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

Tuesday, 16 December 2014
Jonathan D Bent1, Ralph F Keeling2, Britton B Stephens3, Steven C Wofsy4, Bruce C Daube4, Eric A Kort5, Jasna V Pittman4, Rodrigo Jimenez-Pizarro6 and Gregory Santoni4, (1)Scripps Inst of Oceanography, La Jolla, CA, United States, (2)University of California San Diego, La Jolla, CA, United States, (3)National Center for Atmospheric Research, Boulder, CO, United States, (4)Harvard University, Cambridge, MA, United States, (5)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (6)National University of Colombia, Bogota, Colombia
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.