doi:  10.3878/j.issn.1006-9895.1611.16179
一次高原低涡与高原切变线演变过程与机理分析

Evolution and Mechanism Analysis of a Plateau Vortex and Plateau Shear Line
摘要点击 306  全文点击 310  投稿时间:2016-05-30  
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基金:  公益性行业(气象)科研专项GYHY201206042,国家自然科学基金41675057、91337215
中文关键词:  高原低涡  高原切变线  演变过程  机理分析
英文关键词:  Plateau vortex  Plateau shear line  Evolution process  Mechanism analysis
     
作者中文名作者英文名单位
李山山LI Shanshan成都信息工程大学大气科学学院, 成都 610225
李国平LI Guoping成都信息工程大学大气科学学院, 成都 610225
引用:李山山,李国平.2017.一次高原低涡与高原切变线演变过程与机理分析[J].大气科学,41(4):713-726,doi:10.3878/j.issn.1006-9895.1611.16179.
Citation:LI Shanshan,LI Guoping.2017.Evolution and Mechanism Analysis of a Plateau Vortex and Plateau Shear Line[J].Chinese Journal of Atmospheric Sciences (in Chinese),41(4):713-726,doi:10.3878/j.issn.1006-9895.1611.16179.
中文摘要:
      对一次东移高原低涡减弱、高原切变线生成并在有利的环流背景下东南移,进而引发川渝强降水的高原切变线生成机制以及演变过程进行了初步分析。首先引入描写热带气旋的Okubo-Weiss(OW)参数(VOW)来定量表达低涡、切变气流中旋转和变形的相对大小,确定高原切变线的潜在生成区域和发展状况。得出在高原切变线生成阶段,500 hPa等压面上VOW值由正转负,VOW负值带可以很好地指示高原切变线的潜在生成区域。VOW负值强度与高原切变线强度有很好的相关性。高原切变线上以VOW负值中心为主,但也会存在正值中心,说明在切变线上也会有气旋性涡度。此个例高原切变线以伸缩变形为主,高原切变线沿变形场的拉伸轴分布。然后通过涡度方程和总变形方程进一步分析了高原低涡减弱、高原切变线生成的动力机制。高原低涡的减弱、消失主要受散度项的影响,时间演变分析表明系统由强气旋性涡度的高原低涡演变为强辐合性的高原切变线。总变形方程中的扭转项对高原切变线的生成贡献最大,其次为水平气压梯度项,散度项最小;当高原切变线上以拉伸变形为主时,不利于其上高原低涡的发展,切变线可能是影响低涡发展的背景流场。
Abstract:
      The genesis mechanism and evolution of a plateau shear line are analyzed. This process involved the weakening of an eastward moving plateau vortex and the formation of a plateau shear line, which moved southeastward later under the favorable background circulation and caused heavy rain in Sichuan and Chongqing. The Okubo-Weiss (OW) parameter (VOW) is introduced first. The OW parameter is frequently used in tropical cyclone study to measure the relative amount of rotation and deformation in vortex and shear flow, and has a good potential for identifying the location of plateau shear line formation and development. The results show that, at 500 hPa the VOW value changed from positive to negative and VOW negative belt had a good potential for identifying the location of plateau shear line formation at the genesis stage of plateau shear line. The intensity of negative VOW value and plateau shear line had a good correlation. The plateau shear line was dominated by negative VOW centers, but positive center also existed, indicating that cyclonic vorticity also occurred in the shear line. This plateau shear line was dominated by stretching deformation and located along the stretching axis orientation in this case. The dynamic mechanism of plateau vortex weakening and plateau shear line formation is then further analyzed by using the vorticity equation and the total deformation equation. The results show that the weakening and disappearance of the plateau vortex were mainly affected by the divergence term. The temporal evolution analysis indicates that this system transformed from plateau vortex with strong cyclonic vorticity to plateau shear line with strong convergence. The twisting term in the total deformation equation made the largest contribution to the formation of the plateau shear line, followed by the horizontal pressure gradient term, and the divergence term made the minimum contribution. When the plateau shear line was dominated by stretching deformation, it restrained the development of plateau vortex. The shear line could be the background flow field that affected the vortex development.
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