Simulation of a Typical Meiyu Case Over the Yangtze-Huai River in a Record-Breaking Meiyu Period of 2020

Abstract

In the summer of 2020, Jiangsu Province has experienced a long Meiyu period with heavy rainfall, long time and wide range. In order to explore the characteristics of the Meiyu and its related atmospheric circulation background and water vapor transport background, this paper numerically simulates the Meiyu process in Jianghuai region from July 1 to 15, 2020 based on WRF (the Weather Research and Forecasting) model, and analyzes its precipitation characteristics and related causes by selecting the six hour precipitation process from 1800 UTC on July 2. The results show that the heavy rainfall belts in Jiangsu Province are triggered by influence systems in this analyzed period: (1) under the control of cyclonic circulation, the cold air flows to the front of the trough along with the northerly airflow behind the trough, so Jiangsu Province, which is located in front of the trough of low pressure, is attacked by the cold air from the south, and the warm air is forced to rise. During the process, the water vapor is supersaturated and condenses to rain, resulting in the precipitation of the Yangtze River Heavy rainfall in Northern Jiangsu. (2) The West Pacific subtropical high is generally stronger, with the west ridge reaching westwardly and northwardly than usual. The East Asian summer monsoon is weaker, which is conducive to the continuous transportation of water vapor to Jiangsu and Zhejiang. In addition, the warm air moves northward and meets with the cold air southward in southern Jiangsu, Northern Zhejiang and central and southern Anhui, forming the Meiyu front, which maintains near Jiangsu and Zhejiang for a long time, causing the southern Jiangsu A heavy rain in the rainy season. (3) The low-level jet, which has been kept in Jiangsu Province for a long time, transports enough water vapor for the occurrence of precipitation in Meiyu period. With the strong upward movement, the water vapor can reach the upper level, which affects the occurrence of convection in Meiyu rainstorm and the coupling of high-level jet and low-level jet, and provides favorable environmental conditions for the precipitation weather in Meiyu period.