Processes of Colliding Cold Pools Derived from a 356-m-High Shenzhen Met-Tower during an Extremely Heavy Rainfall Event

Abstract

Convectively generated cold pools play a crucial role in the convection initiation and development, but observations of their vertical structure are insufficient. In this study, quantitative vertical evolutions of cold pools during a high-impact heavy rainfall event near the south coast of China were examined using observations from a 356-m high Shenzhen Met-Tower, and their potential impacts on heavy rainfall were further discussed through high-resolution surface station network and radar observations. On 11 April 2019, heavy precipitation occurred near metropolitan Shenzhen, lasting for 50 min at its southern downtown and resulting in 11 deaths. During this event, a shallow cold pool was first observed by the tower and yielded a long-lasting cooling of 2.6 K. Approximately one hour later, another deeper cold pool accompanied by a squall line was added from the west. This addition resulted in a more abrupt and intense surface temperature deficit (5.1 K) and stronger gusty winds (23 m/s). When the two cold pools collided near Shenzhen, the low-level winds converged at their intersection, dynamically enhancing the heavy-rain-producing squall line. Moreover, the collision of the two cold pools reduced the temperature gradient at the northern edge of the merged cold pool, which could inhibit development of the squall line. The area south of the squall line became a relatively favorable environment for convection initiation, given the warm and moist oceanic environment. Consequently, the squall line turned northeast–southwest, forming a training line mode that was nearly parallel to the eastward movement. This training line mode prolonged the precipitation duration in the southern downtown area.

High-Frequency Microbarograph-Observed Pressure Variations Associated with Gust Fronts during an Extreme Rainfall Event

“…The interaction (e.g., merging, intersecting, and colliding) of surface convergent boundaries often produces favorable conditions for convection initiation (CI) or intensification and thus provides guidance for CI nowcasting [20][21][22][23][24][25][26]. Based on ground-based radars, Wilson and Schreiber [21] documented that 71% of boundary collision processes triggered thunderstorms in the Denver, Colorado area.…”