气流辐合对高原低涡切变的影响

利用欧洲中心ERA-interim再分析资料，通过计算Okubo-Weiss（OW）参数，对青藏高原上一次高原切变线诱发高原低涡生成的过程进行了诊断分析。结果表明:（1）OW负值带可以指示高原切变线的可能生成区；OW值趋于0时，切变线变得不稳定，强度逐渐减弱；OW正值区能够指示高原低涡的后续移动趋势以及发展情况，气流辐合区域与OW大正值区有很好的对应关系。（2）此次高原切变线气流活动以拉伸变形为主。切变线生成阶段，其附近气流作拉伸变形运动；切变线成熟阶段，气流拉伸变形运动达到最强；切变线减弱阶段，其气流拉伸变形运动减弱。（3）切变线的生成以及移动主要受总变形方程的局地变化项影响；低涡的生成位置以及后续移动路径与水平涡度方程的散度项有很好的对应关系。气流辐合在高原低涡形成的初期起主要作用，辐合强度的减弱会抑制高原低涡的东移及发展。 

Influence of Airflow Convergence on the Low Vortex Shear of Plateau

Using the ERA-interim reanalysis data of the European Centre and through the calculation of Okubo Weiss (OW) parameter, the process of the formation of plateau vortex induced by the last plateau shear line on the Qinghai Tibet Plateau is analyzed diagnostically. The results show that: (1) The negative belt of OW can indicate the possible generation area of plateau shear line. When the OW value approaches 0, the shear line becomes unstable and the strength decreases gradually. The positive area of OW can indicate the subsequent movement trend and development of the plateau vortex, and the convergence area of air flow has a good corresponding relationship with the positive area of OW. (2) The air flow activity of the plateau shear line is mainly tensile deformation. In the generation stage of shear line, the air flow near the shear line makes tensile deformation movement. In the mature stage of shear line, the air flow tensile deformation reaches the strongest point. In the weakening stage of shear line, the tensile deformation movement of air flow weakens. (3) The generation and movement of shear line are mainly affected by the local variation term of the total deformation equation. The generating position and subsequent movement path of the vortex have a good correspondence with the divergence term of the horizontal vorticity equation. The convergence of air flow plays a major role in the primary stage of plateau vortex, and the weakening of convergence intensity will inhibit the eastward movement and development of plateau vortex.