fire is thought to have contributed to the widespread dominance of Picea abies (Norway spruce) with the successive spruce dominated forest further reducing fire ignition potential. However, humans have altered the natural fire dynamics of Fennoscandia since the early- to mid-Holocene and disentangling the anthropogenic driven fire dynamics from the natural fire dynamics is challenging. Through palaeoecology and sedimentary charcoal deposits we are able to explore the Holocene spatial and temporal variability and changing drivers of fire and vegetation dynamics in Fennoscandia. At the local-scale, two forest hollow environments (history are compared to identify unique and mutual changes in disturbance history. Pollen derived quantitative reconstruction of vegetation at both the local- and regional-scale identifies local-scale disturbance dynamics and large-scale ecosystem response. Spatio-temporal heterogeneity and variability in biomass burning is explored throughout Fennoscandia and Denmark to identify the changing drives of fire dynamics throughout the Holocene. Palaeo-vegetation reconstructions are compared to process-based, climate driven dynamic vegetation model output to test the significance of fire frequency as a driver of vegetation composition and dynamics. Early-Holocene fire regimes in Fennoscandia are driven by natural climate variations and fuel availability. The establishment and spread of Norway spruce is driven by an increase in continentality of climate, but local natural and anthropogenic ecosystem disturbance may have aided this spread. The expansion of spruce led to a step-wise reduction in regional biomass

  12. Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals

    Science.gov (United States)

    Liu, Yajing; Liu, W.; Peng, Z.; Xiao, Y.; Wei, G.; Sun, W.; He, J.; Liu, Gaisheng; Chou, C.-L.

    2009-01-01

    We used positive thermal ionization mass spectrometry (PTIMS) to generate high precision ??11B records in Porites corals of the mid-late Holocene from the South China Sea (SCS). The ??11B values of the Holocene corals vary significantly, ranging from 22.2??? to 25.5???. The paleo-pH records of the SCS, reconstructed from the ??11B data, were not stable as previously thought but show a gradual increase from the Holocene thermal optimal and a sharp decrease to modern values. The latter is likely caused by the large amount of anthropogenic CO2 emissions since the Industrial Revolution but variations of atmospheric pCO2 cannot explain the pH change of the SCS before the Industrial Revolution. We suggest that variations of monsoon intensity during the mid-late Holocene may have driven the sea surface pH increase from the mid to late Holocene. Results of this study indicate that the impact of anthropogenic atmospheric CO2 emissions may have reversed the natural pH trend in the SCS since the mid-Holocene. Such ocean pH records in the current interglacial period can help us better understand the physical and biological controls on ocean pH and possibly predict the long-term impact of climate change on future ocean acidification. ?? 2008 Elsevier Ltd. All rights reserved.

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

    Digital Repository Service at National Institute of Oceanography (India)

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

    by Myanmar Rivers. Figure 2. Downcore variations of (a) ε Nd of SK168 of Alcock seamount (this study - with 2sd error bars) and MD169 of Sewell seamount12 in the Central Andaman Trough (CAT); (b) 87Sr/86Sr of SK168 (this study); the 2sd errors of Sr... in the Central Andaman basin. The isotopic data of core SK168 (this work - northern half of the Central Andaman Trough - CAT) exhibits a narrow range of Nd isotopes (ε Nd − 11.24 to − 9.24; average − 10.15 ± 0.46) (Fig. 3) which fall very close to other...

  14. Variation in the Indian summer monsoon intensity during the Bolling-Allerod and Holocene

    Digital Repository Service at National Institute of Oceanography (India)

    Kessarkar, P.M.; Rao, V.P.; Naqvi, S.W.A.; Karapurkar, S.G.

    to PDB. Repetitive analysis of the NBS 18, 19 and internal laboratory standards revealed that analytical standard deviation was better than ±0.07‰. Total inorganic carbon (TIC) was determined using a coulometer. CaCO3 (%) was calculated... by multiplying TIC with factor of 8.333, the reproducibility was found to be better than 5 %. In order to estimate total organic carbon (Corg), total carbon was measured by CNS elemental analyser (NCS 2500) and Corg was derived from the difference between...

  15. Late Pleistocene to Holocene alluvial tableland formation in an intra-mountainous basin in a tectonically active mountain belt - A case study in the Puli Basin, central Taiwan

    NARCIS (Netherlands)

    Tseng, Chia Han; Lüthgens, Christopher; Tsukamoto, Sumiko; Reimann, Tony; Frechen, Manfred; Böse, Margot

    2016-01-01

    The morphology in Taiwan is a product of high tectonic activity at the convergent margin and East Asian monsoon climate. Tablelands are prominent geomorphic features in the Puli Basin in central Taiwan. These tablelands provide an archive to understand links between past climatic evolution and

  16. Monsoon Variability In The Western Arabian Sea During Last 10,000 Years BP: A Planktic Foraminiferal Abundances And It's Stable Isotope Records

    Science.gov (United States)

    Singh, A. K.; Tiwari, M.; Sinha, D. K.; Ramesh, R.

    2007-12-01

    : The western Arabian Sea responds to the southwest monsoon winds by upwelling colder and nutrient rich waters from the deeper layers, causing a reduction in the sea surface temperature and enhanced biological productivity. A number of paleoclimatic studies have been carried out in this region to elucidate past monsoon variability (Sirocco et al., 1993; Gupta et al, 2003; Tiwari, 2005; Saher et.al.; 2007). Globigerina bulloides, a planktic foraminiferal species normally inhabiting surface ocean waters in temperate latitudes ( Be and Tolderlund , 1977) also becomes abundant at tropical latitudes upwelling occurs, and in these cases its abundance can exceed considerably. The conspicuous fluctuation in the abundance of Gg.bulloides during upwelling and non upwelling intervals is established through several studies ( Thiede and Junger, 1980, Gupta et al, 2003) This robust relation has been used as a proxy for wind velocity at several different times in the past in the Arabian Sea (Anderson et.al., 2002). A significant result from some of these centennially resolved Holocene records is declining abundance of Globigerina bulloides which is paralleled by reduced insolation record and this has been inferred as declining strength of Asian Monsoon. We are presenting here the data from the core SS4018 from near the Gulf of Aden, Western Arabian Sea taken at a water depth of 2830 m, precisely dated by the radiocarbon method using Accelerator Mass Spectrometry on planktonic foraminiferal separates. We have carried out the planktic foraminiferal census counts for each sample to know the relative abundance of key species. In addition to this, we have also employed multi- proxy approach such as oxygen and carbon isotopes of planktic foraminiferal tests, TOC, CaCO3 (%) to strengthen our interpretation and also to understand the relationships amongst the proxies themselves. Abundance of the key planktic foraminiferal species and other proxy records reveal at least 3 major climatic

  17. The Asian Tropopause Aerosol Layer Through Satellite and Balloon-Borne Measurements Combined With Modeling Approaches

    Science.gov (United States)

    Vernier, J.-P.; Fairlie, T. D.; Natarajan, M.; Wegner, T.; Baker, N.; Crawford, J.; Moore, J.; Deshler, T.; Gadhavi, H.; Jayaraman, A.; hide

    2016-01-01

    The Asian Tropopause Aerosol Layer-ATAL is a confined area of enhanced aerosol associated Summer Asia Monsoon spanning from the E. Med Sea to W. China. It essentially extends from top of convective outflow over much of SE Asia Existence recognize through CALIPSO observations.

  18. Holocene climate change in North Africa and the end of the African humid period - results of new high-resolution transient simulations with the MPI-ESM 1.3

    Science.gov (United States)

    Dallmeyer, Anne; Claussen, Martin; Lorenz, Stephan

    2017-04-01

    The Max-Planck-Institute for Meteorology has recently undertaken high-resolution transient Holocene simulations using the fully-coupled Earth System Model MPI-ESM 1.3. The simulations cover the last 8000 years and are forced not only by reconstructed Holocene orbital variations and atmospheric greenhouse gas concentrations, but also by recent compilations of Holocene volcanic aerosol distributions, variations in spectral solar irradiance, stratospheric ozone and land-use change. The simulations reveal the ubiquitous "Holocene conundrum": simulated global mean temperatures increase during the mid-Holocene and stay constant during the late Holocene. Simulated mid-Holocene near-surface temperatures are too cold in large parts of the world. Simulated precipitation, however, agrees much better with reconstruction than temperatures do. Likewise simulated global biome pattern fit reconstructions nicely, except for North Western America. First results of these simulations are presented with the main focus on the North African monsoon region. The amplitude of the mid-Holocene African Humid Period (AHP) is well captured in terms of precipitation and vegetation cover, so is the south-ward transgression of the termination of the AHP seen in reconstructions. The Holocene weakening and southward retreat of the North African monsoon as well as changes in the monsoon dynamic including shifts in the seasonal cycle and their relation to the locally varying termination of the AHP are discussed in detail. Members of the Hamburg Holocene Team: Jürgen Bader (1), Sebastian Bathiany (2), Victor Brovkin (1), Martin Claussen (1,3), Traute Crüger (1), Roberta D'agostino (1), Anne Dallmeyer (1), Sabine Egerer (1), Vivienne Groner (1), Matthias Heinze (1), Tatiana Ilyina (1), Johann Jungclaus (1), Thomas Kleinen (1), Alexander Lemburg (1), Stephan Lorenz (1), Thomas Raddatz (1), Hauke Schmidt (1), Gerhard Schmiedl (3), Bjorn Stevens (1), Claudia Timmreck (1), Matthew Toohey (4) (1) Max

  19. Sources of Holocene variability of oxygen isotopes in paleoclimate archives

    Directory of Open Access Journals (Sweden)

    A. N. LeGrande

    2009-08-01

    Full Text Available Variability in water isotopes has been captured in numerous archives and used to infer past climate changes. Here we examine water isotope variability over the course of the Holocene using the water-isotope enabled, coupled atmosphere-ocean general circulation model, GISS ModelE-R. Eight Holocene time slices, ~1000 years apart are simulated and driven by estimated changes in orbital configuration, greenhouse gases, and ice sheet extent. We find that simulated water isotope archives match well with those seen in ice cores, ocean sediment cores, and speleothems. The climate changes associated with the water isotope changes, however, are more complex than simple modern spatial slope interpretations might suggest. In particular, water isotope variability in Asian speleothems is linked to alterations in landward water vapor transport, not local precipitation, and ice sheet changes over North America lead to the masking of temperature signals in Summit, Greenland. Salinity-seawater isotope variability is complicated by inter-ocean basin exchanges of water vapor. Water isotopes do reflect variability in the hydrology, but are better interpreted in terms of regional hydrological cycle changes rather than as indicators of local climate.

  20. Role of ISM circulations in Western Kachchh, India during Mid-Late Holocene in disarticulation of Human Settlements

    Science.gov (United States)

    Dabhi, M.

    2017-12-01

    Paleoclimatic record indicates that one of the major factors for change in Indian Summer Monsoon (ISM) is North Atlantic Oceanic Circulation (NAO). Climatic changes have often been an influential factor in culture developments and dislocation of human settlements. The climatic transformations in Western India are affected by variation in the Indian Summer Monsoon (ISM). During last millennial scale, Indian sub-continent has observed varied climatic oscillations due to temperature variations in ocean and continent. People and society are the most affected lot due to this climate and monsoonal changes, which finally leads towards migration or colonization of people. Therefore, a high resolution data is required to delineate the complexity of monsoonal variation. This study focuses on the Mid-Late Holocene monsoonal changes from the sediment record of Western Kachchh. The field of study is at the mount of Kali River, a 45 km long river originating from the hills of Western Mainland Kachchh and debouching into Kori Creek. The exposed cross-section along the river bank has a fluvial unit (Unit-1) at the base followed by human settlement marked as Unit-2 culminating with eolian deposits (Unit-3) at the top. Multiproxy analysis (sedimentologically, optically and geochemically) were carried out to ascertain the climatic perturbations in the region. The lower Unit 1 which range in age from 6-5 Ka shows declining monsoon. The above exposed sediments with anthropogenic activity (Unit 2) cover a time span of 3-2.5 ka indicates monsoonal stability with declining trends. The general weakening of monsoon may be a major factor towards the ending or migration of the human settlement leading to the absence of archeological activity above 2.5ka in the area. The eolian sediments resting above the Unit 2 fall between 450 to 230 yrs represent the trends of Little Ice Age. Sediment record from the opposite bank of the river reveals an age of 1100 yrs supports wet condition which is co

  1. Multi-Decadal to Millennial Scale Holocene Hydrologic Variation in the Southern Hemisphere Tropics of South America

    Science.gov (United States)

    Ekdahl, E. J.; Fritz, S. C.; Baker, P. A.; Burns, S. J.; Coley, K.; Rigsby, C. A.

    2005-12-01

    Numerous sites in the Northern Hemisphere show multi-decadal to millennial scale climate variation during the Holocene, many of which have been correlated with changes in atmospheric radiocarbon production or with changes in North Atlantic oceanic circulation. The manifestation of such climate variability in the hydrology of the Southern Hemisphere tropics of South America is unclear, because of the limited number of records at suitably high resolution. In the Lake Titicaca drainage basin of Bolivia and Peru, high-resolution lacustrine records reveal the overall pattern of Holocene lake-level change, the influence of precessional forcing of the South American Summer Monsoon, and the effects of high-frequency climate variability in records of lake productivity and lake ecology. Precessional forcing of regional precipitation is evident in the Lake Titicaca basin as a massive (ca. 85 m) mid-Holocene decline in lake level beginning about 7800 cal yr BP and a subsequent rise in lake level after 4000 cal yr BP. Here we show that multi-decadal to millennial-scale climate variability, superimposed upon the envelope of change at orbital time scales, is similar in timing and pattern to the ice-rafted debris record of Holocene Bond events in the North Atlantic. A high-resolution carbon isotopic record from Lake Titicaca that spans the entire Holocene suggests that cold intervals of Holocene Bond events are periods of increased precipitation, thus indicating an anti-phasing of precipitation variation on the Altiplano relative to the Northern Hemisphere tropics. A similar pattern of variation is also evident in high-resolution (2-30 yr spacing) diatom and geochemical records that span the last 7000 yr from two smaller lakes, Lagos Umayo and Lagunillas, in the Lake Titicaca drainage basin.

  2. Heavy sediment influx during early Holocene: Inference from clay mineral studies in a core from the western Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Reddy, N.P.C.; Rao, K.M.

    is attributed to heavy sediment influx du r- ing Mid Termination (MT) (12,500 ? 10,000 years BP), due to i n creased precipitation and run - off resulting from high inte n sity monsoonal regime. C LAY minerals are a powerful source for the interpret a... to address to the prov e nance of the sediments in a sediment core from the western Bengal Fan. In this paper, we report clay mi n eralogy and provide an explanation for the heavy sed i ment deposition du r ing the Holocene. A sediment core of 650...

  3. Late Quaternary glaciation history of monsoon-dominated Dingad basin, central Himalaya, India

    Science.gov (United States)

    Shukla, Tanuj; Mehta, Manish; Jaiswal, Manoj K.; Srivastava, Pradeep; Dobhal, D. P.; Nainwal, H. C.; Singh, Atul K.

    2018-02-01

    The study presents the Late Quaternary glaciation history of monsoon-dominated Dokriani Glacier valley, Dingad basin, central Himalaya, India. The basin is tested for the mechanism of landforms preservation in high relief and abundant precipitation regimes of the Higher Himalaya. Field geomorphology and remote sensing data, supported by Optical Stimulated Luminescence (OSL) dating enabled identification of five major glacial events of decreasing magnitude. The oldest glacial stage, Dokriani Glacial Stage I (DGS-I), extended down to ∼8 km (2883 m asl) from present-day snout (3965 m asl) followed by other four glaciations events viz. DGS-II, DGS-III, DGS-IV and DGS-V terminating at ∼3211, 3445, 3648 and ∼3733 m asl respectively. The DGS-I glaciation (∼25-∼22 ka BP) occurred during early Marine Isotope Stage (MIS) -2, characterized as Last Glacial Maximum (LGM) extension of the valley. Similarly, DGS-II stage (∼14-∼11 ka BP) represents the global cool and dry Older Dryas and Younger Dryas event glaciation. The DGS-III glaciation (∼8 ka BP) coincides with early Holocene 8.2 ka cooling event, the DGS-IV glaciations (∼4-3.7 ka BP) corresponds to 4.2 ka cool and drier event, DGS-V (∼2.7-∼1 ka BP) represents the cool and moist late Holocene glacial advancement of the valley. This study suggests that the Dokriani Glacier valley responded to the global lowering of temperature and variable precipitation conditions. This study also highlights the close correlation between the monsoon-dominated valley glaciations and Northern Hemisphere cooling events influenced by North Atlantic climate.

  4. Holocene hydrologic variation at Lake Titicaca, Bolivia/Peru, and its relationship to North Atlantic climate variation

    Science.gov (United States)

    Baker, P. A.; Fritz, S. C.; Garland, J.; Ekdahl, E.

    2005-10-01

    A growing number of sites in the Northern Hemisphere show centennial- to millennial-scale climate variation that has been correlated with change in solar variability or with change in North Atlantic circulation. However, it is unclear how (or whether) these oscillations in the climate system are manifest in the Southern Hemisphere because of a lack of sites with suitably high sampling resolution. In this paper, we reconstruct the lake-level history of Lake Titicaca, using the carbon isotopic content of sedimentary organic matter, to evaluate centennial- to millennial-scale precipitation variation and its phasing relative to sites in the Northern Hemisphere. The pattern and timing of lake-level change in Lake Titicaca is similar to the ice-rafted debris record of Holocene Bond events, demonstrating a possible coupling between precipitation variation on the Altiplano and North Atlantic sea-surface temperatures (SSTs). The cold periods of the Holocene Bond events correspond with periods of increased precipitation on the Altiplano. Holocene precipitation variability on the Altiplano is anti-phased with respect to precipitation in the Northern Hemisphere monsoon region. More generally, the tropical Andes underwent large changes in precipitation on centennial-to-millennial timescales during the Holocene.

  5. Monsoon signatures in recent corals from the Laccadive Islands

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.A.S.

    X-radiographs of the coral (Porites sp.) collected from several atolls of Lakshadweep show alternate bands of low and high density, formed in non-monsoon period and monsoon period, respectively. The results reveal annual density variations as well...

  6. Hydrography of the Wadge bank - premonsoon and monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    RamaRaju, V.S.; Rao, T.V.N.; RameshBabu, V.; Anto, A.F.

    The hydrography of the Wadge Bank during premonsoon and monsoon seasons is presented. The thermocline slopes downward towards the central region. Upwelling is prominent in the entire region during monsoon and is observed only in the western...

  7. The monsoon system: Land-sea breeze or the ITCZ?

    Science.gov (United States)

    Gadgil, Sulochana

    2018-02-01

    For well over 300 years, the monsoon has been considered to be a gigantic land-sea breeze driven by the land-ocean contrast in surface temperature. In this paper, this hypothesis and its implications for the variability of the monsoon are discussed and it is shown that the observations of monsoon variability do not support this popular theory of the monsoon. An alternative hypothesis (whose origins can be traced to Blanford's (1886) remarkably perceptive analysis) in which the basic system responsible for the Indian summer monsoon is considered to be the Intertropical Convergence Zone (ITCZ) or the equatorial trough, is then examined and shown to be consistent with the observations. The implications of considering the monsoon as a manifestation of the seasonal migration of the ITCZ for the variability of the Indian summer monsoon and for identification of the monsoonal regions of the world are briefly discussed.

  8. Anomalous behaviour of the Indian summer monsoon 2009

    Indian Academy of Sciences (India)

    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,.

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

    Digital Repository Service at National Institute of Oceanography (India)

    Sadhuram, Y; Maneesha, K.

    peak monsoon (October–November) season and concluded that the frequency of cyclones is modulated by negative and positive IOD rather than El-Nino and La-Nina. In this study, the relationship between southwest monsoon rainfall (June–September) and TNDC... Relationship between summer monsoon rainfall and cyclogenesis over Bay of Bengal during post-monsoon (October–December) season Y Sadhuram∗ and K Maneesha CSIR–National Institute of Oceanography, 176, Lawsons Bay Colony, Visakhapatnam 530 017, India...

  10. Different sub-monsoon signals in stable oxygen isotope in daily precipitation to the northeast of the Tibetan Plateau

    Directory of Open Access Journals (Sweden)

    Xiaoxin Yang

    2016-09-01

    Full Text Available This study presents a stable oxygen isotope (δ18O record in daily precipitation from two sites located to the northeast of the Tibetan Plateau (TP: Yushu on the eastern TP and Xi'an on the eastern Chinese Loess Plateau. It attempts to reveal the unique features associated with variations in atmospheric circulation patterns over inland China. For δ18O in daily precipitation at both stations, temperature effect is significant (p < 0.01 only during non-monsoon, while amount effect is significant only during monsoon. This suggests the coexistence of local recycling with large-scale atmospheric circulation on regional precipitation, which is further verified by the significant correlation of relative humidity with δ18O at both stations during monsoon season. The similarity of δ18O in regions under the supposedly same atmospheric circulation streams is tested for Yushu with that at Lhasa, Lulang and Delingha, demonstrating the lag days of δ18O depletion at Yushu with that at Lulang as varying from 15 to 25 d. This confirms the Bay of Bengal monsoon dominance over Yushu. Daily δ18O at Xi'an is compared with contemporary data at Changsha and Guangzhou, featuring a close correlation with the East Asian summer monsoon evolution processes over eastern China, and reflecting the Meiyu-Baiu front influence during July. Back-trajectory analysis in October–November at Xi'an identified the combined effect of cooling of the atmospheric column by the colder air from the west and the lifting of the warmer air from the east, which coexists with local water vapour source. Interactions of the three result in condensation at lower temperatures that is coupled with the long-distance transport of 2/3 of the available water vapour, thus leading to extremely low δ18O values in the post-monsoon precipitation.

  11. Distribution and sources of particulate organic matter in the Indian monsoonal estuaries during monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    Sarma, V.V.S.S.; Krishna, M.S.; Prasad, V.R.; Kumar, B.S.K.; Naidu, S.A.; Rao, G.D.; Viswanadham, R.; Sridevi, T.; Kumar, P.P.; Reddy, N.P.C.

    The distribution and sources of particulate organic carbon (POC) and nitrogen (PN) in 27 Indian estuaries were examined during the monsoon using the content and isotopic composition of carbon and nitrogen. Higher phytoplankton biomass was noticed...

  12. Young Asian Dutch constructing Asianness: Understanding the role of Asian popular culture

    OpenAIRE

    Kartosen, R.A.

    2016-01-01

    This doctoral thesis is about young Asian Dutch, panethnic Asian identities and identifications, and Asian/Asian Dutch popular culture. It addresses several pressing questions, including: why do young Asian Dutch, who were born and/or raised in the Netherlands, identify as Asian and construct Asian identities? What is the content or meaning of these Asian identities and identifications young Asian Dutch imagine? And how do these relate to young Asian Dutch’ Dutch and homeland identities and i...

  13. Regional-scale relationships between aerosol and summer monsoon circulation, and precipitation over northeast Asia

    Science.gov (United States)

    Yoon, Soon-Chang; Kim, Sang-Woo; Choi, Suk-Jin; Choi, In-Jin

    2010-08-01

    We investigated the regional-scale relationships between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the regional-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001-2008, the increase of almost 40-50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anticyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies in July over the period 2001-2008, we found negative correlations over the areas encompassed by 105-115°E and 30-35°N and by 120-140°E and 35-40°N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation.

  14. Multifaceted intra-seasonal modes over the East Asia-western North Pacific summer monsoon region

    Science.gov (United States)

    Ha, K. J.; Oh, H.

    2017-12-01

    Intra-seasonal monsoon prediction is the most imperative task due to high impact on 2/3 of world populations' daily life, but there remains an enduring challenge in climate science. The present study aims to provide a physical understanding of the sources for prediction of dominant intra-seasonal modes in the East Asian-western North Pacific summer monsoon (EA-WNPSM): preMeiyu&Baiu, Changma&Meiyu, WNPSM, and monsoon gyre modes classified by the self-organizing map analysis. The preMeiyu-Baiu mode is strongly linked to both the anomalous low-level convergence and vertical wind shear through baroclinic instability, and the Changma&Meiyu mode has a strengthened tropic-subtropics connection along the western north Pacific subtropical high, which induces vertical destabilization and strong convective instability. The WNPSM and monsoon gyre modes are characterized by anomalous southeasterly flow of warm and moist air from western north Pacific monsoon, and low-level easterly flow, respectively. Prominent difference in response to the ENSO leads to different effects of the Indian Ocean and western Pacific thermal state, and consequently, the distinct moisture supply and instability variations for the EASM intra-seasonal modes. We attempt to determine the predictability sources for the four modes in the EA-WNPSM using physical-empirical model. The selected predictors are based on the persistent and tendency signals of the SST/2m air temperature and sea level pressure fields, which reflect the asymmetric response to the ENSO and the ocean and land surface anomalous conditions. For the preMeiyu&Baiu mode, the SST cooling tendency over the WNP, which persists into summer, is the distinguishing contributor which is causative of north-south thermal contrast. Since the Changma&Meiyu mode is strongly related to the WNP subtropical high, a major precursor is the persistent SST difference between the Indian Ocean and the western Pacific. The WNPSM mode is mostly affected by the

  15. Indian Monsoon Low-Pressure Systems Feed Up-and-Over Moisture Transport to the Southwestern Tibetan Plateau

    Science.gov (United States)

    Dong, Wenhao; Lin, Yanluan; Wright, Jonathon S.; Xie, Yuanyu; Xu, Fanghua; Xu, Wenqing; Wang, Yan

    2017-11-01

    As an integral part of the South Asian summer monsoon system, monsoon low-pressure systems (LPSs) bring large amounts of precipitation to agrarian north and central India during their passage across the subcontinent. In this study, we investigate the role of LPSs in supplying moisture from north and central India to the southwestern Tibetan Plateau (SWTP) and quantify the contribution of these systems to summer rainfall over the SWTP. The results show that more than 60% of total summer rainfall over the SWTP is related to LPS occurrence. LPSs are associated with a 15% rise in average daily rainfall and a 10% rise in rainy days over the SWTP. This relationship is maintained primarily through up-and-over transport, in which convectively lifted moisture over the Indian subcontinent is swept over the SWTP by southwesterly winds in the middle troposphere. LPSs play two roles in supplying up-and-over moisture transport. First, these systems elevate large amounts of water vapor and condensed water to the midtroposphere. Second, the circulations associated with LPSs interact with the background westerlies to induce southwesterly flow in the midtroposphere, transporting elevated moisture and condensate over the Himalayan Mountains. Our findings indicate that LPSs are influential in extending the northern boundary of the South Asian monsoon system across the Himalayas into the interior of the SWTP. The strength of this connection depends on both LPS characteristics and the configuration of the midtropospheric circulation, particularly the prevailing westerlies upstream of the SWTP.

  16. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene.

    Science.gov (United States)

    Kumaran, Navnith K P; Padmalal, Damodaran; Limaye, Ruta B; S, Vishnu Mohan; Jennerjahn, Tim; Gamre, Pradeep G

    2016-01-01

    Holocene sequences in the humid tropical region of Kerala, South-western (SW) India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub-coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon-lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0-3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The alarming rate of land

  17. Tropical Peat and Peatland Development in the Floodplains of the Greater Pamba Basin, South-Western India during the Holocene.

    Directory of Open Access Journals (Sweden)

    Navnith K P Kumaran

    Full Text Available Holocene sequences in the humid tropical region of Kerala, South-western (SW India have preserved abundance of organic-rich sediments in the form of peat and its rapid development in a narrow time frame towards Middle Holocene has been found to be significant. The sub-coastal areas and flood plains of the Greater Pamba Basin have provided palaeorecords of peat indicating that the deposits are essentially formed within freshwater. The combination of factors like stabilized sea level and its subsequent fall since the Middle Holocene, topographic relief and climatic conditions led to rapid peat accumulation across the coastal lowlands. The high rainfall and massive floods coupled with a rising sea level must have inundated > 75% of the coastal plain land converting it into a veritable lagoon-lake system that eventually led to abrupt termination of the forest ecosystem and also converted the floodplains into peatland where accumulation of peat almost to 2.0-3.0 m thickness in coastal lowlands and river basins during the shorter interval in the Middle Holocene. Vast areas of the coastal plains of Kerala have been converted into carbon rich peatland during the Middle Holocene and transforming the entire coastal stretch and associated landforms as one of the relatively youngest peatlands in the extreme southern tip of India. Unlike the uninterrupted formation of peatlands of considerable extent during the Holocene in Southeast Asia, the south Peninsular Indian region has restricted and short intervals of peatlands in the floodplains and coastal lowlands. Such a scenario is attributed to the topographic relief of the terrain and the prevailing hydrological regimes and environmental conditions as a consequence of monsoon variability since Middle Holocene in SW India. Considering the tropical coastal lowlands and associated peatlands are excellent repositories of carbon, they are very important for regional carbon cycling and habitat diversity. The

  18. Asian gas

    International Nuclear Information System (INIS)

    Masuda, T.

    1990-01-01

    This paper reports on natural gas which now appears ready to take a leading role on the world energy stage. Demand for natural gas, and specifically LNG, will be strong throughout the world, particularly in Asia. Indonesia and Malaysia will become much more dependent on natural gas in the Asian market. In Thailand, where remarkable economic growth has been fueled by imported oil and domestically produced natural gas, LNG may soon have to be imported from neighboring countries. The author sees Thailand's imports of natural gas increasing from 1.5 to 4.5 million tons annually. Similarly, Korea's imports of LNG will rise from 2 to 8 million tons between 1987 and 2000. In Japan, energy demand is expected to increase at an even faster rate in the 1990s. Given the opposition to nuclear power generation and growing concern about the greenhouse effect, it is likely that LNG will satisfy a major portion of Japan's increasing demand for energy. Japanese gas companies are studying the possibility of establishing a national pipeline network to move gas beyond metropolitan areas

  19. New stable isotope records of sediment cores from the SE Arabian Sea - Inferences on the variations in monsoon regime during the late Quaternery

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.

    , Vidyanagar 671 123, India We reconstruct here the changes in regional hydr o- graphy related to the fluctuations in Indian mo n soons du r ing the late Quaternary based on the stable isotope composition of the foraminifers and organic matter in three... value du r ing the early Holocene for the eastern Arabian Sea 21 . The SW monsoon intensity was very weak and the dry NE mo n soon was the dominant feature during the LGM in the Ar a bian Sea 3 . The cool winds of the north - easterly winter...

  20. Young Asian Dutch constructing Asianness: Understanding the role of Asian popular culture

    NARCIS (Netherlands)

    Kartosen, R.A.

    2016-01-01

    This doctoral thesis is about young Asian Dutch, panethnic Asian identities and identifications, and Asian/Asian Dutch popular culture. It addresses several pressing questions, including: why do young Asian Dutch, who were born and/or raised in the Netherlands, identify as Asian and construct Asian

  1. Insolation driven biomagnetic response to Holocene Warm Period in semi-arid East Asia

    OpenAIRE

    Liu, S.; Deng, Chenglong; Xiao, Jule; Li, Jinhua; Paterson, Greig; Chang, Liao; Yi, Liang; Qin, Huafeng; Pan, Yongxin; Zhu, Rixiang

    2015-01-01

    The Holocene Warm Period (HWP) provides valuable insights into the climate system and biotic responses to environmental variability and thus serves as an excellent analogue for future global climate changes. Here we document, for the first time, that warm and wet HWP conditions were highly favourable for magnetofossil proliferation in the semi-arid Asian interior. The pronounced increase of magnetofossil concentrations at ~9.8 ka and decrease at ~5.9 ka in Dali Lake coincided respectively wit...

  2. How much rainfall sustained a Green Sahara during the mid-Holocene?

    Science.gov (United States)

    Hopcroft, Peter; Valdes, Paul; Harper, Anna

    2016-04-01

    The present-day Sahara desert has periodically transformed to an area of lakes and vegetation during the Quaternary in response to orbitally-induced changes in the monsoon circulation. Coupled atmosphere-ocean general circulation model simulations of the mid-Holocene generally underestimate the required monsoon shift, casting doubt on the fidelity of these models. However, the climatic regime that characterised this period remains unclear. To address this, we applied an ensemble of dynamic vegetation model simulations using two different models: JULES (Joint UK Land Environment Simulator) a comprehensive land surface model, and LPJ (Lund-Potsdam-Jena model) a widely used dynamic vegetation model. The simulations are forced with a number of idealized climate scenarios, in which an observational climatology is progressively altered with imposed anomalies of precipitation and other related variables, including cloud cover and humidity. The applied anomalies are based on an ensemble of general circulation model simulations, and include seasonal variations but are spatially uniform across the region. When perturbing precipitation alone, a significant increase of at least 700mm/year is required to produce model simulations with non-negligible vegetation coverage in the Sahara region. Changes in related variables including cloud cover, surface radiation fluxes and humidity are found to be important in the models, as they modify the water balance and so affect plant growth. Including anomalies in all of these variables together reduces the precipitation change required for a Green Sahara compared to the case of increasing precipitation alone. We assess whether the precipitation changes implied by these vegetation model simulations are consistent with reconstructions for the mid-Holocene from pollen samples. Further, Earth System models predict precipitation increases that are significantly smaller than that inferred from these vegetation model simulations. Understanding

  3. Ethnopsychopharmacology considerations for Asians and Asian Americans.

    Science.gov (United States)

    Wong, Felicia K; Pi, Edmond H

    2012-03-01

    Asians comprise more than 60% of the world's population and are the fastest growing minority group in the United States. Today's psychiatrist must learn to recognize and appreciate the unique factors that influence mental health outcomes in this group. Asian Americans are affected by psychiatric disorders at similar rates as non-Asians, but are significantly underrepresented in psychiatric clinics. When Asians and Asian Americans do present for psychiatric treatment, they often do so with higher severity of illness, and variable levels of compliance. Studies over the past three decades have suggested that pharmacokinetic and pharmacodynamic profiles of various psychotropic medications may be different in Asians, leading to differences in dosage requirements and side-effect profiles. These variations appear to be largely determined by genetic predisposition, but are also influenced by other factors such as environment, social support, cultural perceptions, and physicians' prescribing habits. In this paper, we provide an overview of biological and socio-cultural issues as they relate to psychopharmacology in Asians and Asian Americans, with the hope that a better understanding of these issues will lead to improved mental health care delivery to this population both in the United States, as well as in Asian countries. Copyright © 2012 Elsevier B.V. All rights reserved.

  4. Forecasting Monsoon Precipitation Using Artificial Neural Networks

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This paper explores the application of Artificial Intelligent (AI) techniques for climate forecast. It pres ents a study on modelling the monsoon precipitation forecast by means of Artificial Neural Networks (ANNs). Using the historical data of the total amount of summer rainfall over the Delta Area of Yangtze River in China, three ANNs models have been developed to forecast the monsoon precipitation in the corre sponding area one year, five-year, and ten-year forward respectively. Performances of the models have been validated using a 'new' data set that has not been exposed to the models during the processes of model development and test. The experiment results are promising, indicating that the proposed ANNs models have good quality in terms of the accuracy, stability and generalisation ability.

  5. Automated software configuration in the MONSOON system

    Science.gov (United States)

    Daly, Philip N.; Buchholz, Nick C.; Moore, Peter C.

    2004-09-01

    MONSOON is the next generation OUV-IR controller project being developed at NOAO. The design is flexible, emphasizing code re-use, maintainability and scalability as key factors. The software needs to support widely divergent detector systems ranging from multi-chip mosaics (for LSST, QUOTA, ODI and NEWFIRM) down to large single or multi-detector laboratory development systems. In order for this flexibility to be effective and safe, the software must be able to configure itself to the requirements of the attached detector system at startup. The basic building block of all MONSOON systems is the PAN-DHE pair which make up a single data acquisition node. In this paper we discuss the software solutions used in the automatic PAN configuration system.

  6. 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.

    rains happening during the last phase of monsoon development as a consequence of and after (2-5 weeks) the establishment of monsoon circulation or monsoon front. Summer monsoon front, as the term 'monsoon' originally meant, is to be delineated from...

  7. Possible Influences of Air Pollution, Dust and Sandstorms on the Indian Monsoon

    Science.gov (United States)

    Lau, William K. M.; Kim, Kyu-Myong; Hsu, Christina N.; Holben, Brent N.

    2010-01-01

    In Asian monsoon countries, such as China and India, human health and safety problems caused by air pollution are becoming increasingly serious, due to the increased loading of atmospheric pollutants from waste gas emissions and from rising energy demand associated with the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon rain associated with flash floods or prolonged drought, has caused major loss of human life and damage to crops and.property with devastating societal impacts. Historically, air-pollution and monsoons research are treated as separate problems. However recent studies have suggested that the two problems may be intrinsically linked and need to be studied jointly. Fundamentally, aerosols can affect precipitation through radiative effects cif suspended particles in the atmosphere (direct effect) and/or by interfering and changing: the cloud and precipitation formation processes (indirect effect). Based on their optical properties, aerosols can be classified into two types.: those that absorb solar radiation, and those that do not. Both types of aerosols scatter sunlight and reduce the amount of solar radiation from reaching the Earth's surface, causing it to cool. The surface cooling increases atmospheric stability and reduces convection potential, Absorbing aerosols, however, in addition to cooling the surface, can heat the atmosphere. The heating of the atmosphere may reduce the amount of low clouds by increased evaporation in cloud drops. The heating, however, may induce rising motion, enhance low-level moisture, convergence and, hence, increases rainfall, The latent heating from enhanced rainfall may excite feedback processes in the large-scale circulation, further amplify.the initial response to aerosol heating and producing more rain. Additionally, aerosols can increase the concentration of cloud condensation nuclei (CCN), increase cloud amount and decrease coalescence and collision rates, leading to

  8. Osteoporosis and Asian American Women

    Science.gov (United States)

    ... and Asian American Women Osteoporosis and Asian American Women Asian American women are at high risk for ... medications. Are There Any Special Issues for Asian Women Regarding Bone Health? Recent studies indicate a number ...

  9. Late Pleistocene - Holocene development of the Tista megafan (West Bengal, India): 10Be cosmogenic and IRSL age constraints

    Science.gov (United States)

    Abrahami, Rachel; Huyghe, Pascale; van der Beek, Peter; Lowick, Sally; Carcaillet, Julien; Chakraborty, Tapan

    2018-04-01

    The Himalayan proximal foreland is characterized by Quaternary megafans, of which the formational mechanisms remain debated. The Tista megafan spreads over more than 16,000 km2 from the mountain front, where it is strongly incised, to the confluence of the Tista River with the Jamuna/Brahmaputra River, and stores sediments produced in the Sikkim Himalaya. We propose a scenario for the late Pleistocene - Holocene development of the Tista megafan based on new 10Be cosmogenic and Infra-Red Stimulated Luminescence (IRSL) age constraints, and discuss the main potential controls on its evolution. We suggest that two distal lobes developed successively downstream from a common proximal lobe. Deposition in the proximal lobe took place since at least ∼135 ka and incision began at 3.7-0.7+1.0 ka. The western distal lobe of the megafan was deposited early in the history of the megafan, when the Sikkim Himalaya catchment was drained by a tributary of the Ganga River, and was abandoned in the early Holocene (10-11 ka). The eastern, recent (active. Approximately synchronous incision between terraces in the hinterland and megafan surfaces suggests that incision propagated rapidly through the system. Our data do not evidence a direct link between incicion and tectonic processes. Aggradation and incision episodes appear more compatible with a climatic control, through changes in monsoon intensity and associated sediment flux. Depositional episodes in the Tista megafan, as elsewhere in the Himalaya and its foreland, appear to correlate with periods of strong monsoon precipitation and associated high sediment flux toward the foreland. Abandonment and incision of megafan surfaces and hinterland terraces appear associated to both the onset and the ending of phases of strong monsoon precipitation, during which the balance between water and sediment discharge changes rapidly.

  10. Riding the Asian Wave....

    Science.gov (United States)

    Ward, Ben

    1999-01-01

    Discusses strategies U.S. universities are using to deal with declining enrollments by Asian students, brought on by the Asian financial crisis. Strategies include recruiting students from other countries. (Author/VWL)

  11. Obesity and Asian Americans

    Science.gov (United States)

    ... and Data > Minority Population Profiles > Asian American > Obesity Obesity and Asian Americans Non-Hispanic whites are 60% ... youthonline . [Accessed 08/18/2017] HEALTH IMPACT OF OBESITY People who are overweight are more likely to ...

  12. Glaucoma in Asian Populations

    Science.gov (United States)

    ... Involved News About Us Donate In This Section Glaucoma In Asian Populations email Send this article to ... lower than in their Asian counterparts. Normal Tension Glaucoma affects Japanese Japanese populations, however, have a substantially ...

  13. Holocene glacial fluctuations in southern South America

    Science.gov (United States)

    Reynhout, S.; Sagredo, E. A.; Kaplan, M. R.; Aravena, J. C.; Martini, M. A.; Strelin, J. A.; Schaefer, J. M.

    2016-12-01

    Understanding the timing and magnitude of former glacier fluctuations is critical to decipher long-term climatic trends and to unravel both natural cycles and human impact on the current glacial behavior. Despite more than seven decades of research efforts, a unifying model of Holocene glacial fluctuations in Southern South America remains elusive. Here, we present the state-of-the-art regarding the timing of Holocene glacial fluctuation in southern Patagonia-Tierra del Fuego, with a focus on a new generation of high-resolution radiocarbon and 10Be surface exposure dating chronologies. Recently acquired evidence suggest that after receding from advanced Late Glacial positions, Patagonian glaciers were for the most part close to, or even behind, present ice margins during the Early Holocene. On the other hand, emerging chronologies indicate that in some areas there were extensive expansions (century scale?) that punctuated the warm interval. Subsequently, we have evidence of multiple millennial timescale glacial advances starting in the middle Holocene. Several glacial maxima are defined by moraines and other landforms from 7000 years ago to the 19th century, with a gap sometime between 4,500 and 2,500 years ago. The last set of advances began around 800-600 years ago. Although glacial activity is documented in Patagonia at the same time as the European Little Ice Age, the extent of these glacial events are less prominent than those of the mid-Holocene. The causes that may explain these glacial fluctuations remain elusive. Finally, we discuss ongoing efforts to better define the timing and extent of Holocene glaciations in southern South America, and to establish the basis to test competing hypothesis of regional Holocene climate variability.

  14. Association between Empirically Estimated Monsoon Dynamics and Other Weather Factors and Historical Tea Yields in China: Results from a Yield Response Model

    Directory of Open Access Journals (Sweden)

    Rebecca Boehm

    2016-04-01

    Full Text Available Farmers in China’s tea-growing regions report that monsoon dynamics and other weather factors are changing and that this is affecting tea harvest decisions. To assess the effect of climate change on tea production in China, this study uses historical weather and production data from 1980 to 2011 to construct a yield response model that estimates the partial effect of weather factors on tea yields in China, with a specific focus on East Asian Monsoon dynamics. Tea (Camellia sinensis (L. Kunze has not been studied using these methods even though it is an important crop for human nutrition and the economic well-being of rural communities in many countries. Previous studies have approximated the monsoon period using historical average onset and retreat dates, which we believe limits our understanding of how changing monsoon patterns affect crop productivity. In our analysis, we instead estimate the monsoon season across China’s tea growing regions empirically by identifying the unknown breakpoints in the year-by-province cumulative precipitation. We find that a 1% increase in the monsoon retreat date is associated with 0.481%–0.535% reduction in tea yield. In the previous year, we also find that a 1% increase in the date of the monsoon retreat is associated with a 0.604% decrease in tea yields. For precipitation, we find that a 1% increase in average daily precipitation occurring during the monsoon period is associated with a 0.184%–0.262% reduction in tea yields. In addition, our models show that 1% increase in the average daily monsoon precipitation from the previous growing season is associated with 0.258%–0.327% decline in yields. We also find that a 1% decrease in solar radiation in the previous growing season is associated with 0.554%-0.864% decrease in tea yields. These findings suggest the need for adaptive management and harvesting strategies given climate change projections and the known negative association between excess

  15. On the unstable ENSO-Western North Pacific Monsoon relation during the 20th Century

    Science.gov (United States)

    Vega Martín, Inmaculada; Gallego Puyol, David; Ribera Rodriguez, Pedro; Gómez Delgado, Francisco de Paula; Peña-Ortiz, Cristina

    2017-04-01

    The concept of the Western North Pacific Summer Monsoon (WNPSM) appeared for the first time in 1987. Unlike the Indian Summer Monsoon and the East Asian summer monsoon, the WNPSM is an oceanic monsoon driven essentially by the meridional gradient of sea surface temperature. Its circulation is characterized by a northwest-southeast oriented monsoon trough with intense precipitation and low-level southwesterlies and upper-tropospheric easterlies in the region [100°-130° E, 5°-15°N]. Although this monsoon is mainly oceanic, it modulates the precipitation of densely populated areas such as the Philippines. To date, the WNPSM has been quantified by the so-called Western North Pacific Monsoon Index (WNPMI), an index based on wind anomalies over large domains of the Western Pacific. The requirement of continuous observed wind over remote oceanic areas to compute the WNPMI has limited its availability to the 1949-2014 period. In this work we have extended the index by almost 100 years by using historical observations of wind direction taken aboard ships. Our Western North Pacific Directional Index (WNPDI), is defined as the sum of the persistence of the low-level westerly winds in [5°-15°N, 100°-130°E] and easterly winds in [20°-30°N, 110°-140°E]. The new WNPDI index is highly correlated to the existent WNPMI for the concurrent period (1948-2014). (r=+0.88, p<0.01), indicating that the new approach based in the use of wind direction alone (a variable that can be considered instrumental even before the 20th Century), captures most of the monsoonal signal. Previous studies found that, during the second part of the 20th Century the WNPSM exhibited two basic characteristics: first a large interannual variability and second, a significant relation between the WNPSM and the El Niño/Southern Oscillation (ENSO) in a way in which a strong (weak) WNPSM tends to occur during the El Niño (La Niña) developing year or/and La Niña (El Niño) decaying year. The analysis of

  16. Monsoon Rainfall and Landslides in Nepal

    Science.gov (United States)

    Dahal, R. K.; Hasegawa, S.; Bhandary, N. P.; Yatabe, R.

    2009-12-01

    A large number of human settlements on the Nepal Himalayas are situated either on old landslide mass or on landslide-prone areas. As a result, a great number of people are affected by large- and small-scale landslides all over the Himalayas especially during monsoon periods. In Nepal, only in the half monsoon period (June 10 to August 15), 70, 50 and 68 people were killed from landslides in 2007, 2008 and 2009, respectively. In this context, this paper highlights monsoon rainfall and their implications in the Nepal Himalaya. In Nepal, monsoon is major source of rainfall in summer and approximately 80% of the annual total rainfall occurs from June to September. The measured values of mean annual precipitation in Nepal range from a low of approximately 250 mm at area north of the Himalaya to many areas exceeding 6,000 mm. The mean annual rainfall varying between 1500 mm and 2500 mm predominate over most of the country. In Nepal, the daily distribution of precipitation during rainy season is also uneven. Sometime 10% of the total annual precipitation can occur in a single day. Similarly, 50% total annual rainfall also can occur within 10 days of monsoon. This type of uneven distribution plays an important role in triggering many landslides in Nepal. When spatial distribution of landslides was evaluated from record of more than 650 landslides, it is found that more landslides events were concentrated at central Nepal in the area of high mean annual rainfall. When monsoon rainfall and landslide relationship was taken into consideration, it was noticed that a considerable number of landslides were triggered in the Himalaya by continuous rainfall of 3 to 90 days. It has been noticed that continuous rainfall of few days (5 days or 7 days or 10 days) are usually responsible for landsliding in the Nepal Himalaya. Monsoon rains usually fall with interruptions of 2-3 days and are generally characterized by low intensity and long duration. Thus, there is a strong role of

  17. Onset, active and break periods of the Australian monsoon

    International Nuclear Information System (INIS)

    Shaik, Hakeem A; Cleland, Samuel J

    2010-01-01

    Four operational techniques of monsoon monitoring the Australian monsoon at Darwin have been developed in the Darwin Regional Specialised Meteorological Centre. Two techniques used the rainfall only criteria and look into the onset of wet season rainfall/monsoon rainfall. The other two techniques are based purely on Darwin wind data. The data used for the study ranges from 14 to 21 years. The main purpose of the study is to develop near-real time monitoring tools for the Australian monsoon at Darwin. The average date of onset of the monsoon ranges from 19 December to 30 December. The average date of monsoon onset is 28 December. In eleven out of twenty-one years the onset date remained within three days range between the two rainfall techniques, whereas it is eleven out of fourteen years between the wind techniques. The median number of active monsoon spells in a wet season is 3 for the rainfall techniques and 6 for the wind techniques. The average length of each active monsoon spell is around 4 days for all of the techniques. The date of onset of the monsoon has shown negative correlation with the Southern Oscillation Index (SOI) that is late onset is found to occur in El Nino years while early onset is more likely in La Nina years.

  18. Reconstructing Oceanographic Conditions From the Holocene to the Last Glacial Maximum in the Bay of Bengal

    Science.gov (United States)

    Miller, J.; Dekens, P. S.; Weber, M. E.; Spiess, V.; France-Lanord, C.

    2015-12-01

    The International Ocean Discovery Program (IODP) Expedition 354 drilled 7 sites in the Bay of Bengal, providing a unique opportunity to improve our understanding of the link between glacial cycles, tropical oceanographic changes, and monsoon strength. Deep-sea sediment cores of the Bengal Fan fluctuate between sand, hemipelagic and terrestrial sediment layers. All but one of the sites (U1454) contain a layer of calcareous clay in the uppermost part of the core that is late Pleistocene in age. During Expedition 354 site U1452C was sampled at high resolution (every 2cm) by a broad group of collaborators with the goal of reconstructing monsoon strength and oceanographic conditions using a variety of proxies. The top 480 cm of site U1452C (8ºN, 87ºE, 3671m water depth) contains primarily nannofossil rich calcareous clay. The relatively high abundance of foraminifera will allow us to generate a high resolution record of sea surface temperature (SST) and sea surface salinity (SSS) using standard foraminifera proxies. We will present oxygen isotopes (δ18O) and Mg/Ca data of mixed layer planktonic foraminifera from the top 70cm of the core, representing the Holocene to the last glacial maximum. δ18O of planktonic foraminifera records global ice volume and local SST and SSS, while Mg/Ca of foraminifera is a proxy for SST. The paired Mg/Ca and δ18O measurements on the same samples of foraminifera, together with published estimates with global ocean δ18O, can be used to reconstruct both SST and local δ18O of seawater, which is a function of the evaporation/precipitation balance. In future work, the local SSS and SST during the LGM will be paired with terrestrial and other oceanic proxies to increase our understanding of how global climate is connected to monsoon strength.

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

    Science.gov (United States)

    Lau, William K. M.

    2006-01-01

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

  20. Sea surface temperature variability over North Indian Ocean - A study of two contrasting monsoon seasons

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Sathyendranath, S.; Viswambharan, N.K.; Rao, L.V.G.

    Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali...

  1. The Mt Logan Holocene-late Wisconsinan isotope record

    DEFF Research Database (Denmark)

    Dahl-Jensen, Dorthe; Fisher, David; Osterberg, Erich

    2008-01-01

    Mt Logan • stable isotopes • Holocene • ENSO • peat • N Pacific • sudden change Udgivelsesdato: August......Mt Logan • stable isotopes • Holocene • ENSO • peat • N Pacific • sudden change Udgivelsesdato: August...

  2. Effects of volcanic eruptions on China's monsoon precipitation over the past 700 years

    Science.gov (United States)

    Zhuo, Z.; Gao, C.

    2013-12-01

    Tropical volcanic eruptions were found to affect precipitation especially in Asia and Africa monsoon region. However, studies with different types of eruptions suggested different impacts as well as the spatial patterns. In this study, we combined the Monsoon Asia Drought Atlas (MADA, [Cook et al., 2010]) and the Chinese Historical Drought Disaster Index (CHDDI) compiled from the historic meteorological records to study the effect of volcanic eruptions on China's monsoon precipitation over the past 700 years. Histories of past volcanism were compiled from the IVI2[Gao et al., 2008] and Crowley2013[Crowley and Unterman, 2013] reconstructions. Volcanic events were classified into 2×Pinatubo, 1×Pinatubo , ≥5 Tg sulfate aerosols injection in the northern hemisphere (NH) stratosphere for IVI2; and NH sulfate flux more than 20/15/10/5 kg km-2 for Crowley2013. In both cases, average MADA show a drying trend over mainland China from year zero(0) to year three(+3) after the eruption; and the more sulfate aerosol injected into the NH stratosphere or the larger the sulfate flux, the more severe this drying trend seem to reveal. In comparison, a wetting trend was found in the eruption year with Southern Hemisphere (SH) only injections. Superposed epoch analysis with a 10,000 Monte Carlo resampling procedure showed that 97.9% (96.9%) of the observed MADA values are statistically significant at the 95% (99%) confidence level. The drying is probably caused by a reduction of the latent heat flux due to volcanic aerosol' cooling effect, leading to the weakening of south Asian monsoon and decrease of moisture vapor over tropical oceans, which contribute to a reduced moisture flux over china. Spatial distribution of the average MADA show a southward movement of the driest areas in eastern China from year zero to year three after the 1×Pinatubo and 2×Pinatubo eruptions, whereas part of north china experienced unusual wetting condition. This is in good agreement with CHDDI, which

  3. Early forecasting of Indian Summer Monsoon: case study 2016

    Science.gov (United States)

    Surovyatkina, Elena; Stolbova, Veronika; Kurths, Jurgen

    2017-04-01

    The prior knowledge of dates of onset and withdrawal of monsoon is of vital importance for the population of the Indian subcontinent. In May 2016 before monsoon season, India recorded its highest-ever temperature of 51C. Hot waves have decimated crops, killed livestock and left 330 million people without enough water. At the end of monsoon season the floods in Indian this year have also broken previous records. Severe and devastating rainfall poured down, triggering dams spilling and floods. Such extreme conditions pose the vital questions such as: When will the monsoon come? When will the monsoon withdraw? More lead time in monsoon forecast warning is crucial for taking appropriate decisions at various levels - from the farmer's field (e.g. plowing day, seeding) to the central government (e.g. managing water and energy resources, food procurement policies). The Indian Meteorological Department issues forecasts of onset of monsoon for Kerala state in South India on May 15-th. It does not give such predictions for the other 28 states of the country. Our study concerns the central part of India. We made the monsoon forecast using our recently developed method which focuses on Tipping elements of the Indian monsoon [1]. Our prediction relies on observations of near-surface air temperature and relative humidity from both the ERA-40 and NCEP/NCAR reanalyses. We performed both of our forecasts for the onset and withdrawal of monsoon for the central part of India, the Eastern Ghats (20N,80E). We predicted the monsoon arrival to the Eastern Ghats (20N,80E) on the 13th of June with a deviation of +/-4 days. The prediction was made on May 6-th, 2016 [2], that is 40 days in advance of the date of the forecast. The actual monsoon arrival was June 17-th. In this day near-surface air temperature and relative humidity overcame the critical values and the monsoon season started, that was confirmed by observations of meteorological stations located around the EG-region. We

  4. The mtDNA haplogroup P of modern Asian cattle: A genetic legacy of Asian aurochs?

    Science.gov (United States)

    Noda, Aoi; Yonesaka, Riku; Sasazaki, Shinji

    2018-01-01

    Background Aurochs (Bos primigenius) were distributed throughout large parts of Eurasia and Northern Africa during the late Pleistocene and the early Holocene, and all modern cattle are derived from the aurochs. Although the mtDNA haplogroups of most modern cattle belong to haplogroups T and I, several additional haplogroups (P, Q, R, C and E) have been identified in modern cattle and aurochs. Haplogroup P was the most common haplogroup in European aurochs, but so far, it has been identified in only three of >3,000 submitted haplotypes of modern Asian cattle. Methodology We sequenced the complete mtDNA D-loop region of 181 Japanese Shorthorn cattle and analyzed these together with representative bovine mtDNA sequences. The haplotype P of Japanese Shorthorn cattle was analyzed along with that of 36 previously published European aurochs and three modern Asian cattle sequences using the hypervariable 410 bp of the D-loop region. Conclusions We detected the mtDNA haplogroup P in Japanese Shorthorn cattle with an extremely high frequency (83/181). Phylogenetic networks revealed two main clusters, designated as Pa for haplogroup P in European aurochs and Pc in modern Asian cattle. We also report the genetic diversity of haplogroup P compared with the sequences of extinct aurochs. No shared haplotypes are observed between the European aurochs and the modern Asian cattle. This finding suggests the possibility of local and secondary introgression events of haplogroup P in northeast Asian cattle, and will contribute to a better understanding of its origin and genetic diversity. PMID:29304129

  5. The mtDNA haplogroup P of modern Asian cattle: A genetic legacy of Asian aurochs?

    Science.gov (United States)

    Noda, Aoi; Yonesaka, Riku; Sasazaki, Shinji; Mannen, Hideyuki

    2018-01-01

    Aurochs (Bos primigenius) were distributed throughout large parts of Eurasia and Northern Africa during the late Pleistocene and the early Holocene, and all modern cattle are derived from the aurochs. Although the mtDNA haplogroups of most modern cattle belong to haplogroups T and I, several additional haplogroups (P, Q, R, C and E) have been identified in modern cattle and aurochs. Haplogroup P was the most common haplogroup in European aurochs, but so far, it has been identified in only three of >3,000 submitted haplotypes of modern Asian cattle. We sequenced the complete mtDNA D-loop region of 181 Japanese Shorthorn cattle and analyzed these together with representative bovine mtDNA sequences. The haplotype P of Japanese Shorthorn cattle was analyzed along with that of 36 previously published European aurochs and three modern Asian cattle sequences using the hypervariable 410 bp of the D-loop region. We detected the mtDNA haplogroup P in Japanese Shorthorn cattle with an extremely high frequency (83/181). Phylogenetic networks revealed two main clusters, designated as Pa for haplogroup P in European aurochs and Pc in modern Asian cattle. We also report the genetic diversity of haplogroup P compared with the sequences of extinct aurochs. No shared haplotypes are observed between the European aurochs and the modern Asian cattle. This finding suggests the possibility of local and secondary introgression events of haplogroup P in northeast Asian cattle, and will contribute to a better understanding of its origin and genetic diversity.

  6. Evaporation over the Arabian Sea during two contrasting monsoons

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.; Sadhuram, Y.

    monsoon rainfall. It is noticed that in general, the sea surface temperatures are higher in 1983 throughout the monsoon season than in 1979 in the Arabian Sea excepting western region. The mean rates of evaporation on a seasonal scale are found to be equal...

  7. Reconciling societal and scientific definitions for the monsoon

    Science.gov (United States)

    Reeve, Mathew; Stephenson, David

    2014-05-01

    Science defines the monsoon in numerous ways. We can apply these definitions to forecast data, reanalysis data, observations, GCMs and more. In a basic research setting, we hope that this work will advance science and our understanding of the monsoon system. In an applied research setting, we often hope that this work will benefit a specific stakeholder or community. We may want to inform a stakeholder when the monsoon starts, now and in the future. However, what happens if the stakeholders cannot relate to the information because their perceptions do not align with the monsoon definition we use in our analysis? We can resolve this either by teaching the stakeholders or learning from them about how they define the monsoon and when they perceive it to begin. In this work we reconcile different scientific monsoon definitions with the perceptions of agricultural communities in Bangladesh. We have developed a statistical technique that rates different scientific definitions against the people's perceptions of when the monsoon starts and ends. We construct a probability mass function (pmf) around each of the respondent's answers in a questionnaire survey. We can use this pmf to analyze the time series of monsoon onsets and withdrawals from the different scientific definitions. We can thereby quantitatively judge which definition may be most appropriate for a specific applied research setting.

  8. The monsoon system: Land–sea breeze or the ITCZ?

    Indian Academy of Sciences (India)

    Sulochana Gadgil

    2018-01-27

    Jan 27, 2018 ... ocean contrast is one of the main drivers of the monsoon rainfall, in the 5th Assessment Report of the Inter-governmental Panel on Climate Change. (IPCC Climate Change 2013), the likely enhance- ment of monsoon rainfall has been attributed to increased land–sea contrast, and more abundant.

  9. Impact of Climate Change on India's Monsoonal Climate: Present ...

    Indian Academy of Sciences (India)

    Expected Future Changes in Rainfall and Temperature over India under IPCC SRES A1B GHG Scenarios · Expected Future Change in Monsoon Rainfall and Annual Surface Temp for 2020's, 2050's and 2080's · Likely Future Paradox of Monsoon-ENSO Links · High-Resolution Regional Climate Change Scenarios.

  10. Gridded daily Indian monsoon rainfall for 14 seasons: Merged ...

    Indian Academy of Sciences (India)

    Indian monsoon is an important component of earth's climate system. Daily rainfall data for longer period is vital to study components and processes related to Indian monsoon. Daily observed gridded rainfall data covering both land and adjoining oceanic regions are required for numerical model vali- dation and model ...

  11. Site-specific high-resolution models of the monsoon for Africa and Asia

    Science.gov (United States)

    Bryson, R. A.; Bryson, R. U.

    2000-11-01

    Using the macrophysical climate model of Bryson [Bryson, R.A., 1992. A macrophysical model of the Holocene intertropical convergence and jetstream positions and rainfall for the Saharan region. Meteorol. Atmos. Phys., 47, pp. 247-258], it is possible to calculate the monthly latitude of the jetstream and the latitude of the subtropical anticyclones. From these and modern climatic data, it is possible to model the two-century mean latitude of the intertropical convergence (ITC) month by month and estimate the monthly monsoon rainfall using the ITC-Rainfall model of Ilesanmi [Ilesanmi, O.O., 1971. An empirical formulation of an ITD rainfall model for the tropics — a case study of Nigeria. J. Appl. Meteorol., 10, pp. 882-891] and similar relationships. Input to this model is only calculated radiation and atmospheric optical depth estimated from a database of global volcanicity. Recent work has shown that it is possible to extend these estimates to both precipitation and temperature at specific sites, even in mountainous terrain. Testing of the model against archaeological records and climatic proxies is now underway, as well as refining the fundamental model. Preliminary indications are that the timing of fluctuations in the local climate is very well modeled. Especially well matched are the modeled Nile flood based on calculated rainfall on the Blue and White Nile watersheds and the level of Lake Moeris [Hassan, F., 1985. Holocene lakes and prehistoric settlements of the Western Faiyum, Egypt. J. Archaeol. Res., 13, pp. 483-501]. Modeled precipitation histories for specific sites in China, Thailand, the Arabian Peninsula, and North Africa will be presented and contrasted with the simulated rainfall history of Mesopotamia.

  12. The greening of the McGill Paleoclimate Model. Part II: Simulation of Holocene millennial-scale natural climate changes

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yi; Mysak, Lawrence A.; Wang, Zhaomin [McGill University, Department of Atmospheric and Oceanic Sciences and Global Environmental and Climate Change Centre (GEC3), Montreal, Quebec (Canada); Brovkin, Victor [Potsdam Institute for Climate Impact Research (PIK), 601203, Potsdam (Germany)

    2005-04-01

    Various proxy data reveal that in many regions of the Northern Hemisphere (NH), the middle Holocene (6 kyr BP) was warmer than the early Holocene (8 kyr BP) as well as the later Holocene, up to the end of the pre-industrial period (1800 AD). This pattern of warming and then cooling in the NH represents the response of the climate system to changes in orbital forcing, vegetation cover and the Laurentide Ice Sheet (LIS) during the Holocene. In an attempt to better understand these changes in the climate system, the McGill Paleoclimate Model (MPM) has been coupled to the dynamic global vegetation model known as VECODE (see Part I of this two-part paper), and a number of sensitivity experiments have been performed with the ''green'' MPM. The model results illustrate the following: (1) the orbital forcing together with the vegetation - albedo feedback result in the gradual cooling of global SAT from about 6 kyr BP to the end of the pre-industrial period; (2) the disappearance of the LIS over the period 8-6 kyr BP, associated with vegetation - albedo feedback, allows the global SAT to increase and reach its maximum at around 6 kyr BP; (3) the northern limit of the boreal forest moves northward during the period 8-6.4 kyr BP due to the LIS retreat; (4) during the period 6.4-0 kyr BP, the northern limit of the boreal forest moves southward about 120 km in response to the decreasing summer insolation in the NH; and (5) the desertification of northern Africa during the period 8-2.6 kyr BP is mainly explained by the decreasing summer monsoon precipitation. (orig.)

  13. The Holocene warm-humid phases in the North China Plain as recorded by multi-proxy records

    Science.gov (United States)

    Cui, Jianxin; Zhou, Shangzhe; Chang, Hong

    2009-02-01

    The grain size and palinology of sediment and the frequency of 14C dada provide an integrated reconstruction of the Holocene warm-humid phases of the North China Plain. Two clear intense and long-lasting warm-humid phases were identified by comprehensive research in this region. The first phase was dated back to the early Holocene (9 000-7 000 a BP), and the second was centered at 5 000-3 000 a BP. The warm-humid episode between 9 000 and 7 000 a BP was also recognized at other sites showing global climatic trends rather than local events. Compared with the concern to the warm-humid phase of the early Holocene, the second one was not paid enough attention in the last few decades. The compilation of the Holocene paleoclimate data suggests that perhaps the second warm-humid phase was pervasive in monsoon region of China. In perspective of environmental archaeology, much attention should be devoted to it, because the flourish and adaptation of the Neolithic cultures and the building up of the first state seem to corresponding to the general warm-humid climatic conditions of this period. In addition, a warm-humid interval at 7 200-6 500 a BP was recognized by the grain size data from three sites. However, this warm-humid event was not shown in pollen assemblage and temporal distribution of 14C data. Perhaps, the resolution for climatic reconstruction from pollen and temporal distribution of 14C data cited here is relatively low and small-amplitude and short-period climatic events cannot be well reflected by the data. Due to the difference in locality and elevation of sampling site, as well as in resolution of proxy records, it is difficult to make precise correlation. Further work is needed in the future.

  14. Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition

    Science.gov (United States)

    Dong, Yajie; Wu, Naiqin; Li, Fengjiang; Huang, Linpei; Wen, Wenwen

    2015-01-01

    The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS) has previously been assumed to be synchronous with the Marine Isotope Stage (MIS) 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP). However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR) protocol to the 45–63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL) samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3–4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast. PMID:26186443

  15. Time-Transgressive Nature of the Magnetic Susceptibility Record across the Chinese Loess Plateau at the Pleistocene/Holocene Transition.

    Directory of Open Access Journals (Sweden)

    Yajie Dong

    Full Text Available The loess stratigraphic boundary at the Pleistocene/Holocene transition defined by the magnetic susceptibility (MS has previously been assumed to be synchronous with the Marine Isotope Stage (MIS 2/1 boundary, and approximately time-synchronous at different sections across the Chinese Loess Plateau (CLP. However, although this assumption has been used as a basis for proxy-age model of Chinese loess deposits, it has rarely been tested by using absolute dating methods. In this study, we applied a single-aliquot regenerative-dose (SAR protocol to the 45-63 μm quartz grain-size fraction to derive luminescence ages for the last glacial and Holocene sections of three loess sections on a transect from southeast to northwest across the CLP. Based on the 33 closely spaced optically stimulated luminescence (OSL samples from the three sections, OSL chronologies were established using a polynomial curve fit at each section. Based on the OSL chronology, the timing of the Pleistocene/Holocene boundary, as defined by rapid changes in MS values, is dated at ~10.5 ka, 8.5 ka and 7.5 ka in the Yaoxian section, Jingchuan and Huanxian sections respectively. These results are clearly inconsistent with the MIS 2/1 boundary age of 12.05 ka, and therefore we conclude that the automatic correlation of the Pleistocene/Holocene transition, as inferred from the MS record, with the MIS 2/1 boundary is incorrect. The results clearly demonstrate that the marked changes in MS along the southeast to northwest transect are time-transgressive among the different sites, with the timing of significant paleosol development as indicated by the MS record being delayed by 3-4 ka in the northwest compared to the southeast. Our results suggest that this asynchronous paleosol development during the last deglacial was caused by the delayed arrival of the summer monsoon in the northwest CLP compared to the southeast.

  16. Timing and nature of Holocene glacier advances at the northwestern end of the Himalayan-Tibetan orogen

    Science.gov (United States)

    Saha, Sourav; Owen, Lewis A.; Orr, Elizabeth N.; Caffee, Marc W.

    2018-05-01

    Holocene glacial chronostratigraphies are developed for four glaciated valleys at the northwestern end of the Himalayan-Tibetan orogen using geomorphic mapping and cosmogenic 10Be surface exposure dating. The study areas include the Hamtah valley in the Lahul Himalaya, and the Karzok, Lato and upper Stok valleys in Zanskar. Five local glacial stages are dated to ∼10.4, ∼6.1-3.3, ∼2.1-0.9, ∼0.7-0.4, and ∼0.3-0.2 ka based on 49 new moraine boulder ages. Large age dispersions are evident for each of the local glacial stages. This is especially the case for ∼6.1-3.3 and ∼2.1-0.9 ka, which is likely a result of prior and/or incomplete exposures in very young moraine boulders. An additional compilation of 187 published 10Be moraine boulder ages help define seven Himalayan Holocene regional glacial stages (HHs) for the northwestern end of the Himalayan-Tibetan orogen. These HHs date to ∼10.9-9.3, ∼8.2-7.4, ∼6.9-4.3, ∼4.5-2.8, ∼2.7-1.8, ∼1.8-0.9, and forced northerly migration of the Intertropical Convergence Zone and enhanced summer monsoon. The timing of the majority of HHs during mid- and late Holocene corresponds well with the North Atlantic cooling that is likely teleconnected via mid-latitude westerlies, particularly during ∼8 ka and after ∼5 ka. These chronostratigraphies suggest that Holocene glaciation in the northwestern part of the Himalayan-Tibetan orogen is largely influenced by long-term orbital forcing amplified by large-scale migration of the Earth's thermal equator and the associated hemispheric oceanic-atmospheric systems.

  17. A 22,000-Year Record of Monsoonal Precipitation from Northern Chile's Atacama Desert.

    Science.gov (United States)

    Betancourt; Latorre; Rech; Quade; Rylander

    2000-09-01

    Fossil rodent middens and wetland deposits from the central Atacama Desert (22 degrees to 24 degrees S) indicate increasing summer precipitation, grass cover, and groundwater levels from 16.2 to 10.5 calendar kiloyears before present (ky B.P.). Higher elevation shrubs and summer-flowering grasses expanded downslope across what is now the edge of Absolute Desert, a broad expanse now largely devoid of rainfall and vegetation. Paradoxically, this pluvial period coincided with the summer insolation minimum and reduced adiabatic heating over the central Andes. Summer precipitation over the central Andes and central Atacama may depend on remote teleconnections between seasonal insolation forcing in both hemispheres, the Asian monsoon, and Pacific sea surface temperature gradients. A less pronounced episode of higher groundwater levels in the central Atacama from 8 to 3 ky B.P. conflicts with an extreme lowstand of Lake Titicaca, indicating either different climatic forcing or different response times and sensitivities to climatic change.

  18. Prominent Midlatitude Circulation Signature in High Asia's Surface Climate During Monsoon

    Science.gov (United States)

    Mölg, Thomas; Maussion, Fabien; Collier, Emily; Chiang, John C. H.; Scherer, Dieter

    2017-12-01

    High Asia has experienced strong environmental changes in recent decades, as evident in records of glaciers, lakes, tree rings, and vegetation. The multiscale understanding of the climatic drivers, however, is still incomplete. In particular, few systematic assessments have evaluated to what degree, if at all, the midlatitude westerly circulation modifies local surface climates in the reach of the Indian Summer Monsoon. This paper shows that a southward shift of the upper-tropospheric westerlies contributes significantly to climate variability in the core monsoon season (July-September) by two prominent dipole patterns at the surface: cooling in the west of High Asia contrasts with warming in the east, while moist anomalies in the east and northwest occur with drying along the southwestern margins. Circulation anomalies help to understand the dipoles and coincide with shifts in both the westerly wave train and the South Asian High, which imprint on air mass advection and local energy budgets. The relation of the variabilities to a well-established index of midlatitude climate dynamics allows future research on climate proxies to include a fresh hypothesis for the interpretation of environmental changes.

  19. Annual monsoon rains recorded by Jurassic dunes.

    Science.gov (United States)

    Loope, D B; Rowe, C M; Joeckel, R M

    2001-07-05

    Pangaea, the largest landmass in the Earth's history, was nearly bisected by the Equator during the late Palaeozoic and early Mesozoic eras. Modelling experiments and stratigraphic studies have suggested that the supercontinent generated a monsoonal atmospheric circulation that led to extreme seasonality, but direct evidence for annual rainfall periodicity has been lacking. In the Mesozoic era, about 190 million years ago, thick deposits of wind-blown sand accumulated in dunes of a vast, low-latitude desert at Pangaea's western margin. These deposits are now situated in the southwestern USA. Here we analyse slump masses in the annual depositional cycles within these deposits, which have been described for some outcrops of the Navajo Sandstone. Twenty-four slumps, which were generated by heavy rainfall, appear within one interval representing 36 years of dune migration. We interpret the positions of 20 of these masses to indicate slumping during summer monsoon rains, with the other four having been the result of winter storms. The slumped lee faces of these Jurassic dunes therefore represent a prehistoric record of yearly rain events.

  20. The Holocene History of Placentia Bay, Newfoundland

    DEFF Research Database (Denmark)

    Sheldon, Christina; Seidenkrantz, Marit-Solveig; Reynisson, Njall

    2013-01-01

    Marine sediments analyzed from cores taken in Placentia Bay, Newfoundland, located in the Labrador Sea, captured oceanographic and climatic changes from the end of the Younger Dryas through the Holocene. Placentia Bay is an ideal site to capture changes in both the south-flowing Labrador Current ...

  1. Weakening of the North American monsoon with global warming

    Science.gov (United States)

    Pascale, Salvatore; Boos, William R.; Bordoni, Simona; Delworth, Thomas L.; Kapnick, Sarah B.; Murakami, Hiroyuki; Vecchi, Gabriel A.; Zhang, Wei

    2017-11-01

    Future changes in the North American monsoon, a circulation system that brings abundant summer rains to vast areas of the North American Southwest, could have significant consequences for regional water resources. How this monsoon will change with increasing greenhouse gases, however, remains unclear, not least because coarse horizontal resolution and systematic sea-surface temperature biases limit the reliability of its numerical model simulations. Here we investigate the monsoon response to increased atmospheric carbon dioxide (CO2) concentrations using a 50-km-resolution global climate model which features a realistic representation of the monsoon climatology and its synoptic-scale variability. It is found that the monsoon response to CO2 doubling is sensitive to sea-surface temperature biases. When minimizing these biases, the model projects a robust reduction in monsoonal precipitation over the southwestern United States, contrasting with previous multi-model assessments. Most of this precipitation decline can be attributed to increased atmospheric stability, and hence weakened convection, caused by uniform sea-surface warming. These results suggest improved adaptation measures, particularly water resource planning, will be required to cope with projected reductions in monsoon rainfall in the American Southwest.

  2. Large-scale connection between aerosol optical depth and summer monsoon circulation, and precipitation over northeast Asia

    Science.gov (United States)

    Kim, Sang-Woo; Yoon, Soon-Chang; Choi, Suk-Jin; Choi, In-Jin

    2010-05-01

    We investigated the large-scale connection between columnar aerosol loads and summer monsoon circulation, and also the precipitation over northeast Asia using aerosol optical depth (AOD) data obtained from the 8-year MODIS, AERONET Sun/sky radiometer, and precipitation data acquired under the Global Precipitation Climatology Project (GPCP). These high-quality data revealed the large-scale link between AOD and summer monsoon circulation, precipitation in July over northeast Asian countries, and their distinct spatial and annual variabilities. Compared to the mean AOD for the entire period of 2001-2008, the increase of almost 40-50% in the AOD value in July 2005 and July 2007 was found over the downwind regions of China (Yellow Sea, Korean peninsula, and East Sea), with negative precipitation anomalies. This can be attributable to the strong westerly confluent flows, between cyclone flows by continental thermal low centered over the northern China and anti-cyclonic flows by the western North Pacific High, which transport anthropogenic pollution aerosols emitted from east China to aforementioned downwind high AOD regions along the rim of the Pacific marine airmass. In July 2002, however, the easterly flows transported anthropogenic aerosols from east China to the southwestern part of China in July 2002. As a result, the AOD off the coast of China was dramatically reduced in spite of decreasing rainfall. From the calculation of the cross-correlation coefficient between MODIS-derived AOD anomalies and GPCP precipitation anomalies over the period 2001-2008, we found negative correlations over the areas encompassed by 105-115E and 30-35N and by 120-140E and 35-40N (Yellow Sea, Korean peninsula, and East Sea). This suggests that aerosol loads over these regions are easily influenced by the Asian monsoon flow system and associated precipitation.

  3. SPATIO-TEMPORAL ESTIMATION OF INTEGRATED WATER VAPOUR OVER THE MALAYSIAN PENINSULA DURING MONSOON SEASON

    Directory of Open Access Journals (Sweden)

    S. Salihin

    2017-10-01

    Full Text Available This paper provides the precise information on spatial-temporal distribution of water vapour that was retrieved from Zenith Path Delay (ZPD which was estimated by Global Positioning System (GPS processing over the Malaysian Peninsular. A time series analysis of these ZPD and Integrated Water Vapor (IWV values was done to capture the characteristic on their seasonal variation during monsoon seasons. This study was found that the pattern and distribution of atmospheric water vapour over Malaysian Peninsular in whole four years periods were influenced by two inter-monsoon and two monsoon seasons which are First Inter-monsoon, Second Inter-monsoon, Southwest monsoon and Northeast monsoon.

  4. Intensified summer monsoon and the urbanization of Indus Civilization in northwest India.

    Science.gov (United States)

    Dixit, Yama; Hodell, David A; Giesche, Alena; Tandon, Sampat K; Gázquez, Fernando; Saini, Hari S; Skinner, Luke C; Mujtaba, Syed A I; Pawar, Vikas; Singh, Ravindra N; Petrie, Cameron A

    2018-03-09

    Today the desert margins of northwest India are dry and unable to support large populations, but were densely occupied by the populations of the Indus Civilization during the middle to late Holocene. The hydroclimatic conditions under which Indus urbanization took place, which was marked by a period of expanded settlement into the Thar Desert margins, remains poorly understood. We measured the isotopic values (δ 18 O and δD) of gypsum hydration water in paleolake Karsandi sediments in northern Rajasthan to infer past changes in lake hydrology, which is sensitive to changing amounts of precipitation and evaporation. Our record reveals that relatively wet conditions prevailed at the northern edge of Rajasthan from ~5.1 ± 0.2 ka BP, during the beginning of the agricultural-based Early Harappan phase of the Indus Civilization. Monsoon rainfall intensified further between 5.0 and 4.4 ka BP, during the period when Indus urban centres developed in the western Thar Desert margin and on the plains of Haryana to its north. Drier conditions set in sometime after 4.4 ka BP, and by ~3.9 ka BP an eastward shift of populations had occurred. Our findings provide evidence that climate change was associated with both the expansion and contraction of Indus urbanism along the desert margin in northwest India.

  5. Decadal Monsoon-ENSO Relationships Reexamined

    Science.gov (United States)

    Yun, Kyung-Sook; Timmermann, Axel

    2018-02-01

    The strength of the El Niño-Southern Oscillation (ENSO)-Indian summer monsoon rainfall (ISMR) relationship shows considerable decadal fluctuations, which have been previously linked to low-frequency climatic processes such as shifts in ENSO's center of action or the Atlantic Multidecadal Oscillation. However, random variability can also cause similar variations in the relationship between climate phenomena. Here we propose a statistical test to determine whether the observed time-evolving correlations between ENSO and ISMR are different from those expected from a simple stochastic null hypothesis model. The analysis focuses on the time evolution of moving correlations, their expected variance, and probabilities for rapid transitions. The results indicate that the time evolution of the observed running correlation between these climate modes is indistinguishable from a system in which the ISMR signal can be expressed as a stochastically perturbed ENSO signal. This challenges previous deterministic interpretations. Our results are further corroborated by the analysis of climate model simulations.

  6. The New Asian Immigrants.

    Science.gov (United States)

    Wong, Morrison G.; Hirschman, Charles

    In the early 1960s, Asian immigration to the United States was severely limited. The passage of the Immigration Act of 1965 expanded Asian immigration and ended a policy of racial discrimination and exclusion. Currently, over one third of the total immigrant population to the United States is from Asia, particularly China, Japan, Korea, the…

  7. Emerging Asian Economics.

    Science.gov (United States)

    Trezise, Philip H.

    What we can expect in the future from the miracle economies of Japan, South Korea, Taiwan, Singapore, and Hong Kong, whether they pose a threat to the older industrial states of Western Europe and North American, and whether China is to be the next emerging Asian economy are discussed. The amazing economic recovery of these East Asian countries…

  8. Asian American Cultural Resistance.

    Science.gov (United States)

    Libretti, Tim

    1997-01-01

    Explores the encounter of Marxism and Asian American literary theory and imagines an Asian American Marxism. To do so requires theorizing race, class, and gender not as substantive categories of antagonisms but as complementary and coordinated elements of a totality of social relations structuring racial patriarchal capitalism. (SLD)

  9. The Rhetorical Making of the Asian/Asian American Face: Reading and Writing Asian Eyelids

    OpenAIRE

    Sano-Franchini, Jennifer

    2013-01-01

    In The Rhetorical Making of the Asian/Asian American Face: Reading and Writing Asian Eyelids, I examine representations of East Asian blepharoplasty in online video in order to gain a sense of how cultural values change over time. Drawing on scholarship in and around rhetorical theory, cultural rhetorics, Asian American rhetoric, cultural studies, Asian American studies, and postcolonial theory alongside qualitative data analysis of approximately fifty videos and the numerous viewer comments ...

  10. Monsoonal Responses to External Forcings over the Past Millennium: A Model Study (Invited)

    Science.gov (United States)

    Liu, J.; Wang, B.

    2009-12-01

    The climate variations related to Global Monsoon (GM) and East Asian summer monsoon (EASM) rainfall over the past 1000 years were investigated by analysis of a pair of millennium simulations with the coupled climate model named ECHO-G. The free run was generated using fixed external (annual cycle) forcing, while the forced run was obtained using time-varying solar irradiance variability, greenhouse gases (CO2 and CH4) concentration and estimated radiative effect of volcanic aerosols. The model results indicate that the centennial-millennial variation of the GM and EASM is essentially a forced response to the external radiative forcings (insolation, volcanic aerosols, and greenhouse gases). The GM strength responds more directly to the effective solar forcing (insolation plus radiative effect of the volcanoes) when compared to responses of the global mean surface temperature on centennial timescale. The simulated GM precipitation in the forced run exhibits a significant quasi-bi-centennial oscillation. Weak GM precipitation was simulated during the Little Ice Age (1450-1850) with three weakest periods concurring with the Spörer, Maunder, and Dalton Minimum of solar activity. Conversely, strong GM was simulated during the model Medieval Warm Period (ca. 1030-1240). Before the industrial period, the natural variation in effective solar forcing reinforces the thermal contrasts both between the ocean and continent and between the northern and southern hemispheres, resulting in millennium-scale variation and the quasi-bi-centennial oscillation of the GM. The prominent upward trend in the GM precipitation occurring in the last century and the remarkably strengthening of the global monsoon in the period of 1961-1990 appear unprecedented and owed possibly in part to the increase of atmospheric carbon dioxide concentration. The EASM has the largest meridional extent (5oN-55oN) among all the regional monsoons on globe. Thus, the EASM provides an unique opportunity for

  11. Rethinking Indian monsoon rainfall prediction in the context of recent global warming

    Science.gov (United States)

    Wang, Bin; Xiang, Baoqiang; Li, Juan; Webster, Peter J.; Rajeevan, Madhavan N.; Liu, Jian; Ha, Kyung-Ja

    2015-01-01

    Prediction of Indian summer monsoon rainfall (ISMR) is at the heart of tropical climate prediction. Despite enormous progress having been made in predicting ISMR since 1886, the operational forecasts during recent decades (1989–2012) have little skill. Here we show, with both dynamical and physical–empirical models, that this recent failure is largely due to the models' inability to capture new predictability sources emerging during recent global warming, that is, the development of the central-Pacific El Nino-Southern Oscillation (CP–ENSO), the rapid deepening of the Asian Low and the strengthening of North and South Pacific Highs during boreal spring. A physical–empirical model that captures these new predictors can produce an independent forecast skill of 0.51 for 1989–2012 and a 92-year retrospective forecast skill of 0.64 for 1921–2012. The recent low skills of the dynamical models are attributed to deficiencies in capturing the developing CP–ENSO and anomalous Asian Low. The results reveal a considerable gap between ISMR prediction skill and predictability. PMID:25981180

  12. Prediction of monsoon rainfall with a nested grid mesoscale limited ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    At the India Meteorological Department (IMD), New Delhi, a 12-level limited area ... namurti et al (1995, 1998) noted that the Florida .... intensifies into monsoon depression giving rise to .... available to us on rainfall over the sea is the INSAT.

  13. Retrieval of vertical wind profiles during monsoon from satellite ...

    Indian Academy of Sciences (India)

    Complex EOF analysis; cloud motion vector winds; wind profiles; retrieval; monsoon. Proc. Indian Acad. Sci. .... The data gaps are removed using simple linear interpolation .... retrieved via standard linear regression using the two independent ...

  14. Spatial monsoon variability with respect to NAO and SO

    Indian Academy of Sciences (India)

    the negative phase of ESI tendency, almost all subdivisions of India show ... to affect the Indian summer monsoon rainfall indi- ... Monthly composite picture of ESI during (a) positive (28 years) and (b) negative (25 years) tendency of ESI.

  15. Air sea interaction during summer monsoon period of 1979

    Digital Repository Service at National Institute of Oceanography (India)

    RameshKumar, M.R.

    The present study highlights the utility of satellite derived parameters like SST, precipitation, CMV winds in the lower troposphere etc. in supplementing the in-situ observations. This information can lead to a better understanding of the monsoon...

  16. Unusual rainfall shift during monsoon period of 2010 in Pakistan ...

    African Journals Online (AJOL)

    Arslan

    2013-09-04

    Sep 4, 2013 ... Key words: Indus River, monsoon, flooding in 2010, rainfall pattern, Climate ... data was plotted in excel sheet with upper and lower limits defined .... Houze Jr, Rasmussen R, Medina K, Brodzik S, Romatschke SU (2011).

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

    Science.gov (United States)

    Balcerak, Ernie

    2011-08-01

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

  18. Dinoflagellates in a mesotrophic, tropical environment influenced by monsoon

    Digital Repository Service at National Institute of Oceanography (India)

    DeCosta, P.M.; Anil, A.C.; Patil, J.S.; Hegde, S.; DeSilva, M.S.; Chourasia, M.

    The changes in dinoflagellate community structure in both e the water column and sediment in a mesotrophic, tropical port environment were investigated in this study. Since the South West Monsoon (SWM) is the main source of climatic variation...

  19. quantitative precipitation forecasts during the Indian Summer Monsoon

    Indian Academy of Sciences (India)

    65

    the Indian Summer Monsoon: Contiguous Rain Area (CRA) Approach ... 1Centre for Australian Weather and Climate Research, Melbourne, Australia ... are evaluated over India using the Contiguous Rainfall Area (CRA) verification technique.

  20. Spatio-temporal variability of summer monsoon rainfall over Orissa ...

    Indian Academy of Sciences (India)

    decreasing trends in rainfall and number of rainy days over some parts of southwest Orissa during. June and ..... the recent trends and associated physical processes. 3. Results and ... depends on the activity of the monsoon trough. To.

  1. Recent change of the global monsoon precipitation (1979-2008)

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Bin [University of Hawaii at Manoa, Department of Meteorology, Honolulu, HI (United States); University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States); Liu, Jian [Chinese Academy of Sciences, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Nanjing (China); Kim, Hyung-Jin [Japan Agency for Marine-Earth Science and Technology, Research Institute for Global Change, Yokohama, Kanagawa (Japan); Webster, Peter J. [Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, GA (United States); Yim, So-Young [University of Hawaii at Manoa, International Pacific Research Center, Honolulu, HI (United States)

    2012-09-15

    The global monsoon (GM) is a defining feature of the annual variation of Earth's climate system. Quantifying and understanding the present-day monsoon precipitation change are crucial for prediction of its future and reflection of its past. Here we show that regional monsoons are coordinated not only by external solar forcing but also by internal feedback processes such as El Nino-Southern Oscillation (ENSO). From one monsoon year (May to the next April) to the next, most continental monsoon regions, separated by vast areas of arid trade winds and deserts, vary in a cohesive manner driven by ENSO. The ENSO has tighter regulation on the northern hemisphere summer monsoon (NHSM) than on the southern hemisphere summer monsoon (SHSM). More notably, the GM precipitation (GMP) has intensified over the past three decades mainly due to the significant upward trend in NHSM. The intensification of the GMP originates primarily from an enhanced east-west thermal contrast in the Pacific Ocean, which is coupled with a rising pressure in the subtropical eastern Pacific and decreasing pressure over the Indo-Pacific warm pool. While this mechanism tends to amplify both the NHSM and SHSM, the stronger (weaker) warming trend in the NH (SH) creates a hemispheric thermal contrast, which favors intensification of the NHSM but weakens the SHSM. The enhanced Pacific zonal thermal contrast is largely a result of natural variability, whilst the enhanced hemispherical thermal contrast is likely due to anthropogenic forcing. We found that the enhanced global summer monsoon not only amplifies the annual cycle of tropical climate but also promotes directly a ''wet-gets-wetter'' trend pattern and indirectly a ''dry-gets-drier'' trend pattern through coupling with deserts and trade winds. The mechanisms recognized in this study suggest a way forward for understanding past and future changes of the GM in terms of its driven mechanisms. (orig.)

  2. Holocene climate variability and anthropogenic impacts from Lago Paixban, a perennial wetland in Peten, Guatemala

    Science.gov (United States)

    Wahl, David B.; Hansen, Richard D.; Byrne, Roger; Anderson, Lysanna; Schreiner, T.

    2016-01-01

    Analyses of an ~ 6 m sediment core from Lago Paixban in Peten, Guatemala, document the complex evolution of a perennial wetland over the last 10,300 years. The basal sediment is comprised of alluvial/colluvial fill deposited in the early Holocene. The absence of pollen and gastropods in the basal sediments suggests intermittently dry conditions until ~ 9000 cal yr. BP (henceforth BP) when the basin began to hold water perennially. Lowland tropical forest taxa dominated the local vegetation at this time. A distinct band of carbonate dating to ~ 8200 BP suggests regionally dry conditions, possibly associated with the 8.2 ka event. Wetter conditions during the Holocene Thermal Maximum are indicated by evidence of a raised water level and an open water lake. The timing of this interval coincides with strengthening of the Central American Monsoon. An abrupt change at 5500 BP involved the development of a sawgrass marsh and onset of peat deposition. The lowest recorded water levels date to 5500–4500 BP. Pollen, isotope, geochemical, and sedimentological data indicate that the coring site was near the edge of the marsh during this period. A rise in the water table after 4500 BP persisted until around 3500 BP. Clay marl deposition from 3500 to 210 BP corresponds to the period of Maya settlement. An increase in δ13C, the presence of Zea pollen, and a reduction in the percentage of forest taxa pollen indicate agricultural activity at this time. In contrast to several nearby paleoenvironmental studies, proxy evidence from Lago Paixban indicates human presence through the Classic/Postclassic period transition (~ 1000 BP) and persisting until the arrival of Europeans. Cessation of human activity around 210 BP resulted in local afforestation and the re-establishment of the current sawgrass marsh at Lago Paixban.

  3. Holocene climate variability and anthropogenic impacts from Lago Paixban, a perennial wetland in Peten, Guatemala

    Science.gov (United States)

    Wahl, David; Hansen, Richard D.; Byrne, Roger; Anderson, Lysanna; Schreiner, Thomas

    2016-03-01

    Analyses of an 6 m sediment core from Lago Paixban in Peten, Guatemala, document the complex evolution of a perennial wetland over the last 10,300 years. The basal sediment is comprised of alluvial/colluvial fill deposited in the early Holocene. The absence of pollen and gastropods in the basal sediments suggests intermittently dry conditions until 9000 cal yr. BP (henceforth BP) when the basin began to hold water perennially. Lowland tropical forest taxa dominated the local vegetation at this time. A distinct band of carbonate dating to 8200 BP suggests regionally dry conditions, possibly associated with the 8.2 ka event. Wetter conditions during the Holocene Thermal Maximum are indicated by evidence of a raised water level and an open water lake. The timing of this interval coincides with strengthening of the Central American Monsoon. An abrupt change at 5500 BP involved the development of a sawgrass marsh and onset of peat deposition. The lowest recorded water levels date to 5500-4500 BP. Pollen, isotope, geochemical, and sedimentological data indicate that the coring site was near the edge of the marsh during this period. A rise in the water table after 4500 BP persisted until around 3500 BP. Clay marl deposition from 3500 to 210 BP corresponds to the period of Maya settlement. An increase in δ13C, the presence of Zea pollen, and a reduction in the percentage of forest taxa pollen indicate agricultural activity at this time. In contrast to several nearby paleoenvironmental studies, proxy evidence from Lago Paixban indicates human presence through the Classic/Postclassic period transition ( 1000 BP) and persisting until the arrival of Europeans. Cessation of human activity around 210 BP resulted in local afforestation and the re-establishment of the current sawgrass marsh at Lago Paixban.