ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-26-29-2008 Statistical analysis of thermospheric gravity waves from Fabry-Perot Interferometer measurements of atomic oxygen Ford E. A. K. 1 2 Aruliah A. L. 1 Griffin E. M. 1 McWhirter I. 1 Atmospheric Physics Laboratory, Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK 04 02 2008 26 1 29 45 Copyright: © 2008 E. A. K. Ford et al. 2008 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/26/29/2008/angeo-26-29-2008.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/26/29/2008/angeo-26-29-2008.pdf

Data from the Fabry-Perot Interferometers at KEOPS (Sweden), Sodankylä (Finland), and Svalbard (Norway), have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankylä and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general characteristics of the waves that are present in the high latitude upper thermosphere to be determined. Comparisons were made between the different parameters: the atomic oxygen intensities, the thermospheric winds and temperatures, and for each parameter the distribution of frequencies of the waves was determined. No dependence on the number of waves on geomagnetic activity levels, or position in the solar cycle, was found. All the FPIs have had different detectors at various times, producing different time resolutions of the data, so comparisons between the different years, and between data from different sites, showed how the time resolution determines which waves are observed. In addition to the cutoff due to the Nyquist frequency, poor resolution observations significantly reduce the number of short-period waves (<1 h period) that may be detected with confidence. The length of the dataset, which is usually determined by the length of the night, was the main factor influencing the number of long period waves (>5 h) detected. Comparisons between the number of gravity waves detected at KEOPS and Sodankylä over all the seasons showed a similar proportion of waves to the number of nights used for both sites, as expected since the two sites are at similar latitudes and therefore locations with respect to the auroral oval, confirming this as a likely source region. Svalbard showed fewer waves with short periods than KEOPS data for a season when both had the same time resolution data. This gives a clear indication of the direction of flow of the gravity waves, and corroborates that the source is the auroral oval. This is because the energy is dissipated through heating in each cycle of a wave, therefore, over a given distance, short period waves lose more energy than long and dissipate before they reach their target.

 References Aruliah, A. L. and Griffin, E. M.: Evidence of meso-scale structure in the high latitude thermosphere, Ann. Geophys., 19, 37–46, 2001. Aruliah, A. L., Griffin, E. M., McWhirter, I., Aylward, A. D., Ford, E. A. K., Charalambous, A., Kosch, M. J., Davis, C. J., and Howells, V. S. C.: First tristatic studies of meso-scale ion-neutral dynamics and energetics in the high-latitude upper atmosphere using collocated FPIs and EISCAT radar, Geophys. Res. Lett., 31, L03802, https://doi.org/10.1029/2003GL018469, 2004. Aruliah, A. L., Griffin, E. M., Aylward, A. D., Ford, E. A. K., Kosch, M. J., Davis, C. J., Howells, V. S. C., Pryce, E., Middleton, H., and Jussila, J.: First direct evidence of meso-scale variability on ion-neutral dynamics co-located tristatic FPIs and EISCAT radar in Northern Scandinavia, Ann. Geophys., 23, 147–162, 2005. Born, M. and Wolf, E.: Principles of Optics, 6th edition, Oxford, Pergamon Press, 1987. de Deuge, M. A., Greet, P. A., and Jacka, F.: Optical observations of gravity waves in the auroral zone, J. Atmos. Terr. Phys., 56, 617–629, 1994. Ford, E. A. K., Aruliah, A. L., Griffin, E. M., and McWhirter, I.: Thermospheric gravity waves in Fabry-Perot Interferometer measurements of the 630.0 nm OI line, Ann. Geophys., 24, 555–566, 2006. Ford, E. A. K., Aruliah, A. L., Griffin, E. M., and McWhirter, I.: High time resolution measurements of the thermosphere from Fabry-Perot Interferometer measurements of atomic oxygen, Ann. Geophys., 25, 1267–1278, 2007. Fritts, D. C. and Alexander, M. J.: Gravity Wave dynamics and effects in the middle atmosphere, Rev. Geophys., 41, 1003, https://doi.org/10.1029/2001RG000106, 2003. Fritts, D. C. and Hoppe, U. P.: High-Resolution Measurements of Vertical Velocity with the European Incoherent-Scatter VHF Radar 2: Spectral Observations and Model Comparisons, J. Geophys. Res., 100, 16 827–16 838, 1995. Hargreaves, J. K.: The Upper Atmosphere and Solar – Terrestrial Relations, Berkshire, Van Nostrand Reinhold Co. Ltd., 1979. Hecht, E.: Optics, 4th edition, Addison Wesley, 2001. Hernandez, G.:~Fabry-Perot Interferometers,~Cambridge, Cambridge University Press,~1986. Hocke, K. and Schlegel, K.: A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982–1995, Ann. Geophys., 14, 917–940, 1996. Hocke, K.: Phase estimation with the Lomb-Scargle periodogram method, Ann. Geophys., 16, 356–358, 1998. Hunsucker,~R. D.: Atmospheric gravity waves generated in the high-latitude ionosphere: a review, Rev. Geophys. Space Phys., 20, 293–315, 1982. Innis, J. L. and Conde, M.: High-latitude thermospheric vertical wind activity from Dynamics Explorer 2 Wind and Temperature Spectrometer observations: Indications of a source region for polar cap gravity waves, J. Geophys. Res., 107, 1172, https://doi.org/10.1029/2001JA009130, 2002. Innis, J. L. and Conde, M.: Thermospheric vertical wind activity maps derived from Dynamics Explorer-2 WATS observations, Geophys. Res. Lett., 28, 3847–3850, 2001. Innis, J. L., Greet, P. A., and Dyson, P. L.: Thermospheric gravity waves in the southern polar cap from 5 years of photometric observations at Davis, Antarctica, J. Geophys. Res., 106, 15 489–15 500, 2001. Kosch,~M. J., Hagfors,~T., and Rees,~D.: A new Fabry-Perot interferometer for atmospheric studies with the EISCAT incoherent radar, Adv. Space Res., 20, 1133–1136, 1997. Lomb, N. R.: Least squares frequency analysis of unequally spaced data, Astrophys. Space Sci., 39, 447–462, 1976. McIntosh, D. H.: On the Annual Variation of Magnetic Disturbance, Phil. Trans. Royal Soc., A251, 525–552, 1959. Ogawa, T., Igarashi, K., Aikya, K., and Maeno, H.: NNSS satellite observations of medium scale travelling ionospheric disturbances at southern high latitudes, J. Geomagnetism and Geoelectricity, 39, 709–721, 1987. Press, W. H. and Rybicki, G. B.: Fast algorithm for spectral analysis of unevenly sampled data, Astrophys. J., 338, 277–280, 1989. Scargle, J. D.: Studies in Astronomical time series analysis: II Statistical aspects of spectral analysis of unevenly spaced data, Astrophys. J., 263, 835–853, 1982. Solomon, S. C., Hays, P. B., and Abreu, V. J.: The auroral 6300A emission: observations and modeling, J. Geophys. Res., 93, 9867–9882, 1988. Williams,~P. J. S., Virdi,~T. S., Lewis,~R. V., Lester,~M., Rodger,~A. S., McCrea,~I. W., and Freeman,~K. S. C.: Worldwide atmospheric gravity-wave study in the European sector 1985–1990, J. Atmos. Terr. Phys., 55, 683–696, 1993.