洞庭湖区两次致灾大风天气的对比分析

Comparative analysis of two disastrous gale weather in Dongting lake area

利用常规天气资料、NCEP再分析资料及雷达资料,对洞庭湖区2次致灾大风天气进行对比研究。结果表明,①2次过程夜间500 hPa中高纬均为两槽一脊经向环流,过程二低槽的经向度更强,槽后冷平流更强;地面均有暖倒槽或暖低压发展,贝湖以西冷高压过程二更强;日间850 hPa均有锋区,过程二锋区更强,且移动更快;②2次过程大风类型不同,过程一前期为雷雨大风,之后为锋后偏北大风,之间有转南风的时段,过程二为雷暴大风与冷空气大风同时影响的混合大风;雷达基本速度场印证了2次致灾大风的类型;③2次过程均有强垂直温度梯度,过程一0~6 km垂直风切变更大、上干冷下暖湿的层结结构更加明显,即过程一的雷暴大风潜势更大,对流天气更加剧烈;△θse700~850 hPa的负值中心对致灾大风出现的区域有一定的预测作用,且正负值交界线的南压时间对大风开始时间有一定的指示意义;④2次过程初始回波触发条件不同,过程一为弱冷空气入侵露点峰值区触发生成,过程二为锋面触发;且过程一雷暴大风为局地雹云引发,过程二为局地雹云与冷空气共同导致。

Based on the NCEP reanalyzed data,the conventional weather data and radar data,two disastrous gale weather in Dongting lake were comparatively analyzed.The results showed that:①two trough ridge meridional circulations in the middle and high latitudes of 500 hPa in the two processes at night,and the meridional degree of low trough in the second process was stronger,and the cold advection after trough was stronger;There were warm inverted trough or warm low-pressure development on the ground,and the cold high-pressure process in the west of Beihu lake was stronger;There were front areas in the 850 hPa in the daytime,and the process two front areas were stronger and moved faster;②The types of gale in the two processes were different,passing through the first stage was thunderstorm gale,followed by northerly gale behind the front.There was a period of southerly wind between them.The second stage was the mixed gale affected by thunderstorm gale and cold air gale at the same time.The basic velocity field of radar confirmed the type of the two gales;③Both processes had strong vertical temperature gradient,and the vertical wind shear of process 0~6 km changed greatly,and the stratification structure of upper dry cold lower warm wet was more.It was obvious that the potential of thunderstorm and gale in process I was larger,and the convective weather was more severe;The negative center of△θse700~850 hPahad a certain predictive effect on the occurrence area of disaster induced gale,and the time of southward pressure at the boundary of positive and negative values had a certain indicative significance on the start time of gale;④The triggering conditions of initial echo of the two processes were different,process I was the peak of weak cold air intrusion dew point.In process one,thunderstorm and gale were caused by local hail cloud,and process two was caused by local hail cloud and cold air together.