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Ann. Geophys., 23, 3-11, 2005
www.ann-geophys.net/23/3/2005/
© European Geosciences Union 2005
Dynamic rayed aurora and enhanced ion-acoustic radar echoes
E. M. Blixt1, T. Grydeland1, N. Ivchenko2,3, T. Hagfors4, C. La Hoz1,5, B. S. Lanchester1, U. P. Løvhaug1, and T. S. Trondsen6
1Dept. of Physics, University of Tromsø, N-9037 Tromsø, Norway
2School of Physics and Astronomy, University of Southampton, UK
3Alfvén Laboratory, KTH, Stockholm, Sweden
4Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
5Cornell University, Earth and Atmospheric Science Department, Ithaca, USA
6Institute for Space Research, Calgary, Alberta, Canada
Abstract. The generation mechanism for
naturally enhanced
ion-acoustic echoes
is still debated.
One important issue
is how these enhancements are related to auroral activity. All
events of enhanced ion-acoustic echoes observed simultaneously with the EISCAT Svalbard Radar
(ESR) and with high-resolution narrow field-of-view auroral
imagers have been collected and studied.
Characteristic of all the events is the appearance of very
dynamic rayed aurora, and some of the intrinsic features of these
auroral displays are identified. Several of these identified
features are directly related to the presence of low energy
(10-100eV) precipitating electrons in addition to the
higher energy population producing most of the associated light.
The low energy contribution is vital for the formation of the
enhanced ion-acoustic echoes. We argue that this type of aurora is
sufficient for the generation of naturally enhanced ion-acoustic
echoes. In one event two imagers were used to observe the auroral
rays simultaneously, one from the radar site and one 7km
away. The data from these imagers shows that the auroral rays and
the strong backscattering filaments (where the enhanced echoes
are produced) are located on the same field line, which is in
contrast to earlier statements in the litterature that they should
be separated.
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