The Balance of Kinetic and Total Energy Simulated by the OSU Two-Level Atmospheric General Circulation Model for January and July

Abstract

The horizontal structure of the balances of kinetic energy and total energy simulated by the Oregon State University (OSU) two-level atmospheric general circulation model are studied for January and July on the basis of a three-year simulation with prescribed seasonally-varying solar radiation and sea-surface temperature. The various mechanisms responsible for the local energy changes are identified, and the fulfillment of the energy balance requirement is examined. In the upper level of the model atmosphere, the horizontal convergence of the kinetic energy flux and the production of kinetic energy through ageostrophic motion tend to balance each other. Thus an upper-level southerly (northerly) ageostrophic flow is induced in the entrance (exit) region of the middle latitude jet stream. In the lower level of the model, the corresponding energy flux convergence and ageostrophic flow are more complicated for different jet stream regions. In January, the vertical integral of the total energy shows large external heating over the North Pacific and North Atlantic oceans, and cooling over most of the land area of the Northern Hemisphere. In July, an overall seasonal reversal is found. In general, horizontal energy flux convergence is such that energy gained from strong local heating is transported to areas of local heal sinks. Both seasons are also characterized by strong energy flux divergence in the tropics, which is associated with the poleward transport of heat (and momentum). On the global annual average the net frictional dissipation is about 2 W m?2, which is comparable to estimates of the numerical sink of energy within the model as a result of data sampling and inconsistency in the diagnostic schemes.