夏季青藏高原热力场和环流场的诊断分析——Ⅲ:环流场稳定维持的物理机制

The Influence of the Tibetan Plateau on the Summer Thermal and Circulation Fields over East AsiaⅢ. Physical Mechanisms of Maintaining the Stable Circulation Fields

本文使用经过青藏高原气象科学实验测站观测资料订正过的欧洲中心FGGE-Ⅲb资料,对1979年夏季青藏高原地区进行了涡度方程诊断分析,研究了它们的月际变化、逐日变化和日变化,与高原上积云对流活动的强弱变化进行了比较,讨论了夏季高原稳定的环流场维持的物理机制;同时还对同时期热带赤道地区强对流活动区域进行了涡度方程诊断分析,将其涡旋环流场的维持机制与夏季高原地区进行了比较. 通过分析,发现夏季青藏高原月平均涡度方程平衡关系主要是次网格尺度项和散度项的平衡,水平平流项的耗散作用在高空较强,但不如次网格尺度项强,涡度方程其余各项均很小.从月际变化、逐日变化和日变化的比较,发现当积云对流活动发生强弱变化时,ω、D和涡度方程中的散度项、次网格尺度项均伴随很强的相应变化,对应关系很好,说明涡度方程中的次网格尺度项R(余差项)的主要部分来源于积云对流系统的活动,反映了夏季高原上存在的强盛频繁的积云对流活动对高原平均环流场的形成和维持具有重要的作用. 使夏季青藏高原高低层环流场加强的物理机制足高低层气流强大的辐散辐合,耗散机制是积云对流系统对高低层涡度的上下搅拌垂直输送作用和网格尺度水平平流项的非线性耗散作用,其中前者起主要的作用. 从涡旋能量维持的角度看。

Based on the Revised ECMWF FGGE Level-IIIb data which has been corrected by the Tibetan Plateau Meteorology Experiments data , the vorticity balances , and their inter-monthly variability, day-to-day change and diurnal variation, in the Tibetan Plateau atmosphere during the summer of 1979 are analysed . The results are compared with the strength of cumulus convective activities . The physics mechanisms of maintaining the stable circulation fields are de -tailed , and compared with the status in the tropical strong convective activity areas .The budget is that, a large stretching term ηD nearly being compensated by the subgrid-scale process term in lower layers, and by the subgrid-scale process term and the horizontal vorticity advection term in upper levels . The other terms are very small . As soon as the strength of the cumulus convective activities vary, all the vertical velocity , the divergence and the stretching term as well as the subgrid-scale process term have large variations . Such good relationships show that the strong and frequent cumulus convective activities have great effects on the forming and maintaining the mean circulation fields on the plateau .The enhancing mechanism is the strong divergence and convergence processes . The dissipating mechanisms are the vorticity transporting effect of cumulus convective activities, which can mix vorticities in different levels, and the nonlinear grid-scale horizontal vorticity advections whose effects are smaller than former . The other dissipating mechanisms , such as transient eddy forcing , are very small .