登陆热带气旋与夏季风相互作用对暴雨的影响

Interaction Between Landfalling Tropical Cyclone and Summer Monsoon with Influences on Torrential Rain

利用《热带气旋年鉴》资料、NCEP/NCAR再分析资料采用动态合成分析方法,研究了登陆热带气旋降水与夏季风急流之间的关系,同时对登陆热带气旋与夏季风急流发生相互作用的典型个例强热带风暴Bilis(0604)利用数值模拟方法研究了二者之间的相互作用对暴雨的影响。结果表明:登陆后造成大范围强降水的热带气旋往往与低层急流长时间相连,其水汽通量和潜热能显著大于弱降水热带气旋。数值试验结果表明:夏季风低空急流向热带气旋输送水汽对热带气旋结构维持有利,当水汽输送被截断后,热带气旋气旋性结构被破坏,强降水减弱、范围明显缩小;季风急流风速增强时可增加水汽通量输送,使得强降水范围增加、强度增强;在夏季风影响背景下,热带气旋在陆上的移动改变水汽和不稳定能量的分布,而热带气旋本身独特的动力结构使得强降水强度增加。

Based on Tropical Cyclone Yearbooks, NCEP/NCAR reanalysis data and dynamic composite analysis, the relationship between the torrential rain associated with landfalling tropical cyclones and summer mon- soon jets is studied. Several sets of numerical experiments are carried out to analyze influences on heavy rain of interaction between the landfalling tropical cyclone Bilis （2006） and the summer monsoon. Compos- ite analysis show that tropical cyclones resulting in a large range of torrential rain always link with a low- level jet for a long time even after landfall, which makes them obtain sufficient water vapor flux. While for the weak rainfall tropical cyclones, the linking might break before landfall, which cuts off the water vapor transport from the low level jet. Numerical experiments reveal that water vapor transport from the low- level jet of summer monsoon is favorable to the maintenance of the tropical cyclone structure of warm core. Cutoff of the water vapor transport will lead to the stretch of a dry tongue into the cyclonic circulation from the boundary, destruct the tropical cyclone structure, and make the mesoscale and mieroscale synoptic sys- tems weakened, which results in the obvious weakness o（ the rainfall intensity and the reduction of heavy rain coverage. Water vapor transport from the southern boundary is much more important than any other boundary. In the sensibility numerical experiment, the wave spectrum method is applied to alter the me- soscale and microscale winds to strengthen and weaken the monsoon jet speed. Results show that moderate change of wind speed in low level jet only change the distribution and coverage of heavy rain a little, but the grid number of extremely strong rainfall （more than 200 ram） varies notably. Under the background of summer monsoon, a tropical cyclone moving into the monsoon channel will strengthen wind speed of the low level jet, which strengths the transport of water vapor at low level. Furthermore, the movement of tropical cyclone over land changes the distribution of water vapor, instability energy and the relevant heavy rain, and the unique dynamic structure of tropical cyclone, and strong convergence at low level and strong divergence at upper level, could strengthen the rain intensity.