Wave-mean flow interaction in the general circulation: a composite analysis of the Northern Annular Mode in isobaric and isentropic coordinates

Abstract

The effect of the Northern Annular Mode (NAM) on the general circulation of the atmosphere is described in isobaric and isentropic coordinates. ERA-Interim Reanalysis data has been used to identify four exceptionally strong, persistent positive and negative NAM-events during boreal winter. An attempt is made to understand the dynamics of the NAM in terms of both the widely used quasi-geostrophic Transformed Eulerian Mean (TEM) theory in isobaric or pressure coordinates as well as the potential vorticity point of view in isentropic coordinates, using isentropic mass fluxes and vorticity fluxes as central concepts.