Satistical Features of the Substorm Expansion-Phase as Observed by the AMPTE/CCE Spacecraft
- Joseph R. Kan,
- Thomas A. Potemra,
- Susumu Kokubun and
- Takesi Iijima
Published Online: 19 MAR 2013
Copyright 1991 by the American Geophysical Union.
How to Cite
Daglis, I. A., Paschalidis, N. P., Sarris, E. T., Axford, W. I., Kremser, G., Wilken, B. and Gloeckler, G. (1991) Satistical Features of the Substorm Expansion-Phase as Observed by the AMPTE/CCE Spacecraft, in Magnetospheric Substorms (eds J. R. Kan, T. A. Potemra, S. Kokubun and T. Iijima), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM064p0323
- Published Online: 19 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900308
Online ISBN: 9781118663981
- Magnetospheric substorms—Congresses
We present a statistical study of the substorm expansion phase in terms of variations of the energy density of the major ions (H+, O+, He++ , He+). The data were collected by the Charge-Energy-Mass (CHEM) spectrometer on board the AMPTE/CCE satellite in the equatorial (within ±16° magnetic latitude) nightside magnetosphere, at geocentric distances ≤9 RE, and cover the period from March 1985 to December 1987 (which makes a total of 1255 CCE orbits with the apogee located on the nightside). Previous statistical studies of magnetospheric populations were limited to energies less than 32 keV/e at geosynchronous altitudes, less than 17 keV/e at other altitudes, and energies greater than about 200 keV/nucleon; the CHEM data (energies ∼1 to 300 keV7/e) fill the energy gap, in which the bulk of the region's energy density is contained. Furthermore, there are two major differences between this study and previous ones: first we explicitly used time intervals just after substorm onset and not active times in general; second we examined the energy density instead of the number density, since we were mainly interested in the energy budget evolution and not in the composition of the ion population. Our observations show a remarkable difference between the energy-densities of O+ and He++ ions in the early expansion phase of the substorm: the ionospheric-origin O+ energy density grows non-linearly with AE, while the solar wind-origin He++ energy density seems almost uncorrelated with AE. The mixed-origin H+ and He+ energy-densities exhibit an intermediate behavior by increasing with AE, but in a lesser degree than O+. We suggest that the trend of O+ energy density is associated with increased direct feeding of the near-Earth magnetotail with energetic ionospheric ions, during highly active periods. The outflowing energetic ionospheric plasma can participate in the cross-tail current enhancement during late growth-phase (Daglis et al.,1990,1991) and subsequently favour the growth of instabilities in the plasma sheet (e.g. Baker et al., 1982). Another interesting feature is the tendency of the He++ energy density to higher values towards dawn; this may be interpreted as a result of increased penetration of solar wind ions from the magnetosheath through the dawnside magnetopause (Lennartson and Sharp, 1982).