江苏沿海“7.26”飑线大风过程诊断模拟分析

Diagnostic simulation analysis of"7.26"squall line gale process along Jiangsu coast

利用加密自动观测资料、EAR50.25°×0.25°再分析资料、常州和盐城SA天气雷达资料等和基于三维变分技术(3DVAR)的多雷达风场反演技术,并利用WRF数值模式,对2022年7月26日发生在江苏的一次大范围飑线大风过程进行了分析。结果表明:在此次飑线大风过程中,高空出流区辐散、低层低涡切变辐合,上干冷下暖湿的环境并且配合低空西南急流源源不断输送水汽,为对流的触发和组织化发展提供了较好的动力、水汽条件;飑线入海前,不稳定能量、垂直风切变、垂直上升和水汽条件均较好,而飑线入海后,众物理量配置较差,这与飑线在陆上的组织化发展、强度维持及入海后强度减弱的变化对应较好;飑线入海后,底层后侧入流减弱,使得干空气减少,不利于飑线维持,导致海上大风强度减弱。同时,纬向海陆热力差异变小使得海风的强度也逐渐减小,导致风场辐合效果变差,这可能是飑线系统入海减弱和其引发的海上大风风力变弱的原因之一,数值试验成功模拟了减小纬向热力差异会引发飑线对流系统的减弱。

Based on data from ground-based observations,0.25°×0.25°reanalysis data of ERA5,SA weather radar data in Changzhou and Yancheng,3DVAR-based radar-retrieved wind data and the WRF simulation,a large scale squall line gale process occurred in Jiangsu Province on July 26,2022 is analyzed.The results show that the squall line gale process is characterized by divergent air motion in the upper outflow area and shear convergent air motion in the lower vortex area.The upper dry-cold and the lower warm-wet condition along with the continuous moisture transport of the low-level southwest jet provide a good dynamical background for triggering and maintaining the convection.The instability energy,vertical wind shear,vertical ascending and water vapor conditions are optimal when the squall line is inland,while after the squall line moves into the ocean,the environmental condition is getting worse.The change of the environmental condition corresponds well with the development of the squall line.After the squall line enters the ocean,the inflow at the back of the squall line bottom layer weakens,leading to the reduction of dry air and the weakening of the squall line,and thus the strength of the gale wind.Meanwhile,as a possible cause of the weakening of the squall line and sea gale during its motion in the ocean,the reduction of the zonal land-sea thermal difference reduces the intensity of the sea breeze,which leads to weaker convergent wind motion.The numerical experiment successfully simulates the process of the zonal thermal difference reduction leading to the weakening of the squall line convection system.