Eb. Wodnicka et M. Banaszkiewicz, OUTFLOWING IONOSPHERIC OXYGEN-ION MOTION IN A RECONFIGURATING MAGNETOSPHERE, Annales geophysicae, 15(1), 1997, pp. 5-16
During substorms, large-scale changes of the topology of the Earth's m
agnetosphere following the variation of the characteristics of the int
erplanetary medium are accompanied by the induction of the electric fi
eld. In this study a model of a time-dependent magnetosphere is constr
ucted and the large-scale features of the induced electric field are d
escribed. Local-time sectors with upward or downward field-aligned com
ponent and with intense perpendicular component of the electric field
are distinguished. The electric-field structure implies the existence
of outflow regions particularly effective in ion energization. With th
e vector potential adopted in the study, the region from which the mos
t energized ions originate is defined by the local-time sector near 21
00 MLT and latitude zone near 71 degrees MLAT. The motion of ionospher
ic oxygen ions of energy 0.3-3 keV is investigated during a 5-min reco
nfiguration event when the tail-like magnetospheric field relaxes to t
he dipole-like field. As the characteristics of plasma in the regions
near the equatorial plane affect the substorm evolution, the energy, p
itch angle, and the magnetic moment of ions in these regions are analy
zed. These quantities depend on the initial energy and pitch angle of
the ion and on the magnetic and electric field it encounters on its wa
y. With the vector potential adopted, the energy attained in the equat
orial regions can reach hundreds of keV. Three regimes of magnetic-mom
ent changes are identified: adiabatic, oscillating, and monotonous, de
pending on the ion initial energy and pitch angle and on the magnetic-
and electric-field spatial and temporal scales. The implications for
the global substorm dynamics are discussed.