Air Mass Origin in the Arctic and its Response to Future Warming

Friday, 19 December 2014: 10:35 AM
Clara Orbe, NASA Goddard Space Flight Center, Greenbelt, MD, United States, Paul A. Newman, NASA GSFC, Code 610, Greenbelt, MD, United States, Darryn W Waugh, Johns Hopkins Univ, Baltimore, MD, United States, Mark B Holzer, University of New South Wales, Sydney, Australia, Luke Oman, NASA/GSFC, Greenbelt, MD, United States, Lorenzo M Polvani, Columbia University, New York, NY, United States and Feng Li, Goddard Earth Science Technology and Research, Greenbelt, MD, United States
Long-range transport from Northern Hemisphere (NH) midlatitudes plays a key role in setting the distributions of trace species and aerosols in the Arctic. While comprehensive models project a strengthening and poleward shift in the midlatitude tropospheric jets in response to future warming, relatively little attention has been paid to assessing the large-scale transport response in the Arctic. A natural way to quantify transport and its future changes is in terms of rigorously defined air masses that partition air according to where it last contacted the planetary boundary layer (PBL). Here we present climatologies of Arctic air mass origin for NH winter and summer, computed from two integrations of the Goddard Earth Observing System chemistry-climate model (GEOSCCM) subject to present-day and future climate forcings. The modeled transport response to A1B greenhouse-gas induced warming reveals that in the future ~10% more air in the Arctic will originate over NH midlatitudes, with a slighter weaker albeit significant increase in winter compared to summer. Our results indicate that transport changes alone may lead to “cleaner” Arctic winters, as air will be 5-10% more likely to have last contacted the PBL over the East Pacific and the Atlantic Oceans and less likely to have originated over Europe and North America. Conversely, in future summers the air mass fractions originating over Asia and North America increase by ~10%, indicating that Arctic pollutant levels may be enhanced owing solely to changes in transport. In particular, our results suggest that more stringent emissions caps may be needed to combat enhanced transport into the Arctic from Asia, where increases in black carbon emissions have already posed concerns. Future changes in air mass fractions are interpreted in terms of large-scale circulation responses that are consistent with CMIP5 multi-model mean projections – namely, upward and poleward shifted meridional transient eddies in future winters and an overall weakening in large scale summertime convective transport throughout the NH midlatitude lower and middle troposphere.