摘要
为了进一步研究高原涡、西南涡对西南地区暴雨的影响,本文用中国气象局自动站与CMORPH降水数据融合的逐时降水资料、国家卫星气象中心的逐时FY-2E卫星的云顶亮温(TBB)资料、欧洲气象资料中心(ERA-interim)的再分析资料,通过天气学诊断分析方法以及拉格朗日轨迹模式HYSPLITv4.9,对发生在四川盆地的有高原涡东移影响西南涡发展引发暴雨的两次过程进行对比分析,发现:(1)两次暴雨过程的降水强度和分布有明显区别,并且TBB活动特征显示在过程一中有MCC(Mesoscale Convective Complex)的产生和发展,过程二则没有。(2)对于过程一,500 hPa上,高原涡逐渐减弱为高原槽并伸展到四川盆地上空,850 hPa上,在鞍型场附近有MCC的产生和发展,200 hPa上,高原涡在南亚高压北部偏西风急流下方的强辐散区内,位于南亚高压东南侧急流区下方稳定少动,偏东风急流北部有辐散中心,有利于西南涡的加强。对于过程二,500 hPa高原涡东移在四川盆地上空与西南涡耦合,形成一个稳定且深厚的系统,这也是过程二的暴雨强度比过程一强的最主要原因。200 hPa上,四川盆地始终位于南亚高压东侧的西北气流中,"抽吸作用"明显。(3)在过程一中,位涡逐渐东传且位涡增加的地方对应强降水区与MCC发展区,反映了暴雨和位涡的发展基本一致。在过程二中,中层位涡高值区从高原上东移并下传至盆地上空,两涡耦合使得上下层打通,位涡值比耦合之前单独的两涡强度更强。MCC产生的必要条件是中层大气要有强正涡度、强辐合和强上升运动,在未产生MCC前,过程一与过程二在盆地上空的动力条件甚至是相反的;从热力条件看,过程一中有明显的干冷空气入侵,增强不稳定条件,有利于MCC的产生并引发强降水;另一方面,本文也应证了二阶位涡的水平分布与暴雨落区有较好的对应关系。(4)通过拉格朗日方法的水汽轨迹追踪模式和聚类分析方法分析可得两次暴雨过程的水汽输送源地和通道也有明显区别,过程一主要有两条水汽通道,通道一来自阿拉伯海和孟加拉湾洋面的底层,通道二来自四川南部750 m以下高度;而过程二的主要水汽输送通道有三条,通道一来自西方地中海、黑海和里海上空1500~2500 m高度附近,通道二来自阿拉伯海和印度洋的底层,通道三的水汽从孟加拉湾低层绕过云贵高原直接输送到四川盆地。
This paper comparatively analyzes two rainstorm processes in Sichuan Province affected by the Tibetan Plateau vortex and Southwest vortex based on the ECMWF ERA-Interim reanalysis dataset, the CMORPH data(which is derived from station observations and satellite retrievals of precipitation), the hourly cloud top TBB(black body temperature) data of FY-2 E and results of the Lagrangian trajectory model HYSPLIT v4.9. Major results are as follows.(1) The intensity and distribution of precipitation are significantly different in the two heavy rain processes, and the characteristics of mesoscale convective cloud system showed that MCC(mesoscale convective complex) was triggered in process one, but not found in process two.(2) During process one, the Tibetan Plateau vortex gradually weakened into a plateau trough and spread over the Sichuan Basin at 500 hPa. At 850 h Pa, the MCC was triggered near the wind convergence zone. At 200 hPa, the southwest vortex was located to the southeast of South Asia high in an area of strong divergence below the westerly jet, which contributes to the intensification of the Southwest vortex. For the second process, however, the Tibetan Plateau vortex was gradually coupled with the southwest vortex, resulting in a stable, deep system. At 200 hPa, a distinct pumping effect can be found over the Sichuan Basin since it was always located below the northwesterly flow of the South Asian high.(3) During process one, PV(potential vortex) gradually spread to the east and the area where PV increased corresponds to strong precipitation area and MCC outburst area, which reflects the basic consistency between the development of rainstorm and PV. Besides, in the second process, the high PV value zone in the mid-level moved eastward from the plateau and the high PV was transmitted down to the basin. The coupling of the two vortices makes the PV value lager than that of each single vortex. Also, this article has confirmed a good relationship between the distribution of abnormal second-order PV and heavy rain.(4) The main difference between the two processes is the generation of MCC, which requires an atmospheric condition with strong positive vorticity, strong convergence and strong ascending movement. And the dynamic conditions in the two rainstorm processes may be opposite before the formation of MCC. From the thermodynamic perspective, there is an invasion of dry and cold air in process one, and the large gradient of potential pseudo-equivalent temperature benefits the generation of mesoscale convective system and causes heavy rain.(5) According to the Lagrangian trajectory model and clustering analysis method, there are two water vapor channels in process one: the first channel is from the bottom layer of the Arabian Sea and the Bay of Bengal, while the second channel is from the south of Sichuan at 750 m above the ground. In the second process, there are three main vapor transport channels. Channel 1 is from the western Mediterranean, Black Sea and Liberia in the layer between 1500 m to 2500 m. Channel 2 is from the bottom of the Arabian Sea and the Indian Ocean. Water vapor of channel 3 is directly transported to the Sichuan Basin from the bottom of the Bay of Bengal, passing by the Yunnan-Guizhou Plateau.
作者
周玉淑
颜玲
吴天贻
谢泽明
ZHOU Yushu;YAN Ling;WU Tianyi;XIE Zeming(Key Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS),Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029;Plateau Atmosphere and Environment Key Laboratory of Sichuan Province,Chengdu 610225;Key Laboratory of Meteorological Disaster,Ministry of Education/Joint International Research Laboratory of Climate and Environment Change/Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,Nanjing University of Information Science and Technology,Nanjing 210044;Jinhua Meteorological Service,Jinhua,Zhejiang Province 321000;Cold and Arid Regions Enviromental and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou 730000)
出处
《大气科学》
CSCD
北大核心
2019年第4期813-830,共18页
Chinese Journal of Atmospheric Sciences
基金
国家重点研发计划项目2018YFC1505705
中国科学院战略性先导科技专项(A类)XDA17010105
国家自然科学基金项目41661144024
高原大气与环境四川省重点实验室开放课题PAEKL-2017-K2~~
关键词
高原涡
西南涡
四川盆地暴雨
对比分析
中尺度对流复合体(MCC)
水汽源
Plateau vortex
Southwest vortex
Rainstorms in Sichuan Basin
Comparative analysis
Mesoscale Convective Complex(MCC)
Moisture source
