Observations of a stratospheric depletion and annual mean interhemispheric gradient in the atmospheric Ar/N2 ratio from the HIPPO Global campaign

Jonathan D Bent1, Ralph F Keeling2, Britton B Stephens3, Steven C Wofsy4, Bruce C Daube5, Eric A Kort6, Jasna V. Pittman4, Rodrigo Jimenez-Pizarro7 and Gregory Santoni8, (1)Scripps Inst of Oceanography, La Jolla, CA, United States, (2)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (3)NSF National Center for Atmospheric Research, Earth Observing Laboratory, Boulder, United States, (4)Harvard University, Harvard John A. Paulson School of Engineering and Applied Sciences, Cambridge, United States, (5)Harvard University, John A. Paulson School of Engineering and Applied Sciences, Cambridge, United States, (6)University of Michigan Ann Arbor, Climate and Space Sciences and Engineering, Ann Arbor, MI, United States, (7)National University of Colombia, Chemical and Environmental Engineering, Air Quality Research Group, Bogotá, Colombia, (8)Harvard University, Cambridge, MA, United States
Abstract:
The atmospheric Ar/N2 ratio varies on a seasonal basis due to temperature-dependent solubility changes in the surface ocean. Low signal:noise ratios, limited vertical coverage, and sampler-sampler offsets have historically hampered characterization of vertical and inter-hemispheric gradients. We present data from the HIPPO Global campaign (2009-11) showing that Ar/N2 and interannually-detrended N2O correlate well in the lower stratosphere, suggesting that, as stratospheric air ages and loses N2O to photolysis and photo-oxidation, it also gradually loses argon to gravity as the heavier atom preferentially “rains out” of the air parcel. The HIPPO Ar/N2 data from the lower troposphere also resolve seasonal cycles in each hemisphere, as well as a gradient in the annual mean between hemispheres, with higher values in the southern hemisphere. The HIPPO cycles and inter-hemispheric gradient are in good agreement with data from surface stations.
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