上海“0731”局地强对流观测分析

Observation Analysis of Local Severe Convection Event in Shanghai on 31 July 2011

利用1994-2012年上海自动站观测资料对该地区强对流的时空分布特征及夏季热岛变化特征进行了分析,然后利用上海近地层加密观测网资料,分析了城市热岛、海陆风、湖陆风在"0731"局地强对流中的作用。结果表明,上海城市热岛效应的范围有所扩大,强对流天气发生频次增加,具有中心城区及沿江、沿湖地区多发的特点。热岛效应促使边界层急流形成;午后南北两支海陆风和湖陆风的出现,为上海带来了水汽;热岛效应的叠加加速了不稳定能量累积和近地层上升运动的增强。当海陆风在上海中心城区形成地面辐合线时,触发了不稳定能量释放,并加剧了对流发展。

Considering the peculiar geography of Shanghai,the influences of the complicated underlying surface on the initiation and development of early-afternoon summer convections is an important topic in short-range weather forecasts. Firstly,using automatic weather station observations of Shanghai from 1994 to 2012,the temporal and spatial distributions of the local severe convections and the characteristics of the Urban Heat Island( UHI) in Shanghai summer were studied,after that,using observations from near-surface dense observation network,the role of UHI,sea breeze,lake breeze in the initiation and development of the ‘0731'local severe convection event was analyzed and discussed. The results indicated that the zone of UHI in Shanghai was expanding. The frequency of severe convection in Shanghai summer was increasing and these severe convections mostly occurred in downtown area and regions along rivers or lakes. Due to the Shanghai UHI effects,the boundary layer jet was preserved,the appearance of sea breeze and lake breeze brought moisture to Shanghai area,while the superposition of the UHI effects accelerated the accumulation of unstable energy and the enhancements of the updrafts,once the surface convergence line in downtown area was formed due to the sea breeze effects,the trigger of unstable energy releasing was turned on and the development of the convections was enhanced further.