Analysis on the spatiotemporal difference of rainfall in a Guangxi late autumn rainstorm event

Abstract

The spatiotemporal difference of rainfall in a late autumn rainstorm event in Guangxi on 20 November 2015 was analyzed using data from the ground, sounding, automatic weather station and Doppler radar observations and NCEP FNL reanalysis. The results show that the rainstorm was developed under a warm and wet climatologically anomalous condition, when the subtropical high was further westward and northward. The spatiotemporal characteristics of rainfall are different. The rainfall in north Guangxi was sustained and concentrated, and the rainfall in the south was more torrential, transitory and discrete. Conditional symmetric instability in north Guangxi led to weaker and more sustained convections than under the condition unstable stratification in the south. The vapor flux convergence was intensive in the north and the moist layer is deep. The vapor flux caused by southerly was important to sustain the rain. The upper dry and low moist stratification caused the strengthened downdraft and the accelerated squall line in the south. Wind direction vertical shear in north Guangxi is small, which caused the multi-cell storm propagated backward. Train effect led to sustained rainfall. In the opposite, the squall line propagated rightward, moved easterly rapidly or suddenly in the south. The difference in background circulation and element distribution caused the different characteristics of mesoscale convective systems, finally led to the spatiotemporal difference of rainfall.

Keywords

• late autumn rainstorm
• spatiotemporal difference of rainfall
• mechanism of instability
• water vapor
• train effect
• storm propagation