新疆天山北坡中部一次冰雹天气成因分析

Comprehensive Analysis of a Severe Hail in the Middle Section on Northern Slope of Tianshan Mountain in Xinjiang

利用常规观测资料、NCEP再分析资料、自动站资料和石河子CINRAD/CC多普勒天气雷达观测资料,对2010年7月11日发生在新疆天山北坡中部的一次强对流天气进行了综合分析。结果表明:这次冰雹天气发生在巴尔喀什湖低涡的环流背景形势下,较好的水汽条件、对流不稳定条件、0℃层和-20℃层的适宜高度以及较强的垂直风切变促使冰雹等强对流天气过程发生发展,同时山区和平原交界处的地形和热力不稳定作用对对流风暴的触发和发展成为冰雹云有着重要的作用。通过对多普勒雷达PUP产品的分析得出:这次强对流天气在组合反射率因子(CR)图出现了中心强度为63dBZ强对流单体和大面积>50 dBZ的强回波区;在反射率因子剖面(RCS)上表现为60 dBZ强回波区的高度已达到5 km,50 dBZ强回波区的高度达到7.3 km,整个回波顶高度达到12 km的强回波墙,十分有利于冰雹的形成;在冰雹发生前期,平均径向速度图上出现了中气旋,促使对流风暴单体加强和维持;在冰雹形成区有低层辐合、高层辐散等特征;垂直累积液态含水量的跃增及其密度>3.5 g/m3十分利于冰雹的产生。

Based on the conventional data, the NCEP reanalysis data, the data of automatic weather station and the CINRAD/CC data in Shihezi, a severe hail event occurred in the middle section on northern slope of Tianshan mountain in Xinjiang on 11 July 2010 was analyzed. The results show that this hailing process happened under Balkhash Lake vortex circulation background. Favorable vapor conditions, unstable convection, suitable height of 0 ℃ and -20 ℃ layers and strong vertical wind shear promoted the generation and development of severe convection weather. Meanwhile, the special terrain and thermal instability at the border of the mountain and plain played an important role in triggering convective storm and further forming hail storm. Through the analysis of the Doppler radar products PUP：on the combined reflectivity factor （CR） chart, there was a strong convective cell where the echo was more than 50 dBZ and the intensity of echo was 63 dBZ in the center. The reflectivity section （RCS） showed the height of 60 dBZ strong echo had run up to 5 km as well as the height ofS0 dBZ strong echo up to 7.3 km, and there was a strong echo wall with the top reaching to 12 km. The height of 50 dBZ strong echo was much higher than the - 20 ℃ layer height, which was beneficial to the formation of hail. On the av- erage radial velocity maps, there was a mesocyclone before the hail coming, which maintained and strengthened convective storm. And there were convergence at the lower level and divergence at the upper level in the hail area. The leap increase of VIL and the density of VIL more than 3.5 g · m-3 were the good condition for the hailstorm formation.