Title: What controls the Brewer-Dobson Circulation?

Abstract
The Brewer-Dobson Circulation describes the slow overturning circulation of the stratosphere, which transports mass up into the tropics and then poleward until it returns to the troposphere. In concert with chemical processes, it sets the distribution of stratospheric ozone and water vapor, which have significant impacts on surface climate. An idealized atmospheric model allows us to explore the impact of tropospheric and stratospheric processes on the Brewer-Dobson Circulation, both in terms of the residual mean overturning of mass and the transport of trace species such as ozone.

The residual mean circulation is understood through the lens of the “downward control principal” (Haynes et al. 1991), where the circulation, at least in the steady state, can be explained as a response to mechanical wave driving, effected primarily by planetary-scale Rossby waves and small-scale gravity waves. The use of interactive models, however, allows us to explore reverse “control” by the mean flow and diabatic processes on the wave driving. Interactive models also reveal strong interactions between the Rossby and gravity waves driving, the latter which must be parameterized in most atmospheric models. These interactions may in part explain a vexing concern in the field in recent years, where it has appeared that models agree on the overall amplitude and increasing trend of the Brewer Dobson Circulation, but provide little consensus on which waves (i.e. resolved Rossby waves or parameterized gravity waves) are doing the work.