Flow over the Rocky and Andes Mountains: Application of an Analytical Model

Abstract

The effects of vertical shear on a steady eastward flow of a compressible, stably stratified fluid over a shallow topography in the beta plane are examined using a theory developed earlier by one of the authors (Janowitz, 1977). Shear increases the wavelength and decreases the particle deflections associated with the orographically generated Iee Rossby wave. These changes are greater than can be accounted for by replacing the sheared flow with an unsheared flow of equivalent mean or root-mean-square velocity. In addition, the vertical variation of the downstream wave is determined to he negligible for all cases considered. By superposing Green's function solutions, a realistic simulation of the Rocky Mountains and the Andes Mountains is achieved. Comparison with actual data verifies that orographic effects are the primary factor causing the deflection of the winter westerlies over the United States, and that the high upstream vertical shear is responsible for the smaller amplititude of the wave associated with the Andes.