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Bin Wang - One of the best experts on this subject based on the ideXlab platform.
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The global Monsoon across timescales: coherent variability of regional Monsoons
Climate of the Past, 2014Co-Authors: Pinxian Wang, Zhengtang Guo, Bin Wang, Hai Cheng, John T. Fasullo, Thorsten Kiefer, Zhengyu LiuAbstract:Abstract. Monsoon has earned increasing attention from the climate community since the last century, yet only recently have regional Monsoons been recognized as a global system. It remains a debated issue, however, as to what extent and at which timescales the global Monsoon can be viewed as a major mode of climate variability. For this purpose, a PAGES (Past Global Changes) working group (WG) was set up to investigate the concept of the global Monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional Monsoons can vary coherently, although not perfectly, at various timescales, varying between interannual, interdecadal, centennial, millennial, orbital and tectonic timescales, conforming to the global Monsoon concept across timescales. Within the global Monsoon system, each subsystem has its own features, depending on its geographic and topographic conditions. Discrimination between global and regional components in the Monsoon system is a key to revealing the driving factors in Monsoon variations; hence, the global Monsoon concept helps to enhance our understanding and to improve future projections of the regional Monsoons. This paper starts with a historical review of the global Monsoon concept in both modern and paleo-climatology, and an assessment of Monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various timescales, providing evidence of the coherent global Monsoon system. The paper concludes with a projection of future Monsoon shifts in a warming world. The synthesis will be followed by a companion paper addressing driving mechanisms and outstanding issues in global Monsoon studies.
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The Global Monsoon across Time Scales: is there coherent variability of regional Monsoons?
Climate of the Past Discussions, 2014Co-Authors: Pinxian Wang, Zhengtang Guo, Bin Wang, Hai Cheng, John T. Fasullo, Thorsten Kiefer, Zhengyu LiuAbstract:Abstract. Monsoon has earned increasing attention from the climate community since the last century, yet only recently regional Monsoons have been recognized as a global system. It remains a debated issue, however, as to what extent and at which time scales the global Monsoon can be viewed as a major mode of climate variability. For this purpose a PAGES Working Group (WG) was set up to investigate the concept of the global Monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional Monsoons can vary coherently, although not perfectly, at various time scales, ranging from interannual, interdecadal, centennial and millennial, up to orbital and tectonics time scales, conforming the global Monsoon concept across time scales. Within the global Monsoon system each subsystem has its own features depending on its geographic and topographic conditions. Discrimination of global and regional components in the Monsoon system is a key to reveal the driving factors of Monsoon variations, hence the global Monsoon concept helps to enhance our understanding and to improve future projection of the regional Monsoons. This paper starts with a historical review of the global Monsoon concept in both modern and paleo-climatology, and an assessment of Monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various time scales, providing evidence for the coherent global Monsoon system. The paper concludes with a projection of future Monsoon shifts into a warming world. The synthesis will be followed by a companying paper to discuss driving mechanisms and outstanding issues in the global Monsoon studies.
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A comparison of regional Monsoon variability using Monsoon indices
Climate Dynamics, 2013Co-Authors: So-young Yim, Bin Wang, Jian LiuAbstract:The present study aims to (a) examine meteo- rological basis for construction of regional Monsoon indi- ces and (b) explore the commonality and differences among tropical regional Monsoons, especially the tele- connection and Monsoon-ENSO relationship. We show that the area-averaged summer precipitation intensity is generally a meaningful precipitation index for tropical Monsoons because it represents very well both the ampli- tude of annual cycle and the leading mode of year-to-year rainfall variability with a nearly uniform spatial pattern. The regional Monsoon circulation indices can be defined in a unified way (measuring Monsoon trough vorticity) for seven tropical Monsoon regions, viz.: Indian, Australian, western North Pacific, North and South American, and Northern and Southern African Monsoons. The structures of the tropical Monsoons are commonly characterized by a pair of upper-level double anticyclones residing in the subtropics of both hemispheres; notably the winter hemi- spheric anticyclone has a barotropic structure and is a passive response. Two types of upper-level teleconnection patterns are identified. One is a zonal wave train emanating from the double anticyclones downstream along the wes- terly jets in both hemispheres, including Indian, Northern African and Australian Monsoons; the other is a meridional wave train emanating from the double anticyclones pole- wards, such as the South American and western North Pacific Monsoons. Over the past 55 years all regional summer Monsoons have non-stationary relationship with ENSO except the Australian Monsoon. The regional mon- soon-ENSO relationship is found to have common changing points in 1970s. The relationships were enhanced for the western North Pacific, Northern African, North American and South American summer Monsoons, but weakened for the Indian summer Monsoon (with a recovery in late 1990s). Regardless the large regional differences, the Monsoon precipitations over land areas of all tropical Monsoon regions are significantly correlated with the ENSO, suggesting that ENSO drives global tropical mon- soon rainfall variability. These results provide useful guidance for monitoring sub-seasonal to seasonal varia- tions of the regional Monsoons currently done at NCEP and for assessment of the climate models' performances in representing regional and global Monsoon variability.
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recent change of the global Monsoon precipitation 1979 2008
Climate Dynamics, 2012Co-Authors: Bin Wang, Jian Liu, Hyungjin Kim, Peter J Webster, So-young YimAbstract: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.
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Global Monsoon across timescales
Climate Dynamics, 2012Co-Authors: Pinxian Wang, Bin Wang, Thorsten KieferAbstract:Scientific focus on Monsoons can be traced back nearly 350 years. However, only recently have Monsoons been analyzed as a global system. Traditionally, the variability of the Monsoon has been studied almost exclusively on regional scales, in both the modern and paleo-Monsoon communities. With the application of remote sensing and other new techniques, the concept of ‘‘Global Monsoon’’ has been introduced as a global-scale seasonally varying atmospheric overturning circulation (Trenberth et al. 2000) associated with seasonal migration of the Monsoon trough and intertropical convergence zone. The Global Monsoon represents the dominant mode of annual variation of the Earth’s climate system. However, it remains a debated issue as to what extent the Global Monsoon can be viewed as a major mode of climate variability. In an effort to better understand the dynamics of Monsoon variability, the PAGES Working Group ‘‘Global Monsoon and Low-Latitude Processes: Evolution and Variability’’ has held two symposia at Tongji University, Shanghai (Wang et al. 2009, 2011a). The symposia brought together paleoand modern climatologists as well as dataproducers and modelers to compare Monsoon studies from all regional Monsoon systems to identify their similarities and differences across a range of timescales from interannual to tectonic, and to unravel the mechanisms causing variations in the Global Monsoon system and regional deviations from the global trend. A collection of 13 contributions to the symposia are published here as a first Global Monsoon special issue, trying to put regional Monsoons into the context of the global system and to analyze their variations across a range of timescales. The papers discuss Monsoon response to internal feedback processes of the climate system (e.g. El Nino-Southern Oscillation) and to external forcing by orbital insolation changes and tectonic factors such as the uplift of the Tibetan Plateau. Some papers provide observational evidence in support of the Global Monsoon concept (Wang et al. 2011b; Cheng et al. 2012). A particularly prominent example is provided by the speleotheme records from Asia and South America. Their nearly symmetric response of Monsoons from the two Hemispheres to precession cycles clearly demonstrates the global connectivity of regional Monsoon systems at geological timescales (Cheng et al. 2012). Meanwhile, this Special Issue is slightly imbalanced as a number of important contributions devoted to paleoclimate proxy records are not included in this issue, but being published elsewhere in paleoclimatic journals. Since Global Monsoon is a new concept, we are well aware that there is a long way to go before a global view on Monsoon P. Wang State Key Laboratory of Marine Geology, Tongji University, Shanghai, China
Sandy P Harrison - One of the best experts on this subject based on the ideXlab platform.
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mid holocene Monsoons a multi model analysis of the inter hemispheric differences in the responses to orbital forcing and ocean feedbacks
Climate Dynamics, 2012Co-Authors: Sandy P Harrison, Y. ZhaoAbstract:The response of Monsoon circulation in the northern and southern hemisphere to 6 ka orbital forcing has been examined in 17 atmospheric general circulation models and 11 coupled ocean–atmosphere general circulation models. The atmospheric response to increased summer insolation at 6 ka in the northern subtropics strengthens the northern-hemisphere summer Monsoons and leads to increased Monsoonal precipitation in western North America, northern Africa and China; ocean feedbacks amplify this response and lead to further increase in Monsoon precipitation in these three regions. The atmospheric response to reduced summer insolation at 6 ka in the southern subtropics weakens the southern-hemisphere summer Monsoons and leads to decreased Monsoonal precipitation in northern South America, southern Africa and northern Australia; ocean feedbacks weaken this response so that the decrease in rainfall is smaller than might otherwise be expected. The role of the ocean in Monsoonal circulation in other regions is more complex. There is no discernable impact of orbital forcing in the Monsoon region of North America in the atmosphere-only simulations but a strong increase in precipitation in the ocean–atmosphere simulations. In contrast, there is a strong atmospheric response to orbital forcing over northern India but ocean feedback reduces the strength of the change in the Monsoon although it still remains stronger than today. Although there are differences in magnitude and exact location of regional precipitation changes from model to model, the same basic mechanisms are involved in the oceanic modulation of the response to orbital forcing and this gives rise to a robust ensemble response for each of the Monsoon systems. Comparison of simulated and reconstructed changes in regional climate suggest that the coupled ocean–atmosphere simulations produce more realistic changes in the northern-hemisphere Monsoons than atmosphere-only simulations, though they underestimate the observed changes in precipitation in all regions. Evaluation of the southern-hemisphere Monsoons is limited by lack of quantitative reconstructions, but suggest that model skill in simulating these Monsoons is limited.
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Global Monsoons in the mid-Holocene and oceanic feedback
Climate Dynamics, 2004Co-Authors: Z. Liu, J. Kutzbach, Sandy P Harrison, B. Otto-bliesnerAbstract: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.26 page(s
S L Weber - One of the best experts on this subject based on the ideXlab platform.
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Monsoonal response to mid holocene orbital forcing in a high resolution gcm
Climate of The Past, 2011Co-Authors: Joyce H C Bosmans, S S Drijfhout, E Tuenter, Lucas Joost Lourens, Frederik J Hilgen, S L WeberAbstract:In this study, we use a sophisticated high- resolution atmosphere-ocean coupled climate model, EC- Earth, to investigate the effect of Mid-Holocene orbital forc- ing 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 in- creased 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 sim- ulations. In north-westernmost Africa, precipitation extends up to 35 N. Over tropical Africa, internal feedbacks com- pletely overcome the direct warming effect of increased in- solation. 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 ex- pense 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 mon- soon through decreased Monsoon winds and less convection, as well as an equatorward shift in the ITCZ. This study cor- roborates the findings of paleodata research as well as previ- ous model studies, while giving a more detailed account of Mid-Holocene Monsoons.
Kenneth R Sperber - One of the best experts on this subject based on the ideXlab platform.
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The use of fractional accumulated precipitation for the evaluation of the annual cycle of Monsoons
Climate Dynamics, 2014Co-Authors: Kenneth R Sperber, H AnnamalaiAbstract:Using pentad rainfall data we demonstrate the benefits of using accumulated rainfall and fractional accumulated rainfall for the evaluation of the annual cycle of rainfall over various Monsoon domains. Our approach circumvents issues related to using threshold-based analysis techniques for investigating the life-cycle of Monsoon rainfall. In the Coupled Model Intercomparison Project-5 models we find systematic errors in the phase of the annual cycle of rainfall. The models are delayed in the onset of summer rainfall over India, the Gulf of Guinea, and the South American Monsoon, with early onset prevalent for the Sahel and the North American Monsoon. This, in combination with the rapid fractional accumulation rate, impacts the ability of the models to simulate the fractional accumulation observed during summer. The rapid fractional accumulation rate and the time at which the accumulation begins are metrics that indicate how well the models concentrate the Monsoon rainfall over the peak rainfall season, and the extent to which there is a phase error in the annual cycle. The lack of consistency in the phase error across all domains suggests that a “global” approach to the study of Monsoons may not be sufficient to rectify the regional differences. Rather, regional process studies are necessary for diagnosing the underlying causes of the regionally-specific systematic model biases over the different Monsoon domains. Despite the afore-mentioned biases, most models simulate well the interannual variability in the date of Monsoon onset, the exceptions being models with the most pronounced dry biases. Two methods for estimating Monsoon duration are presented, one of which includes nonlinear aspects of the fractional accumulation. The summer fractional accumulation of rainfall provides an objective way to estimate the extent of the Monsoon domain, even in models with substantial dry biases for which Monsoon is not defined using threshold-based techniques.
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the south asian summer Monsoon and its relationship with enso in the ipcc ar4 simulations
Journal of Climate, 2007Co-Authors: H Annamalai, Kevin Hamilton, Kenneth R SperberAbstract:Abstract In this paper the extensive integrations produced for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) are used to examine the relationship between ENSO and Monsoons at interannual and decadal time scales. The study begins with an analysis of the Monsoon simulation in the twentieth-century integrations. Six of the 18 models were found to have a reasonably realistic representation of Monsoon precipitation climatology. For each of these six models SST and anomalous precipitation evolution along the equatorial Pacific during El Nino events display considerable differences when compared to observations. Out of these six models only four [Geophysical Fluid Dynamics Laboratory Climate Model versions 2.0 and 2.1 (GFDL_CM_2.0 and GFDL_CM_2.1), Meteorological Research Institute (MRI) model, and Max Planck Institute ECHAM5 (MPI_ECHAM5)] exhibit a robust ENSO–Monsoon contemporaneous teleconnection, including the known inverse relationship between ENSO and rainfall variatio...
Hai Cheng - One of the best experts on this subject based on the ideXlab platform.
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The global Monsoon across timescales: coherent variability of regional Monsoons
Climate of the Past, 2014Co-Authors: Pinxian Wang, Zhengtang Guo, Bin Wang, Hai Cheng, John T. Fasullo, Thorsten Kiefer, Zhengyu LiuAbstract:Abstract. Monsoon has earned increasing attention from the climate community since the last century, yet only recently have regional Monsoons been recognized as a global system. It remains a debated issue, however, as to what extent and at which timescales the global Monsoon can be viewed as a major mode of climate variability. For this purpose, a PAGES (Past Global Changes) working group (WG) was set up to investigate the concept of the global Monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional Monsoons can vary coherently, although not perfectly, at various timescales, varying between interannual, interdecadal, centennial, millennial, orbital and tectonic timescales, conforming to the global Monsoon concept across timescales. Within the global Monsoon system, each subsystem has its own features, depending on its geographic and topographic conditions. Discrimination between global and regional components in the Monsoon system is a key to revealing the driving factors in Monsoon variations; hence, the global Monsoon concept helps to enhance our understanding and to improve future projections of the regional Monsoons. This paper starts with a historical review of the global Monsoon concept in both modern and paleo-climatology, and an assessment of Monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various timescales, providing evidence of the coherent global Monsoon system. The paper concludes with a projection of future Monsoon shifts in a warming world. The synthesis will be followed by a companion paper addressing driving mechanisms and outstanding issues in global Monsoon studies.
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variation in the asian Monsoon intensity and dry wet conditions since the little ice age in central china revealed by an aragonite stalagmite
Climate of The Past, 2014Co-Authors: Jianjun Yin, Hai Cheng, D X Yuan, R L Edwards, Yu Shih Lin, J M Qin, W Tang, Z Y Zhao, Horngsheng MiiAbstract:Abstract. 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 Nino–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 Nino conditions, 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 conditions in the study area under stronger summer Monsoon during warm periods, and vice versa. During cold periods, the Walker Circulation will shift toward the central Pacific under El Nino conditions, resulting in a further weakening of Asian summer Monsoons.
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The Global Monsoon across Time Scales: is there coherent variability of regional Monsoons?
Climate of the Past Discussions, 2014Co-Authors: Pinxian Wang, Zhengtang Guo, Bin Wang, Hai Cheng, John T. Fasullo, Thorsten Kiefer, Zhengyu LiuAbstract:Abstract. Monsoon has earned increasing attention from the climate community since the last century, yet only recently regional Monsoons have been recognized as a global system. It remains a debated issue, however, as to what extent and at which time scales the global Monsoon can be viewed as a major mode of climate variability. For this purpose a PAGES Working Group (WG) was set up to investigate the concept of the global Monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional Monsoons can vary coherently, although not perfectly, at various time scales, ranging from interannual, interdecadal, centennial and millennial, up to orbital and tectonics time scales, conforming the global Monsoon concept across time scales. Within the global Monsoon system each subsystem has its own features depending on its geographic and topographic conditions. Discrimination of global and regional components in the Monsoon system is a key to reveal the driving factors of Monsoon variations, hence the global Monsoon concept helps to enhance our understanding and to improve future projection of the regional Monsoons. This paper starts with a historical review of the global Monsoon concept in both modern and paleo-climatology, and an assessment of Monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various time scales, providing evidence for the coherent global Monsoon system. The paper concludes with a projection of future Monsoon shifts into a warming world. The synthesis will be followed by a companying paper to discuss driving mechanisms and outstanding issues in the global Monsoon studies.
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the global paleoMonsoon as seen through speleothem records from asia and the americas
Climate Dynamics, 2012Co-Authors: Hai Cheng, Ashish Sinha, Xianfeng Wang, Francisco W Cruz, Lawrence R EdwardsAbstract:The regional Monsoons of the world have long been viewed as seasonal atmospheric circulation reversal—analogous to a thermally-driven land-sea breeze on a continental scale. This conventional view of Monsoons is now being integrated at a global scale and accordingly, a new paradigm has emerged which considers regional Monsoons to be manifestations of global-scale seasonal changes in response to overturning of atmospheric circulation in the tropics and subtropics, and henceforth, interactive components of a singular Global Monsoon (GM) system. The paleoclimate community, however, tends to view ‘paleoMonsoon’ (PM), largely in terms of regional circulation phenomena. In the past decade, many high-quality speleothem oxygen isotope (δ18O) records have been established from the Asian Monsoon and the South American Monsoon regions that primarily reflect changes in the integrated intensities of Monsoons on orbital-to-decadal timescales. With the emergence of these high-resolution and absolute-dated records from both sides of the Equator, it is now possible to test a concept of the ‘Global-Paleo-Monsoon’ (GPM) on a wide-range of timescales. Here we present a comprehensive synthesis of globally-distributed speleothem δ18O records and highlight three aspects of the GPM that are comparable to the modern GM: (1) the GPM intensity swings on different timescales; (2) their global extent; and (3) an anti-phased inter-hemispheric relationship between the Asian and South American Monsoon systems on a wide range of timescales.
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abrupt variations in south american Monsoon rainfall during the holocene based on a speleothem record from central eastern brazil
Geology, 2011Co-Authors: Nicolas M Strikis, Hai Cheng, Xianfeng Wang, Francisco W Cruz, Lawrence R Edwards, Ivo Karmann, Mathias Vuille, Marcos Saito De Paula, Valdir F NovelloAbstract:Well-dated high-resolution oxygen isotope records of speleothems in central-eastern Brazil spanning from 1.3 to 10.2 kyr B.P. reveal that the occurrence of abrupt variations in Monsoon precipitation is not random. They show a striking match with Bond events and a significant pacing at ∼800 yr, a dominant periodicity present in sea surface temperature records from both the North Atlantic and equatorial Pacific Oceans that is possibly related to periods of low solar activity (high 14 C based on the atmospheric Δ 14 C record). The precipitation variations over central-eastern Brazil are broadly antiphased with the Asian and Indian Monsoons during Bond events and show marked differences in duration and structure between the early and late Holocene. Our results suggest that these abrupt multicentennial precipitation events are primarily linked to changes in the North Atlantic meridional overturning circulation (AMOC). Anomalous cross-equatorial flow induced by negative AMOC phases may have modulated not only the Monsoon in South America but also affected El Nino–like conditions in the tropical Pacific during the Holocene.