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SWAP land surface model, developed by the authors of this article, was used to carry out many-year calculations of snow cover characteristics for forest and field areas in the main regions of Asian Russia: West Siberia, East Siberia, and Far East for a historic period (1967−2019). The comparison of simulation results with the appropriate data of route snow surveys at meteorological stations in the Asian part of RF showed that SWAP adequately reproduces the dynamics of snow water equivalent, snow depth and density in open areas and under forest canopy at the chosen sites. For all sites located in snow survey areas, climatic values of the characteristics of snow cover formation regime were obtained for two types of the land surface (forest and field) and two climatic periods (1967−1992 and 1993−2019) and used to identify trends in changes in these characteristics in the historic period. It was shown that the direction of changes in the climatic values of snow cover characteristics in forest and field areas in West Siberia, East Siberia, and Far East is the same and corresponds to projections for the XXI century derived from climate models. [ABSTRACT FROM AUTHOR]

In the context of China's "dual carbon" goal, emissions of air pollutants are expected to significantly decrease in the future. Thus, the direct climate effects of black carbon (BC) aerosols in East Asia are investigated under this goal using an updated regional climate and chemistry model. The simulated annual average BC concentration over East Asia is approximately 1.29 μg/m3 in the last decade. Compared to those in 2010–2020, both the BC column burden and instantaneous direct radiative forcing in East Asia decrease by more than 55% and 80%, respectively, in the carbon peak year (2030s) and the carbon neutrality year (2060s). Conversely, the BC effective radiative forcing (ERF) and regional climate responses to BC exhibit substantial nonlinearity to emission reduction, possibly resulting from different adjustments of thermal‐dynamic fields and clouds from BC‐radiation interactions. The regional mean BC ERF at the tropopause over East Asia is approximately +1.11 W/m2 in 2010–2020 while negative in the 2060s. BC‐radiation interactions in the present‐day impose a significant annual mean cooling of −0.2 to −0.5 K in central China but warming +0.3 K in the Tibetan Plateau. As China's BC emissions decline, surface temperature responses show a mixed picture compared to 2010–2020, with more cooling in eastern China and Tibet of −0.2 to −0.3 K in the 2030s, but more warming in central China of approximately +0.3 K by the 2060s. The Indian BC might play a more important role in East Asian climate with reduction of BC emissions in China. Plain Language Summary: Black carbon (BC) aerosols, which are among the air pollutants that will be reduced in China under the "dual carbon" goal, can have an impact on the regional climate by absorbing solar radiation. We use a regional climate model to simulate the climate effect of BC over East Asia under the "dual carbon" goal of China. The results showed that the BC concentration and column burden in East Asia, as well as the instantaneous direct radiative forcing, will decrease significantly under future regional emission reduction policies. However, the effective radiative forcing of BC and regional climate responses do not exhibit simple linear relationships with emissions. The BC‐induced atmospheric thermal‐dynamic anomalies are the main drivers of this nonlinearity. Similarly, BC emissions from India might also influence the East Asian climate. Key Points: The East Asian black carbon (BC) loadings and instantaneous direct radiative forcings significantly decrease under the "dual carbon" goal of ChinaThe BC induced regional climate changes show nonlinear responses to the BC emission reductionThe Indian BC might play an increasingly important role in East Asian climate with decreasing BC emissions in China [ABSTRACT FROM AUTHOR]

The Millennium Eruption of Changbaishan Volcano is heralded as one of the largest explosive eruptions in the Late Holocene and produced huge quantities of tephra. The petrogeochemical method estimates that the Millennium Eruption emitted up to 45 Tg of sulfur into the atmosphere—more than in the Tambora eruption in 1815 CE, which caused "a year without a summer" across the Northern Hemisphere in 1816 CE. Despite such massive emissions, evidence for this eruption's climate impact in East Asia remains elusive. To explain this contradiction, this study used 67 high‐resolution tree‐ring‐width records from the Northern Hemisphere spanning the past two millennia, complemented by volcanic sensitivity experiments conducted with the Community Earth System Model. Results reveal a prevailing decreasing/negative trend in the proxy records during the potential eruption period, with 945 CE marking the most notable negative anomaly, suggesting that the Millennium Eruption likely occurred in 945 CE rather than 946 CE. Sensitivity experiments, corroborated by proxy records, demonstrate that the Millennium Eruption induced substantial negative temperature anomalies at middle and high latitudes, alongside an increase in Meiyu‐Baiu‐Changma precipitation in the middle and lower reaches of the Yangtze River and southwestern Japan and a decrease in precipitation in India, northern China, and the South China Sea in the first post‐eruption year. This study offers a novel perspective on the climate impact of the Millennium Eruption, reconciling previous discrepancies regarding its climate impact. Plain Language Summary: About a thousand years ago, the Changbaishan volcano erupted with incredible force, ranking as one of the largest historical eruptions in the past 2000 yrs. Despite its size, evidence for this eruption's climate impact in East Asia has remained elusive. We delved into this mystery by examining detailed high‐resolution proxy records and performing climate model simulations. Our findings suggest that the climate effects of the eruption may have been unexpectedly strong, with the Millennium Eruption potentially occurring in 945 CE that is earlier than previously thought. The Millennium Eruption triggered notable cooling at middle and high latitudes, increased Meiyu‐Baiu‐Changma precipitation in the middle and lower reaches of the Yangtze River and southwestern Japan, and reduced precipitation in India, northern China, and the South China Sea. This research helps us understand how large volcanic eruptions can interact with other natural factors to influence our climate. Key Points: Sulfur emissions of the Millennium Eruption estimated from a petrogeochemical method are inconsistent with the signal from ice‐core samplesA consistent negative response in the high‐resolution paleoclimate records suggests a significant climate impact of the Millennium EruptionThe eruption enhanced the Meiyu‐Baiu‐Changma precipitation while diminishing precipitation in India, northern China, and the South China Sea [ABSTRACT FROM AUTHOR]

The oxygen isotope (δ18O) records of paleo‐precipitation contain abundant information on past climate changes. Nevertheless, at the orbital scale, our current understanding about the characteristics and mechanisms of precipitation oxygen isotope (δ18Op) variations in the Northern Hemisphere (NH) mid‐latitudes remains limited due to the lack of abundant long‐term geological records. In this study, based on a 300‐ka transient simulation involving stable isotope fractionation processes, we systematically analyzed the characteristics of the orbital‐scale δ18Op variations and their potential mechanisms, especially in two representative regions: mid‐latitude East Asia (MEA) and mid‐latitude North America (MNA) located in the Eastern and Western Hemispheres respectively. Our findings reveal that the MEA δ18Op is dominated by a 23‐ka cycle, ultimately driven by the precession‐induced insolation variation; while the MNA δ18Op primarily exhibits a 100‐ka glacial‐interglacial cycle and is eventually governed by the ice volume forcing. The δ18Op changes in these two regions not only present diverse dominant cycles and forcing factors, but also involve distinct physical processes. In MEA, water vapor transport by the westerly circulation during the rainy season (May–August) is the key process linking the April–July boreal insolation with the annual/rainy‐season δ18Op variations. In contrast, the annual δ18Op changes in MNA mainly depend on the water vapor transport processes triggered by the expansion and retreat of the North American ice sheet, albeit with certain influence of the temperature effect as well. These results suggest that the dominant periodicities and forcing mechanisms of the orbital‐scale δ18Op variations across the NH mid‐latitudes are complex and varied. Plain Language Summary: The changes in precipitation δ18O (δ18Op) can indicate the evolution history of Earth's climate. However, previous studies have paid less attention to the mid‐latitude regions and the mechanisms of climate evolution at the orbital scale in this region are not fully understood. Based on the output of an isotope‐enabled climate model, we examined the variation characteristics of δ18Op among different lands in the Northern Hemisphere mid‐latitudes. We found that on the orbital scale, the δ18Op variations in mid‐latitude East Asia have a dominant period of 23‐ka, and are controlled by the April–July insolation that alters the atmospheric circulation. In contrast, the δ18Op variations in mid‐latitude North America are governed by a 100‐ka cycle and are influenced by the Northern American ice sheet. This linkage is accomplished through different circulation processes and temperature changes arising from the expansion and retreat of the North American ice sheet. Key Points: The orbital‐scale variations in precipitation δ18O (δ18Op) have significant regional differencesThe 23‐ka cycle‐dominated annual δ18Op variation in mid‐latitude East Asia is driven by precession‐controlled boreal April–July insolationThe 100‐ka cycle‐dominated annual δ18Op variation in mid‐latitude North America is controlled by North American ice sheet volume fluctuation [ABSTRACT FROM AUTHOR]

Obvious biases in simulating tropical cyclone (TC) genesis of the current climate models hamper our understanding of TC changes. In this study, we found a delay of the seasonal cycle of TC genesis frequency over the western North Pacific (WNP) in most Coupled Model Intercomparison Project Phase 6 models. During the active TC season, the simulated south‐warming and north‐cooling surface temperature bias amplifies the meridional gradient and excites thermal winds. This weakens the western North Pacific Subtropical High and easterly monsoon trough, which further reduces TC genesis frequency over the western WNP in summer. But in autumn, positive TC genesis biases were only observed in coupled models over the eastern WNP. Both seasons contribute to the delayed seasonal cycle of TC frequency in models. Our findings highlight the importance of accurate simulation of surface temperature by climate models to TC simulations and aid in future model improvements. Plain Language Summary: Tropical cyclone (TC) is a devastating weather system generated over the tropical ocean, and the climate model serves as an important tool to study the long‐term variability of TC activity. Hence, it is imperative to explore the biases of climate models in simulating TC genesis. In this investigation, we find a substantial influence of surface temperature bias in Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models on the simulation of the seasonal cycle of TC genesis frequency over the western North Pacific (WNP). The delay in the seasonal cycle of TC genesis frequency is widespread among most CMIP6 models. During boreal summer and autumn, the simulated bias of south‐warming and north‐cooling surface temperature increases its meridional gradient and triggers thermal winds. In summer, the weak western North Pacific Subtropical High and easterly monsoon trough, two crucial large‐scale circulation systems, cause a large negative TC genesis bias in models over the western WNP, substantially contributing to the delay of the seasonal cycle. Meanwhile, the relatively small positive bias of coupled models over the eastern WNP in autumn makes a secondary contribution. The combined contributions of these biases cause delays in seasonal simulation of TC genesis frequency. Key Points: Coupled Model Intercomparison Project Phase 6 models produce delayed seasonal cycles of tropical cyclone genesis frequency over the western North PacificBiases in East Asia summer monsoon and western North Pacific subtropical high lead to underestimation of tropical cyclone genesis during summerThe biased large‐scale circulation systems are further related to a warm southern and cold northern surface temperature bias [ABSTRACT FROM AUTHOR]

Deciphering how modern precipitation patterns became established in monsoon‐dominated East Asia and the arid interior Asia is crucial for predicting future precipitation trends under accelerated global warming and increased climate extremes. However, this effort is hindered by a scarcity of quantitative paleo‐precipitation data in this region. Here we reconstruct the pattern of Middle to Late Miocene paleo‐precipitation across an east‐to‐west transect from the summer monsoon‐dominated East Asian region through the transition zone and into interior Asia. Our work is based on a newly established precipitation calculation equation and quantitative pollen‐based precipitation conversion. Analysis indicates a common trend of precipitation across the studied region prior to ca, 11 Ma, followed by a clear divergence of precipitation variations between East and interior Asia since at least 11–9 Ma. This divergence is characterized by increasing precipitation in East Asia, but a coeval decrease in rainfall in the transition zone and interior Asia. The timing of this precipitation divergence was contemporaneous with intense tectonic activity in the northern Tibetan Plateau, which differentially affected the efficacy of water vapor transport into East and interior Asia. Modeling work using different topographic settings corroborates this tectonic influence. Our study demonstrates the early establishment of modern‐like precipitation patterns in East‐interior Asia at least in the early Late Miocene. Plain Language Summary: The present Asian climate consists of a monsoon‐dominated East Asia, and arid interior Asia. Increasing catastrophic flooding and storm events in monsoon region and an increasing dust storm events within interior Asia in recent years indicate an accelerated divergence in the climate conditions of these two regions. As such, deciphering how modern precipitation patterns became established in East‐interior Asia is crucial for understanding their future climate trends and mitigating possible damaging consequences. Here we developed a quantitative proxy for paleo‐precipitation and reconstruct the Middle to Late Miocene paleo‐precipitation pattern across an east‐to‐west transect from the summer‐monsoonal transition zone to interior Asia. We find that the modern precipitation pattern was established across East to interior Asia during ∼11–9 Ma, distinct with their parallel precipitation variations before this interval. We link the timing of this precipitation divergence to the contemporaneous extensive tectonism associated with the uplift of the northern Tibetan region. This speculation was further corroborated by our high resolution climate modeling. Our study demonstrates an early establishment of modern precipitation patterns in East‐interior Asia at least 9 Ma. Their further precipitation patterns may be subsequently enhanced by global warming events, thus providing corresponding implications for future climate trends in Asia. Key Points: Late Miocene quantitative precipitation reconstruction for different sites in AsiaA modern precipitation pattern between East and Interior Asia established at 11–9 MaIntense upgrowth‐eastward outgrowth of northern Tibetan Plateau is the driving force [ABSTRACT FROM AUTHOR]

We validate the multiyear potential predictability of wintertime heavy precipitation potential in East Asia by combining initialized decadal hindcasts of the global climate model and large ensemble simulations from a high‐resolution global atmospheric model. By analyzing a set of initialized hindcasts, the major predictive components of sea surface temperature (SST) variability beyond interannual timescales are identified as high‐latitudes multidecadal variability and the so‐called trans‐basin variability (TBV). A set of 100 ensemble simulations using a high‐resolution atmospheric model showed a significantly large signal‐to‐noise ratio for the wintertime heavy precipitation potential in East Asia, which is closely related to the TBV. When the SST around the maritime continent is higher, the anomalously low pressure in the northwestern Pacific enhances low‐level cold air transport due to the winter monsoon. Consequently, the resultant weaker baroclinicity in the lower atmosphere reduces storm activity and wintertime heavy precipitation potential in East Asia. Plain Language Summary: Statistical changes in extreme weather and climate events have attracted much attention as potential sources of natural disasters. Numerical experiments to obtain huge ensembles of multiyear predictions with initialization using a high‐resolution model represent a direct approach but a difficult solution for the computational resources available currently. Here, we validated the multiyear potential predictability of wintertime heavy precipitation potential in East Asia, by combining initialized decadal hindcasts of the global climate model and large ensemble simulations from a high‐resolution global atmospheric model. By analyzing a set of initialized hindcasts, we identified one of the major predictive components of sea surface temperature (SST) variability beyond interannual timescales as the so‐called trans‐basin variability (TBV). A set of 100 ensemble simulations using a high‐resolution atmospheric model show a significantly large signal‐to‐noise ratio for the wintertime heavy precipitation potential in East Asia, which is closely related to the TBV. When the SST around the maritime continent is higher, the anomalously low pressure in the northwestern Pacific enhances low‐level cold air transport due to the winter monsoon. Consequently, the resultant weaker baroclinicity in the lower atmosphere reduces storm activity and wintertime heavy precipitation potential in East Asia. Key Points: Multiyear potential predictability is validated for the storm activity and wintertime heavy precipitation potential in East AsiaWe combine initialized decadal hindcasts of global climate model with large ensembles of high‐resolution atmospheric simulationTrans‐basin variability as a predictive climate mode controls the precipitation potential through sea surface temperature changes around the maritime continent [ABSTRACT FROM AUTHOR]

Cold extremes have large impacts on human society. Understanding the physical processes dominating the changes in cold extremes is crucial for a reliable projection of future climate change. The observed cold extremes have decreased during the last several decades, and this trend will continue under future global warming. Here, we quantitatively identify the contributions of dynamic (changes in large-scale atmospheric circulation) and thermodynamic (rising temperatures resulting from global warming) effects to East Asian cold extremes in the past several decades and in a future warm climate by using two sets of large-ensemble simulations of climate models. We show that the dynamic component accounts for over 80 % of the cold-month (coldest 5 % boreal winter months) surface air temperature (SAT) anomaly over the past 5 decades. However, in a future warm climate, the thermodynamic change is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the dynamic change is also contributive. The intensity of East Asian cold extremes will decrease by around 5 °C at the end of the 21st century, in which the thermodynamic (dynamic) change contributes approximately 75 % (25 %). The present-day (1986–2005) East Asian cold extremes will almost never occur after around 2035, and this will happen 10 years later due solely to thermodynamic change. The upward trend of a positive Arctic Oscillation-like sea level pressure pattern dominates the changes in the dynamic component. The finding provides a useful reference for policymakers in climate change adaptation activities. [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]

This study analyzed systematic biases in surface air temperature (SAT) within Far East Asia during the boreal winter using the SNURCM and WRF regional climate models (RCMs) from the Coordinated Regional Downscaling Experiment (CORDEX)-East Asia phase II. The SAT biases were examined in relation to the East Asian winter monsoon (EAWM). The models consistently simulated lower winter temperatures over East Asia, particularly in the Manchuria (MC) region, compared to the observation, showing a positive correlation with the EAWM. This study assessed the models' ability to capture EAWM variability and revealed relationships between SAT biases and discrepancies in low-level and near-surface EAWM conditions. The findings emphasized the value of analyzing extreme monsoon years, with the RCMs exhibiting larger cold SAT biases during strong EAWM years. Systematic biases in sea-level pressure contrast and lower-level winds over the MC region were evident during years with a robust monsoon. The overestimation of low-level winds during strong EAWM years contributed to increased cold advection, affecting the MC region. These systematic errors are influenced by the internal factors of the model, such as the physics parameterization schemes, rather than large-scale circulation forced by the reanalysis data (perfect boundary condition). These results provide insights for model improvements, understanding EAWM dynamics, and call for investigation of processes in the planetary boundary layer and coupled air-sea interaction. [ABSTRACT FROM AUTHOR]

The wet bulb temperature (Tw) has gained considerable attention as a crucial indicator of heat-related health risks. Here we report south-to-north spatially heterogeneous trends of Tw in China over 1979-2018. We find that actual water vapor pressure (Ea) changes play a dominant role in determining the different trend of Tw in southern and northern China, which is attributed to the faster warming of high-latitude regions of East Asia as a response to climate change. This warming effect regulates large-scale atmospheric features and leads to extended impacts of the South Asia high (SAH) and the western Pacific subtropical high (WPSH) over southern China and to suppressed moisture transport. Attribution analysis using climate model simulations confirms these findings. We further find that the entire eastern China, that accommodates 94% of the country's population, is likely to experience widespread and uniform elevated thermal stress the end of this century. Our findings highlight the necessity for development of adaptation measures in eastern China to avoid adverse impacts of heat stress, suggesting similar implications for other regions as well. Attributing spatially heterogeneous heat stress trends to water vapor pressure changes driven by climate change-induced rapid warming in high-latitudes of East Asia, the authors predict widespread and uniform future heat stress in eastern China. [ABSTRACT FROM AUTHOR]

The impacts of Arctic sea ice on climate in middle and high latitudes have been extensively studied. However, its effects on climate in low latitudes, particularly on summer monsoon rainfall in the South China Sea (SCS), have received limited attention. Thus, this study investigates the connection between the Arctic sea ice concentration (SIC) anomaly and the early summer monsoon rainfall (ESMR) in the SCS and its underlying physical mechanism. The results reveal a significant positive correlation between the Barents Sea (BS) SIC in May and the ESMR in the SCS. When there is more (less) SIC in the Barents Sea (BS) during May, this results in a positive (negative) anomaly of the local turbulent heat flux, which lasts until June. This, in turn, excites an upward (downward) air motion anomaly in the vicinity of the BS, causing a corresponding downward (upward) motion anomaly over the Black Sea. Consequently, this triggers a wave train similar to the Eurasian (SEU) teleconnection, propagating eastward towards East Asia. The SEU further leads to an (a) upward (downward) motion anomaly and weakens (strengthens) the western Pacific subtropical high (WPSH) over the SCS, which is accompanied by a southwest adequate (scarce) water vapor anomaly transporting from the Indian Ocean, resulting in more (less) precipitation in the SCS. Furthermore, the response of ESMR in the SCS to the SIC in the BS is further verified by using the Community Atmosphere Model version 5.3 (CAM5.3). This study introduces novel precursor factors that influence the South China Sea summer monsoon (SCSSM), presenting a new insight for climate prediction in this region, which holds significant implications. [ABSTRACT FROM AUTHOR]

Drought risk threatens pastoralism in rangelands, which are already under strain from climatic and socioeconomic changes. We examine the future drought risk (2031–2060 and 2071–2100) to rangeland productivity across Eurasia (West, Central, and East Asia) using a well-tested process-based ecosystem model and projections of five climate models under three shared socioeconomic pathway (SSP) scenarios of low (SSP1−2.6), medium (SSP3−7.0), and high (SSP5−8.5) warming relative to 1985–2014. We employ a probabilistic approach, with risk defined as the expected productivity loss induced by the probability of hazardous droughts (determined by a precipitation-based index) and vulnerability (the response of rangeland productivity to hazardous droughts). Drought risk and vulnerability are projected to increase in magnitude and area across Eurasian rangelands, with greater increases in 2071–2100 under the medium and high warming scenarios than in 2031–2060. Increasing risk in West Asia is caused by longer and more intense droughts and vulnerability, whereas higher risk in Central and East Asia is mainly associated with increased vulnerability, indicating overall risk is higher where vulnerability increases. These findings suggest that future droughts may exacerbate livestock feed shortages and negatively impact pastoralism. The results have practical implications for rangeland management that should be adapted to the ecological and socioeconomic contexts of the different countries in the region. Existing traditional ecological knowledge can be promoted to adapt to drought risk and embedded in a wider set of adaptation measures involving management improvements, social transformations, capacity building, and policy reforms addressing multiple stakeholders. [ABSTRACT FROM AUTHOR]

Long-term ozone (O3) changes in the middle to upper troposphere are critical to climate radiative forcing and tropospheric O3 pollution. Yet, these changes remain poorly quantified through observations in East Asia. Concerns also persist regarding the data quality of the ozonesondes available at the World Ozone and Ultraviolet Data Center (WOUDC) for this region. This study aims to address these gaps by analyzing O3 soundings at four sites along the northwestern Pacific coastal region over the past three decades, and assessing their consistency with an atmospheric chemistry-climate model simulation. Utilizing the European Centre for Medium-Range Weather Forecasts (ECMWF) – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) nudged simulations, it is demonstrated that trends between model and ozonesonde measurements are overall consistent, thereby gaining confidence in the model's ability to simulate ozone trends and confirming the utility of potentially imperfect observational data. A notable increase in O3 mixing ratio around 0.29–0.82 ppb a-1 extending from the middle to upper troposphere is observed in both observations and model simulations between 1990 and 2020, primarily during spring and summer. The timing of these O3 hotspots is delayed when moving from south to north along the measurement sites, transitioning from late spring to summer. Investigation into the drivers of these trends using tagged model tracers reveals that ozone of stratospheric origin (O3S) dominates the absolute O3 mixing ratios over the middle-to-upper troposphere in the subtropics, contributing to the observed O3 increases by up to 96 % (40 %) during winter (summer), whereas ozone of tropospheric origin (O3T) governs the absolute value throughout the tropical troposphere and contributes generally much more than 60 % to the positive O3 changes, especially during summer and autumn. During winter and spring, a decrease of O3S is partly counterbalanced by an increase of O3T in the tropical troposphere. This study highlights that the enhanced downward transport of stratospheric O3 into the troposphere in the subtropics and a surge of tropospheric source O3 in the tropics are the two key factors driving the enhancement of O3 in the middle-upper troposphere along the Northwest Pacific region. [ABSTRACT FROM AUTHOR]

The synoptic cold surge is a weather event that frequently occurs in the Northern Hemisphere, often causing severe damage accompanied with intense winds and precipitation. It is reported that the Arctic Oscillation and the North Atlantic Oscillation can affect the cold surge. However, on interacting with tropical circulation, the cold surge potentially links to the Antarctic sea‐ice loss with influence extending to Tropics. Therefore, this research aims to investigate the potential link between Antarctic sea‐ice loss and Northern Hemisphere cold surges and corresponding wind–precipitation compound events. To study this link, twin numerical experiments using a physically based atmosphere model with a prescribed 30% Antarctic sea‐ice loss scenario were used. The results show that the cold surge occurs more frequently in most regions of the world, except for central North America and central Eurasia. In Europe, the cold surges occur closer to the lower latitudes in the Antarctic sea‐ice loss scenario. Additionally, the Antarctic sea‐ice loss can result in intensified wind and precipitation extremes within compound events. The intensified precipitation extremes are caused by increased moisture transportation by tropical easterlies and higher local temperature after the cold surge occurrence, providing more moisture available for precipitation in East Asia and East North America, respectively. Overall, the results of the numerical experiments provide evidence that Antarctic sea‐ice loss influences cold surges in Northern Hemisphere through atmospheric teleconnections. It is important to continue investigating the link between Antarctic sea‐ice loss and weather events like cold surges, as this research can help improve our understanding of the impacts of polar climate change on lower latitudes. [ABSTRACT FROM AUTHOR]

The performance of the Meteorological Research Institute-Atmospheric General Circulation model version 3.2 (MRI-AGCM3.2) in simulating precipitation is compared with that of global atmospheric models registered to the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The Atmospheric Model Intercomparison Project (AMIP) experiments simulated by 36 Atmospheric General Circulation Model (AGCM)s and the High Resolution Model Intercomparison Project (HighResMIP) highresSST-present experiments simulated by 23 AGCMs were analyzed. Simulations by MRI-AGCM3.2S (20-km grid size) and MRI-AGCM3.2H (60-km grid size) are included as a part of the HighResMIP highresSST-present experiments. MRI-AGCM3.2S has the highest horizontal resolution of all 59 AGCMs. As for the global distribution of seasonal and annual average precipitation, monthly precipitation over East Asia, and the seasonal march of rainy zone over Japan, MRI-AGCM3.2 models perform better than or equal to CMIP6 AMIP AGCMs and HighResMIP AGCMs. HighResMIP AGCMs (average grid size 78 km) perform better than CMIP6 AMIP AGCMs (180 km) in simulating seasonal and annual precipitation over the globe, and summer (June to August) precipitation over East Asia. MRI-AGCM3.2 models perform better than or equal to CMIP6 AMIP AGCMs and HighResMIP AGCMs in simulating extreme precipitation events over the globe. Correlation analysis between grid size and model performance using all 59 models revealed that higher horizontal resolution models are better than lower resolution models in simulating the global distribution of seasonal and annual precipitation and the global distribution of intense precipitation, and the local distribution of summer precipitation over East Asia. [ABSTRACT FROM AUTHOR]

The quantitative assessment of the uncertainty components of future climate projections is critical for decision-makers and organizations to establish climate change adaptation and mitigation strategies at regional or local scales. This is the first study in which the changes in the uncertainty components of future temperature and precipitation projections are quantitatively evaluated using multiple regional climate models over East Asia, vulnerable to future climate change. For temperature, internal variability and model uncertainty were the main factors affecting the near-term projections. The scenario uncertainty continued to increase and was estimated to be the dominant factor affecting the uncertainty after the mid-term projections. Although precipitation has the same main uncertainty factors as the temperature in the near-term projections, it considerably differs from temperature because the internal variability notably contributes to the fraction to the total variance, even in the long-term projections. The internal variability of the temperature and precipitation in the near-term projections were predicted to be larger in Korea than that in East Asia. This was confirmed by regional climate models as well as previous studies using global climate models as to the importance of internal variability at smaller regional scales during the near-term projections. This study is meaningful because it provides new possibilities with respect to the consideration of climate uncertainties to the establishment of climate change policies in more detail on the regional scale. [ABSTRACT FROM AUTHOR]

Anthropogenic aerosols (AA) induce pronounced East Asian summer monsoon (EASM) changes since the industrial revolution. However, the regional contribution from different AA emission sources is hard to quantify due to AA's heterogeneous spatial distribution and the nonmonotonic trend at decadal time scale. Using coupled climate models from Coupled Model Intercomparison Project Phase 6 (CMIP6) and Community Earth System Model 1 (CESM1) large ensemble simulations, we investigate EASM responses between 1950–1980 and 1980–2010, to understand how the remote influence of changes in the AA emissions from Europe modulates the EASM at decadal time scale. AA emissions from Europe increased early in the latter half of the twentieth century and then decreased rapidly after the 1980s. During 1950–1980, the increase of AA emissions from Europe, together with the localized increase of AA emissions from East Asia, weakens the EASM by generating the tropospheric cooling and shifting the East Asian subtropical jet equatorward. However, during 1980–2010, the declined AA emissions from Europe generate the tropospheric warming and induce an atmospheric teleconnection pattern that initiate at the heating anomaly and propagate downstream to northeast Asia following the westerly jet, leading to an enhanced EASM. This enhancement due to the remote influence of declined AA emissions from Europe explains why after the 1980s, despite the localized increase of AA emissions from East Asia, coupled climate models results show that the EASM is intensified by the anomalous southerlies and the precipitation increase in Northeast Asia. Our results imply that at the long-term change view, the local AA emissions dominate the EASM response, while the non-local European AA emissions play a more important role in shaping the decadal EASM changes. [ABSTRACT FROM AUTHOR]

The concentration of carbonaceous aerosols, black carbon (BC) and organic aerosol (OA), in the atmosphere is related to co-emitted or co-produced trace gases. In this study, we investigate the most relevant proportional relationships between both BC and OA with the following trace gases: carbon monoxide (CO), formaldehyde (HCHO), nitrogen dioxide (NO2), ozone (O3), and sulfur dioxide (SO2). One motivation for selecting these trace gases is that they can be observed using remote sensing measurements from satellite instrumentation, and could therefore be used to predict spatial changes in the amounts of BC and OA. Airborne measurements are optimal for the analysis of both the composition of aerosols and trace gases in different environments ranging from unpolluted oceanic air masses to those in heavily polluted city plumes. The two aircraft campaigns of the EMeRGe (Effect of Megacities on the Transport and Transformation of Pollutants on the Regional to Global Scales) project have created a unique database, with flight plans dedicated to studying city plumes in two regions, Europe (2017) and East Asia (2018), along with identical instrumental payload. Using linear regression analysis, three relevant relationships between carbonaceous aerosol and trace gases are identified: - The BC/OA ratio observed in the Asian campaign is three times higher (≈ 0.3) than in the European campaign (≈ 0.1), whereas the Pearson correlation coefficient (R) between BC and OA is much higher in Europe (R ≈ 0.8) than in Asia (R ≈ 0.6). - The CO/BC ratio is also observed higher in the Asian campaign (≈ 240) than in the European campaign (≈ 170), whereas the R-value between CO and BC is similar for both campaigns (R ≈ 0.7). - The HCHO/OA ratio is similar in both campaigns (≈0.32), but the observed R-values between HCHO and OA is higher in Europe than in the Asia (R ≈ 0.7 compared to ≈ 0.3). By focusing on heavily polluted air masses sampled downwind in the city plumes, the ratios between the observed carbonaceous aerosols and the five trace gases change, and the R-values increase with O3 for both BC and OA (R ≈ 0.5). To assess the performance of atmospheric models with respect to the most relevant observed relationships, an air quality model ensemble is used to represent the current state of atmospheric modeling, consisting of two global and two regional simulations. The evaluation shows that these proportional relationships are not satisfactorily reproduced by the model ensemble. The relationships between BC and OA or between CO and BC are modeled with stronger correlations than the observed ones, and their higher ratios observed in Asia compared to Europe are not reproduced. Furthermore, the modeled HCHO/OA ratio is underestimated in the Asian campaign and overestimated in the European campaign. This analysis of the proportional relationships between carbonaceous aerosols and trace gases implies that the observed relationships can be used to constrain models and improve anthropogenic emission inventories. In addition, it implies that information about the lower tropospheric concentration of carbonaceous aerosols can potentially be inferred from satellite retrievals of trace gases, particularly in the plumes from megacities. [ABSTRACT FROM AUTHOR]

Organic aerosols from marine sources over the western Pacific Ocean of East Asia were investigated using an online coupled regional chemistry–climate model RIEMS-Chem for the entire year 2014. Model evaluation against a wide variety of observations from research cruises and in situ measurements demonstrated a good skill of the model in simulating temporal variation and spatial distribution of particulate matter with aerodynamic diameter less than 2.5 and 10 µm (PM 2.5 and PM 10), black carbon (BC), organic carbon (OC), sodium, and aerosol optical depth (AOD) in the marine atmosphere. The inclusion of marine organic aerosols improved model performance on OC concentration by reducing model biases of up to 20 %. The regional and annual mean near-surface marine organic aerosol (MOA) concentration was estimated to be 0.27 µgm-3 , with the maximum in spring and the minimum in winter, and contributed 26 % of the total organic aerosol concentration on average over the western Pacific. Marine primary organic aerosol (MPOA) accounted for the majority of marine organic aerosol (MOA) mass, and the MPOA concentration exhibited the maximum in autumn and the minimum in summer, whereas marine secondary organic aerosol (MSOA) was approximately 1–2 orders of magnitude lower than MPOA, having a distinct summer maximum and a winter minimum. MOA induced a direct radiative effect (DRE MOA) of - 0.27 Wm-2 and an indirect radiative effect (IRE MOA) of - 0.66 Wm-2 at the top of the atmosphere (TOA) in terms of annual and oceanic average over the western Pacific, with the highest seasonal mean IRE MOA up to - 0.94 Wm-2 in spring. IRE MOA was stronger than, but in a similar magnitude to, the IRE due to sea salt aerosol on average, and it was approximately 9 % of the IRE due to anthropogenic aerosols in terms of annual mean over the western Pacific. This ratio increased to 19 % in the northern parts of the western Pacific in autumn. This study reveals an important role of MOA in perturbing cloud properties and shortwave radiation fluxes in the western Pacific of East Asia. [ABSTRACT FROM AUTHOR]

The Taklimakan Desert is one of key climate regions in East Asia, both highly influencing and highly sensitive to local/regional climate change. Based on a comprehensive observation experiment from 1 to 31 May 2022 in the hinterland of the Taklimakan Desert, the characteristics and mechanisms of turbulence intermittency are investigated in this study, with the purpose to correct turbulent fluxes. Using an improved algorithm to decompose turbulence and submeso motions, two intermittency regimes are recognized in the Taklimakan Desert, namely, D and T intermittency and onD intermittency. The former occurs under strongly stable conditions, characterized by the coexistence of dynamic and thermodynamic turbulence intermittency. The latter occurs under strongly unstable conditions and represents only dynamic turbulence intermittency. Physically, the D and T intermittency regime is related to submeso waves, whereas the onD regime is caused by the horizontal convergence/divergence of convective circulations. With the influence of intermittency and submeso motions, the observed turbulent statistics deviate from reality, which would mask the similarity relationships. To overcome the problem, turbulent statistics are corrected by removing submeso components from original fluctuations. The effectiveness of this method is demonstrated based on the flux–gradient relationships. It is also suggested that, for a big dataset, the impact of onD intermittency can be simply corrected by a correction factor while that of D and T intermittency cannot. The results of this study are helpful to develop the parameterization of turbulent exchange processes in the Taklimakan Desert, which is significant to improve the accuracy of weather forecasting and climate prediction. Significance Statement: The Taklimakan Desert plays an important role in the evolution of weather and climate in East Asia. With strong surface thermal forcing, turbulence often shows distinctive intermittency, which largely constrains the evaluation of land–atmosphere exchange in this key climate region. This study aims to understand the characteristics of turbulence intermittency and its physical mechanisms, and further to correct the influence of turbulence intermittency on turbulent fluxes in the Taklimakan Desert. This is significant because the results are helpful to improve the parameterization of subgrid processes in the key climate region for atmospheric models, which points the way toward enhancing the accuracy of weather forecasting and climate prediction. [ABSTRACT FROM AUTHOR]

This study explores the differences in performance and results by various versions of the ISORROPIA thermodynamic module implemented within the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. Three different versions of the module were used, ISORROPIA II v1, ISORROPIA II v2.3, and ISORROPIA-lite. First, ISORROPIA II v2.3 replaced ISORROPIA II v1 in EMAC to improve pH predictions close to neutral conditions. The newly developed ISORROPIA-lite has been added to EMAC alongside ISORROPIA II v2.3. ISORROPIA-lite is more computationally efficient and assumes that atmospheric aerosols exist always as supersaturated aqueous (metastable) solutions, while ISORROPIA II includes the option to allow for the formation of solid salts at low RH conditions (stable state). The predictions of EMAC by employing all three aerosol thermodynamic models were compared to each other and evaluated against surface measurements from three regional observational networks in the polluted Northern Hemisphere (Interagency Monitoring of Protected Visual Environments (IMPROVE), European Monitoring and Evaluation Programme (EMEP), and Acid Deposition Monitoring Network of East Asia (EANET)). The differences between ISORROPIA II v2.3 and ISORROPIA-lite were minimal in all comparisons with the normalized mean absolute difference for the concentrations of all major aerosol components being less than 11 % even when different phase state assumptions were used. The most notable differences were lower aerosol concentrations predicted by ISORROPIA-lite in regions with relative humidity in the range of 20 % to 60 % compared to the predictions of ISORROPIA II v2.3 in stable mode. The comparison against observations yielded satisfactory agreement especially over the USA and Europe but higher deviations over East Asia, where the overprediction of EMAC for nitrate was as high as 4 µ g m -3 (∼20%). The mean annual aerosol pH predicted by ISORROPIA-lite was on average less than a unit lower than ISORROPIA II v2.3 in stable mode, mainly for coarse-mode aerosols over the Middle East. The use of ISORROPIA-lite accelerated EMAC by nearly 5 % compared to the use of ISORROPIA II v2.3 even if the aerosol thermodynamic calculations consume a relatively small fraction of the EMAC computational time. ISORROPIA-lite can therefore be a reliable and computationally efficient alternative to the previous thermodynamic module in EMAC. [ABSTRACT FROM AUTHOR]

Based on outputs of 28 coupled models from the Phase 6 of the Coupled Model Intercomparison Project (CMIP6), we show that the response of the Southeast Asian summer monsoon to the El Niño‐Southern Oscillation (ENSO) during post‐ENSO summer will likely strengthen in a warmer climate, which can be attributed to concurrently weakened sea‐surface temperature anomalies (SSTAs) in the western equatorial Pacific (WEP). The weakened WEP SSTAs are primarily caused by enhanced latent heat damping due to increased surface wind speed anomalies, which are associated with the eastward shift of the El Niño‐induced anomalous Walker circulation due to El Niño‐like sea surface temperature change in the tropical Pacific under global warming. Besides, the climatological zonal ocean currents will slow down due to the weakening of climatological Walker circulation, which also acts to weaken the WEP SSTAs via reducing the advection of anomalous temperature by the mean current. Plain Language Summary: As an important component of the Asian monsoon system, the Southeast Asian summer monsoon (SEASM) is crucial for the livelihoods of billions of people in East Asia, and is closely connected to a climate phenomenon called El Niño‐Southern Oscillation (ENSO). Understanding how the relationship between SEASM and ENSO will change in the future is important for enhancing our knowledge of climate change in East Asia. Outputs of 28 climate models from the Phase 6 of the Coupled Model Intercomparison Project show that ENSO will exert enhanced impacts on the SEASM in a warmer climate. The enhanced influences of ENSO on the monsoon will exacerbate the reduction of rainfall over the western North Pacific during the post‐El Niño summer. We find that such projected changes are mainly caused by weakened warm sea surface temperature (SST) anomalies (SSTAs) in the western equatorial Pacific (WEP). Further analyses indicate that the change in WEP SSTAs can be linked to the El Niño‐like change in climatological SSTs in the tropical Pacific. This study depicts detailed physical processes responsible for the projected changes in ENSO's impacts on the SEASM. Key Points: The effects of the El Niño‐Southern Oscillation on the Southeast Asian summer monsoon will strengthen under global warmingThe enhanced El Niño's impacts result from the weakened warm sea‐surface temperature (SST) anomalies in the western equatorial Pacific (WEP)The weakened WEP SST anomalies are related to the eastward shift of anomalous Walker circulation and the slackened mean zonal ocean currents [ABSTRACT FROM AUTHOR]

Utilizing the Open Integrated Forecasting System, the responses of Ural blocking (UB) to different stratospheric warming scenarios are investigated. Numerical results show that stratospheric warming with moderate strength in minor patterns prolongs the UB duration and enhances its intensity, while strong stratospheric warming in minor patterns tends to shorten its duration and weaken its intensity, even leading to the collapse of the UB events. Further diagnosis reveals that the planetary wave activity flux propagates downward from the stratosphere to the troposphere after stratospheric warming. Moreover, the convergence of planetary wave activity flux is a key factor for UB enhancement and maintenance. In addition, the weakened meridional temperature gradients, decelerated zonal westerly winds, and a reduced meridional potential vorticity gradient (PVy) result in UB enhancement in response to stratospheric warming with moderate strength. As stratospheric warming strengthens, planetary wave activity flux diverges, westerly winds in the tropospheric mid‐latitudes accelerate and the PVy in the Ural sector enlarges, which further weakens UB. Regarding the stratospheric perturbations in major patterns, they have similar influences on UB events, that is, UB enhances with moderate stratospheric warming and weakens with strong warming. However, the strengthened warming would trigger UB re‐enhancement, which is closely associated with anomalous activities of tropospheric synoptic‐scale waves induced by stratospheric perturbations. These results reveal UB events respond differently to stratospheric warming with various intensities and patterns in the short term, which makes a contribution to understanding stratosphere‐troposphere coupling. Plain Language Summary: Tropospheric Ural blocking (UB) is an important factor in modulating the weather and climate in East Asia, while stratospheric warming in the Arctic has great influences on UB in winter. Therefore, the influence of stratospheric warming on UB events is investigated with a complicated atmospheric model. We find that the anomalous energy from stratospheric warming propagates downward to the troposphere within 15 days, which in turn affects the UB events. Moderate stratospheric warmings can decelerate the mid‐latitude westerly winds, leading to enhanced UB. As the stratospheric warming strengthens, the UB weakens or even collapses due to the accelerated mid‐latitude westerly winds. These findings reveal the impact of stratospheric warming on UB events in the short term and contribute to a better understanding of the relationship between the stratosphere and the troposphere. Key Points: Stratospheric warming has notable effects on Ural blocking (UB) events within 15 daysThe moderate stratospheric warmings both in minor and major patterns enhance UB eventsStrengthened warming in major patterns would trigger UB re‐enhancement [ABSTRACT FROM AUTHOR]

Cold extremes have large impacts on human society. Understanding the physical processes dominating the changes of cold extremes is crucial for a reliable projection of future climate change. The observed cold extremes have been decreased during last several decades and this trend will continue under the future global warming. Here, we quantitatively identify the contributions of dynamic (changes in large-scale atmospheric circulation) and thermodynamic (rising temperatures resulting from global warming) effects to East Asian cold extremes in the past several decades and in a future warm climate by using two sets of large ensemble simulation of climate models. We show that the dynamic component accounts for over 80 % of the cold-month (coldest 5 % boreal winter months) surface air temperature (SAT) anomaly in the past five decades. However, in a future warm climate, the thermodynamic change is the main contributor to the decreases in the intensity and occurrence probability of East Asian cold extremes, while the dynamic change is also contributive. The intensity of East Asian cold extremes will decrease by around 5℃ at the end of the 21st century, in which the thermodynamic (dynamic) change contributes approximately 75 % (25 %). The present-day (1986–2005) East Asian cold extremes will almost never occur after around 2035, and this will happen eight years later due solely to thermodynamic change. The upward trend of a positive Arctic Oscillation-like sea level pressure pattern dominates the changes in the dynamic component. The finding provides a useful reference for policymakers in climate change adaptation activities. [ABSTRACT FROM AUTHOR]

Utilizing the Community Atmosphere Model, version 4, the influence of Arctic sea-ice concentration (SIC) on the extended-range prediction of three simulated cold events (CEs) in East Asia is investigated. Numerical results show that the Arctic SIC is crucial for the extended-range prediction of CEs in East Asia. The conditional nonlinear optimal perturbation approach is adopted to identify the optimal Arctic SIC perturbations with the largest influence on CE prediction on the extended-range time scale. It shows that the optimal SIC perturbations are more inclined to weaken the CEs and cause large prediction errors in the fourth pentad, as compared with random SIC perturbations under the same constraint. Further diagnosis reveals that the optimal SIC perturbations first modulate the local temperature through the diabatic process, and then influence the remote temperature by horizontal advection and vertical convection terms. Consequently, the optimal SIC perturbations trigger a warming center in East Asia through the propagation of Rossby wave trains, leading to the largest prediction uncertainty of the CEs in the fourth pentad. These results may provide scientific support for targeted observation of Arctic SIC to improve the extended-range CE prediction skill. [ABSTRACT FROM AUTHOR]

The cosmogenic radionuclides 7 Be and 10 Be are useful tracers for atmospheric transport studies. Combining 7 Be and 10 Be measurements with an atmospheric transport model can not only improve our understanding of the radionuclide transport and deposition processes but also provide an evaluation of the transport process in the model. To simulate these aerosol tracers, it is critical to evaluate the influence of radionuclide production uncertainties on simulations. Here we use the GEOS-Chem chemical transport model driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis to simulate 7 Be and 10 Be with the state-of-the-art production rate from the CRAC:Be (Cosmic Ray Atmospheric Cascade: Beryllium) model considering realistic spatial geomagnetic cutoff rigidities (denoted as P16spa). We also perform two sensitivity simulations: one with the default production rate in GEOS-Chem based on an empirical approach (denoted as LP67) and the other with the production rate from the CRAC:Be but considering only geomagnetic cutoff rigidities for a geocentric axial dipole (denoted as P16). The model results are comprehensively evaluated with a large number of measurements including surface air concentrations and deposition fluxes. The simulation with the P16spa production can reproduce the absolute values and temporal variability of 7 Be and 10 Be surface concentrations and deposition fluxes on annual and sub-annual scales, as well as the vertical profiles of air concentrations. The simulation with the LP67 production tends to overestimate the absolute values of 7 Be and 10 Be concentrations. The P16 simulation suggests less than 10 % differences compared to P16spa but a significant positive bias (∼18 %) in the 7 Be deposition fluxes over East Asia. We find that the deposition fluxes are more sensitive to the production in the troposphere and downward transport from the stratosphere. Independent of the production models, surface air concentrations and deposition fluxes from all simulations show similar seasonal variations, suggesting a dominant meteorological influence. The model can also reasonably simulate the stratosphere–troposphere exchange process of 7 Be and 10 Be by producing stratospheric contribution and 10Be/7Be ratio values that agree with measurements. Finally, we illustrate the importance of including the time-varying solar modulations in the production calculation, which significantly improve the agreement between model results and measurements, especially at mid-latitudes and high latitudes. Reduced uncertainties in the production rates, as demonstrated in this study, improve the utility of 7 Be and 10 Be as aerosol tracers for evaluating and testing transport and scavenging processes in global models. For future GEOS-Chem simulations of 7 Be and 10 Be, we recommend using the P16spa (versus default LP67) production rate. [ABSTRACT FROM AUTHOR]

In the study, we evaluate extreme precipitation of the East Asia regional reanalysis system (EARS‐CMA), ERA‐Interim and ERA5 applying Tropical Rainfall Measuring Mission 3B42V7 (TRMM), Climate Prediction Center Morphing Method satellite‐gauge blended product (CMORPH) and CN05.1 over land‐only East Asia in 2008–2017. The added value of EARS‐CMA is also calculated to identify the small‐scale processes at different timescales and spatial resolutions. Compared to TRMM, CMORPH has a better agreement with CN05.1 for the annual, summer and winter spatial pattern and amplitude of most extreme precipitation indices. EARS‐CMA is capable to reproduce amplitude and locations of most extreme precipitation indices for annual and summertime precipitation over China mainland against CN05.1. For land‐only East Asia, ERA5 can reproduce the closest spatial features of various extreme precipitation indices to CMORPH for annual, summer and winter precipitation, followed by EARS‐CMA. All reanalysis datasets show worse skill on the spatial characteristics of duration indicators than on other extreme precipitation indices against CN05.1, but perform better than TRMM and CMORPH. The real added value, potential added value and relative added value of EARS‐CMA show that EARS‐CMA can capture the mesoscale processes over south China, Yangtze River basin, Tibetan Plateau and Indo‐China efficiently, especially the daily and subseasonal timescales over the Tibetan Plateau subregion, which benefits from fine‐scale topographical detail over the complex terrain region in the regional climate model. Also, higher extreme precipitation of aggregating EARS‐CMA than ERA‐Interim can be obtained at the same resolution, which implies that the added value obtained with EARS‐CMA is not merely the contribution of a higher resolution, but also the physical processes resolved by the dynamical downscaling technique. [ABSTRACT FROM AUTHOR]

The variability of the summer North Pacific Subtropical High (NPSH) has substantial socioeconomic impacts. However, state‐of‐the‐art climate models significantly disagree on the response of the NPSH to anthropogenic warming. Inter‐model spread in NPSH projections originates from models' inconsistency in simulating tropical precipitation changes. This inconsistency in precipitation changes is partly due to inter‐model spread in tropical sea surface temperature (SST) changes, but it can also occur independently of uncertainty in SST changes. Here, we show that both types of precipitation uncertainty influence the NPSH via the Matsuno‐Gill wave response, but their relative impact varies by region. Through the modulation of low cloud fraction, inter‐model spread of the NPSH can have a further impact on extra‐tropical land surface temperature. The teleconnection between tropical precipitation and the NPSH is examined through a series of numerical experiments. Plain Language Summary: The North Pacific Subtropical High (NPSH) is a semi‐permanent high‐pressure system located in the subtropical North Pacific. The variability in the summer NPSH has a significant impact on the monsoon and typhoons over East Asia and the hydroclimate of California. However, future projections of the NPSH using state‐of‐the‐art climate models remain highly uncertain. By evaluating how much individual models deviate from the multi‐model mean at different locations, we find four hot spots of high uncertainty in NPSH projections. Our analysis further reveals that the primary source of model variance in changes in the NPSH is tropical precipitation, which can be attributed to both inter‐model SST‐driven and non‐inter‐model SST‐driven factors. Through numerical experiments, we demonstrate that the teleconnection between tropical precipitation and the NPSH is achieved through wave propagation. Key Points: Model spread in the response of the summer North Pacific Subtropical High (NPSH) to CO2 stems from model spread in simulating tropical processesModel spread in tropical sea surface temperature (SST) changes modulates the NPSH by influencing tropical precipitationModel spread in tropical precipitation changes independent of model spread in SST changes also adds to the uncertainty of the NPSH response [ABSTRACT FROM AUTHOR]

Studies have shown that regional climate models (RCMs) can simulate local climates at a higher resolution for specific regions compared to global climate models (GCMs), making dynamic downscaling using RCMs a more effective approach. Therefore, RCMs have become valuable tools for evaluating the potential impacts of climate change on specific regions and for informing local adaptation strategies. To fully understand the added value (AV) of RCMs, it is essential to understand how the characteristics differ between land and ocean. The complex topography of East Asia, including land and sea, makes it a suitable region for evaluating the AV of RCMs. In this study, we compared two regional simulations that integrated the same RCMs but employed different GCMs from the Coordinated Regional Climate Downscaling Experiment for their ability to simulate storm tracks in East Asia. The results of the RCMs for the period from 1982 to 2005 were compared with their host Coupled Model Intercomparison Project GCM projections and high‐resolution reanalysis. In mountainous regions, the AV of the RCMs weakened the bias of the GCM and improved its agreement with the reanalysis due to the dynamical process near the high‐resolution topography. In plains and coastal areas, owing to the increase in horizontal resolution and clearly determined coastline in RCMs, small‐scale phenomena are well represented, and the storm track of RCMs shows similar values to that of the GCM in maritime regions. This study demonstrates the value of RCMs for improving the accuracy of climate projections in East Asia, informing adaptation strategies, and enhancing climate research. Plain Language Summary: This study looked at how regional climate models can better simulate local climates in specific regions compared to global climate models. By analyzing storm tracks in East Asia, researchers compared regional climate models integrated with different global climate models to better understand the added value of regional climate models. The study found that the regional climate models improved the accuracy of global climate models over mountainous regions and brought them closer to high‐resolution reanalysis. In the plains and coastal areas, the regional climate models accurately represented small‐scale phenomena due to the increase in horizontal resolution. Overall, this study shows that regional climate models are valuable tools for evaluating climate change in specific regions and can provide more accurate predictions than global climate models alone. This research is essential for improving our understanding of how climate models work and can be used to better predict the future climate of different regions, which can help inform decision‐making about mitigating climate change. Key Points: Regional climate models improve accuracy of climate projections for East Asia by simulating local climates at higher resolution than global climate modelsRegional climate models effectively evaluate potential impacts of local climate variability on specific regions and inform local adaptation strategiesThe added value of regional climate models in improving global climate models' bias and agreement with high‐resolution reanalysis in mountainous regions is shown [ABSTRACT FROM AUTHOR]

Summer monsoon frontal rainfall in East Asia (EA) is crucial for water resources and flood hazards in densely populated areas. Recent studies have documented the increasing intensity of summer frontal rainfall over recent decades. However, the extent of ongoing climate change on the intensification of the EA frontal precipitation system remains uncertain. Using an objective method for detecting frontal systems, we found a 17 ± 3% increase in observed frontal rainfall intensity during 1958 to 2015. Climate model simulations with and without greenhouse gases suggest that anthropogenic warming plays a key role in the intensification of EA summer frontal precipitation by 5.8% from 1991 to 2015. The analysis highlights that enhanced water vapor convergence and reinforced western North Pacific subtropical High collectively increased moisture transport to the region, resulting in intensified EA frontal precipitation. The results lend support to the anthropogenic warming-induced enhancement of the EA frontal precipitation and its persistence in the future. [ABSTRACT FROM AUTHOR]

The East Asian winter monsoon (EAWM) is a crucial climate system in Asia, with significant social and economic impacts. Orbital‐scale variability of the EAWM during the Holocene and its associated mechanisms, however, are still not fully understood. Based on a high‐resolution transient simulation by a coupled climate model, we present here a continuous climate evolution of the EAWM in response to orbital forcing. Our simulated springtime EAWM variations, consistent with grain size records of loess, exhibit an obvious strengthening trend since the mid‐Holocene. In winter, a similar increasing trend is also simulated although not statistically significant. Our results suggest that the Holocene EAWM is basically controlled by meridional temperature gradients between high and low latitudes in both seasons. Other than northern insolation forcing, the feedbacks from Arctic sea ice and Eurasian snow cover also modulate the meridional temperature gradients, highlighting their important roles in driving EAWM evolution during the Holocene. Plain Language Summary: Understanding the past climate change in the East Asian winter monsoon (EAWM) is necessary for assessing future climate scenarios in Asia. However, our current knowledge about the Holocene EAWM changes and associated mechanisms, based on geological proxies and numerical simulations, remains controversial, impeding understanding of the climate factors driving future EAWM change. In our study, we conducted a high‐resolution transient simulation to investigate the evolution of EAWM. Our results reveal that the EAWM has been strengthening since the mid‐Holocene, as evidenced by grain size records of loess. The EAWM during the Holocene is primarily influenced by meridional temperature gradients, rather than local temperature. More pronounced changes in Arctic ice cover can amplify the latitudinal temperature gradient between low and high latitudes via albedo feedback. These insights contribute to a better understanding of long‐term climate variability in East Asia and its implications for projecting future climate change under anthropogenic warming scenario. Key Points: Transient simulation reveals strengthened East Asian winter monsoon (EAWM) in both winter and spring since the mid‐HoloceneThe EAWM during the Holocene is primarily influenced by meridional temperature gradients between high and low latitudesIn addition to northern insolation, feedbacks from Arctic sea ice and Eurasian snow cover also affect temperature structure [ABSTRACT FROM AUTHOR]

The East Asian Summer Monsoon (EASM) provides the majority of annual rainfall to countries in East Asia. Although state-of-the-art models broadly project increased EASM rainfall, the spread of projections is large and simulations of present-day rainfall show significant climatological biases. Systematic evapotranspiration biases occur locally over East Asia, and globally over land, in simulations both with and without a coupled ocean. This study explores the relationship between evapotranspiration and EASM precipitation biases. First, idealized model simulations are presented in which the parameterization of land evaporation is modified, while sea surface temperature is fixed. The results suggest a feedback whereby excessive evapotranspiration over East Asia results in cooling of land, a weakened monsoon low, and a shift of rainfall from the Philippine Sea to China, further fueling evapotranspiration. Cross-model regressions against evapotranspiration over China indicate a similar pattern of behavior in Atmospheric Model Intercomparison Project (AMIP) simulations. Possible causes of this pattern are investigated. The feedback is not explained by an overly intense global hydrological cycle or by differences in radiative processes. Analysis of land-only simulations indicates that evapotranspiration biases are present even when models are forced with prescribed rainfall. These are strengthened when coupled to the atmosphere, suggesting a role for land-model errors in driving atmospheric biases. Coupled atmosphere-ocean models are shown to have similar evapotranspiration biases to those in AMIP over China, but different precipitation biases, including a northward shift in the ITCZ over the Pacific and Atlantic Oceans. [ABSTRACT FROM AUTHOR]

The seasonal changes in East Asian monsoon precipitation during the Last Glacial Maximum (LGM, 23,000–19,000 years B.P.) and its isotopic expression remain ambiguous. This study investigates changes in the seasonal precipitation δ18O (δ18Op) over East Asia during the LGM relative to the preindustrial (PI) and the underlying mechanisms using an isotope‐enabled atmospheric general circulation model. We show more depleted δ18Op in summer and a meridional tripolar δ18Op pattern in winter during the LGM compared to the PI. The depletion of summer δ18Op resulted from stronger upstream convective rainout due to the intensification of the Intertropical Convergence Zone. In contrast, the mechanisms for winter δ18Op changes were more complicated. With a series of sensitivity tests, we demonstrate that sea surface temperature controlled δ18Op changes across the whole of East Asia in summer and in the southern part of East Asia in winter. The depletion of winter δ18Op in central China arose largely from the suppression of droplet evaporation due to higher snow fraction. Our work provides important insights into the aspect of seasonal isotope changes during the LGM and may help facilitate an improved level of paleoclimatic interpretation of speleothem δ18O records from East Asia. Plain Language Summary: The climate over East Asia during the Last Glacial Maximum (LGM) was colder and drier than it is today according to paleoclimatic records. However, interpretations of paleo‐isotopic records have been inconsistent in previous research, and the seasonal isotope changes are still unclear. Here we use an isotope‐equipped climate model to explore summer and winter precipitation δ18O (δ18Op) behaviors in East Asia during the LGM. Compared to the preindustrial, the LGM was characterized by depleted summer δ18Op, largely due to the intensification of the Intertropical Convergence Zone which resulted in stronger rainout along the moisture transport pathways. The winter δ18Op, however, was more complex and exhibited a tripolar spatial pattern, with δ18Op depletion in central China but enrichment in both south and north. This pattern probably reflected the combined effect of sea surface temperature driven rainout en route and droplet evaporation. Key Points: Isotope‐enabled atmospheric general circulation model reasonably reproduces East Asian climate and precipitation δ18O changes between the Last Glacial Maximum (LGM) and preindustrialDepleted δ18O in LGM summer precipitation was driven by upstream rainout due to an intensification of the Intertropical Convergence ZoneWinter precipitation δ18O changes in southern and central China were controlled by rainout and droplet evaporation, respectively [ABSTRACT FROM AUTHOR]

The ozone valley over the Tibetan Plateau (OVTP) has experienced significant interannual variations during the past decades. Previous studies have primarily focused on the origins of OVTP rather than its climate impact. This study reveals that OVTP during its peak season (May–July) explains up to 15% of the summer precipitation variability in East Asia. The results suggest that the surface temperature (Ts) anomaly over the Tibetan Plateau (TP) acts as a link between OVTP and East Asian precipitation. Through the positive land-atmosphere feedback, the Ts anomaly over the TP is amplified. The anomalous Ts pattern persists into summer (June–August) due to the land memory effect and impacts the East Asian precipitation by modulating the local circulation. The Specified-Chemistry version of the Whole Atmosphere Community Climate Model is employed to validate that MJJ OVTP results in a substantial increase of Ts over TP and induces an anomalous anti-cyclone centered over the Yangtze-Huaihe River Basin during summer. Consequently, negative precipitation anomalies are observed in the Yangtze River Basin, while positive precipitation anomalies occur in Southern China. The linear baroclinic model further demonstrates that the diabatic heating over the TP serves as the link between MJJ OVTP and East Asian summer precipitation patterns. Our analysis of Coupled Model Intercomparison Project Phase 6 models reveals that a more accurate prediction of East Asian precipitation requires an improved understanding of the relationship between OVTP and TP Ts. [ABSTRACT FROM AUTHOR]

Atmospheric instability affects the formation of convective storms, but how it has changed during recent decades is unknown. Here we analyze the occurrence frequency of stable and unstable atmospheric conditions over land using homogenized radiosonde data from 1979 to 2020. We show that atmospheric stable (unstable) conditions have decreased (increased) significantly by ∼8%–32% (of time) from 1979 to 2020 over most land areas. In boreal summer, the mean positive buoyancy (i.e., convective available potential energy [CAPE]) also increases over East Asia while mean negative buoyancy (i.e., convective inhibition [CIN]) strengthens over Europe and North America from midnight‐dawn for unstable cases. The increased unstable cases and mean CAPE result from increased low‐level specific humidity and air temperature, which increase the buoyancy of a lifted parcel. The stronger CIN results from decreased near‐surface relatively humidity and decreased lapse rate in the lower troposphere. Our results suggest that the atmosphere has become increasingly unstable, which could lead to more convective storms. Plain Language Summary: Severe weather events such as tornados and intense thunderstorms often cause significant loss of life and property. Their formation requires instability or unstable conditions in the atmosphere. Climate models project increased unstable conditions under greenhouse gas‐induced global warming, but how atmospheric instability has changed during recent decades is unclear. Through analysis of newly homogenized radiosonde data, here we show that the atmosphere has become increasingly unstable over most land areas over the Northern Hemisphere from 1979 to 2020, with an increasing number of unstable conditions (i.e., with positive buoyancy) but a decreasing number of stable conditions (i.e., with zero or negative buoyancy). These changes result mainly from increased low‐level moisture content and warmer air temperature. Such instability changes favor increased occurrence of convective storms. Key Points: Newly homogenized radiosonde humidity and temperature data allow quantitative assessment of historical changes in atmospheric instabilityThere are increasingly more unstable conditions with positive buoyancy in all seasons over most land areas from 1979 to 2020The increased unstable conditions mainly result from increased low‐level moisture content and warmer air temperature [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 offshore region of East Asia has a crucial role in recycling precipitation, especially in the current context of a warming climate. This is because the atmospheric feedback from the sea offshore East Asia directly impacts and modifies precipitation patterns by influencing the seasonal cycles of the surface energy and water budgets. We used a regional climate model incorporating sea–air coupling to investigate and better understand these climate feedback mechanisms in East Asia. We identified a reduction in precipitation caused by sea-air coupling over East Asia during the time period 1991 − 2014 under present day conditions. Specifically, we observed an average decrease in precipitation of about 0.1 ± 0.40 mm day−1 during June–July–August. This decrease in precipitation can be attributed to a combination of factors, including the effects of upward solar radiation, the asymmetry of the thermal contrast between the land and the sea, decreased evaporation in the southeastern ocean and the weakened transport of water vapor from the sea to the land. Our research suggests that the decrease triggered by sea–air coupling will be partially alleviated under future conditions, although not completely reversed, in terms of its impact on precipitation in eastern China. Although some relief is anticipated, the overall influence of sea–air coupling on patterns of precipitation in East Asia will persist, especially south of the Yellow River in eastern China. [ABSTRACT FROM AUTHOR]

Meiyu occurs in Yangtze‐Huaihe River valley (YHRV) every summer. Its intensity, distribution, and intraseasonal variation are greatly influenced by atmospheric forcings from different directions, such as the monsoon southwesterlies from the south, the western Pacific subtropical high (WPSH) in the east, the atmospheric longwave activities in the north, the southwest vortex from the west, and so on. In this study, to explore the contributions of the atmospheric forcings from different directions to 2020 extreme Meiyu, Regional Climate Model version 4.6 (RegCM4.6) is employed. A series of sensitivity experiments are conducted with realistic or climatological averaged lateral boundary conditions. The results show that the monsoon westerlies from the south transport moisture and heat to YHRV, converge with the cold air brought by the frequent atmospheric longwave activities in the north, and result in this extreme Meiyu. The frequent cold air from the north can lift warm air, provide unstable conditions, and make the distribution of precipitation similar to the teleconnection pattern in East Asia. The stable WPSH in the east anchors the 2020 Meiyu rainband to the YHTV for a long time. In addition, the contributions of the atmospheric forcings from different directions to evolution of 2020 Meiyu change with time. Before 10 June, the WPSH in the east mainly contributes to the Meiyu evolution. From 11 June to 3 July, the combined effects of atmospheric forcings from the south and north are dominant. From 3 July to 10 July, the cold air from the north plays a major role. Plain Language Summary: The typical rainy season of the East Asian summer monsoon, Meiyu, occurs in Yangtze‐Huaihe River valley (YHRV) in China every summer. Its intensity, distribution and intraseasonal variation are greatly influenced by the monsoon southwesterlies from the south, the western Pacific subtropical high in the east, the atmospheric longwave activities in the north, the southwest vortex from the west and so on. In the summer of 2020, the record‐breaking Meiyu rainfall, featuring an early onset, delayed retreat, abundant precipitation, and frequent heavy rainstorm processes, appeared in the YHRV. However, the contributions and roles of atmospheric forcings from different directions to 2020 Meiyu have not been well analyzed. In this study, Regional Climate Model version 4.6 (RegCM4.6) is employed to simulate the 2020 Meiyu, and a series of sensitivity experiments are conducted. The results show that atmospheric forcings from different directions play different roles in the occurrence and movement of the Meiyu rain belt in 2020. In addition, the contributions of atmospheric forcings to the 2020 Meiyu from different directions change with time. The results improve the understanding of the occurrence and maintenance mechanisms of Meiyu. Key Points: The extreme Meiyu in 2020 occurs due to specific atmospheric forcings which are different from the climatological conditionsThe atmospheric forcings from different directions play different roles in the occurrence and evolution of the Meiyu rain belt in 2020The contributions of atmospheric forcings to the 2020 Meiyu from different directions change with time during the Meiyu period [ABSTRACT FROM AUTHOR]

This study investigated future projections of extreme precipitation (PR) over the Korean Peninsula (KP) under global warming levels of 1.5 °C and 2.0 °C (GWL 1.5 °C and 2.0 °C). The bias-corrected large ensemble of the Regional Climate Model (RCM) in the Coordinated Regional Climate Downscaling Experiment–East Asia Phase 2 was used. Under GWL 1.5 °C, the RCM multi-model ensemble (MME) predicted the extreme PR intensity (RX1day) to increase by 10.14% more than the mean PR of 4.69%. A regional difference was observed in the projection, with a larger increase over the northern KP (NKP) and southern KP (SKP) than central KP. Accordingly, the distribution of extreme PR was expected to shift with the right, and extreme events occurring once every 20 years over the SKP and NKP were expected to change to a reoccurrence of 12.56 years and 10.04 years, respectively. The mechanism of extreme PR was examined for cases from June to September. The expected increase in extreme PR per warming over the SKP and NKP was 5.64% °C−1 and 8.37% °C−1, respectively, which was close to the Clausius-Clapeyron scale (7.7% °C−1). This implies that increased moisture capability from the warming will affect the change in extreme PR. Other possible factors were investigated and the RCM MME predicted vertical instability over East Asia to continue, and moisture flux and convergence around the KP to be intensified. Meanwhile, under GWL 2.0 °C, mean PR and extreme PR were projected to increase more than under GWL 1.5 °C. [ABSTRACT FROM AUTHOR]

The summer North American dipole (NAD) is a pattern of climate variability linked to variations in boreal forest seed production and migration of seed-eating birds. This is a modeling investigation of two teleconnections identified as drivers of the NAD in prior observational work: 1) tropically sourced atmospheric Rossby waves associated with anomalies in the phase distribution of the Madden–Julian oscillation (MJO) (i.e., phases 1 and 6 are anomalously prominent), and 2) a pan-Pacific atmospheric Rossby wave linked to East Asian monsoonal (EAM) convection. Sea surface temperature (SST) boundary forcing experiments were conducted with the Community Earth System Model 2 (CESM2) to trigger convection patterns that align with those observed during EAM and nonuniform phase distributions of MJO. For the EAM case, an El Niño–like SST dipole pattern combined with cool southern Japan SST forcing produced a convection and jet stream shift anomaly over East Asia and the northern Pacific with a positive NAD pattern downstream over North America, similar to the observed pattern when precipitation over East Asia (PEA) is relatively high. A companion experiment with only ENSO-like SST forcing also produced the NAD but featured a different structure over the Eurasian continent with a response resembling the summer east Atlantic (SEA) pattern over eastern North America and the eastern Atlantic. Simulation results suggest that the southern Japan SST forcing region has a secondary importance in triggering the NAD, producing only a somewhat NAD-like pattern by itself and only slightly improving the NAD produced by ENSO-like forcing. Simulations using SST forcing to induce seasonal convection anomalies with spatial patterns similar to anomalously frequent occurrence of MJO phase 1 (phase 6) produced circulation response patterns resembling the positive NAD (negative NAD). [ABSTRACT FROM AUTHOR]

Numerous palaeoclimatic records have shown that precession plays a dominant role in the Asian monsoon precipitation. However, the impact and mechanism of precession change on the East Asian summer monsoon (EASM) under high CO 2 conditions have yet to be studied. The mid-Pliocene (∼3.3–3.0 Ma) was the most recent warm interval during which atmospheric CO 2 concentrations were similar to the present level of ∼400 ppmv. Therefore, it is often regarded as an analog for a near-future climate scenario. Here, the influence of precession change on EASM is investigated through numerical climate modeling using the mid-Pliocene as a test case. The results show that from the minimum to maximum of the precession, the summer temperature maximum zone shifted northward from ∼30°N to ∼45°N and the summer precipitation increased by ∼60% over the mainland East Asia. The simulations also show that the top-of-atmosphere insolation increased significantly in the Northern Hemisphere summer over mid- and high-latitudes and increased slightly over low latitudes from the precession minimum to maximum, leading to a substantial increase in the thermal contrast between the mainland East Asia and the equatorial western North Pacific. In this scenario, the western North Pacific subtropical high intensified and expanded, and the ITCZ migrated northward over South and Southeast Asia and was shifted southward over the area between the 110°E and 130°E, thereby leading to the rain belt penetration into northern China. [ABSTRACT FROM AUTHOR]

This study explores the differences in performance and results by various versions of the ISORROPIA thermodynamic module implemented within the global atmospheric chemistry model EMAC. Three different versions of the module were used, ISORROPIA II v1, ISORROPIA II v2.3, and ISORROPIA-lite. First, ISORROPIA II v2.3 replaced ISORROPIA II v1 in EMAC to improve pH predictions close to neutral conditions. The newly developed ISORROPIA-lite has been added to EMAC alongside ISORROPIA II v2.3. ISORROPIA-lite is more computationally efficient and assumes that atmospheric aerosols exist always as supersaturated aqueous (metastable) solutions while ISORROPIA II includes the option to allow the formation of solid salts at low RH conditions (stable state). The predictions of EMAC by employing all three aerosol thermodynamic models were compared to each other and evaluated against surface measurements from three regional observational networks (IMPROVE, EMEP, EANET) in the polluted Northern Hemisphere. The differences between ISORROPIA II v2.3 and ISORROPIA-lite were minimal in all comparisons with the normalized mean absolute difference for the concentrations of all major aerosol components being less than 10 % even when different phase state assumptions were used. The most notable differences were lower aerosol concentrations predicted by ISORROPIA-lite in regions with relative humidity in the range of 20% to 60% compared to the predictions of ISORROPIA II v2.3 in stable mode. The comparison against observations yielded satisfactory agreement especially over the US and Europe, but higher deviations over East Asia, where the overprediction of EMAC for nitrate was as high as 4 μg m-3 (~ 20%). The mean annual aerosol pH predicted by ISORROPIAlite was on average less than a unit lower than ISORROPIA II v2.3 in stable mode, mainly for coarse mode aerosols over Middle East. The use of ISORROPIA-lite accelerated EMAC by 5 % compared to the use of ISORROPIA II v2.3 even if the aerosol thermodynamic calculations consume a relatively small fraction of the EMAC computational time. ISORROPIA-lite can therefore be a reliable and computationally effective replacement of the previous thermodynamic module in EMAC. [ABSTRACT FROM AUTHOR]

The multi-year simulation of tropical cyclones (TCs) over the Western North Pacific (WNP) in the variable resolution (VR) CAM-MPAS model is studied. Experiments with the global quasi-uniform low resolution of 120 km (MPAS-UR) and the variable resolution mesh of 30–120 km refined over East Asia (MPAS-VR) are integrated from 1980 to 2005 following the Atmospheric Model Intercomparison Project protocol. By utilizing an objective detection method, TCs in ERA5 reanalysis and model simulations are tracked and compared against observations. MPAS-VR shows significant advantages over MPAS-UR as indicated by more realistic TC counts, intensities, lifetime distribution, and seasonal variation. The large-scale circulation and precipitation patterns associated with TCs are also improved in MPAS-VR relative to MPAS-UR. Based on the theory of Dynamic Genesis Potential Index, the multi-year TC records are further used to quantify the dependence of TC genesis on various dynamical environmental factors from the perspective of seasonal variation. We find that in ERA5, the relative contribution of the 500 hPa vertical pressure velocity term to TC genesis exceeds that of the 200–850 hPa vertical wind shear term, which is responsible for the August peak and strong seasonal variation of TC genesis. MPAS-UR fails to capture such relationship while MPAS-VR performs much better in this regard, suggesting that the higher skills in simulating the relative contributions from different dynamical environmental factors to the simulated seasonal cycle of TC genesis may explain the improvements from MPAS-UR to MPAS-VR. [ABSTRACT FROM AUTHOR]

The effect of model resolution on the simulation of tropical cyclone (TC) landfall frequency in East Asia [including the South China Sea (SCS), Taiwan and coastal areas of East China (TWCN) and Japan (JP)] was investigated by comparing Atmospheric Model Intercomparison Project (AMIP) type simulations on the basis of 50-km High Resolution Atmospheric Models (HiRAMs) and 25-km HiRAM. The number of TC landfalls in the TWCN region was realistically simulated by the 50-km HiRAM ensemble model. However, fewer (more) TCs were steered westward (northward) toward the SCS (JP) because of an overestimation of the monsoon trough in the western North Pacific (WNP). The overestimation created a low-level cyclonic circulation anomaly in the WNP, which substantially modified steering flow. Consequently, more (less) TC made landfall in JP (SCS). The overestimation of the monsoon trough in model was primarily resulted from compounding factors, including the AMIP type simulation, upscale feedback of TCs to mean flow and the monsoon flow–topography interaction in the Indochina Peninsula Mountains and Philippine. First, the SST was negatively correlated with precipitation in the WNP during the typhoon season for the observation. Conversely, the SST–precipitation relationship was positive in the AMIP run. Second, the upscale feedback of TCs to mean flow (monsoon trough) was overestimated, which in term contributed to the overestimation of monsoon trough. Third, the model underestimated the mountain lifting effect in the Indochina Peninsula and Philippine. Overall, the aforementioned biases were substantially improved by increasing model's horizontal resolution from 50-km to 25-km HiRAM. [ABSTRACT FROM AUTHOR]

The adverse impacts of extreme heat on human health when a concurrent daytime and nighttime heatwave (CDNHW) occurs are greater than when daytime or nighttime heatwaves occur individually, because of the reduced recovery time from heat exposure. This study projects increases in CDNHW over the whole of East Asia under two Representative Concentration Pathway scenarios (RCP2.6 and RCP8.5) and two Shared Socioeconomic Pathway scenarios (SSP1‐2.6 and SSP5‐8.5). The daily maximum and minimum temperatures, which are used to define a CDNHW, are calculated of 3‐hourly temperatures of 25 km horizontal resolution produced by 12 general circulation model and regional climate model chains participating in the Coordinated Regional Climate Downscaling Experiment East Asia phase 2 project. In Historical simulation (1981–2005), occurrence period and occurrence rate of CDNHW from April to September area‐averaged in East Asia are 10.9 days and 0.9%, respectively. In projections for the future (2071–2100), occurrence period and occurrence rate of CDNHW will be 3 weeks and 3.7% (RCP2.6), 2 months and 20.5% (RCP8.5), 2 months and 15.6% (SSP1‐2.6), and 3 months and 45.7% (SSP5‐8.5). In addition, it is expected that the CDNHW intensity will increase, and the spatial extent of CDNHW will be extended. Although a CDNHW lasting less than 3 days is the most common, the proportion of CDNHWs lasting more than 10 days, compared to the total CDNHW frequency, will increase to 1.2% (RCP2.6), 7.2% (RCP8.5), 6.1% (SSP1‐2.6), and 17.3% (SSP5‐8.5) from 0.2% (Historical). Both occurrence rate and intensity of CDNHW will increase to a relatively large extent in Indochina, East and West China, and India. If the current greenhouse gas emissions continue, East Asia will experience unprecedented heat stress because the frequency and intensity of CDNHWs, which rarely occur during present‐day, will increase significantly over all regions by the end of the 21st century. [ABSTRACT FROM AUTHOR]

Northern Hemispheric summer monsoons were more intense during the mid-Holocene (MH ~ 6000 years ago) and coincided with a northward shift of the Intertropical Convergence Zone (ITCZ) compared to the pre-industrial (PI) climate. Ancient civilizations in the Indus valley, Mesopotamia, and Egypt appear to have flourished during this period, thanks to abundant water availability. This study exploits a high-resolution variable grid global atmosphere model to understand the role of orbital forcing and ocean surface conditions in strengthening the monsoons and shifting the ITCZ northward over Africa, India, and East Asia during the MH. The combined impact of orbital forcing and sea surface temperature (SST) boundary conditions led to a change in monsoon rainfall of around 42, 30, 21, and 41% over Africa, East Asia, India, and northwest India (NWI) relative to the PI conditions. Changes in orbital parameters alone account for more than 36 and 26% of total rainfall increases in Africa and East Asia. Over the Indian subcontinent, the strengthening of monsoon was primarily a combined effect of SST and orbital forcing. In contrast, the SST boundary condition alone could explain the 39% of rainfall increase over NWI, where the Indus valley civilization once existed. Through moisture budget analysis, the study further illustrates the role of dynamic and thermodynamic factors responsible for the changes in monsoon precipitation. The enhanced monsoon resulted in a northward shift of ITCZ by around 3°N, 1.9°N, and 2.5°N over Africa, East Asia, and India, respectively, compared to its PI position. Analogous to the precipitation changes, orbital forcing mostly mediated ITCZ changes across Africa and East Asia, but the combined impact of orbital forcing and SST was responsible for the changes over India. [ABSTRACT FROM AUTHOR]

A double-plume convective parameterization scheme is revised to improve the precipitation simulation of a global model (Global-to-Regional Integrated Forecast System; GRIST). The improvement is achieved by considering the effects of large-scale dynamic processes on the trigger of deep convection. The closure, based on dynamic CAPE, is improved accordingly to allow other processes to consume CAPE under the more restricted convective trigger condition. The revised convective parameterization is evaluated with a variable-resolution model setup (110−35 km, refined over East Asia). The Atmospheric Model Intercomparison Project (AMIP) simulations demonstrate that the revised convective parameterization substantially delays the daytime precipitation peaks over most land areas, leading to an improved simulated diurnal cycle, evidenced by delayed and less frequent afternoon precipitation. Meanwhile, changes to the threshold of the trigger function yield a small impact on the diurnal amplitude of precipitation because of the consistent setting of dCAPE-based trigger and closure. The simulated mean precipitation remains reasonable, with some improvements evident along the southern slopes of the Tibetan Plateau. The revised scheme increases convective precipitation at the lower levels of the windward slope and reduces the large-scale precipitation over the upper slope, ultimately shifting the rainfall peak southward, which is in better agreement with the observations. [ABSTRACT FROM AUTHOR]

Owing to the complicated spatial–temporal characteristics of East Asian precipitation (EAP), climate models have limited skills in simulating the modern Asian climate. This consequently leads to large uncertainties in simulations of the past EAP variation and future projections. Here, we explore the performance of the newly developed Alfred Wegener Institute Climate Model, version 3 (AWI‐CM3) in simulating the climatological summer EAP. To test whether the model's skill depends on its atmosphere resolution, we design two AWI‐CM3 simulations with different horizontal resolutions. The result shows that both simulations have acceptable performance in simulating the summer mean EAP, generally better than the majority of individual models participating in the Coupled Model Intercomparison Project (CMIP6). However, for the monthly EAP from June to August, AWI‐CM3 exhibits a decayed skill, which is due to the subseasonal movement of the western Pacific subtropical high bias. The higher‐resolution AWI‐CM3 simulation shows an overall improvement relative to the one performed at a relatively lower resolution in all aspects taken into account regarding the EAP. We conclude that AWI‐CM3 is a suitable tool for exploring the EAP for the observational period. Having verified the model's skill for modern climate, we suggest employing the AWI‐CM3, especially with high atmosphere resolution, both for applications in paleoclimate studies and future projections. [ABSTRACT FROM AUTHOR]