一次锋前暖区暴雨成因分析

Cause Analysis of a Heavy Rainfall Process in Warm Sector Ahead of Cold Front

利用常规气象观测、自动站、区域雨量站、卫星、雷达、再分析等资料,对2015年8月发生的一次锋前暖区暴雨进行了综合分析。结果表明:此次暴雨发生在西风槽东移和副高东退南压的环流背景下,以热力条件为主导引发的锋前暖区强对流性降水是此次暴雨产生的主要贡献者;暴雨发生在高空急流右后侧的显著辐散区,700 h Pa暖式切变线、850 h Pa冷式切变线、地面干线以及SI<-2℃相重叠的区域;850 h Pa切变线上的中尺度气旋性涡旋、自动站极大风速风场切变线以及中尺度涡旋是本次暴雨的直接触发系统;由于数值模式850 h Pa切变线位置预报的偏差,使得中低层流型配置由前倾误导为后倾结构,直接影响了模式热力条件预报的准确性,其结果是增强了西部动力条件而弱化了东部热力条件,最终导致暴雨落区预报偏差;锋前暖区暴雨预报的关键是触发不稳定能量释放的条件,对于此类暴雨应多关注边界层风场的变化,加强新型监测资料的综合分析和应用。

Based on data of conventional meteorological observation, automatic stations, regional rainfallstations, satellite, radar and reanalysis, a heavy rainfall process in warm sector before cold front in August 2015 was analyzed. The results showed that： this heavy rainfall process happened in the background of westerlytrough moved eastward and the subtropical high retreated southeast, and the strong convective precipitation ledby thermal condition in warm sector before cold front was the main contribution of the heavy rainfall. Therainstorm appeared in the overlapping area of the significant divergence zone at the right rear of the upper-level jet, warm shear line at 700 h Pa, cold shear line at 850 h Pa, surface dry line and the region where SI wasless than-2℃; the mesoscale cyclone vortex on 850 h Pa shear line together with the shear lines of extremewind of automatic stations and mesoscale vortex directly triggered the rainstorm. Due to the deviation error ofthe model forecast in position of the 850 h Pa shear line, the mid-lower flow configuration was misled from aforward- tilting to be a backward- tilting structure, which directly affected the model accuracy in thermalcondition forecast, and the result was that enhanced the western dynamic condition and weakened the easternthermal condition, which ended up with a deviation error of heavy rainfall area forecast. The key of heavyrainfall in warm sector before cold front forecast was the conditions of triggering the release of unstable energy.For such rainstorm forecast, we should pay more attention to the wind field changes in boundary layer andstrengthen the comprehensive analysis and application of the monitoring data.