Spectral and Spatial Energetics of the GISS Model Atmosphere

Abstract

A calculation of the spectral and spatial energetics of the Goddard Institute for Space Studies (GISS) 9-level model of the global atmosphere is given. Results are presented from a model simulation of January 1973 and compared with previous model studies and an observational analysis for the Northern Hemisphere. The spectral analysis permits detailed study of those physical processes of scale larger than the grid spacing and allows indirect conclusions concerning unresolved subgrid-scale processes. For larger-than-grid-scale processes we conclude that: 1) the GISS model with a relatively coarse resolution of 4° latitude by 5° longitude produces significant nonlinear energy transfers; 2) baroclini conversion is large near planetary wavenumber 6, but both the GISS model and another orographic model show a less peaked structure than non-orographic models and observations; and 3) Saltzman?s previously published compilation of observed spectral energetics is based on analyses that, when normalized, are probably too large by about 25%. A linear fit to the kinetic energy spectrum yields a power law of ?2.6 in the wavenumber region 8 to 15. For subgrid-scale processes, the turbulence theory result of very small energy flux cascade is obtained. For the spatial energetics we find good agreement with recently published climatological data.