GCM and Observational Diagnoses of the Seasonal and Interannual Variations of the Pacific Storm Track during the Cool Season

Abstract

Abstract Previous work has found that the Pacific storm track intensity during the cool season is negatively correlated with the upper-tropospheric jet strength. In the seasonal march, such a variation manifests itself as the midwinter suppression of the storm track intensity, while in interannual variations the storm track intensity during midwinter is found to be weaker during years in which the Pacific jet is particularly strong. In this paper, GCM simulations and observational data have been analyzed to shed light on the physical mechanisms responsible for such variations. By examining the eddy energy budget and eddy structure, two different mechanisms have been found to contribute to the reduction in storm track activity associated with increases in jet intensity and baroclinicity in midwinter. For the seasonal variations, it was found that the major difference between fall and midwinter lies in the changing role of diabatic heating. During fall and spring, diabatic heating acts to generate eddy pote...