Eliassen–Palm Flux Diagnosis Based on Isentropic Representation

Abstract

Abstract This paper demonstrates an isentropic representation of the Eliassen–Palm flux (EP flux) as a tool for diagnosis of the atmospheric zonal mean states. This is a full extension of the transformed Eulerian mean (TEM) to express lower boundary conditions and finite-amplitude effects of waves. The isentropic EP flux is diagnosed from the NCEP–NCAR reanalysis for 12 yr and compared with the TEM. In the free atmosphere, the two diagnoses show similarities in the mass streamfunction and in the EP flux except that the EP flux divergence is somewhat different near the polar vortex. The similarities reflect the equivalency between the two schemes under the quasigeostrophic assumptions. However, the lower boundary values are very different between the two schemes. In the TEM, the vertical EP flux inaccurately suggests a much larger momentum flux coming out from the surface. In the isentropic diagnosis, the lower boundary value of vertical EP flux, which expresses the momentum exchange with the earth's surfa...