一次长生命史超级单体风暴双偏振参量结构及演变特征

Dual-Polarization Parameter Structure and Evolution Characteristics of a Long-Life Supercell Storm

利用石家庄新乐S波段双偏振多普勒天气雷达探测资料和常规气象观测资料,以及区域自动气象站观测资料,对2020年6月25日造成河北中部大冰雹的长生命史超级单体风暴双偏振参量结构演变特征进行了分析。结果表明:超级单体风暴产生在强热力不稳定和强的垂直风切变环境下。冰雹增长过程中超级单体风暴低层强回波中心大冰雹与强降水共存,反射率因子超过65 dBz,对应较小的差分反射率因子(Z DR)和相关系数(CC),超级单体风暴左侧前后强回波区为弱降雨和少量融化的小冰雹,反射率因子在50~55 dBz,Z DR、CC和差分传播相移率(K DP)较大。超级单体风暴中层的Z DR柱、CC低值区、K DP柱位于有界弱回波区左右两侧,左侧CC低值区位于强回波中心,由于存在混合相态且结构差异较大,CC更小;右侧K DP柱更强,位于有界弱回波区内。高层狭窄的Z DR柱位于强回波中心右侧边缘,CC低值区位于强回波中心。在中高层有界弱回波区和强回波中心区域存在强的上升气流。在大冰雹下落过程中,Z DR洞扩展到最低仰角且宽度加大,这可作为大冰雹即将落地的判据。低层Z DR弧加强表明低层旋转加强。虽然强回波中心对应的CC低值区、Z DR柱高度迅速下降且强度明显减弱,但一直存在,表明较强上升气流一直存在,因此超级单体能够长时间维持。

Based on the detection data of S-band dual-polarization Doppler weather radar in Xinle of Shijia-zhuang,Hebei Province,the conventional meteorological observation data and the regional automatic weather station observation data,this article analyzes the evolution characteristics of dual-polarization parameter structure of long-life supercell storm that caused large hail in central Hebei on 25 June 2020.The results show that the supercell storm occurred in an environment of strong thermal instability and strong vertical wind shear.With the process of hail growth,large hails coexisted with severe precipitation in the strong low-level echo center of the supercell storm,and the reflectivity factor exceeded 65 dBz,corresponding to small differential reflectivity factor(Z DR)and correlation coefficient(CC).Weak rainfall and a small amount of melted hails were located in the strong echo area on the left side of the supercell storm.The reflectivity factor was between 50 dBz and 55 dBz,and Z DR,CC and the specific differential phase(K DP)were larger.The Z DR column,CC low value area and K DP column in the middle layer of the supercell storm were located on the left and right sides of the bounded weak echo area,and the left CC low value area was in the center of the strong echo.The CC was smaller due to the existence of mixed phases of precipitation and the larger structural differences.The right K DP column was stronger and located within bounded weak echo area.The narrow Z DR column in the upper layer was located on the right edge of the strong echo center,and the CC low value area was in the strong echo center.There was a strong updraft in the strong echo center area and the bounded weak echo area in the middle and upper layers.The Z DR hole expanded to the lowest elevation angle and the width increased during the falling process of large hails.This can be used as the criterion for judging the imminent landing of large hail.The low-level Z DR arc intensification indicated that rotation intensifies in the low level.Although the height of the Z DR column and CC low value area in the strong echo center dropped rapidly and the intensity was obviously weakened,they existed all the time,indicating that the stronge updraft was there all the time,which supported the long time maintenance of the supercell.