甘肃省倒槽暴雨的个例分析

1976年8月2日,甘肃省中部地区发生了一次暴雨.在热带东风带中,当西移的倒槽和高原北部东移的低涡相结合时,就会使倒槽强烈发展并伸入内陆.倒槽东侧深厚的东南气流,造成该区深厚的位势不稳定,并使水汽输入到西北区东部,它与冷锋后部的西北气流相遇后,产生大范围水汽通量的辐合,这是本次暴雨的大尺度条件.次天气尺度的低涡是产生这次暴雨的直接影响系统.当对流层上部的扰动与低层扰动上下叠置,形成一个深厚的次天气尺度低涡时,易产生对流性暴雨.次天气尺度的低涡,是雨团迅猛加强的背景,南移的低层切变线起触发作用,而该地早先存在的一个暖湿的地方性中低压,则是合适的局地环境场.当低层切变线移入此中低压时,往往造成中尺度雨团的合併,出现急骤加强,形成暴雨.

A CASE STUDY OF HEAVY RAIN IN GANSU PROVINCE

In this paper the heavy rain on August 2,1976 in the central part of Gansu has been analysed.It took place when a trough of tropical easterlies moved in and developed on encountering a small depression from the Tibetan plateau.Accompanying the deep humid south-eastern flow in the lower troposphere,cold upper tropospheric air moved to Gansu and a deep layer of potential instability was produced and met the cold north-western flow later on.The convergence of vapour flux was introduced Analysis of hourly synoptic charts reveals that an intense subsynoptic depression is responsible for the heavy rain.The structure and life history of subsynoptic depression and the accompanying shear line are also discussed.When the shear line of low layer moved to the subsynoptic depression,the heavy rain was formed.