甘肃东南部两次极端致灾暴雨对比分析

为了研究甘肃东南部相同气候背景条件下极端暴雨天气的成因,提高极端暴雨强度和落区预报的准确率,利用NCEP再分析、自动气象站降水、常规观测资料及卫星云图资料,对2013年8月7日和2017年8月7日发生在甘肃东南部两次极端暴雨进行对比分析。结果表明:两次极端暴雨天气过程都伴随着短时强降水等强对流性天气,具有降水量大、雨强强、灾害重的特点,其中冷空气的强度对暴雨落区、空间分布以及影响系统移动以及对流强度产生重要影响。在强冷空气和高空低槽、低层切变线影响下,暴雨区偏南,强降水区域小,持续时间短,不稳定条件更好,对流强度更强;在弱冷空气和高原槽、低层低涡、低空急流作用下,暴雨区偏北,强降水范围大,持续时间长,大气湿层厚度大,低层水汽辐合强度、涡度以及垂直速度更强,降水效率更高,但对流强度相对较弱。卫星云图上,在强冷空气的影响下对流发展旺盛,形成强中尺度对流云团,对流云团呈带状;在弱冷空气作用下对流云团尺度小,发展范围小,有暖云降水特征,降水效率高。

Contrast Analysis of Two Extreme Disaster Rainstorms in southeastern Gansu

By using the NCEP reanalysis data, automatic weather station precipitation data and conventional observation data, satellite data, two extreme torrential rainstorms in southeastern Gansu occurred in early August are comparatively analyzed under such a climatic situation and to improve the accuracy of extreme rainfall intensity and forecast. The results show that both extreme rainstorm weather processes are accompanied by severe convective weather such as short-time heavy rainfall, which has the characteristics of large precipitation, strong rain and heavy disaster. The rainstorm area and spatial distribution are different. The heavy rain area is southerly, the heavy precipitation area is small and the duration is short of the 1387 rainstorm process; the 1787 rainstorm process area is northerly, with a large range of heavy precipitation and a long duration. The main influencing systems are high altitude trough, low level shear line, plateau trough and low level vortex respectively. At the same time, under the influence of strong cold air, the 1387 rainstorm process has better unstable conditions and stronger convection intensity. Under the combined action of weak cold air, low air jet and low vortex, the 1787 rainstorm process has thick wet layer, stronger water-vapor convergence strength, vorticity and vertical velocity, resulting in higher precipitation efficiency and weaker convection intensity. on the satellite cloud, the 1387 rainstorm process has a strong convective development, forming a strong mesoscale convective cloud cluster, the rainstorm area and the convective cloud cluster are banded; In the rainstorm process of the 1787 rainstorm process, the scale of convective cloud is small and the development scope is small. It has the characteristics of warm cloud precipitation, high precipitation efficiency, long precipitation duration, larger rainstorm range and more short-time heavy precipitation stations.