三峡坝区一次强风害天气多普勒雷达回波分析

Features of Doppler Radar Echoes during a Severe Storm around Three Gorges Dam

2002年4月15日夜间发生在三峡坝区的强风暴属于典型的地面冷锋侵入西南倒槽天气背景下的强对流过程,其瞬间最大风力达11级,降水强度达50 mm/h左右。多普勒雷达发现风暴成熟阶段的回波具有中气旋等特征。强回波历时近4 h,根据当地短时大风的记录近地面伴随较强的下泄气流,造成灾害性大风。灾害性大风的能量可能来自对流层中层对流不稳定能量的积聚,能量大小对风害的强度有很好的指示性,对流不稳定能量层消失时刻预示风害爆发时刻。此个例灾害性大风和强降水发生在最强回波、最高回波顶和最大垂直累积液态水含量之后。强烈的天气现象与天气雷达回波指示值之间的时间差可作为预报员今后预报此类天气的重要参考。

A severe storm happened around the Three Gorges Dam area at midnight on 15 April 2002, which is the typical convective weather occurred under the condition that the cold front invades into the southwest inverted trough. The instant wind force reached 11, and the rainfall was about 50 mm per hour. The Doppler radar detected the mature thunderstorm echoes possessing the features of mesocyclones （V-pattern notches） . The reinforced echoes maintained about 4 hours. According to the local records of instantaneous gusts, it is deduced that there might be strong downdraft currents near the surface, which led to catastrophic gusts. The energy of the strong gusts might come from the unstable convective energy accumulated in the middle troposphere, which is strongly indicative of the intensity of catastrophic gusts near the surface. It suggests that the strong gusts burst out when the unstable layer disappears. Different from other examples, the strong gusts and heavy rain in this case happened about one hour later of the occurrence of the strongest echo, highest echo top and largest vertically integrated liquid water content. The temporal lag can be the most important reference for weather forecasters to predict severe weather.