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The South China Sea summer monsoon (SCSSM) onset and withdrawal have critical impacts on the climate of East Asia. However, using different reanalysis data may lead to the uncertainty of the SCSSM. This study uses reanalysis datasets including JRA‐55, ERA5, NCEP‐NCAR NCEP‐1 and NCEP‐DOE NCEP‐2 to calculate onset and withdrawal dates and index of SCSSM from 1991 to 2020, analyses the uncertainty and figures out the possible reasons. Results reveal that the four reanalysis datasets have obvious uncertainty in calculating the withdrawal date of SCSSM, with the deviation being up to 3.4 pentads. Further analysis shows that large differences in thermal conditions and lead to the uncertainties. From the perspective of precipitation, Greater uncertainty exists in the relationship between monsoon retreat and September–October precipitation, NCEP1 and NCEP2 datasets show weak correlation in southern China and Indonesia. Moreover, the uncertainty can be also found in the correlations of SCSSM with global sea surface temperature (SST) anomalies. JRA‐55 and ERA5 show a strong correlation of with SST in several areas, and exhibit a distinct Pacific decadal oscillation (PDO) mode with monsoon onset, while NCEP‐1 and NCEP‐2 have a weaker correlation with SST anomalies than JRA‐55 or ERA5. Comparing multiple factors comprehensively, this paper concludes that JRA‐55 may be more representative in the monsoon study, followed by ERA data. In short, depending on the specific research questions, researchers can choose appropriate data sources to study the SCSSM based on the different aspects and the uncertainty also deserve our special attention when selecting the reanalysis datasets. [ABSTRACT FROM AUTHOR]

In this paper, the physical processes underlying recent winter cold anomalies over East Asia (EA) are examined via statistical analysis. It is found that the EA cold anomaly depends on the warming in the North Atlantic, sea ice loss in the Barents–Kara Sea (BKS), and atmospheric teleconnection patterns. Specifically, the sea ice loss in the BKS can anchor teleconnection patterns originating from different North Atlantic sea surface temperature (SST) patterns. Different patterns of North Atlantic warming can affect the position of the cold anomaly region through altering the atmospheric circulations. In addition, whether the relevant teleconnection pattern leads to enhanced cold anomaly over EA crucially depends on the sea ice loss in the BKS, because it can anchor the blocking anticyclone embedded in the teleconnection pattern over the Ural region and make it more persistent and quasi‐stationary. Furthermore, it is found that the role of SST modes in the EA cold anomaly depends on their time scales. Although the strong basin‐scale warming (north–south SST tripolar mode) in the North Atlantic mid‐ to high‐latitudes plays a major role in decadal (interannual) cold anomaly over EA, it appears that the Atlantic east–west SST dipole structure dominates winter temperature variations over EA in recent decades on both the interannual and decadal time scales. [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]

Autumn precipitation in the central region of China (APCC) can considerably influence on agricultural production and human livelihood. With reanalysis data from 1979 to 2020, it revealed that APCC is significantly affected by the second mode of the meridional wind field at 200 hPa over the Eurasian continent on the interannual scale, which featured a quasi‐barotropic "+‐+" wave‐like pattern from Europe to China (EC pattern) in extratropical zone. When the EC pattern is in a positive phase, central China lags behind the downstream positive geopotential height (anticyclone) anomaly. In this context, the transport of moisture from the south and east is enhanced and the advancement of the southerly monsoon is blocked, providing sufficient water vapor to support the occurrence of APCC. Further diagnosis revealed that local ascending motion is strengthened owing to the warm advection induced by anomalous southerly and positive vorticity advection associated with the anomalous anticyclone over East Asia. Additionally, wave flux analysis and model simulation suggest that the EC pattern results from the propagation of stationary Rossby wave, which could be excited by dipole sea surface temperature anomalies in the North Atlantic. These discoveries will contribute to improving the predictability of APCC. Plain Language Summary: The interannual variability of autumn precipitation in central China (APCC) is largely affected by a wave train over the Eurasian continent (EC pattern), which can influence the local moisture and dynamic uplift conditions by an anomalous anticyclone over East Asia. The North Atlantic dipole sea surface temperatur anomalies play an important role in the prediction of APCC, and could stimulate an extratropical teleconnection to shape the EC pattern over the Eurasian continent, as confirmed in the linear baroclinic model. Key Points: The autumn rainfall in central China is related to the second mode of V200 (EOF2) over the Eurasian continent on interannual timescaleEOF2 features in a "+‐+" wave‐like pattern, resulting in an anticyclone anomaly over East Asia in its positive phaseExtratropical EOF2 pattern wave train could be excited by the North Atlantic dipole sea surface temperature anomaly [ABSTRACT FROM AUTHOR]

In the background of long‐term global warming, the northern hemisphere experienced an extremely hot summer in 2022 with the hottest on record for Europe and China, and the second‐hottest for North America and Asia. The hot summer concurred with a triple‐dip La Niña in the tropical Pacific. Given the extremity of the hot summer in East Asia in 2022, in this work, we examine the associated atmospheric circulation and assess the real‐time predictions from the North American Multimodel Ensemble (NMME). Also, we identify the contributions of long‐term warming trends, sea surface temperature (SST) forcing, and an atmospheric feedback to the hot summer. The hot summer in East Asia in 2022 is due to the extremely strong and westward expanded western Pacific subtropical high. That leads to cloud cover reduction and increases in net downward shortwave radiation at the surface, and further strengthens the positive surface air temperature (SAT) anomalies. In contrast, the seasonal‐interannual variation of SST has a minor impact. Thus, the hot summer is mainly associated with the long‐term trend and amplified by the positive feedback among the SAT, cloud cover, and net downward shortwave radiation. NMME with the initial conditions in May 2022 predicts positive SAT anomalies in most regions of East Asia, but does not capture the observed spatial distribution pattern and amplitudes. The failure implies the challenge of state‐of‐the‐art climate models in predicting such extreme events. Plain Language Summary: In the context of global warming, the northern hemisphere experienced an extremely hot summer in 2022 with the hottest on record for Europe and China. The hot summer concurred with a triple‐dip La Niña in the tropical Pacific during 2020–2023. In this work, we examine the causes and assess the real‐time predictions and predictability of the hot summer in East Asia. The hot summer in 2022 is due to the extremely strong and westward expanded western Pacific subtropical high. For the averages in the main hot summer region in East Asia in 2022, the largest contribution is from the long‐term trend (∼50%), and for the rest 50%, half of them is from the feedback among atmospheric circulation‐surface air temperature‐cloud cover‐net downward shortwave radiation. In contrast, the seasonal‐interannual components of the global sea surface temperatures play a secondary role. Multi‐model ensemble with the initial conditions in May 2022 predicts positive surface air temperature anomalies in most regions of East Asia, especially in August. However, compared with the observations, both the spatial distribution pattern of surface air temperature anomalies and their amplitudes have distinguished biases in the North American Multimodel Ensemble predictions. The failure implies the challenge of state‐of‐the‐art climate models in predicting such extreme events. Key Points: The hot summer in East Asia in 2022 is due to the extremely strong and westward expanded western Pacific subtropical highThe hot summer is caused by the long‐term trend and amplified by positive feedback among the surface air temperature (SAT), cloud, and downward shortwave radiationNorth American Multi‐model Ensemble does not capture the observed spatial distribution pattern and amplitudes of SAT anomalies [ABSTRACT FROM AUTHOR]

In the mid‐latitudes, the strongly meandering jet stream has contributed to worldwide weather patterns and climate variations. However, the shape variations of the jet and its climatic impacts remain unclear. In this study, we introduced an ellipse‐fitting technique to fit the high‐value wind speeds and identified the location, shape, and strength variations of the winter‐averaged North Pacific jet (NPJ). Particularly, this method has the advantage of objectively detecting the shape variations of the NPJ, including the area and orientation. Focused on the NPJ shape, the area and orientation variations are generally out‐of‐phase, leading to a large‐straight jet and a small‐tilted jet. The shape variation of the NPJ is highly linked to the variations in both mean and extreme temperatures in winter over East Asia and North America. Associated with the small‐tilted NPJ, northern East Asia and northern North America frequently suffer from warm and cold events in winter, respectively, while associated with the large‐straight NPJ, the patterns are almost opposite but with an asymmetric distribution to the small‐tilted NPJ. The distribution of the 300 hPa wind speed anomalies shows a spatial‐asymmetric feature at the exit and entrance of the NPJ. Large positive (negative) anomalies and the poleward (equatorward) shift at the NPJ exit and locations downstream (170°E−140°W) act in combination on the formation and maintenance of the large‐straight (small‐tilted) jet, which may be strongly connected with the sea surface temperature variations and synoptic‐scale transient eddy activities there. Our findings would be helpful in providing potential indicators of temperature variations. Plain Language Summary: The shape of the upper‐level jet stream is closely associated with weather and climate variations, which is not clearly understood yet. In this study, we introduced an ellipse‐fitting technique to fit high‐value wind speeds and identify the location, shape, and strength variations of the North Pacific jet (NPJ). This method has the advantage of objectively detecting characteristics of the jet stream, particularly for shape variations. The shape variations of the NPJ are closely linked to the variations both in winter mean and extreme temperature, particularly over East Asia and North America. Associated with the small‐tilted NPJ, warm events would more frequently occur in the northern part of East Asia, while cold events would easily affect northern North America. Sea surface temperature anomalies and the increased presence of surface high and low‐pressure systems around the jet exit region may have a strong connection with the different structures of the NPJ. Our findings would be helpful in providing a potential indicator of temperature variations. Key Points: An ellipse‐fitting technique has been introduced to detect the jet stream automatically and objectivelyPrimary combinations of the North Pacific jet's (NPJ's) shape include a large‐straight and small‐tilted jetVariations in the NPJ's shape are highly linked to out‐of‐phase variations in temperature extremes over East Asia and North America [ABSTRACT FROM AUTHOR]

Previous studies suggested that fast‐decay El Niño events are more favorable in generating the western North Pacific anticyclone (WNPAC) in the decaying summer. However, we found that this is not the case for all fast‐decay El Niño events. By comparing two groups of fast‐decay El Niño events with significant and insignificant WNPAC in the following summer, we found that the westward extension of the equatorial Pacific cold sea surface temperature anomalies (SSTA) and the subtropical central‐north Pacific cold SSTA play important roles in the generation and intensification of the WNPAC during decaying summer. Further analyses indicated that the internal atmospheric mode—North Pacific Oscillation during boreal spring can affect the formation of the cold SSTA over the subtropical central‐north Pacific and the westward extension of the equatorial Pacific cold SSTA during summer. Additional effects of tropical Indian and Atlantic forcing on the maintenance of the WNPAC are also shown. Plain Language Summary: The boreal summer western North Pacific anticyclone (WNPAC) is an important low‐level circulation over the western Pacific, which can have great impacts on the East Asia climate. Previous studies pointed out that the fast‐decay El Niño events are favorable in inducing the WNPAC in the decaying summer. However, our observational and modeling results suggested that not all the fast‐decay El Niño events can generate WNPAC in the decaying summer. By dividing fast‐decay El Niño events into two groups, one with significant WNPAC in the following summer and the other without, we found that the difference in the equatorial Pacific cold sea surface temperature anomalies (SSTA) westward extension, the subtropical central‐northern Pacific cold SSTA and the tropical Indian/Atlantic warm SSTA are important in causing the diverse response of the WNPAC to the fast‐decay El Niño events during decaying summer. Further analyses indicated that the internal atmospheric mode—North Pacific Oscillation during boreal spring can affect the cold SSTA over the subtropical central‐north Pacific and the westward extension of the equatorial Pacific cold SSTA during boreal summer. The tropical Indian and Atlantic warming, can also directly influence the WNPAC intensity or feedback to the equatorial and subtropical Pacific cooling to influence the WNPAC. Key Points: Fast‐decay El Niño is more favorable in generating western North Pacific anticyclone (WNPAC) in the decaying summer but this is not the case for all fast‐decay El NiñoEquatorial Pacific, subtropical Pacific cold sea surface temperature anomalies (SSTA) and tropical Indian/Atlantic warm SSTA in summer are key to the diverse response of WNPACThe spring North Pacific Oscillation is important in causing the diverse equatorial and subtropical Pacific cold SSTA forcing in summer [ABSTRACT FROM AUTHOR]

In this study, we developed a regional coupled model for the western North Pacific (WNP) and East Asian region. The atmospheric/oceanic component of the coupled model was the Weather Research and Forecasting and the Regional Ocean Modeling System, coupled through the National Center for Atmospheric Research Coupler version 7 (CPL7). An evaluation is provided through the simulation of the climatology and interannual variability of the summer monsoon climate from 1982 to 2015. The coupled model is also compared with a solely atmospheric run, which is driven by the observed sea surface temperature (SST) as the surface boundary. The results show that the coupled model has good capability in modeling the climate in the WNP and East Asian domain, including the climatology of summer precipitation and circulation, the subseasonal (month‐to‐month) variation in the western Pacific subtropical high and associated precipitation, and the seasonal cycle of the East Asian rain belt. One merit of this model is its ability to simulate the northward and eastward shift from early to late summer. With respect to the interannual variability, the model captures the spatial pattern of the leading mode of summer precipitation, with a north–south dipole mode in the studied region. The model also reproduces the larger SST variability in the northern part of this region. The temporal correlation coefficient between the coupled simulation and observation was 0.70 for the precipitation and 0.53 for the SST leading mode. The coupled model also captures the precipitation–SST relationship, which results from reasonably considering the air–sea coupling processes in the coupled run. Plain Language Summary: Due to the resolution of global models is relatively coarse and cannot describe the regional features, especially in the monsoon regions, regional climate model is an essential solution for regional climate simulation and projection. Compared with atmospheric alone model which is driven by prescribed sea surface temperature, regional air‐sea coupled model can describe reasonably the air‐sea coupling processes and has better performance. In this study, an regional coupled model is developed based on the Community Earth System Model coupler version 7 framework. Based on our analysis, the regional coupled model reasonably reproduced most key characteristics in the East Asian monsoon region. In addition to being used in regional climate simulation and projection, it can also be conveniently coupled with global models through the coupler 7. Thus with this useful tool in future we can develop global‐regional two‐way coupling simulation system for climate predictions and projections. Key Points: A regional coupled model is developed for East Asia and western North Pacific region based on Community Earth System Model frameworkClimatology and interannual variability of the summer monsoon climate have been evaluatedThe model can well capture the climatological northward and eastward movements of the western Pacific subtropical high from June to August [ABSTRACT FROM AUTHOR]

The Pacific‐Japan (PJ) pattern is the dominant teleconnection over East Asia, closely related to the summer precipitation on various time scales. However, studies on the connection between the interdecadal variations of the PJ pattern and sea surface temperature (SST) forcing are still limited. This study indicates that the relationship between the PJ pattern and ENSO presents a pronounced interdecadal change around 1997/1998. The PJ pattern shows a baroclinic structure over the northwest Pacific and a barotropic structure near Japan during 1979–1997, while its baroclinic structure in the tropics weakens remarkably during 1998–2021, with a southward shift of its midlatitude barotropic structure. As a result, the connection between the PJ pattern and summer precipitation over East Asia exhibits an interdecadal transition in the late 1990s. In the slow La Niña decaying summer of 1979–1997, the cold SST anomalies in the tropical Indian Ocean (TIO) excite an eastward‐propagating Kelvin wave that enhances convection over the northwest Pacific, resulting in the formation of the PJ pattern. In contrast, the cold SST anomalies in the Maritime Continent rather than the TIO yield a zonally confined Kelvin wave in the rapid La Niña decaying summer of 1998–2021. The elongated Kelvin wave penetrating the central Pacific weakens convective anomalies over the northwest Pacific, thereby weakening the baroclinic structure of the PJ pattern in the tropics. Meanwhile, the warm SST anomalies in the Kuroshio Extension (KE) induce a northward shift of the East Asian subtropical westerly jet, with the anomalous anticyclonic circulation over the KE significantly affecting summer precipitation along the Meiyu belt. Therefore, the midlatitude barotropic structure of the PJ pattern shifts southward after the late 1990s. [ABSTRACT FROM AUTHOR]

Northeast China cold vortex (NECV) is the major influencing weather system in northern China. Yet the impacts of complex terrain on the evolution of NECV remains poorly understood. This work studies the influence of subgrid orographic drag (SOD) on a heavy‐rain‐producing NECV occurred in July 2011 using the Weather Research and Forecasting model. A series of numerical experiments are conducted with different parameterizations of SOD including turbulent orographic form drag (TOFD), flow blocking drag (FBD), and mountain wave drag (MWD). Results show that the NECV intensity is overestimated in the absence of SOD parameterization, accompanied with too‐low geopotential height (GPH) and too‐strong horizontal winds. The parameterization of TOFD can significantly decelerate the 10‐m winds, whereas the FBD and MWD play a minor role. However, the influence of TOFD is overwhelmed by FBD and MWD in the troposphere, especially the latter. This implies that the breaking of mountain waves play a more important role in weakening the NECV than the low‐level flow blocking. The lower‐tropospheric MWD directly weakens the convergence and ascent motion of the NECV, producing an anti‐cyclonic circulation that uplifts the GPH under the constraint of quasi‐geostrophic vertical vorticity. This MWD‐induced circulation indirectly weakens the NECV in the mid‐upper troposphere by producing a warm advection that counters the low‐level cold advection to the southwest of the NECV. The findings provide useful insights into the impacts of complex terrain on the NECV and highlight the importance of topographic drag parameterization in the simulation and short‐range forecast of NECV. Plain Language Summary: Northeast China cold vortex (NECV) is a major influencing weather system in northern China which often promotes severe convective weather like heavy rainfall, hail, and tornado. Past studies have revealed the importance of atmospheric circulations (e.g., Rossby waves associated with Eurasian blocking), sea surface temperature anomalies over North Pacific, and large‐scale orography in East Asia on the evolution of NECV. However, the underlying terrain in East Asia is much complex. It is still unclear how the NECV is affected by complex terrain. This work studies a NECV case using the Weather Research and Forecasting model, focusing on the impacts of different topographic drags including turbulent orographic form drag (TOFD), mountain wave drag (MWD), and flow blocking drag (FBD) produced by complex terrain. The influence of TOFD is basically confined in the boundary layer whereas the FBD and MWD play a major role in the troposphere, especially the latter. The low‐level MWD directly weakens the NECV in the lower troposphere by inducing an anti‐cyclonic circulation. Consequently, the low‐level cold advection to the southwest of the NECV is suppressed which indirectly weakens the NECV in the mid‐upper troposphere. The findings highlight the importance of topographic drag parameterization in the simulation and short‐range forecast of NECV. Key Points: The impacts of different topographic drag on the Northeast China cold vortex are firstly studied using numerical sensitivity experimentsTurbulent orographic form drag dominates the impact on near‐surface winds, while mountain wave drag plays a major role in the troposphereLow‐level mountain wave drag directly and indirectly weakens the cold vortex in the lower and mid‐upper troposphere, respectively [ABSTRACT FROM AUTHOR]

Based on the daily minimum temperature data from 199 meteorological stations in northeast China (NEC), the cold wave (CW) processes in winter from 1980 to 2020 are identified. Then, by using the reanalysis 500‐hPa geopotential height data provided by the European Centre for Medium‐Range Weather Forecasts (ECMWF), the CWs are objectively classified into two types (abbreviated as Type 1 and Type 2) according to the corresponding atmospheric circulation through the hierarchical cluster algorithm (HCA). The relationships of the CWs with the Arctic sea sic (SIC) and sea surface temperature (SST) are revealed. For Type 1, the SIC in the north of the Barents Sea–Kara Sea is relatively less in the previous autumn, and a wave train propagating from the polar regions to Northeast Asia is stimulated under the ice–atmosphere interaction. This wave train further cooperates with the positive SST anomaly in the southern Indian Ocean to excite the low‐vortex circulation under the negative phase of Arctic Oscillation (AO) in winter, which is conducive to the occurrence of Type 1. However, the relatively low SST in the western Pacific warm pool in previous autumn stimulates a northward propagating wave train along the meridian, which increases the degree of meridionality of the atmospheric circulation over East Asia and thus indirectly causes the polar‐vortex‐splitting circulation under the positive AO phase, which favours the formation of Type 2. The numerical simulations can well reproduce the observational facts, further confirming the possible impact of the SIC and SST in the previous autumn on the two types of CW over the NEC. [ABSTRACT FROM AUTHOR]

The western Pacific subtropical high (WPSH) substantially affects the climate in the Pacific and East Asia. Previous studies have revealed that the springtime Indo‐Pacific warm pool (IPWP) sea surface temperature zonal gradient (SSTG) could be used as a predictor of the subsequent summertime WPSH's intensity. Here, we find that the interannual variability of the springtime IPWP SSTG has greatly decreased after the late 1990s, accompanied by the weakened relationship between the springtime IPWP SSTG and the following summertime WPSH, which may reduce the efficiency of the springtime IPWP SSTG as a key predictor for the summertime WPSH in recent decades. This observed recent weakening IPWP SSTG–WPSH relationship could be largely contributed by the decadal shift of the El Niño–Southern Oscillation (ENSO) and the WPSH around the late 1990s. The ENSO regime shift from the eastern Pacific (EP) type to the central Pacific (CP) type could alter the spatial pattern of the springtime IPWP sea surface temperature (SST) dipole and further weaken the local air–sea interaction between the underlying IPWP SST and the WPSH. From another perspective of the WPSH decadal shift, the WPSH‐related first leading mode before (after) the late 1990s, characterized by a large‐scale uniform (dipole) pattern with an oscillating period of ~4–5 year (~2–3 year), tended to promote a stronger (weaker) linkage with the springtime IPWP SSTG. In addition, the recent enhancement of the tropical Atlantic SST influences is considered to possibly promote the decadal shifts of the ENSO and the WPSH‐related leading mode. After the springtime tropical Atlantic SST was added as a predictor, the predicting skills of the empirical equation for the summertime WPSH could be substantially improved. The results herein have important implications for the further improvement of the seasonal WPSH prediction, which is of great practical significance in the prevention and mitigation of climate disasters. [ABSTRACT FROM AUTHOR]

Extreme precipitation in July across Henan Province and the possible mechanisms involved were investigated. The precipitation in Henan reaches its maximum in July. During 1979–2021, the precipitation in July changed weakly, but the intensity (R99p) and frequency (R99f) of extreme precipitation showed certain increasing trends, with a significant increase in northern Henan. The proportion of extreme precipitation in total precipitation exhibited a significant upward trend. Wavelet analysis results showed that the extreme precipitation in Henan mainly has a 2–3‐year periodicity, and remarkable interannual variation. Furthermore, nearly 80% of the July extreme precipitation events within the magnitude of 50–100 mm occurred 2–3 times. The first two empirical orthogonal function modes of July R99p exhibited a quasi‐monopole pattern (EOF1) and meridional dipole pattern (EOF2), respectively. Further analysis revealed that EOF1 and EOF2 were related to the Silk Road teleconnection pattern (SRP) and the East Asia/Pacific teleconnection pattern (EAP). Circulation factors influenced the interannual variation of R99p, especially in recent years. Furthermore, the associated sea surface temperature anomalies over the Western Pacific and Indian Ocean can intensify the eastward extension of the South Asian high and westward strengthening of the western Pacific subtropical high, which further impacted the SRP and EAP pattern and enhanced the increment of extreme precipitation in Henan Province. [ABSTRACT FROM AUTHOR]

Under the background of global warming, the summer precipitation over northwest China (NW) has experienced a significant interdecadal shift since the early 1990s, followed by a great increase in precipitation. This increase was mainly due to the anomalous water vapour input from the eastern boundary, whose transport has gradually become the main moisture transport belt affecting summer precipitation over NW in the past 30 years. Further research indicates that the anomalous easterly water vapour transport mainly originates from the Arctic and North Pacific Oceans. The interdecadal increase in precipitation and changes in water vapour transport pathways are related to the interdecadal warming of the North Atlantic (NA) and Indian‐Pacific warm pool (IPWP) in the mid‐1980s. The IPWP warming potentially weakens the land–sea thermal gradient, dampens the meridional circulation in East Asia, and thereby significantly reduces the southerly water vapour transport of the Asian summer monsoon, and generates anomalous northeasterly water vapour transport from high latitudes over East Asia. Moreover, the warmer sea surface temperature (SST) over the IPWP and NA can induce an anomalous teleconnection wave train, with anomalous anticyclones over Lake Baikal and the Aleutian Islands, and an anomalous cyclone over Japan. This type of teleconnection wave train contributes to anomalous northerly winds over eastern China and easterly winds over NW. The above‐mentioned anomalous circulation favours moisture transport from both the Arctic and North Pacific toward the NW, resulting in an increase in summer precipitation associated with the anomalous regional ascending motion. [ABSTRACT FROM AUTHOR]

The Asian summer monsoon (ASM), controlled by tropical ocean‐atmosphere systems, and the westerlies, directly linked to high‐latitude climates, interact in mid‐latitude East Asia. Located at a climate junction, the northeastern Qinghai‐Tibetan Plateau (QTP) is a sensitive zone for the interaction of the westerlies and ASM. In the current work, we present a new loess data set from the northeastern QTP since the last deglaciation, including grain size, stable isotope (δ13Corg and δ18Ocarb), total organic carbon, total nitrogen, magnetic susceptibility, and mineral composition. The PMIP3‐CMIP5 multi‐model ensemble and TraCE‐21ka transient simulation are used synthetically to analyze climate mechanisms. All proxies suggest instable glacial climate and stable interglacial climate in the northeastern QTP. The coarser grain size during the last deglaciation compared with the Holocene reflects intensified westerlies controlled by the weakening of Atlantic Meridional Overturning Circulation and existing ice sheets. More positive δ18Ocarb values during abrupt cooling events [Heinrich event 1 (H1) and the Younger Dryas (YD)] indicate the effect of a weakened monsoon triggered by the low‐latitude solar insolation and sea surface temperature. Therefore, the anti‐phase pattern between the ASM and westerlies is the primary reason for differences in climate stability. Moreover, low temperature favors the predomination of C3 plants and the development of permafrost, leading to more negative δ13Corg values and fine grain size during the H1 and YD. Taken together, the anti‐phase relationship between the westerlies and ASM emphasizes the complicated dynamic characteristics of atmospheric systems in the mid‐latitudes and the challenges for future predictions. Plain Language Summary: The relationship between the westerly circulation and Asian summer monsoon (ASM) system at different timescales is still under discussion in both meteorology and paleoclimatology communities in recent years. Due to the huge differences in the dynamic mechanisms of the two circulation systems, relevant previous studies on millennial‐scale climate change distinguished the westerlies and ASM based on various paleoclimate indicators, and rarely defined the meaning and specific process of their interaction. Under global warming, clarifying the interactions of the westerlies and ASM is critical to understanding the pattern and mechanism of climate change in mid‐latitudes. Therefore, the comprehensive analysis of surface sediments, paleoclimate records, and paleoclimate simulation on long‐term timescales are conducted in the northeastern Qinghai‐Tibetan Plateau which is a sensitive zone for the synergistic effect of the westerlies and ASM. The results show that the ASM mainly affects the Holocene climate, while the westerlies dominate during the last deglaciation in the northeastern Qinghai‐Tibetan Plateau. The anti‐phase pattern between the ASM and westerlies leads to instable glacial climate and stable interglacial climate. Key Points: Anti‐phase pattern between the Asian summer monsoon and westerlies triggers the difference in climate stability during glacial and interglacial periodsCoarser grain size during the last deglaciation compared with the Holocene reflects intensified westerlies linked to weakening Atlantic Meridional Overturning CirculationMore positive δ18Ocarb values during abrupt cooling events (H1 and Younger Dryas) indicate the influence of the weakened monsoon [ABSTRACT FROM AUTHOR]

Using a series of data from the National Oceanic and Atmospheric Administration (NOAA) and singular value decomposition (SVD) method, the dominant coupled mode between sea surface temperature (SST) anomaly in Maritime Continent (MC) and circulation anomaly in East Asia in summertime and its underlying mechanism are revealed. Results show that the first SVD mode is characterized by the in‐phase variations of SST anomaly in the entire MC and sea level pressure (SLP) anomaly in East Asia, and their co‐variation is measured by an SVD joint index, Isvd1 ${I}_{\mathrm{s}\mathrm{v}\mathrm{d}1}$. Based on composite difference fields, the ocean mixed layer heat budget reveals that the maintenance of the MC regional SST anomaly is jointly determined by ocean dynamics and heat flux. The anomalous SST warming near Java Island is dominated by the meridional advection of ocean current, while the SST warming in the Bay of Bengal, the South China Sea and the Northwest Pacific are mainly contributed by the increased downward latent heat flux and shortwave radiation flux. The SLP anomaly pattern in East Asia coupled with SST anomaly in the MC region is represented by the anomalous anticyclone in the Northwest Pacific, which can be maintained by the Isvd1 ${I}_{\mathrm{s}\mathrm{v}\mathrm{d}1}$‐related atmospheric vertical cell. The Isvd1 ${I}_{\mathrm{s}\mathrm{v}\mathrm{d}1}$‐related circulation anomalies tend to favor the summer precipitation in the middle and lower reaches of the Yangtze River and the south of Yunnan‐Guizhou Plateau, but lead to negative precipitation anomaly in central and Northeast China. Key Points: Summer sea surface temperature (SST) anomaly in the Maritime Continent (MC) varies in‐phase with sea level pressure anomaly in East Asia (EA)The MC SST‐EA circulation coupling mode is related to El Niño‐Southern Oscillation and maintained by the local ocean dynamical and thermodynamical processesThe anomalous circulation related to the coupling mode has important impact on summer precipitation in China [ABSTRACT FROM AUTHOR]

This study investigates the historical simulation of the Bay of Bengal–East Asia–Pacific (BEAP) teleconnection and its relationship with the El Niño–Southern Oscillation (ENSO) using 16 models from the Coupled Model Intercomparison Project phase 6 (CMIP6). The CMIP6 models can reasonably well reproduce the BEAP‐related diabatic heating variables and the ENSO sea surface temperature anomaly (SSTA). The CMIP6 models also show good performance in simulating the BEAP pattern at subseasonal and interannual time scales. Further investigation reveals that the BEAP–ENSO relationship changes from statistically insignificant to significant on an interdecadal timescale. Significant BEAP–ENSO correlation is associated with more positive SSTA over the tropical Indian Ocean (TIO) than in the period of insignificant BEAP–ENSO correlation. The positive SSTA difference acts as a heat source that intensifies the in situ atmospheric convection to generate considerable diabatic heating around the BEAP source region. The covariation of the Indo‐Pacific SSTA exhibits a tripole pattern, namely positive SSTA over the TIO, negative SSTA over the tropical central‐western Pacific, and positive SSTA over the tropical eastern Pacific. The SSTA tripole pattern is ascribed to the Indo‐Pacific capacitor effect and zonal advective feedback. The surface wind stress is weaker during the period of significant BEAP–ENSO correlation than during the non‐significant BEAP–ENSO period. The surface wind stress is also identified as a crucial factor in the projected changes in the BEAP teleconnection. The results indicate that the enhanced zonal wind stress results in more positive BEAP cases in the 21st‐century projection. Key Points: The Bay of Bengal–East Asia–Pacific (BEAP)–El Niño‐Southern Oscillation (ENSO) relationship changes from statistically insignificant to significant on an interdecadal timescaleSurface wind stress is a key factor for simulation of the BEAP teleconnection and the BEAP–ENSO relationshipEnhanced zonal wind stress results in more positive BEAP cases in 21st‐century projections [ABSTRACT FROM AUTHOR]

The evolution of hydroclimate in East Asia during the Pliocene—a potential analog of the future greenhouse climate—remains highly uncertain. Here we reconstruct changes in the hydroclimate of Northern China during this epoch. Our results reveal previously undocumented severe drought conditions that persisted through the early Pliocene with a significantly greater magnitude than suggested by other records. Using a broad hierarchy of climate simulations, we find that reduction in the Pacific meridional sea surface temperature (SST) gradient has particularly strong impacts on precipitation over Northern China, which suggests its key role in maintaining drought conditions during the early Pliocene. The weaker Pacific meridional SST gradient causes the weakening of the East Asian summer monsoon precipitation over this region via a reduction of atmospheric northward moisture transport from the ocean, which enhances aridity inland. Our results highlight the fundamental control of the tropical ocean on the extra‐tropical hydrological cycle. Plain Language Summary: Understanding East Asian rainfall changes with global warming is an important issue of climate sciences. The Pliocene epoch provides a potential analog to the future greenhouse climate. Here, for the first time we reconstruct high‐resolution aridity changes over the Chinese Loess Plateau (CLP) in northern East Asia during the Pliocene. Our results indicate persistent drought conditions over CLP during the early Pliocene. Analyzing a broad range of climate model simulations, we find that the reduced meridional sea surface temperature gradient is a critical factor in the weakening of the East Asian summer monsoon over Northern China and in maintaining drought conditions during the early Pliocene relative to the late Pliocene. Our results expand the Asian inland paleoclimate records during the Pliocene, providing new information on past Asian monsoon precipitation variations during the warm Pliocene with potential implications for future hydroclimate changes under greenhouse warming in East Asia. Key Points: Severe drought conditions persisted throughout the early Pliocene epoch over Northern ChinaWe link these conditions to the reduced meridional temperature gradient in the Pacific OceanThe reduced Pacific meridional temperature gradient acts to weaken the summer East Asian monsoon precipitation over Northern China [ABSTRACT FROM AUTHOR]

In this study, the East Asian summer (June–July–August) monsoon (EASM) atmospheric moisture transport variability under global warming are examined using ERA‐Interim reanalysis data from 1979 to 2019. The total EASM atmospheric moisture transport is decomposed into the thermodynamic (δTH) and dynamic (δMCD) components, which are related to specific humidity and wind velocity, respectively. Based on empirical orthogonal function (EOF) analysis, both the second and the fourth modes of δTH are linked to δMCD, indicating that δMCD can impact the moisture distribution and consequently influence δTH indirectly. Both the first (δTH_EOF1) and the third (δTH_EOF3) modes of δTH show considerable interdecadal changes. It is noted that their principal components exhibit significant increasing trends in recent decades. The response of EASM moisture transport to global warming is probably reflected in these two modes. δTH_EOF1 is associated with negative phases of the Interdecadal Pacific Oscillation (IPO)/Pacific Decadal Oscillation (PDO). This causes the western North Pacific subtropical high (WNPSH) to extend westward and the strengthening of Pacific trade winds. As a result, positive precipitable water anomalies dominate East Asia and δTH_EOF1 is characterized by anomalous southwesterly moisture transport along the East China Sea to southern Japan. δTH_EOF3 corresponds to anomalous moisture transport over the Indochina Peninsula and Japan. The precipitable water associated with δTH_EOF3 in general represents a meridional dipole. Anomalous southward wind induced by the eastward extension of the WNPSH is the main reason for positive (negative) precipitable water anomalies in southern (northern) East Asian. The anomalous circulation associated with the anomalous east–west sea surface temperature gradient over the Indian Ocean affects atmospheric moisture in southern East Asian and can dramatically impact δTH_EOF3. [ABSTRACT FROM AUTHOR]

This study investigates inter‐model spreading of changes in East Asian winter monsoon circulation and the underlying reasons under 1.5 and 2.0°C global warming for Representative Concentration Pathway 8.5. Results show that the spatial patterns of multi‐model ensemble and inter‐model spreading of changes in 850‐hPa zonal and meridional winds over East Asia are similar under the two global warming targets. The multi‐model ensemble changes in 850‐hPa meridional wind (V850) over southern China are near zero under the two targets. Meanwhile, the V850 changes over southern China exhibit large inter‐model spreading, which is closely related to those of regional differences in sea surface temperature changes (DSSTC) in the tropical Pacific. Models with positive V850 anomalies over southern China tend to project weak (strong) surface warming in the western North Pacific (South China Sea and the equatorial central and eastern Pacific). Such a configuration results in decreased precipitation over the east of the Philippines and hence an anomalous lower‐level high to its northwest. Accordingly, southwesterly anomalies prevail over southern China. The southwesterly anomalies are further enhanced by related positive feedback processes. Models with negative V850 anomalies tend to project strong (weak) surface warming in the western North Pacific (South China Sea). The projected surface warming in the equatorial central and eastern Pacific is also strong, but weaker than that of models with positive V850 anomalies. Therefore, the induced precipitation and circulation changes over the East Asia–western North Pacific are basically opposite to those described above. Besides, the inter‐model spreading of V850 changes over southern China decrease by about 36.2% from 1.5 to 2.0°C global warming, which can be partly attributed to the decrease in the inter‐model spreading of DSSTC in the tropical Pacific. Numerical experiments confirm the role of the sea surface temperature changes in the tropical Pacific. [ABSTRACT FROM AUTHOR]

Typhoons decrease sea surface temperature (SST) along their wakes through upwelling of subsurface water, vertical mixing in the upper ocean, and heat release from the sea surface, and these cold wakes can influence subsequent typhoons. In this study, we investigated interactions between the upper ocean and typhoons in the North Pacific subtropical gyre with focuses on Kuroshio's response and feedback using atmosphere–ocean coupled model simulations. In late August and early September 2018, typhoons SOULIK, CIMARON, and JEBI passed through the northwestern subtropical gyre. During the passages of SOULIK and CIMARON, SST decreased along their paths due to vertical mixing except in the Kuroshio region. We quantitatively revealed that the Kuroshio stayed warm because the deep mixed layer along its path and small vertical temperature gradient around the mixed layer base, which are unfavorable conditions for cooling by vertical mixing, limited the cooling effects. After SOULIK and CIMARON had passed, SST recovered through horizontal Kuroshio heat transport and radiative heating. The possibility that the SST field after SOULIK and CIMARON passages influences JEBI was also discussed. Although impacts on JEBI intensity were not identified, it is implied that the turbulent heat flux (THF; sum of the sensible and latent heat fluxes) around JEBI was modulated by the SST field: heat release from the ocean was reduced in the region with decreased SST and enhanced over the sustained high SST of the Kuroshio. Furthermore, the large THF over the Kuroshio may have caused an increase of JEBI‐associated precipitation around Japan. Plain Language Summary: Tropical cyclones that develop in the western North Pacific are called typhoons. Typhoons migrate westward or northwestward from the tropical North Pacific in accordance with the large‐scale atmospheric circulation and often bring heavy rainfall or windstorms to islands and coastal regions of Southeast and East Asia. Because typhoons derive energy from the ocean, to improve typhoon forecasts and to reduce the damage that they can cause, it is important to understand ocean–typhoon interactions. We studied three typhoons that occurred in the North Pacific subtropical region in 2018 and examined the associated ocean–typhoon interactions. Generally, typhoons decrease sea surface temperature along their wakes, and occasionally the cold wakes of preceding typhoons weaken subsequent typhoons. However, we found that the warm Kuroshio current, which flows northeastward along the south coast of Japan, remained warm even after the typhoons had passed. Moreover, the sustained warmth of the Kuroshio might release large amounts of heat and moisture to the subsequent typhoon. Thus, heat and moisture supplied from the Kuroshio can cause intensification of typhoons and increased precipitation. Our results suggest that studies of ocean–typhoon interactions in the Kuroshio region can advance the science of typhoon forecasting and disaster prevention in Southeast and East Asia. Key Points: In 2018, three typhoons, SOULIK, CIMARON, and JEBI, passed the western North Pacific successively decreasing sea surface temperature (SST)The Kuroshio stayed warm during the passages of SOULIK and CIMARON due to weak stratification with high resistance to surface coolingImpact of the sustained high SSTs over the Kuroshio on JEBI through surface heat fluxes was suggested from our coupled model simulations [ABSTRACT FROM AUTHOR]

It is well known that the El Niño‐Southern Oscillation (ENSO) has a profound impact on climate over southern China (SC). This study indicates that independent from the ENSO variability, a meridional tripolar sea surface temperature (SST) pattern over tropical‐North Pacific in February has a close relationship with interannual variations in the frequency of spring extreme consecutive dry days (extreme‐CDDs) over SC. Further analyses suggest that the tripolar SST pattern has a good persistence from February to the following spring and could influence the variations of SC extreme‐CDDs through two ways. On one hand, the extratropical SST anomalies of the tripolar pattern can cause the meridional shift of the North Pacific subarctic oceanic front, resulting in a meridional dipole atmospheric pattern over the region from the North Pacific to East Asia through eddy‐mean flow interaction. The meridional atmospheric pattern can influence the East Asian upper‐level jet and western Pacific subtropical high (WPSH), leading to anomalous vertical motion and moisture transport over SC. On the other hand, the SST anomalies of the tripolar pattern over the tropical western Pacific can excite an overturning circulation and influence the WPSH through the Matsuno‐Gill response, also contributing to anomalous vertical motion and moisture transport over SC. These physical processes are further confirmed by numerical simulations. Therefore, through the aforementioned two physical ways, the February tripolar SST pattern can influence the moisture and dynamical conditions associated with the occurrence of extreme‐CDDs, consequently providing a factor and predictor for the variations of SC spring extreme‐CDDs. Key Points: The interannual variations of spring southern China (SC) extreme consecutive dry days (extreme‐CDDs) are related to a tripolar sea surface temperature (SST) pattern over tropical‐North Pacific in FebruaryThe tripolar SST pattern affects SC extreme‐CDDs through mid‐latitude eddy‐mean flow interaction and tropical overturning circulationThe February tripolar SST pattern provides a prediction source for the interannual variations of SC spring extreme‐CDDs [ABSTRACT FROM AUTHOR]

In this study, we investigate the interdecadal variation characteristics of the dominant mode of summer precipitation over East Asia‐Northwest Pacific (EA‐NWP) before and after late 1990s, reveal the physical mechanism, and address its possible connection with the regional ocean warming background. Study results show that the empirical orthogonal function mode 1 (EOF1) of summer precipitation anomalies over EA‐NWP during the global ocean warming acceleration period (1979–1998) present a more significant dipole pattern between Yangtze River Basin (YRB) and tropical NWP compared with that during the global ocean warming slowdown period (1999–2012). And then we find that the anomalous dipoles of low‐level winds, geopotential height, convection, and associated wave activity fluxes over NWP significantly shift westward (eastward) and enhance (weaken) in 1979–1998 (1999–2012), which are regarded as the direct cause of the adjustment of dipole pattern between YRB and tropical NWP. Further analysis reveals that the negative sea surface temperature (SST) anomalies in the tropical NWP are prominent (not prominent), resulting in the stronger (weaker) Pacific–Japan Teleconnection over Japan and Tropics in NWP during the period 1979–1998 (1999–2012), and ultimately lead to the change of summer precipitation EOF1 in EA‐NWP. By regressing vertical velocity, outgoing longwave radiation, relative vorticity, wave activity fluxes, and precipitation onto the NWP SST in the two periods, the impacts of the SST in the NWP on the interdecadal variation of summer precipitation EOF1 in EA‐NWP are verified. Finally, the mechanism diagram of interdecadal variation of summer precipitation is given, which can be useful for short‐term precipitation prediction of East Asia. [ABSTRACT FROM AUTHOR]

The middle and lower reaches of Yangtze River (MLYR) experienced a historically high number of persistent cloudy and rainy days throughout winter 2018/2019. The persistent cold and rainy weather caused severe social impacts and economic losses. Climatic monitoring shows that a weak central Pacific (CP) El Niño event initiated in November 2018 with an increase in the sea surface temperature (SST) in the central and eastern tropical Pacific. During the mature phase of the CP El Niño, the western North Pacific Subtropical High (WNPSH) was stronger than normal and the western boundary moved westward. However, the weak CP El Niño event alone is not enough to explain the abnormally strong and northward displacement of WNPSH and associated heavy rainfall in winter of 2018/2019. This study highlights the eastward propagating Rossby wave train in the middle‐upper troposphere along with the Asian westerly jet‐induced anomalous high pressure and anticyclonic circulation over East Asia, which contributed to the intensification and northward displacement of WNPSH. The synergic influence of both the CP El Niño and Rossby wave train over Eurasia resulted in an intensified and northward shifted WNPSH, which, together with the intensification of the India Burma trough, strengthened the transport of water vapour into the MLYR basin. Accompanied by frequent outbreaks of cold air and confluence of cold and warm air over the MLYR basin, cold and rainy weather persisted in winter 2018/2019 in this region. [ABSTRACT FROM AUTHOR]

Based on 10 pairs of atmospheric general circulation models from the Coupled Model Intercomparison Project Phase 6 High Resolution Model Intercomparison Project, we find that high‐resolution models (HRMs, ∼50 km) perform better than low‐resolution models (LRMs, ∼100 km) in simulating the East Asian summer monsoon (EASM) rain belt. We attribute the increased rainfall to enhanced vertical advection of water vapor in the HRMs which is mainly contributed by enhanced vertical motion. Based on moist static energy analyses, the stronger vertical motion in the HRMSs is mainly balanced by enhanced net energy flux into the atmosphere column in the "Meiyu‐Baiu" (MB) region due to the increase of air‐sea turbulent latent heat fluxes along the Kuroshio and sensible heat fluxes over land. The increased net energy flux in the HRMs drives stronger ascending motion, resulting in more realistic rainfall in the MB region. Higher saturated specific humidity determined by finer sea surface temperature, less near‐surface specific humidity along the Kuroshio, and stronger near‐surface winds on western side of the western North Pacific Subtropical High strengthened by the enhanced pressure gradient together contribute to higher ventilation efficiencies and enhanced ocean forcing along the Kuroshio, leading to more turbulent latent heat fluxes in the HRMs. Additionally, drier and less cloudy atmosphere in the HRMs result in more downward shortwave radiation heating over the land, which partly contributes to the increased sensible heat flux. This understanding of the sensitivity of simulated MB to model resolution has implications for precipitation simulation and prediction over East Asia. Plain Language Summary: Improving the Meiyu‐Baiu simulation is a long‐term challenge for the climate‐modeling community. One way to achieve such improvement is to develop high‐resolution global climate models, since there are many mesoscale systems embedded in the large‐scale monsoon circulation that need small grid spacing to be resolved. By analyzing ten pairs of models, we show that the high‐resolution models (HRMs) generally show better performance in Meiyu‐Baiu simulations than the low‐resolution models (LRMs), with a reduction in bias of 31%. The increased air‐sea latent heat flux in the HRMs is a dominant energy source driving increased Meiyu‐Baiu rainfall. Stronger near‐surface winds and drier air in the HRMs favor increased evaporation, resulting in a more turbulent latent heat flux. Hence, we explain the processes that can help improve Meiyu‐Baiu simulation when improving the horizontal resolution from ∼100 to ∼50 km in General climate models. Key Points: High‐resolution models (∼50 km) perform better than low‐resolution models (∼100 km) in simulating Meiyu‐BaiuThis added value is mainly attributed to the enhanced air‐sea turbulent latent heat fluxes along KuroshioStronger near‐surface wind and drier air in high‐resolution model favor the more turbulent latent heat fluxes [ABSTRACT FROM AUTHOR]

The different impacts of El Niño on the East Asian summer precipitation (EASP) between its developing and decaying stages are investigated in observations. The EASP responses are almost opposite between the two stages, with an anomalous wet (dry) in Southeast China and an anomalous dry (wet) in North China in the developing (decaying) summer. In the developing summer, El Niño influence on EASP is through its direct impact of the sea surface temperature (SST) anomaly in the tropical Pacific, which induces heating perturbations that excite an upper‐level zonally propagating wave train in mid‐latitude and a lower‐level meridional wave train along the East Asian coast. In contrast, in the decaying summer, El Niño affects EASP through the El Niño‐generated SST anomalies outside the equatorial Pacific, which are combined to produce an uplift of geopotential height around the upper‐level tropics and a lower‐level Pacific‐Japan (PJ) wave train. [ABSTRACT FROM AUTHOR]

The impacts and corresponding mechanisms of land use/cover change (LUCC), mainly crops and pasture, on the spatial patterns of summer precipitation over eastern China at the decadal timescale during the last millennium are investigated, using a set of land use/cover sensitivity experiments from the Community Earth System Model (CESM) Last Millennium Ensemble (LME) archive. Two leading modes of summer precipitation over eastern China at decadal scale before (with slight LUCC) and after (with drastic LUCC) 1750 AD are compared. The results show that the LUCC plays an important role in modulating the spatial patterns of summer precipitation over eastern China at decadal scale. Before 1750 AD, the first leading mode exhibits a meridional dipole pattern, while the second leading mode exhibits a meridional tripole pattern. After 1750 AD, the order of the spatial patterns switches, that is, the tripole pattern as the first leading mode and the dipole pattern as the second leading mode. During both periods, the "dry north‐wet south" dipole pattern is associated with an anomalous "A‐C" (anticyclone‐cyclone) low‐level circulation pattern and the related water vapour divergence‐convergence pattern from north to south over the eastern part of East Asia, whereas the tripole pattern corresponds to an anomalous "A‐C‐A" (anticyclone‐cyclone‐anticyclone) circulation pattern along with the corresponding tripole pattern of water vapour divergence/convergence. The regressions of sea surface temperature (SST) during boreal winter resemble obvious Pacific decadal oscillation (PDO) or Atlantic multi‐decadal oscillation (AMO) modes. In addition, the AMO index displays a decreasing trend during the last millennium under the LUCC forcing, while the PDO index does not show an obvious changing trend. The possibility of coupled PDO‐AMO anti‐phase (in‐phase) increases (decreases) after 1750 AD, leading to the increased (decreased) possibility of the tripole (dipole) pattern in eastern China. Our findings confirm the necessity of including LUCC as an important forcing factor in predictions of future climate changes, especially at the regional scale and also at longer timescales. [ABSTRACT FROM AUTHOR]

Future changes in the frequency and destructiveness of landfalling tropical cyclones (TCs) over East Asia were investigated by analyzing the simulations of two high‐resolution (20–25‐km) atmospheric general circulation models forced by sea surface temperature (SST) in the present period (1979–2003) and under future warming conditions (2075–2099) of the RCP8.5 scenario. The present‐day simulations capture well the genesis count, tracks, and intensity associated with TCs striking the coastal areas of Taiwan‐East China (TWCN), the South China Sea‐Indochina (SCS) and the vicinity of Japan (JP). The frequency of landfalling TCs over TWCN, SCS, and JP is projected to nearly half by the end of the 21st century. However, these landfalling TCs induce enhanced destructive threats of stronger winds and heavier precipitation under the future warmer climate. Through attribution analysis we found the reduced frequency of landfalling TCs to be mainly caused by a decline in TC genesis count (rather than TC track changes), while the increased intensity of landfalling TCs is linked with changes in the TC intensification rate (as opposed to duration changes). Diagnoses of the genesis potential index and eddy energetics further suggest that the mid‐tropospheric drying and weakened synoptic‐scale eddy activity resulting from anticyclonic and downward circulations over the main TC genesis region create an unfavorable environment for TC genesis. In contrast, warmer SST, reduced vertical wind shear and enhanced efficiency of eddy kinetic energy generations appear over the regions before TC landfall, resulting in a more rapid intensification of TCs that later approach the coastal areas. Key Points: The frequency of landfalling tropical cyclones (TCs) over East Asia is projected to nearly half by the end of 21st centuryThe destructiveness of landfalling TCs show a tendency to strengthen in the future, with stronger winds and heavier precipitationThe reduced frequency is attributed to less TC genesis, while the enhanced intensity is attributed to a higher intensification rate [ABSTRACT FROM AUTHOR]

Increasing lines of evidence question the homogenous response of Asian Summer Monsoon (ASM) precipitation patterns, requiring rethinking of the forcing mechanisms. Here we show a ~15,000‐year quantitative precipitation history based on well‐dated lake levels at Lake Chenghai, subtropical China. Lake levels and the inferred precipitation were high during the Bølling‐Allerød, early and late Holocene, but low during the middle Holocene. The orbital scale precipitation trend is out of phase with boreal summer insolation, the later has been widely suggested as the driver of ASM precipitation. Lake Chenghai long‐term lake levels are synchronous with trends in tropical Pacific sea surface temperatures, the related zonal sea surface temperature gradients, and interhemispheric temperature gradients. We propose that changes in either the interhemispheric or zonal Pacific temperature gradients modulate the intensity and location of the western Pacific subtropical high, which is juxtaposed on the ASM, leading to heterogeneous hydroclimatic conditions over subtropical East Asia. Plain Language Summary: We present a 15,000‐year record of southern China precipitation based on well‐dated (n=130 radiometric ages) lake level variations of a closed basin lake. The reconstructed long‐term southern China precipitation trend is out of phase with boreal summer insolation, which has been shown to drive ASM precipitation, but broadly follows trends in tropical Pacific sea surface temperatures (SSTs), the related zonal SST gradients, and interhemispheric temperature gradients. We propose that changes in either the interhemispheric or zonal Pacific temperature gradients modulate the intensity and location of the western Pacific subtropical high and are juxtaposed on the ASM, leading to heterogeneous hydroclimatic conditions over subtropical East Asia, including an unexpected southern China mid‐Holocene drought. The results of this study are unique in that (1) precipitation was robustly reconstructed from beach evidence, which is a first‐order measure of the balance between rainfall amount and evaporation. (2) A new mechanism driving long‐term precipitation changes over subtropical East Asia is proposed. Providing the mechanism stands, increasing SST gradients under the expected global warming scenario could enhance the role of western Pacific subtropical high and lead to less precipitation over subtropical East Asia. Key Points: A 15,000‐year precipitation history over subtropical China was reconstructed based on well‐dated (n=130 radiometric ages) lake levelsSubtropical China precipitation trend does not resemble Asian summer monsoon trend but is synchronized with trends in tropical Pacific SSTJuxtaposition of western Pacific subtropical high on Asian summer monsoon could have shaped the subtropical East Asian precipitation [ABSTRACT FROM AUTHOR]

Based on 34 coupled models from Phase 5 of the Coupled Model Intercomparison Project, we found that the projected changes in the western North Pacific anomalous anticyclone (WNPAC) during El Niño decaying summers show large spread among the models due to different decaying paces of El Niño. Models with a slower (faster) decaying El Niño are followed by weakened (intensified) tropical central Pacific cooling, which further drives a weaker (stronger) WNPAC through inducing weakened (intensified) descending Rossby waves to its west. The decaying pace of El Niño is dominated by the wintertime WNPAC because the easterly surface wind anomalies to its southern flank are critical to El Niño demise. Both the El Niño‐related sea surface temperature anomaly and the precipitation sensitivity to such kind of sea surface temperature anomaly under global warming could affect the wintertime WNPAC. Plain Language Summary: The western North Pacific anomalous anticyclone (WNPAC) is the key atmospheric circulation system that connects El Niño and East Asian climate variability. Understanding how the WNPAC will change in the future is of vital importance to people living in East Asia‐western Pacific region. There is extensive literature on the topic of changes in the WNPAC in response to global warming but how such kind of connection would change under global warming remains inconclusive. The causes of uncertainty in the WNPAC projection and the dominant mechanisms remain unknown. Based on 34 state‐of‐art climate coupled models, we show evidence that uncertainty in El Niño projection is a source of uncertainty in the WNPAC projection. Our results highlight the importance of a reliable projection of El Niño decaying pace to the projection of climate variability over the western Pacific and East Asia. Key Points: The projected changes in the WNPAC during El Niño decaying summers are uncertain among different climate modelsThe uncertainty of El Niño‐northwestern Pacific climate relationship projection is determined by the El Niño decaying pace under global warmingChanges in El Niño decaying pace depend on the strength of wintertime WNPAC [ABSTRACT FROM AUTHOR]

The evolutionary and population demographic history of marine red algae in East Asia is poorly understood. Here, we reconstructed the phylogeographies of two upper intertidal species endemic to East Asia, Gelidiophycus divaricatus and G. freshwateri. Phylogenetic and phylogeographic inferences of 393 mitochondrial cox1, 128 plastid rbcL, and 342 nuclear ITS2 sequences were complemented with ecological niche models. Gelidiophycus divaricatus, a southern species adapted to warm water, is characterized by a high genetic diversity and a strong geographical population structure, characteristic of stable population sizes and sudden reduction to recent expansion. In contrast, G. freshwateri, a northern species adapted to cold temperate conditions, is genetically relatively homogeneous with a shallow population structure resulting from steady population growth and recent equilibrium. The overlap zone of the two species roughly matches summer and winter isotherms, indicating that surface seawater temperature is a key feature influencing species range. Unidirectional genetic introgression was detected at two sites on Jeju Island where G. divaricatus was rare while G. freshwateri was common, suggesting the occurrence of asymmetric natural hybrids, a rarely reported event for rhodophytes. Our results illustrate that Quaternary climate oscillations have left strong imprints on the current day genetic structure and highlight the importance of seawater temperature and sea level change in driving speciation in upper intertidal seaweed species. [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]

This study investigates the interannual variability of rainfall over the middle and lower reaches of Yangtze River Valley (MLYRV) and that over the South China Sea and Philippine Sea (SCS‐PS) during boreal summer (June–August) from 1979 to 2012. Results exhibit out‐of‐phase rainfall variations between the MLYRV and the SCS‐PS, which is closely related to the tropical zonal sea surface temperature gradient (ZSG) between the northern Indian Ocean (NIO; 5°–25°N, 60°–100°E) and the equatorial central and eastern Pacific (CEP; 5°S–5°N, 180°–130°W). The ZSG can explain as much as 40% of the total variance of the summer rainfall over the MLYRV and the SCS‐PS in the past 40 years. This is much higher than that explained by the NIO SST (24%), CEP SST (14%) and Niño‐3.4 index (16%) alone. A positive ZSG between the warm NIO and the cold CEP tends to increase rainfall over the MLYRV and decrease rainfall over the SCS‐PS, whereas a negative ZSG between the cold NIO and the warm CEP is generally favourable for rainfall over the SCS‐PS and unfavourable for rainfall over MLYRV. The close connection between the ZSG and the out‐of‐phase interannual rainfall variation over the two regions can be explained by influences of the ZSG on atmospheric circulation over East Asia. A positive ZSG induces anomalous easterlies and Walker‐like circulation in the tropics, which results in an anomalous subsidence and boundary layer divergence over the SCS‐PS. As a result, summer rainfall decreases in this region. Meanwhile, moisture transport increases due to the anomalously strong southwesterlies along the northwestern flank of the intensified western Pacific subtropical high, providing more precipitable water to the MLYRV region. In contrast, a negative ZSG induces surface westerlies and favourable environmental condition for rainfall over the SCS‐PS. Dry descending flow induced by local anomalous Hadley circulation develops over the MLYRV around 30°N, which is unfavourable for rainfall over the MLYRV. The mechanism further examined using numerical experiments. These thermal‐dynamical processes induced by the ZSG work together to cause the out‐of‐phase interannual changes of rainfall between the MLYRV and the SCS‐PS, suggesting that the ZSG is highly indicative of the interannual change of summer rainfall in the two regions. [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]

Future change of the rainy season over East Asia region is investigated using the high horizontal resolution global atmospheric model called the Meteorological Research Institute-Atmospheric General Circulation Model (MRI-AGCM) version 3.2S (20-km grid) and 3.2H (60 km). Higher reproducibility of precipitation during East Asian rainy season gives reliability of future projections. For the present-day simulations (1983-2003, 21 years), the models are forced with observed historical sea surface temperature (SST). For the future simulations (1979-2099, 21 years), the models are forced with future SST projected by Atmosphere-Ocean General Circulation Models (AOGCMs) participated to the fifth phase of the Coupled Model Intercomparison Project (CMIP5). In order to estimate the uncertainty of future change, we execute ensemble simulations with three kinds of cumulus convection schemes and four kinds of SST distributions using 60-km version to meet the limitation of computer resources. For each grid point, the onset and retreat of rainy season are defined from time evolution of pentad mean precipitation. The onset of rainy season becomes earlier in most regions over East Asia, but onset will delay in some area of western Japan. Retreat delays over China and Korea. Duration increases in most part of East Asia especially over China and Korea. This can be caused by enhanced water vapor transport from the tropics. The delay of onset over western Japan can be attributed to the decrease of water vapor transport associated with the southward shift of the subtropical high. Future change presented in higher horizontal resolution compared with previous studies is useful for impact, adaptation and mitigation studies of global warming. [ABSTRACT FROM AUTHOR]