Analysis on the asymmetrical precipitation and evolution of dynamic and thermodynamic structure of typhoon Ewiniar

Before and after the second landing of typhoon Ewiniar (No 1804) in Guangdong, the precipitation showed significant asymmetric distribution characteristics, and heavy precipitation was mainly located on the right side of its path. Based on the reanalysis data of ECMWF ERA5 and wind profiler observations and rainfall observations, the circulation background and evolution characteristics of the dynamic and thermal structures responsible for the asymmetric precipitation are analyzed. The results show that the differences in water vapor transport and dynamic and thermal conditions between the left and right sides of Ewiniar were the main reason for the asymmetric precipitation. The enhanced low-level jet and water vapor transport associated with typhoon Maliksi (No 1805) provided a better water vapor background for the occurrence of heavy rainfall on the right side of the typhoon, and the enhancement of the low-level jet combined with the strong divergence and suction in the upper levels led to significantly larger ascending movement on the right side than on the left side. In the boundary layer, the strong low-level jet and large friction and convergence above the underlying surface of the Pearl River Delta resulted in a stronger radial inflow, a deeper inflow layer and a higher boundary layer in the front right side of Ewiniar. The above phenomenon was more obvious in areas close to the typhoon eye wall, where the wind speed was also large. Therefore, the dynamic and water vapor conditions both were favorable for the generation of heavy rainfall. During the period of heavy rainfall, the lower atmosphere on the right side of Ewiniar remained unstable. Further analysis shows that the strong pseudo equivalent potential temperature advection and its weakening with height made up for the energy loss caused by heavy rainfall, which was an important mechanism for the maintenance of unstable energy.