冷涡背景下呼和浩特市冰雹特征分析

Analysis on characteristics of the hail in Hohhot under a background of cold vortex

利用呼和浩特多普勒天气雷达、卫星云图及NCEP(1°×1°)逐6 h再分析资料,对2015年7月29日呼和浩特市的一次冷涡后部环境条件下发生的冰雹天气过程进行分析,结果表明:在冷涡后部,高层冷平流和低层暖平流有利于对流不稳定度加大,较大的对流有效位能(CAPE)和假相当位温(θse)高能区反映了不稳定能量在冰雹区积聚;中低层水汽输送、0~6 km风场强烈顺时针旋转和中等强度的垂直风切变,为冰雹发生提供可能;地面辐合线、冷空气侵入及干线是冰雹的主要触发条件,冰雹主要发生在低层高能区和干线附近靠近湿区一侧。组合反射率因子图上呈现"钩状回波"和"弓形回波",最强反射率因子大于等于60 d Bz,反射率垂直剖面图上可识别低层弱回波区和中高层回波悬垂,回波顶高14~15km,大于等于45 d Bz的回波达到8 km,扩展到-20℃高度层;径向速度图上具有气旋式旋转辐合和"逆风区";垂直累积液态水含量VIL达到64 kg·m^(-2),且降雹前有明显的跃增现象。

Based on Doppler radar, satellite and the NCEP 1°×1° 6 h interval reanalysis data, a hail weather event is analyzed, which occurred in the rear of the cold vortex on July 29, 2015 in Hohhot. The results indicate that in the rear of the cold vortex, the convective instability of atmosphere increased with cold advection in upper level and warm advection in lower level. Especially, the warm advection in the lower level is more conductive to the accumulation of unstable energy in the hail area and to the formation of large CAPE. Water vapor transportation of middle and lower atmosphere, strong clockwise rotation in low-level winds (0～6 km) and the moderate vertical wind shears are advantageous to the development of convective storms. The surface convergence line, cold air and dry line are the main triggering factors of the hail.The hail was generated in the lower atmosphere with high-energy area and is close to the moist area of the dry line. The characteristics of “hook echo”and“bow echo”were presented in the basic reflectivity factor figure, and there was a weak echo area in the vertical section of basic reflectivity factor figure, while great than or equal to 45 dBz echo reached above the height of -20 ℃ level. Cyclonic rotation convergence and upwind section can be seen in the radial velocity figure. VIL reached great than or equal to 64 kg·m-2, and it jumped significantly before the hail occurred.