Séminaire
This talk will discuss the spinup of equatorial westerly jets by tropical eddies, relevant for the problem of planetary superrotation. Motivated by the well-established phenomenology of extratropical eddy-driven jets, most superrotation models have focussed on the latitudinal propagation of the eddies and hence on meridional eddy momentum fluxes. However, it will be argued in this talk that because tropical vorticity dynamics makes meridional momentum advection inefficient accelerating the mean flow in the tropics, equatorial superrotation will be driven by vertical momentum advection in many cases of interest. We first consider the limit of small absolute vorticity in the tropics, relevant for the equilibration of Kelvin-Rossby instability. In this limit, vorticity fluxes are small and meridional momentum advection weak. More generally, it will be argued that meridional advection can only decelerate the mean flow with weak vorticity forcing. This is shown to be the case in the Earth’s deep tropics with the exception of the Northern monsoon season.
bruno.deremble@ens.fr