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Precipitation δ18O has offered valuable insights into the evolution of the Asian monsoon. Recent researches focusing on precipitation Δ′17O has enhanced our understanding by offering new perspectives beyond those of δ18O, revealing insights into vapor sources and continental recycling. Nevertheless, there remains a lack of interannual triple oxygen isotope data, particularly in the Asian monsoon region. In this study, we analyzed the triple oxygen isotopes and hydrogen isotopes in monthly precipitation samples collected from Chongqing in Southwest China between 2019 and 2022 A.D. Seasonal variations in δD, δ18O, δ17O, and d‐excess values were observed, with lower values during the rainy season and higher values during the dry season, highlighting the impact of changes in moisture sources and local meteorological conditions on seasonal shifts in δD, δ18O, and δ17O. While, mean Δ′17O values were higher in rainy season and lower in dry season. Notably, during rainy season, there is a negative correlation between monthly Δ′17O values and the RH of the vapor source area, as well as a positive correlation with d‐excess. Recalculated Δ′17O values based on RH of oceanic moisture source, are higher than the measured values for this period, indicating the contribution of terrigenous moisture to precipitation in SW China. Precipitation Δ′17O values provide a more precise reflection of changes in moisture source, continental recycling, and evapotranspiration processes that drive water cycling compared Integrating modeling works in future will facilitate the use of precipitation Δ′17O values to quantify the impact of different moisture source on precipitation. Plain Language Summary: In the context of climatic warming, changes in water vapor source areas have substantial implications for the stability of regional water resources. Despite the importance of these changes, few studies have analyzed them using precipitation data from SW China. We conducted monthly measurements of isotopic compositions in precipitation samples collected in monsoonal SW China between 2019 and 2022 A.D. Seasonal variations in δD, δ18O, δ17O, and d‐excess revealed low values during the rainy season (May–October) and significantly higher values during the dry season (November–April). These variations are primarily attributed to different water vapor sources in distinct seasons. Moreover, we observed a negative correlation between precipitation Δ′17O and relative humidity in the source area of the water vapor during the rainy season, suggesting that Δ′17O contains valuable information about the water vapor's source area. Additionally, the relatively higher Δ′17O values observed in the rainy season imply the influence of continental recycling and evapotranspiration processes. Key Points: Characteristics of triple oxygen and hydrogen isotopes in precipitation were analyzed based on a 4‐year monitoring period in Southwest ChinaTriple oxygen isotopes in precipitation serve as indicators of the extent of isotopic fractionation in water vapor between different seasonsChanges in precipitation Δ′17O show a negative correlation with relative humidity from the moisture source area during the rainy season [ABSTRACT FROM AUTHOR]

Objective The formation of monsoon climates is attributed to the seasonal reversal of wind direction and precipitation caused by the difference in thermal capacity between land and ocean. Asia is recognized as the most prominent region globally, with monsoon climates, that affect the largest population. The heavy rainfall accompanying monsoons can result in various secondary disasters, substatially jeopardizing human safety and productivity in the region. Consequently, comprehending the formation process of the Asian monsoon holds paramount importance. Methods This study aim to employ geological concepts to establish a connection between the past and present, providing an overview of the components of Asian monsoons, identifying the primary factors influencing their formation and evolution, and summarizing research progress on the South Asian and East Asian monsoons based on sediment records from key Asian locations. Results The findings indicate that during the Cenozoic, the collision between the Indian Plate and the southern margin of the Asian continent altered the distribution of land and sea in Asia. Consequently, the Tibetan Plateau experienced initial uplift, contributing to the emergence of monsoon climates in South Asia and East Asia. However, at this stage, the East Asian region was still primarily influenced by the planetary wind system, and the East Asian monsoon was in its early stages, predominantly restricted to the southern margin of the South China Plate in a localized manner. In contrast, the South Asian Monsoon covered a relatively extensive area. This discrepancy may be attributed to the delayed opening of marginal seas in the East Asian region compared to the relatively earlier occurrence of land and sea distribution in South Asia. However, as the Tibetan Plateau continued to uplift and approach its current altitude during the middle to late Cenozoic, the Asian monsoon entered a strengthening phase, notably impacting regional geological evolution processes. Since the middle to late Cenozoic, the development of the North and South Polar ice caps and the upliftment of the Tibetan Plateau have controlled the Asian monsoon, leading it to undergo multiple stable periods of development. Conclusion The development and evolution of the East Asian and South Asian monsoons are mainly driven by the distribution of sea and land in the Asia, the upliftment of the Tibetan Plateau and the global climate change during the Cenozoic. Significance These findings provide valuable insights into the scientific and rational utilization of the Asian monsoon for conducting systematic Earth science research in Asia.

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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]

Here, we infer the historical biogeography and evolutionary diversification of the genus Lilium. For this purpose, we used the complete plastomes of 64 currently accepted species in the genus Lilium (14 plastomes were newly sequenced) to recover the phylogenetic backbone of the genus and a time-calibrated phylogenetic framework to estimate biogeographical history scenarios and evolutionary diversification rates of Lilium. Our results suggest that ancient climatic changes and geological tectonic activities jointly shaped the distribution range and drove evolutionary radiation of Lilium, including the Middle Miocene Climate Optimum (MMCO), the late Miocene global cooling, as well as the successive uplift of the Qinghai-Tibet Plateau (QTP) and the strengthening of the monsoon climate in East Asia during the late Miocene and the Pliocene. This case study suggests that the unique geological and climatic events in the Neogene of East Asia, in particular the uplift of QTP and the enhancement of monsoonal climate, may have played an essential role in formation of uneven distribution of plant diversity in the Northern Hemisphere.

Influence of land-surface memory effects over the Tibetan Plateau on the Asian summer monsoon has long been studied, but not quantified because of the difficulty of extracting only these effects from observational data. This study examines the impact of spring land-surface conditions, including surface air temperature (SAT) and snow cover, over the Tibetan Plateau and its surrounding regions on the early stage of the Asian summer monsoon using large-ensemble experiments produced by an atmospheric global climate model (AGCM). The results show that the above-normal SAT over and around the Tibetan Plateau in May can enhance June monsoon circulation without the sea surface temperature (SST) forcing. The physical mechanism behind this involves warmed surface air over the plateau enhancing the north–south SAT gradient, leading to strengthening the Asian summer monsoon circulation and precipitation. Inter-ensemble correlation analysis indicated that SAT warming over the plateau is clearly associated with upper-tropospheric anti-cyclonic circulation anomalies in May. Also, although winter land-surface signals do not persist until late spring, SAT anomalies in March tend to persist until May, explaining 10–20% of the total SAT variance in May. Interestingly, the spring SAT impacts on June monsoon circulations vary interannually, indicating that the contribution of the land–atmosphere (L–A) coupling process to interannual monsoon variability differs from year to year. Active L–A coupling years tend to coincide with cooler SSTs with anomalous low-level divergence and upper-level convergence over and around the Maritime continent, implying that SST forcing is associated with the L–A coupling strength. Specifically, in May of the developing stage of monsoon circulation, the weak Walker circulation over the equatorial and northern Indian Ocean and undeveloped monsoon circulation are suitable for the L–A coupling to influence the development of the monsoon circulation effectively. However, the well-known oceanic events, such as El Ni n ~ o, are found to be less connected with the interannual L–A coupling variations. [ABSTRACT FROM AUTHOR]

The current reconstructions of the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO) primarily rely on marine sediment proxies. However, the limited resolution of these records makes it difficult to precisely understand the short‐term dynamics of the PDO and AMO, and consequently, their influence on global climate. This study unveils two new Holocene reconstructions of AMO and PDO derived from a large‐scale compilation of speleothem isotope records (δ18Os) from Chinese monsoon region, in which spatial patterns of summer rainfall are generally accepted as good indicators of internal variability. Principal component analysis applied to Chinese δ18Os records identifies the first principal component as representative of Holocene Asian monsoon (AM) variation. This data‐driven approach reveals a significant shift in hydroclimatic conditions after 8.2 ka, potentially providing valuable insights into the underlying forcing mechanisms driving these changes. The remanent components, which show spatial rainfall patterns, are effectively validated through independent records of AMO and PDO derived from the previous paleo‐proxy based reconstructions and model simulations. The present reconstructions suggest a significantly enhanced stability of the AMO and PDO in the middle Holocene, which may explain the concurrent more stable and optimum climate observed in the AM region. These findings also imply that the Holocene AM intensity recorded in Chinese cave records is largely controlled by external forcing, whereas the regionally heterogenous rainfall is regulated by internal variability. The successful attempt on the Holocene AMO and PDO reconstructions indicates an effective isolation between different modes of climate variability from paleoclimate records. Key Points: Different modes of climate variability are isolated from a large‐scale compilation of Chinese speleothem δ18O recordsHolocene high‐resolution Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation variations are reconstructed based on Chinese speleothem δ18O recordsHigh stability of internal variability in the middle Holocene may explain the Holocene climate optimum [ABSTRACT FROM AUTHOR]

Study region: Kamikochi area in the Japanese Northern Alps Study focus: For mountains with high precipitation and hydraulic gradients, understanding the hydrologic cycle is important for disaster prevention (i.e., floods and landslides) and water resource management. Mountainous regions with an Asian monsoon climate have higher precipitation than other parts of the world, and the runoff processes that accompany significant precipitation remain largely unresolved. We conducted hydrological observations to clarify the runoff process in mountainous regions with an Asian monsoon climate using the difference in runoff characteristics between mountain-block and floodplain springs in the Kamikochi area. New hydrological insight into the region: Hydrological observations and analysis under dry/wet conditions have revealed that the floodplain spring has a higher seasonally variable water temperature than the mountain-block spring. Under steady-state conditions, mountain-block groundwater has a larger discharge and helps maintain the baseflow. During precipitation events, the mountain-block spring exhibits a more pronounced increase in runoff than the floodplain spring under wet conditions. This is because the latter interacts with the mainstream through permeable sand/gravel beds, whereas the former is pushed out of the bedrock by precipitation. Thus, the hydrologic cycle in mountainous regions with an Asian monsoon climate is driven by the supply of high-potential mountain-block groundwater to the valley floor. Mountain-block groundwater not only maintains the baseflow but also drives the hydrologic cycle system in mountainous regions.

The Asian Monsoonal rainfall accounts for the majority of annual regional precipitation in East and South Asia and could be remotely regulated by El Niño‐Southern Oscillation (ENSO). Besides, several paleoclimate records and simulations have indicated solar signals in the Asian Monsoon, implying the impact of solar activity on the regional monsoon precipitation. By conducting multi‐linear regression analysis to the solar irradiance forced single‐forcing experiment in the last millennium, this study presents the comparison of solar and ENSO effects on monsoonal precipitation in South and East Asia during early summer (May–June). Increased total solar irradiance during high solar activity years tends to trigger a favorable environment for developing monsoon onset, leading to more precipitation against ENSO‐related patterns over Southeast and South Asia before peak‐summer (July–August). The result supports reconstructed terrestrial records and underlines considerable influences of the solar cycle on the variation of the Asian Summer Monsoon. Plain Language Summary: Previous studies have shown the influence of the solar cycle on various climate systems, such as El Niño‐Southern Oscillation (ENSO), Atlantic Oscillation, Pacific Decadal Oscillation, etc., despite the relatively small amount of solar irradiance variations to the total amount of solar insolation. In addition, paleo‐records indicate the correlation between the long‐term solar cycle and the variation of the Asian Monsoon. This study attempts to clarify the role of solar activity in monsoonal precipitation over South and East Asia. We find that during early summer (May–June), high solar activity tends to enhance the meridional temperature gradient over the northern Indian Ocean. An associated meridional circulation is thereby intensified and well‐coupled with monsoonal circulations. The coupling contributes to more moisture transport and increased precipitation over the subcontinent, contrasting with the reduced rainfall and suppressed monsoonal circulation over the northern Indian Ocean during warmer ENSO events. This result indicates that the effects of changes in solar irradiation on climate systems should be considered, particularly in the Asian Monsoon region. Furthermore, a physical explanation is provided for the solar signals in the Asian Monsoon in paleo‐evidences. Key Points: The Multi‐Linear Regression analysis is used to isolate solar activity and El Niño‐Southern Oscillation (ENSO) signals from the CESM‐LME project's solar‐only experimentSub‐seasonal analyses to the Asian Summer Monsoon are highlighted by varied responses to solar activity in early and peak summerHigher solar activity increases early summer rainfall around Southeast Asia against ENSO‐related patterns by enhancing monsoonal circulation [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]

Observations show that the teleconnection between the El Niño‐Southern Oscillation (ENSO) and the Asian summer monsoon (ASM) is non‐stationary. However, the underlying mechanisms are poorly understood due to inadequate availability of reliable, long‐term observations. This study uses two state‐of‐the‐art data assimilation‐based reconstructions of last millennium climate to examine changes in the ENSO–ASM teleconnection; we investigate how modes of (multi‐)decadal climate variability (namely, the Pacific Decadal Oscillation, PDO, and the Atlantic Multidecadal Oscillation, AMO) modulate the ENSO–ASM relationship. Our analyses reveal that the PDO exerts a more pronounced impact on ASM variability than the AMO. By comparing different linear regression models, we find that including the PDO in addition to ENSO cycles can improve prediction of the ASM, especially for the Indian summer monsoon. In particular, dry (wet) anomalies caused by El Niño (La Niña) over India become enhanced during the positive (negative) PDO phases due to a compounding effect. However, composite differences in the ENSO–ASM relationship between positive and negative phases of the PDO and AMO are not statistically significant. A significant influence of the PDO/AMO on the ENSO–ASM relationship occurred only over a limited period within the last millennium. By leveraging the long‐term paleoclimate reconstructions, we document and interrogate the non‐stationary nature of the PDO and AMO in modulating the ENSO–ASM relationship. Plain Language Summary: Sea surface temperatures in the tropical Pacific oscillate between warmer and cooler conditions every 2–7 years. These oscillations are called "The El Niño‐Southern Oscillation (ENSO)" and have been shown to affect weather and climate in remote locations. For example, ENSO has been shown to alter rainfall of the Asian summer monsoon (ASM). However, the connection between ENSO and the ASM is not dependable, making accurate ASM prediction a challenge, especially in a changing climate. Here, we use a new technique that combines geological archives of past climates like ice cores, corals, or lake sediments with climate models to examine alterations in the ENSO–ASM relationship over the past thousand years. In particular, we focus on how other oscillatory ocean temperature patterns, the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), might affect the ENSO–ASM relationship. In the context of the last millennium, we find the differences in the ENSO–ASM relationship between all positive and negative PDO/AMO phases are not statistically significant, as the PDO/AMO modulation on the ENSO–ASM relationship evolves over long time scales. Nevertheless, the PDO itself strongly regulates the Indian summer monsoon, and the consideration of PDO in addition to ENSO enhances monsoon prediction. This information is useful for anticipating decadal‐scale changes in the ASM in our changing climate. Key Points: We investigate how the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) modulate the relationship between El Niño‐Southern Oscillation (ENSO) and the Asian summer monsoon (ASM) using paleo‐data assimilation productsWe find that the PDO impacts ASM variability more than the AMO, and its consideration yields improved Indian summer monsoon predictionsNotably, the influence of the PDO and AMO on the ENSO–ASM relationship is highly non‐stationary across the last millennium [ABSTRACT FROM AUTHOR]

Abstract Background The Sino-Himalayan flora harbors highly diverse high-elevation biotas, but our understanding of its evolutionary history in temporal and spatial dimensions is limited. In this study, we integrated a dated phylogenetic tree with comprehensive species distribution data to investigate changes over time and space in floristic elements, including the tropical, Tethys, northern temperate, and East Asian floristic elements, across the entire Sino-Himalaya and its three floristic regions: the Yunnan Plateau, Hengduan Mountains, and East Himalaya regions. Results Our results revealed that the Sino-Himalayan flora developed from lowland biomes and was predominantly characterized by tropical floristic elements before the collision between the Indian subcontinent and Eurasia during the Early Cenozoic. Subsequently, from the Late Eocene onwards, the uplifts of the Himalaya and Hengduan Mountains transformed the Sino-Himalayan region into a wet and cold plateau, on which harsh and diverse ecological conditions forced the rapid evolution of local angiosperms, giving birth to characteristic taxa adapted to the high altitudes and cold habitat. The percentage of temperate floristic elements increased and exceeded that of tropical floristic elements by the Late Miocene. Conclusions The Sino-Himalayan flora underwent four significant formation periods and experienced a considerable increase in endemic genera and species in the Miocene, which remain crucial to the present-day patterns of plant diversity. Our findings support the view that the Sino-Himalayan flora is relatively young but has ancient origins. The three major shifts in the divergence of genera and species during the four formation periods were primarily influenced by the uplifts of the Himalaya and Hengduan Mountains and the onset and intensification of the Asian monsoon system. Additionally, the temporal patterns of floristic elements differed among the three floristic regions of the Sino-Himalaya, indicating that the uplift of the Himalaya and surrounding areas was asynchronous. Compared to the Yunnan Plateau region, the East Himalaya and Hengduan Mountains experienced more recent and drastic uplifts, resulting in highly intricate topography with diverse habitats that promoted the rapid radiation of endemic genera and species in these regions.

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 The Asian Monsoonal rainfall accounts for the majority of annual regional precipitation in East and South Asia and could be remotely regulated by El Niño‐Southern Oscillation (ENSO). Besides, several paleoclimate records and simulations have indicated solar signals in the Asian Monsoon, implying the impact of solar activity on the regional monsoon precipitation. By conducting multi‐linear regression analysis to the solar irradiance forced single‐forcing experiment in the last millennium, this study presents the comparison of solar and ENSO effects on monsoonal precipitation in South and East Asia during early summer (May–June). Increased total solar irradiance during high solar activity years tends to trigger a favorable environment for developing monsoon onset, leading to more precipitation against ENSO‐related patterns over Southeast and South Asia before peak‐summer (July–August). The result supports reconstructed terrestrial records and underlines considerable influences of the solar cycle on the variation of the Asian Summer Monsoon.

The Qinghai-Tibet Plateau (QTP) has experienced an overall increase in humidity over recent decades, but the changes in aridity and humidity within the transitional climate zone, as well as the underlying factors driving these changes, remain unclear. We present a framework to quantify the spatiotemporal variations transitional zone indicated by 400 mm isohyets and its driving factors on the QTP. The results show that the 400 mm isohyets has moved an average of 87.85 km to the north-west direction, moving an average 0.04 km per year, and a maximum distance traveled of 261 km (northernmost orientation) during the past four decades. Over time, the variation in isohyets exhibited distinct piecewise characteristics and obvious spatial differences. The central section (95°E–101°E) remained relatively stable, whereas the eastern section (101°E–104°E) and western section (91°E–95°E) experienced violent fluctuations. The east–west boundary of the spatiotemporal movement of the 400 mm isohyets was utilized to delineate the eastern humid zone, transitional zone, and western arid zone. The transition zone interannual precipitation has experiences more significant interdecadal oscillations between dry and wet climates, while the western region has experienced the opposite. The East Asian summer monsoon (EASM) exhibited a positive correlation with precipitation, increased precipitation is the main factor driving the westward and northward movement of the 400 mm isohyets. The vegetation response to precipitation exhibited greater variability in the transitional zone. This study provides a novel reference for quantitatively comprehending the aridity and humidity of climatic conditions, as well as the driving mechanisms behind regional climate change in the QTP.

Reconstructing the Holocene megaflood history is a key component of understanding the mechanism of past climate change and assessing the potential impact of future catastrophic events. The Pearl River is the longest watercourse in southern China, and its lower reach has been identified as one of the world's most vulnerable regions for flood exposure. However, there is a complete lack of millennial-scale geological records of paleomegafloods for the future prediction of once-in-a-hundred (even once-in-a-thousand) year floods in southern China. Here, we identified a series of paleomegaflood deposits interbedded with wood-rich peat layers in the lower West Pearl River area. All paleoflood layers have been well dated using AMS 14C dating method. According to the regional correlation of the flood sequence, sediment characteristics and provenance analysis, there have been at least 7 megafloods corresponding to once-in-a-thousand-year events in the lower reaches of the West Pearl River during the past 6000 years, with an average return period of approximately 855 years. The identified paleomegafloods were coeval with periods of strong El Niño-Southern Oscillation (ENSO), indicating that weakening of the Asian summer monsoon, associated with enhanced ENSO variability, may have triggered abnormally high precipitation leading to flooding of exceptional magnitude in southern China. In addition, the most prominent paleomegafloods identified in the lower Pearl River coincided with intervals of lower precipitation and fewer storms in central-eastern China, indicating the intensification of the meridional "tripole" pattern of precipitation across eastern China during the latter half of the Holocene. Increased land use and deforestation over the last 2000 years have resulted in soil loss and rapid degradation of local primeval forest ecosystems, leading to more catastrophic flooding. Large amounts of rice pollen in the uppermost flood layer during the Song Dynasty indicate that this megaflood may have inundated a large area of cultivated land. The periodic occurrence of Holocene megafloods not only caused damage to human existence, but also affected the evolution of local civilization. This study reveals for the first time a series of Holocene millennial-scale megafloods and sheds new light on the importance of atmosphere-ocean interactions in the tropical Pacific and monsoon subtropical climate dynamics for precipitation anomalies in East Asia. Our data yield valuable information for future research into climate extremes and hazard prevention. [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]

Background: The Sino-Himalayan flora harbors highly diverse high-elevation biotas, but our understanding of its evolutionary history in temporal and spatial dimensions is limited. In this study, we integrated a dated phylogenetic tree with comprehensive species distribution data to investigate changes over time and space in floristic elements, including the tropical, Tethys, northern temperate, and East Asian floristic elements, across the entire Sino-Himalaya and its three floristic regions: the Yunnan Plateau, Hengduan Mountains, and East Himalaya regions. Results: Our results revealed that the Sino-Himalayan flora developed from lowland biomes and was predominantly characterized by tropical floristic elements before the collision between the Indian subcontinent and Eurasia during the Early Cenozoic. Subsequently, from the Late Eocene onwards, the uplifts of the Himalaya and Hengduan Mountains transformed the Sino-Himalayan region into a wet and cold plateau, on which harsh and diverse ecological conditions forced the rapid evolution of local angiosperms, giving birth to characteristic taxa adapted to the high altitudes and cold habitat. The percentage of temperate floristic elements increased and exceeded that of tropical floristic elements by the Late Miocene. Conclusions: The Sino-Himalayan flora underwent four significant formation periods and experienced a considerable increase in endemic genera and species in the Miocene, which remain crucial to the present-day patterns of plant diversity. Our findings support the view that the Sino-Himalayan flora is relatively young but has ancient origins. The three major shifts in the divergence of genera and species during the four formation periods were primarily influenced by the uplifts of the Himalaya and Hengduan Mountains and the onset and intensification of the Asian monsoon system. Additionally, the temporal patterns of floristic elements differed among the three floristic regions of the Sino-Himalaya, indicating that the uplift of the Himalaya and surrounding areas was asynchronous. Compared to the Yunnan Plateau region, the East Himalaya and Hengduan Mountains experienced more recent and drastic uplifts, resulting in highly intricate topography with diverse habitats that promoted the rapid radiation of endemic genera and species in these regions. [ABSTRACT FROM AUTHOR]

Large uncertainties exist in climate model projections of the Asian summer monsoon (ASM). The El Niño‐Southern Oscillation (ENSO) is an important modulator of the ASM, but the ENSO‐ASM teleconnection is not stationary. Furthermore, teleconnections between ENSO and the East Asian versus South Asian subcomponents of the ASM exhibit distinct characteristics. Therefore, understanding the variability of the ENSO‐ASM teleconnection is critical for anticipating future variations in ASM intensity. To this end, we here use paleoclimate records to extend temporal coverage beyond the instrumental era by millennia. Recently, data assimilation techniques have been applied for the last millennium, which facilitates physically consistent, globally gridded climate reconstructions informed by paleoclimate observations. We use these novel data assimilation products to investigate variations in the ENSO‐ASM relationship over the last 1,000 years. We find that correlations between ENSO and ASM indices are mostly negative in the last millennium, suggesting that strong ASM years are often associated with La Niña events. During periods of weak correlations between ENSO and the East Asian summer monsoon, we observe an El Niño‐like sea surface temperature (SST) pattern in the Pacific. Additionally, SST patterns associated with periods of weak correlations between ENSO and South Asian summer monsoon rainfall are not consistent among data assimilation products. This underscores the importance of developing more precipitation‐sensitive paleoclimate proxies in the Indian subcontinental realm over the last millennium. Our study serves as a baseline for future appraisals of paleoclimate assimilation products and an example of informing our understanding of decadal‐scale ENSO‐ASM teleconnection variability using paleoclimate data sets. Plain Language Summary: A large fraction of floods and droughts in Asia are associated with extreme Asian summer monsoon (ASM) events, but unfortunately, the prediction of the ASM is still highly uncertain. Scientists often use El Niño—warm sea surface temperature (SST) events in the eastern Pacific Ocean that occur before the ASM—as a basis to predict the ASM, but it does not work perfectly all the time. In order to understand why El Niño fails to predict the ASM sometimes, we looked at climate data spanning the last 1,000 years. The data was based on paleoclimate reconstructions using archives including tree rings, corals, speleothems, and ice cores. Scientists recently synthesized all these data together with climate model simulations. We find that more intense summer monsoon rainfall in East and South Asia likely corresponds to colder SSTs in the Eastern Pacific Ocean. Also, when El Niño fails to predict the monsoon in East Asia, the background SST in the eastern Pacific is warmer than normal. Our results could help better predict ASM rainfall in the future and mitigate impacts of fire and flooding caused by extreme monsoon events. Key Points: The El Niño‐Southern Oscillation (ENSO) teleconnections to the Asian summer monsoon have evident decadal‐to‐centennial variability in the last 1,000 yearsDuring most of the last 1,000 years, El Niño tends to be associated with weak Asian summer monsoon rainfallWeak ENSO‐East Asian summer monsoon teleconnection is associated with sea surface temperature anomalies resembling El Niño events [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]

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]

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The Asian monsoon region is highly dependent on boreal summer rainfall, which directly impacts the socio-economic stability and welfare of billions of people each year. Precipitation variability over East China has been extensively studied and is known to be characterized by meridional tripole and dipole precipitation structures. In contrast, few studies have focused on precipitation variability over Mainland Southeast Asia (MSEA) and the possible relationship with the variability over East China. Here we focus on how interannual precipitation variability across MSEA during 1983–2017 may be associated with the tripole or dipole patterns using an empirical orthogonal function (EOF) analysis. The first EOF shows a meridional tripole pattern in East China summer precipitation and an in-phase relationship between MSEA and South China precipitation. In contrast, the second EOF shows a meridional dipole pattern in East China precipitation and an out-of-phase relationship between MSEA and South China precipitation. We show that the first EOF mode is a delayed precipitation response to the El Niño-Southern Oscillation (ENSO), while the second EOF mode is a simultaneous precipitation response to the remote influence of the North Atlantic Oscillation (NAO). Therefore, the in-phase or out-of-phase variations in precipitation between MSEA and South China may be used to gauge the relative importance of local Pacific and remote Atlantic influences on Asian monsoon climate.

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]

We present a new teak (Tectona grandis L.f.) tree-ring stable oxygen isotope (δ18OTR) chronology from Mae Tuen (MT) site, Tak province, northwestern Thailand at inter-annual (167-year, A.D.1850–2016) and intra-annual (A.D.2006–2016) timescales. The inter-annual δ18OTR chronology showed a significant negative correlation (r = −0.678, p < 0.01) with the May–October amount of regional rainfall obtained from CRU TS4.03. We established a linear regression model that explained 46.0% of the actual rainfall variance and reconstructed monsoon season rainfall back to A.D.1850. The seasonal variations in moisture conditions were reflected in inter-annual δ18OTR variability. The rainfall amount and δ18O in precipitation (δ18Op) mainly controlled intra-annual variations in teak δ18OTR. These results show that the variation in Thai teak δ18OTR is dominated by rainfall, highlighting the strength of δ18OTR as a monsoon rainfall proxy. [ABSTRACT FROM AUTHOR]

This study describes seasonal changes in the fluxes of planktonic foraminifera in response to changes in environmental conditions during the Asian Monsoon. Sediment trap systems were deployed for a period of 1 year at two locations in the Maldives: Kardiva Channel and Inner Sea. Twenty-six (26) planktonic foraminifera were recognized, of which six species (Trilobatus sacculifer, Globorotalia menardii, Globigerinoides ruber, Globigerina siphonifera, Neogloboquadrina dutertrei, and G. bulloides) dominated the assemblage (82%–84%) in both sites. Planktonic foraminifera fluxes and chlorophyll-a concentrations are higher in the Inner Sea. Total planktonic foraminifera fluxes show preference to high nutrient conditions during monsoon periods. Planktonic foraminifera fluxes generally follow the trend of carbonate fluxes except during October-November 2014. Species flux generally reached maximum during the NE monsoon as a response to increase in nutrient concentration brought by the movement of the North Equatorial Current over the trap sites. The expansion of nutrient-rich surface waters, occurring eastward during the SW monsoon and westward during the NE monsoon, led to an increase in the population of species dwelling in both shallow (T. sacculifer and G. ruber) and deep waters (N. dutertrei and G. bulloides). Dominance of shallow-dwelling species T. sacculifer and G. ruber throughout the sampling period suggests stable stratification of the water column. This supports the idea of wind-mixing rather than local upwelling as the driving force for enrichment of nutrients and subsequent increase in planktonic foraminifera fluxes. Lateral advection and resuspension in settling of particles to the traps is evident based on the presence of benthic foraminifera in the Inner Sea samples. These processes, however, did not significantly mask climate and surface ocean signals since there remains a clear correlation between planktonic foraminifera fluxes and environmental conditions.

Abstract 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.

The South and East Asian summer monsoons are globally significant meteorological features, creating a strongly seasonal pattern of precipitation. The stability of such a strongly seasonal hydrological cycle is of extreme importance for a vast range of ecosystems and for the livelihoods of a large share of the world's population. Simulations are performed with an intermediate complexity climate model, PLASIM, to assess the future response of the monsoons to changing concentrations of aerosols and greenhouse gases. The aerosol loading consists of a mid-tropospheric warming and a surface cooling, which is applied to India, Southeast Asia and East China, both concurrently and independently. The primary effect of increased aerosol loading is a decrease in summer precipitation in the vicinity of the applied forcing, although the regional response varies significantly. The decrease in precipitation is only partially ascribable to a decrease in the precipitable water, and instead derives from a reduction of the precipitation efficiency, due to changes in the stratification of the atmosphere. When the aerosol loading is added in all regions simultaneously, precipitation in East China is most strongly affected, with a quite distinct transition to a low precipitation regime as the radiative forcing increases beyond 60 W/m2. The response is less abrupt as we move westward, with precipitation in South India being least affected. This lower sensitivity in South India is attributed to aerosol forcing over East China. Additionally, the effect on precipitation is approximately linear with the forcing. The impact of doubling carbon dioxide levels is to increase precipitation over the regions and weaken the circulation. When the carbon dioxide and aerosol forcings are applied at the same time, the carbon dioxide forcing partially offsets the surface cooling and reduction in precipitation associated with the aerosol response. [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 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]

Accurate reconstruction of geological dust activity is crucial for understanding past climate change and its interaction with dust cycle. Loess on the Chinese Loess Plateau (CLP) is an ideal and sensitive material for revisiting past dust activity. Previously, the changes in the dust mass accumulation rate (MAR) over various time scales were widely established on the CLP. However, few absolutely dated dust records have been obtained and synthesized for the Holocene. This study addresses this gap by compiling 23 optically stimulated luminescence-dated Holocene loess sections across the CLP. We developed a high-quality chronology via Bayesian age-depth modeling and derived a MAR record for each section. Then, we obtained a mean MAR record for the CLP by stacking individual records. We propose that, in contrast to site-specific MARs, stacked MARs represent the mean dust accumulation conditions for the entire CLP and can be used to track relatively large-scale dust activity and climate change. The stacked MAR record suggests a moderate weakening trend of dust accumulation from ∼11.5 to 7.5 thousand years ago (ka BP), followed by a pronounced strengthening trend from ∼7.5 to 3.0 ka BP. A comparison with other regional dust records reveals a shift in dust activity at ∼8–6 ka BP in northern China and western Mongolia. We argue that the East Asian winter and summer monsoons jointly contributed to Holocene mean dust MAR variations on the CLP by changing dust transport wind energy and dust source aridity, respectively. A comparison of Holocene dust records in Asia with those in the northwestern Pacific Ocean and Greenland suggests asynchronous variations in dust activity between proximal and distal Asia-sourced dust deposition. This is because, unlike proximal deposition, distal deposition can be controlled not only by the dust source conditions but also by the intensity and the position of the Westerlies. • An OSL-dated, stacked Holocene dust MAR record from loess on the CLP. • A trend shift of Holocene dust activity in northern China at ∼8–6 ka BP. • The Asian winter and summer monsoons contribute to dust activity on the CLP. • Asynchronous changes in Holocene dust activity in Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Eolian dust darkens the snowpack, accelerates the snowmelt and alters atmospheric radiative budget and climate. Last Glacial Maximum (LGM), a typical geological cold stage, is featured by more dust and snow cover than present day, which seems to own a stronger snow-darkening. In this study, we used a couple of climate model experiments in order to evaluate the effect of dust-in-snow changes on Northern Hemispheric climate and Asian monsoon. The results show that, compared to present day, more dust and snow cover in LGM allows heavier dust deposition and snowmelt, which produces a larger snow-albedo-temperature feedback. This snow-darkening leads to an annually averaged northern hemisphere warming of 0.31 °C, stronger in boreal spring and summer. Spatially, the prominent warming centers are found around LGM ice sheets and Tibetan Plateau (TP), up to 2–3 °C annually, which significantly contributes to the melt of ice and triggers the termination of glaciation. Over Asia, the present snow-darkening weakens the Indian and East Asian summer monsoon although not significant. However, strong LGM forcing does not amplify the weakening but intensifies the Indian and East Asian monsoon and precipitation. Thus, the potential role of dust and its interaction with snow cover should be mentioned in the glacial-scale climate change. • The snow darkening effect during the LGM caused dramatic warming in the Northern Hemisphere. • Dust darkened snow cover change over mid-high latitude Asia is significant during LGM. • Snow cover change over Asia intensifies the Indian and East Asian summer monsoon. [ABSTRACT FROM AUTHOR]

To find a plausible initiation mechanism of quasi-stationary convective bands (QSCBs) that lead to disasters, we investigated an extreme heavy precipitation event in Kyushu, southwestern Japan, in the middle of August 2021, using a regional spectral model incorporated with isotopic tracers aided by a water-tagging method. In the synoptic environment, the horizontal pressure gradient at low levels between an eastward-migrating Baiu frontal depression (BFD) and the North Pacific subtropical high (NPSH) is intensified to the south of a synoptic-scale front. To the south of the front, QSCBs also lie from the East China Sea to inland Kyushu. We confirm that the merging of the Asian monsoon moisture and the NPSH moisture creates a deep moist layer reaching middle levels from the surface in the vicinity of the QSCBs, providing an extremely unstable condition. Although such an unstable condition is indispensable for the maintenance of the QSCBs, an initiation mechanism is required that accounts for why the QSCBs emerge around the oceanic region where the two primary moisture merges; that appears to be the Ekman pumping mechanism. The strong boundary layer inflow of the NPSH moisture origin enhances the convective instability to the south of the QSCBs. Since the horizontal pressure gradient is attenuated in the vicinity of the BFD's center, on the contrary, the boundary layer flow north of the QSCBs decelerates rapidly, giving rise to upwelling due to the Ekman convergence. The persistent upwelling estimated in this event can lift the air of the Ekman layer up to a few hundred meters in a few hours, allowing it to readily reach the level of free convection. It is reasonable to conjecture that the persistent upwelling triggers the release of enhanced convective instability, leading to the formation of QSCBs. Continuous merging of the two remote moisture origins under the pronounced horizontal pressure gradient will further contribute to the reinforcement of the QSCBs. • A combination of the Baiu frontal depression (BFD) and North Pacific subtropical high (NPSH) facilitates moisture transport. • Merging of the Asian monsoon and NPSH moisture creates a deep moist layer, providing a very unstable condition. • The Ekman convergence is induced under the weakened horizontal pressure gradient. • The release of convective instability due to upwelling is a key process for triggering quasi-stationary convective bands. [ABSTRACT FROM AUTHOR]

In this study, we employ biological, geochemical and mineral, and physical proxies to quantitatively and semi-quantitatively reconstruct regional paleoclimate variations in China over the past ∼21 thousand years (ka). We have constructed state-of-the-art transfer functions between proxies and climatic variables in East Asia, revealing substantial paleoclimate variability, and demonstrate significant diversity of paleoclimate variations in regions of China over the past ∼21 ka. Compared with observational data between 1961 and 1990, averaged mean annual temperature (MAT) was ∼5 °C (3–8 °C) lower during the Last Glacial Maximum (LGM, ∼21 ± 3 ka), and ∼ 2 °C (1–3 °C) higher during Holocene Optimum (HO, ±9 ka) in China; while averaged mean annual precipitation (MAP) and averaged summer precipitation varied between 30 and 150%, with enhanced seasonality during the warmer Holocene (8–5 ka). Our quantitative and semi-quantitative paleoclimate reconstructions reveal both similarities and contrasts with previous studies of regional temperature and precipitation variability. The most remarkable paleoclimate variability is recorded in the transitional zone between the humid monsoon and arid desert regions of central and northern China. We conducted a dynamic downscaling paleoclimate simulation with a regional climate model (RegCM4), using the output from the fully-forced transient simulation of the global climate (TraCE-21 K) as the prescribed boundary conditions, to simulate regional climate changes at high spatial resolution in China over the past ∼21 ka. The results improve paleoclimate simulations at regional scales, but reveal differences in comparison with TraCE-21 K, thereby highlighting uncertainties in the simulation modeling. Moreover, we compare proxy-based paleoclimate reconstructions and the output of TraCE-21 K to identify inconsistencies in relation to regional paleoclimate variations, and confirm a generally consistent warming trend in MAT from the LGM to the HO followed by a cooling trend during the late Holocene. An overall increase in both annual and summer precipitation is observed from LGM to Holocene. This general paleoclimate pattern is likely to have been driven by northern hemisphere ice volume and atmospheric greenhouse gas concentrations (GHGs) during the last deglaciation, and boreal summer insolation during the Holocene. This study represents the first attempt to use multi sources and large datasets of proxy reconstructions and numerical simulations to evaluate regional paleoclimate variability in China since the LGM. Our research provides a comprehensive overview of climate change over the past 21 ka and underscores the critical importance of conducting high-resolution simulations and quantitative paleoclimate studies. This approach is essential for deciphering patterns of paleoclimate change that are currently poorly defined. • The first synthesis of regional paleoclimate variations in China over the past ∼21 ka. • State-of-the-art transfer functions between proxies and climate varibales in East Asia. • Averaged MAT in China was ∼5 °C lower during LGM, and 1–3 °C higher during HO. • Averaged MAP varied between 30 and 150%, with a greater seasonality during 8–5 ka. [ABSTRACT FROM AUTHOR]

[Display omitted] The uplift of eastern Tibet, Asian monsoon development and the evolution of globally significant Asian biodiversity are all linked, but in obscure ways. Sedimentology, geochronology, clumped isotope thermometry, and fossil leaf-derived numerical climate data from the Relu Basin, eastern Tibet, show at ∼50–45 Ma the basin was a hot (mean annual air temperature, MAAT, ∼27 °C) dry desert at a low-elevation of 0.6 ± 0.6 km. Rapid basin rise to 2.0 ± 0.9 km at 45–42 Ma and to 2.9 ± 0.9 km at 42–40 Ma, with MAATs of ∼20 and ∼16 °C, respectively, accompanied seasonally varying increased annual precipitation to > 1500 mm. From ∼39 to 34 Ma, the basin attained 3.5 ± 1.0 km, near its present-day elevation (∼3.7 km), and MAAT cooled to ∼6 °C. Numerically-modelled Asian monsoon strength increased significantly when this Eocene uplift of eastern Tibet was incorporated. The simulation/proxy congruence points to a distinctive Eocene Asian monsoon, quite unlike that seen today, in that it featured bimodal precipitation and a winter-wet regime, and this enhanced biodiversity modernisation across eastern Asia. The Paleogene biodiversity of Asia evolved under a continually modifying monsoon influence, with the modern Asian monsoon system being unique to the present and a product of a long gradual development in the context of an ever-changing Earth system. [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]

We generate trajectories in storm‐resolving simulations in order to quantify the effect of ice microphysics on tropical upper‐tropospheric cloud‐radiative heating. The pressure and flow field tracked along the trajectories are used to run different ice microphysical schemes, both one‐ and two‐moment formulations within the Icosahedral Non‐hydrostatic Model model and a separate offline box microphysics model (CLaMS‐Ice). This computational approach allows us to isolate purely microphysical differences in a variant of "microphysical piggybacking;" feedbacks of microphysics onto pressure and the flow field, for example, via latent heating, are suppressed. Despite these constraints, we find about a 5‐fold difference in median cloud ice mass mixing ratios (qi) and ice crystal number (Ni) between the microphysical schemes and very distinct qi distributions versus temperature and relative humidity with respect to ice along the trajectories. After investigating microphysical formulations for nucleation, depositional growth, and sedimentation, we propose three cirrus lifecycles: a weak source‐strong sink lifecycle whose longwave and shortwave heating are smallest due to short lifetime and low optical depth, a strong source‐weak sink lifecycle whose longwave and shortwave heating are largest due to long lifetime and high optical depth, and a strong source‐strong sink lifecycle with intermediate radiative properties. Plain Language Summary: The number and mass of ice crystals in upper‐level clouds affect how much infrared radiation these clouds absorb and how much sunlight they reflect. Changing the description of how these crystals form and grow in models directly alters the crystal number and mass. But it can also indirectly alter the number and mass by changing temperature or available moisture via, for example, latent heating. We control for these indirect changes by using the same set of variables to run different models of ice crystal formation and growth. Even with the indirect changes suppressed, we produce a large variation in the number and mass of ice crystals with different models. We dig into why this is by looking at parameters describing crystal formation, growth, and sedimentation. The strength of these three processes generates distinct ice cloud lifecycles for which infrared radiation and sunlight are also absorbed and reflected with differing strength. Key Points: Even with feedbacks constrained, ice mass varies 5‐fold with structural differences in cirrus microphysicsThese differences develop rapidly within trajectory lifetime due to differences in representations of ice nucleationThree cirrus lifecycles with distinct radiative signatures are proposed [ABSTRACT FROM AUTHOR]

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]

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 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]

Abstract We generate trajectories in storm‐resolving simulations in order to quantify the effect of ice microphysics on tropical upper‐tropospheric cloud‐radiative heating. The pressure and flow field tracked along the trajectories are used to run different ice microphysical schemes, both one‐ and two‐moment formulations within the Icosahedral Non‐hydrostatic Model model and a separate offline box microphysics model (CLaMS‐Ice). This computational approach allows us to isolate purely microphysical differences in a variant of “microphysical piggybacking;” feedbacks of microphysics onto pressure and the flow field, for example, via latent heating, are suppressed. Despite these constraints, we find about a 5‐fold difference in median cloud ice mass mixing ratios (qi) and ice crystal number (Ni) between the microphysical schemes and very distinct qi distributions versus temperature and relative humidity with respect to ice along the trajectories. After investigating microphysical formulations for nucleation, depositional growth, and sedimentation, we propose three cirrus lifecycles: a weak source‐strong sink lifecycle whose longwave and shortwave heating are smallest due to short lifetime and low optical depth, a strong source‐weak sink lifecycle whose longwave and shortwave heating are largest due to long lifetime and high optical depth, and a strong source‐strong sink lifecycle with intermediate radiative properties.

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.

Abstract 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.