登陆台风降水的大尺度环流诊断分析

Diagnostic analysis of large-scale circulation features associated with strong and weak landfalling typhoon precipitation events

强度相似的登陆台风造成的强降水可能差异很大。为研究大尺度环流对登陆台风降水的影响,利用热带气旋年鉴和NCEP/NCAR再分析资料,运用动态合成分析方法,对比分析了登陆后48小时内降水特征迥异而强度、路径相似的两组登陆台风的大尺度环流特征。合成分析结果表明,西南气流的水汽输送对台风降水至关重要,造成大范围强降水的台风往往在登陆后仍与深厚西南急流相连并持续很长时间。高空强辐散场是登陆台风造成大范围强降水的一个基本动力特征。造成强降水的登陆台风其环境场的上升气流不仅强,其气旋性环流的伸展高度高且能长时间维持。登陆台风造成降水的范围和强度与登陆前台风下游大陆环境大气的稳定度有关。下游高温高湿的大气有利于能量尤其是潜热能的大量补充,对强降水增强和维持都十分有利。因此,大尺度环流对登陆台风降水有明显影响。其中,与台风相连的西南急流强度和深厚程度是最重要的因子,高低空辐散辐合强度、台风及环境风场结构以及台风下游大陆上空大气湿热状态等都是需要加以考虑的。

Based on the Tropical Cyclone （TC） Yearbook, the NCEP/NCAR reanalysis data and t he dynamic composite analysis, largescale circulation characteristics are anal yzed for two kinds of typhoons, the strongrainfall typhoon （SRT） and the weak rainfall typhoon （WRT）, which have tracks and TC intensity but distinct rainf all intensity in 48 h after the typhoon landfall. The results show that, transport of water vapor in the southwestern air stream is crucial to typhoon rainfall. A deep southwestern jet is usually associated with a SRT for a long time even a fter its landfall. Basically, SRTs are characterized by strong divergence at upper levels. They extend into the upper troposphere and the cyclonic circulation a nd strong up drafts are maintained steadily. The instability of atmosphere in th e downstream region of the typhoon before its landfall can also affect the rainf all area and intensity. Warm and moist atmosphere is favorable for the intensifi cation and maintenance of heavy rain due to the supplement of total energy espec ially the latent energy. Therefore, large-scale circulations have a significantimpact on typhoon rainfall. The largescale features such as the depth and int ensity of the southwestern air stream linking with the typhoon, the intensity of low-level convergence and upper-level divergence, the environmental wind stru cture of the typhoon circulation, and the thermodynamical and humidity condition of the environmental atmosphere, should all be taken into consideration in orde r to correctly forecast typhoon precipitation.