A diagnostic and modeling study of the monthly mean wintertime anomalies appearing in a 100-year GCM experiment

In this experiment, the seasonally varying, climatological sea surface temperature was prescribed throughout the world oceans. The principal modes of variability in the model experiment were identified by applying a rotated empirical orthogonal function (EOF) analysis to the Northern Hemisphere monthly averaged 515-mb geopotential height for the winter season (November through March). The individual leading spatial modes are similar to the observed north-south dipoles over the North Atlantic and North Pacific, as well as wavelike patterns in the Pacific/North American and Northern Asian sectors. Both the tendency calculations and the stationary wave model results indicate the crucial role of vorticity transports by transient eddies. The linear model solutions also illustrate the importance of incorporating the climatological stationary waves in the basic state. These findings hence suggest that the monthly mean anomalies in this GCM experiment are intimately linked to barotropic interactions between transient fluctuations of different time scales, and between the monthly mean anomalies and the climatological stationary waves. -from Authors