Browsing by Author "OMAN, LUKE D."
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Item Air-mass Origin in the Arctic. Part II: Response to Increases in Greenhouse Gases(AMS, 2015-12-01) ORBE, CLARA; EWMAN, PAUL A.; WAUGH, DARRYN W.; HOLZER, MARK; OMAN, LUKE D.; LI, FENG; POLVANI, LORENZO M.Future changes in transport from Northern Hemisphere (NH) midlatitudes into the Arctic are examined using rigorously defined air-mass fractions that partition air in the Arctic according to where it last had contact with the planetary boundary layer (PBL). Boreal winter (December–February) and summer (June–August) air-mass fraction climatologies are calculated for the modeled climate of the Goddard Earth Observing System Chemistry–Climate Model (GEOSCCM) forced with the end-of-twenty-first century greenhouse gases and ozone-depleting substances. The modeled projections indicate that the fraction of air in the Arctic that last contacted the PBL over NH midlatitudes (or air of ‘‘midlatitude origin’’) will increase by about 10% in both winter and summer. The projected increases during winter are largest in the upper and middle Arctic troposphere, where they reflect an upward and poleward shift in the transient eddy meridional wind, a robust dynamical response among comprehensive climate models. The boreal winter response is dominated by (;5%–10%) increases in the air-mass fractions originating over the eastern Pacific and the Atlantic, while the response in boreal summer mainly reflects (;5%) increases in air of Asian and North American origin. The results herein suggest that future changes in transport from midlatitudes may impact the composition—and, hence, radiative budget—in the Arctic, independent of changes in emissions.Item Airmass Origin in the Arctic. Part I: Seasonality(AMS, 2015-06-15) ORBE, CLARA; NEWMAN, PAUL A.; WAUGH, DARRYN W.; HOLZER, MARK; OMAN, LUKE D.; LI, FENG; POLVANI, LORENZO M.The first climatology of airmass origin in the Arctic is presented in terms of rigorously defined airmass fractions that partition air according to where it last contacted the planetary boundary layer (PBL). Results from a present-day climate integration of the Goddard Earth Observing System Chemistry–Climate Model (GEOSCCM) reveal that the majority of air in the Arctic below 700 mb last contacted the PBL poleward of 608N. By comparison, 62% (±0.8%) of the air above 700 mb originates over Northern Hemisphere midlatitudes (i.e., ‘‘midlatitude air’’). Seasonal variations in the airmass fractions above 700 mb reveal that during boreal winter air from midlatitudes originates primarily over the oceans, with 26% (±1.9%) last contacting the PBL over the eastern Pacific, 21% (±0.87%) over the Atlantic, and 16% (±1.2%) over the western Pacific. During summer, by comparison, midlatitude air originates primarily over land, overwhelmingly so over Asia [41% (±1.0%)] and, to a lesser extent, over North America [24% (±1.5%)]. Seasonal variations in the airmass fractions are interpreted in terms of changes in the large-scale ventilation of the midlatitude boundary layer and the midlatitude tropospheric jet.