西南季风水汽输送对热带气旋Bilis降水影响分析和数值试验

以一个登陆强度并不强,但在内陆长久维持并引发大暴雨造成巨灾的热带气旋Bilis(0604)为研究对象,首先利用实测资料分析了Bilis造成中国南方大暴雨过程的环流形势和物理量场特征,指出西南季风和Bilis残留低压相互作用为本次大暴雨的发生提供了有利的水汽和动力条件;然后利用中尺度模式MM5模拟分析了西南季风强度和水汽输送变化对本次大暴雨过程的影响。结果表明,降水受西南季风自身强度影响不大,但对水汽输送多寡十分敏感,水汽减少将导致降水强度明显下降,外界水汽输送有助于Bilis雨带中强对流活动,使雨量加强。

Analysis and Numerical Experiments of the Impact of Moisture Transportation by Southwest Monsoon on Precipitation of the Tropical Cyclone Bills

The landfalling tropical cyclone Bilis (0604) was not strong but stayed over land long and led to serious disaster by heavy rain. Based on the real data, this paper first analyzes the circulation features and the physical conditions of rainstorm in South China.The results show that the combined action of southwest monsoon and Bilis' remaining cyclone circulation provides moisture and dynamic conditions for the heavy rain. By means of MM5 model, this paper then studies the changes of precipitation after southwest monsoon and moisture transportation become weakened. The results show that the rainfall is not sensitive to strength of southwest monsoon itself but to the amount of moisture transportation. If moisture transportation is weakened by 50 percents, the rainfall will decrease significantly. Plentiful moisture supply contributes to Bilis' convective activities.