Exploring the differences in precipitation moisture sources and their mechanisms during the rainy season in northwest China

Abstract

Abstract Moisture sources, as the material basis, will directly influence the regional precipitation variability. However, there are limited understanding of the characteristics and mechanisms of climate variability and the combined influence of multiple atmospheric circulation systems over the Northwest China (NW). Thus, this studying uses ERA5 reanalysis data, atmospheric circulation index and 128 observation stations in rainy season from 1960-2017. Based on the moisture budget equation, the characteristics of precipitation change and its influence mechanism were analyzed in wet and drought years. The results show that the precipitation showed a significant upward trend during 1960-2017,with a climate tendency rate was 2.8 mm/10a and a huge difference in changes between western and eastern regions. The NW was dominated by westerly water vapor transport. During the wet year, the western region was controlled by the Mongol-Baikal high pressure and the eastern region was controlled by the Western North Pacific high pressure, both of which form abnormal anticyclones. The western Pacific subtropical high pressure extends westward. During the drought year, the western region was controlled by the Mongolia-Baikal low pressure,while the eastern region was controlled by the western North Pacific high pressure, which resulted in the formation of an anomalous cyclone and an anomalous anticyclone, respectively. Over the last 58 years, the North Atlantic Oscillation (NAO) has shifted from positive to negative phase, however Atlantic Multidecadal Oscillation (AMO) is the opposite. These shifts caused anomalies in the monsoon and westerly circulation, which induced anomalies in the dynamical processes of the vertical moisture advection term.