Observations of mesospheric nitric oxide and ozone variability above Halley station, Antarctica

Thursday, 18 December 2014
David Newnham1, Mark A. Clilverd1, Richard B. Horne1, Craig J Rodger2, Annika Seppälä1,3, Pekka T Verronen3, Monika E. Andersson3, Daniel Robert Marsh4, Tamas Kovacs5 and John M C Plane6, (1)British Antarctic Survey, Cambridge, United Kingdom, (2)University of Otago, Dunedin, New Zealand, (3)Finnish Meteorological Institute, Helsinki, Finland, (4)National Center for Atmospheric Research, Boulder, CO, United States, (5)University of Leeds, School of Chemistry, Leeds, United Kingdom, (6)University of Leeds, School of Chemistry, Leeds, LS2, United Kingdom
Production of odd nitrogen species (NOx = NO + NO2) in the polar middle atmosphere by energetic electrons and protons, and its effect in chemically perturbing stratospheric ozone distributions, is well established. NOx is likely to be produced frequently and persistently in the mesosphere and lower thermosphere by energetic electrons. However the electron processes are less well understood than those involving solar protons. Uncertainties include which electron energy ranges have the greatest impact on NOx concentrations either by direct production or indirectly via transport. We have investigated the effect of energetic electron precipitation on nitric oxide (NO) and ozone abundances in the Antarctic middle atmosphere close to solar maximum. During 2013 low to moderate geomagnetic activity occurred, with minimum Dst index of - 132 nT, driven primarily by sub-storms associated with coronal mass ejections. Near-continuous ground-based observations were made by a semi-autonomous 230-250 GHz passive microwave radiometer at Halley station (75°37’S, 26°14’W, L = 4.6, geomagnetic latitude -62°), Antarctica. This location is directly under the region of radiation belt electron precipitation, equator-ward of the auroral zone, and deep within the polar vortex during the Austral winter. We observe enhanced mesospheric NO volume mixing ratio reaching 1.6 ppmv at 65-80 km on 2013 day 158 (7 June). Co-located 30 MHz riometer absorption increased when Kp index ≥ 4, indicating increased ionisation due to geomagnetic activity at 75-90 km directly above Halley. NOx production by energetic electron precipitation is discussed in the context of Polar-orbiting Operational Environmental Satellites electron count rates for the second generation Space Environment Monitor - Medium Energy Proton and Electron Detector. In order to evaluate the in situ production of NOx versus transport, we have incorporated in the Whole Atmosphere Community Climate Model (WACCM) a reduced version of the Sodankylä Ion-Neutral Chemistry Model. The reduction procedure using the normalised Jacobian method, and initial WACCM results, will be briefly presented.