一次低涡型冰雹天气的环境条件和中尺度特征分析

Environmental Conditions and Mesoscale Characteristics of a Low Vortex Hail Weather

利用常规天气观测、多普勒天气雷达、自动气象站和NCEP1°×1°格点再分析资料,研究在绍兴发生的一次典型低涡型冰雹天气过程环境场和中尺度特征,结果表明:此次冰雹天气出现在西北冷涡的右前方,中高层的干侵入激发了对流不稳定;中尺度辐合线出现在对流风暴的前沿,是由冷池出流与外界暖湿气流交汇而形成,为强对流的发展提供了近地面辐合抬升条件;本次过程先后有三个明显的强单体风暴产生,回波核心区高度均扩展到-20℃层以上,符合弱回波区、悬垂回波和中低层径向辐合的强对流风暴结构,还具有标志大冰雹的三体散射特征(TBSS)。在降雹前最大反射率因子(DBZM)及其所在高度(DBZMHT)的突降和垂直累积液态水含量(VIL)的突增可作为判断降雹的指标。

Based on data from conventional weather observation, Doppler weather radar, and automatic weather station, as well as NCEP 1°×1° reanalysis data, the environmental field and mesoscale characteristics of a typical low vortex hail weather process in Shaoxing are studied. The results show that the hail weather appears in the right front of the northwest cold eddy, and the dry intrusion of the middle and upper levels stimulates convective instability. Mesoscale convergence line appears at the front of convective storm, which is formed by the convergence of cold pool outflow and warm-humid air flow outside, which provides the condition of near-surface convergence and uplift for the development of strong convection. There are three distinct strong monomer storms in this process and the echo core area all extends above - 20 ℃, which conforms to the structure of strong convective storms in weak echo area, suspended echo and radial convergence in the middle and lower layers. It also has the characteristics of three-body scattering (TBSS), which marks the large hail. The sudden drop of maximum reflectance factor (DBZM) and its height (DBZM HT) as well as the sudden increase of vertically integrated liquid water content (VIL) before hail fall can be used as indicators to judge hail.