Comparison of two types of persistent heavy rainfall events during sixteen warm seasons in the Sichuan Basin

Abstract

Based on hourly precipitation from national surface stations, persistent heavy rainfall events (PHREs) over the Sichuan Basin (SCB) are explored during the warm season (May to September) from 2000 to 2015 to compare synoptic circulations and maintenance mechanisms between different PHRE types. There are two main types of PHREs: one is characterized by a rain belt west of 106°E over the SCB (WSB-PHREs), and the other features a rain belt east of 106°E over the SCB (ESB-PHREs). In total, there are 18 ESB-PHREs and 10 WSB-PHREs during the study period. Overall, the rain belts of WSB-PHREs are along the terrain distribution east of the Tibetan Plateau, while the precipitation intensity of ESB-PHREs is stronger. For the two types of PHREs, the shortwave trough over the SCB and the western Pacific subtropical high act as their favorable background environments, particularly for ESB-PHREs. The water vapor of WSB-PHREs is mainly transported from the South China Sea, whereas for ESB-PHREs the South China Sea and Bay of Bengal are their main moisture sources. The composite vorticity budgets of southwest vortices during their mature stage indicate that the convergence effect is a dominant factor for maintaining the two types of PHREs, and the strong vertical vorticity advection is also favorable, but the relative contribution of vertical advection is larger for WSB-PHREs.摘要本文筛选出四川盆地西部 (盆西型) 和盆地东部 (盆东型) 持续性暴雨个例, 深入对比两类持续性暴雨的大气环流特征和直接造成持续性暴雨的西南低涡维持的机理. 四川盆地的短波槽和西太平洋副热带高压的配置有利于持续性暴雨的维持, 盆东型的降水强度较盆西型个例强, 高空急流位置偏南, 南亚高压的强度更强, 高层辐散更强, 对流层中层副热带高压偏东偏南. 盆西型的水汽输送主要来自南海, 而盆东型的水汽输送主要来自南海和孟加拉湾. 合成涡度收支的结果表明散度项是两类持续暴雨中西南涡维持的主要原因, 但盆西型中, 垂直平流的作用更强.