ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Statistical Characteristics of Downbursts Under Weak Vertical Wind Shear in Jiangsu Province
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Abstract:
To study the characteristics of downburst under weak vertical wind shear, based on the SA Doppler weather radar, sounding and surface (10 m) maximum wind data and the cloud images from stationary meteorological satellites, we selected 381 downburst events that occurred under weak vertical wind shear from June to September in 2019-2020 in Jiangsu Province and divided them into three categories according to the scales of microburst, macroburst and downburst cluster. The statistical results show that 64.9% of thunderstorm days in Jiangsu from June to September are accompanied by downbursts, with an average of 8 downburst events per downburst day. The proportions of three types of downbursts are 21.7% for microbursts, 47.6% for macrobursts and 30.7% for downburst clusters, and they all tend to occur in the time period of 15:00-16:00 BT. According to radar radial velocity, the average duration of downbursts is 25.4 min, and the average intensity (radial velocity difference of divergence couplets or extreme radial velocity at low elevation) is 22 m·s-1. Only 7 downburst samples reach the standard of disaster gale (extreme radial velocity at low elevation reaches 25 m·s-1 or radial velocity difference of divergence couplets attains 40 m·s-1). The average surface maximum wind caused by downburst observed by surface meteorological stations is 15.5 m·s-1, indicating that disaster-causing potential of downburst is not significant. The low-elevation radial velocity modes of downburst are dominated by divergence vel-ocity couplet (73.3%), but the majorities are asymmetric while only 6.1% for symmetrical divergence velocity couplet. There are 26.7% of downburst characterized by strong wind at low elevation.
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