The Brewer-Dobson Circulation describes the overturning circulation of the stratosphere, which transports mass up into the tropics and then poleward until it returns down to the troposphere in the extratropics. In concert with chemical processes, it sets the distribution of stratospheric ozone and water vapor, which have significant impacts on surface climate. Climate models almost uniformly project an increase in the Brewer-Dobson Circulation in response to anthropogenic forcing, but differ when it comes to explaining how this change is effected. When the changes are decomposed using the downward control principle, models disagree considerably whether resolved Rossby or parameterized gravity waves are most important. Given this uncertainty, there has been justifiable concern about the model projections.

Using a hierarchy of atmospheric models, we show that that the conventional downward control decomposition is flawed in that it fails to account for interactions between parameterized wave forcing and the resolved circulation. We argue that the response of the Brewer Dobson circulation in models is fairly generic, and misuse of downward control has obscured the mechanism(s). None-the-less, straightforward metrics are needed to justify the computation expenses required for sophisticated gravity wave parameterizations. Thus we propose a new framework for interpreting the role of gravity waves in the Brewer-Dobson Circulation.

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*email: gerber@cims.nyu.edu
*Preference: Invited