On the role of viscosity in ideal Hadley circulation models

A comparison is made between inviscid and viscous solutions of an axially symmetric nonlinear Shallow Water Model (SWM) of the Hadley circulation on the spherical rotating Earth that includes vertical advection of momentum and Rayleigh friction. The results of the 1D SWM are compared with those of 2D (latitude-height) nonlinear axially symmetric models. It is shown that solutions obtained from inviscid models do not predict correctly the main features of the circulation outside the Tropics. Specifically, the latitudes of the subtropical jets depend strongly on viscosity and on the pole-to-equator temperature difference. The differences from inviscid theory are attributed to the increased rate of energy dissipation in the viscous atmosphere. At the Tropics, however, the inviscid solutions of the SWM predict well the latitude and strength of the easterly jet and the weak temperature gradient.