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Ann. Geophys., 22, 1765-1771, 2004
www.ann-geophys.net/22/1765/2004/
© European Geosciences Union 2004
Evidence for storm-time ionospheric ion precipitation in the cusp with magnetosheath energy
H. Stenuit and J.-A. Sauvaud
CESR/CNRS, 9 av. du colonel Roche, 31028 Toulouse, France
Abstract. We present evidence for a sporadic precipitation into the north polar cusp
of ionospheric O+ and He+ ions accelerated up to the magnetosheath
flow speed during a magnetic storm. This is deduced from data obtained
on board the Interball-Auroral satellite showing that the energy/charge
ratios of the H+, He++, He+ and O+ populations are
similar to those of ion masses. These measurements pertain to a very
disturbed magnetic period. A storm was in progress with a Dst reaching -149nT
during the cusp measurements, while the AE index reached values higher
than 1000nT. This result is discussed in terms of ion circulation from the
magnetosphere to the magnetosheath and back to the magnetosphere. We suggest
that the acceleration of O+ and He+ ions up to a
magnetosheath-like velocity is directly linked to the large By component
of the IMF.
Key words. Magnetospheric physics (magnetopause, cusp
and boundary layers; magnetosheath; storms and substorms)
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