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The Western Ghats (WG) is one of the important biodiversity hotspots and rainfall intense regions in south Asia. In this paper, the long-term trend analysis is carried out during southwest monsoon rainfall over different latitudinal regions of the WG. Further, the gridded daily rainfall data (0.25 × 0.25 spatial grid resolution) is classified into six intensity bins: dry, low, moderate, heavy, very heavy, and extreme, from 1951 to 2015. A detailed trend and variability analysis of rainfall and its frequency in different intensity bins along with their relative contribution were carried out. The results of different rainfall intensity bins depict that the moderate and low intensity bins contribute a maximum share in seasonal rainfall with 45% and 20%, respectively, from the 30% and 50% rainy days in all the regions. Heavy and very heavy intensity bins together contribute about 30% of the seasonal rainfall from about 9% rainy days. Extreme intensity bin recorded an alarming share of 6% with only 1% rainy day occurrences. In general, the relative contribution shows an ascending pattern of moderate, low, very heavy, heavy, extreme, and dry intensity bins. A decreasing trend in rainfall was observed in heavy and very heavy intensity bins, while other intensity bins illustrated mixed trends in different study regions. Extreme rainfall events marked a major shift upward in the WG region during the study period. Overall, our result portrays a negative trend in rainfall during the southwest monsoon season over all the study regions during the study period. [ABSTRACT FROM AUTHOR]

Space-based measurements, such as the Greenhouse gases Observing SATellite (GOSAT) and the TROPOspheric Monitoring Instrument (TROPOMI) aboard the Sentinel-5 Precursor satellite, provide global observations of the column-averaged CH4 concentration (XCH4). Due to the irregular observations and data gaps in the retrievals, studies on the spatial and temporal variations of regional atmospheric CH4 concentrations are limited. In this paper, we mapped XCH4 data over monsoon Asia using GOSAT and TROPOMI observations from April 2009 to December 2021 and analyzed the spatial and temporal pattern of atmospheric CH4 variations and emissions. The results show that atmospheric CH4 concentrations over monsoon Asia have long-term increases with an annual growth rate of roughly 8.4 ppb. The spatial and temporal trends of XCH4 data are significantly correlated with anthropogenic CH4 emissions from the bottom-up emission inventory of EDGAR. The spatial pattern of gridded XCH4 temporal variations in China presents a basically consistent distribution with the Heihe–Tengchong Line, which is mainly related to the difference in anthropogenic emissions in the eastern and western areas. Using the mapping of XCH4 data from 2019 to 2021, this study further revealed the response of atmospheric CH4 concentrations to anthropogenic emissions in different urban agglomerations. For the urban agglomerations, the triangle of Central China (TCC), the Chengdu–Chongqing City Group (CCG), and the Yangtze River Delta (YRD) show higher CH4 concentrations and emissions than the Beijing–Tianjin–Hebei region and nearby areas (BTH). The results reveal the spatial and temporal distribution of CH4 concentrations and quantify the differences between urban agglomerations, which will support further studies on the drivers of methane emissions. [ABSTRACT FROM AUTHOR]

A few well-annotated datasets for land-cover semantic segmentation have recently been introduced to advance the field of earth observation technologies. However, these datasets overlook the significant diversity among geographic areas with different climates, which can greatly impact and diversify land cover. Consequently, this leads to a domain gap in remote sensing images and severe performance degradation of the segmentation models. To enhance land-cover semantic segmentation with improved generalization ability, we conducted the first investigation into the impact of climate on this task. In this paper, we present a unique large-scale Climate-Aware Satellite Images Dataset (CASID) specifically designed for domain adaptive land-cover semantic segmentation. It consists of 980 satellite images with a size of 5000 × 5000 pixels, collected from 30 different regions around Asia, covering over 24,500 square kilometers. These images are gathered from four distinct climate zones, namely temperate monsoon, subtropical monsoon, tropical monsoon, and tropical rainforest. It includes four sub-datasets/domains, each representing one of the aforementioned climate zones. This characteristic makes CASID the first climate-aware land-cover semantic segmentation dataset with multiple domains. Additionally, we provide a comprehensive analysis of the samples from the four climate zones, emphasizing differences in global image features, image texture, category distribution, spectral value, and object shape. These analyses offer valuable insights for subsequent research in this field. Moreover, we conduct extensive experiments to evaluate the latest semantic segmentation and unsupervised domain adaptation methods on the CASID dataset. These results serve as a robust baseline for future research endeavors. Our dataset will be made publicly available soon at the following link: https://github.com/Linwei-Chen/CASID. [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 vast majority of current structural design codes and standards do not separately consider the wind and turbulence profiles for different storm types. Based on the 356-m-high Shenzhen Meteorological Gradient Tower, which is the tallest of its kind in Asia, this paper investigates the characteristics and vertical profiles of mean wind and turbulence for different types of strong wind events, including typhoons, monsoons, and thunderstorms, from a comparative perspective. Commonalities and differences among the vertical profiles of mean wind speed, turbulence intensity, and turbulence integral length scale for these storm events are comprehensively investigated. It is observed that the wind and turbulence profiles in typhoons and monsoons can be reasonably described by design codes and standards, while those in thunderstorms substantially deviate from typhoons and monsoons as well as code stipulations. The outcome of this study is expected to facilitate the different forms of wind and turbulence profiles for typhoons, monsoons, and thunderstorms to be taken into consideration in design codes and standards and improve the wind-resistant design of high-rise structures in regions that are prone to these storm events. [ABSTRACT FROM AUTHOR]

East Asian summer monsoon precipitation is projected to increase under greenhouse warming with strong intraseasonal variation. Using a 35-member CESM Large Ensemble and 30 CMIP6 models, this study reveals that in July and August, maximum rainfall changes in East Asia take place in the midlatitudes, influencing regions encompassing North and Northeast China, the Korean Peninsula, and Japan. The intensified precipitation is attributed to the combined effect of the thermodynamic and dynamic components. The former stems from the enriched low-level moisture, which peaks in continental East Asia in July and August, under global warming. The dynamic effect is due to the enhanced upward motion, associated with the enhanced southerlies throughout the troposphere over midlatitude East Asia. The southerlies also act to intensify the low-level monsoonal circulation, strengthening moisture transport from the tropical ocean to the midlatitudes. In addition to the mean-state changes, the precipitation interannual variability in this region also intensifies, partly due to the enhanced low-level moisture and partly associated with enhanced large-scale circulation anomalies, such as the northwestern Pacific anticyclone. The enhanced background precipitation, along with the intensified interannual variability, may lead to more rainy summers in a warmer climate, with instances where historically extreme precipitation events become more frequent, posing challenges for water resource management and agriculture in the region. [ABSTRACT FROM AUTHOR]

Afro-Asian summer monsoon precipitation (AfroASMP) is the life blood of billions of people living in many developing countries covering West Africa and Asia. Its complex variabilities are always accompanied by natural disasters like floods, landslides and droughts. Reliable AfroASMP prediction several months in advance is valuable for not only decision-makers but also regional socioeconomic sustainability. To address the current predicament of the AfroASMP seasonal prediction, this study provides an effective machine-learning model (Y-model). Y-model uses the monsoon related big climate data for searching the potential predictors, encompassing atmospheric internal factors and external forcings. Only the predictors associated with significant anomalies in summer horizonal winds at 850 hPa over the monsoon domain are retained. These selected predictors are then reorganized into a large ensemble based upon different thresholds of four fundamental principles. These principles include the focused sample sizes, the relationships between predictors and predictand, the independence among predictors, and the extremities of predictors in the forecast year. Real-time predictions can be generated based on the ensemble mean of skillful members during an independent hindcast period. Y-model skillfully predicts four monsoon precipitation indices of AfroASMP during 2011–2022 at lead 4–12 months, correlation skills range from 0.58 to 0.90 and root mean square error skills are reduced by 11–53% compared to CFS v2 model at lead 1 month. This study offers an effective method for preprocessing predictors in seasonal climate prediction. [ABSTRACT FROM AUTHOR]

Reliable attribution of Asian summer monsoon variations to aerosol forcing is critical to reducing uncertainties in future projections of regional water availability, which is of utmost importance for risk management and adaptation planning in this densely populated region. Yet, simulating the monsoon remains a challenge for climate models that suffer from long-standing biases, undermining their reliability in attributing anthropogenically forced changes. We analyze a suite of climate model experiments to identify a link between model biases and monsoon responses to Asian aerosols and associated physical mechanisms, including the role of large-scale circulation changes. The aerosol impact on monsoon precipitation and circulation is strongly influenced by a model's ability to simulate the spatio-temporal variability in the climatological monsoon winds, clouds, and precipitation across Asia, which modulates the magnitude and efficacy of aerosol–cloud–precipitation interactions, an important component of the total aerosol response. There is a strong interplay between South Asia and East Asia monsoon precipitation biases and their relative predominance in driving the overall monsoon response. We found a striking contrast between the early- and late-summer aerosol-driven changes ascribable to opposite signs and seasonal evolution of the biases in the two regions. A realistic simulation of the evolution of the large-scale atmospheric circulation is crucial to realize the full extent of the aerosol impact over Asia. These findings provide important implications for better understanding and constraining the diversity and inconsistencies of model responses to aerosol changes over Asia in historical simulations and future projections. [ABSTRACT FROM AUTHOR]

• Lake evolution of Sumxi Co has been reconstructed from lacustrine carbonate isotopes. • Hydrological conditions were mainly dominated by regional precipitation on the northwestern QTP. • Millennial hydroclimate events were responding to globally cooling events and solar irradiance. Climatic and hydrological changes on the Qinghai-Tibetan Plateau (QTP) are controlled by the Asian summer monsoon and the mid-latitude westerlies, which directly affect a large population in Asia. However, the millennial temporal and spatial patterns of Holocene hydroclimate variations on the QTP remain unclear due to the lack of high-quality paleoclimatic records. This paper examines high-resolution stable oxygen and carbon isotopes of authigenic carbonate (δ18O carb and δ13C carb) covering the past 5,000 years taken from Sumxi Co, a hydrologically closed lake lies outside the direct influence of the large ice caps on the northwestern QTP. The hydrological environment of Sumxi Co inferred from the covariance between δ18O carb and δ13C carb values was unstable during the middle to late Holocene, with abrupt increases in lake-levels during the 5.0–4.0 cal ka BP, 3.2–3.1 cal ka BP, 1.8–1.3 cal ka BP, and 0.7 cal ka BP to present. Past millennial hydrological fluctuations coincide temporally with the occurrences of glacier advances on the northwestern QTP, implying increased regional moisture and precipitation during cold periods in the region. The 'cold and wet' hydroclimatic pattern is comparable in other records to the arid areas of central Asia dominated by westerlies before the current anthropogenic warming. The four millennial-scale humid events are synchronous with reduced solar irradiance within dating errors, supporting the hypotheses that the regional pattern of hydroclimatic evolution in arid central Asia responds dominantly and directly to changes in solar activity. This external forcing may be amplified by North Atlantic cooling events and southward shifts of the intertropical convergence, which have further modulated the position of mid-latitude westerlies and the strength of the Indian summer monsoon. [ABSTRACT FROM AUTHOR]

The evolution of global temperature during Holocene is crucial for understanding the mechanisms of climate change and future climate trends. However, there is a discrepancy between the temperature trends reconstructed from proxy and model, which is attributed to the seasonal biases and the appearance of the Holocene thermal maximum was dominated by the temperature of the warm season. In this paper, fossil charcoal assemblages from the southern Chinese Loess Plateau were analysed to provide quantitative mean annual temperatures (MAT) and four-season temperature records during 6.55–3.45 cal ka BP. The results indicate that both the seasonal temperatures and MAT during the middle Holocene reached warm peaks between 5.55 and 5.35 cal ka BP. The similar trend between the winter temperature (WIT) and MAT denotes the highest contribution of WIT changes to the MAT in the study area since the mid-Holocene. • Flowering functional group was used to reconstruct spring-autumn temperature. • Nonhardy plants were used to reconstruct winter temperature. • Winter temperature contributed the most to the annual temperature since mid-Holocene. • Middle-Holocene temperature was not showing a long-term warming trend. [ABSTRACT FROM AUTHOR]

We describe the use of regional relaxation ("nudging") experiments carried out in initialised hindcasts to shed light on the contribution from particular regions to the errors developing in the Asian Summer Monsoon. Results so far confirm previous hypotheses that errors in the Maritime Continent region contribute substantially to the East Asia Summer Monsoon (EASM) circulation errors through their effects on the Western North Pacific Subtropical High. Locally forced errors over the Indian region also contribute to the EASM errors. Errors arising over the Maritime Continent region also affect the circulation and sea surface temperatures in the Equatorial Indian Ocean region, contributing to a persistent error pattern resembling a positive Indian Ocean Dipole phase. This is associated with circulation errors over India and the strengthening and extension of the westerly jet across southeast Asia and the South China Sea into the Western Pacific, thereby affecting the ASM circulation and rainfall patterns as a whole. However, errors developing rapidly in the deeper equatorial Indian Ocean, apparently independently of the atmosphere errors, are also contributing to this bias pattern. Preliminary analysis of nudging increments over the Maritime Continent region suggests that these errors may at least partly be related to deficiencies in the convection and boundary layer parametrisations. [ABSTRACT FROM AUTHOR]

Reconstruction and observational studies imply a potential linkage of moisture and precipitation change in arid central Asia and monsoonal East Asia, in which the evolution of moisture and precipitation in central Asia is out of phase with that in northern China but in phase with that in southern China. In order to ascertain whether there is a robust linkage between the changes in climate in Asian arid regions and monsoon regions and to elucidate the underlying dynamic mechanisms, we analyzed the Last Millennium Reanalysis dataset and outputs from the Community Earth System Model Last Millennium Ensemble (CESM-LME). The results indicate a significant decadal linkage between precipitation changes in central Asia's arid region and the Asian monsoon region during the last millennium, which is primarily driven by the Interdecadal Pacific Oscillation (IPO). In spring, the positive IPO could enhance westerlies over the Mediterranean Sea and to its east, which could transport more water vapor and cause increased precipitation over central Asia. In summer, the positive IPO is accompanied by a weakened Asian monsoon and southward Asian subtropical westerly jet, which can lead to increased (decreased) summer precipitation over southern China (over northern China and South Asia). The IPO plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Model results suggest that this decadal linkage stems entirely from the internal variability present in the CESM-LME control and all single-forcing simulations. Changes in external forcing factors do not alter this inherent linkage caused by the IPO. Moreover, based on analyses of the aridity index and soil moisture content, this relationship of precipitation variation also causes a similar decadal linkage of moisture changes in central Asia and monsoonal Asia. The differences in the multi-centennial-scale moisture and precipitation variations in the Asian arid region and the monsoon region between the Medieval Climate Anomaly and Little Ice Age are also likely caused by IPO-like sea surface temperature anomalies. [ABSTRACT FROM AUTHOR]

Interannual variability of the Indian summer monsoon rainfall (ISMR) is explained through the total column water vapor in the atmosphere, primarily controlled by the incoming zonal moisture flux over the Arabian Sea ( F W ) and outgoing flux over the Bay of Bengal ( F E ). In this study, we discern the underlying mechanisms driving F W and F E leading to ISMR droughts in the observations and seasonal hindcasts by the Climate Forecast System version 2 (CFSv2) model. In observations, a reduction in F W is essential for droughts to occur. In addition, an increase in F E results in a severe drought. On the contrary, droughts in CFSv2 primarily occur due to an enhancement in F E , seldom accompanied by a decrease in F W . This hypersensitivity of the CFSv2 ISMR to F E is further explained using Matsuno–Gill response to moist convection. During El Nino droughts, precipitation decreases over the equatorial western Pacific and eastern Indian Oceans. The resulting anomalous diabatic cooling increases local surface pressure ( SP ), intensifying meridional SP gradient, and thus, F E . The reduction in F W , however, is associated with a cooling of the central north Pacific Ocean in tandem with El Nino. During non-El Nino droughts, frequent occurrences of cold sea surface temperature over the western north Pacific Ocean are noticed. This cooling decreases SP over east Asia, resulting in an increase in F E . To summarize, droughts in CFSv2 are controlled by the pan-Pacific climate, significantly increasing F E but weakly decreasing F W . But in observations, a strong decrease in F W and a moderate increase in F E together lead to droughts. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) is a unique regional monsoon in the extratropics involving not only tropical but midlatitude processes. Most of the previous studies identified the role of condensational heating which is largely relevant to the tropical moisture transport in determining the dynamical structure of EASM. However, how midlatitude synoptic eddy activities can affect the EASM structure has not been well recognized. With dynamical diagnoses, this study revisits the EASM structure by emphasizing the roles of feedbacks of condensational heating versus synoptic eddy activities. As EASM is characterized by a grand low-level low with strong humid southerly flows extending from the tropics to the northeastern Asia, its vertical structure is found to have a dramatic meridional difference bounded at around 35.5°N. In the southern domain, EASM features a meridional overturning cell and a baroclinic structure with an upper-level high versus a lower-level low in geopotential height, which are primarily controlled by substantial condensational heating due to abundant monsoon precipitation. However, in the northern domain, EASM exhibits an equivalent barotropic structure with an upper-level low versus a lower-level low. Such a unique structure results from a combined effect of feedbacks of condensational heating and synoptic eddy activities, in which the upper-level low is dominated by the synoptic eddy dynamical feedback while the lower-level low is induced by the both feedbacks. The role of the midlatitude synoptic eddy activities in shaping the EASM structure proposed in this study provides a new perspective for understanding the formation and variation of EASM. [ABSTRACT FROM AUTHOR]

Whether the South Asian summer monsoon (SASM) is controlled by local or remote insolation at the orbital band remains uncertain. Here, we perform a transient simulation forced by Earth's orbital parameters between 400 and 350 ka BP, a period characterized by significant contrast between local and remote insolation, to identify the SASM's response to insolation forcing. Simulation results suggest that the primary driver of orbital‐scale SASM variability is the Northern Hemisphere high‐latitude June insolation, as opposed to local insolation. High June insolation in the Southern Hemisphere might reduce the SASM intensity. Remote insolation influences the SASM by altering the latitudinal thermal gradient and, consequently, the meridional position of the South Asian high (SAH). The SAH is associated with intense convection and hence drives the meridional shift of the intertropical convergence zone and the SASM rain belt. Thus, orbital‐scale SASM variability is strongly related to remote insolation forcing. Plain Language Summary: Because the monsoon is directly related to the movement of the subsolar point, insolation changes are important in regulating the South Asian summer monsoon (SASM) intensity at an orbital timescale. However, it remains unclear whether the SASM is driven by local insolation that directly strikes southern Asia, or remote insolation in the high‐latitude Northern Hemisphere or the Southern Hemisphere at the precession band. We find a time window between 400 and 350 ka BP (ka = thousand years, BP = before present) when local and remote insolations differ significantly, allowing us to determine which insolation dominates the SASM at orbital timescales. We use an Earth system model with orbital forcing to run a transient simulation between 400 and 350 ka BP. Simulations suggest that the SASM is primarily influenced by Northern Hemisphere high‐latitude summer insolation rather than local insolation. Additionally, Southern Hemisphere insolation has a negative impact on orbital‐scale SASM variability. Remote insolation influences the SASM by inducing an anomalous meridional thermal gradient, which moves the South Asian high and thus the Intertropical Convergence Zone. Our findings are significant for future SASM projections because the obvious difference between remote and local insolation will reappear in the next 50 ka. Key Points: Local insolation is not the direct driver for orbital‐scale variability of the South Asian summer monsoon (SASM)The meridional shift of the South Asian high (SAH) affects orbital‐scale SASM variabilityRemote insolation influences the meridional shift in the SAH through altering the latitudinal thermal contrast [ABSTRACT FROM AUTHOR]

Water isotopes‐climate correlations are used to reconstruct paleoclimate from various natural archives. Intra‐seasonal oscillation is one of the major atmospheric patterns that modulate the ratio of precipitation isotope in low latitudes, yet their spatial and temporal distribution patterns are unclear. Here we presented a detailed analysis of how the intra‐seasonal oscillations (MJO, Madden‐Julian Oscillation, and BSISO, Boreal Summer Intra‐seasonal Oscillation) modulate precipitation δ18O and vapor δ18O over the Asian monsoon region and the equatorial region. This analysis found consistent intra‐seasonal variations between the ISO and rain δ18O. We interpret it as the ISO regulating the active and inactive convective systems on the regional scale, leading to the intra‐seasonal oscillations in precipitation δ18O, with amplitudes from 4‰ up to 15‰. The MJO (BSISO) leads to eastward (northeastward) propagation of δ18O intra‐seasonal oscillations in the Asian equatorial (monsoon) region, coinciding with the spatial patterns of OLR oscillations, reflecting the response of precipitation/vapor δ18O to the oscillation of large‐scale convective activity or accumulated depletion of regional precipitation. We proved that the amplitudes of intra‐seasonal variation of precipitation δ18O are comparable to seasonal variations, and both of them are the main patterns for precipitation δ18O in study regions. Our results are conducive to the accurate interpretation of δ18O in climate proxies such as precipitation, ice cores, tree cellulose, cave stalagmites, et al. on the intra‐seasonal scale in this region. Plain Language Summary: Periodicity is a phenomenon in which similar characteristics or states of things reappear steadily and continuously. The Tropical Intra‐seasonal Oscillation (Andersen et al., 2004, https://doi.org/10.1038/nature02805) is the reappearance of a large‐scale envelope of more abundant convective rain systems moving eastward in the tropical regions with a typical oscillatory period of 30–60 days. The ratios of H218O and HDO vary during the cycle of continuous circulation of water in the atmosphere, and therefore are widely used as proxies for climate records. We used the measured data of precipitation or vapor isotopes to reveal that the propagation of ISO can be recorded by the ratio of H218O covering Asian tropical and monsoon regions. Furthermore, the increased (decreased) ISO intensity leads to the increased (decreased) amplitude of convection intensity, which results in the increased (decreased) amplitude of the H218O ratio in precipitation or vapor. Key Points: The intra‐seasonal oscillations are one of the main patterns of precipitation δ18O covering the Asian monsoon and equatorial regionsThe stronger δ18O intra‐seasonal oscillation corresponds to the season with active convective activities, more rainfall, and low‐level δ18OThe stronger regional convective intensity leads to the cumulative effect in the depletion of rain δ18O during the convective phases of ISO [ABSTRACT FROM AUTHOR]

The relationship between the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM) across time scales has been an interesting topic for decades. In this study, we quantitatively investigate the EASM–EAWM relationship at the obliquity time scales using a set of accelerated transient simulations. By comparing different indices defined with different variables, we find that the EASM and EAWM intensities are positively correlated under obliquity forcing. High obliquity leads to warmer summertime and cooler wintertime surface temperatures, with a stronger response observed over land than over the oceans. The warmer summertime and cooler wintertime temperature responses are accompanied by a strengthened Asian low in summer and Siberian high in winter, with enhanced southerlies in summer and northerlies in winter, indicating an enhanced EASM and EAWM. Modulated by ice sheet forcing, however, the evolution of the simulated EAWM shifts toward the ice sheet maximum, such that the circulation-based EASM–EAWM relationship in the realistically forced simulation exhibits a phase shift of approximately 11 kyr, closer to the phase between the composite δ18O and loess grain size in observations. Our results may have implications for better understanding the distinct changes in the proxy-based EASM–EAWM relationship before and after the rapid growth of global ice volume at around 3 Ma. Significance Statement: Studying the relationship between the EASM and EAWM can help us understand the characteristics and mechanisms of the regional climate in response to external forcings at different time scales. By investigating the EASM–EAWM relationship over the past 300 000 years, we find that, forced by obliquity variations, the EASM and EAWM are positively correlated at the obliquity time scales. The ice sheet forcing, meanwhile, also influences the circulation over East Asia and modulates the evolutionary phases between the EASM and EAWM. Our results highlight the importance of the combined impacts of orbital parameters and ice sheets on past climate changes over Asia. [ABSTRACT FROM AUTHOR]

Rainfall in the Asia summer monsoon (ASM) domain has a complex spatial pattern with the temporal variability at different timescales and their long‐term change has not been fully characterized. An updated 320 multiple proxies network is used to reconstruct the May–October precipitation during the past millennium for eight regions in the ASM domain. The spatial consistency of summer monsoon precipitation variability and the possible links to the internal climate oscillations are investigated. The results show that the regional precipitations over the last millennium in the ASM regions are dominated by the interannual cycle of 2–2.5a and 3.5‐5a, the decadal cycle of ~11a and 15–25a and the multidecadal cycle of ~30a and 40–80a. Coherent dry decades in different regions appear in 1100–1250, 1600–1650 and 1960–2000, while the wet decades appear in 970–990, 1330–1350, 1380–1430, 1550–1580, 1700–1780 and 1810–1910. On interannual scale, the relationships between precipitation for each region and El Niño–Southern Oscillation (ENSO) in both developing and decaying stages are unstable over the entire millennium, but they have opposite‐sign correlations most of the time, which implies that the summer precipitation anomaly for a region tends to reverse in the next summer when a strong ENSO event occurs in the winter. For the long‐term change from multidecadal to centennial scales, the longest dry period of the 12th to 13th centuries in eastern Asia coincides with the period with the lowest ENSO variability due to the in phase change of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation, which could result in the neutral interbasin east–west cell in Tropics and low frequency of ENSO events. [ABSTRACT FROM AUTHOR]

Using abundant rainfall gauge measurements and Global Precipitation Mission (GPM) data, spatial patterns of rainfall diurnal cycles and their seasonality over high mountain Asia (HMA) were examined. Spatial distributions of rainfall diurnal cycles over the HMA have a prominent seasonality regulated by circulations at different spatiotemporal scales, within which large regional contrasts are embedded. Rainfall diurnal variability is relatively weak in the premonsoon season, with larger amplitude over the western HMA, the southeastern HMA, as well as southern periphery regions, characterized by a dominant late afternoon to morning rainfall preference. The pattern of rainfall spatial distributions is closely related to the midlatitude westerlies. Both the mean rainfall and amplitudes of diurnal cycles become more pronounced with the advance of monsoon season but weaken during postmonsoon. The widespread late afternoon to night pattern over HMA migrating with seasonal atmospheric circulation is consistent with the lifetime of convective systems, which become active from the afternoon due to radiative heating and decay during the night. Stationary terrain-dependent night-to-morning rainfall patterns are visible in those east–west-orientated valleys over HMA and the Qaidam basin throughout the seasons. This salient geographical dependence is associated with local circulation produced by the strong differential thermal conditions over mountains and valleys, which can lift the warm moist air at the mouth of the valley and trigger nocturnal convection. Significance Statement: The main purpose of this study is to explore how spatial patterns of rainfall diurnal cycles over high mountain Asia vary with the seasons. Our results show that the widespread late afternoon to night rainfall over high mountain Asia migrating with seasonal atmospheric circulation is consistent with the lifetime of convective systems. Stationary terrain-dependent night-to-morning rainfall patterns are visible in those east–west-orientated valleys over high mountain Asia and the Qaidam basin throughout the seasons. These results highlight the importance of large-scale atmospheric circulation and local circulation on precipitation, which is critical for water resources over high mountain Asia. [ABSTRACT FROM AUTHOR]

Long-term multi-decadal scale variability of South Asian Summer Monsoon (SASM) is known to be associated with the Atlantic Multidecadal Oscillation (AMO) with positive phase associated with above-normal rainfall and vice-versa over SASM region. Analysis of the 120-year historical record suggests that the relationship between the AMO and the SASM has weakened in recent decades. Two possible reasons emerge from the analyses of observational datasets and model experiments. Enhanced Indian Ocean warming and weakened North Atlantic Subtropical High (NASH) are the prime factors weakening AMO-SASM association in the recent decades. Indian Ocean warming co-occurred during the recent AMO warm phase weakens the meridional temperature gradient, weakening the regional Hadley cell, large-scale monsoon circulation and precipitation. The suppressed convection triggers a Rossby wave which manifests as a cyclonic circulation over west central Asia weakening the Tibetan anticyclone. In addition, weakening of NASH weakens the Circum-Global Teleconnection (CGT) connecting AMO to the SASM, leading to weakening of AMO-SASM association. Projected warming of the Indian Ocean and Atlantic demands better understanding of the AMO-SASM teleconnection and their projected changes for assessing future changes in SASM in a warming world. [ABSTRACT FROM AUTHOR]

Global warming has increased the spatio-temporal variations of Extreme Precipitation (EP), causing floods, in turn leading to losses of life and economic damage across the globe. It is found that EP variability strongly correlates with large-scale climate teleconnection resulting from ocean–atmosphere oscillations. In this study, the Non-Stationary Generalized Extreme Value (NSGEV) framework is used to model EP for high resolution daily gridded (0.5° latitude × 0.5° longitude) APHRODITE dataset over Monsoon Asian Region (MAR) using climate indices as covariates. The proposed framework has three major components (i) Selection of non-uniform time-lag climate indices as covariates, (ii) Regionalization of NSGEV model parameters, and (iii) Estimation of zone-wise EP changes. According to Akaike Information Criterion (AICc), results reveal that the NSGEV model is prevalent in 92% of the grid locations across MAR compared to Stationary(S) GEV models. The Gaussian Mixture Model (GMM) clustering algorithm has identified six zones for MAR. It is observed that the derived zonal parameters of NSGEV model is able to mimic the EP characteristics. Further, zone-wise estimation of EP changes for selected return periods shows that the relative percentage change in intensity ranges between 4 and 11% across the six zones. The change in EP is significantly higher in the monsoonal windward and coastal regions when compared to the other parts of MAR. Overall, the intensities of the EP across MAR are increasing, and return periods are decreasing, which can majorly impact on planning, design and operations of the water infrastructure in the region. [ABSTRACT FROM AUTHOR]

Northern Hemisphere planetary waves exhibit an abrupt change in early summer and a significant impact on East Asian summer monsoon rainfall. Although great achievements have been made toward understanding the characteristics and maintenance of planetary waves during winter and summer, the transition of planetary waves during the abrupt-change period is less well understood. This study aims to assess the relative contribution of harmonic waves to the planetary wave transition and mechanism from the perspective of full nonlinear responses to the mountains of Asia (above 500 m) during May and June, with a primary focus on the largest positive geopotential height anomaly over northeastern Asia. The largest positive geopotential height anomaly over northeastern Asia is primarily contributed by wavelengths of around 7000 km, which corresponds to zonal wavenumber 3. The mid–high latitudes planetary waves mainly consist of wavelengths of around 10,000 km (zonal wavenumber 2, roughly) and 7000 km, which are in-phase (out-of-phase) with each other over the Western (Eastern) Hemisphere. Wavelengths of around 10,000 km weaken and displace eastward, while those of 7000 km magnify and hence contribute to the largest positive geopotential height anomaly over northeastern Asia. The full nonlinear response to the forcing by the mountains of Asia provides a considerable contribution to the largest geopotential height anomaly over northeastern Asia. Such a positive contribution comes mainly from the full nonlinear response to sensible heating associated with the mountains over Asia, which is partially offset by the full nonlinear response to dynamical forcing of the Asian mountains. [ABSTRACT FROM AUTHOR]

Eastern Asia is a major source of global air pollution. The distribution and intensity of these emissions are becoming well characterized, but their impact on the earth surface considering regional hydroclimatological settings has yet to be quantified. Here we show high-resolution spatiotemporal trace metal distributions of precipitation samples collected throughout the Japanese archipelago in 2013, when the world's coal consumption was the greatest, to depict the mass transportation and deposition of pollution. The results show that metals emitted through coal combustion transported from the continent via prevailing wind were intensively deposited along the western coast of the archipelago during winter due to heavy snowing, resulting in lead (Pb) concentration of precipitations exceed the critical level (> 10 μg l−1). About 1497 tons of Pb of continental origin loaded through wet deposition accounted for over ca. 87% of the total annual flux in 2013, which constituted ca. 18.5% of the total emissions from China in 2012. This study presents the first detailed picture of monsoon climate-controlled atmospheric metal transportation and loading in the hotspot region after the phase-out of leaded gasoline in the twentieth century. The dataset can serve as a base for evaluating the effect of countermeasures implemented recent year. [ABSTRACT FROM AUTHOR]

Efficient transport pathways for ozone-depleting very short-lived substances (VSLSs) from their source regions into the stratosphere are a matter of current scientific debate; however they have yet to be fully identified on an observational basis. Understanding the increasing impact of chlorine-containing VSLSs (Cl-VSLSs) on stratospheric ozone depletion is important in order to validate and improve model simulations and future predictions. We report on a transport study using airborne in situ measurements of the Cl-VSLSs dichloromethane (CH 2 Cl 2) and trichloromethane (chloroform, CHCl 3) to derive a detailed description of two transport pathways from (sub)tropical source regions into the extratropical upper troposphere and lower stratosphere (Ex-UTLS) in the Northern Hemisphere (NH) late summer. The Cl-VSLS measurements were obtained in the upper troposphere and lower stratosphere (UTLS) above western Europe and the midlatitude Atlantic Ocean in the frame of the WISE (Wave-driven ISentropic Exchange) aircraft campaign in autumn 2017 and are combined with the results from a three-dimensional simulation of a Lagrangian transport model as well as back-trajectory calculations. Compared to background measurements of similar age we find up to 150 % enhanced CH 2 Cl 2 and up to 100 % enhanced CHCl 3 mixing ratios in the extratropical lower stratosphere (Ex-LS). We link the measurements of enhanced CH 2 Cl 2 and CHCl 3 mixing ratios to emissions in the region of southern and eastern Asia. Transport from this area to the Ex-LS at potential temperatures in the range of 370–400 K takes about 6–11 weeks via the Asian summer monsoon anticyclone (ASMA). Our measurements suggest anthropogenic sources to be the cause of these strongly elevated Cl-VSLS concentrations observed at the top of the lowermost stratosphere (LMS). A faster transport pathway into the Ex-LS is derived from particularly low CH 2 Cl 2 and CHCl 3 mixing ratios in the UTLS. These low mixing ratios reflect weak emissions and a local seasonal minimum of both species in the boundary layer of Central America and the tropical Atlantic. We show that air masses uplifted by hurricanes, the North American monsoon, and general convection above Central America into the tropical tropopause layer to potential temperatures of about 360–370 K are transported isentropically within 5–9 weeks from the boundary layer into the Ex-LS. This transport pathway linked to the North American monsoon mainly impacts the middle and lower part of the LMS with particularly low CH 2 Cl 2 and CHCl 3 mixing ratios. In a case study, we specifically analyze air samples directly linked to the uplift by the Category 5 Hurricane Maria that occurred during October 2017 above the Atlantic Ocean. CH 2 Cl 2 and CHCl 3 have similar atmospheric sinks and lifetimes, but the fraction of biogenic emissions is clearly higher for CHCl 3 than for the mainly anthropogenically emitted CH 2 Cl 2 ; consequently lower CHCl 3 : CH 2 Cl 2 ratios are expected in air parcels showing a higher impact of anthropogenic emissions. The observed CHCl 3 : CH 2 Cl 2 ratio suggests clearly stronger anthropogenic emissions in the region of southern and eastern Asia compared to those in the region of Central America and the tropical Atlantic. Overall, the transport of strongly enhanced CH 2 Cl 2 and CHCl 3 mixing ratios from southern and eastern Asia via the ASMA is the main factor in increasing the chlorine loading from the analyzed VSLSs in the Ex-LS during the NH late summer. Thus, further increases in Asian CH 2 Cl 2 and CHCl 3 emissions, as frequently reported in recent years, will further increase the impact of Cl-VSLSs on stratospheric ozone depletion. [ABSTRACT FROM AUTHOR]

Our confidence in future climate projection depends on the ability of climate models to simulate the current climate, and model performance in simulating atmospheric circulation affects its ability of simulating extreme events. In this study, the self-organizing map (SOM) method is used to evaluate the frequency, persistence, and transition characteristics of models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) for different ensembles of daily 500 hPa geopotential height (Z500) in Asia, and then all ensembles are ranked according to a comprehensive ranking metric (MR). Our results show that the SOM method is a powerful tool for assessing the daily-scale circulation simulation skills in Asia, and the results will not be significantly affected by different map sizes. Positive associations between each two of the performance in frequency, persistence and transition were found, indicating that a good ensemble of simulation for one metric is good for the others. The r10i1p1f1 ensemble of CanESM5 best simulates Z500 in Asia comprehensively, and it is also the best of simulating frequency characteristics. The MR simulation of the highest 10 ensembles for the Western North Pacific Subtropical High (WNPSH) and the South Asia High (SAH) are far better than those of the lowest 10. Such differences may lead to errors in the simulation of extreme events. This study will help future studies in the choice of ensembles with better circulation simulation skills to improve the credibility of their conclusions. [ABSTRACT FROM AUTHOR]

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Across the Miocene–Pliocene boundary (MPB; 5.3 million years ago, Ma), late Miocene cooling gave way to the early-to-middle Pliocene Warm Period. This transition, across which atmospheric CO2 concentrations increased to levels similar to present, holds potential for deciphering regional climate responses in Asia—currently home to more than half of the world's population— to global climate change. Here we find that CO2-induced MPB warming both increased summer monsoon moisture transport over East Asia, and enhanced aridification over large parts of Central Asia by increasing evaporation, based on integration of our ~1–2-thousand-year (kyr) resolution summer monsoon records from the Chinese Loess Plateau aeolian red clay with existing terrestrial records, land-sea correlations, and climate model simulations. Our results offer palaeoclimate-based support for 'wet-gets-wetter and dry-gets-drier' projections of future regional hydroclimate responses to sustained anthropogenic forcing. Moreover, our high-resolution monsoon records reveal a dynamic response to eccentricity modulation of solar insolation, with predominant 405-kyr and ~100-kyr periodicities between 8.1 and 3.4 Ma. Global warming drove 'wet gets wetter and dry gets drier' climate shifts in Asia ~5.3 million years ago with monsoon pacing by ~400,000 and ~ 100,000 year cycles. This could be a template for future Asian climate response to anthropogenic warming. [ABSTRACT FROM AUTHOR]