Contributions of Individual Atmospheric Diabatic Heating Processes to the Generation of Available Potential Energy

The generation of zonal and eddy available potential energy (G(z) and G(e)) as formulated by Lorenz are computed on a global-, daily-, and synoptic-scale basis to consider the contribution of each diabatic heating component separately and in combination. Using global, mostly satellite-derived datasets for the diabatic heating components and the temperature enables us to obtain G(z) and, especially, G(e) from observations for the first time and at higher temporal and spatial resolution than previously possible. The role of clouds in maintaining G is investigated. The global annual mean G(z) is 1.52 W m(-2). Values reach a minimum of 0.63 W m(-2) in the Northern Hemisphere during spring and a maximum of 2.27 W m(-2) in the Southern Hemisphere during winter. The largest contributors to G(z) are latent heating in the tropical upper troposphere, associated with the intertropical convergence zone in the summer hemisphere and surface sensible heat fluxes in the winter pole. Diabatic cooling by radiative fluxes (mostly longwave) generally destroys G(z). The value of G(e) is negative and is about an order of magnitude smaller than G(z), with a global annual mean of -0.29 W m(-2). However, the small value of G(e) results from the cancellation of the contributions from the individual diabatic heating terms, which are actually roughly similar in magnitude to their G(z) contributions. The results presented herein suggest that the large-scale dynamics of the atmosphere organize the spatial and temporal distribution of clouds and precipitation in such a way as to increase the energy available to drive the circulation, a kind of positive feedback.