Analysis on a Heavy Rainstorm in Qinba Region Caused by Southwest Vortex and Northwest Vortex

Abstract

A heavy rainstorm in Qinba region caused by northwest vortex and southwest vortex on 3 -4 September 2021 is analyzed based on conventional observational data， ERA-5 reanalysis data and FY-4A satellite data， for discussing the mesoscale environment characteristics and process of southwest vortex.The result shows that α-mesoscale MCC caused by northwest vortex and southwest vortex leading to the heavy rainstorm， and strong precipitation area coincides with the cold center of the cloud black body and large gradient of TBB.Before the formation of southwest vortex， the convergence of north wind behind northwest vortex and southwest wind formed mesoscale shear line， triggering convective instability to form mesoscale convective clouds.Under the influence of southwest vortex and northwest vortex， the water vapor transport， the positive vorticity， strong convergence and updraft at lower troposphere in Qinba region are significantly enhanced， together with development of β-and γ-mesoscale convective clouds， leading to the heavy rainstorm in Qinba region.The southwest vortex is generated by downward positive vorticity and large potential vorticity caused by low vortex at 500 hPa， leading northerly wind behind the northwest vortex and southwest wind to form cyclonic circulation.Vertical coupling of southwest vortex and low vortex at 500 hPa can make southwest vortex a strong system， strengthening the convergence and vertical ascend movement of water vapor to enhance precipitation.

Keywords

• qinba region
• northwest vortex
• southwest vortex
• heavy rainstorm
• mcc
• potential vorticity