The Brewer-Dobson circulation during the last glacial maximum

We examine vertical mass fluxes, age of stratospheric air, and the transformed Eulerian mean stream function and find that the modeled annual-mean Brewer-Dobson circulation during the LGM is almost everywhere slower than that in the modern climate (with or without anthropogenic ozone depleting substances).

Compared to the modern climate, the annual-mean tropical upwelling in the LGM is 11.3-16.9%, 11.2-15.8%, and 4.4-10.2% weaker, respectively, at 100, 70, and 30 hPa. Simulated decreases in annual-mean mass fluxes at 70 and 100 hPa are caused by a weaker parameterized orographic gravity wave drag and resolved wave drag, respectively.