Covariation of finite-amplitude Rossby wave pseudo-momentum density and zonal-mean zonal flow in the mid-latitude troposphere

Co-variation of the Rossby wave pseudomomentum density and the zonal-mean zonal momentum is studied for the Earth's mid-latitude troposphere. From the theoretical perspective, the tendency of the pseudo-momentum density of conservative waves is expected to mirror the tendency of the zonal-mean zonal flow. In reanalysis data, a strong anticorrelation is indeed found between their barotropic components on the time scale of 10 ~ 20 days. As a mechanism for the time-scale selection for the pseudomomentum density variation, we propose two fundamental kinds of vacillations to be relevant among flow regimes in differentially heated rotating fluids: (1) amplitude vacillation arising from nonlinear wave-wave interaction. (2) structural vacillation of baroclinic eddies arising from the interference of intermittent quasi-modes. We show the existence of these two vacillations and their distinct roles on shaping the eddy fluxes in reanalysis data, one-layer barotropic quasigeostrophic model and two-layer baroclinic quasigeostrophic model.