A Linear Primitive Equation Model of African Wave Disturbances

Abstract

A 10-level, linearized primitive equation model with boundary-layer friction, latent heating and cumulus momentum mixing is used to explore the instability properties of the environment of African wave disturbances. It is found that a realistic mean jet profile, constructed from a one-week average of the zonal wind at 5°E, produces a most unstable mode with propagation and structural characteristics close to the observed. The inclusion of parameterizations of diabatic heating and convective momentum transport results in a substantial increase in the mid-tropospheric vertical motions as well as the wind and divergence perturbations in the upper and lower troposphere. This suggests an important role for convection in extending and coupling the influence of the disturbances away from the jet level, where barotropic instability appears to dominate in both the model and observations.