湖北宜昌超级单体风暴发生的环境条件分析

利用Micaps高空、地面实况资料以及雷达基数据产品资料,分析2004—2009年湖北宜昌境内出现的10例强对流天气过程中的超级单体风暴生成的环境条件和回波结构。结果表明:产生冰雹的湿层相对浅薄,产生强降水的湿层较深厚。使用雷暴发生前地面温度和露点进行订正后的CAPE值可判断午后是否有冰雹发生:若订正后CAPE值有较大幅度增长,其值超过1000J.kg-1以上,则出现冰雹的可能性较大;反之则小。0—6km中等到强的垂直风切变有利超级单体风暴生成和发展,垂直风切变越大,越有利出现极端大风。若超级单体风暴高度的特征值和特征底有迅速下降迹象,则未来0.5h内很可能出现8级以上大风。超级单体风暴中正负速度对的切变值越大,风力越大,风灾越明显。超级单体风暴反射率因子的低层或表现为钩状、或向着入流方向突起、或密实块状等回波特征,中高层有强度达55dBz的强回波。超级单体风暴中,中气旋大多从逆风区或切变区中发展而来,且其在垂直气流结构上表现为低层气旋式辐合,中层辐合逐渐增强,为气旋式旋转,有时出现气旋式旋转与反气旋式旋转共存的双涡结构,至高层,则转为反气旋,表现为辐散。VIL密度(DVIL)对大冰雹有一定的指示意义,当DVIL≥3.5g.m-3时,出现直径超过2cm的大冰雹的可能性非常大。

Analysis on environment conditions of supercell storms over Yichang, Hubei province

Using real-time upper-air and surface observations from Micaps and radar based data, the environmental condition and echo structure of supercell storms in 10 severe convective weathers over Yichang, Hubei province from 2004 to 2009 have been analyzed. The re-sults show that hail occurred in shallow wet layer, but severe precipitation occurred in deep wet layer. CAPE revised by ground temperature and dew point before the thunderstorm occurred can be used to judge whether the hail will occur in the afternoon. If the revised CAPE value increases greatly （CAPE ≥ 1 000 J·kg^-1）, the possibility of hail generating is higher, otherwise the possibility is lower. Vertical wind shear （0-6 km） from moderate to strong grade is favorable to the generation and development of supercells, and the stronger vertical wind shear is, the more easily extreme wind emerges. If the characteristic value and characteristic bottom of height of the supercell storms show a rapid decline, gale of more than 8 levels is likely to come in half an hour. When the greater shear means are with the positive / negative velocity area in the supercell storms, the greater wind power is, and the more obvious wind disaster is. Basic refIectivity factors of the supercell storms in the low-level present such echo characteristics as hook-shaped or protuberance to inflow direction or dense bulk, and strong echoes with more than 55 dBz is situated in the mid-and upper-level. In the supercell storms, mesocyclones is mostly developed from the head wind zones or shear zones, and as for the vertical airflow structure it shows cyclonic convergence in the low and cyclonic rotation with reinforcement of con-vergence in the medium. Sometimes the double vortex structure appears with coexisting cyclonic rotation and anticyclonic rotation, and it shows divergence with anticyclone in upper air. D VIE （vertical integrated liquid density） has certain prediction significance for large hail fore- casting, when D VIE ≥ 3.5 g·m^-3, the possibility of appearance of large hail with the diameter of more than 2 cm is much higher.