Causality analysis of difference of heavy rainfall distribution in Fujian caused by typhoons Soulik and Trami along similar tracks in 2013

Abstract

Based on the best typhoon track data from CMA, intensive observations from automatic weather stations, SRTM30 data and ERA5 reanalysis data, we have performed the causality analysis of the difference of heavy rainfall distribution in Fujian caused by typhoons Soulik and Trami along similar tracks in 2013. Results are as follows. (1) Severe precipitation distribution in Fujian is different before and after typhoon landing with respect to the position of typhoon moving path during the two typhoon rainfall events mentioned above. The severe precipitation before both typhoons landing is located on the north side, namely northeast Fujian, of typhoon path. After typhoon landing, the severe precipitation caused by typhoon Soulik is located on the southern side of its path, and that caused by typhoon Trami locates near its path. (2) Before typhoon landing, comparing to the typhoon Soulik, typhoon Trami are associated with strong water vapor transport in the low latitudes. The warm and wet air produced the suction effect by convergence in the mid-and low-level and divergence in the upper level over the northeastern Fujian. Coordinating with the horizontal positive vorticity structure and the topographic lifting, it lead to the strong and high ascending motion in the northeastern Fujian and the intensive and extensive rainfall in the northern side of its path. (3) After typhoon landing, there are the strong vapor convergence center, airflow writhing zone and energy frontal zone in the southern side of Soulik typhoon path. In addition, the vertical positive vorticity column inclines southward, and ascending motion and convective instability are strong. While nearby the Trami moving path is a strong vapor convergence center, the northwest airflow and westerly airflow writhe, the warm and wet structure maintains, and the positive vorticity column is located near the typhoon center, coordinating with the convergence in the mid-and low-level and divergence in the upper level and the strong vertical ascending motion. Guided and blocked by the terrain, the convergence and uplift of the low-level airflow are accelerated, which is conducive to the maintenance and strengthening of severe precipitation. (4) There is a good correspondence between typhoon severe precipitation zone and ambient wind vertical shear (VWS). Severe precipitation zones locate mainly on the downstream and left side of the VWS. Before and after Soulik and Trami landfall, the strength and direction of the VWS are different, which may be one of the important reasons for the difference of heavy rainfall distribution in Fujian.

Keywords

• typhoon
• moving path
• heavy rainfall distribution
• ambient wind vertical shear