Integrated and Spectral Energetics Studies of the GLAS General Circulation Model

Abstract

Integrated and spectral energetics of the Goddard Laboratory for Atmospheric Sciences (GLAS) general circulation model are compared with observations and examined when subdivided beyond hemispheric integrals. In the monthly mean zonal averages, we find qualitative improvements over previous versions of the model in eddy kinetic energy and barotropic conversions although vertical shear above the subtropical jet remains weak. We trace this problem to the erroneous growth of kinetic energy above strong jets, show that this difficulty is common to all orographic general circulation models, and suggest that this problem has significant effects on upper-level long-wave predictability. In particular, we consider whether hemispherically integrated kinetic energy or low-wavenumber spectral coefficients retain any skill as one approaches the predictability limit. In the time-dependent comparisons, the model shows significant skill in predicting the hemispherically integrated eddy kinetic energy out to two weeks for one of two cases. The low-order spectral coefficients show less skill, particularly for wavenumber 3. We examine other diagnostic properties of the spectral decomposition, and observe that both the model and observations show evidence of single wavenumber dominance in eddy kinetic energy and a positive correlation between spectral kinetic and potential energy.