Stratospheric circulation diagnostics from age of air

The circulation of the stratosphere is important for the transport of trace gases that are important for climate, such as ozone and water vapor. However, the circulation is difficult to quantify from measurements. We present theory for calculating the stratospheric circulation from the idealized tracer age of air. By looking at the difference between the age of air that is downwelling and the age of air that is upwelling through an isentrope, we can calculate the diabatic circulation strength. This diabatic circulation strength on isentropes is then related to more traditional measures of the Brewer-Dobson Circulation, including different methods for calculating the residual circulation. In addition, we separate the two hemispheres and characterize the diabatic circulation strength in each hemisphere. Furthermore, the adiabatic mixing is shown to be related to the vertical gradient of the age of air, and this metric is explored in the Whole Atmosphere Community Climate Model. Thus we have derived quantitative integrated measures of both the diabatic circulation and the adiabatic mixing for each hemisphere.