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Surface ozone (O3) pollution under global climate change has become one of the top environmental issues. In this study, we focused on the coastal region in Southeast China with relatively low O3 precursor's emissions and complicated synoptic conditions, where the O3 trends and meteorological contributions remain unclear. An increasing trend of O3 concentrations in the cities (0.3–4.6 μg m−3 yr−1) from 2015 to 2020 was observed. Twenty‐three synoptic patterns were clustered based on weather typing method, in which cyclone‐related types and southwesterly type were generally associated with low O3 concentrations, and high O3 levels occurred with anticyclone‐related types. Considering both frequency and intensity of synoptic patterns, reconstructed O3 series captured 46.0%–58.3% of the observed variability. Using Kolmogorov‐Zurbenko filter, an increasing trend of long‐term O3 was found. By implementing the multiple linear regression model between O3 concentrations and meteorological factors, the meteorological contributions to O3 variabilities (44.7%–66.1%) were quantified. The results indicated the meteorological conditions were particularly important in O3 pollution with the reductions of O3 precursor's emissions, among which relative humidity, boundary layer height, solar radiation along with low cloud cover were proved to play important roles. The weakening southwest winds along with more anti‐cyclone systems under climate change could increase surface O3. This study elucidated the crucial meteorological drivers on the O3 variability in relatively clean areas and implied the challenges for local governments to mitigate O3 pollution under global climate change. Plain Language Summary: Ozone (O3) pollution has become one of the top environmental issues in recent years and can be affected not only by O3 precursors (volatile organic compounds and nitrogen oxides) but also meteorological condition. Under global climate change, there is a need to deeply understand the impact of meteorological factors on surface O3 concentrations with the decrease of O3 precursors. In this study, we focus on the coast area of Southeast China with relatively low O3 precursors emissions and influenced by the East Asia monsoon. Temporal and spatial variations of O3 concentrations along with the meteorological impacts on O3 variabilities from 2015 to 2020 were analyzed. The results show that the relative meteorological contributions on O3 trends were 44.7%–66.1%. The higher temperature, lower relative humidity, more solar radiation, weakening southwest winds along with more anti‐cyclone systems under climate change could increase surface O3. This study is beneficial to understand different mechanisms of meteorological impacts on O3 variations in the relatively clean areas, and find out the key drivers to cause O3 pollution with the decrease of O3 precursors emissions and climate change. Key Points: Temporal and spatial variations of O3 concentrations in the coastal of southeast China from 2015 to 2020 were analyzedWeather typing was applied to identify the dominant synoptic patterns and related meteorological factors lead on high O3 concentrationThe contributions of synoptic patterns and meteorological factors on long‐term O3 trends were quantified [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]

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]

In June‐July 2020, the Middle and Lower Yangtze River Region (MLYR) encountered the most severe precipitation event over the past 60 years. The Indian Ocean Dipole (IOD) in the previous autumn of the unusual precipitation event was the main contributing factor. Nonetheless, not every strong IOD event could bring anomalously high precipitation in the MLYR. This study showed significantly enhanced influence of IOD on East Asia climate since 2000. The IOD's effect on MLYR summer precipitation has strengthened significantly with the correlation coefficient up to 0.55 during 2000–2020. The northward movement of East Asia–Pacific pattern associated with IOD since 2000 (as compared with before) was primarily responsible for the enhanced effect. Since 2000, the MLYR has been controlled by a deep baroclinic instability system with anomalous low pressure in the lower troposphere and anomalous high pressure (completely different from before). Furthermore, the western Pacific subtropical high shifted northward and westerly jets were significantly enhanced with eastward expansion. All of these patterns contributed to the water vapor convergence and precipitation generation in the MLYR, which was not the case in the past. The record‐breaking IOD in 2019 autumn and the enhanced IOD's climatic effect in 2000–2020 contribute to the extreme Meiyu in 2020 jointly. The significant change in the influence of IOD and the enhanced climate effect of IOD highlight exciting new avenues for improving climate predictions in the MLYR. Plain Language Summary: The excessive Meiyu rainfall over the Middle and Lower Yangtze River Region (MLYR) during summer 2020 was beyond expectations of meteorologists, because in the 2019/20 winter, the Niño3.4 index was marginal at only 0.5°C as compared to 2.4°C and 2.6°C in 1997/98 and 2015/16 winters, respectively. Researches pointed out that the severely positive Indian Ocean Dipole (IOD) in the previous season was the main contributing factor on 2020 extreme Meiyu event in the MLYR. Nonetheless, not every strong IOD event could bring anomalously high precipitation in the MLYR. Our study shows significantly enhanced influence of IOD on East Asia climate since 2000. The IOD's effect on MLYR summer precipitation has strengthened significantly with the correlation coefficient up to 0.55 during 2000–2020. The IOD‐induced circulation patterns, including East Asia–Pacific pattern, the western Pacific subtropical high, and westerly jets, shifted northward with stronger intensity since 2000 (as compared with before). These results help us to reconsider the influence of tropical Indian Ocean sea surface temperature when forecasting weather or the possible climate changes under global warming. Key Points: The impact of Indian Ocean Dipole (IOD) on the Yangtze precipitation has enhanced in recent decadesThe IOD‐induced East Asia–Pacific pattern moves northward since 2000The interdecadal change in IOD's climatic effect largely contributes to the extreme Meiyu in 2020 [ABSTRACT FROM AUTHOR]

The intraseasonal meridional wave trains are the major features of East Asia summer monsoon (EASM), but the complete physical pictures of dynamic pathways from tropical and mid‐high latitudes and their climate impacts have not been fully illustrated. With NCEP‐DOE Reanalysis‐II daily data set, two boreal summer intraseasonal meridional oscillations (ISMOs) are isolated and identified by extended EOF of zonal wind anomalies along the coast of East Asia on 10‐ to 30‐day timescale, that is, ISMO1 and ISMO2. They both demonstrate obvious quasi‐biweekly oscillations with an equivalent barotropic structure in troposphere, and ISMO1 represents the southward propagating wave train with large variances in upper level, which is initiated from the West Europe and primarily forced by the soil moisture anomalies over mid‐high latitudes of Eurasian continent, whereas ISMO2 propagates northward in mid‐lower troposphere from the tropical western North Pacific to East Asia that is closely related to BSISO2. The two ISMOs are capable of explaining a large fraction of the total intraseasonal variances of EASM, wherein, ISMO1 is responsible for a meridional dipole pattern of precipitation anomalies over eastern China, while ISMO2 has major influence in southern China. Generally, ISMO‐caused changes of extreme precipitation probability are in good accordance with the spatial pattern of its related 10‐ to 30‐day intraseasonal precipitation anomalies. Since ISMO1 and ISMO2 can clearly separate the tropical and extratropical‐origin meridional oscillations and further have robust influences on precipitation over East Asia, they can be used as the new monitoring and predicting factors to the intraseasonal variations of EASM and their associated extreme precipitation. Key Points: Two intraseasonal meridional oscillations (ISMOs) over East Asia are identified with equivalent barotropic structure and biweekly periodISMOs can be forced by the tropical convection and the mid‐high latitude land surface and propagate northward and southward, respectivelyISMOs represent a large fraction of intraseasonal climate variations over East Asia and have significant impact on extreme precipitation [ABSTRACT FROM AUTHOR]

Understanding the climate controls of precipitation δ18O in the Tibetan Plateau (TP) is crucial for paleoclimate reconstructions from a wealth of regional archives. We use the outputs of iCAM5 model to quantify the different moisture contribution to local precipitation δ18O and to understand the climate controls of precipitation δ18O in the TP based on water‐tagging. The model shows some deficiencies in simulating the spatial and temporal characteristics of precipitation δ18O and the local climatic controls across the TP. Among all the tagged source regions, South Asia and the Indian Ocean contribute the most to the precipitation δ18O in the monsoon‐controlled domain, followed by the East Asia source region. The westerlies are identified as major moisture sources to the precipitation δ18O in the westerlies‐controlled domain. South Asia and the Indian Ocean also contribute substantially for the westerlies‐controlled domain. On interannual time scales, summer precipitation δ18O in the monsoon‐controlled domain is dominated by rainout processes occurring along the moisture transport pathway, indicating that precipitation δ18O variations here potentially record changes in the regional upstream convection. The δ18O signal can be altered by changes in the moisture source location, which implies that enhanced moisture delivery from remote source regions leads to more negative precipitation δ18O due to an increase in the rainout effect during transport. Our results have implications for the interpretation of past variations of archives with precipitation stable isotopes, such as ice cores, tree rings, lake sediments, and speleothems in the TP and surrounding regions. Plain Language Summary: Precipitation δ18O signal stored in climate proxy records from the Tibetan Plateau has long been used for paleoclimate reconstructions. However, the controls on precipitation δ18O over the TP remain debated. Studies of modern‐day climate controls on precipitation δ18O is crucial for interpreting past climate variations. We use the iCAM5 global atmospheric general circulation model fitted with water‐tagging capability to quantitatively decipher different climatic controls on precipitation δ18O across the TP. The model shows some deficiencies in simulating the spatial and temporal characteristics of precipitation δ18O and the local climatic controls across the TP. Among all the tagged source regions, South Asia and the Indian Ocean are identified as the most dominant moisture sources for the precipitation δ18O in the monsoon‐controlled domain, followed by the East Asia source region. For the westerlies‐controlled domain, the highest fractional contribution is from the westerlies. Changes in the rainout of water vapor during transport are the main driver of the interannual variability of precipitation δ18O in the monsoon‐controlled southern TP domain. The δ18O signal can be altered by changes in relative moisture contributions from different source regions. The amount effect contributes little to the precipitation δ18O variability in the southern TP. Key Points: Precipitation δ18O over the Tibetan Plateau (TP) is simulated with an AGCM implemented with water‐tagging capabilitySouth Asia and the Indian Ocean (the westerlies) contribute the most to precipitation δ18O in the southern (northern) TPVariability of precipitation δ18O in the monsoon‐controlled domain is dominated by rainout processes and moisture location changes [ABSTRACT FROM AUTHOR]

Countries in East Asia have set ambitious goals for the development of wind energy to meet the increasing energy demand and to mitigate anthropogenic climate change. However, few studies have investigated changes in wind energy over East Asia under future climatic conditions. In this study, we investigate future changes of 100‐m wind speed and wind energy potential over the CORDEX‐East Asia region under the Representative Concentration Pathway (RCP) 8.5 scenario, by using ensemble simulations from the regional climate model Consortium for small‐scale modeling in CLimate Mode (CCLM). A multivariate bias adjustment method based on the N‐dimensional probability density function transform is used to correct raw simulated horizontal wind components. The comparison between future climate (2021–2050 and 2070–2099) and the present climate (1971–2000) shows decreases in wind speed, wind power density, and wind energy output over most of the CORDEX‐East Asia region, especially in the tropics. Projected increases are pronounced over the Himalayan regions, the Indo‐China Peninsula, the South China Sea, and the western Pacific Ocean in summer and over northeastern China, parts of Western China and the Indo‐China Peninsula in winter. Interannual and intra‐annual variability of wind power density are projected to intensify significantly for most of the CORDEX‐East Asia region. The occurrence of weak wind speeds (<3 m/s) is projected to increase, while strong wind speeds (>11 m/s) are projected to decrease over most of the ocean. Key Points: Future changes in 100‐m wind energy potentials over CORDEX‐East Asia are evaluated by using CCLM ensemble simulationsThe multivariate bias adjustment method is used to correct raw simulated wind components and is shown to be robust in reducing biasWind energy potentials are projected to decrease over most of the CORDEX‐East Asia region, especially for 2070–2099 [ABSTRACT FROM AUTHOR]

The winter temperature in East Asia from 1958 to 2001 has shown an obvious warming trend superposed with a large amplitude of decadal oscillations. To separate the relative contributions of external forcing and internal variability to the decadal change in winter temperature, we propose a method which combines reanalysis data, global atmosphere‐ocean coupled model outputs, and regional climate model. The results show that the weakening of the East Asian winter monsoon accounts for warming trend in the south Mongolia, the southeastern coast of Asia, and the adjacent seas to a large extent. In contrast, radiative forcing causes the warming trend in middle and high latitudes. The increasing concentration of aerosols could have resulted in local cooling in some areas. The winter temperature shows a decadal oscillation of 0.6 °C at a time scale of 8–20 a, which is mainly due to the oscillation of the Siberian‐Mongolia High and volcanic activities. The amplitude of temperature oscillations caused by volcanic activities was one third of that induced by the Siberian‐Mongolia High. Key Points: The winter warming in East Asia during 1958–2001 was due to greenhouse gas emissions and the weakening of the East Asia winter monsoonRadiative‐forced warming had a uniform pattern, while the warming caused by weakening monsoon was located in the eastern coast of EurasiaVolcanic aerosols caused an interdecadal oscillation of 0.2 °C, which was one third of the strength caused by internal variability [ABSTRACT FROM AUTHOR]

This study revisits precipitation change in East Asia caused by the Madden‐Julian oscillation (MJO) and its interannual variation due to the quasi‐biennial oscillation (QBO). Specifically, boreal‐winter precipitation, derived from weather stations across China, Korea, and Japan, is examined for MJO phases 2–3 and 6–8. Consistent with previous findings, precipitation in southern China and southern Japan increases by up to 36% during MJO phases 2–3, when the MJO convection is located in the Indian Ocean. In contrast, during MJO phases 6–8, precipitation decreases by 13%. More importantly, these MJO‐related precipitation anomalies become larger and more organized when the QBO is in its easterly phase. The difference in precipitation anomalies between the QBO easterly and westerly phases is approximately 40% for MJO phases 2–3 and 70% for MJO phases 6–8 from southern China to Japan. This result reaffirms that the QBO can affect surface weather in the northern extratropics through MJO teleconnection. Plain Language Summary: Deep convections in the tropics influence distant regions via propagation of energy in the form of waves. With its change dominant on the intraseasonal timescale, the Madden‐Julian oscillation (MJO) is known to change daily winter precipitation in East Asia. At the same time, far above in the tropical stratosphere, there is a year‐to‐year variation in zonal wind called the quasi‐biennial oscillation (QBO). It is widely believed that the MJO is stronger and more persistent when the QBO blows from east to west (easterly) than when it blows from west to east. Based on this belief, how MJO‐induced precipitation in East Asia is affected by the QBO is investigated. As expected, the degree of change in precipitation is larger with a stronger MJO amplitude during easterly QBO winters. During easterly QBO winters, MJO‐induced vertical motion near coastlines of East Asia is amplified by stronger upper‐level circulations. Furthermore, moisture transport from the subtropics is also enhanced with the stronger low‐level circulation in easterly QBO winters. In the sense that the QBO has a longer timescale as well as a longer memory than the MJO, we expect to utilize the QBO to predict MJO‐related surface weather changes in the extratropics better and earlier. Key Points: The MJO‐induced precipitation anomaly in East Asia is significantly influenced by QBO phaseThe MJO teleconnection in East Asia is strengthened during easterly QBO winters, when the MJO amplitude is enhancedThe moisture supply to East Asia by MJO‐induced circulation is enhanced during easterly QBO winters [ABSTRACT FROM AUTHOR]