Numerical experiments with planetary scale mountain barrier waves in a simple model

Abstract

A two-level, σ-coordinate, β-plane, general circulation model (10,000 km meridional and 30,000 km zonal dimensions) is used to study the effect of planetary scale mountain barriers on vacillation of energy and heat transfer. The results of numerical experiments using models with flat topography (and land-sea heating contrasts) are compared with those using model representations of the Rockies and Himalayas. The mountain barriers were seen to have a crucial effect on the time variation of total eddy kinetic energy, K’, meridional temperature gradients, VT, and in creating the stationary components of poleward transport of heat and westerly momentum. Preferred regions of high meridional temperature gradients and cyclonic systems formed north-east of the Rockies but north-west of the Himalayas. When K’ was partitioned into the values appropriate to the western and eastern halves of the β-plane channel, the time variations of K’ associated with each half were frequently out of phase; increasing K’(t) in one half and decreasing K’(t) in the other half was related to eastward moving peaks of baroclinic activity (created downstream of a barrier). A similar process was found in an analysis of atmospheric data for 1961–63, the orientation of the polar vortex being closely related to the west-east oscillation of K’; the model results suggest that the mountain barrier system has a large influence. Time variations in regional weather characteristics are likely to be closely related to this process; it is clearly an important factor to be represented in climatic change modelling.