2013年3月20日湖南和广东雷暴大风过程的特征分析

Characteristics of the Thunderstorm Gale Process in Hunan and Guangdong on 20 March 2013

利用常规探空资料、多普勒天气雷达资料和风廓线雷达资料对2013年3月19日夜里到20日凌晨发生在湖南中南部和广东北部的一次区域性雷暴大风天气进行了分析,发现本次强对流天气过程的天气尺度背景是北支高压脊的崩溃和南支槽的建立,槽前出现较强的低空急流和切变线并在湖南中南部和广东北部形成了上干冷下暖湿的温湿配置结构下发生并强烈发展的;地面自动站观测显示北风侵入到前期露点温度较高的贵州黄平地区并形成风向辐合触发了对流,之后对流单体东移进入前期地面辐合线和露点锋相配合,同时500 hPa极为干冷的湖南中部偏南地区不断发展加强成对流带;雷达观测显示19日夜里在湖南西部不断出现对流单体并在其东移南下过程中最终形成飑线结构,该飑线中存在多个超级单体;通过多普勒天气雷达的中气旋产品与雷暴大风出现时间对应比较发现:大多数由中气旋引发的雷暴大风,在雷暴大风出现前2~3个体扫,其中气旋底高不断下降至2 km左右或以下,且在雷暴大风出现前1~2个体扫,中气旋的最强切变高度显著下降至中气旋底高位置附近;通过风廓线雷达数据与雷暴大风出现时间对应比较发现:底层大气折射率结构常数(C_n^2)大幅度的跃升通常在雷暴大风出现前10~15 min左右出现,其对雷暴大风的出现可能具有一定的指示意义。

Based on the conventional sounding observation data,Doppler radar data and wind-profiling radar data,a thunderstorm gale process that occurred in Hunan and Guangdong from the night of 19 to the morning of 20 March 2013 is analyzed.The results show that the background of this strong convective weather process is the collapse of the northern branch ridge and the establishment of the southern branch trough.Strong low-level jet and the shear line appear before the trough,which causes the dry and cold air above the level of the warm and humid air and makes the convection develop strongly.The automatic observation shows that the convective cell is triggered when the north wind enters into Huangping Guizhou（where the dew point temperature is higher than the surrounding areas） and forms wind convergence.After that,the convective cells moves into the south region of Hunan where there is a convergence line matching a dew point front and strengthens to a severe convective zone while it is extremely cold and dry at500 hPa.Over the night of the 19 th many convective cells emerge in the western Hunan,forming a squal line at last.There are many supercells in the squal line.By comparing the mesocyclone product of the radar with the time of the thunderstorm gale,it is found that the bottom of the mesocyclones continues droping to below 2 km about 2-3 volume scans before the appearance of the most thunderstorm winds resulting from the mesocyclone,and the strongest shear height drops to the bottom height of mesocyclone about1-2 volume scans before the appearance of the thunderstorm gale.In addition,after comparing the wind profiler radar data with the time of thunderstorm gale,we also get conclusion that a substantial jump of the bottom refraction index structure constant（C_n^2）always appears about 10-15 min before the time of thunderstorm wind,which is probably indicative to the appearance of wind.