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Ann. Geophys., 18, 1097-1107, 2000
www.ann-geophys.net/18/1097/2000/
© European Geosciences Union 2000
The dawn and dusk electrojet response to substorm onset
E. Borälv1, P. Eglitis1, H. J. Opgenoorth1,2, E. Donovan3, G. Reeves4, and P. Stauning5
1Swedish Institute of Space Physics, Box 537, S-751 21 Uppsala, Sweden
2Finnish Meteorological Institute, Geophysical Research, P.O. Box 503, FIN-00101 Helsinki, Finland
3Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada T2N 1N4
4Los Alamos National Laboratory, Mail Stop D-436, NM 87545, USA
5Solar-Terrestrial Physics Division, Danish Meterological Institute, Lyngbyyvej 100, DK-2100 Copenhagen, Denmark
Correspondence to: E. Borälv
e-mail: eb@irfu.se
Abstract. We have investigated the time delay between
substorm onset and related reactions in the dawn and dusk ionospheric
electrojets, clearly separated from the nightside located substorm current wedge
by several hours in MLT. We looked for substorm onsets occurring over Greenland,
where the onset was identified by a LANL satellite and DMI magnetometers located
on Greenland. With this setup the MARIA magnetometer network was located at
dusk, monitoring the eastward electrojet, and the IMAGE chain at dawn, for the
westward jet. In the first few minutes following substorm onset, sudden
enhancements of the electrojets were identified by looking for rapid changes in
magnetograms. These results show that the speed of information transfer between
the region of onset and the dawn and dusk ionosphere is very high. A number of
events where the reaction seemed to preceed the onset were explained by either
unfavorable instrument locations, preventing proper onset timing, or by the
inner magnetosphere's reaction to the Earthward fast flows from the near-Earth
neutral line model. Case studies with ionospheric coherent (SuperDARN) and
incoherent (EISCAT) radars have been performed to see whether a
convection-induced electric field or enhanced conductivity is the main agent for
the reactions in the electrojets. The results indicate an imposed electric field
enhancement.
Key words: Ionosphere (auroral ionosphere; electric
fields and currents) - Magnetospheric physics (storms and substorms)
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