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Following the description of the basic climatic characteristics of Meiyu in East Asia, we present a comprehensive review of multi–time scale variabilities of the Meiyu together with the long‐term change of extreme precipitation during the Meiyu in this paper. The dynamic prediction skills of the Meiyu on subseasonal to seasonal time scales are further described and illustrated by using present numerical prediction models. For the multi–time scale variabilities of the East Asian Meiyu, they are closely related with the impacts of both quasi‐biweekly and 30–60 day oscillation from both the tropics and the middle and high latitudes on intraseasonal time scale, the influences of El Niño–Southern Oscillation and the Tropospheric Biennial Oscillation on interannual time scale, the variations of East Asian summer monsoon on decadal time scale, and the continued impacts of global warming, Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation on interdecadal scale and long‐term trend. Under the background of the global warming and the influences of urbanization and aerosol effects, the Meiyu shows some specific characteristics including significantly weakened continuous rain, uneven spatial distribution of precipitation, and increased (decreased) number of strong (weak) precipitation days. Improvements of prediction on rain belt location, total precipitation amount, persistent heavy precipitation events, and low‐frequency variability oscillation during Meiyu season have been achieved with the improved dynamic models of the Beijing Climate Center since 2010. Key Points: Meiyu's variabilities are related with intraseasonal oscillation, interannual to multidecadal oscillation of ocean, and global warmingMeiyu impacted by global warming, urbanization, and aerosol effects exhibits stronger rainfall eventsImprovements of prediction of East Asian Meiyu on multi‐time scale have been achieved with the present operational climate models [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In East Asia, where concentrated summer precipitation often leads to climate disasters, understanding the factors that cause such extreme rainfall is crucial for effective forecasting and preparedness. The western North Pacific subtropical high (WNPSH) is a key driver of summer precipitation variability, and therefore, its monitoring is critical to predicting the wet or dry periods during the East Asian summer monsoon. Using the Geo-KOMPSAT 2A (GK2A) satellite cloud amount data and ERA5 reanalysis data during the years 2020–2023, this study identified three leading empirical orthogonal function (EOF) modes and investigated the associated WNPSH variability at synoptic and subseasonal scales. The analysis includes a linear regression of meteorological fields onto the principal component (PC) time series. All three modes play a role in the spatiotemporal variability of the WNPSH, exhibiting lead–lag relationships. In particular, the second mode is responsible for its northwestward shift and intensification. As the WNPSH moves northwestward, the position of the monsoon rain band also shifts, and its intensity is modulated mainly by the moisture transport along the WNPSH boundary. Our results highlight the potential of high-resolution, real-time data from the GK2A satellite to elucidate WNPSH variability and its impact on the East Asian summer monsoon. By addressing the variability of the WNSPH using GK2A data, we pave the way for the development of a real-time monitoring framework with GK2A, which will improve our predictability and readiness for extreme weather events in East Asia. [ABSTRACT FROM AUTHOR]

Land surface processes play an important role in the East Asian Summer Monsoon (EASM) system. Parameterization schemes of land surface processes may cause uncertainties in regional climate model (RCM) studies for the EASM. In this paper, we investigate the sensitivity of a RCM to land surface parameterization (LSP) schemes for long-term simulation of the EASM. The Weather Research and Forecasting (WRF) Model coupled with four different LSP schemes (Noah-MP, CLM4, Pleim-Xiu and SSiB), hereafter referred to as Sim-Noah, Sim-CLM, Sim-PX and Sim-SSiB respectively, have been applied for 22-summer EASM simulations. The 22-summer averaged spatial distributions and strengths of downscaled large-scale circulation, 2-m temperature and precipitation are comprehensively compared with ERA-Interim reanalysis and dense station observations in China. Results show that the downscaling ability of RCM for the EASM is sensitive to LSP schemes. Furthermore, this study confirms that RCM does add more information to the EASM compared to reanalysis that imposes the lateral boundary conditions (LBC) because it provides 2-m temperature and precipitation that are with higher resolution and more realistic compared to LBC. For 2-m temperature and monsoon precipitation, Sim-PX and Sim-SSiB simulations are more consistent with observation than simulations of Sim-Noah and Sim-CLM. To further explore the physical and dynamic mechanisms behind the RCM sensitivity to LSP schemes, differences in the surface energy budget between simulations of Ens-Noah-CLM (ensemble mean averaging Sim-Noah and Sim-CLM) and Ens-PX-SSiB (ensemble mean averaging Sim-PX and Sim-SSiB) are investigated and their subsequent impacts on the atmospheric circulation are analyzed. It is found that the intensity of simulated sensible heat flux over Asian continent in Ens-Noah-CLM is stronger than that in Ens-PX-SSiB, which induces a higher tropospheric temperature in Ens-Noah-CLM than in Ens-PX-SSiB over land. The adaptive modulation of geopotential height gradients affects wind field (through geostrophic balance) simulation especially at lower levels, which subsequently affects the simulation of large-scale circulation, 2-m temperature and monsoon precipitation as well as RCM's downscaling ability. [ABSTRACT FROM AUTHOR]

This paper focuses on the relationship between the phase transition of the Pacific decadal oscillation (PDO) and decadal variation of the East Asian summer monsoon (EASM) in the twentieth century. The first transition occurred in the 1940s, with an enhanced SST in the North Pacific and reduced SST in the tropical eastern Pacific and South Indian Ocean. In agreement with these SST changes, a higher SLP was found in most parts of the Pacific, while a lower SLP was found in the North Pacific and most parts of the Indian Ocean. In this case, the EASM was largely enhanced with a southerly anomaly in the lower troposphere along the east coast of China. Correspondingly, there was less rainfall in the Yangtze River valley and more rainfall in northern and southern China. An opposite change was found when the PDO reversed its phase in the late 1970s. In the tropical Indian Ocean and western Pacific, however, the SST was enhanced in both the 1940s and 1970s. As a result, the western Pacific subtropical high (WPSH) tended to extend westward with a larger magnitude in the 1970s. The major features were reasonably reproduced by an atmospheric general circulation model (IAP AGCM4.0) prescribed with observed SST and sea ice. On the other hand, the westward extension of the WPSH was exaggerated in the 1970s, while it was underestimated in the 1940s. Besides, the spatial pattern of the simulated summer rainfall in eastern China tended to shift southward compared with the observation. [ABSTRACT FROM AUTHOR]

The differences between the two global warming targets of the Paris Agreement, 1.5 °C and 2 °C above pre-industrial levels, have drawn much attention from the scientific community. However, there is a remaining gap to distinguish regional climate responses in these two most typical pathways, i.e., transient and stabilization simulations, toward specific warming levels. In this study, we discern the East Asia summer monsoon (EASM) responses between these two types of simulations at low-warming targets, based on the fully coupled community Earth system model (CESM). The two types of responses display a similar increase pattern in the EASM precipitation. However, the quantitative differences between these two types of responses are as large as those between the 1.5 °C and 2 °C warming scenarios. The moist budget analysis reveals that the EASM precipitation differences are mainly caused by the thermodynamic, dynamic, and transient eddy effects. Specifically, the thermodynamic effect contributes to the precipitation increment in the coastal area of East Asia in both types of responses, with the enhanced low-level specific humidity. The dynamic contribution shows tripolar and bipolar patterns in East Asia in the transient and stabilization responses, respectively. Remarkably, the transient eddy effect contribution emerges only in the stabilization responses. Further, we reveal the dominant role of the East Asian subtropical jet (EASJ) in determining the contributions from dynamic and transient eddy effects. The changes in the EASJ's position and intensity are greatly regulated by the temperature change patterns at the mid-high levels in response to different greenhouse gas emission pathways. Our study highlights the differences between transient and stabilization climate states on a regional scale. [ABSTRACT FROM AUTHOR]

Marine Isotope Stage (MIS) 13, an interglacial about 500,000 years ago, is unique due to an exceptionally strong East Asia summer monsoon (EASM) occurring in a relatively cool climate with low greenhouse gas concentrations (GHG). This paper attempts to find one of the possible mechanisms for this seeming paradox. Simulations with an Earth System model LOVECLIM show that the presence of ice sheets over North America and Eurasia during MIS-13 induces a positive phase of the winter North Atlantic Oscillation (NAO) like feature. The ocean having a longer memory than the atmosphere, the oceanic anomalies associated with NAO persists until summer. The signals of summer NAO are transmitted to East Asia to reinforce the monsoon there through the stationary waves excited at the Asian Jet entrance. The geopotential height shows clearly a mid-latitude wave train with positive anomalies over the eastern Mediterranean/Caspian Sea and the Okhotsk Sea and a negative anomaly over Lake Baikal. This reinforces the effect of the high-latitude wave train induced independently by the Eurasian ice sheet topography as shown in previous study. These features reinforce the Meiyu front and enhance the precipitation over East Asia. The results obtained from LOVECLIM are further confirmed by an atmospheric general circulation model, ARPEGE. [ABSTRACT FROM AUTHOR]

Vegetation–climate relationships are often different at varying spatial scales, which is seldom taken into account in reconstructing past climate changes from fossil pollen spectra represent more local vegetation composition but using regional or extra-regional modern pollen–climate calibration set. In this paper, we employ 2620 surface pollen spectra and six pollen sequences from continental East Asia to reconstruct Holocene climate with modern analogue technique. A novel data set of vegetation sensitivity index (VSI) is introduced to examine vegetation–climate relationships in 0.5° search windows around the fossil sites (local) and in the tailored calibration sets (regional). Then, we compare them to the explanatory abilities of (reconstructed) climate variables on explaining the pollen variance in calibration sets and in the fossil pollen data sets using constrained ordination, cross-validation and significance test. By this procedure that we called local–regional–fossil comparison, we can better determine which variable reconstruction is valid and useful. In our cases, moisture variable reconstructions in temperate forest-steppe ecotone at the East Asian summer monsoon margin are reliable. Consistent Holocene moisture variations with a strong monsoon influence during 8.6–4.0 cal ka BP which can help us to better interpret human adaptations along the Great Wall. However, quantitative climate reconstructions at some sites are less reliable due to highly heterogeneous vegetation sensitivities surrounding the site, particularly for areas with complicated topographical contexts. We stress that vegetation sensitivities at local and regional scales both need to be investigated before conducting quantitative climate reconstruction. [ABSTRACT FROM AUTHOR]

The Maritime Continent (MC) is an important region where the Tropical Pacific and the Indian Ocean interact with each other via "the atmospheric bridge" and a key region for the interaction between the Asian and Australian monsoons. Using the NCEP/NCAR and CMAP monthly mean reanalysis over the period of 1979-2012, the interdecadal variations of diabatic forcing over the key region of the Maritime Continent and its possible relations with the East Asian summer monsoon have been investigated in the present paper. Our results show that climate variations in the Maritime Continent is particularly significant in the area of95-145°E, l0°S-10°N, which is thus defined as the key area of the MC (i.e., KMC area). Without the input of latent heat release in the atmosphere, distinct interdecadal change of diabatic heating is found to exist from 1979 to 2012; it intensified before 1980s and peaked in the late 1980s and weakened after this period. By analyzing each individual component that contributes to the diabatic heating in the KMC area, surface latent heat flux and net long-wave radiation in the atmosphere are found to be the two dominant components. With negative diabatic heating anomalies over KMC, there will be more precipitation on islands and less precipitation over sea, and more rainfall around the equator, which is in correspondence with the convergence center around the equator in the KMC area . Along the meridional-vertical section averaged between 115-1 20°E, the well-defined vertical circulation anomalies are observed with the ascending branches over KMC and the area around 30°N respectively, and the descending branch over the South China Sea. Water vapor transports from the Bay of Bengal and South China Sea to eastern China to benefit the positive precipitation anomalies. The meridional-vertical circulation in East Asia plays a critical role in linking the interdecadal variability of diabatic heating over the KMC and East Asian summer monsoon anomalies. [ABSTRACT FROM AUTHOR]

Few studies have investigated the retreat of the East Asian summer monsoon (EASM) in comparison to its seasonal advances. This study examined the climatological characteristics of the EASM retreat based on the Japanese 55-year Reanalysis data and multiple observation data. First, the retreat date of EASM is defined based on the reversal of 850 hPa meridional winds over coastal East Asia. Then, the climatological characteristics of the EASM retreat are investigated based on the retreat date of the EASM. At lower troposphere, the differences of the 850-hPa winds between after and before the EASM retreat display an anticyclone (cyclone) over the East Asian continent (the subtropical western Pacific), resulting in the strengthening of northerly winds over the coastal region of East Asia. Such northerly winds lead to decrease of moisture transport over East Asia and bring colder air from higher latitudes to the coastal East Asia, both favoring the retreat of the EASM. At middle troposphere, the WPSH moves eastward, and a mid-latitude trough appears over northeast Asia. In addition, the difference fields show descending (ascending) motion and cold (warm) advection in the rear (front) of the mid-latitude trough. At upper troposphere, a divergent center exhibits a southeastward movement, which shifts from the Philippine Islands to the western North Pacific. As such, a convergence center appears over the coastal East Asia in the difference map. The retreat of the EASM is also associated with the decreased rainfall, the demise of the wet season, and the broadscale cooling over East Asia. [ABSTRACT FROM AUTHOR]

Copyright of Advances in Atmospheric Sciences is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Water management is a crucial issue in East Asia and is significantly influenced by climate change. Because East Asia's precipitation characteristics are varied and complex, it is necessary to implement the analysis of the future changes in precipitation on an objectively classified, specific sub‐regional level to effectively solve these problems. In this study, sub‐regions were objectively classified according to their precipitation characteristics, based on the present observations in East Asia. Additionally, the bias‐correction technique was applied to the regional climate model (RCM) to yield more reliable future precipitation predictions for the sub‐regions. We obtained the following four key results in this study. (1) The classified sub‐regions corresponded well to the observed annual precipitation distribution and adequately reflected the influence of the summer monsoon. The annual precipitation of the classified sub‐regions exhibited a decreasing trend in arid regions and an increasing trend in humid areas. (2) Because the bias‐corrected RCM was able to simulate annual precipitation reasonably, this technique was applied to future scenarios to analyse future changes in precipitation for each classified sub‐region. (3) Future annual precipitation will increase significantly in the region spanning from the western part of Southern China to the area around the Bohai Sea, while the temporal variations of the climatological daily precipitation indicated that sub‐regions under the influence of the East Asian summer monsoon (EASM) will be predicted an increase in second peaks during the summer. Hence, in the future, the EASM rain belt will be strengthened and its average location will move northward from its present location. (4) Because the high‐intensity extreme precipitation indices are expected to have a more considerable increase in all the classified sub‐regions, there is a need to solidify response measures against disasters that could arise from these changes in the East Asian region. [ABSTRACT FROM AUTHOR]

A regional Climate‐Weather Research and Forecasting (CWRF) model with a 30‐km horizontal resolution was applied to simulate the East Asian summer monsoon (EASM) and climate in China from 1980 to 2016. As compared with observations and reanalysis data, the model can reasonably reproduce the spatial distributions of the climatological mean atmospheric circulation and water vapour transport in East Asia, as well as the seasonal advance and retreat of EASM and rain bands. The correlation coefficient between the EASM circulation index in the simulation and reanalysis is.97. The model can well represent the geographic distributions of summer mean temperature and precipitation over most of China. However, model biases still exist, in particular the skill in the Yangtze–Huaihe River basin is relatively low. The simulated climatological mean temperature and precipitation deviations from observations may be related to the model's systematic circulation biases, with a thicker lower troposphere (i.e., higher temperature between 500 and 1,000 hPa) over most of China (except for the south and southwest) and a thinner one over the coastal oceans in summertime. Compared with the reanalysis, the model overestimates the land‐ocean thermal contrast, which causes the South Asian High shifted to the north and east, as well as the subtropical high and tropical convective activity located further north and persisted longer. Consequently, more water vapour transports northward, leading to more precipitation over North China–Northeast China and less precipitation over the Yangtze and Huaihe River basin. Therefore, the enhanced land‐ocean thermal contrast may be a major factor for the stronger EASM in the model, and corresponding precipitation and temperature biases in China. This analysis provides important information for further improving model performance in EASM simulation. [ABSTRACT FROM AUTHOR]

Projecting regional rainfall changes in a warmer climate attracts ongoing attention. However, large uncertainty still exists in multi-model projection. In this study, we introduce a bias-corrected method to correct the multi-model projection of changes in East Asian summer monsoon (EASM) rainfall based on the historical and RCP8.5 runs of 25 models from phase 5 of Coupled Model Intercomparison Project. Firstly, the total rainfall changes are separated into the thermodynamic component due to increased specific humidity and the dynamic component due to circulation changes. The thermodynamic component is corrected using the observed present-day rainfall and the increase rate of specific humidity based on the wet-get-wetter mechanism. On the other hand, the dynamic component with the circulation changes is corrected based on a "spatial emergent constraint" method, which is further validated by the perfect model approach. Together, these corrections give an integrated projection for EASM rainfall changes under global warming. Such an approach can improve the signal-to-noise ratio of projection effectively, from the original 0.73 of the multimodel mean to around 1.9. The corrected projection of EASM rainfall changes shows a pronounced increase in southern China, the northwest Pacific and a belt from northern China to northeastern China, and a weak increase in other EASM regions. [ABSTRACT FROM AUTHOR]

Investigation into the intraseasonal variation of the South Asian high (SAH) and its relationship with the Indian and East Asian summer monsoon rainfalls indicates that the 10–20 day period dominates the subseasonal zonal oscillation of the SAH between the Iranian mode and the Tibetan mode. The eastward shift of SAH lags a rainfall decrease over northern India by about 1 day, but leads a rainfall increase over the Yangtze River valley (YRV) by about 3 days. Interactive processes are also revealed on quasi‐biweekly time scales. The latent heating over northern India contributes to the southwestward shift of a pair of cyclone‐anticyclone anomalies from the midlatitudes to the SAH region, resulting in the zonal shift of the SAH. An associated upper‐level divergence over eastern China leads to the rainfall increase over the YRV 3 days later. The lead‐lag relationships revealed may benefit the subseasonal rainfall prediction over the two monsoon regions. Plain Language Summary: The Indian summer monsoon (ISM) and the East Asian summer monsoon (EASM) are two crucial monsoon systems, affecting more than half of the population in the world. The upper‐level high‐pressure system, the South Asian high (SAH) plays an important role in connecting the ISM and EASM rainfalls on intraseasonal time scales. The zonal shift of SAH center between the Iranian Plateau and the Tibetan Plateau exhibits a quasi‐biweekly oscillation with a peak period about 13 days. The eastward shift of the SAH lags a decrease in rainfall over northern India by about 1 day, but leads an increase in rainfall over the Yangtze River valley by about 3 days. Such lead‐lag relationship implies an interaction among the SAH and the ISM and EASM rainfalls. Abundant rainfall over northern India causes the zonal shift of the SAH, which in turn influences the rainfall over East Asia. Key Points: Quasi‐biweekly oscillation is a dominant feature in the intraseasonal zonal shift of the South Asian highThe zonal shift of SAH lags the variation of rainfall over northern India by 1 day and leads that over the Yangtze River valley by 3 daysThe SAH plays an important role in connecting the Indian and East Asian summer monsoons on intraseasonal time scales [ABSTRACT FROM AUTHOR]

The prediction skill and source of the predictability of the East Asian summer monsoon (EASM) system are examined in this work based on four state‐of‐the‐art seasonal climate forecast models including BCC_CSM1.1, ECMWF_SYS4, NCEP_CFS2 and TCC_CPS2. The prediction of the climatology and interannual EASM pattern and the impact on the prediction are further investigated. It is noted that the four models have some skill in predicting summer rainfall in the East Asia, however, the skill is low on average and also largely regional dependence. The interannual variation of EASM measured by monsoon circulation index is well reproduced, implying that the broad‐scale feature/pattern of EASM has higher predictability than the detailed spatial variation of EASM rainfall. The possible sources of predictability of the interannual variability of EASM are associated with the El Niño‐Southern Oscillation (ENSO) and the north Indian Ocean (NIO) sea surface temperature (SST) anomalies. The correlation pattern of rainfall with the NIO SST is characterized by a tripole pattern from south to north of East Asia, which is different from the correlation distribution of the southern‐northern dipole with ENSO, suggesting that NIO SST may exert influence on the EASM independently. The major biases in climatology of EASM in the models are the northward shift of the western Pacific subtropical high (WPSH) and weak monsoonal southerly over the coast of East Asia, which leads to the prediction bias of the Meiyu/Baiu/Changma (MBC) rainfall belt. The prediction of the interannual EASM pattern presents two deficiencies: too weak rainfall variability and northward shift of the dipole rainfall pattern (opposite variation between MBC and the northwestern Pacific), that may be caused by the biases of WPSH in the models. [ABSTRACT FROM AUTHOR]

The South Asian high (SAH) and the North Pacific subtropical high (NPSH) are two crucial systems affecting the summer rainfall over East Asia. Features of the relative vorticity of the SAH and its dynamic effect on zonal extension of the western NPSH (WNPSH) are investigated on interannual timescales using data diagnosis and numerical model experiments. Results show that two climatological centres of negative relative vorticity are observed along the northern flank of the SAH over the Tibetan Plateau and northern West Asia at 200 hPa during boreal summer. The relatively more intense centre over the Tibetan Plateau (TPV) shows a pronounced southeast‐northwest (SE‐NW) variation, indicating a SE‐NW shift of the SAH. When the SAH shifts southeastward, an anomalous anticyclone occurs over eastern China at 200 hPa. In the middle troposphere, this anomalous anticyclone is located over southern China and the northern South China Sea, leading to a westward extension of the WNPSH. A diagnostic analysis of the vorticity equation indicates that the negative relative vorticity anomalies at 500 hPa are mainly caused by the downward advection of the mean relative vorticity by anomalous sinking motions. When the SAH extends southeastward, intense convergence on the southeastern flank of the anomalous upper‐level anticyclone induces descending motions that cause downward advection of mean negative vorticity. Consequently, negative vorticity anomaly is formed at 500 hPa, leading to a westward extension of the WNPSH. Results from the experiments using an idealized anomalous atmospheric general circulation model further demonstrate that the upper‐level anomalous anticyclone associated with a southeastward extension of the SAH triggers an anomalous anticyclone at the middle level, causing a westward extension of the WNPSH. [ABSTRACT FROM AUTHOR]

Land–atmosphere interaction plays an important role in regional weather and climate. Using the soil moisture (SM) data from the Global Land Data Assimilation System V2.0, the present study examines the land–atmosphere interaction during spring over the Indo-China Peninsula (ICP) and its effect on the following summer climate over the Yangtze River basin. The analyses show that the abnormal SM over the ICP in spring would significantly change the local surface air temperature by affecting the evapotranspiration. In particular, such a SM effect on the local air temperature can persist to the following summer owing to a strong ICP SM memory, which can in turn influence the East Asian summer monsoon as well as the remote precipitation and temperature over the Yangtze River basin. The persistent abnormally lower (higher) SM over the ICP induces less (more) local evapotranspiration, increasing (decreasing) the surface temperature. The resultant anomalous heating (cooling) over the ICP raises (lowers) the local geopotential height, which attracts (repels) the Western Pacific Subtropical High (WPSH) extending westward. Accompanied by an excessive westward extension of the summer WPSH, an anomalously enhanced southwesterly wind would bring more moisture to the Yangtze River basin at the lower troposphere. This situation intensifies the Meiyu front and precipitation over the Yangtze River basin. Further thermodynamic and dynamic analyses support that the monsoonal circulation anomalies associated with the westward extension of the WPSH mainly contribute to the summer precipitation anomalies over the Yangtze River basin. In addition, more precipitation accompanied with more cloud cover and less downward solar radiation that reduce the local air temperature, and vice versa. This highlights that the spring SM over the ICP is an important predictor for the following summer climate over the East Asia. The implication for predicting extreme weather events in summer over the Yangtze River basin is also discussed. [ABSTRACT FROM AUTHOR]

Data from the Global Precipitation Climatology Centre (GPCC) were used in investigating long-term variability of anomalies of the total amount of atmospheric precipitation within the Selenga river basin in July. We identified several long periods (four years and longer) with negative precipitation anomalies: 1935–1939, 1955–1958, 1977–1981, 2007–2011, and 2013–2017. The last period is characterized by the smallest precipitation amount. Day-to-day variations in total precipitation were also analyzed for each July from 1982 to 2016. The analysis revealed a tendency to a decrease of the number of days with a large precipitation amount and to an increase of dry periods. Based on ECMWF Era Interim data, we examined the features in the atmospheric blocking Europe, Siberia and the Far East for periods with large and small precipitation amounts within the Selenga river basin. To identify the blocking in the atmosphere used the southern gradient of the geopotential. It was shown that in periods with large precipitation amounts blockings occurred most frequently over Eastern Siberia and more rarely over Europe and the Far East (especially if they were accompanied by blocking over Western Siberia). Atmospheric precipitation within the Selenga basin is associated not only with blocking but also with the position of the jet stream and with dynamic blocking formation schemes. The significance of these factors has been demonstrated in a number of specific situations of the atmospheric circulation in years with large and small precipitation amounts within the Selenga basin. Long-term transformations of these characteristics caused by climate change and the general atmospheric circulation can lead to a disturbance of the correlations between blocking and precipitation amounts within the river basin. In all likelihood, the correlation of blocking with precipitation regimes, rather than with precipitation in the region, will be more rigid. A functional dependence of the Selenga flow on climate change appears to be determined by the position of the monsoon front and by the wave properties of atmospheric flows in midlatitudes. [ABSTRACT FROM AUTHOR]

The abilities of three models (Climate Forecast System version 2 [CFSv2], Canadian Coupled Climate Model version 3 [CanCM3] and Canadian Coupled Climate Model version 4 [CanCM4]) in the North American Multimodel Ensemble for the East Asian summer monsoon (EASM) forecast were evaluated with their 29‐year hindcast data (1982–2010). Many EASM features including monsoon precipitation centres, large‐scale monsoon circulations and monsoon onset and retreat are generally captured by the three models and their ensemble mean, and the multimodel ensemble has the best performance. Since the East Asian domain includes the tropical western North Pacific summer monsoon (WNPSM) and the subtropical continent monsoon, two well‐known monsoon indices, the WNPSM index (WNPSMI) and EASM index (EASMI), and their associated low‐level winds and precipitation anomalies are well forecasted by the models. However, the forecast performance generally decreases as the leads increase, and the performance of EASMI is not as good as that of WNPSMI. CFSv2 forecasts well at leads up to 6 months whereas the skill of CanCM3 (CanCM4) decreases rapidly when the lead increases to 2 months (3 months). The failure of CanCM3 is mainly attributed to the poor forecast of the relationship of EASMI with the El Niño‐Southern Oscillation and Northern Indian Ocean‐western North Pacific (WNP) sea surface temperature anomaly. However, the causes of the poor forecast of CanCM4 for EASMI require further investigation. Sources of the forecast error (FE), which is the difference between model and observation for monsoon precipitation, are more significant than those of the predictability error (PE), which originates from the initial condition error, indicating that model deficiency plays a dominant role in limiting the EASM precipitation forecast. However, the PE cannot be neglected over the tropical western Pacific in CFSv2, over the WNP in CanCM3 and over the Tibetan Plateau in CanCM4. As the lead time increases, the FE does not remarkably change whereas the PE decreases significantly. [ABSTRACT FROM AUTHOR]

Anthropogenic aerosols (AA) can affect cloud and precipitation through aerosol–radiation interaction (ARI) and aerosol–cloud interaction (ACI). Over the past few decades, anthropogenic aerosol emissions have exhibited remarkable changes in the magnitude and in spatial pattern. The most significant changes are the increased emissions over both South Asia and East Asia. In this study, the atmospheric component of a state-of-the-art climate model that includes eight species of tropospheric aerosols, coupled to a multi-level mixed-layer ocean model, has been used to investigate the impacts of Asian anthropogenic aerosol precursor emission changes from 1970s to 2000s on large scale circulation and precipitation in boreal summer over East Asia. Results reveal significant changes in circulation and clouds over East Asia and over the tropical and western North Pacific (WNP). Increased Asian AA emissions lead to anomalous cyclonic circulation over the Maritime continent (MC) and anomalous anticyclonic circulation over the WNP, resulting in anomalous moisture transport convergence over the MC and therefore increased precipitation. They also lead to anomalous moisture flux divergence over both the WNP and large land areas of East Asia, especially over northern China, and therefore decreased precipitation there. These large scale circulation anomalies over the adjacent oceans are related to aerosol change induced ocean feedbacks, predominantly through ACI. It is the slow responses over the adjacent oceans (e.g., SST changes) through coupled atmosphere–ocean interaction in pre-monsoon seasons and summer that shape the changes of the East Asian summer monsoon and local precipitation. The results in this study suggest that increased Asian AA emissions from 1970s to 2000s may have played an important role for the observed southward shift of the Pacific intertropical convergence zone and precipitation belt, weakening of East Asian summer monsoon and reduced precipitation over northern China in East Asia during the latter half of the twentieth century. [ABSTRACT FROM AUTHOR]

As a unique continental archive, speleothem has been widely used in reconstructing paleoclimate change. However, the interpretation of Chinese speleothems δ18O has remained a subject of debate. Recently, a Community Atmosphere Model version 3 (CAM3) study indicated that the stalagmite δ18O from eastern China reflected the Indian summer monsoon (ISM) intensity rather than the East Asian summer monsoon (EASM) intensity during Heinrich events. Here, we present a high-resolution speleothem δ18O record from Xianglong Cave in Shaanxi province, China, covering the period of 25.5–10.9 ka BP. The XL15 record shows similar variations with ice core record from Greenland and other climate records from China and India on millennial scale, including Heinrich 2 (H2), Heinrich 1 (H1), Bølling–Allerød (BA) and Younger Dryas (YD) events, supporting the connection between the Asian monsoon and northern high latitude climate. The δ18O amplitude of our record is larger than or similar to the stalagmite δ18O records from India during these events. In addition, differences of stalagmite δ18O in eastern China and the ISM region were observed on glacial-interglacial as well as decadal timescales. That means the ISM is not the sole controlling factor of Chinese stalagmite δ18O during Heinrich events. When subtracting the Indian stalagmite δ18O series from our XL15 record during H1 period, we found a significant negative correlation with sea surface temperature (SST) record of Western Pacific Warm Pool (WPWP). Consequently, our study suggests that the Chinese stalagmite δ18O is controlled by both the ISM and EASM on orbital-, millennial-, and decadal timescales. [ABSTRACT FROM AUTHOR]

Summer precipitation in the north fringe of East Asian Summer Monsoon (NFEASM) accounts for the majority of annual regional precipitation and plays an important role in regional climatology and agriculture development. Here we analyze variations in summer precipitation in the NFEASM over the past millennium using several simulations with Earth System Models and compare with two dendroclimatological hydroclimate reconstructions that partly cover the past millennium. Both reconstructed records show good agreement on past hydroclimate variations but do not show overly anomalous hydroclimate periods, except for clear drying trends in the second half of the twentieth century. The reconstructed decadal hydroclimate variations are not correlated with any of the simulations, and the simulations are not correlated among themselves either, which strongly suggests that the decadal variability is not linked to the external climate forcing. In addition, the superposed epoch analysis also does not identify a response of simulated precipitation to volcanic eruptions. Therefore, precipitation variability in this region over the past millennium seems to have been driven by internal climate processes. In the simulations, regional summer precipitation is positively and significantly correlated with sea-level-pressure (SLP) over the North Pacific and is negatively and significantly correlated with SLP in southwestern China at both interannual and decadal time scales. This agrees with the teleconnection patterns identified from meteorological reanalysis datasets, indicating that this dipole correlation pattern is robust. Therefore, the SLP difference between these two areas is used as an index to identify the atmosphere circulation pattern favorable to summer precipitation in the NFEASM. This SLP index shows spatial variable correlations with sea-surface-temperature (SST) in the North Pacific: there is a significant positive correlation in the northern North Pacific, while a significant negative correlation in the southern North Pacific. Although the underlying mechanisms for these correlations likely differ between two subareas, it appears that the atmosphere drives SST anomalies in the both subareas. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) has significant impacts on local and global hydrological and climatic systems. However, most current atmospheric and coupled models have difficulty in capturing the climatological mean state of the EASM. The present study investigated the possible improvement of EASM simulation via coupling the Stochastic Multicloud Model (SMCM) to the state-of-the-art ECHAM6.3 atmosphere model. Evaluated by the pattern correlation coefficient and root-mean-square error, the modified ECHAM6.3, i.e., with SMCM coupling, showed better performance in simulating the EASM in terms of the precipitation pattern and intensity, the pattern of the western North Pacific subtropical high, the monsoon onset, and its seasonal evolution. Analyses also revealed that the modified ECHAM6.3 outperformed the default ECHAM6.3 in terms of large-scale circulation and vertically integrated moisture transport. Finally, it was that the intensified land–sea thermal contrast in both the meridional and zonal directions, as well as the stronger meridional temperature gradient in the upper troposphere and enhanced diabatic heating over the Tibetan Plateau, which are associated with the stochastic cloud, were the main reasons for the better performance of the modified ECHAM6.3 in simulating the EASM. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) shows notable change during the summer after El Niño peak. This "delayed" response, however, is variable and difficult to predict. Here, we revisit this issue by separating El Niño decays into early transition and late transition. In the summer after an early transition, the central-to-eastern Pacific evolves into a La Niña condition, with positive rainfall anomaly occurring over most parts of eastern China. In contrast, in the summer after a late transition, the central-to-eastern Pacific sea surface temperature (SST) anomaly remains neutral or slightly above normal; correspondingly, the East Asian rainfall anomaly shows a tripolar structure with positive anomaly over the Yangtze-Huaihe River valley and negative anomalies over northern and southern China. These different rainfall responses are mainly related to different locations of the anomalous anticyclone (AAC) over the western North Pacific (WNP): it is centered at (165°E, 25°N) for late-transition El Niños, but at (135°E, 16°N) for early-transition El Niños. During the late transition, the AAC–SST feedback, identified by the dipole SST mode consisting of WNP cooling and northern Indian Ocean (NIO) warming, mainly works to support the WNP AAC. During the early transition, the AAC–SST feedback is weak and mainly attributed to NIO warming. The strong easterly anomaly over the western equatorial Pacific, which is tied to the central-to-eastern equatorial Pacific cooling and dipole precipitation pattern from western equatorial Pacific to the Maritime Continent, occurs to support the AAC and pulls it equatorward. These distinct responses exist in the last century, and the CMIP5 models can reproduce these distinct responses well except that the models underestimate the AAC–SST feedback for late-transition El Niños. The findings in this study help predict the EASM rainfall in post-El Niño years, but the key is the accurate prediction of the timing of decay. [ABSTRACT FROM AUTHOR]

Using the data from ERA‐interim, the Hadley Centre Global Sea Surface Temperature data set, and the Climate Prediction Center Merged Analysis of Precipitation, after removing the simultaneous El Niño and Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) signals, we have investigated variations of anomalous convergence around Kalimantan Island in lower troposphere in associations with the East Asian summer and Australian winter monsoons. Results indicate that when negative sea surface temperature anomalies appear in the western Pacific on both sides of the equator, the atmospheric cooling over the northwestern Pacific and from the South Pacific Convergence Zone (SPCZ) to Australia is favorable for the maintenance of anticyclonic anomalies over the areas from the western Pacific to the South China Sea and from the south of the equator to the northeast of Australia. These anomalous anticyclonic circulations can induce equatorial easterly anomalies, which subsequently facilitate the maintenance of anomalous convergence around Kalimantan Island. In turn, the anomalous convergence in Kalimantan Island is favorable for the maintenance of anomalous anticyclonic over the northwestern Pacific and SPCZ and thereby intensifies both the western Pacific subtropical high and the Australian High, inducing concurrent intensifications of the East Asian summer monsoon and Australian winter monsoon. Related to the anomalous convergence over Kalimantan Island, precipitation and temperature decrease from the western Pacific to SPCZ but increase from the Indian Ocean to western Maritime Continent and Australia, while temperature is lower than normal in Kalimantan. The above results have remarkable implications for in‐depth understanding of the mechanism behind anomalies of the East Asian summer monsoon and Australian winter monsoon. Key Points: The anomalous convergence in Kalimantan Island is related to the forcing of SST anomalies in the Pacific and Indian OceanThe convergence anomaly in Kalimantan Island is highly correlated with anomalous activities of the Australian High and the WPSHCirculation anomalies related to the anomalous convergence in Kalimantan Island would affect climate variations in East Asia and Australia [ABSTRACT FROM AUTHOR]

In order to study the spatial structure and dynamical mechanism of extreme precipitation in East Asia, a corresponding climate network is constructed by employing the method of event synchronization. It is found that the area of East Asian summer extreme precipitation can be separated into two regions: one with high area-weighted connectivity receiving heavy precipitation mostly during the active phase of the East Asian Summer Monsoon (EASM), and another one with low area-weighted connectivity receiving heavy precipitation during both the active and the retreating phase of the EASM. Besides, a new way for the prediction of extreme precipitation is also developed by constructing a directed climate networks. The simulation accuracy in East Asia is 58% with a 0-day lead, and the prediction accuracy is 21% and average 12% with a 1-day and an n-day (2≤n≤10) lead, respectively. Compared to the normal EASM year, the prediction accuracy is low in weak years and high in strong years, which is relevant to the differences of correlations and extreme precipitation rates in different EASM situations. Recognizing and indentifying these effects is good for understanding and predicting extreme precipitation in East Asia. [ABSTRACT FROM AUTHOR]

Glacial-interglacial changes in the distribution of C3/C4 vegetation on the Chinese Loess Plateau have been related to East Asian summer monsoon intensity and position, and could provide insights into future changes caused by global warming. Here, we present δ13C records of bulk organic matter since the Last Glacial Maximum (LGM) from 21 loess sections across the Loess Plateau. The δ13C values (range: -25%o to -16%o) increased gradually both from the LGM to the mid-Holocene in each section and from northwest to southeast in each time interval. During the LGM, C4 biomass increased from <5% in the northwest to 10-20% in the southeast, while during the mid-Holocene C4 vegetation increased throughout the Plateau, with estimated biomass increasing from 10% to 20% in the northwest to >40% in the southeast. The spatial pattern of C4 biomass in both the LGM and the mid-Holocene closely resembles that of modern warm-season precipitation, and thus can serve as a robust analog for the contemporary East Asian summer monsoon rain belt. Using the 10-20% isolines for 4 biomass in the cold LGM as a reference, we derived a minimum 300-km northwestward migration of the monsoon rain belt for the warm Holocene. Our results strongly support the prediction that Earth's thermal equator will move northward in a warmer world. The southward displacement of the monsoon rain belt and the drying trend observed during the last few decades in northern China will soon reverse as global warming continues. [ABSTRACT FROM AUTHOR]

The interdecadal variation of the western Pacific subtropical high (WPSH) in summer (June-July-August) during 1979-2009 relative to 1948-1978 was investigated based upon NCEP-NCAR reanalysis data. Since the WPSH appeared to be much more stable and stronger in the lower troposphere compared to the middle troposphere and had great influences on the East Asian summer climate with the lower-level southerlies or southwesterlies at its western and southern edge, the interdecadal changes of the WPSH at low levels were examined in this study. Over the area of interest (~15°-30°N, 120°-150°E), the 850-hPa anticyclone circulation was weakened, the sea level pressure decreased, the relative vorticity at middle and lower levels (1,000-600 hPa) increased, and the maximum meridional wind at each latitude (between 17.5° and 32.5°N) moved eastward. All the above decadal variations suggested that the WPSH recessed eastward during 1979-2009 relative to 1948-1978, which can be displayed in the 850-hPa eddy geopotential height field. In association with the eastward recession of the WPSH, the water vapor transport from the Indian summer monsoon played a more important role in the summer precipitation over the middle and lower reaches of the Yangtze River valley during 1979-2009 relative to 1948-1978. [ABSTRACT FROM AUTHOR]

The spatial patterns and regional-scale surface air temperature (SAT) changes during the last millennium, as well as the variability of the East Asian summer monsoon (EASM) were simulated with a low-resolution version of Flexible Global Ocean-Atmosphere-Land-Sea-ice (FGOALS-gl) model. The model was driven by both natural and anthropogenic forcing agents. Major features of the simulated past millennial Northern Hemisphere (NH) mean SAT variations, including the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the 20th Century Warming (20CW), were generally consistent with the reconstructions. The simulated MCA showed a global cooling pattern with reference to the 1961-90 mean conditions, indicating the 20CW to be unprecedented over the last millennium in the simulation. The LIA was characterized by pronounced coldness over the continental extratropical NH in both the reconstruction and the simulation. The simulated global mean SAT difference between the MCA and LIA was 0.14°C, with enhanced warming over high-latitude NH continental regions. Consistencies between the simulation and the reconstruction on regional scales were lower than those on hemispheric scales. The major features agreed well between the simulated and reconstructed SAT variations over the Chinese domain, despite some inconsistency in details among different reconstructions. The EASM circulation during the MCA was stronger than that during the LIA The corresponding rainfall anomalies exhibited excessive rainfall in the north but deficient rainfall in the south. Both the zonal and meridional thermal contrast were enhanced during the MCA. This temperature anomaly pattern favored a stronger monsoon circulation. [ABSTRACT FROM AUTHOR]

This study focuses on the intraseasonal variation of the East Asian summer monsoon (EASM) simulated by IAP AGCM 4.0, the fourth-generation atmospheric general circulation model recently developed at the Institute of Atmospheric Physics, Chinese Academy of Sciences. In general, the model simulates the intraseasonal evolution of the EASM and the related rain belt. Besides, the model also simulates the two northward jumps of the western Pacific subtropical high (WPSH), which are closely related to the convective activities in the warm pool region and Rossby wave activities in high latitudes. Nevertheless, some evident biases in the model were found to exist. Due to a stronger WPSH, the model fails to simulate the rain belt in southern China during May and June. Besides, the model simulates a later retreat of the EASM, which is attributed to the overestimated land-sea thermal contrast in August. In particular, the timing of the two northward jumps of the WPSH in the model is not coincident with the observation, with a later jump by two pentads for the first jump and an earlier jump by one pentad for the second, i.e., the interval between the two jumps is shorter than the observation. This bias is mainly ascribed to a shorter oscillating periodicity of convection in the tropical northwestern Pacific. [ABSTRACT FROM AUTHOR]

The variability of the East Asian winter monsoon (EAWM) can be divided into an ENSO-related part (EAW) and an ENSO-unrelated part (EAWM). The influence of EAWM on the ENSO-East Asian summer monsoon (EASM) relationship in the decaying stages of ENSO is investigated in the present study. To achieve this, ENSO is divided into four groups based on the EAWM: (1) weak EAWM-El Niño (WEAWM-EN); (2) strong EAWM-El Niño (SEAWM- EN); (3) weak EAWM-La Niña (WEAWM-LN); (4) strong EAWM-La Niña (SEAWM-LN). Composite results demonstrate that the EAWM may enhance the atmospheric responses over East Asia to ENSO for WEAWM-EN and SEAWM-LN. The corresponding low-level anticyclonic (cyclonic) anomalies over the western North Pacific (WNP) associated with El Niño (La Niña) tend to be strong. Importantly, this feature may persist into the following summer, causing abundant rainfall in northern China for WEAWM-EN cases and in southwestern China for SEAWM-LN cases. In contrast, for the SEAWM-EN and WEAWM-LN groups, the EAWMres tends to weaken the atmospheric circulation anomalies associated with El Niño or La Niña. In these cases, the anomalous WNP anticyclone or cyclone tend to be reduced and confined to lower latitudes, which results in deficient summer rainfall in northern China for SEAWM-EN and in southwestern China for WEAWM-LN. Further study suggests that anomalous EAWM may have an effect on the extra-tropical sea surface temperature anomaly, which persists into the ensuing summer and may interfere with the influences of ENSO. [ABSTRACT FROM AUTHOR]

East Asia has experienced a significant interdecadal climate shift since the late 1970s. This shift was accompanied by a decadal change of global SST. Previous studies have suggested that the decadal shift of global SST background status played a substantial role in such a climatic shift. However, the individual roles of different regional SSTs remain unclear. In this study, we investigated these roles using ensemble experiments of an atmospheric general circulation model, GFDL (Geophysical Fluid Dynamics Laboratory) AM2. Two kinds of ensembles were performed. The first was a control ensemble in which the model was driven with the observed climatological SSTs. The second was an experimental ensemble in which the model was driven with the observed climatological SSTs plus interdecadal SST background shifts in separate ocean regions. The results suggest that the SST shift in the tropics exerted more important influence than those in the extratropics, although the latter contribute to the shift modestly. The variations of summer monsoonal circulation systems, including the South Asian High, the West Pacific Subtropical High, and the lower-level air flow, were analyzed. The results show that, in comparison with those induced by extratropical SSTs, the shifts induced by tropical SSTs bear more similarity to the observations and to the simulations with global SSTs prescribed. In particular, the observed SST shift in the tropical Pacific Ocean, rather than the Indian Ocean, contributed significantly to the shift of East Asian summer monsoon since the 1970s. [ABSTRACT FROM AUTHOR]

Future change in precipitation intensity of East Asian summer monsoon is investigated using the present-day climate simulations (1991-2000) and the future climate simulations (2091-2100, A1B emission scenario) by the Couple Model Intercomparison Project 3 (CMIP3) models. Target period is the month from June to July which is the main part of the rainy season over Japan and Korea. In the present-day climate simulations, we have quantitatively evaluated model's reproducibility of precipitation climatology and Simple Daily precipitation Intensity Index (SDII), using skill S proposed by Taylor (J Geophys Res 106:7183-7192, ). Models with higher reproducibility of precipitation climatology tend to show higher reproducibility of precipitation intensity. In the future climate simulations, simple Multi-Model Ensemble (MME) average using all models show the increase of precipitation intensity over almost all regions of East Asia. Introduction of S as weighting factor does not make large difference in the geographical distribution of precipitation intensity change. In case of MME using five best models, the geographical pattern of precipitation intensity change is qualitatively similar to that using all models, but the local magnitude of changes are much affected by the best model. In order to interpret future change in precipitation climatology and SDII, we have calculated change in vertically integrated horizontal transport of moisture. Changes in precipitation climatology and SDII can be interpreted as the moisture convergence change associated with change in horizontal transport of moisture. Large moisture convergence was found due to either intensification or weakening of subtropical high depending on models. [ABSTRACT FROM AUTHOR]

Global warming projection experiments were conducted using a 20-km mesh global atmospheric model, focusing on the change in the rain band of East Asian summer monsoon. To assess the uncertainty of climate change projections, we performed ensemble simulations with the 60-km resolution model combining four different SSTs and three atmospheric initial conditions. In the present-day climate simulations, the 20-km model reproduces the rain band of East Asian summer monsoon better than lower resolution models in terms of geographical distribution and seasonal march. In the future climate simulation by the 20-km model, precipitation increases over the Yangtze River valley in May through July, Korean peninsula in May, and Japan in July. The termination of rainy season over Japan tends to be delayed until August. Ensemble simulations by the 60-km model show that precipitation in the future climate for July increases over the Yangtze River valley, the East China Sea and Japan. These changes in precipitation are partly consistent with those projected by the 20-km model. Simulations by the 20-km and 60-km models consistently show that in the future climate the termination of rainy season over Japan tends to be delayed until August. The changes in the vertically integrated water vapor flux show the intensification of clockwise moisture transport over the western Pacific subtropical high. Most precipitation changes over the East Asia can be interpreted as the moisture convergence resulting from change in the horizontal transport of water vapor. [ABSTRACT FROM AUTHOR]

In the present study the links between spring Arctic Oscillation (AO) and East Asian summer monsoon (EASM) was investigated with focus on the importance of the North Pacific atmospheric circulation and sea surface temperature (SST). To reduce the statistical uncertainty, we analyzed high-pass filtered data with the inter-annual time scales, and excluded the El Niño/Southern Oscillation signals in the climate fields using a linear fitting method. The significant relationship between spring AO and EASM are supported by the changes of multi-monsoon components, including monsoon indices, precipitation, and three-dimensional atmospheric circulations. Following a stronger positive spring AO, an anomalous cyclonic circulation at 850 hPa appears in southeastern Asia and the western North Pacific in summer, with the easterly anomalies spanning from the Pacific to Asian continent along 25°N-30°N and the westerly anomalies south of 15°N. At the same time, the summer western North Pacific subtropical high becomes weaker. Consistently, the positive precipitation anomalies are developed over a broad region south of 30°N stretching from southern China to the western Pacific and the negative precipitation anomalies appear in the lower valley of the Yangtze River and southern Japan. The anomalous cyclone in the western North Pacific persisting from spring to summer plays a key role in modulating EASM and monsoon precipitation by a positive air-sea feedback mechanism. During spring the AO-associated atmospheric circulation change produces warmer SSTs between 150°E-180° near the equator. The anomalous sensible and latent heating, in turn, intensifies the cyclone through a Gill-type response of the atmosphere. Through this positive feedback, the tropical atmosphere and SST patterns sustain their strength from spring to summer, that consequently modifies the monsoon trough and the western North Pacific subtropical high and eventually the EASM precipitation. Moreover, the SST response to AO-circulation is supported by the numerical simulations of an ocean model, and the anomalous atmospheric circulation over the western North Pacific is also reproduced by the dedicated numerical simulations using the coupled atmosphere-ocean model. The observation evidence and numerical simulations suggest the spring AO can impact the EASM via triggering tropical air-sea feedback over the western North Pacific. [ABSTRACT FROM AUTHOR]

The centennial-millennial variation of the East Asian summer monsoon (EASM) precipitation over the past 1000 years was investigated through the analysis of a millennium simulation of the coupled ECHO-G model. The model results indicate that the centennial-millennial variation of the EASM is essentially a forced response to the external radiative forcing (insolation, volcanic aerosol, and green house gases). The strength of the response depends on latitude; and the spatial structure of the centennial-millennial variation differs from the interannual variability that arises primarily from the internal feedback processes within the climate system. On millennial time scale, the extratropical and subtropical precipitation was generally strong during Medieval Warm Period (MWP) and weak during Little Ice Age (LIA). The tropical rainfall is insensitive to the effective solar radiation forcing (insolation plus radiative effect of volcanic aerosols) but significantly responds to the modern anthropogenic radiative forcing. On centennial time scale, the variation of the extratropical and subtropical rainfall also tends to follow the effective solar radiation forcing closely. The forced response features in-phase rainfall variability between the extratropics and subtropics, which is in contrast to the anti-correlation on the interannual time scale. Further, the behavior of the interannual-decadal variation in the extratropics is effectively modulated by change of the mean states on the millennial time scale, suggesting that the structure of the internal mode may vary with significant changes in the external forcing. These findings imply that on the millennial time scale, (a) the proxy data in the extratropical EA may more sensitively reflect the EASM rainfall variations, and (b) the Meiyu and the northern China rainfall provide a consistent measure for the EASM strength. [ABSTRACT FROM AUTHOR]

Relationship between the Southern Hemisphere upper troposphere zonal wind variability and the East Asian summer monsoon was studied. The mean zonal wind difference in 150 hPa between 60°S and 30°S is defined as an index (ISH). The research reveals that ISH is negatively correlated with the East Asian summer monsoon (EASM) circulation in the interannual scale. It is also suggested that the meridional teleconnection in the zonal wind field, with the main part in Eastern Hemisphere, from mid-and-high latitudes in the Southern Hemisphere to the tropical region is responsible for the ISH-EASM linkage. The teleconnection may result in changes of the wind fields and pressure system changes causing variability of the East Asian monsoon. In addition, the anomalous teleconnection pattern in Eurasia is likely to be another mechanism. ISH and EASM circulation are found to have both simultaneous and lag correlations, thus, the relationship has implications for seasonal climate prediction over East Asia. [ABSTRACT FROM AUTHOR]

Although some studies reported the impact of black carbon (BC) on the climate over the Tibetan Plateau (TP), the contribution and mechanisms of BC affecting the water vapor transport to Tibet are not fully understood yet. Here, utilizing the satellite observations and reanalysis data, the effects of BC on the climate over the TP and water vapor transport to the Tibet were investigated by the Community Earth System Model (CESM 2.1.0). Due to the addition of BC, a positive net heat forcing (average is 0.39 W/m2) is exerted at the surface, which induces a pronounced warming effect over the TP and consequently intensifies the East Asian Summer monsoon (EASM). However, significant cooling effects in northern India, Pakistan, Afghanistan and Iran are induced due to the BC and related feedbacks, which reduces significantly the meridional land–sea thermal contrast and finally weakens the South Asian summer monsoon (SASM). Consequently, the water vapor transport to the south border will be decreased due to addition of BC. Moreover, through affecting the atmospheric circulation, the BC could induce an increase in the imported water vapor from the west and east borders of the TP, and an increase outflowing away from the north border of the TP. Overall, due to the BC, the annual mean net importing water vapor over TP is around 271 Gt, which could enhance the precipitation over the TP. The results show that the mean increase in the precipitation over TP is about 0.56 mm/day. [ABSTRACT FROM AUTHOR]

In this study, the atmospheric moisture transport involved in the East Asian summer monsoon (EASM) water cycle is examined. Observational estimates are contrasted with the Met Office Unified Model (MetUM) climate simulations to evaluate the model's ability to capture this transport. We explore the role of large circulation in determining the regional water cycle by analyzing key systematic errors in the model. MetUM exhibits robust errors in its representation of the summer Asian-Pacific monsoon system, including dry biases in the Indian peninsula and wet biases in the tropical Indian Ocean and tropical West Pacific. Such errors are consistent with errors in the atmospheric moisture convergence in the area. Diabatic heating biases in the Maritime Continent domain are shown, via nudging sensitivity experiments, to play a crucial role in remotely forcing the model circulation and moisture transport errors in the East Asian area. We also examine changes in the regional water cycle in response to interannual variability of the West Pacific subtropical high (WPSH). It is shown by water budget analysis that, although the model in general is not able to faithfully reproduce the response on a month to month basis, it gives comparable seasonal trends in regional moisture convergence and precipitation associated with shifts of the WPSH. [ABSTRACT FROM AUTHOR]

The Plum Rains process is a complex process, and its spatiotemporal variations and influencing factors on different time scales still need further study. Based on a dataset on the Plum Rains in the Yangtze River Delta, from 33 meteorological stations during the period of 1960 to 2012, we investigated the spatiotemporal variations of Plum Rains and their relation with the East Asian Summer Monsoon (EASM), the El Niño-Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO) using an integrated approach that combines ensemble empirical mode decomposition (EEMD), empirical orthogonal function (EOF), and correlation analysis. The main conclusions were as follows: (1) the plum rainfall (i.e., the rainfall during the period of Plum Rains) showed a trend of increasing first and then decreasing, and it had a three-year and six-year cycle on the inter-annual scale and a 13-year and 33-year cycle on the inter-decadal scale. The effect of the onset and termination of Plum Rains and the daily intensity of plum rainfall on plum rainfall on the inter-annual scale was greater than the inter-decadal scale, (2) the EOF analysis of plum rainfall revealed a dominant basin-wide in-phase pattern (EOF1) and a north-south out-of-phase pattern (EOF2), and (3) ENSO and EASM were the main influencing factors in the three-year and six-year periods, respectively. [ABSTRACT FROM AUTHOR]

Excessive rainfall was observed over Southwest China in July 2018, leading to floods in several major tributaries of the Yangtze River and landslide and debris flow in the neighboring provinces. The rainfall during 7–11 July was unusually heavy and broke the record that can be traced back to 1961. The occurrence of the excessive rain can be attributed to the anomalous convection over the western North Pacific and the presence of a mid-latitude Rossby wave train. On one hand, the convection over the western North Pacific was anomalously strong in July 2018, and it could have excited the negative phase of the Pacific–Japan pattern and led to a northwestward shift of the western Pacific subtropical high. Hence, the water vapor transport toward inland China including Southwest China was enhanced, providing a favorable moisture environment for precipitation. On the other hand, a mid-latitude Rossby wave train was observed to propagate from Northern Europe towards East Asia, which was conducive to anomalous ascending motion over Southwest China via warm advection and differential vorticity advection, creating a favorable dynamical condition for precipitation. As a result, the combination of the two effects mentioned above led to the occurrence of the flood over Southwest China in July 2018. [ABSTRACT FROM AUTHOR]