利用NCEP GFS 0.5°×0.5°再分析资料, 结合卫星、雷达、加密自动气象站资料, 通过合成诊断分析研究了湖北10次由边界层准静止干线触发的中尺度暴雨过程的形成机理, 结果表明, 该类型暴雨多发生在暖区内, 强降水中心稳定少动, 范围小, 降水维持时间长, 雨强一般在30~50 mm。动力机制主要为500 hPa正涡度平流向暴雨区伸展, 促使边界层气旋性涡度加强, 正涡度柱发展; 同时, 干线两侧干湿平流加强, 产生局部锋生, 且边界层正、负温度平流呈偶极分布, 产生边界层小扰动, 加强了上升运动的发展。对流系统运动表现为明显的后向传播, 且后部新生对流单体呈线性排列, 依次经过同一位置产生列车效应, 有利于降水在同一地点长时间维持。其暴雨落区主要位于边界层干线南侧的湿舌顶端、靠近温湿平流零线的暖湿一侧。
NCEP GFS reanalysis data with the satellite,radar,automatic station and synthetic diagnosis method were used to analyze ten mesoscale rainstorms triggered by quasi-stationary in boundary layer.The results showed that this type rainstorm often happened in warm area, having strong instability energy the rainstorm center was small and stable while the precipitation time was longer.Generally, it's rainfall intensity was between 30 mm and 50 mm.The dynamic mechanism can be drawn as follows.Positive vorticity advection on 500 hPa extending to rainstorm area, enhanced cyclonic vorticity in boundary layer, positive vorticity advection column developed.Meanwhile, with the development of northerly significant flow in boundary layer, dry and wet advection enhanced at two sides of dry line respectively, dry air was involved in wet air, produced local frontogenesis, and small perturbation were produced due to dipole distribution of positive and negative temperature advections in boundary layer, lead to ascending motion enhancing.The average air flow was consistent with the moving direction of the convective system, high temperature and humidity instability region was located in the upper reaches of the convective system, so the convective motion of the system is obviously backward propagation, the new convection monomer linear and followed by the same position, lead to the train effect, conducive to the precipitation in the same place long time maintenance.The rainfall region was discovered that wet tongue tip on the south side of the dry line in boundary, and close to warm moist side of the zero line of temperature and humidity advection.
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