上海城市在热岛和海风锋影响下特大暴雨的初步分析

上海地处长江三角洲冲积平原,由于沿江滨海,水网交错,在特定的环流形势背景下,可在市区形成集中降水。本文针对1985年8月31日(以下简称8.31)发生于上海的一次特大暴雨,在对环流形势分析的基础上,进行气流升速等7个物理量的计算,研究了下垫面对局地强雷暴活动的动力、热力和地形作用。结果表明:南下的冷空气与太平洋副热带高压西缘暖湿气流的辐合是造成这次雷暴雨的发生源,而在副高短期稳定,西风槽少动的条件下,海风锋和城市热岛可对最大降水落区起到触发机制或“诱导”、增幅作用。

Primary Analysis of Very Heavy Rain Under the Influence of Urban Heat Island and Sea Breeze Front in Shanghai

Aiming at the heavy rainfall on 31 August,1985 in Shanghai,physical quantities connected with precipitation,i.e.vertical velocity,divergence,moisture flux divergence etc.are computed based on analysis of circulation.Dynamical,thermal and topographic effects on local severe thunderstorms are discussed.Converging between southward cold air and the warm and moisture current brought by Pacific subtropical high was the origin of this severe thunderstorm.The subtropical high being steady and westerlies's trough moving slowly during a short time,the sea breeze front and urban heat island acted on the concentrated precipitation area as trigger mechanism.