Generation of a large-scale barotropic circulation in rotating convection

We recently reported on the existence of a slow-growing large scale barotropic mode in DNS of rotating Rayleigh-Benard convection using the non-hydrostatic balanced geostrophic equations (NHBGE) (Julien et al 2012). Such large scale modes had been previously observed as an inverse cascade in stable layer quasi-geostophic dynamics or via instability mechanisms of thermal Rossby waves occuring in presence of sloping endwalls (i.e quasi-geostrophic beta-convection). In this talk we report on the early time history of this large scale mode and discuss the generating physical mechanism as a ``symmetry-breaking'' forcing function of the barotropic vorticity equation. Impacts of the large scale barotropic mode on the smaller scale baroclinic components of the flow are detailed with a specific emphasis on the changing nature of the heat transport as the barotropic mode evolves.