涡旋发展和移动的动力和热力问题Ⅰ:PV-Q观点

Dynamical and thermal problems in vortex development and movement.PartⅠ:A PV-Q view

基于从三维埃尔特尔位涡(PV_e)方程推导出的垂直涡度的拉格朗日变化方程,从位涡和非绝热加热(PV-Q)的观点研究涡旋的发展和移动,阐明了涡旋中非均匀的非绝热加热在垂直和水平方向的非对称分布对涡旋发展和移动的影响。应用得到的理论结果分析了2008年7月下旬一次青藏高原低涡的发展和移动过程,该低涡形成于青藏高原中西部,东移滑山青藏高原然后继续东移,给四川盆地和长江中下游带来强降水。低涡的垂直涡度发展可分解成由非绝热加热、位涡水平分量(PV_2)和静力稳定度(θ_z)变化引起的3个部分。结果表明,在大多数情形下,非绝热加热对垂直涡度发展起着主导作用;其次是位涡水平分量(PV_2)变化的作用;当稳定大气变得更稳定时θ_z变化起负作用,当大气趋向中性层结时θ_z变化则起正作用。2008年7月22日06—12时(世界时),当青藏高原低涡沿着四川盆地东北边的斜坡爬升时,低涡加强主要是由位于涡旋东边的强降水凝结潜热加热引起的。非绝热加热的垂直梯度在非绝热加热的最大中心的下(上)层产生正(负)PV_c制造,正的PV_e制造不仅加强低层涡旋的发展,而且,增强涡旋的垂直范围。非绝热加热的水平梯度对位涡变化的影响取决于加热中心处的水平风的垂直切变,其在该水平风的垂直切变的右(左)边产生了正(负)的PV_e制造。水平风的垂直切变的右边的正PV_e制造不仅加强了该处的垂直涡度,而且,影响着低涡的移动方向。这些诊断结果证实了PV-Q观点的理论结果。

Based on the Lagrangian change equation of vertical vorticity deduced from the equation of three-dimensional Ertel potential vorticity（PVe）,the development and movement of vortex are investigated from the view of potential vorticity and dia-batic heating（PV-Q）.It is demonstrated that the asymmetric distribution in the vortex of the non-uniform diahatic heating in both vertical and horizontal can lead to the vortex＇s development and movement. The theoretical results are used to analyze the development and movement of a Tibetan Plateau（TP） vortex（TPV）,which appeared over the TP,then slid down and moved eastward in late July 2008,resulting in heavy rainfall in Sichuan Province and along the middle and lower reaches of the Yangtze River. The relative contributions to the vertical vorticity development of the TPV are decomposed into three parts：the diahatic heating,the change in horizontal component of PVe（defined as PV2）,and the change in static stability θz. The results show that in most cases,diahatic heating plays a leading role,followed by the change in PV2,while the change of θz usually has a negative impact in a stable atmosphere when the atmosphere hecomes more stahle,and has a positive contribution when the atmosphere approaches neutral stratification. The intensification of the TPV from 06：00 to 12：00 UTC 22 July 2008 is mainly due to the diahatic heating associated with the precipitation on the eastern side of the TPV when it uplifted on the up-slope of the northeastern edge of the Sichuan basin. The vertical gradient of diahatic heating makes positive（negative） PVe generation below（ahove） the maximum of diahatic heating;the positive PVe generation not only intensifies the low-level vortex but also enhances the vertical extent of the vortex as it uplifts. The change in PVe due to the horizontal gradient of diahatic heating depends on the vertical shear of horizontal wind that passes through the center of diahatic heating. The horizontal gradient of diabatic heating makes positive（negative） PVe generation on the right（left） side of the vertical shear of horizontal wind. The positive PVe generation on the right side of the vertical shear of horizontal wind not only intensifies the local vertical vorticity but also affects direction of movement of the TPV. These diagnostic results are in good agreement with the theoretic results devel-oped from the PV-Q view.