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The Asian summer monsoon (ASM) as a chemical transport system is investigated using a suite of models in preparation for an airborne field campaign over the Western Pacific. Results show that the dynamical process of anticyclone eddy shedding in the upper troposphere rapidly transports convectively uplifted Asian boundary layer air masses to the upper troposphere and lower stratosphere over the Western Pacific. The models show that the transported air masses contain significantly enhanced aerosol loading and a complex chemical mixture of trace gases that are relevant to ozone chemistry. The chemical forecast models consistently predict the occurrence of the shedding events, but the predicted concentrations of transported trace gases and aerosols often differ between models. The airborne measurements to be obtained in the field campaign are expected to help reduce the model uncertainties. Furthermore, the large‐scale seasonal chemical structure of the monsoon system is obtained from modeled carbon monoxide, a tracer of the convective transport of pollutants, which provides a new perspective of the ASM circulation, complementing the dynamical characterization of the monsoon. Plain Language Summary: The Asian summer monsoon has been known as a weather system for centuries, but only in the recent decades has the system been recognized for its importance in atmospheric composition. Monsoon deep convection lofts near surface air to 15–17 km altitudes thus altering the chemical composition of the tropopause layer. The process also sends aerosols and chemically active trace gas species into the stratosphere where they affect climate through their impacts on ozone and aerosol radiative forcing. To understand the monsoon transport process and its impacts on climate system, a large airborne field campaign, the Asian summer monsoon Chemical and Climate Impact Project, was planned. This paper presents a set of results from precampaign model studies. These results serve as the hypotheses for the field investigation and provide guidance for its operational planning. Key Points: This model study is conducted in preparation for an airborne field campaign investigating the Asian monsoon transportResult shows that eastward eddy shedding of the anticyclone significantly alters upper tropospheric composition over the Western PacificCO seasonal distribution provides a chemical perspective of the monsoon system and sheds new light on monsoon dynamics and circulation [ABSTRACT FROM AUTHOR]

As wind‐borne migration of insects is strongly influenced by atmospheric circulation and weather systems, the relationships between insect population abundance and meteorological conditions are substantial. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major wind‐borne insects hampering rice production in Asia, and its migration is significantly influenced by the Asian monsoon, a main component of the Asian climate system. However, the degree and mechanisms of the effects of monsoon on BPH migration have been little studied. In this paper, the effect of the Asian monsoon on the northward migration of BPH from the Indochina Peninsula to northern South China (NSC) was investigated based on the BPH light‐trap data and meteorological data for 39 years. The results show that the level of BPH migration in May could indicate the degree of annual pest outbreaks in NSC and that the southeast monsoon was more critical in this northward migration than the previously recognized southwest monsoon. The significance of the southeast monsoon stemmed from the strong effect of South China Sea subtropical high on BPH migration under a unique weather system distribution, the Polar low–Continental low–West Pacific subtropical high pattern. Furthermore, based on the key areas of migration obtained from the composite analysis, the multivariable linear regression prediction model could effectively predict the occurrence of BPH in NSC. These results indicate the importance of interactions between monsoons during BPH northward migration, which reflects the complex relationship between BPH migration and atmospheric motion. [ABSTRACT FROM AUTHOR]

The variability and dynamics of the Asian monsoon (AM, hereafter indicates both of the summer and winter monsoons.) at orbital and millennial timescales has attracted wide interest. Chinese loess deposits, covering an area of ~500 × 103 km2 and with a thickness of several tens to more than three hundred meters, is an ideal continental archive to reconstruct AM variations during the Quaternary epoch. Over the past thirty years, since the earliest paper published in an international journal that linked the Asian monsoon and Chinese loess deposits, many studies have been undertaken focusing on this research topic. These results have greatly deepened our understanding of the variations of the AM climate and their driving mechanisms during the past ~2.6 Myr. In this paper, we emphasize recent progress on the AM variability and dynamics revealed by Chinese loess records; in particular, we discuss the reliability and precision of the timescale and the monsoon proxy indicators for the loess-paleosol sequences, which are two fundamental aspects for understanding AM behavior. We analyze what we know and discuss what we do not know about the AM. We refine the timescale for the typical loess-paleosol sequence in the central Chinese Loess Plateau (CLP), which can be used as a new timescale to study palaeoclimate and palaeoenvironmental changes in the monsoonal Asia. We conclude that low-latitude insolation changes induced by precession, and global ice volume, temperature at high-latitudes, as well as sea-level changes forced variations of the AM at orbital time scales. High-latitude cooling events and low-latitude hydroclimate process at millennial time scales, such as climate changes associated with Heinrich events and Dansgaard-Oeschger cycles in Northern Atlantic and Greenland, have also modulated AM variability. We suggest that high-latitude forcing of AM variations occurs through ocean and atmospheric circulation linkages, although the roles of atmospheric CO 2 , ocean and vegetation feedbacks need further investigation. In future study, high-resolution independent dating, novel proxy indices and transient numerical simulations are still basic tools to understand the loess deposition and AM variations that require considerably more work. Issues such as reliable spatial comparison and regional linkages of records (dependent on precise and accurate numerical chronologies), and quantitative reconstruction of the AM variations, should be given priority in the study the past climate change in Asia, and low-latitude hydroclimate process. [ABSTRACT FROM AUTHOR]

The Asian monsoon influences the lives of more than a third of the world's population, and understanding its spatial and temporal variability is fundamental to sustainable development. The complex dynamics of this climatic system are therefore of broad scientific and societal interest. In this virtual special issue (VSI), we present 19 papers dealing with the Asian monsoon since the Last Glacial Maximum (LGM, ∼21 kyr BP), with a focus on understanding variability and forcing mechanisms. Findings use recently developed quantitative reconstructions combined with numerical simulations, and present novel insights as follows: (1) analyses of comprehensive datasets of pollen, diatom, brGDGTs, oxygen and hydrogen isotopes and frequency magnetic susceptibility, as well as an innovative algorithm model for the lake energy-water balance, improve the reliability of quantitative reconstructions of Asian monsoon climate variations; (2) studies of quantitative climate parameters in central East Asia show that mean annual temperature (MAT) was ∼5 °C (or ∼ 7.9 °C using brGDGTs) lower during the LGM, ∼1.5 °C (±41% using brGDGTs) higher around the Holocene thermal optimum (HO) and mean annual precipitation (MAP) varied between 30 and 150% with marked seasonality during 8–5 ka; (3) dynamical downscaling palaeoclimatic simulations improve the accuracy of past monsoon variations, revealing strong variability in monsoon precipitation across the LGM and HO. The holistic study of Asian monsoon variations at orbital to centennial timescales in these VSI papers presents reliable observations of monsoon variability and its driving mechanisms, providing high-resolution quantitative paleoclimate reconstructions that fill existing gaps in spatial coverage, as well as offering an improved understanding, thorough numerical simulation, of coupled sea-level change and vegetation feedbacks. • An introduction to Asian monsoon variations over the past 21 ka. • Transfer functions, sedimentary records and numerical simulation are developed for studying past Asian monsoon. • Averaged MAP in East Asia varied between 30-150 % over the past 21 ka. [ABSTRACT FROM AUTHOR]

Studies of the multi-scale climate variability of the Asian monsoon are essential to an advanced understanding of the physical processes of the global climate system. In this paper, the progress achieved in this field is systematically reviewed, with a focus on the past several years. The achievements are summarized into the following topics: (1) the onset of the South China Sea summer monsoon; (2) the East Asian summer monsoon; (3) the East Asian winter monsoon; and (4) the Indian summer monsoon. Specifically, new results are highlighted, including the advanced or delayed local monsoon onset tending to be synchronized over the Arabian Sea, Bay of Bengal, Indochina Peninsula, and South China Sea; the basic features of the record-breaking mei-yu in 2020, which have been extensively investigated with an emphasis on the role of multi-scale processes; the recovery of the East Asian winter monsoon intensity after the early 2000s in the presence of continuing greenhouse gas emissions, which is believed to have been dominated by internal climate variability (mostly the Arctic Oscillation); and the accelerated warming over South Asia, which exceeded the tropical Indian Ocean warming, is considered to be the main driver of the Indian summer monsoon rainfall recovery since 1999. A brief summary is provided in the final section along with some further discussion on future research directions regarding our understanding of the Asian monsoon variability. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper draws on recent optically stimulated luminescence (OSL) dating to evaluate the long-held assumption that dust accumulation rates in the Loess Plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time, because both are controlled by the strength of the Asian monsoons and also possibly because the dunefields are proximal loess sources. The results show there is little evidence that high rates of loess accumulation coincided with well-dated episodes of extensive dune activity in the Mu Us, Otindag, and Horqin dunefields, at 11-8 ka and 1-0 ka. Explanations for the apparent lack of coupling include local variation in the trapping of dust and post-depositional preservation of the loess and dune sediments, in response to varying local environmental conditions. In addition, a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields. The results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale. The dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale, but the timing of late Quaternary dune activity, along with a variety of other evidence, indicates that moisture changes in many of the drylands of northern China may not be in phase with precipitation in core regions of the Asian monsoons. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rainfall in Vietnam is strongly influenced by climate drivers which are caused by anomalies in sea surface temperature (SST), sea level pressure (SLP) or geopotential height in the Pacific and the Indian Ocean. This paper analyses the rainfall records at different sites in various regions of Vietnam to determine the influence of the three major climate drivers, the ENSO (El Niño–Southern Oscillation), IPO (Interdecadal Pacific Oscillation) and IOD (Indian Ocean Dipole) and their interaction on the rainfall at each of these sites. A statistical technique called Bayesian model averaging (BMA) is used to discuss and address the uncertainties problem in model and variable selection when fitting observed rainfall data with climate drivers' indices. The results show that the ENSO, IPO and IOD and their interaction overall have very minor roles in influencing the rainfall in Northern Vietnam but they have some influences on the rainfall in the central and southern parts of Vietnam. Furthermore, seasonality analysis shows the spring rainfall in Vietnam is strongly influenced by the ENSO, IOD and ENSO*IOD interaction, with ENSO*IOD interaction strongest in the north. The situation in summer is similar but the IOD is most dominant compared to the ENSO and ENSO*IOD interaction. In autumn, the IOD and ENSO influences on rainfall are weaker while the IPO has strong influence in the Central and Southern Vietnam and no climate driver has any influence in the north. And during winter, the IPO, ENSO and IPO*ENSO interaction are associated with rainfall variability across Vietnam while the IOD influence is insignificant. The results also confirm the previous studies on the teleconnection roles of SST in the Pacific and Indian Oceans on rainfall variability in Vietnam. Influence scale of climate drivers on spring rainfall at various sites in Vietnam. [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) accounts for over half of the moisture source of Asian monsoon rainfall, which has been significantly altered by anthropogenic forcings. However, how individual anthropogenic forcing affects the ET over monsoonal Asia is still elusive. In this study, we found a significant decline in ET over the Asian monsoon region during the period of 1950–2014 in Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The attribution analysis suggests that anthropogenic aerosol forcing is the primary cause of the weakening in ET in the historical simulation, while it is only partially compensated by the strengthening effect from GHGs, although GHGs are the dominant forcings for surface temperature increase. The physical mechanisms responsible for ET changes are different between aerosol and GHG forcings. The increase in aerosol emissions enhances the reflection and scattering of the downward solar radiation, which decreases the net surface irradiance for ET. GHGs, on the one hand, increase the moisture capability of the atmosphere and, thus, the ensuing rainfall; on the other hand, they increase the ascending motion over the Indian subcontinent, leading to an increase in rainfall. Both processes are beneficial for an ET increase. The results from this study suggest that future changes in the land–water cycle may mainly rely on the aerosol emission policy rather than the carbon reduction policy. [ABSTRACT FROM AUTHOR]

This paper describes the operational seasonal prediction system of the Japan Meteorological Agency (JMA), the Japan Meteorological Agency/Meteorological Research Institute-Coupled Prediction System version 1 (JMA/MRI-CPS1), which was in operation at JMA during the period between February 2010 and May 2015. The predictive skill of the system was assessed with a set of retrospective seasonal predictions (reforecasts) covering 30 years (1981-2010). JMA/MRI-CPS1 showed reasonable predictive skill for the El Niño-Southern Oscillation, comparable to the skills of other state-of-the-art systems. The one-tiered approach adopted in JMA/MRI-CPS1 improved its overall predictive skills for atmospheric predictions over those of the two-tiered approach of the previous uncoupled system. For 3-month predictions with a 1-month lead, JMA/MRI-CPS1 showed statistically significant skills in predicting 500-hPa geopotential height and 2-m temperature in East Asia in most seasons; thus, it is capable of providing skillful seasonal predictions for that region. Furthermore, JMA/MRI-CPS1 was superior overall to the previous system for atmospheric predictions with longer (4-month) lead times. In particular, JMA/MRI-CPS1 was much better able to predict the Asian Summer Monsoon than the previous two-tiered system. This enhanced performance was attributed to the system's ability to represent atmosphere-ocean coupled variability over the Indian Ocean and the western North Pacific from boreal winter to summer following winter El Niño events, which in turn influences the East Asian summer climate through the Pacific-Japan teleconnection pattern. These substantial improvements obtained by using an atmosphere-ocean coupled general circulation model underpin its success in providing more skillful seasonal forecasts on an operational basis. [ABSTRACT FROM AUTHOR]

This paper investigates the reversibility of CO induced climate change and in particular the potential impacts of different rates of CO reduction using a coupled climate model. Atmospheric CO concentration is ramped up by 0.5 %/year from the preindustrial value to 4×CO and then ramped down from 2×CO to 4×CO with different rates. How the response of the climate system is affected by the peak atmospheric CO concentration and the rate of long term decline is vital information for those considering hypothetical geoengineering options to remove CO. Major components of the climate system including global mean surface air temperature and precipitation, contribution of thermal expansion to global sea level rise, loss of the Arctic sea ice, weakening of the Atlantic meridional overturning circulation (AMOC) and the South Asia monsoon are analyzed. We have found no 'tipping points' or thresholds beyond which CO induced climate change in these components become irreversible within this model under the specific scenarios. However, there are strong inertias and path-dependent hysteresis in the climate system linked through oceanic memory. Initially the strengthened global hydrological cycle accelerates further in response to a CO ramp-down before weakening. Thermal expansion of the oceans continues for many decades after CO concentration starts to decrease. A 0.5 %/year reduction from 4×CO could see a further 25 % sea level rise. The weakening of the AMOC is reversible, but the build-up of highly saline subtropical waters during global warming drives an overshoot of the AMOC after the CO ramp-down and extends the warming of the northern high latitudes by many decades. The South Asia monsoon strengthens in response to a CO ramp-up marked by an increase in summer monsoon rainfall. This increase reverses rapidly following a CO ramp-down, displaying an undershoot in monsoon rainfall for rapid CO reductions. [ABSTRACT FROM AUTHOR]

This paper reviews progress in the study of Tibetan Plateau (TP) climate dynamics over the past decade. Several theoretical frameworks, including thermal adaptation and the TP sensible heat (SH) driving air-pump, have been developed to identify the mechanisms responsible for the circulation anomaly produced by thermal forcing of the TP. Numerical simulations demonstrate that the thermal effects of large-scale orography, including the Tibetan and Iranian Plateaus (TIP), are crucial for the formation of the East Asian and South Asian summer monsoons (SASM) because the surface SH of the TIP is the major driver of the water vapor transport required for the genesis of the north branch of the SASM.The large-scale orography of the TP affects the Asian climate through thermal forcing in spring and summer, and mechanical forcing in winter. The TP forcing can also influence the Asian summer monsoon (ASM) onset over the Bay of Bengal (BOB) by enhancing the BOB warm pool at the surface and by modulating the South Asian High (SAH) in the upper troposphere. On intra-seasonal timescales, the TP thermal forcing significantly modulates spring rainfall in southern China and generates the biweekly oscillation of the SAH in summer. Despite climate warming, the atmospheric heat source over the TP, particularly the spring SH, exhibits a clear weakening trend from the 1980s to 2000s. This weakening of the spring SH contributed to the anomalous 'dry in the north' and 'wet in the south' rainfall pattern observed over East China. Also discussed are challenges to further understanding the mechanism of TP forcing on the multi-scale variability of the ASM. [ABSTRACT FROM AUTHOR]

Diatom records in tropical settings have been used to appraise paleomonsoons throughout the Quaternary period due to their ubiquitous presence, rapid response, and preservation in sediments. Despite this, diatoms have been rarely used to assess the Asian monsoonal climate. As the Asian monsoon comprises the Indian and East Asian subsystems, it plays a significant role in global hydrological and energy cycles. Keeping global climate in mind, we reviewed the dynamics and causes of Asian monsoon variability (covering major records exclusive from the tropics) on different spatial and temporal scales using diatoms as a proxy record. The data have been compiled from 50 papers spanning fresh and marine sediment archives, covering entire monsoon regimes, predominantly from Southeast Asia. This study classified the data based on various geological periods ranging from the Pleistocene Epoch to the Holocene Meghalayan age (600 ka −300 a BP). Diatom proxies indicate fluctuating hydrological conditions and varying monsoon intensity throughout the Quaternary period and show regional scale coherence for specific climatic events. Diatom records from both inland and marine sediment archives indicate a wet and warm period during the mid–Pleistocene (590–300 kyr) and a cold climate and weakened East Asian monsoon during 300–140 kyr. Through the late Pleistocene period (75 to 15 kyr), monsoonal conditions were intense, wet and warm during the interglacial stages and weaker and dry during glacial stages across South and East Asia. During the Last Glacial Maximum (24.5–18 kyr), the monsoon significantly weakened with cold climatic conditions in southern Asia, and increased precipitation across East Asia. A majority of the published records witnessed an enhanced Asian monsoon and a warm and humid period towards the early to mid–Holocene, with a decline in the monsoon after the mid–Holocene accompanying intermittent intense wetter conditions. Diatom records from the sediment archives at many geographic locations hold signatures of extreme events such as the Younger Dryas cold event around 13.3–11.3 kyr BP, the Medieval Warm Period around 1.3 to 0.8 kyr, and the Little Ice Age in between 0.6 and 0.3 kyr. Further, we indicate that several sites from different monsoon-dominated geographic-climatic zones should be re-investigated with high resolution across spatial and temporal palaeoclimatic periods (including existing databases) with careful diatom taxonomy to strengthen a climatic reconstruction of this monsoon-dominated region of Asia. [ABSTRACT FROM AUTHOR]

The relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)--currently the largest monsoon system--remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy-and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial. [ABSTRACT FROM AUTHOR]

As one of the most important geological events in Cenozoic era, the uplift of the Tibetan Plateau (TP) has had profound influences on the Asian and global climate and environment evolution. During the past four decades, many scholars from China and abroad have studied climatic and environmental effects of the TP uplift by using a variety of geological records and paleoclimate numerical simulations. The existing research results enrich our understanding of the mechanisms of Asian monsoon changes and interior aridification, but so far there are still a lot of issues that need to be thought deeply and investigated further. This paper attempts to review the research on the influence of the TP uplift on the Asian monsoon-arid environment, summarize three types of numerical simulations including bulk-plateau uplift, phased uplift and sub-regional uplift, and especially to analyze regional differences in responses of climate and environment to different forms of tectonic uplifts. From previous modeling results, the land-sea distribution and the Himalayan uplift may have a large effect in the establishment and development of the South Asian monsoon. However, the formation and evolution of the monsoon in northern East Asia, the intensified dryness north of the TP and enhanced Asian dust cycle may be more closely related to the uplift of the main body, especially the northern part of the TP. In this review, we also discuss relative roles of the TP uplift and other impact factors, origins of the South Asian monsoon and East Asian monsoon, feedback effects and nonlinear responses of climatic and environmental changes to the plateau uplift. Finally, we make comparisons between numerical simulations and geological records, discuss their uncertainties, and highlight some problems worthy of further studying. [ABSTRACT FROM AUTHOR]

In arid regions, because of spatial variability, using single climate records is difficult to reconstruct the past climate change for the drainage basins. Holocene environmental records were collected from the upper, middle and lower regions of the Shiyang River drainage basin in the marginal area of the Asian monsoon (northwest China). The main objective of this paper was to compare the records from the terminal lake and the middle and upper reaches of the basin to study the basin-wide environmental changes. During the early Holocene the vegetation was sparse, and the effective moisture was relatively low in the basin. The Holocene Climatic Optimum started between 7.0 and 8.0 cal ka BP, during which the lake level reached the highest level in the terminal lake; the vegetation density and the effective moisture reached the highest level during the Holocene in the drainage basin. From 4.7 cal ka BP the terminal lake began to shrink, while the vegetation density decreased dramatically. In the middle and upper regions of the drainage, the effective moisture began to decrease since 3.5 cal ka BP, and the arid tendency was earlier in the terminal lake than it was in the middle and upper regions of the drainage basin. During the early Holocene the relatively arid environment was affected by the gradually intensifying East Asian monsoon and the dry westerly winds. The mid-Holocene Optimum benefited from the intensive East Asian monsoon and the humid westerly winds. Then, the East Asian monsoon retreated since the late-Holocene. In the basin the arid tendency may be related to the retracting of the East Asian monsoon. However, the intensifying acidification after 1.5 cal ka BP may be correlated to the increasing dryness of the westerly winds. [ABSTRACT FROM AUTHOR]

In this paper, correlation between modern leaf physiognomy and climate in China are examined, to optimize the use of leaf characters as a palaeoclimate proxy. A large dataset was compiled, recording the distribution of leaf physiognomic characters among 3166 native dicot trees species across 732 calibration grids on a county level. Grids span a range of ecological environments (tropical rainforests to alpine shrubs) across humid areas. Thirteen climatic parameters were included for each grid and 22 leaf physiognomic characters were scored for each tree species. The correlation between leaf physiognomic characters and climatic parameters were calculated based on single linear regressions (SLR) and multiple linear regressions (MLR). Results indicate clear spatial distribution patterns, linked to latitude, exist for all leaf characters, with temperature (Coldest Month Mean Temperature, CMMT) and precipitation (Growing Season Precipitation, GSP) being the main climate controls. Moreover, because leaf characters are more closely correlated with Precipitation during the Three Wettest Consecutive Months (P3WET), rather than with Precipitation during the Three Driest Consecutive Months (P3DRY), seasonal variations in rainfall associated with the Asian Monsoon might especially influence leaf physiognomic characters. Closer correlations between leaf physiognomy and climate are seen using MLR compared with SLR; therefore Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) based on MLR equations provide the most promising basis for palaeoclimate reconstructions in China. • Spatial distribution of 21 leaf physiognomic characters in China is established. • Relationships between leaf physiognomic characters and climatic parameters are established. • The seasonal variations in rainfall under the Asian monsoon climate shapes leaf physiognomic characters. • Paleoclimate can be reconstructed based on such large-scale modern dataset. [ABSTRACT FROM AUTHOR]

The expedition of Zheng He's fleet to the Western Ocean1 in the first half of the 15th century is an important event in the history of navigation, which has attracted the broad attention of domestic and foreign scholars from different fields2. This paper reveals the relation between Zheng He's voyages and the Asian Monsoon from a geographical perspective. Historical records show that Zheng He's seven voyages to the Western Ocean were precisely organized and successfully carried out due to careful consideration of the conditions and periodical patterns of the Asian tropical and subtropical monsoon. Details such as fleet routes, sailing schedules, wind-waiting points, divergent and rendezvous points were painstakingly planned and arranged in advance by the organizers of the expedition, who all paid close attention to the changing patterns of the Asian Monsoon. [ABSTRACT FROM AUTHOR]

The Shiyang River drainage basin is located in the northwest margin of the Asian monsoon region. Previous studies reached different conclusions about Holocene climatic changes in the basin. Some studies suggested the Holocene climatic changes were mainly controlled by the Asian monsoon and that the climate was relatively humid during the early Holocene (11.6--7.1 cal ka BP). Other studies found the mid-Holocene Climatic Optimum (7.0--5.0 cal ka BP), and this climate condition was similar to the Holocene westerly wind pattern in arid Central Asia. The modern climate is affected by the Asian monsoon and westerly wind in the drainage basin, and the Holocene climatic records showed two different Holocene climatic patterns--a westerly wind pattern and monsoonal pattern. However, it remains unclear what caused the two different Holocene climatic patterns to co-exist in the region. The palynological records are the main evidence for the Holocene climatic changes in the basin. This paper focuses on palynological records for different parts of the drainage basin. Among them, QTH02, QTL-03 and Sanjiaocheng records are located in the terminal lake, and the Hongshuihe record is located in the middle reaches of the basin. In the terminal lake, the palynological records of QTH02 and QTL-03 are similar, but the Sanjiaocheng record differs. The difference is mainly affected by the variable pollen assemblages in the different locations of the lake basin. From comparison and synthesis of the four palynological records, we concluded that the millennial-scale Holocene climatic changes were affected by the combined effects of the Asian monsoon and westerly wind in the drainage basin, which show the complicated Holocene climatic pattern in the northwest margin of the Asian monsoon. [ABSTRACT FROM AUTHOR]

Abstract This special issue provides new studies in the field of Cenozoic climate change in eastern Asia. The papers in this volume are multidisciplinary in nature and examine a range of topics including paleovegetation, sedimentology, clay mineralogy, geochemistry, magnetostratigraphy, and climate modelling. The findings of these studies demonstrate that analysis of terrestrial paleoclimate changes in eastern Asia may offer insights into the effects of Tibetan Plateau uplift, and ultimately the dynamic processes of global change that took hold throughout the Cenozoic. The second part of this special issue, to be published later, will add a paleoecology component, examining how Cenozoic climate change has impacted floras and faunas in eastern Asia. [ABSTRACT FROM AUTHOR]

Aerosols can affect the cloud-radiation feedback and the precipitation over the Indian monsoon region. In this paper, we propose that another pathway by which aerosols can modulate the multi-scale aspect of Indian monsoons is by altering the land–atmosphere interactions. The nonlinear feedbacks due to aerosol/diffuse radiation on coupled interactions over the Indian monsoon region are studied by: (1) reviewing recent field measurements and modeling studies, (2) analyzing the MODIS and AERONET aerosol optical depth datasets, and (3) diagnosing the results from sensitivity experiments using a mesoscale modeling system. The results of this study suggest that the large magnitude of aerosol loading and its impact on land–atmosphere interactions can significantly influence the mesoscale monsoonal characteristics in the Indo-Ganges Basin. [ABSTRACT FROM AUTHOR]

Using annual precipitation and discharge data measured in the past five decades, this paper analyzed the regional differences over west China in terms of climate and discharge variations, and investigated the relationship between the regional characteristics and the activities of South and East Asian summer monsoon. Results revealed that the precipitation and discharge in the upper reaches of the Yellow River (Central West China) have a negative correlation with those in Xinjiang (northwest China) and the Yarlung Zangbo River (the upper reaches of the Brahmaputra Rive, southwest China) regions. The geographical patterns of precipitation and discharge variations are different over west China, i.e. the regional climate displays the alteration of dry-wet-dry or wet-dry-wet from north to south in west China. The negative correlation of annual discharges between Xinjiang and the upper reaches of the Yellow River is found statistically significant in the decadal scale, and that between the Yarlung Zangbo River and the upper reaches of the Yellow River is found active in the interannual scale. The regional characteristics indicate that the discharge/precipitation variations in the upper reaches of the Yellow River are dominated by the East Asian summer monsoon while their variations in Xinjiang are affected by both the west wind and East Asian summer monsoon. [ABSTRACT FROM AUTHOR]

The abrupt weakening of the East Asian summer monsoon (EASM) during Younger Dryas (YD) has been attributed to freshwater discharge into the North Atlantic ocean and resultant Northern Hemisphere cooling. Recent studies have found that sea ice variability in the Nordic Sea during the YD exerted a great influence upon the northern high-latitude climate. However, the influence of sea ice upon EASM evolution during YD event remains unclear. In this paper, we report two precisely-dated speleothem oxygen isotope records from the EASM-dominated region of central China. Our records archive abrupt changes in EASM variability during the YD event. Initially, there was a significant strengthening of the EASM during the mid-YD following the gradually increased Atlantic meridional overturning circulation (AMOC). Later this trend reversed at ∼12.15 ka due to northern high-latitude sea ice fluctuations and a consequent reduction of AMOC. At the YD termination, abrupt intensification of the EASM was synchronous with the rapid decline of sea-ice and recovery of the AMOC indicating that sea ice variability was a significant influence on high latitude climate and EASM variation during the YD. • A new speleothem δ18O record show significant EASM strengthening during mid-YD. • Mid-YD oscillation in EASM linked with NH sea ice variability. • Abrupt EASM intensification at YD termination synchronous with the rapid decline of sea ice. • Drier interval following the YD termination in central China. [ABSTRACT FROM AUTHOR]

The interpretation and understanding of the relationship between Middle to Late Holocene climate change in monsoon margins of northwest China with the westerlies and Asian monsoon (AM) remain controversial. Here we present a new multi-proxy sedimentary dataset from the Heihe River basin in the middle part of the Hexi Corridor on the northern margin of the Qinghai-Tibet Plateau (QTP), which is a sensitive zone for the interaction between the westerlies and AM. Fluctuations in grain size, δ13Corg, δ18O, magnetic susceptibility, total organic carbon, total nitrogen, and C/N ratio document regional lake and climate evolution since 5334 cal yr BP. Results show that climate conditions on the millennial timescale are humid in the late Middle Holocene (MH) and dry to wet in the Late Holocene (LH). Combined with the multi-model ensemble simulation from PMIP3-CMIP5, high lake levels and wetter climate in the late MH are closely linked to the strengthening Asian summer monsoon. Simultaneously, the slight wetting trend since the late LH may be the superimposing effect of enhanced westerlies and the weakening Asian winter monsoon. These findings can provide insights into the interpretation of the interaction between the westerlies and AM during the Holocene in East Asia. [ABSTRACT FROM AUTHOR]

China is the country with the most population in the world, and its climate is extremely diverse due to tremendous differences in latitude, longitude, and altitude, ranging from tropical in the far south to subarctic in the far north and alpine in the higher elevations of the Qinghai-Tibetan Plateau. Accurate assessment of its modern climate change is conductive to addressing global warming threat. Along with the development of Past Global Changes (PAGES) research, the focus has changed from paleo-climate reconstructions to using paleo-data for assessing the present and predicting the future. Previous studies have been devoted to climate change assessment using modern climate observations and simulations. This paper presents a new assessment approach based on the mid-Holocene, which provides a naturally oriented warming that can be compared to modern human-made global warming. A variety of climatic data, including modern observations, paleo-climate records, CMIP5 (Coupled Model Intercomparison Project Phase 5) and PMIP3 (Paleoclimate Modelling Intercomparison Project 3) simulations, as well as lake level models, were applied in this synthesis. Numerical climate classification was introduced to evaluate climate change impacts to Chinese climate zones on various time scales. The results show that winter and summer seasons have different response to the naturally oriented mid-Holocene warming but human-made global warming makes the warming trend appear in all seasons. Temperate and continental dry winter climates expand dramatically during the mid-Holocene warm period; however, the future global warming could have few impacts to Chinese climate zones. Furthermore, the East Asian summer monsoon was strengthened obviously by the mid-Holocene warm climate and strong low-latitude insolation. There is no consistent trend both for the winter and summer monsoon on the background of human-made global warming. In this study, a new benchmark was established based on paleo-climate to evaluate the impacts of human-made global warming. [ABSTRACT FROM AUTHOR]

A comprehensive and integrative view of East Asian monsoon evolution during the Holocene is still under debate, and additional high-resolution proxy records from climatically sensitive locations are requisite to solve this complex issue. In this paper, we present three well-dated mud/peat cores from a paleo-pingo depression in the Sanjiang Plain, a climatically sensitive region to monsoon variation, to reveal the paleoenvironmental history of the wetland and discuss the regional impacts from monsoon evolution. A paleolake developed in the study area before 5.5 ka BP, and a peatland initiated thereafter consequent upon the gradual shrinking of the paleolake. This transition lasted until 4.5 ka BP, when the paleolake changed entirely to a wetland. Considering the prevalent monsoon climate in the Sanjiang Plain, we suggest that the lake-to-wetland transition from 5.5 to 4.5 ka BP indicates a rapid decline of the East Asian summer monsoon in addition to autogenic basin infilling processes. Such a remarkable monsoon weakening event has been documented across northern China, and we associate this with ocean–atmosphere interactions throughout low-latitude regions. [ABSTRACT FROM AUTHOR]

In this paper, the global and regional features of the seasonal variation of general circulation, and especially the Asian monsoon simulated by the Institute of Atmospheric Physics Two-level AGCM coupled with a sophisticated land-surface model (IAP94-GCM) are presented and compared with the observation. The comparison is made by using the equilibrium multiyear seasonal cycle climate from a 100-year integration. In the integration sea surface temperature (SST) and sea ice are taken from the observed climatological data (with seasonal variation) because our purpose is to see the improvement of simulation due to the coupling with an advanced land surface model. Overall, the IAP94-GCM provides a reasonably realistic simulation of the interseasonal and intraseasonal climatology of the Asian monsoon and yields an important information that sheds light on the thermal underpinning and the thermodynamics of the seasonal and even multiscale variabilities associated with the Asian summer monsoon. [ABSTRACT FROM AUTHOR]

The simulation skill of the perturbed parameter ensemble (PPE) of HadGEM3‐GC3.05 on the mean climate pattern of the Asian summer monsoon (ASM) is evaluated in this study. The sensitivities of the model bias to the perturbed parameters are investigated based on metrics. The results show that the PPE mean (PPE‐20M) could effectively capture the general ASM precipitation and wind patterns, with a correlation coefficient of 0.78. PPE‐20M mainly shows positive precipitation biases over the tropical western Pacific, southern slope of the Tibetan Plateau, Indochina Peninsula, and South China and negative precipitation biases over the Indian continent and Bay of Bengal. The magnitude of the precipitation biases is more sensitive than its pattern to the variation of the perturbed parameters. Four parameters (ent_fac_dp, qlmin, ps_cloud‐ph, and psm) are found to be crucial for simulating the ASM precipitation intensity, and their combined effects are related to the simulated precipitation biases. Plain Language Summary: The simulation of the Asian summer monsoon (ASM) has attracted much attention in recent decades. However, state‐of‐the‐art coupled models still show similar systematic biases when simulating monsoon precipitation from CMIP3 to CMIP6. Recently, a perturbed parameter ensemble (PPE) method has been applied in the development of HadGEM3‐GC3.05 with the aim of improving the overall simulation skill of the coupled model. The PPE can also be used to understand the related physical processes in the model simulations. Thus, in this study, we aim to evaluate the simulation skills of PPE on the mean climate distributions of ASM. Four parameters were found to be the most critical in the precipitation simulations, which could be potential tunable parameters to reduce the biases of precipitation intensity over the monsoon regions. This study provides possible pathways to reduce model bias that could benefit the model development community. Key Points: The perturbed parameter ensemble mean captures the climate pattern of the Asian summer monsoon (ASM) but mainly overestimates precipitation over the western PacificFour parameters (ent_fac_dp, qlmin, ps_cloud‐ph, and psm) are crucial for simulating ASM precipitation in coupled runThe joint effect of these parameters, especially the deep entrainment amplitude, are dominant control for the bias in the western Pacific [ABSTRACT FROM AUTHOR]

The first ever comprehensive study on wildland fires in Bangladesh is carried out to develop a fire prevention and prediction method. The major causes of huge wildland fires (88%) in the subtropical Chittagong Hill forest (43% of total) of southern Bangladesh are reported as shifting cultivation, grazing and unauthorized settlement. We used satellite hotspot (HS) data from 2003 to 2021 (a total of 54,669 HSs) to clarify the spatio-temporal structure of wildland fires. Fire weather conditions were analyzed using various weather data and synoptic-scale weather maps at different air levels. Fires concentrated from March through April or a transitional period from the dry season, caused by the Asian winter monsoon, to the wet season, due to the Asian summer monsoon. Fire occurrence depended on dry conditions and pre-monsoon showers and their timing. The difference in 925 hPa heights of high and low pressure systems may be attributed to the different types of the Asian winter and summer monsoons. The average maximum air temperature and incident shortwave solar energy in April were the highest and strongest, contributing fire-prone weather conditions. Based on the analysis, a fire prevention and prediction method will be developed, and this report may also facilitate the establishment of future CO2 reduction measures for Bangladesh. [ABSTRACT FROM AUTHOR]

The past Asian precipitation δ18O (δ18Op) records from stalagmites and other deposits have shown significant orbital-scale variations, but their climatic implications and regional differences are still not fully understood. This study, as the first attempt of a 300-kyr transient stable isotope-enabled simulation, investigated the characteristics and mechanisms of the orbital-scale δ18Op variations in three representative regions of Asia: arid Central Asia (CA), monsoonal South Asia (SA) and monsoonal East Asia (EA). The modelling results showed that the variations in the CA, SA and EA annual δ18Op exhibited significant but asynchronous 23-kyr precession cycles. Further analyses revealed that although the precession-induced insolation variation was the ultimate cause of the δ18Op variation in all three regions, the dominant mechanisms and the involved physical processes were distinct among them. For the CA region, the rainy-season (November–March) temperature effect and water vapour transport by the westerly circulation were identified as the key precession-scale processes linking the October–February boreal mid-latitude insolation to the rainy-season or annual δ18Op. In the SA region, the rainy-season (June–September) precipitation amount effect and upstream depletion of the monsoonal water vapour δ18O served as the main mechanisms linking the rainy-season or annual δ18Op to the April–July insolation variation at the precession scale. For the EA region, however, the precession-scale annual δ18Op was mainly controlled by the late-monsoon (August–September) and pre-monsoon (April–May) water vapour transport patterns, which were driven by the July–August insolation and the global ice volume, respectively. These results suggest that the climatic implications of the orbital-scale Asia δ18Op variations are sensitive to their geographic locations as determined by the combined effects of insolation and regional circulation patterns associated with the respective rainy seasons. This study provides new insights into understanding the regional differences and formation mechanisms of the Asian orbital-scale δ18Op variations. [ABSTRACT FROM AUTHOR]

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To explore the history of the changes in monsoon precipitation and their driving mechanisms in the context of global warming, climatology studies using tree-ring stable oxygen isotopes (δ18O) were carried out in Shanxi Province, China. Based on a tree-ring δ18O series from Pinus tabulaeformis Carr. on Heng Mountain, a 230-year June–July precipitation sequence from 1784 to 2013 AD was reconstructed that explained 45% of the total variance (44% after adjusting the degrees of freedom). The reconstructed sequence captured the characteristics of the variations in precipitation. Periods of drought occurred mainly in 1820–1840 AD, 1855–1865 AD, 1895–1910 AD, 1925–1930 AD, and 1970–1995 AD, and wet periods occurred mainly in 1880–1895 AD, 1910–1925 AD, and 1935–1960 AD. The dry and wet years in the precipitation reconstruction corresponded well to the years in which disaster events were documented in historical records. A spatial correlation analysis with Climatic Research Unit (CRU)-gridded precipitation data indicated that the reconstructed precipitation provided good regional representation and reflected large-scale June–July precipitation changes in northern China. In addition, the reconstructed precipitation sequence was also significantly correlated with the dry and wet index (DWI) and other tree-ring dry/wet reconstructions from the surrounding areas. The correlation between the reconstructed precipitation and the Asian monsoon index showed that the precipitation can indicate the intensity of the Asian summer monsoon. Moreover, a significant negative correlation was found between the El Niño–Southern Oscillation (ENSO) and the reconstructed precipitation. At the decadal scale, the negative phase of the Pacific Decadal Oscillation (PDO) and the positive phase of the Atlantic Multidecadal Oscillation (AMO) may co-promote summer precipitation in the study area. [ABSTRACT FROM AUTHOR]

The role of the diurnal atmospheric circulation cycle around the eastern Indian subcontinent, leeward of the monsoon westerlies, on the hydroclimate of South Asia remains unknown. Here, we reveal that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB), and then flow onto the Gangetic Plain enhancing onshore moisture flux and nocturnal precipitation over the Himalayas and the Meghalaya Plateau. This nocturnal surge is strongly controlled by the diurnal cycle of dynamic and thermodynamic effects around the subcontinent. At night, nocturnal westerly low‐level jets appear over the subcontinent. Strong low‐level southwesterly flow with a low‐level jet structure also appears parallel to the coastline over the western BoB, extending from the west of Sri Lanka. The low‐level westerlies from the subcontinent and the low‐level southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge. Plain Language Summary: Nocturnal precipitation is a well‐known phenomenon around the Himalayas and the Meghalaya Plateau in South Asia in summer. Such precipitation is a major supply source for glaciers in the central–eastern Himalayas and the headwaters of major rivers such as the Ganges and the Brahmaputra. In this study, we show that low‐level moist southerlies are greatly enhanced at night parallel to the coastline over the western Bay of Bengal (BoB) and then flow onto the Gangetic Plain, enhancing moisture transport toward land and nocturnal precipitation in South Asia. Here, we refer to the phenomenon as the nocturnal southerly moist surge. This nocturnal surge is strongly affected by the diurnal cycle of the thermal and topographic effects of the Indian subcontinent. At night, a strong low‐level westerly jet appears above the nocturnal stable layer over the Indian subcontinent. Strong low‐level southwesterlies with a low‐level jet structure also appear over the western BoB, extending from the strait between the southernmost tip of the Indian subcontinent and Sri Lanka. The low‐level westerlies flowing from the subcontinent and the southwesterlies merge into a single strong southwesterly flow, forming the low‐level moist surge over the western BoB. Key Points: Nocturnal low‐level southerly moist surge occurs parallel to the western Bay of Bengal coastline and flows over the Gangetic PlainThe surge consists of strong low‐level westerlies from the Indian subcontinent and southwesterlies extending from the west of Sri LankaDynamic and thermodynamic effects of the Indian subcontinent likely play an important role in forming the nocturnal surge [ABSTRACT FROM AUTHOR]

Robust and uncertain sea-level pressure patterns over summertime East Asia in the future global warming projections and their causes are studied by applying the inter-model empirical orthogonal function (EOF) analysis to the multi-model experiments in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and focusing on common features with the previous CMIP5 analysis. The ensemble average and the first to third EOF modes associated with future pressure changes are similar to the corresponding modes from CMIP5. The first and second modes represent strengthened and weakened high-pressure systems in subtropical and northern East Asia, respectively. The third mode is the reverse anomaly of the climatological pressure pattern over summertime East Asia, which indicates weakened southerly monsoon winds. The second mode pattern makes positive contributions to almost all the CMIP6 future pressure changes, representing a robust future projection pattern. The robust mode is the result of surface warming over the northern continents and neighboring seas that is stronger than the global average. The first and third modes are considered to be uncertain (but major) patterns in the ensemble projections as the signs of their contributions to the future changes are dependent on the model used. Suppressed vertical motion over the equatorial (northern) Indian Ocean caused by the vertically stabilized atmosphere under the global warming scenario is the source of the first (third) mode, together with the counter vertical motion anomaly over the equatorial (northern) Pacific. The aforementioned characteristics of the modes are essentially similar to those identified in the CMIP5 analysis, whereas the different sea surface temperature anomalies are related to the secondary structures of the modes. Some uncertainties in the future projections can be attributed to the systematic differences in the model climatology of the present-day precipitation, which determines the distribution of the suppressed vertical motion under the future warmer climate. [ABSTRACT FROM AUTHOR]

Abstract As wind‐borne migration of insects is strongly influenced by atmospheric circulation and weather systems, the relationships between insect population abundance and meteorological conditions are substantial. The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the major wind‐borne insects hampering rice production in Asia, and its migration is significantly influenced by the Asian monsoon, a main component of the Asian climate system. However, the degree and mechanisms of the effects of monsoon on BPH migration have been little studied. In this paper, the effect of the Asian monsoon on the northward migration of BPH from the Indochina Peninsula to northern South China (NSC) was investigated based on the BPH light‐trap data and meteorological data for 39 years. The results show that the level of BPH migration in May could indicate the degree of annual pest outbreaks in NSC and that the southeast monsoon was more critical in this northward migration than the previously recognized southwest monsoon. The significance of the southeast monsoon stemmed from the strong effect of South China Sea subtropical high on BPH migration under a unique weather system distribution, the Polar low–Continental low–West Pacific subtropical high pattern. Furthermore, based on the key areas of migration obtained from the composite analysis, the multivariable linear regression prediction model could effectively predict the occurrence of BPH in NSC. These results indicate the importance of interactions between monsoons during BPH northward migration, which reflects the complex relationship between BPH migration and atmospheric motion.

Bangladesh receives most of its precipitation from June to September in the form of rainfall as a part of the Asian summer monsoon system. Bangladesh is a relatively flat region, surrounded by the southern Himalayas and Meghalaya Plateau in the north, Arakan Mountains in the east, and the Bay of Bengal (BOB) in the south. Although several studies have investigated the mechanisms that drive the Asian monsoon precipitation, very few studies have focused on the monsoon precipitation in Bangladesh. This study investigated the influence of the topography of the surrounding regions and sea surface temperature on the summer monsoon precipitation of Bangladesh and the surrounding regions. Using observed data, we showed that moisture convergence near the mountains contributes to the precipitation of Bangladesh, whereas the BOB acts as a source of moisture. A strong low‐level jet carries the moisture inland as the land–sea thermal contrast intensifies the wind circulation during the summer. Three differently forced simulations of the Euro‐Mediterranean Centre on Climate Change coupled climate model (CMCC CM2) were analysed to investigate the influence of the surrounding region's topography and sea surface temperature on the summer monsoon precipitation. The low‐resolution simulation showed no spatial variability of precipitation and dry bias due to the overly smooth topographical representation of mountains. The high‐resolution coupled simulation, with a better representation of topography, improved the moisture convergence at the foothills and precipitation bias. The high‐resolution prescribed sea surface temperature further improved the precipitation bias by intensifying the low‐level jet that transports moisture over Bangladesh. [ABSTRACT FROM AUTHOR]

The monsoon development in the early rainy season in East Asia is analysed by the evolution of daily weather types (WTs). The WTs are classified by a k‐means clustering analysis based on 850 hPa winds from April 1 to July 31 in the 40‐year period of 1979–2018. Five WTs are identified, typifying the progression of weather regimes in the monsoonal evolution. WTs 1 and 2, with easterly winds in the South China Sea (SCS), occurs mostly in April and early May, corresponding to typical WTs before the SCS monsoon onset. In WT3, winds in the SCS turns westerly, and a rain band emerges in South China, extending east‐northeastward to the Pacific Ocean south of Japan, which signifies the May–June Mei‐yu in South China. Then, with the rain band moved to Yangtze River Valley (YRV) in WT4, this WT corresponds to the June–July Mei‐Yu in central and eastern China along the YRV. Finally, WT5 occurs more frequently towards the end of July, and corresponds to the post‐Mei‐Yu WT, indicating the ending of the early summer rainfall season in East Asia. The evolution of the WTs is gradual but intermittent, representing the weather‐within‐climate information. Each WT likely persists to itself. But WT1 and WT2 also progress to each other. The long persistence of WT3 and WT4 up to several weeks indicates the quasi‐stationary Mei‐Yu in South China and the YRV, respectively. The year‐to‐year variability of the WTs is also evident in the WTs. The El Niño–Southern Oscillation (ENSO) impact on the precipitation in the East Asian region is analysed for three types of ENSO: Eastern Pacific, Central Pacific, and mixed El Niño and La Niña. The seasonal mean precipitation anomalies can be interpreted by the frequencies of the daily WTs under different ENSO conditions. [ABSTRACT FROM AUTHOR]

Coastal hypoxia—harmfully low levels of oxygen—is a mounting problem that jeopardizes coastal ecosystems and economies. The northern Indian Ocean is particularly susceptible due to human‐induced impacts, vast naturally occurring oxygen minimum zones, and strong variability associated with the seasonal monsoons and interannual Indian Ocean Dipole (IOD). We assess how natural factors influence the risk of coastal hypoxia by combining a large set of oxygen measurements with satellite observations to examine how the IOD amplifies or suppresses seasonal hypoxia tied to the Asian Monsoon. We show that on both seasonal and interannual timescales hypoxia is controlled by wind‐ and coastal Kelvin wave‐driven upwelling of oxygen‐poor waters onto the continental shelf and reinforcing biological feedbacks (increased subsurface oxygen demand). Seasonally, the risk of hypoxia is highest in the western Arabian Sea in summer/fall (71% probability of hypoxia). Major year‐to‐year impacts attributed to the IOD occur during positive phases along the eastern Bay of Bengal (EBoB), where the risk of coastal hypoxia increases from moderate to high in summer/fall (21%–46%) and winter/spring (31%–42%), and along the eastern Arabian Sea (i.e., India, Pakistan) where the risk drops from high to moderate in summer/fall (53%–34%). Strong effects are also seen in the EBoB during negative IOD phases, when the risk reduces from moderate to low year‐round (∼25% to ∼5%). This basin‐scale mapping of hypoxic risk is key to aid national and international efforts that monitor, forecast, and mitigate the impacts of hypoxia on coastal ecosystems and ecosystem services. Plain Language Summary: Coastal "dead zones," with vanishingly low oxygen levels, stress marine organisms, compress their habitats, threaten the sustainability of fisheries, and can lead to mass mortality of marine life. The northern Indian Ocean is particularly vulnerable due to natural physical processes that bring oxygen‐poor water onto the continental shelf from vast offshore regions of low‐oxygen, and biological processes that can intensify coastal dead zones. Alongside these natural processes, coastal dead zones in the Indian Ocean are also influenced by human activity, such as fertilizer use and waste water management. In this study we use a large set of observations in the northern Indian Ocean to quantify how natural processes trigger coastal dead zones seasonally, and how they increase or decrease the risk of coastal dead zones from year‐to‐year. This information, on where and when coastal dead zones are most likely to occur, is key to anticipate and mitigate impacts on ecosystems and economies. Key Points: Regions at higher risk of coastal hypoxia in the northern Indian Ocean are identified using coastal oxygen observationsThe Indian Ocean Dipole (IOD) can amplify or suppress the seasonal risk of hypoxia by modulating coastal upwelling/downwellingThe risk is most amplified during positive IOD phases along the coast of the eastern Bay of Bengal [ABSTRACT FROM AUTHOR]

Variations of precipitation in tropical-subtropical regions are fundamentally important to human sustainable development. However, the dominant cyclicity and the mechanism of orbital-scale precipitation variations remain under extensive debate. Here, we used a newly drilled core from the Tianyang (TY) maar lake (South China) to reconstruct Asian monsoon precipitation variations over the past ~ 250,000 years, providing a new independent paleoprecipitation record for the core tropical monsoon region. The measured magnetic susceptibility and grain size records of TY maar lake reveal dominant precession and semiprecession cycles, evidencing the low-latitude insolation forcing on tropical monsoon precipitation variations. Feedbacks of Intertropical Convergence Zone shifts and orbital-scale El Niño/Southern Oscillation variations are suggested to play important roles in this forcing mechanism. Moreover, we detected correlation between the rainstorms and the tropical zonal sea surface temperature gradient during the moderate Marine Isotope Stage (MIS) 5a. This correspondence further confirms the effect of tropical internal feedbacks on orbital-scale precipitation variations. However, the glacial-interglacial cycle is weak in our record, indicating that the variability of Asian monsoon precipitation is likely modulated by certain other processes such as latitudinal effects and air-sea feedback. [ABSTRACT FROM AUTHOR]

We analyzed a large ensemble dataset called the database for Policy Decision Making for Future climate change (d4PDF), which contains 60-km resolution atmospheric general circulation model output and 20-km resolution dynamical downscaling for the Japanese domain. The increase in moisture and precipitation, and their global warming response in June–July–August were described focusing on the differences between Hokkaido and Kyushu; Hokkaido is cool and dry and Kyushu is hot and humid in the current climate. The results suggested that the specific humidity increased almost following the Clausius Clapeyron relation, but the change in stationary circulation suppressed the precipitation increase, except for in western Kyushu. The + 4 K climate in Hokkaido would be as hot and humid as the present climate in Kyushu. The circulation change related to the southward shift of the jet stream and an eastward shift of the Bonin high weakened the moisture flux convergence via a stationary field over central Japan including eastern Kyushu. The transient eddy activity counteracted the increase in humidity, so that the moisture flux convergence and precipitation did not change much over Hokkaido. Because the contribution of tropical cyclones to the total precipitation was at most 10%, the decrease in the number of tropical cyclones did not explain the predicted change in precipitation. [ABSTRACT FROM AUTHOR]

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

Abstract: In this paper, we present the first annual oxygen isotope (δ18O) record (1902 to 2004) from the latewood cellulose of trees growing in a temperate-moist forest in southwestern China. Tree-ring δ18O ranges from 12.8 to 18.6‰ and averages 15.2‰. δ18O in the latewood negatively correlates with total cloud cover, relative humidity, and precipitation during the moist months (August to October) from 1951 to 2004 and, to a lesser extent, positively correlates with the temperature in June. Spatial correlation analysis revealed that tree-ring latewood δ18O is more strongly related to variability in regional cloud cover and precipitation in autumn. Tree-ring δ18O negatively correlates with the indices of the Indian summer monsoon (1948 to 2004), the western North Pacific monsoon (1948 to 2004), and with the East Asian summer monsoon (1902 to 2000), suggesting that these monsoons strongly influence the regional climate. Under global warming of last century, we found a strong inverse correlation between tree-ring δ18O and the Southern Oscillation index in different periods, indicating a complex association between the El Niño-Southern Oscillation and the regional climate, which in turn affects tree-ring δ18O. Correlation with the global sea surface temperature (SST) indicates that climatic conditions in the Indian Ocean might play a dominant role in modulating cloud cover and precipitation over the study region during the monsoon seasons. We also found a significant correlation between tree-ring δ18O and SST over the western-north Pacific Ocean. Our results suggest strong links between tropical oceans and an ENSO-like climate with the oxygen-isotope sources and discrimination for trees in the study region. [Copyright &y& Elsevier]

An article by Zhang et al. questions the interpretation of our oxygen isotope record from Wanxiang Cave and the sediment titanium record from Lake Huguang Maar, and the possible linkage between climate change and Chinese culture. In response, we explain that their approach lacks logical rigor and their major argument is broadly consistent with, rather than contradictory to our original conclusions. We also note that climate-culture relationships similar to those that we observe in China have been observed for other cultures around the world. [ABSTRACT FROM AUTHOR]

This study quantitatively examined the relative importance of Rossby wave breaking (RWB) east of Japan to a formation of the Pacific-Japan (PJ) pattern compared with that of tropical atmospheric and oceanographic variabilities. First, cases of the positive and negative PJ patterns are classified into those with and without the RWB occurrence. The result of the classification indicates that the cases of the positive PJ pattern triggered by the RWB account for approximately 20 % of the whole cases of the positive PJ pattern. The number of positive PJ cases with the RWB further accounts for approximately 80 % of those in the cases associated with the RWB. Results of a lag composite analysis and the related Q-vector diagnosis for the cases of the positive PJ pattern with the presence of RWB show that the RWB east of Japan promotes the formation of the PJ pattern through the southwestward intrusion of high potential vorticity air mass toward the subtropical western North Pacific (WNP) and the consequent dynamically induced enhanced convection over the region, consistent with results of previous studies. By contrast, the composite for the cases the negative PJ pattern accompanied by the RWB indicates that the RWB-related upper-tropospheric zonally elongated anomalous circulation and basin-wide sea surface temperature (SST) warming over the Indian Ocean can contribute suppressed convective activities over the subtropical WNP and the consequent formation of the negative PJ pattern although the RWB occurs. The composite for the cases of positive and negative PJ patterns with the absence of RWB further indicates that the convective activities over the subtropical WNP move northwestward with time, causing the formation of the PJ pattern. The formation of the PJ pattern with the absence of RWB is also closely associated with tropical SST and phase of the boreal summer intraseasonal oscillation, illuminating "pure" tropical impacts on the formation of a PJ pattern. [ABSTRACT FROM AUTHOR]