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Ann. Geophys., 20, 1361-1375, 2002
www.ann-geophys.net/20/1361/2002/
© European Geosciences Union 2002
Study of auroral forms and electron precipitation with the IRIS, DASI and EISCAT systems
C. F. del Pozo, F. Honary, N. Stamatiou, and M. J. Kosch
Department of Communication Systems, Lancaster University, Lancaster LA1 4YR, UK
Correspondence to: C. F. del Pozo
(c.del.pozo@lancaster.ac.uk)
Abstract. Simultaneous observations
with the IRIS, DASI and EISCAT systems are employed in the study of the spatial
distribution and temporal evolution of auroral forms and precipitation regions
during substorm activity. The evolution of the spectrum of precipitating
electrons above Tromsø during the various phases of substorms is discussed.
The flux-energy spectrum in the 1–320 keV range is derived from EISCAT
electron density profiles in the 70–140 km altitude range. At the late growth
phase the precipitation flux at the higher energies increases faster than at
the lower energies. The flux is always greater in the lower energy side of the
spectrum and reaches a maximum a few minutes after substorm onset, then it
decays while the spectrum narrows. The systematic analysis of 2-D structures
corresponding with well-defined optical and absorption features is also
discussed. The orientation, characteristic lengths (elongation and width) and
the gravity centre of these spatial features are determined. The statistical
analysis of centre position and the sizes of the corresponding signatures is
presented. When substorm onset falls within the common field of view, there is
a close correspondence between the optical and the absorption signatures of the
auroral forms, as well as in their over-all north-south motion characteristic
of the various phases of the substorm. Optical signatures of arcs are more
evenly distributed in space, being narrower and elongated along the L-shells,
while the absorption regions appear more structured and patchy, although
generally following the arcs’ shape and alignment. Cross-correlation of the
time series of maximum absorption and maximum green-line emission is very high
and seems to show a systematic delay of absorption relative to optical
emission. Time delays are generally larger for disturbed conditions (40 to 60
s) than for moderately active conditions (10 to 20 s).
Key words. Interplanetary physics
(energetic particles) – Ionosphere (auroral ionosphere; ionosphere–magnetosphere
interactions)
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