江淮灾害性大风飑线的特征分析

General Features of Squall Lines with Disastrous Gale in the Yangtze-Huaihe Area

本文利用2000—2017年4—9月的多普勒雷达资料、地面和高空探测资料,识别出江淮地区35条飑线。空间分布显示,飑线主要形成于长江以北的平原地区。时间分布显示,40%的飑线发生在7月,其中7月下旬有一峰值;约37%的飑线形成于中午到下午,在午后到傍晚成熟,在下午至夜间消亡。较多的飑线向东南方向移动,移速集中于8～16 m·s^(-1),长度为200～250 km,强度为60～65 dBz,生命史为3～4 h。飑线的主要形成方式为离散区型(broken areal型),组织方式以后部层状云型(trailing stratiform型)居多,主要消散方式为逆向断线型(reversed broken line型)。把飑线的天气背景分成五种类型:浅槽型、深槽型、高压边缘型、槽后型和冷涡型。江淮飑线多出现在西风槽前;深槽型飑线引起的地面降温幅度最大;深槽型和冷涡型飑线的雷达回波核较高,天气也更为剧烈,除了降水和雷暴大风外,还可出现冰雹或龙卷。五种天气型的相同之处是对流有效位能大于1300 J·kg^(-1),0～6 km的垂直风切变大于10 m·s^(-1),抬升凝结高度多低于930 hPa,即低层为高温潮湿的环境。

Based on the Doppler radar data, surface observation and rawinsonde data collected from April to September during 2000 — 2017, 35 squall line cases in the Yangtze-Huaihe Area are identified. These squall lines occur most frequently in the plain to the north of the Yangtse River. The squall lines peak in July and a large proportion of them generate in early afternoon, mature in late afternoon, and dissipate in evening.The squall lines have a dominant southeast motion at the speed of 8-16 m · s-1. They are characterized by the maximum length of 200 — 250 km, the maximum intensity of 60 — 65 dBz, and the duration of 3 — 4 h.The squall lines commonly form in a broken-areal pattern, display a trailing-stratiform pattern, and dissipate in a reversed broken-line pattern. The ambient flows of the squall lines are classified into five synoptic patterns,which are pre-short trough, pre-long trough, cold vortex, around subtropical-high and posttrough patterns. About 62. 9% of the squall lines form in the dominant pre-trough pattern. Pre-long trough squall line causes the largest surface cooling. The radar echo cores of pre-long trough and cold vortex squall lines are higher and the weather is more severe. Besides precipitation and thunderstorms, hail or tornado can also occur. Favorable conditions for the different patterns have been analyzed in the terms of instability, vertical wind shear and so on.