The Brewer-Dobson Circulation and its Impact on Stratosphere-troposphere Ozone Exchange during the Last Glacial Maximum

Abstract:

Stratosphere-troposphere exchange (STE) of ozone impacts surface ozone concentration, the tropospheric oxidation capacity, and the methane lifetime. Using the Whole Atmosphere Community Climate Model 6, changes in the STE of ozone in the Last Glacial Maximum (LGM) as compared with preindustrial (PI) climate are investigated. Relative to the PI, the net stratosphere-to-troposphere (STT) ozone flux in the LGM decreased in both hemispheres and in all seasons, which is consistent with a predicted increase in a future, warmer climate. The decrease is caused by a reduction in the net STT air mass fluxes due to both weakening of the Brewer-Dobson circulations and the widening of its upwelling branch during the LGM, along with a smaller ozone concentration in the lower stratosphere over the extratropics. It is found that the widening of the upwelling branch of the Brewer-Dobson circulation in the LGM makes the largest contribution to the net STT ozone flux change. The impact of STE ozone flux on the tropospheric ozone budget will also be studied.