毛乌素沙漠东部边缘一次雹暴三维结构的观测分析

Observational Analysis on the 3-Dimensional Structure of a Hailstorm in the Eastern Part of Maowusu Desert

利用新一代天气雷达和MICAPS提供的实况资料(包括用实况资料计算的其它物理量),对2006年7月27日发生在榆林市西北部部分乡镇的一次雹暴天气过程进行了连续的监测和分析。诊断分析表明:当日08:00,大气层结是稳定的,但925 hPa湿正压场上生成从东南方向伸入雹区的窄的强对流不稳定舌;雹暴发生前2 h,雹区地面邻近上游生成中β尺度能量比高值中心和反映弱冷空气活动的中β尺度能量比低值舌;雹暴的发生也伴随雹区对流层低层大气湿斜压性的增强、边界层温度出现跃升等现象;中尺度纬向次级环流圈的形成,为雹暴的发生、发展和维持提供了动力条件。雷达反射率因子分析表明,强冰雹狂风是由超级单体风暴引发的,超级单体风暴是由中β尺度小钩状回波和由干侵入引发的新生中γ尺度强对流单体在钩状区合并而形成。超级单体风暴具有独特的动力学特征:除了伴随一个持久深厚的中气旋外,对流层低层入流急流持续时间长达50 min,钩状区近地层出现未曾见过或罕见的(由强下沉气流产生)中β尺度环形辐散区和环形辐散区向外扩展的特征。在0.5°仰角速度场,雹暴区气流经历了由径向辐合、气旋性辐合、气旋性旋转、再到径向辐合的演变过程。

A hail storm weather event occurred in northwestern Yulin on July 27, 2006, was continuously monitored and analyzed by using real time data provided by the new generation weather radar and MICAPS observed data including other physical quantity calculated upon them. The diagnostic analysis shows that the atmospheric stratification was stable at 08：00 that day, but a narrow strong convectivelyinstable tongue generated in the moist barotropic field at 925 hPa level extending from southeast to hail zone. In 2 hours before the hail storm near the up neighbor of the hail zone, there emerged a β mesoscale high energy ratio center and a β meso-scale low energy ratio tongue reflecting the weak cold air movement. The hailstorm also developed with the strengthening of moist atmospheric baroclinicity in lower troposphere and temperature leap in boundary layer. Dynamic situation for generating and maintaining hail storm derived from formation of the mesoscale secondary circulation along latitude. Radar reflectivity analysis indicates that strong hail and high wind were induced by the super cell storm which was a combination of the β mesoscale hook echo and a new γ mesoscale evere convective cell generated in the hook area by dry invasion. The super cell storm has unique dynamical features, except which accompanied by a long-lasting deep mesoscale vortex, in lower troposphere, the inflowing jet stream maintained full 50 minutes, the rare β mesoscale ring divergence emerged in hook area near surface level and represented features of outward expansion. In 0.5°velocity field, stream in hailstorm zone experienced a evolution of longitudinal convergence, eyclonical convergence, cyclonical twist and longitudinal convergence till the end.