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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, 1675–1686, 2004
https://doi.org/10.5194/angeo-22-1675-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 1675–1686, 2004
https://doi.org/10.5194/angeo-22-1675-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  08 Apr 2004

08 Apr 2004

Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

J. R. T. Jussila1, A. T. Aikio1, S. Shalimov2, and S. R. Marple3 J. R. T. Jussila et al.
  • 1Department of Physical Sciences, P.O. Box 3000, FIN-90014 University of Oulu, Finland
  • 2Institute of physics of the Earth, Moscow, Russia
  • 3Department of Communication systems, University of Lancaster, UK

Abstract. Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature (Te) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced Te play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation.

Key words. Ionosphere (auroral ionosphere; particle precipitation; electric fields and currents)

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