干旱地区一次局地对流性大暴雨成因分析

Cause Analysis of a Local Convective Heavy Rain in Arid Area

综合使用常规Micaps资料、临河雷达ROSE资料等,对2023年8月9日河套平原一次局地对流性大暴雨过程进行了分析,重点讨论了过程发生的中尺度环境条件时空演变特征及暴雨成因。结果表明:副高快速大幅度北跳后南落使短期内对流层中高层下沉气流的增温作用达到、下沉气流的对流抑制作用减弱,但低层暖湿高能状态仍然维持;中高海拔地区无抑制、低海拔地区小量抬升可突破抑制释放大量储藏能量的不稳定性空间分布为夜间乌加河河谷地带的强对流的发生提供了有利的大气层结背景条件;前半夜暖中心前部热力不稳仍然较强,低海拔地区局地动力抬升使抑制消失则局地触发强对流,西南部地面露点较高、850 hPa比湿较大,易形成局地强降水。阴山最高峰与乌加河河谷离最高峰最近处沙海镇巨大海拔差所产生的热力差异,为此次夜间局地强对流提供了有利的山风热力环流条件;对流层中低层的强劲的东南风与山风环流高层的东南风一直,进而加强了山风环流;山风产生的冷空气抬升各沟口自西南向东北依次展开,由于沙海镇受多条沟口的冷出流影响,因此动力抬升时间最长、抬升幅度最大;最佳抬升层较低时,模式850 hPa风场在分析乌加河河谷水汽能量输送方向时有较强指示作用。

The process of a local convective heavy rain in Hetao Plain on August 9, 2023 is analyzed by using conventional Micaps data and ROSE data of riverfront radar. The spatio-temporal evolution of mesoscale environmental conditions and the cause of the rainstorm are discussed. The results show that the subtropical high quickly and sharply jump to the north and then set to the south makes the warming effect of the downdraft in the middle and upper troposphere reach and the convective suppression effect of the downdraft weaken in the short term, but the warm and humid high energy state in the lower layer is still maintained. The spatial distribution of instability with no inhibition in the middle and high altitudes and a small amount of uplift in the low altitudes can break through the inhibition and release a large amount of stored energy provides a favorable atmospheric stratification background for the occurrence of strong convection in the Uga River valley at night. In the early night, the thermal instability in the front of the warm center is still strong, and the local dynamic uplift in the low altitude area causes the local strong convection to disappear. The surface dew point in the southwest is higher and the specific humidity of 850 hPa is larger, which is easy to form local heavy precipitation. The thermal difference caused by the huge altitude difference between the highest peak of Yinshan Mountain and Shahai Town, the closest place to the highest peak in the valley of Wujia River, provided favorable conditions for the local strong convection at night. The strong southeasterly wind in the middle and lower troposphere is consistent with the southeasterly wind in the upper troposphere, which further strengthens the mountain wind circulation. The cold air generated by the mountain wind spreads from southwest to northeast. Shahai Town is affected by the cold outflow of several gullies, so the dynamic uplift time is the longest and the uplift amplitude is the largest. When the optimal uplift layer is low, the wind field of model 850 hPa has a strong indication in the analysis of the direction of water vapor energy transport in the Uga River valley.