Linear Stationary Wave Simulations of the Time-Mean Climatological Flow

Abstract

A spectral, σ-coordinate model linearized about a zonal mean flow is used to investigate the maintenance of the December?February climatological stationary waves. The model is generally run with 15 levels in the vertical and a T31 truncation. The sum of the response to orography, diabatic heating and transient eddy flux convergences specified from data gives a generally good Northern Hemisphere simulation at 200 mb with some deterioration in the lower troposphere. The same is true for the Southern Hemisphere, but only when the forcing terms from recent years are used. The response is broken down into that associated with particular orographic features, tropical and midlatitude heating and transient vorticity and heat flux convergence. All of these are shown to be significant. In particular, orography accounts for approximately 30% of the total 200 mb planetary wave response. In midlatitudes the diabatic heating maxima in the two storm tracks are important. This heating is related to latent and sensible heating associated with transient disturbances. The explicit transient eddy terms in the vorticity and thermodynamic equations force a complicated upper-level flow pattern. The effects of truncation, dissipative parameterization, tropical heating profile and nonlinearity are discussed.