A linear stochastic model of a GCM's midlatitude storm tracks

A linear stochastic model is used to simulate the midlatitude storm tracks produced by an atmospheric GCM. A series of six perpetual insolation/SST GC M experiments are first performed for each month. These experiments capture the "midwinter suppression" of the Pacific storm track in a particularly c lean way. The stochastic model is constructed by linearizing the GCM about its January climatology and finding damping and stirring parameters that be st reproduce that model's eddy statistics. The model is tested by examining its ability to simulate other GCM integrations when the basic slate is cha nged to the mean how of those models, while keeping the stirring and dampin g unchanged. The stochastic model shows an impressive ability to simulate a variety of e ddy statistics. It captures the midwinter suppression of the Pacific storm track qualitatively and is also capable of simulating storm track responses to El Nino. The model results are sensitive to the manner in which the mod el is stirred. Best results for eddy variances and fluxes are obtained by s tirring the temperature and vorticity at low levels. However, a better simu lation of the spatial structure of the dominant wave train as defined by co variance maps is obtained by stirring the temperature equation only, and at all levels.