Analysis of influencing factors on frequent occurrence of Southwest China Vortexes with different vortex sources from 2012 to 2017

Based on NCEP/FNL, surface observation and upper-air sounding data, and entries of the Southwest China Vortexes(SCVs) Yearbook, we analyzed the activities of Southwest China Vortexes with different vortex sources from 2012 to 2017. Composite and comparative analyses are conducted to the respective wind and other composite physical fields for the characteristics of Jiulong vortex, basin vortex and Xiaojin vortex prior and during the generation phase in the most frequent occurrence time of the year. The effects of background wind, cold and warm air flows, and frontogenesis on the generation of Jiulong vortex, basin vortex and Xiaojin vortex are then obtained. Results are as follows. (1) The main generation and moving period of SCV is from March to June. Jiulong vortex has the main role in SCV, followed by basin vortex. Xiaojing vortex is the least but has the biggest chance to move out of the source. (2) The formation of the Jiulong Vortex and the Xiaojin Vortex is related to the open shape topography of the southwest airflow flowing into their respective vortexes and the wind in Xiaojing vortex is stronger. The formation of the basin vortexes is related to the shear line. (3) The formation of Jiulong vortex and Xiaojin vortex is also related to the positive non-thermal wind vorticity in the warm advection area due to the influence of surface heating and southwest airflow on the leeward slope of the Plateau. However, the warm advection area of Jiulong vortex is larger than that of Xiaojin vortex, and its intensity is much lower than that of Xiaojin vortex. The formation of basin vortex is related to the stronger baroclinic effect of the cold air. (4) The formation of Jiulong vortex, Xiaojin vortex and basin vortex is all related to the enhancement of frontogenesis intensity of the respective vortex sources. But the factors influencing frontogenesis are different. The generation of Xiaojin vortex is mainly affected by the non-adiabatic pro?cess, and the formation of Jiulong vortex is mainly affected by the non-adiabatic change process, together with the horizontal and vertical motion of the airflow. The basin vortex generation is mainly affected by the vertical motion and the non-adiabatic also has some impact on it.