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

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 pertur-bation 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.