Basin Vortex is a type of Southwest Vortex,which refers to the vortex generated in the Sichuan Basin on the 700 hPa isobaric surface,with two consecutive low pressures with closed Contour line or cyclonic circula-tion in the wind direction of three stations.It is the main system that causes precipitation in the Sichuan Basin,and the"southwest type"Basin Vortex is the most frequent and strong type of Basin Vortex.This article utilizes ERA5(0.25°×0.25°)hourly reanalysis data,GPM satellite precipitation data,and the Southwest Low Eddy Yearbook explored the characteristics and development mechanism of a typical"southwest type"Basin Vortex that occurred in the Sichuan Basin from June 26 to 28,2020.The results indicate that the Basin Vortex was gener-ated in the southwestern part of the Sichuan Basin,then moved towards the northeast direction,reached the northeastern part of Sichuan,turned eastward,and disappeared after entering Chongqing,with a total life histo-ry of 48 hours.The formation and development of the Basin Vortex are closely related to its divergence zone lo-cated on the northeast side of the 200 hPa South Asian High and on the right side of the entrance area of the high-altitude jet stream,as well as the low-level decompression caused by the positive vorticity advection in front of the 500 hPa short wave trough.The southwest part of the Sichuan Basin at 700 hPa is located to the left front of the low-level jet stream,which is conducive to the development of convergent upward motion and the formation of low eddies.The high value area of frontogenesis in the northeast direction of the 700 hPa Basin Vortex,the strengthening of the low-level jet and the guidance of the southwest airflow in front of the 500 hPa high altitude trough are the main factors for the movement of the Basin Vortex towards the northeast direction.As the center of the 200 hPa South Asian High moves eastward over the Yangtze-Huaihe River and the upper level jet weakens,the 500 hPa shortwave trough moves eastward,and the Basin Vortex is located in the negative vorticity advection zone behind the trough.The vertical direction turns into a sinking motion,with surface pressure increasing and the low vortex gradually weakening and disappearing.Analysis of the vorticity budget equation reveals that low-level convergence is the main contributor to the increase in the Basin Vortex intensity,and the increase in posi-tive vorticity of the Basin Vortex caused by low-level convergence almost runs through the entire life cycle of the vortex.In addition,the existence of high-altitude orthonormal vortices and the release of condensation latent heat from the Basin Vortex precipitation also play an important role in the development and movement of the Basin Vortex.
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