Direct observations of nitric oxide produced by energetic el

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TitleDirect observations of nitric oxide produced by energetic electron precipitation into the Antarctic middle atmosphereAbstractWe report the first ground-based passive microwave observations made from Troll station, Antarctica, which show enhanced mesospheric nitric oxide (NO) volume mixing ratio reaching levels of 1.2 ppmv, or 2-3 orders of magnitude above background, at 70-80 km during small, relatively isolated geomagnetic storms in 2008. The mesospheric NO peaked 2 days after enhanced NO at higher altitudes (110-150 km) measured by the SABER satellite, and 2 days after peaks in the >30 keV and >300 keV electron flux measured by POES, although the 300 keV electron flux remained high. High time resolution data shows that mesospheric NO was enhanced at night and decayed during the day and built up to high levels over a period of 3-4 days. The altitude profile of mesospheric NO suggests direct production by âˆ¼300 keV electron precipitation. Simulations using the Sodankyl Ion and Neutral Chemistry model show that the delay between thermospheric and mesospheric NO enhancements was primarily a result of the weaker production rate at lower altitudes by ~300 keV electrons competing against strong day-time losses. Copyright 2011 by the American Geophysical Union.AcknowledgementsAS was supported by the European Commission project FP7-PEOPLE-IEF-2008/237461. We thank Atle Markussen, Paul Breen, and Joachim Urban for their help. The Norwegian Institute for Air Research (NILU) and The Research Council of Norway are acknowledged for providing meteorological data. This work was supported in part by the UK Natural Environment Research Council. The authors thank the anonymous referees for their valuable comments.

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1st AuthorNewnham, D.AuthorNewnham, D.Espy, P.Clilverd, M.Rodger, C.Seppälä, A.Maxfield, D.Hartogh, P.Holmén, K.Horne, R.Year2011JournalGeophysical Research LettersVolume38Number20DOI10.1029/2011GL048666URLhttps://www.scopus.com/inward/recor.....29f520b9969f279a479f3fb57KeywordsComputer simulationGeomagnetismMagnetosphereNitric oxide, Altitude profilesAntarcticaDirect productionElectron fluxElectron precipitationEnergetic electron precipitationGeomagnetic stormGround basedHigh-time resolutionMiddle atmosphereNeutral chemistryOrders of magnitudePassive microwavesProduction ratesVolume mixing ratios, Electrons, altitudeatmospheric chemistrybackground levelelectrongeomagnetic stormground-based measurementmesospheremicrowave imagerymixing rationitric oxideprecipitation (chemistry)satellite imagerysatellite missionthermosphere, Antarctica, rank1

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TypeArticleCitationNewnham, D., Espy, P., Clilverd, M., Rodger, C., Seppälä, A., Maxfield, D., Hartogh, P., Holmén, K. and Horne, R. (2011) Direct observations of nitric oxide produced by energetic electron precipitation into the Antarctic middle atmosphere. Geophysical Research Letters, 38(20) doi:10.1029/2011GL048666