The Brewer–Dobson Circulation during the Last Glacial Maximum

During the Last Glacial Maximum (LGM) the stratosphere in terms of both temperature and Brewer-Dobson circulation (BDC) could be very different from the present day, as a result of different radiative constituent concentrations, surface boundary conditions, sea surface temperatures. The BDC during the LGM is investigated using the Whole Atmosphere Community Climate Model (WACCM). We find that the BDC during the LGM is significantly slower than that in current climate regardless of seasons, altitudes, hemispheres and BDC branches, and with and without including the anthropogenic ozone depletion. It is shown that the annual mean upwelling mass fluxes in the tropics at 100 hPa, 70 hPa, and 30 hPa during the LGM are about 21%, 16%, and 12% smaller, respectively, than those in current climate, with small seasonal and hemispheric dependences. We test the sensitivity of the BDC to the SST distribution in the LGM, and to the representation of the Laurentide ice sheet roughness. We also investigate the effects of the BDC changes on atmospheric O₃.