Implications of the Pacific meridional mode for summer precipitation extremes over China

This study examines the association between the Pacific meridional mode (PMM) and summer precipitation extremes over China using observational and reanalysis datasets. Results suggest that positive PMM phases are accompanied by suppressed extreme precipitation over the mid-lower reaches of the Yangtze River basin (MLYRB) and strengthened rainfall extremes over North China (NC). The teleconnections of PMM to regional precipitation extremes are mainly through a low-level westward and an upper-level eastward propagation of signals emanating from PMM. In the lower atmosphere, a prominent anomalous cyclone is generated as a Gill-Matsuno-type response to increased diabatic heating associated with the warming component of PMM. This cyclone excites a meridional circulation over eastern China with an anomalous anticyclone over the MLYRB and cyclone over NC, showing a Pacific-Japan-like pattern. The upper-tropospheric circulation changes are characterized by an eastward Rossby wave train and a poleward shift of the East Asian jet stream. Both the lower- and upper-atmospheric configurations are conducive to descending motion and decreases in summertime precipitation extremes over the MLYRB and ascent and increases in precipitation extremes over NC during the positive PMM phase. Our findings reveal that PMM plays a role in shaping the spatial pattern of summertime precipitation extremes, and understanding their association can be beneficial to the forecasting of regional precipitation extremes over China.