Quasi-Linear Blocks Forced by Orography in a Hemispheric, Quasi-Geostrophic Barotropic Model

Abstract

Stationary linear perturbation responses to Northern Hemisphere orography are calculated in a quasi-geostrophic barotropic model in solid-body rotation. The stationary mountain torque induced by these perturbations is then used to construct graphical solutions to the steady-state wave, mean-flow interaction problem. It is shown that multiple solutions exist in the system and are near either the forcing equilibrium of the zonal forcing or near the resonance points in the system. Some of these near-resonance solutions have blocklike configurations with a confluence zone upstream from a large-amplitude structure consisting of a high at high latitudes and a low at low latitudes. These blocklike configurations are shown to be near stable solutions of the system. Time-dependent calculations show that the initial state and the zonal forcing equilibrium are important in determining the long-term time evolution of the system.