鲁西北连续两次强降水过程对比分析

Comparative Analysis of Two Consecutive Heavy Rainfall Events in Northwestern Shandong Province

利用各种观测资料和NCEP/NCAR 1×1°再分析资料,对2012年7月30日夜间和31日夜间鲁西北连续两天强降雨天气进行诊断和对比分析。结果表明:强降水产生在西风槽前和副热带高压边缘的偏南暖湿气流中,西风槽稳定少动,台风在东南沿海北上,副高加强北抬,为鲁西北连续两天的强降水提供了天气尺度背景。925hPa及以下的低层,来自于渤海的偏东气流和来自于华东沿海的东南气流同时向鲁西北强降水区输送水汽,低层比湿大,CAPE和K指数较高。第1次强降水产生在偏南气流的暖区中,降水强度大,维持时间短。第2次强降水期间,低层有冷空气锲入,把暖湿气流抬升,前期为对流性降水,中后期转为稳定性降水,降水强度小,维持时间较长。850hPa及以下倒槽式切变线和中尺度低涡环流是造成强降水的中尺度影响系统,近地面层来自于渤海的东北气流与来自于东南沿海的东南暖湿气流形成中尺度涡旋,产生气旋式辐合上升,触发对流不稳定能量释放。对流云团在鲁西北形成长形的中尺度对流系统(MCS),稳定少动,有明显的列车效应和后向传播特征。强降水具有较强的日变化,夜间发展增强,白天减弱。

Using a variety of observational data and NCEP/NCAR 1°×1°reanalysis data,a diagnostic analysis is made of two consecutive heavy rainfall events on 30 July and 1 August 2012 in the northwestern Shandong Province.The results show that the heavy rainfall formed in the warm air around the south edge of the subtropical high in front of the steady westerly trough;a typhoon moved northward along the coast of Southeast China;the subtropical high strengthened and moved northward;which provided a synoptic background for the heavy rainfall events for two consecutive days.At the lower level blow 925 hPa,both the southeast winds from the southeast coast and the east winds from Bohai provided moisture and energy supply for the heavy rainfall,leading to higher humidity,high temperature,convective instability,and high CAPE.The first heavy rain occurred in south winds and warm air with strong intensity and short duration.During the second heavy rain,the low-level cold air invaded and the warm air were lifted;there was convective precipitation in the early stage and stable rainfall in the later,with weaker intensity and longer duration.The shear line with a reverse trough and mesoscale vortex circulation in 850 hPa and below were the influencing systems for the heavy rainfall events.At lower levels,the northeast air flow from the Bohai Sea and the southeast warm air from the coast of Southeast China generated a mesoscale vortex,which induced cyclonic converging ascending and triggered the release of instable convective energy.Convective cloud clusters formed a stable Mesoscale Convective System（MCS）in the northwestern Shandong,resulting in obvious train effect and backward-propagation characteristic.The heavy rainfall had a strong diurnal variation,enhanced at night and weakened in daytime.