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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 5
Ann. Geophys., 22, 1843–1849, 2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 1843–1849, 2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  08 Apr 2004

08 Apr 2004

The effects of high-frequency ULF wave activity on the spectral characteristics of coherent HF radar returns: a case study

D. M. Wright1, T. K. Yeoman1, and E. E. Woodfield2 D. M. Wright et al.
  • 1Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
  • 2National Center for Atmospheric Research/High Altitude Observatory, P.O. Box 3000, Boulder, Colorado, 80307-3000, USA

Abstract. It is now a common practice to employ ground-based radars in an attempt to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed magnetic field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromsø, Norway (66° N geomagnetic). On this occasion, a number of equatorward excursions of the SWB in the radar backscatter are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band as the SWB passes overhead. Thus, these observations support the possibility that high-frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the nightside ionosphere.

Key words. Ionosphere (auroral ionosphere) – Magnetospheric physics (MHD waves and instabilities) – Radio science (ionospheric physics)

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