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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 12
Ann. Geophys., 18, 1531–1549, 2000
https://doi.org/10.1007/s00585-001-1531-2
© European Geosciences Union 2000
Ann. Geophys., 18, 1531–1549, 2000
https://doi.org/10.1007/s00585-001-1531-2
© European Geosciences Union 2000

  31 Dec 2000

31 Dec 2000

On the collocation between dayside auroral activity and coherent HF radar backscatter

J. Moen4,1, H. C. Carlson2, S. E. Milan3, N. Shumilov1, B. Lybekk4, P. E. Sandholt4, and M. Lester3 J. Moen et al.
  • 1Arctic Geophysics, University Courses on Svalbard, N-9170 Longyearbyen, Norway
  • 2Air Force Research Laboratory, AFOSR, 801 Stafford St., Arlington, VA 22203, USA
  • 3Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
  • 4Department of Physics, University of Oslo, PO Box. 1048 Blindern, N-0316 Oslo, Norway

Abstract. The 2D morphology of coherent HF radar and optical cusp aurora has been studied for conditions of predominantly southward IMF conditions, which favours low-latitude boundary layer reconnection. Despite the variability in shape of radar cusp Doppler spectra, the spectral width criterion of > 220 m s–1 proves to be a robust cusp discriminator. For extended periods of well-developed radar backscatter echoes, the equatorward boundary of the > 220 m s–1 spectral width enhancement lines up remarkably well with the equatorward boundary of the optical cusp aurora. The spectral width boundary is however poorly determined during development and fading of radar cusp backscatter. Closer inspection of radar Doppler profile characteristics suggests that a combination of spectral width and shape may advance boundary layer identification by HF radar. For the two December days studied the onset of radar cusp backscatter occurred within pre-existing 630.0 nm cusp auroral activity and appear to be initiated by sunrise, i.e. favourable radio wave propagation conditions had to develop. Better methods are put forward for analysing optical data, and for physical interpretation of HF radar data, and for combining these data, as applied to detection, tracking, and better understanding of dayside aurora. The broader motivation of this work is to develop wider use by the scientific community, of results of these techniques, to accelerate understanding of dynamic high-latitude boundary-processes. The contributions in this work are: (1) improved techniques of analysis of observational data, yielding meaningfully enhanced accuracy for deduced cusp locations; (2) a correspondingly more pronounced validation of correlation of boundary locations derived from the observational data set; and (3) a firmer physical rationale as to why the good correlation observed should theoretically be expected.

Key words: Ionosphere (ionospheric irregularities; polar ionosphere)

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