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Ann. Geophys., 20, 1321-1334, 2002
www.ann-geophys.net/20/1321/2002/
© European Geosciences Union 2002
Substorm related changes in precipitation in the dayside auroral zone – a multi instrument case study
A. J. Kavanagh1,2, F. Honary1, I. W. McCrea2, E. Donovan3, E. E. Woodfield4, J. Manninen5, and P. C. Anderson6
1Department of Communication Systems, Lancaster University, Lancaster, UK
2EISCAT Group, Space Science and Technology Dept., Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, UK
3University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada
4Department of Physics and Astronomy, University of Leicester, Leicester, UK
5Sodankylä Geophysical Observatory, Tähteläntie 112, FIN-99600 Sodankylä, Finland
6Aerospace Corporation, Space and Environmental Technology Center, Los Angeles, USA
Correspondence to: A. J. Kavanagh
(a.j.Kavanagh@lancs.ac.uk)
Abstract. A period (08:10–14:40
MLT, 11 February 1997) of enhanced electron density in the D- and E-regions is
investigated using EISCAT, IRIS and other complementary instruments. The
precipitation is determined to be due to substorm processes occurring close to
magnetic midnight. Energetic electrons drift eastward after substorm injection
and precipitate in the morning sector. The precipitation is triggered by small
pulses in the solar wind pressure, which drive wave particle interactions. The
characteristic energy of precipitation is inferred from drift timing on
different L-shells and apparently verified by EISCAT measurements. The IMF
influence on the precipitation in the auroral zone is also briefly discussed. A
large change in the precipitation spectrum is attributed to increased numbers
of ions and much reduced electron fluxes. These are detected by a close passing
DMSP satellite. The possibility that these ions are from the low latitude
boundary layer (LLBL) is discussed with reference to structured narrow band Pc1
waves observed by a search coil magnetometer, co-located with IRIS. The
intensity of the waves grows with increased distance equatorward of the cusp
position (determined by both satellite and HF radar), contrary to expectations
if the precipitation is linked to the LLBL. It is suggested that the ion
precipitation is, instead, due to the recovery phase of a small geomagnetic
storm, following on from very active conditions. The movement of absorption in
the later stages of the event is compared with observations of the ionospheric
convection velocities. A good agreement is found to exist in this time interval
suggesting that E × B drift has become the dominant drift
mechanism over the gradient-curvature drift separation of the moving absorption
patches observed at the beginning of the morning precipitation event.
Key words. Ionosphere (auroral
ionosphere; particle precipitation) Magnetospheric physics (storms and
substorms)
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