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Ann. Geophys., 23, 579-591, 2005
www.ann-geophys.net/23/579/2005/
© European Geosciences Union 2005
Role of substorm-associated impulsive electric fields in the ring current development during storms
N. Yu. Ganushkina1, T. I. Pulkkinen1, and T. Fritz2
1Finnish Meteorological Institute, Geophysical Research Division, P.O. Box 503, FIN-00101 Helsinki, Finland
2Boston University, Department of Astronomy, 725 Commonwealth Ave., Boston, MA 02215, USA
Abstract. Particles with different energies produce varying contributions
to the total ring current energy density as the storm progresses.
Ring current energy densities and total ring current energies
were obtained using particle data from the Polar CAMMICE/MICS
instrument during several storms observed during the years
1996-1998. Four different energy ranges for particles are
considered: total (1-200keV), low (1-20keV),
medium (20-80keV) and high (80-200keV). Evolution
of contributions from particles with different energy ranges to
the total energy density of the ring current during all storm
phases is followed. To model this evolution we trace protons
with arbitrary pitch angles numerically in the drift
approximation. Tracing is performed in the large-scale and
small-scale stationary and time-dependent magnetic and electric
field models. Small-scale time-dependent electric field is given
by a Gaussian electric field pulse with an azimuthal field component
propagating inward with a velocity dependent on radial distance.
We model particle inward motion and energization by a series of
electric field pulses representing substorm activations during
storm events. We demonstrate that such fluctuating fields in the
form of localized electromagnetic pulses can effectively
energize the plasma sheet particles to higher energies
(>80keV) and transport them inward to closed drift
shells. The contribution from these high energy particles dominates
the total ring current energy during storm recovery phase. We
analyse the model contributions from particles with different
energy ranges to the total energy density of the ring current
during all storm phases. By comparing these results with
observations we show that the formation of the ring current is a
combination of large-scale convection and pulsed inward shift
and consequent energization of the ring current particles.
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