The dynamical influence of large‐scale heat sources and sinks on the quasi‐stationary mean motions of the atmosphere

Abstract

AbstractThe classical convective theory for the influence of large‐scale zonally asymmetric heating and cooling on the quasi‐stationary mean motions is re‐examined and shown to be inconsistent with observation. Scale considerations indicate that the classical mechanism cannot be applied to heating on a scale larger than that responsible for sea‐breezes. In analogy with the theory of orographically produced stationary disturbances, heat sources and sinks of planetary dimensions produce quasi‐static and quasi‐geostrophic perturbations. A thermally active model is constructed in which all motions except those of large scale are filtered out a priori. The small perturbations produced by an idealized large‐scale distribution of heat sources and sinks acting on a horizontally uniform baroclinic zonal current confined between rigid horizontal planes are then studied. The influence of surface friction is taken into account. Calculations are also performed on a model with no friction and on the assumption that entropy is advected horizontally. The results generally show good agreement with those for the more general model. When the stratosphere is taken into account, the disturbances in the upper troposphere are reduced in magnitude. The conditions for resonance in the absence of friction are determined. The passage through the resonant state is shown to modify significantly the character of the motions. The observed normals are discussed at some length in light of the theoretical computations. It is found that the magnitude and spatial distribution of the model disturbances display substantial correspondence with observation when allowance is made for orographic effects. Finally a method is suggested for quantitatively deducing the three‐dimensional field of non‐adiabatic heating and cooling from the observed normal maps by dynamical considerations.