A Note on the Effect of Horizontal Momentum Fluxes by Unresolved Synoptic-Scale Eddies in a Low-Resolution Spectral General Circulation Model

Eero Holopainen Department of Meteorology, University of Helsinki, 00100 Helsinki 10, Finland

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Bette L. Otto-Bliesner Department of Meteorology, University of Wisconsin, Madison 53706

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Abstract

Two long-term simulations of a low-resolution spectral general circulation model (Otto-Bliesner et al., 1982) have been made. The single difference between these two runs is that in one (CONTROL) the horizontal flux of momentum by unresolved synoptic eddies is represented by a second-degree, Fickian-type diffusion scheme (down-gradient), whereas in the other (DIFFEX), this flux is zero. The amount of eddy kinetic energy in DIFFEX is found to be significantly larger and more realistic than in CONTROL. Also, the spectral distributions of both eddy kinetic energy and eddy available potential energy in DIFFEX are more realistic than in CONTROL. However, the long-term mean circulations are not statistically different in the two runs.

Abstract

Two long-term simulations of a low-resolution spectral general circulation model (Otto-Bliesner et al., 1982) have been made. The single difference between these two runs is that in one (CONTROL) the horizontal flux of momentum by unresolved synoptic eddies is represented by a second-degree, Fickian-type diffusion scheme (down-gradient), whereas in the other (DIFFEX), this flux is zero. The amount of eddy kinetic energy in DIFFEX is found to be significantly larger and more realistic than in CONTROL. Also, the spectral distributions of both eddy kinetic energy and eddy available potential energy in DIFFEX are more realistic than in CONTROL. However, the long-term mean circulations are not statistically different in the two runs.

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