Attribution of Persistent Precipitation in the Yangtze-Huaihe River Basin during February 2019

Abstract

In February 2019, a month-long persistent precipitation event occurred in the Yangtze-Huaihe River basin. The geopotential height field that affected the duration of this frontal rainfall was divided into a high-latitude part and a low-latitude part for analysis. In the high-latitude part, a two-wave structure led to quasi-stationary circulation, and the change of both the blocking high pressure and Arctic Oscillation phase caused cold air to invade South China continuously and changed the frontal position. In mid-to-low latitudes, the persistent precipitation showed quasi-biweekly oscillation characteristics. The so-called “subtropical high-precipitation-anticyclone” (SHPA) feedback mechanism blocked the circulation systems in the mid-to-low latitudes and provided a continuous supply of water vapor for precipitation. As for the effect of sea surface temperature, the western North Pacific anomalous anticyclone stimulated by El Niño strengthened the intensity of the southerly wind and provided support for the redevelopment of the anticyclone system in the SHPA feedback mechanism. The sea surface temperature anomaly in the South China Sea provided sensible heating for precipitation, and convergent rising airflow was conducive to the occurrence of precipitation. Additionally, the SHPA mechanism provides a reliable basis for the prediction of persistent precipitation in winter in the mid-to-low latitudes.

摘要

2019年2月, 江淮流域发生了为期一个月的极端持续性降水事件, 给当地人民生命财产安全带来了巨大损失。我们将影响该锋面降雨持续时间的位势高度场分为中高纬度地区和中低纬度地区进行分析。结果表明, 在高纬度地区, 500hPa环流的谐波分析出现两波的准静止形势, 同时欧洲地区的异常阻塞高压强度和北极涛动相位的变化既维持了冷空气入侵江淮地区, 也导致锋面位置徘徊在江淮地区。在中低纬度地区, 此次持续性降水表现为准双周振荡特征。在此基础上, 我们提出了“副热带高压-降水-反气旋”(SHPA)正反馈机制, 用以揭示三者间的关系、入海后的反气旋再发展、降水的水汽来源以及降水持续的原因。海温对此次持续性降水也有不可忽视的影响, 厄尔尼诺现象激发的西北太平洋异常反气旋增强了输送水汽的南风的强度, 并为SHPA正反馈机制中反气旋系统的再发展提供了支持。南海海温异常带来的感热加热使得暖湿气流不断上升, 促进了降水的发生。此外, SHPA机制为预测中低纬度冬季的持续降水提供了可靠的基础。