Thursday 02 Feb 2017: Tropical vorticity dynamics and the role of vertical momentum advection in equatorial superrotation
Prof. Pablo Zurita-Gotor - Universidad Complutense, Madrid
Motivated by Hide's theorem, most models of equatorial superrotation in planetary atmospheres have focussed on the latitudinal propagation of tropical 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 monsoon season.