摘要
利用NCEP格点再分析资料、观测资料和MM5模式的高分辨率输出资料，对2004年9月4～6日发生在四川盆地东部地区的大暴雨过程进行了诊断分析和数值模拟，重点分析引发这次大暴雨的西南低涡的结构和演变特征及其在暴雨发生发展过程中的作用。对低层850hPa、700hPa候平均水汽通量和各时刻整层水汽通量的分析表明，此次西南低涡暴雨的水汽主要来自于南海，水汽沿西太平洋副热带高压的西南侧经青藏高原东部流入四川盆地。在西南低涡的发展过程中，“桑达”台风向西北移动，阻断了西太平洋副热带高压的东退并切断副高，被切断的高压部分滞留在西南低涡东侧，导致低涡不能顺利东移。数值模拟研究发现，在西南低涡的发展过程中，中层400-500hPa附近一直伴有涡旋的存在，且此涡旋的发展演变过程与低层涡旋明显不同；中层涡旋的发展不像低层涡旋那样呈现单边持续地增长或衰减的特征，而是呈现明显的增长-衰减-再增长的演变特征，其最大值增长时段和低层涡旋也并不一致。分析表明这个中层涡旋实际上是中层大气里一个中尺度闭合低压造成的，这个闭合低压是由高空槽加深发展而来的。数值模拟输出结果还显示，发生在西南低涡东侧切变线里的对流垂直运动是由高空槽里的闭合低压激发出来的。
Using NCEP data of 1°× 1° with 6-hour interval, observation and MM5 model output data, the evolution of Southwest Vortex （SW） causing heavy rainfall in eastern Sichuan basin during 4 - 6 September 2004 is investigated. The diagnostic analyses indicate that the vapor of low level mainly came from the South China Sea, the vapor moisture reached Sichuan Basin by passing through the southwest of the western Pacific subtropical high （WPSH）. During the development of SW, the typhoon named Sangda moved toward China mainland and finally cut off WPSH. The destroyed part of W-PSH remained on mainland and prevented eastward movement of SW. The numerical simulations reproduce fully the evolution characteristics of SW from monotone increasing to monotone decreasing. The simulation also shows a vortex which had been existing in the middle level during the development of SW. Its center was located on the south of SW, and the evolution of the vortex was different from SW. The middle-level vortex evolution presented the characteristics from increasing to decreasing and again increasing, and the stage of the largest increasing was also different from SW. The analysis indicates that this middle-level vortex resulted from the middle-level mesoscale low, and the deepening Of middle-level trough caused the development of the mesoscale low. The simulation also indicates that the strong convection in the shear line located on the east part of SW was triggered by the middle-level mesoscale low.
出处
《大气科学》
CSCD
北大核心
2008年第1期141-154,共14页
Chinese Journal of Atmospheric Sciences
基金
国家重点基础研究发展规划项目2004CB418304
国家自然科学基金资助项目40745026
关键词
西南低涡
切变线
对流
暴雨
southwest vortex, shear line, convection, heavy rainfall
作者简介
于波，女，1979年出生，硕士。E-mail：yubo_0@126．com
