台风“暹芭”(2203)残涡陆上维持并引发大范围降水过程的成因

Analysis of the Prolonged Maintenance and the Accompanying Widespread Precipitation of Typhoon Chaba(2203)Remnant after Landfall

利用中国气象局上海台风研究所最佳路径数据、 FNL 0.25°×0.25°再分析资料和NOAA 0.5°×0.5°全球日降水数据分析了登陆台风“暹芭”残涡长时间维持并且产生大范围降水的成因。结果表明,第一阶段(2022年7月3-4日)“暹芭”残涡维持的主要水汽来源是偏南风低空急流,第二阶段(2022年7月5-6日)主要是偏南风低空急流和边界层东风急流共同作用,这使得大气可降水量达到罕见的75 mm。双低空急流的耦合形成的垂直风切变和水汽辐合为暴雨的发生和维持提供了良好的动力条件。冷空气开始入侵“暹芭”残涡后,在其西侧近地面形成冷池,这使得“暹芭”残涡逐渐变性为温带气旋,斜压动能发生显著增长。利用位势散度诊断发现,由于“暹芭”残涡不断北上接近副热带高空西风急流增大了高低层垂直风切变,高空冷涡携带的冷空气侵入“暹芭”残涡使其斜压性增大,边界层东风急流使得850hPa以下层结不稳定度显著增大,这为暴雨的发生和维持提供了不稳定能量条件。

We conducted a comprehensive analysis on the causes of prolonged maintenance and widespread precipitation after the landfall of Typhoon Chaba,using the best track data from the Shanghai Typhoon Research Institute of the China Meteorological Administration,the FNL 0.25°×0.25°reanalysis data and the NOAA 0.5°×0.5°global daily precipitation data.The results show that the main moisture source of the remnant of Chaba in the first phase(3-4 July)was the southerly low-level jet,and the second phase(5-6 July)it was mainly the combination of the southerly low-level jet and the boundary layer easterly jet,which resulted in a rare entire atmosphere precipitable water of 75 mm.The vertical wind shear and water vapor convergence formed by the coupling of the double low-level jets provided favorable dynamic conditions for the occurrence and maintenance of heavy rainfall.A cold pool was formed near the surface to the west of the vortex with the intrusion of cold air,which caused the Chaba remnant to gradually degenerate into an extratropical cyclone with a significant increase in baroclinic kinetic energy.In the view of potential divergence diagnosis,we found that as the Chaba remnant kept moving northward to approach the subtropical westerly jet,the vertical wind shear at high and low levels increased.The cold air carried by the high-altitude cold vortex turns the Chaba residual vortex to baroclinic system.The easterly wind jet in the boundary layer increased the instability of the layer below 850 hPa,which provided unstable energy conditions for the occurrence and maintenance of heavy rainfall.