关键词: 不同季节, 飑线, 对比分析, 中气旋

Abstract:

Based on the conventional and unconventional data, two squall line processes on 28 March and 18 July 2014 in Hunan Province were analyzed comparatively. The results show that two squall lines happened under extremely unstable atmospheric stratification conditions, the vapor transports were obvious in middle and lower troposphere, the characteristics of atmospheric stratification with dry in upper layer and moist in lower layer were significant, and two squall lines were triggered nearby lower layer wind shear and surface convergence line. However, the thermal-dynamic structure and radar echo characteristics of two squall lines had a certain differences. The thermal features of squall line on 18 July 2014 (a.k.a. ‘7.18’ squall line) were stronger than those of squall line on 28 March 2014 (a.k.a. ‘3.28’ squall line), such as K index, Showalter index, convective available potential energy (CAPE) and downdraft convective available potential energy (DCAPE), etc., but the stratification instability and dynamic conditions, such as vertical upward motions and deep layer vertical wind shear, etc., were weaker than the later. The high value areas of velocity on low elevation and radial convergence in middle layer in radar echo figures were forecasting key points of two weather processes. Compared with ‘7.18’ squall line, the range of high value area of velocity for ‘3.28’ squall line was larger, and there were bull’s-eyes structures of radial velocity, more obvious bow echo and several mesocyclones. Moreover, the vertically integrated liquid (VIL) and echo top height (ET) of ‘3.28’ squall line were less than that of ‘7.18’ squall line, so the threshold of early warning should be adjusted properly according to different seasons.

Key words: different seasons, squall line, contrastive analysis, mesocyclone