On the Evolution of a Long‐Lived Mesoscale Convective Vortex that Acted as a Crucial Condition for the Extremely Strong Hourly Precipitation in Zhengzhou

Abstract

AbstractFrom 17–22 July 2021, Henan Province experienced the most severe torrential rainfall event since 1975 with a maximum hourly precipitation of 201.9 mm appeared in Zhengzhou, which was the largest hourly rainfall thus far observed by meteorological observation stations over the Chinese Mainland. The appearance of a long‐lived (21‐hr) northwestward‐moving mesoscale convective vortex (MCV) and its interaction with its parent mesoscale convective system (MCS) was crucial to produce the extremely strong heavy rainfall in Zhengzhou. The backward trajectory analysis indicates that air particles in the lower troposphere beneath the MCS over Henan contributed mostly to the MCV's formation. These air particles experienced notable ascending motions and condensation with their strong cyclonic vorticity mostly produced 1‐hr before the MCV's formation. Vorticity budget denotes that strong upward transport of cyclonic vorticity and convergence‐related vertical stretching, both of which were mainly due to convection associated with the parent MCS, acted as dominant factors for the MCV's formation. After formation, the MCV first coupled with its parent MCS, during which its intensity, thickness, and precipitation were all maximized; then, it moved northwestward and decoupled from the MCS, during which it weakened rapidly and finally dissipated. Convection‐related upward cyclonic vorticity transport and inward horizontal advection of cyclonic vorticity associated with an inverted trough over the Henan Province dominated the vortex's development/maintenance in the coupling stage; whereas outward horizontal advection of cyclonic vorticity dominated the MCV's dissipation after it completely decoupled from its parent MCS. These differ notably from the findings documented in previous MCV‐related literature.