These quotes are from “The cause of the general circulation of the atmosphere” by Eady (1950?).
“If we neglect frictional forces large-scale meridional circulations are impossible” (p. 159)
“Meridional circulations could be maintained if the increasing angular momentum difference between poleward and equatorward currents were contiually being destoryed by fricitonal forces, the only plausible mechanism being the transfer of angular momentum by turbulence, i.e., eddy-viscosity.” (p. 159)
“Of course a complete theory of the whole life-history of disturbances must take friction into account directly but the rudimentary theory of the initial stages is sufficient to prove that turbulence must develop.” (p. 161)
For the case of the atmosphere, Eady presents a model where the change in potential vorticity occurs in the surface viscous layer, while most of the high altitude meridional eddy transport is inviscid.