陕北两次暴雨过程成因及极端性分析

Analysis of the Causes and Extremes of Two Rainstorms in Northern Shaanxi

摘要:

利用常规观测及ERA5再分析资料，对2022年陕北降水异常偏多背景下，7月11日（简称“7·11暴雨”）、8月9日（简称“8·9暴雨”）两次特强暴雨成因及其极端性进行分析。结果表明：（1）“7·11暴雨”低空急流提供了持续的水汽输送，湿层深厚，深厚的中尺度低涡为大范围暴雨提供了有利的动力条件。强降水持续时间相对较长，雨势较缓。（2）“8·9暴雨”陕北受副高控制，对流有效位能和整层可降水量大，地面辐合线触发不稳定能量释放，形成对流性暴雨天气。雨强大、单站降水持续时间短，β中尺度对流复合体维持造成雨强大于80 mm·h-1的极端强降水。（3）“7·11暴雨”700 hPa、850 hPa水汽通量标准化异常（SD）超过3σ，表征动力和水汽的多个物理量达到或接近当地特强暴雨过程最大值，极端性强；“8·9暴雨”整层可降水量SD超过3σ，对流有效位能达到特强暴雨过程上四分位值。物理量大值区配合强的SD对极端天气预报有较好的指示意义。

Abstract:

By using conventional observations data and ERA5 reanalysis data, the causes and extremes of the two rainstorms in Northern Shaanxi, which occurred on July 11 (“7·11”) and August 9 (“8·9”), were analyzed based on the background of abnormally high precipitation in 2022. Results showed that: (1) The low-level jet provided continuous water vapor transport and the wet layer is deep during “7·11” rainstorm. The development of deep mesoscale vortex system provided favorable dynamic conditions for large-scale rainstorm.Rainstorms with a long duration and low intensity. (2) Northern Shaanxi was controlled by the subtropical high and with strong convective effective potential energy and large whole layer precipitable water vapor during “8·9” rainstorm. The surface convergence line triggered the release of unstable energy and resulted in convective rainstorms which had intense hourly precipitation and short duration of single station precipitation.The maintenance of theβmesoscale convective complex resulted in rainfall intensity greater than 80 mm·h-1. (3) The water vapor flux standardized deviation (SD) exceeded 3σ at 700 and 850 hPa during “7·11” rainstorm and many physical quantities representing the water vapor and dynamic conditions reached or approached the maximum value of extremely strong rainstorm process, which indicated strong extremity. The whole layer precipitable water vapor SD exceeded 3 σ in “8·9” rainstorm and the convective effective potential energy reached the upper quartile value of extremely strong rainstorm process. The large value region of physical quantities with high SD had good indication significance for extreme rainfall prediction.