Stage characteristics and causes of a mixed severe convective weather process

Abstract

Based on the conventional observation data, the intensive automatic weather station data, the 1°×1° Final Operational Global Analysis data and the Doppler radar data, this study analyzes the stage characteristics and causes of a mixed severe convective weather process in Hunan Province from April 23 to 24, 2019. The results show that this severe convective weather mainly has two stages. In the first stage, the disastrous weather is mainly the short-term heavy precipitation. The convective weather in this stage is a severe mixed convective weather process forced by warm advection. The short-term heavy precipitation is mainly caused by the continuous influence of multi-cell storms. The disastrous weather in the second stage is mainly the thunderstorm gale. It is a squall line process forced by upper-level cold advection. Besides, there is apparent mid-altitude radial convergence and high wind core on the radial velocity map. The surface convergence line is the primary dynamic uplift condition triggering the mixed convection in the first stage, and there are several abnormal low centers of three-hour pressure change in the western and southern Hunan. The severe convective weather process in the second stage is mainly triggered by the forward-tilted trough. The dynamic conditions and energy conditions are favourable for the convections at both stages. Compared with the second stage, water vapor is more abundant in the first stage, which is more favorable for the occurrence of short-term heavy precipitation. The three-body scatter spike of hail is not obvious before the formation of the squall line. The early warning signals are mainly the height of the strong echo and vertical integrated liquid water content, both of which increase significantly before the formation of the squall line. The early warning of thunderstorm gale after the formation of the squall line can be issued in advance by monitoring the low-level wind in the downstream areas of the squall line.