Equatorially Trapped Middle Atmosphere Response to Global-Scale Forcing

Equatorially trapped motions are well known in the middle atmosphere. Some examples are the quasi-biennial oscillation and the Hadley circulation. By using simple physical inequalities, we characterize the different manners in which the equatorial and extratropical middle atmospheres respond to forcing, both by wave momentum fluxes and by differential heating. Scaling is used to estimate the latitudinal range in which the atmospheric response to both types of forcing is equatorial. This is shown to be quite consistent with the results of detailed numerical calculations.