Lagrangian-mean circulation and wave-mean flow interactions of eady’s baroclinic instability waves

In order to comprehend the Lagrangian-mean circulations and wave-mean flow interactions in the mid-latitude troposphere, the Eady baroclinic mode is examined using the transformed Eulerian-mean method in pressure-isentrope hybrid vertical coordinates (pt-TEM) proposed by Iwasaki (1989). The intersection of isentropes with an upper or lower boundary is shown to be essential for the formation of Lagrangian-mean circulation and wave-mean flow interactions of the Eady mode. The regions of isentropes intersecting the lower or upper boundary are called boundary isentrope layers. Based on the pt-TEM, the linear Eady mode forms a direct circulation with poleward and equatorward flows in upper and lower boundary isentrope layers, respectively. The Eliassen Palm (EP) flux is converted from the Coriolis acceleration of mean flows within the lower boundary layer and absorbed in the mean flows within the upper boundary layer. Taking into consideration the Q effect (latitudinal variation of the Coriolis parameter), the poleward mean-meridional flows and EP flux convergence zones are expected to exist in the whole troposphere except for the lower boundary layer. These results account well for the pt-TEM analysis of a GCM (NCAR CCM1) run.