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This study explored the interannual characteristics of the out‐of‐phase pattern of summer precipitation over northern China during the past years, as well as the possible underlying mechanisms. The out‐of‐phase pattern is characterized by the positive precipitation anomaly in Northwest China (NWC) and the negative anomaly in North China (NC). Our analyses indicate that the variation of Asian westerly jet (AWJ) is found evidently associated with this out‐of‐phase pattern of summer precipitation. The meridional displacement of AWJ induces opposite trends in water vapour transport and circulation anomalies between NWC and NC, leading to the out‐of‐phase pattern. Further analyses suggest that the anomalies of Arctic sea ice concentration (SIC), North Atlantic and Northwest Pacific sea surface temperature (SST) can impact the variation of AWJ by triggering the Eurasian (EU), polar‐Eurasia (POL) and Pacific‐Japan (PJ) teleconnection patterns, respectively, which in turn modulate the formation of this pattern. The precipitation in NWC is primarily affected by the North Atlantic and Northwest Pacific SST anomalies, whereas the precipitation in NC is notably influenced by both SST anomalies and the Arctic SIC anomaly. However, the role of SST anomalies on precipitation in NWC and NC exhibits an evident contrast, leading to the out‐of‐phase pattern of summer precipitation. [ABSTRACT FROM AUTHOR]

This study investigates the anthropogenic contribution to the summer precipitation changes over southern China and the underlying physical mechanisms. Observations show a wetting trend over southeastern China (SEC) but a drying trend over southwestern China (SWC) in summer of 1961–2014. The dipole pattern can be reasonably reproduced by the anthropogenic forcing simulations of CMIP6 models but with weak trends under the external natural forcing simulations, suggesting the vital human contribution to the observed changes. Particularly, anthropogenic greenhouse gases (GHG) dominate the wetting trend over SEC, while the drying trend over SWC is primarily attributed to anthropogenic aerosol (AA) emissions. Further analysis shows that the GHG concentrations enhance the subtropical high over the western North Pacific (WNP) via the heterogeneous warming of the sea surface temperature, decrease the sea level pressure over eastern China, and increase the atmospheric moisture, facilitating the moisture flux convergence (MFC) and the precipitation over SEC. The GHG‐induced wetting trend is somewhat offset by the inhibited evaporation due to the AA forcing. For SWC, the decreased precipitation is influenced by the anomalous high pressure from India to WNP, which is closely associated with the enhanced Asian AA emission and the interhemispheric asymmetrical distribution of AA emissions. In the upper troposphere, the uneven AA emissions between South and East Asia and Europe weaken the East Asian summer subtropical jet, resisting the western moisture to SWC. Both factors in the low‐and‐high levels suppress the MFC and precipitation over SWC, counteracted by the thermodynamical effects of GHG forcing. Plain Language Summary: Previous studies have documented the emergence of human signal in changes in precipitation over China, but how the anthropogenic forcing affects the precipitation changes across China is still unclear. This study examines the influence of human activities, such as greenhouse gases (GHG) and anthropogenic aerosol (AA) emissions, on summer precipitation changes in southern China. Observations show a wetting trend in southeastern China (SEC) and a drying trend in southwestern China (SWC) from 1961 to 2014. The simulations indicate that GHG contribute to the wetting trend in SEC, while AA emissions are responsible for the drying trend in SWC. GHG enhance the subtropical high over the WNP, increase atmospheric moisture, and promote precipitation in SEC. In SWC, the high pressures influenced by increased Asian AA emissions weaken moisture flow, leading to decreased precipitation. Uneven AA emissions between regions also impact the transport of moisture. Overall, human activities have a significant impact on the observed changes in summer precipitation in southern China. Key Points: The wetting trend in southeastern China is primarily attributed to the greenhouse gases emission through both dynamic and thermodynamic effectsAerosol emissions are responsible for the drying trend in southwestern China and the dynamic processes dominate the decreased precipitationAerosol induced evaporation decreases precipitation in southeastern China and the drying trend in southwestern China is offset by GHG effect [ABSTRACT FROM AUTHOR]

One prominent mode of the variability in the summer wet‐bulb temperature (WBT) over eastern China exhibits a distinct north‒south dipole pattern. This pattern demonstrates a positive center in northern China (NC), while a negative center is observed in southern China (SC). Our results indicate that the dipole mode of WBT could be partially ascribed to the impact of spring snow anomalies in eastern Europe–western Siberia (EEWS). The reduction in the snow depth, coupled with dry soil conditions, enhances the surface heat flux and consequently leads to an increase in the near‐surface air temperature. The signal of soil moisture could persist from spring to summer, stimulating the generation of zonal Rossby waves. Consequently, the significant wave flux anomalies propagate from EEWS downstream and influence the atmospheric circulation over eastern China. These patterns play a role in the increase in the surface air temperature and moisture accumulation over NC, ultimately leading to the establishment of the dipole mode of WBT over eastern China in summer. Further analysis indicates that the atypical low sea surface temperature in the tropical Ocean, induced by the El Niño‐Southern Oscillation, establishes a climatic context favorable for the persistence of an anomalous cyclone in the Northwest Pacific (NWP) throughout the summer season. The strengthened convection over the NWP and SC induces a dipole pattern of atmospheric circulation by stimulating a meridional wave train. This pattern creates favorable temperature and moisture conditions, contributing to the development of the dipole mode of the summer WBT across eastern China. Plain Language Summary: In recent decades, the social loss associated with high‐temperature and high‐humidity conditions has sharply increased. The wet‐bulb temperature (WBT) is widely regarded as a highly effective metric for characterizing the combined stress of humidity and heat. In this study, we emphasized one of the important modes (a north‒south dipole pattern) of the variability in the summer WBT over eastern China and revealed the corresponding underlying mechanisms. We found that mid‐high and low latitudinal dynamic processes may exert a synergistic effect on WBT over eastern China. On one side, spring snow depth anomalies could be coupled with spring soil moisture anomalies over eastern Europe–western Siberia and subsequently influence the dipole mode of the summer WBT over eastern China by triggering the stimulation of zonal Rossby waves. On the flip side, the anomalous low sea surface temperature in the tropical Ocean, driven by the ENSO, could yield a climatic state that supports the prolonged existence of an anomalous cyclone over the Northwest Pacific throughout the summer season. This cyclone exerts a significant impact on the dipole mode of the summer WBT over eastern China. Our study compensates for the lack of humid heat effect‐related research across eastern China and contributes to establishing a solid theoretical foundation for comprehending and forecasting the summer WBT in the region. Key Points: One significant pattern of the variability in the summer wet‐bulb temperature (WBT) over eastern China is manifested as a north‒south dipole modeAnomalous spring snowfall over Eurasia can impact the dipole mode of summer WBT over eastern China via the stimulation of zonal Rossby wavesThe anomalous sea surface temperature over tropical ocean, triggered by El Niño‐Southern Oscillation, establishes a climatic context conducive to the dipole mode over eastern China [ABSTRACT FROM AUTHOR]

Winter precipitation is critical for glacier growth, snow accumulation, and terrestrial storage on the Tibetan Plateau (TP). However, less attention has been paid to the changes in winter precipitation on the TP. In this study, based on the newly developed high-accuracy precipitation dataset, our diagnosis illustrated a distinct precipitation deficit over the southern TP and northern Indian continent (STNI) in December. Together with the ERA5 reanalysis, CESM1.1 large ensemble experiments, and pacemaker experiments, the dynamic diagnosis revealed that the precipitation deficit was attributed to the decrease in dynamic effects. In particular, the enhanced descending motion, accompanied by the strengthened anticyclone and regional meridional circulation over the STNI, resulted in the precipitation deficit. The changes in circulation system related to the precipitation deficit could be attributed to the Pacific and Indian sea surface temperature (SST) variability. With the negative interdecadal Pacific oscillation (IPO), there were circumglobal alternative geopotential height anomalies and an anomalous anticyclone over the southern TP, and descending motion around the STNI associated with the enhanced Walker circulation over the Indo-Pacific, which exhibited a similar pattern to the precipitation deficit over the STNI in the observations. In addition, the synergistic effect of Pacific and Indian SST variability can improve the simulated precipitation deficit over the STNI relative to the Pacific SST variability alone. These results imply a contribution of the tropical SST variability to the precipitation trends over the STNI in early winter and provide an insight into the understanding of climate warming on the winter climate over the TP. [ABSTRACT FROM AUTHOR]

This study reveals a significant subseasonal reversal of precipitation on the western Tibetan Plateau (WTP) from a deficit in December to an increase in January and February (JF). Changes in vertical moisture advection induced by the dynamic effects contribute mostly to the subseasonal precipitation trend reversal. This process involves the reversal of the subseasonal westerly driven uplift, accompanied by the weakened (enhanced) subtropical westerly jet and anticyclonic (cyclonic) anomalies over the WTP in December (JF). Further analysis shows that the North Atlantic Tripolar‐like (NAT) sea surface temperature (SST) modes could regulate the sunseasonal winter precipitation reversal over the WTP. The spatially inconsistent changes in SST can result in subseasonal reversed turbulent heat flux anomalies over Iceland‐Scandinavia in December and JF. In particular, the suppressed turbulent heat flux over the extratropical Northeast Atlantic in December leads to significant descending motion and upper tropospheric convergence. The advection of absolute vorticity induced by convergent winds associated with the NAT favors the generation of Rossby wave sources over Iceland‐Scandinavia, which then enhances the wave activity fluxes propagation. However, there are no significant changes in wave sources over Iceland‐Scandinavia in JF. The discrepancies in wave propagation intensity over Iceland‐Scandinavia determine the changes in the atmospheric pattern over the WTP, with anomalous anticyclone in December and cyclone in JF, and ultimately lead to the precipitation reversal. Furthermore, our results show that the suppressed transient eddies over the Atlantic storm track in JF may also contribute to the weakened wave propagation over Iceland‐Scandinavia. Key Points: A subseasonal reversal of precipitation in winter is evident in precipitation anomalies over the western Tibetan PlateauThe main contributor to the precipitation reversal is the subseasonal reversal of vertical moisture advection due to dynamic effectsThe Atlantic tripolar sea surface temperature anomalies could regulate precipitation reversal through stimulating asymmetric circulation mode over Eurasia [ABSTRACT FROM AUTHOR]

Different evolutionary patterns of the East Asian trough (EAT) anomaly could cause different climate patterns over East Asia. In this study, the leading mode of month-to-month variation in winter (December–January–February) EAT during 1979/80–2018/19 is investigated using the extended empirical orthogonal function (EEOF). The first EEOF mode (EEOF1) shows a persistent anomalous EAT pattern throughout the three winter months, which results in persistent air temperature anomalies over East Asia. Mechanism analyses indicate that the El Niño-Southern Oscillation (ENSO) negatively relates to the EEOF1, but its significant influence on the EAT is only in December. In contrast, a dipole pattern of sea surface temperature (SST) anomalies over the Eastern North Atlantic-Eastern Mediterranean Sea closely links with the EAT EEOF1. Further analyses indicate that the connection of the dipole SST pattern with the EAT EEOF1 depends on its persistence. When there is positive feedback between the local atmosphere and sea, the dipole SST pattern is well-sustained in the three winter months and further leads to a persistent EAT anomaly by exciting the Rossby wave train over mid-latitude Eurasia. Numerical simulations by the linear baroclinic model further validate the role of dipole SST pattern-related diabatic and vorticity forcing in air-sea interactions. In contrast, in the SST poorly-sustained years, the dipole SST pattern has a weak connection with the EAT EEOF1. Based on the aforementioned analysis, we propose a combined index using the dipole SST pattern and anomalous Northeast Atlantic cyclone in December, which could provide valuable information to predict the dipole SST pattern persistence and EAT EEOF1 in winter. [ABSTRACT FROM AUTHOR]

This study aimed to explore the changing characteristics of summer, compound, extreme hot–humid events over eastern China in recent decades and the associated underlying mechanisms. Results showed that the summer extreme hot–humid events over eastern China have tended to increase but with strong interannual variability in recent decades. Further analyses indicated that the summer sea surface temperature (SST) anomalies over the northwest Pacific (NW Pacific) and western tropical Pacific, and the May Arctic sea ice concentration (SIC) anomalies are the key elements that are closely connected to the variations in extreme hot–humid events over eastern China. The positive SST anomalies over the NW Pacific in summer, on the one hand, could strengthen the local circulation patterns that lead to the anomalous anticyclonic circulation over eastern China. On the other hand, the positive SST anomalies over the western tropical Pacific excite an anomaly pattern similar to the Pacific–Japan pattern that weakens the westerly jet and enhances the anticyclone circulation anomalies over the upper level of eastern China. Both of them provide favorable conditions for extreme hot–humid events over eastern China with increased moisture and temperatures. The sensitivity experiments by the Community Atmosphere Model, version 5 (CAM5), with SST forcing yield similar influencing processes to the observations. Additionally, the effect of SIC may be potentially responsible for the hot conditions in extreme hot–humid events over eastern China. The signal of declining May SIC could persist to summer and then influence the SST anomalies to its south, which could also produce a beneficial background for extreme hot–humid events to increase over eastern China by exciting the Rossby wave train propagating southeastward across the Mongolia–Lake Baikal region. [ABSTRACT FROM AUTHOR]

This study examines August droughts in northern China (north of 35°N) at interannual and interdecadal timescales. During the period from 1968 to 1992, the precipitation in the western and eastern regions of northern China showed an out‐of‐phase pattern. During the period from 1994 to 2018, the climate in the Tarim Basin became wetter, but there was no significant connection with drought in North China. Further studies demonstrated that the Atlantic sea surface temperature (SST) and regional soil moisture anomalies were related to drought changes in northern China. Before the early 1990s, the east‐west standardized precipitation index dipole mode in northern China was physically linked with the wet soil in central Asia in the preceding June; moreover, the wet land surface could persist until August and cause anticyclonic and cyclonic systems over Mongolia and the subtropical northwestern Pacific, thus contributing to precipitation surplus in northwest China and a deficit in North China. After the early 1990s, however, wet conditions over the Tarim Basin were related to wet soil in the East European Plain in the preceding July: the wet soil could persist into August and generate anomalous circulation over the Tarim Basin, leading to abnormal humidity. Additionally, the SST conditions in the North (South) Atlantic are key sources of climate predictability for northern China drought at the interseasonal scale after (before) the early 1990s. Key Points: The spatial distribution of the standardized precipitation index in northern China shows a marked zonal dipole patternThe drought in northern China underwent a remarkable interdecadal change in approximately 1992The Atlantic sea surface temperature and regional soil moisture anomalies were responsible for the drought changes in northern China [ABSTRACT FROM AUTHOR]

This study explores the spatial–temporal variations in summer extreme precipitation over Southwestern China (SWC). The frequency of summer extreme precipitation (FEP) has exhibited strong interannual variation with slightly strengthened intensity in recent decades. The associated anomalous water vapour transport mainly originates from northern China, the Indian Ocean, the South China Sea and the Northwest Pacific. The high FEP over SWC is generally associated with the strong Eurasian (EU) pattern and the pattern that is similar to Pacific‐Japan (PJ) teleconnection. The results further indicate that the anomalous May Arctic sea ice concentration and the sea surface temperature anomaly over the Northwest Pacific play an important role in the variation of FEP over SWC. On the one hand, the reduction in Arctic sea ice concentration intensifies Rossby wave propagation and then stimulates the formation of EU teleconnection pattern. The associated anomalous northeasterly integrated water vapour transport and high‐level westerly anomalies can result in strong interannual changes in FEP over SWC. On the other hand, the sea surface temperature anomaly over the Northwest Pacific can induce an anomalous PJ‐like pattern, and the associated anomalous southwesterly water vapour transport also exerts an impact on the change in FEP over SWC. [ABSTRACT FROM AUTHOR]

Based on the long-term reanalysis datasets and the multivariate copula method, this study reveals that the frequency of summer hot drought events (SHDEs) over northeastern China (NEC) shows interdecadal variations during 1925–2010. It is revealed that the summer sea surface temperature (SST) over the North Atlantic has a significant positive correlation with the frequency of SHDEs over NEC on the decadal time scale, indicating a potential influence of the Atlantic multidecadal oscillation (AMO). Further analyses indicate that during the positive phases of the AMO, the warming SST over the North Atlantic can trigger a stationary Rossby wave originating from the North Atlantic, which splits into two wave trains propagating along two different routes. One is a zonally orientated wave train that resembles the Silk Road pattern, whereas the other is an arching wave train that resembles the polar–Eurasian pattern. A negative (positive) phase of the Silk Road pattern (polar–Eurasian pattern) may result in the weakened westerly wind along the jet stream, the downward vertical motion, and the anomalous positive geopotential center over NEC, providing favorable conditions for precipitation deficiency and high temperature and resulting in increased SHDEs. Thus, the Silk Road pattern and the polar–Eurasian pattern serve as linkages between the AMO and SHDEs over northeastern China in summer on the interdecadal time scale. Model simulations from CAM4 perturbed with warmer SST in the North Atlantic show precipitation deficiency and high temperature conditions over northeastern China in summer, supporting the potential impacts of the North Atlantic SST on SHDEs over northeastern China. The results suggest that the phase of the AMO should be taken into account in the decadal prediction of SHDEs over northeastern China in summer. [ABSTRACT FROM AUTHOR]

This study assessed the capability of the historical simulations of phase 5 and 6 of the Coupled Model Intercomparison Project (CMIP5/6) in reproducing the temporal and spatial characteristics of the Interdecadal Pacific Oscillation (IPO) and its impact on global surface air temperature (SAT), surface equivalent potential temperature (Thetae_sfc) and precipitation. The IPO index time series simulated by CMIP5/6 models deviated from observations and struggled to capture the phase evolution characteristics of the IPO. Nevertheless, CMIP5/6 models successfully captured the horseshoe‐shaped sea surface temperature anomaly in the Pacific. Additionally, the CMIP5/6 models were able to simulate the IPO's 10–30‐year period. Notably, the simulated IPO index exhibited a statistically significant upward trend, which was absent in observations. Additionally, the IPO‐related global land SAT, Thetae_sfc and precipitation simulated by CMIP5/6 models performed differently in boreal winter and boreal summer. Furthermore, the IPO‐related global land SAT performed better in CMIP5/6 models during boreal winter than that in boreal summer. In CMIP6 models, it improved during both boreal winter and summer compared to CMIP5 models. In terms of the IPO‐related global land Thetae_sfc, CMIP5/6 models also performed better during boreal winter than in boreal summer. However, CMIP5 models outperformed CMIP6 models during the boreal summer. In terms of the IPO‐related global land precipitation, CMIP5/6 models performed better during boreal summer compared to boreal winter. Moreover, the IPO‐related global land precipitation in CMIP6 models improved significantly in boreal winter, but almost the same in boreal summer, compared to CMIP5 models. Further studies showed that the enhancements in simulating IPO's spatial pattern did not correspond to improvements in the model's ability to simulate IPO's global teleconnections. [ABSTRACT FROM AUTHOR]