The dominant modes wintertime precipitation in northwest China (NWC) and the possible causes are investigated during the period 1961-2013 in the inter-annual timescale, as winter climate condition could greatly affect local economic development and people's lives. The analysis of this study is divided into three parts. First, the spatiotemporal variability of dominant modes wintertime precipitation is described by an empirical orthogonal function (EOF) method. The atmospheric circulation anomalies associated with wintertime precipitation variations are then discussed through regression and composite analysis. Third, the relationships between wintertime precipitation and sea surface temperature (SST) anomalies are investigated. The results indicate that the leading mode (EOF1) shows a uniform sign in the entire region, and the second mode (EOF2) exhibits a zonal-dipole pattern; they account for 25.6 and 15.7% of the total variance, respectively. The atmospheric circulation anomalies EOF1 closely related to is the Eurasian (EU) teleconnection pattern. Years when a negative phase of EU pattern occurs tend to be rainy with anomalous southerly transporting water vapour from low-latitudes and profound ascending motion anomalies. Atmospheric circulation anomalies associated with the second mode resemble the Arctic Oscillation (AO) pattern. AO pattern influences EOF2 precipitation variations through the anomalous circulations over Mongolia and western Europe. The sea surface temperature (SST) anomalies related to EOF1 show an El Niño-Southern Oscillation (ENSO) like pattern, which may modulate the wintertime precipitation mode through the western North Pacific anticyclone. The EOF2 mode has a close relationship with a tripole SST anomaly mode in the North Atlantic Ocean. This SST pattern is likely to influence wintertime precipitation by modulating the North Atlantic Oscillation (NAO). The results of this study could be beneficial for wintertime precipitation prediction and the decrease of economic losses in NWC and may also provide useful references for other areas with similar climatic features such as the central Asia. K E Y W O R D SAO teleconnection pattern, belt and road initiative, EU teleconnection pattern, northwest China, sea surface temperature, wintertime precipitation

In this study, the interdecadal change in the size of the Indo-Pacific warm pool (IPWP) and its connection with the intensity of the South China Sea summer monsoon (SCSSM) in May are investigated. The results show that the size of the IPWP experienced a marked interdecadal extension in the late 1980s, and its impacts on the SCSSM have also strengthened. Further analyses indicate that interdecadal changes in the connection between the IPWP and SCSSM variations are related to the changes in the atmospheric circulation anomalies over the tropical western Pacific due to the size of the IPWP. During 1951-1986, the IPWP was smaller than the climatologic size, which led to suppressed convection over the tropical western Pacific and easterly anomalies north of the equator. The Philippines and South China Sea (SCS) region was controlled by anomalous anticyclonic circulation, which was not conducive to the formation and development of the SCSSM. In contrast, during 1987-2018, the IPWP expanded significantly eastward. As a response to the IPWP size extension, convective activities were enhanced over the tropical western Pacific. Anomalous cyclonic circulation was located over the Philippines and SCS regions, which favored the enhancement of the SCSSM through wide westerly flow in the Bay of Bengal and tropical western Pacific. Moreover, it is shown that the interdecadally enhanced intraseasonal oscillations (ISOs) over the tropical western Pacific in the late 1980s also favored reinforcement of the SCSSM intensity.