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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 24, issue 2
Ann. Geophys., 24, 475–491, 2006
https://doi.org/10.5194/angeo-24-475-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 24, 475–491, 2006
https://doi.org/10.5194/angeo-24-475-2006
© Author(s) 2006. This work is distributed under
the Creative Commons Attribution 3.0 License.

  23 Mar 2006

23 Mar 2006

Infrasound - the cause of strong Polar Mesosphere Winter Echoes?

S. Kirkwood1, P. Chilson2, E. Belova1, P. Dalin1, I. Häggström3, M. Rietveld4, and W. Singer5 S. Kirkwood et al.
  • 1Swedish Institute of Space Physics, Box 812, 98128 Kiruna, Sweden
  • 2School of Meteorology, University of Oklahoma, Norman, OK, USA
  • 3EISCAT Scientific Association, Kiruna, Sweden
  • 4EISCAT Scientific Association, Ramfjordmoen, Norway
  • 5Leibniz Institute of Atmospheric Physics, Kühlungsborn, Germany

Abstract. The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE) during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and high aspect sensitivity, with echo arrival angles spread over as little as 0.3°. ESRAD also detected, on some occasions, discrete scattering regions moving across the field of view with periodicities of a few seconds. The very narrow, vertically directed beam of the more powerful EISCAT radar allowed measurements of the spectral widths of the radar echoes both inside the PMWE and from the background plasma above and below the PMWE. Spectral widths inside the PMWE were found to be indistinguishable from those from the background plasma. We propose that scatter from highly-damped ion-acoustic waves generated by partial reflection of infrasonic waves provides a reasonable explanation of the characteristics of the very strong PMWE reported here.

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