Impacts of two types of northward jumps of the East Asian upper-tropospheric jet stream in midsummer on rainfall in eastern China

The East Asian upper-tropospheric jet stream (EAJS) typically jumps north of 45°N in midsummer. These annual northward jumps are mostly classified into two dominant types: the first type corresponds to the enhanced westerly to the north of the EAJS’s axis (type A), while the second type is related to the weakened westerly within the EAJS’s axis (type B). In this study, the impacts of these two types of northward jumps on rainfall in eastern China are investigated. Our results show that rainfall significantly increases in northern Northeast China and decreases in the Yellow River-Huaihe River valleys, as well as in North China, during the type A jump. As a result of the type B jump, rainfall is enhanced in North China and suppressed in the Yangtze River valley. The changes in rainfall in eastern China during these two types of northward jumps are mainly caused by the northward shifts of the ascending air flow that is directly related to the EAJS. Concurrent with the type A (B) jump, the EAJS-related ascending branch moves from the Yangtze-Huai River valley to northern Northeast (North) China when the EAJS’s axis jumps from 40°N to 55°N (50°N). Meanwhile, the type A jump also strengthens the Northeast Asian low in the lower troposphere, leading to more moisture transport to northern Northeast China. The type B jump, however, induces a northwestward extension of the lower-tropospheric western North Pacific subtropical high and more moisture transport to North China.