Science update: Unravelling impact factors for future changes in the Brewer Dobson Circulation

S. Oberländer and co-authors investigate the different processes affecting the Brewer Dobson Circulation in future using the EMAC chemistry-climate model in a new JGR article. Using several sensitivity simulations they isolate the effects of external forcings such as greenhouse gases, sea surface temperatures (SSTs) and ozone-depleting substances. They find that in boreal winter the tropical upward mass flux increases by about 1%/decade (2%/decade) in the upper (lower) stratosphere until the end of the 21st century. The mean stratospheric age of air decreases by up to 60 and 30 days/decade, respectively. Changes in transient planetary and synoptic waves account for the strengthening of the BDC in the lower stratosphere, whereas upper stratospheric changes are due to improved propagation properties for gravity waves in future climate. The radiative impact of increasing GHG concentrations is detected only in the upper stratosphere, whereas the effect of increasing SSTs dominates the lower stratospheric signal. Changes in tropical SSTs influence not only the shallow but also the deep branch of the BDC as confirmed from both changes in residual circulation and mixing. Declining ODSs were found to slightly counteract the BDC increase in the Southern Hemisphere. The full abstract can be found here.