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Ann. Geophys., 16, 1056-1069, 1998
www.ann-geophys.net/16/1056/1998/
© European Geosciences Union 1998
The ion experiment onboard the Interball-Aurora satellite; initial results on velocity-dispersed structures in the cleft and inside the auroral oval
J. A. Sauvaud1, H. Barthe1, C. Aoustin1, J. J. Thocaven1, J. Rouzaud1, E. Penou1, D. Popescu1, R. A. Kovrazhkin2, and K. G. Afanasiev2
1Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31029, Toulouse, France
e-mail: sauvaud@cesr.cnes.fr
2Space Research Institute, Profsoyuznaya 84/32, Moscow, Russia
Abstract. The Toulouse ION experiment flown on the
Russian Interball-Aurora mission performs simultaneous ion and electron
measurements. Two mass spectrometers looking in opposing directions
perpendicular to the satellite spin axis, which points toward the sun, measure
ions in the mass and energy ranges 1–32 amu and ~0–14 000 eV. Two electron
spectrometers also looking in opposing directions perform measurements in the
energy range ~10 eV–20 000 eV. The Interball-Aurora spacecraft was launched on
29 August 1996 into a 62.8° inclination orbit with an apogee of ~3 RE.
The satellite orbital period is 6 h, so that every four orbits the satellite
sweeps about the same region of the auroral zone; the orbit plane drifts around
the pole in ~9 months. We present a description of the ION experiment and
discuss initial measurements performed in the cusp near noon, in the polar cleft
at dusk, and inside the proton aurora at dawn. Ion-dispersed energy structures
resulting from time-of-flight effects are observed both in the polar cleft at
~16 hours MLT and in the dawnside proton aurora close to 06 hours MLT.
Magnetosheath plasma injections in the polar cleft, which appear as overlapping
energy bands in particle energy-time spectrograms, are traced backwards in time
using a particle trajectory model using 3D electric and magnetic field models.
We found that the cleft ion source is located at distances of the order of 18 RE
from the earth at about 19 MLT, i.e., on the flank of the magnetopause. These
observations are in agreement with flux transfer events (FTE) occurring not only
on the front part of the magnetopause but also in a region extending at least to
dusk. We also show that, during quiet magnetic conditions, time-of-flight ion
dispersions can also be measured inside the dawn proton aurora. A method similar
to that used for the cleft is applied to these auroral energy dispersion
signatures. Unexpectedly, the ion source is found to be at distances of the
order of 60–80 RE, at the dawn flank of the magnetosphere. These
results are discussed in terms of possible entry, acceleration, and
precipitation mechanisms.
Key words. Magnetospheric physics · Auroral phenomena
· Energetic particles · Magnetopause · cusp · and boundary layers ·
Interball-Aurora satellite.
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