陕西三次强致灾性初夏区域性暴雨动力诊断对比分析

Comparative Analysis on Dynamic Diagnosis of Three Strong Disaster Causing Regional Rainstorms in Early Summer in Shaanxi

利用常规气象观测资料和0.25°×0.25°逐小时ERA5再分析资料,对综合评价强度指数300以上的三次陕西初夏区域性暴雨过程从水汽、动力垂直结构上进行对比分析。结果表明:①强致灾性初夏区域性暴雨发生前,中高层水汽输送来自西南气流,低层来自偏东气流,低层水汽辐合发展加强,动力强迫主要表现为700 hPa以下正涡度区发展加强并向高层延伸,对应200 hPa附近出现强负涡度中心;②暴雨开始后,低层偏东水汽输送在暴雨过程中会发生变化,水汽辐合持续加强并向高层持续输送,散度场出现低层强辐合、高层辐散的结构,而关中有双重辐合-辐散特殊结构,且正涡度区继续向高层延伸、动力抬升促使上升运动延伸至400 hPa及以上;③初夏暴雨陕南动力强迫相比关中较弱,但水汽输送、水汽含量比关中好,降水效率更高、降水总量更大。

Three regional rainstorm processes in early summer in Shaanxi with a comprehensive assessment intensity index of more than 300 are compared and analyzed in terms of water vapor and dynamic vertical structure by using conventional observation data and 0.25°×0.25°hourly ERA5 reanalysis data.The results show that:①Before the occurrence of the strong disastrous regional rainstorm in early summer,the middle and upper levels of water vapor transport came from the southwest airflow,and the lower levels came from the easterly airflow.The development of water vapor convergence in the lower levels was strengthened,and the dynamic forcing was mainly manifested in the positive vorticity area below 700 hPa and extended to the upper levels,corresponding to the strong negative vorticity center near 200 hPa;②After the beginning of the rainstorm,the water vapor transport at the lower level to the east would change during the precipitation process.The water vapor convergence at the lower level continued to strengthen,prompting the water vapor transport to the upper level.The divergence field had a structure of strong convergence at the lower level and divergence at the upper level.However,Guanzhong had a special structure of double convergence-divergence,and the positive vorticity area continued to extend to the upper level,and the dynamic uplift promoted the upward movement to extend to 400 hPa and above;③The dynamic forcing of rainstorm in early summer in southern Shaanxi was weaker than that in Guanzhong,but the water vapor transport and content were better than those in Guanzhong,with higher precipitation efficiency and larger total precipitation.