南海夏季风爆发前后柳州地区前汛期南风型暖区暴雨特征

摘要

利用常规气象观测站、区域自动气象站及NCEP/NCAR(National Centers for Environmental Prediction/National Cen-ter for Atmospheric Research)的1°×1°再分析资料,对比分析了2010-2015年南海夏季风爆发前后柳州地区前汛期南风型暖区暴雨的特征及环流形势.结果表明:72.7%的南风型暖区暴雨出现在南海夏季风爆发后;南海夏季风爆发前后两类暖区暴雨发生时500 hPa均有正涡度的输送,辐合区主要位于925 hPa附近或以下,超低空急流及边界层较强的南风风速辐合是暖区暴雨重要的触发机制;柳州北部地区的地形在一定程度上触发了暖区暴雨的发生,加大了柳州北部地区暴雨的发生频次;南海夏季风爆发前,暴雨区上空湿层较浅薄,中层干冷空气的侵入增加了暴雨区上空的不稳定度,高层辐散机制主要为副热带西风急流;而南海夏季风爆发后,南亚高压提供高层辐散机制,且高层辐散强于低层辐合,高层强烈的"抽吸"作用使暴雨区上空维持旺盛的上升运动,暴雨区湿层深厚,整层高湿的环境有利于降水效率的提高和中尺度对流系统的产生.%The characteristics and circulation patterns of warm-sector rainstorms with the southerly flow in Liuzhou area occurring before or after the summer monsoon over the South China Sea from 2010 to 2015 were analyzed,u-sing observational data at conventional meteorological stations and regional automatic weather stations,as well as reanalysis data of National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) with the resolution of 1° ×1°.The results indicated that 72.7% of the warm-sector rainstorms with southerly flow occur after the break of summer monsoon over the South China Sea.The warm-sector rain-storms occurring before or after the summer monsoon over the South China Sea are characterized by a transport of positive vorticity at 500 hPa and a convergence zone near or below 925 hPa.The jets at super-low altitudes and the strong convergence of southerly flow within the boundary layer are the important triggering mechanism of the warm-sector rainstorms.The topography in the northern part of Liuzhou also favors the occurrence of a warm-sec-tor rainstorm,leading to a higher occurrence frequency of warm-sector rainstorm in this region.Before the occur-rence of summer monsoon in the South China Sea,the wet layer above the rainstorm area is very shallow,the inva-sion of dry and cold air at the middle levels favors the instability of atmospheric at upper levels of the rainstorm ar-ea,and the subtropics westerly jet is the major mechanism of divergence at upper levels.While after the occurrence of the summer monsoon in the South China Sea,the high pressure at South Asia is the mechanism of divergence at upper levels and the divergence is stronger at upper levels than lower levels.The strong "suction" action sustains the ascending motion at the upper levels of the rainstorm area.The deep wet layer in the rainstorm area is benefi-cial to enhance the precipitation efficiency and the formation of quasi-stationary mesoscale convective systems.