甘肃白银市一次局地暴雨天气过程分析

Analysis of a Local Rainstorm Process Occurred on May 28,2011 in Baiying of Gansu Province

对2011年5月28日下午至傍晚白银市辖区的靖远、平川等地出现的局地暴雨天气进行诊断分析。结果表明:在有利的大尺度环流背景下,造成此次局地暴雨天气的中尺度影响系统为本地上空700 hPa层上的切变线和地面辐合线,才触发了强对流天气不稳定能量的释放,并且高空急流轴上强风速中心附近的次级环流上升支与低层辐合上升耦合对暴雨过程有明显的增强作用。暴雨天气过程前低层温度脊发展强盛,中高层有干冷空气入侵使对流不稳定性显著增强;过程中低层为显著湿区,为暴雨的形成提供了很好的水汽条件。散度、涡度等动力条件,假相当位温、K指数等热力条件,比湿、水汽通量散度等水汽条件等特征值超过强对流天气发生的临界值;SWAN系统为此次强对流天气的监测预报预警提供了强有力的技术支撑。

This paper makes a diagnosis on the local heavy rainfall occurred in Jingyuan, Pingchuan and some other areas of Baiying city on May 28, 2011. The results indicate that under the favorable background of large- scale circulation, the mesoseale influencing systems that contributed to this local heavy rainfall were the shear line on the level of 700 hPa and the surface convergence line, which triggered release of a strong convective unstable energy. The secondary circulation ascending branch and the low convergence ascending coupling near the center of the strong wind speed on the high level jet axis had an obvious strengthening effect on this rainstorm process. Before this heavy rainfall the temperature - ridge on low level developed strongly, the convective instability significantly en- hanced owing to the invasion of the dry cold air on the middle and top levels. The middle and low levels were notable wet areas during this process, which made a well water vapor condition for this heavy rainfall. In addition, divergence, vorticity and other dynamic con- ditions, pseudo -equivalent potential temperature, K index and other thermal conditions, water vapor conditions such as specific hu- midity, water vapor flux divergence and some other features all exceeded the critical value of strong convective weather occurrence ; the SWAN system provided a strong technical support for the monitoring, forecasting and early warning of this heavy convective weather.