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Ann. Geophys., 20, 349-364, 2002
www.ann-geophys.net/20/349/2002/
© European Geosciences Union 2002
Two types of ion spectral gaps in the quiet inner magnetosphere: Interball-2 observations and modeling
N. Y. Buzulukova1, Y. I. Galperin1,(†), R. A. Kovrazhkin1, A. L. Glazunov1, G. A. Vladimirova1, H. Stenuit2, J. A. Sauvaud2, and D. C. Delcourt3
1IKI, Moscow, Russia
2CESR/CNRS, Toulouse, France
3CETP – CNRS, Saint-Maur des Fosses, France
(†)passed away on the 28 December 2001
Correspondence to: N. Buzulukova (nat@aster.iki.rssi.ru)
Abstract. We analyse measurements
of ion spectral gaps (ISGs) observed by the ION particle spectrometer on board
the Interball-2 satellite. The ISG represents a sharp decrease in H+
flux at a particular narrow energy range. ISGs are practically always observed
in the inner magnetosphere in a wide MLT range during quiet times. Clear
examples of ISG in the morning, dayside, evening and nightside sectors of the
magnetosphere are selected for detailed analysis and modeling. To obtain a
model ISG, the trajectories of ions drifting in the equatorial plane from their
nightside source to the observation point were computed for the energy range
0.1–15 keV. Three global convection models (McIlwain, 1972, 1986; Volland,
1973; Stern, 1975) were tested to reproduce the observed ISGs in all MLT
sectors. Qualitative agreement is obtained for all three models, but the better
agreement for quiet times is reached with the McIlwain (1972) convection model.
It is shown that the ISGs observed by the ION spectrometer throughout the inner
magnetosphere are the result of super-position of the two effects, already
described in the literature (e.g. McIlwain, 1972; Shirai et al., 1997), but
acting under different conditions. Also, the role of particle source location
on the model gaps is investigated. It may be concluded that despite the
evidence of large amplitude and directional local fluctuations of electric
fields in the inner magnetosphere (Quinn et al., 1999), the existence of a
stationary average convection pattern is confirmed by this modeling. This fact
directly follows from observations of ISGs and from a good agreement of
observations with modeled gaps calculated in the frames of adiabatic theory for
a stationary (average) convection pattern.
Key words. Magnetospheric physics
(plasma convection; electric fields)
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