Rossby wave modes and eddy momentum flux

The meridional component of eddy momentum flux plays an important role in the maintenance and variability of jets in the Earth's midlatitude atmosphere. However, theorizing the eddy momentum flux (i.e. the zonal average of u'v') from first principles still remains a challenging problem. In this study, we examine two plausible mechanisms for the variability in eddy momentum flux: (1) linear interference of discrete normal modes of Rossby waves (Lindzen et al 1981) and (2) mixing of modes through nonlinearity (wave-wave interaction). We will explore the extent to which these processes explain the alternating signs of eddy momentum flux observed in numerical simulations of geostrophic turbulence and in the real atmosphere.