Observations of nitric oxide in the Antarctic middle atmosph

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TitleObservations of nitric oxide in the Antarctic middle atmosphere during recurrent geomagnetic stormsAbstractWe report ground-based measurements of the polar middle atmosphere made using a 230-250 GHz passive microwave radiometer deployed at Troll station (72°01′S 02°32′E, L shell of L=4.8), Antarctica. Our observations show enhanced mesospheric nitric oxide (NO) volume mixing ratio (VMR) during a series of small recurrent geomagnetic storms in the 2008 austral winter, reaching 1.2 ppmv on day 200 (18 July). The Lomb normalized periodogram of the NO VMR time series averaged over 65-80 km for days 130 to 220 of 2008 (9 May to 7 August) shows a peak exceeding the 95% confidence limit at 25.8 days, close to the synodic rotation period for low-latitude solar coronal holes. The highest correlations between the radiometer NO VMR data and trapped and quasi-trapped electron count rates for L = 3.5-5.5 from the Polar Orbiting Environment Satellites 90^circ telescope are for the >30 keV (90e1) channel (rmax = 0.56, lag time of 5.1 days) and >100 keV (90e2) channel (rmax = 0.57, lag time of 4.4 days). Maximum correlation between NO VMR and the >700 keV (90P6) channel data is lower but lag times are close to zero. Superposed epoch analyses for the eight most significant geomagnetic storm periods and three Carrington rotations (2070-2072) within the 90 day observation period indicate that significant NO abundance observed at 65-80 km in the Antarctic mesosphere may be produced directly by >200 keV electron precipitation or originate from a source at higher altitudes, e.g., production by >30 keV electrons followed by downward transport. Key Points Polar mesospheric NO increases during small recurrent geomagnetic storms Enhanced NO observed at 65-80 km is due to >30 keV electron precipitation Horizontal and vertical transport redistributes NO in the polar winter â"'2013. American Geophysical Union. All Rights Reserved.AcknowledgementsAS was supported by the EuropeanCommission project FP7-PEOPLE-IEF-2008/237461 and Finnish Academyprojects 258165 and 265005. The work of CS has been funded by the Norwegian Polar Institute Antarctic Program under the grant "Observations of carbon monoxide and ozone in the Antarctic and Arctic: Implications for the inter-hemispheric coupling of vertical motions." We thank Atle Markussen, Paul Breen, and Joachim Urban for their help. We thank Anne K. Smith for providing the SD-WACCM data and routines to calculate the trajectories used in this paper. 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 and the New Zealand Marsden Fund. Robert Lysak thanks the reviewers for their assistance in evaluatingthis paper.Funding DetailsFP7-PEOPLE-IEF-2008/237461, EC, European Commission

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1st AuthorNewnham, D.AuthorNewnham, D.Espy, P.Clilverd, M.Rodger, C.Seppälä, A.Maxfield, D.Hartogh, P.Straub, C.Holmén, K.Horne, R.Year2013JournalJournal of Geophysical Research: Space PhysicsVolume118Number12Pages7874-7885DOI10.1002/2013JA019056URLhttps://www.scopus.com/inward/recor.....2cbcdced09f15a0d7e19a8fbeKeywordsrank1Author Keywordsenergetic particlemesospherenitric oxidepolarthermosphere

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TypeArticleCitationNewnham, D., Espy, P., Clilverd, M., Rodger, C., Seppälä, A., Maxfield, D., Hartogh, P., Straub, C., Holmén, K. and Horne, R. (2013) Observations of nitric oxide in the Antarctic middle atmosphere during recurrent geomagnetic storms. Journal of Geophysical Research: Space Physics, 118(12): 7874-7885 doi:10.1002/2013JA019056