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Feldstein, S. B., and S. Lee, 1995: The intraseasonal evolution of angular momentum in aquaplanet and realistic GCMs. J. Atmos. Sci., 52, 625-649.


ABSTRACT

This paper describes the evolution of global angular momentum (GAM) on intraseasonal timescales in data from two general circulation model (GCM) runs: an aquaplanet GCM and a fully "realistic" GCM that includes continents, topography, and observed climatological sea surface temperatures.

For both GCMS, the angular momentum budget is quite well balanced. Composites of various quantities are calculated at different lags relative to the maximum GAM and GAM tendency. In both GCMS, this composite analysis shows that the GAM tendency is largest as a precipitation anomaly propagates eastward along the equator. Associated with this precipitation anomaly is a tropical circulation that shows some of the characteristics of the Gill model, particularly in the aquaplanet GCM, and a Rossby wave train that propagates from the tropics into midlatitudes. It is the anomalous midiatitude surface wind field associated with this Rossby wave train that is primarily responsible for the anomalous friction torques in both models. In the realistic GCM, this Rossby wave train has the appropriate structure to induce a large mountain torque, particularly at the Rocky Mountains. Also, it is found that the friction and mountain torques contribute about equally to the intraseasonal evolution of GAM, with the anomalous friction torque leading the anomalous mountain torque by three days.

After the precipitation anomaly weakens, the Rossby wave train completely propagates out of the tropics and leaves behind a pattern resembling that of a Kelvin wave. Consistent with this wave propagation, in both GCMs, eddies transport the angular momentum gained at the surface in midlatitudes toward the equator. Lastly, the effects of zonal inhomogencities on the wave dynamics associated with GAM evolution are discussed.