Misuse of Kuo–Eliassen Equation in Studies of the Climatological Mean Meridional Circulation

The Kuo–Eliassen equation provides the mean meridional circulation that must be present for the axisymmetric component of a flow forced by heat and momentum sources to remain balanced as it evolves. It does not tell us whether or not the flow is steady. Using this equation to explain how the mean meridional circulation is perturbed due to a change in thermal or momentum forcing, including the forcing due to large-scale eddies, requires a division of the forcing into prescribed and reactive parts and, most importantly, a physical theory for the latter. It should not be used without explicit discussion of the assumptions being made about the reactive component of the forcing and justification for the choice being made.