登陆热带气旋降水增幅的合成诊断分析

Composite analysis of the rainfall reinforcement associated with landfalling tropical cyclones

利用NCEP/NCAR再分析资料,采用动态合成分析方法,对登陆后降水增幅类和非增幅类热带气旋的大尺度环流特征做了合成分析和动力诊断。结果表明:增幅类热带气旋处于强经向型环流之中,中高纬度为阻塞形势,高层有急流入口区南侧的强辐散,并与西风槽相互叠加;低层有急流和水汽通道的长时间联结;热带气旋东侧还有次级环流相伴。非增幅类热带气旋环流背景相对平直,高空辐散弱,无西风槽叠加;低空急流减弱迅速,且水汽通道较早出现断裂;无次级环流出现。增幅类热带气旋高层存在显著非地转运动,高层南风急流入口区的强次地转运动和降水增幅紧密相关。

Tropical cyclones （TCs） often bring about heavy rainfalls when they make landfall. Generally rainfalls gradually di- minish after their landfall. However, some landfalling TCs may produce even stronger rains than those during their landfalling. Such precipitation reinvigorating phenomena are known as rainfall reinforcement associated with landfalling tropical cyclones. Taking use of the NCEP/NCAR reanalysis data and a dynamic composite technique, the characteristics of atmospheric large scale circulation of rainfall reinforcement associated with landfalling tropical cyclones are investigated. The results show that the rainfall reinforcement with the TCs is mainly attributed to the strong divergence to the south side of the high level jet en- trance, their interaction with the westerly trought, and the low level jet and vapor flux maintenance as well as a secondary cir- culation to the east of the TCs. While for the TCs without rainfall reinforcement, there is the weak high level divergence, no westerly trough interaction aloft, the low level jet and vapor flux weaken quickly after their landfall and no secondary circula tion. There is prominent ageostrophic motion in the high levels for the TCs with rainfall reinforcement, in which strong sub ageostrophic motion in the souther jet entrance has a close relation to rainfall reinforcement.