相似天气背景下深圳两次前汛期降水过程对比分析

在高空槽和低层切变线配合的相似环流背景下,2019年4月11日深圳出现短时暴雨(简称"2019年过程"),2020年4月11日以稳定性弱降水为主(简称"2020年过程"),利用ERA5再分析数据等对深圳这两次前汛期降水过程进行了对比分析。结果表明,2019年过程,温湿层结等对流条件和高空辐散条件较好,低空辐合动力条件相对较弱,在边界层辐合线触发下产生明显的中尺度对流系统(mesoscale convective system,MCS)活动,导致深圳出现短时强降水和雷暴大风。2020年过程,低层辐合等动力条件较好,但对流条件相对较弱,降水以稳定性降水为主。对比分析说明,温度和湿度层结条件较动力条件对华南前汛期MCS生成作用更为明显,强对流发生前12 h深圳等珠三角地区Q矢量辐合明显,对MCS活动以及强对流发生有较好的指示意义。

Comparative analysis of two precipitation events in Shenzhen under similar synoptic background in early rainy season

In Shenzhen, a short-lived rainstorm accompanied by gale occurred on 11 Apri1 2019, while a weak stable precipitation event happened on 11 Apri1 2020. The two distinct rainfall events take place in the similar circulation backgrounds of upper-level trough and lower-level shear. The features and associated mechanisms of the two events in the early rainy season are analyzed by using ERA5 reanalysis data. The short-lived rainstorm in 2019 comes along with a typical mesoscale convective system (MCS) , which migrates eastwards and leads to the short-time torrential rain and thunderstorm gale in Shenzhen. The MCS is triggered by the boundary layer convergence line, and then develops in good convective conditions of temperature and humidity and divergence at upper level, but unfavorable dynamic conditions such as weak convergence at lower level. In contrast, Shenzhen sees a much more tender and stable rain in 2020, which happens in the beneficial dynamic conditions of lower-level convergence but weak convective conditions. The comparison suggests the convective conditions such as temperature and humidity play more important role than dynamic conditions in the development of MCSs in the early rainy season of South China. The Q-vector shows significant convergence over Pearl River Delta areas such as Shenzhen up to12 h in advance of the strong convection,which is a skillful precursor for the occurrence of MCS and convection.