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This study compares the physical processes responsible for the heavy and light rain variations from the perspective of spring precipitation over Southern China. The results indicate that, heavy rain variation has a closer connection with the western North Pacific anticyclone. Intensified western North Pacific anticyclone and associated warm and humid air transport, coupled with intensified East Asian subtropical jet, favor significant moisture convergence and enhanced convective feedback over the key region, which causes increased heavy rain rather than light rain over there. In comparison, light rain variation shows a close relationship with the anomalous low over Lake Balkhash, which causes lower-tropospheric cyclone over the key region. On the one hand, anomalous cyclone favors lower-tropospheric cooling; concurred with cyclone-induced increased moisture, the lower-tropospheric relative humidity increases over there. On the other hand, the lower-tropospheric cooling center shifts northward with height and causes enhanced atmospheric baroclinity over there. Such atmospheric conditions are conducive to the occurrence of low cloud and more light rain. In addition, intensified East Asian subtropical jet associated with Lake Balkhash anomalous low also provides favorable dynamic lifting condition. Moreover, heavy and light rain variations are more related to El Niño-Southern Oscillation and North Atlantic horseshoe sea surface temperature in preceding winter, respectively. In addition, heavy rain shows a closer relationship with total precipitation amount variation, whereas light rain is more related to extreme consecutive dry days variation. [ABSTRACT FROM AUTHOR]

Mongolian extratropical cyclones (ETCs) play a crucial role in the weather and climate over East Asia, and the use of datasets with higher spatiotemporal resolutions can improve the understanding of Mongolian ETCs. Based on an automatic detection and tracking algorithm and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) dataset, the characteristics of the frequency, lifetime, moving distance, moving speed, and intensity of Mongolian ETCs in spring during 1979–2021 are investigated. The results show that 92.6% of the Mongolian ETCs are locally formed. There were two decadal changes in the Mongolian ETC frequency in approximately 1993 and 2004, showing a "high–low–high" variation. In terms of ETC passages, there is an increasing trend from central Mongolia to Northeast China and a decreasing trend east of Lake Baikal, indicating that the Mongolian ETC tracks are located more southward. Based on the standard deviation ellipse method and K-means clustering, the Mongolian ETCs are clustered into three categories, namely, southern track (ST, accounting for 53.4% of Mongolian ETCs) ETCs, northern track (NT, accounting for 43.8%) ETCs, and long track (LT, accounting for 2.8%) ETCs. The ST ETCs have a significant increasing trend, while the NT ETCs show a significant decreasing trend. Moreover, the other properties of Mongolian ETCs also show significant decadal variability. The sequences of lifetime, moving distance, moving speed and intensity exhibit decadal changes in the 1990s, with longer lifetime and moving distance, faster moving speed, and stronger intensity after the abrupt change. [ABSTRACT FROM AUTHOR]

This study analyzes the interannual relationship between preceding winter Aleutian low (AL) and spring extreme consecutive dry days (extreme-CDDs) in the Yangtze-Huai River region (YHR) during 1979–2019. The results show that, independent from the El Niño-Southern Oscillation variability, a weakened AL in February is accompanied by more spring extreme-CDDs in YHR. Additionally, such a relationship shows a remarkable decadal enhancement after the late-1990s, in which the changes in the Bering Sea ice (BSI) and stratospheric polar vortex (SPV) play bridging roles. On the one hand, the weakened AL could lead to decreased BSI in spring during the whole period by inducing anomalous warm-moist air transport and the resultant radiation effect. After the late-1990s, the decreased BSI could cause a stronger anomalous high over Lake Baikal in spring by exciting an eastward propagated atmospheric wave train, favoring downward motions and more extreme-CDDs in YHR. On the other hand, after the late-1990s, the weakened AL could induce an intensified SPV persisting from late February to early spring by inhibiting the upward propagation of planetary wave. The SPV signal could in turn propagate downward to the troposphere, also contributing to anomalous high over Lake Baikal in spring and more extreme-CDDs in YHR. In contrast, the stratosphere-troposphere interaction associated with anomalous AL is weak before the late-1990s. Through the above-mentioned physical processes, the February AL could have a significantly lagged impact on spring extreme-CDDs in YHR after the late-1990s, consequently providing valuable prediction source for the variability of spring extreme-CDDs in YHR. [ABSTRACT FROM AUTHOR]

Northeast China (NEC) is an important crop production base in East Asia. The monthly evolution of precipitation during spring sowing from April to May is of significance for agricultural activity and production over NEC. This study first investigates the predominant modes of April-to-May precipitation evolution over NEC and then explores their connections with North Atlantic sea surface temperature (SST) anomalies during 1979–2016. The first mode obtained using a multivariate empirical orthogonal function (MV-EOF1) shows an out-of-phase change in NEC precipitation anomalies from April to May, but the second mode (MV-EOF2) shows an in-phase change. Further analysis indicates that SST variability over mid-latitude North Atlantic (MNA) is related to MV-EOF1 by exciting a wave train from MNA to Eurasia. The wave train position is located more westward in May relative to April, leading to reverse atmospheric circulation and precipitation anomalies over NEC between April and May. The changes in position of circulations may be related to the westward shift of the North Atlantic storm track from April to May. MV-EOF2 is related to SST variability over northern tropical Atlantic (NTA). In April, NTA SST anomalies impact NEC precipitation through mid-latitude Eurasian wave train and Walker-like circulation anomalies between the Atlantic and Pacific Oceans. In May, the mid-latitude pathway is effective; however, the tropical pathway is significantly weakened, which may be related to the weakened intensity of NTA SST-induced tropical diabatic heating. Numerical simulations can reproduce the linkage between the North Atlantic SSTs and the pronounced atmospheric circulation anomalies in the observation, further confirming the impacts of North Atlantic SSTs on NEC April-to-May precipitation evolution. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between the North Atlantic sea surface temperature (NASST) in autumn (September–October–November, SON) and the tropospheric Asian polar vortex (APV) in the following winter (December–January–February, DJF). The results show that the SON SST anomaly over the mid-latitude North Atlantic conditionally provides a valuable source for the prediction of the DJF APV's interannual variability. When the SON NASST anomaly can persist into DJF, there is a practical prediction of the DJF APV. Physical diagnosis indicates that the presence/absence of an active air–sea interaction determines whether the SON SST anomaly signals could be maintained to DJF. During the years when the SON NASST anomaly is well sustained, the SST anomaly could efficiently heat the air column above. The resultant atmospheric circulation anomalies, in turn, change the low-level climatological winds and induce anomalous turbulent heat flux, which further exerts impacts on the NASST anomaly, resulting in a similar SST anomaly pattern with the pronounced NASST anomaly. Therefore, the resultant atmospheric circulation anomalies provide positive feedback to the anomalous SST and favor the persistence of the SST anomaly. In DJF, the NASST anomaly can excite a wave train pattern to influence the APV. However, during the poorly sustained years, the air–sea interaction over the North Atlantic is weak, and the SST anomaly can hardly influence the overlying air column. Without the positive air–sea feedback, the SON NASST anomaly cannot persist into DJF and cannot affect the DJF APV. [ABSTRACT FROM AUTHOR]

The boreal spring relationship between variabilities of East China precipitation (ECP) and tropical Ocean sea surface temperature (SST) during the period 1951-2014 is investigated in this study. The results show that the leading mode of the ECP variability exhibits an enhanced response to the anomalous El Niño-Southern Oscillation (ENSO)-like SST after the late 1970s, when the SST underwent a decadal change, with two positive centers over the eastern tropical Pacific (ETP) and tropical Indian Ocean (TIO). To further understand the relative roles of the ETP and TIO SST anomalies (SSTAs) in the variability of ECP after the late 1970s, partial regression and correlation methods are used. It is found that, without the contribution of the TIO, ETP SSTA plays a limited role in the variability of ECP after the late 1970s; comparatively, a significant correlation between TIO SST and ECP is identified during the same period, when the ETP signal is linearly removed. Physical analyses show that, after the late 1970s, the TIO SSTA affects East Asian atmospheric circulation in two ways: by exciting a zonal wave-train pattern over the mid-latitude Eurasian Continent and by inducing anomalous convection over the Maritime Continent. Via these two mechanisms, the TIO SST variability results in an anomalous East Asian trough and vertical motion over East China and consequently leads to anomalous precipitation over the region. The physical processes linking the ECP and TIO SST are confirmed by an atmospheric general circulation model experiment forced with idealized TIO warming. [ABSTRACT FROM AUTHOR]

In this study, a possible mechanism for the decadal variability in the East Asian winter monsoon (EAWM) is proposed. Specifically, the North Pacific sea surface temperature (SST) may play an important role. An analysis of the observations shows that the North Pacific SST has a remarkable decadal pattern whose phase shifted around the mid-1980s. This North Pacific SST decadal pattern can weaken the East Asian trough and enhance the North Pacific Oscillation through changing air-sea interactions over the North Pacific. The weak East Asian trough enhances the zonal circulation and weakens the meridional circulation over East Asia, consequently leading to a weaker southward cold surge and East Asia warming around the mid-1980s. The numerical experiment further confirms the pronounced physical processes. In addition, over the longer period of 1871-2012, the indices of the EAWM and North Pacific SST decadal pattern are also highly consistent on the decadal timescale, which further confirms the impact of the North Pacific SST decadal pattern on the EAWM decadal variability. [ABSTRACT FROM AUTHOR]

The temporal and spatial distributions of winter precipitation variability over eastern China were analyzed on the basis of the empirical orthogonal function method. The results showed that the primary mode of winter precipitation variability over this area presented a homogeneous change during the study period, with a significant decadal change around the late 1980s. The factors that influenced winter precipitation variability over eastern China changed over different interdecadal periods. Before the late 1980s, the Eurasian (EU) mode and North Pacific Oscillation (NPO) mode were the two major atmospheric factors. After the late 1980s, the influence of the EU mode remained. However, the impact of the NPO weakened significantly, and a new Rossby Wave (RW) pattern became a key factor. Further analyses of both observations and numerical simulations indicated that the convective activity over the western tropical Pacific strengthened significantly around the late 1980s; the convection encouraged the RW mode and ultimately contributed to the anomalous winter precipitation over eastern China after the late 1980s. The results imply that the prediction of winter precipitation should consider different interdecadal backgrounds; otherwise, the changing factors could result in failure of the prediction over some decadal periods. [ABSTRACT FROM AUTHOR]

China faces an increasing challenge in water resources in the coming decades; thus high-confidence climate projection is of particular importance for the country's future. In this paper, we evaluate the performance of a long high-resolution continuous simulation over China based on multiple observations and the corresponding historical simulation. The simulation is completed using the Weather Research and Forecasting (WRF) model driven by the Model for Interdisciplinary Research on Climate version 5 (MIROC5) in the context of the Coupled Model Intercomparison Project Phase 5. The results show that both MIROC5 and WRF can capture the distribution and variability of temperature over China, whereas WRF shows improvements, particularly for simulation of regional features. Compared with MIROC5, WRF can reproduce the spatial distribution, annual cycle, probability distribution, and seasonal evolution of the precipitation over mainland China and the sub-regions with better performance. The trend is of fundamental importance in the future projection estimations, and WRF shows better skill in simulating the annual mean precipitation trend. However, there is overestimation of precipitation in Southeast China while negative one in the middle latitude of China in WRF simulation, which can be traced back to model bias in atmospheric circulation and water vapor transportation in these regions. Several extreme climate indices are selected to further assess the model's performance in simulating climate extremes, WRF can well reproduce the main features with better model skill compared with MIROC5. The better performance of WRF indicates the necessity of the dynamical downscaling technique and the robustness of regional climate simulation in future regional climate projection over China. [ABSTRACT FROM AUTHOR]