Maintenance of equatorial superrotation in the atmospheres of Venus and Titan

This paper extends Leovyʹs theory on Venus’ equatorial superrotation by analytically examining additional terms in the mean zonal momentum equation that stably balances the momentum source of pumping by thermal tides. The general analytical solution is applied to the atmospheres of both Venus and Saturnʹs moon Titan. The main results are: (i) Venus’ equatorial superrotation of 118 m s−1 results primarily from a balance between the momentum source of pumping by thermal tides and the momentum sink of meridional advection of wind shear by horizontal branches of the Hadley circulation; (ii) no solution is found for Titanʹs stratospheric equatorial superrotation centered at the 1-hPa level; (iii) however, if the main solar radiation absorption layer in Titanʹs stratosphere is lifted from 1 hPa (∼185 km) to 0.1 hPa (∼288 km), an equatorial superrotation of ∼110 m s−1 centered at 0.1-hPa could be maintained. Titanʹs equatorial superrotation results mainly from a balance between the momentum source of tidal pumping and the momentum sink of frictional drag.