Comparative analysis of thermal structure in the activities of Southwest China vortexes

Abstract

The Southwest China vortex (SWCV) is an important weather system that affects warm-season rainfall in China, but forecasting its path of activity remains difficult. In this study, we chose six historical cases to analyze the thermodynamic differences between the less-moving pattern (LMP) and the moving pattern (MP) of SWCV activity, the principal results were as follows. (1) Regardless of whether the SWCV moved, an approximate “dipole pattern” of cold–warm advection was evident in the vortex circulation. Generally, dry–cold advection was found in the northeasterly airflow of the SWCV circulation, and wet–warm advection occurred in the southwesterly airflow. (2) In the LMP, the range of dry–cold advection was smaller than that of wet–warm advection in the horizontal direction. In the MP, the range of dry–cold advection at the rear of the SWCV along the direction of motion expanded and promoted movement of the SWCV. In the vertical direction, the front of the SWCV was always characterized by wet–warm advection, and the rear was characterized by dry–cold advection under eastward movement of the MP, but such a feature was not obvious in the LMP. To a certain extent, the approximate dipole pattern of cold–warm advection in the horizontal direction facilitates the maintenance of a complete cyclonic circulation, but it also supports SWCV movement when the dry–cold advection expands and becomes deeper in the vertical direction. Based on these findings, we tried to define a thermodynamic index for determining SWCV movement.