An assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized Eliassen-Palm flux diagnostics.

For time mean flows, a localized E-P flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking. The focus here is on the mean momentum equations. Eddy transports and the associated induced meridional circulations, and other internal adjustments necessary to maintain the thermal wind balance, are gathered together allowing the residual circulation and the effects of the eddies to be determined. For the blocking episode, defined as 20 July-31 August 1979, transient eddies were steered around the location of the blocking anticyclones. However, the transient eddies in each branch differed in character, both from each other and from those in the main Southern Hemisphere storm track that extends across the southern Indian Ocean near 50^oS. Where the main westerly jet splits as part of the blocking flow configuration, both the barotropic and baroclinic local E-P flux components are acting to decelerate the westerlies. The main differences between the storm track and blocking regions arise in the barotropic component of the local E-P flux. It appears that the configuration of the split westerly jet acts to systematically deform the transient eddies in such a way that they feed back to help maintain the split structure.-from Author