北半球两大地形下游冬季环流的动力分析——Ⅱ.行星波的垂直传播

THE ANALYSIS OF DYNAMIC EFFECTS ON WINTER CIRCULATION OF THE TWO MAIN MOUNTAINS IN THE NORTHERN HEMISPHERE Ⅱ. Vertical Propagation of Planetary Waves

线性、定常、多层半球谱模式模拟结果表明,在东亚纬向气流下,青藏高原能在平流层激发出强大的1波扰动,脊槽分别位于太平洋和大西洋上空。在北美纬向气流下,落基山在平流层激发的1波很弱。观测资料计算指出,对流层行星1波很难通过北美对流层顶上传,但却能自由穿过东亚高纬度地区的对流层顶向平流层传播。北美地形所激发的波动在上传过程中均折向低纬传播。青藏高原所激发的行星1波和2波在上传过程中有分支:折向低纬的一支主要局限在对流层中;折向高纬的一支进入平流层。模拟和分析证明,这些差异是北半球两大地形不同的动力作用的结果。

A linear, hemispheric and stationary spectral model with multilayers in the vertical is employed to simulate the vertical propagation of waves triggered by mountains. Results show that, in cooperation with the East Asian zonal mean flow, Tibetan plateau can excite a strong wave number 1 perturbation in the stratosphere with its ridge and trough respectively located over Pacific and Atlantic Ocean; whereas it is very weak the stratospheric wave number 1 perturbation caused by the mechanical forcing of the Rocky Mountains in cooperation with the North American zonal mean flow. The calculations from observational data of the vertical profile of the critical wave number for vertically propagating waves imply that the tropospheric wavenumber 1 perturbation can hardly penetrate the North American tropopause upwards, whereas it can freely propagate through the East Asian tropopause into the stratosphere.Two dimensional EP cross-sections obtained from both observation data and simulation results also demonstrate that waves excited by the Rocky Mountains are reflected towards low latitudes in the troposphere during their upward propagation; whereas, in addition to the above mentioned equatorward leaning branch, the wavenumber 1 and 2 planetary waves excited by Tibetan Plateau possess another branch which is reflected to high latitudes during upward propagation and penetrates the tropopause into the stratosphere. It is therefore concluded that the difference in the two half hemispheres of the horizontal as well as vertical propagations of waves with wavenumber 1 and 2 is a result of the different dynamical forcing induced by the two main mountains in the Northern Hemisphere.