影响辽东半岛的热带气旋降水分析

THE ANALYSIS OF TROPICAL CYCLONE PRECIPITATION AFFECTING THE LIAODONG PENINSULA

选取移动路径和转向趋势极为相似的两个热带气旋——9711(Winnie)和9406(Tim)为例,对其路径、降水量、移动速度进行对比分析,结果表明,Winnie路径偏东,转向后移动速度增幅大,在辽东半岛地区的降水量大;Tim路径偏西,转向后移动速度增幅小,强降水偏西。并针对其在辽东半岛造成的降水量的差异,采用NCEP全球分析资料,诊断分析其环境流场和结构特征,分析表明,除了地形和海洋的影响,副热带高压位置、高低空急流和锋区与辽东半岛地区的强降水有直接关系。Winnie影响期间,有利、稳定的副高位置使来自东南和西南的暖湿空气输送到辽东半岛上空,并阻挡着低压系统东移出海,使降水持续增加;高低空急流在高空急流入口区上升支环流圈内耦合,对流层上层强辐散场的抽吸作用及高位涡的向下输送,有利于气旋的发展加强;东、西两侧冷空气作用使其变性加强,形成温带气旋,引起强降水。Tim影响期间,副高中心偏西、偏北,高低空急流在高空急流出口区下沉支环流圈内相互作用,其上空辐散强度较弱,只是Winnie的八分之一,不利于气旋的发展加强;Tim位于高空槽后,获得负涡度平流,在东部弱冷空气作用下,引起台风弱变性,并没有形成气旋,在东北地区被西风槽合并后消失,辽东半岛只出现10mm以下的降水。

Winnie（9711） and Tim（9406） are two tropical cyclones whose track and trend of direction turning are similar, Their tracks, precipitation and moving velocity are used in comparison and analysis. The results show that the track of Winnie is to the east, its increment of moving velocity is bigger after turning, and the precipitation over Liaodong Peninsula is larger; The track of Tim is to the west, its enhancement of moving velocity is smaller, and the center of severe precipitation is in North China. For their precipitation difference over Liaodong Peninsula, NCEP reanalysis 2.5 - degree grid data was performed to diagnose and analyze the large-scale conditions and structural features of Winnie and Tim. The analyses show that the location of Subtropical High （SH）, upper-level and lower-level jets and frontal zones are closely related to the heavy rainfall over Liaodong Peninsula, besides impacts of the topography and the sea. During the life cycle of Winnie, the favorable and stable SH caused the transportation of moist water vapor over Liaodong Peninsula, barred the low pressure system from moving easterly, and sustained the duration of precipitation. The coupling of upper-level and lower-level jets in the updraft field, the pumping of intense field of divergence in the upper troposphere and the transportation southerly of higher potential vorticity were favorable for cyclone＇s development and intensification. The proper intensity of cold air from the west and east made Winnie extratropical transition（ET）, formed extratropical cyclone（EC） and produced severe precipitation. During the life cycle of Tim, the center of SH is to the west and north, the coupling of upper-level and lower-level jets in the downdraft field and the intensity of divergence in the upper troposphere were weaker, whose value is merely one-eighths of that of Winnie, were not favorable for the development and intensification of the cyclone. Tim located in the rear of a high-level trough and obtained negative vorticity advection, with the effect of the feeble cold air from the east, only formed weak cold front in North China, and precipitation on Liaodong Peninsula was less than 10 mm.