Vertical modes in a moist convecting atmosphere

A vertical empirical orthogonal function (EOF) decomposition is performed on a series of cloud resolving model simulations of large three dimensional domains on an equatorial beta plane. The model's diabatic fluxes of heat and moisture are accelerated while Earth's size is rescaled (the so called DARE approach) allowing the resolved convection to interact with a modeled large scale circulation of near global size. The moist static energy, h = Cp*T + g*z + Lv*q, is first decomposed into vertical EOFs resulting in two dominant modes. The first mode, H1, is characterized by in phase boundary layer and mid-troposphere perturbations (a moist boundary layer and moist mid-troposphere), while the second mode, H2, is characterized by out of phase perturbations in the boundary layer and mid-troposphere (a moist boundary layer and dry mid-troposphere). The horizontal wind is then split into its divergent and rotational components and similarly decomposed into EOFs.

For the divergent circulation, two dominant modes arise, a "top heavy" first baroclinic mode and the second baroclinic mode. By projecting these modes along with those from the moist static energy onto the moist static energy budget, it is seen that the first baroclinic mode and H1 are convectively coupled, as well as the second baroclinic mode and H2, with minimal coupling between the modes. For the rotational circulation, a single baroclinic mode projects strongly onto the budget. These results have implications for the understanding of both the steady circulation as well as for wave dynamics.