How does the South Asian High influence extreme precipitation over eastern China?

摘要

Based on the high-resolution observed daily precipitation data, three characteristic regions over eastern China are first defined through the rotated empirical orthogonal function. Then, the relationship between summer (June-July-August) extreme precipitation across the three characteristic regions of eastern China and the South Asian High (SAH) is examined to determine how the northwest-southeast movement and area (magnitude) of SAH influence the summer extreme precipitation across eastern China. When the South Asian High is located anomalously northwest, there is more extreme precipitation over the northern part of eastern China but less extreme precipitation over the Jiang-Huai River Basin. When the SAH intensifies, there is more extreme precipitation over the Jiang-Huai River Basin. The mechanisms are that under the conditions of anomalously northwestward displacements, the positive geopotential anomalies over central Asia induce a deep barotropic Korean High through a Rossby wave train, resulting in more water vapor transportation to eastern China with more convergence over the northern part of eastern China located at the northwestern edge of the Korean High but with a divergence over the Jiang-Huai River Basin. When the SAH intensifies, accompanied by an enhanced and westward extended western Pacific subtropical High, the convergence over the Jiang-Huai River Basin increases with enhanced water vapor transportation due to the confluence of warm and cold advections. These mechanisms are achieved through shifts toward the high tail (low tail) of the daily precipitation cumulative distributions of these two regions and finally increases (decreases) in the occurrence of extreme precipitation.