Characteristics of storm-time electric fields in the inner magnetosphere

H. Matsui (1), P. A. Puhl-Quinn (2), J. W. Bonnell (3), C. J. Farrugia (1),
V. K. Jordanova (4), Yu. V. Khotyaintsev (5), P.-A. Lindqvist (6),
E. Georgescu (7), and R. B. Torbert (1)

(1) University of New Hampshire, USA
(2) AER, Inc., USA
(3) University of California, Berkeley, USA
(4) Los Alamos National Laboratory, USA
(5) Swedish Institute of Space Physics, Uppsala, Sweden
(6) Royal Institute of Technology, Sweden
(7) Max-Planck-Institut für Sonnensystemforschung, Germany

We study storm-time electric fields in the inner magnetosphere measured by
Cluster. First we show two event studies around minimum Dst values. In one
event in the eveningside, we have measured subauroral ion drifts (SAID) and/or
undershielding. In the other event in the nightside, we have measured large
electric fields with or without dipolarization signatures. The spatial
coherence of electric field between multiple spacecraft is not high, indicating
the variable nature of this event. Next we show statistical results. The
electric field is enhanced around minimum Dst at all local times. The electric
field decays more quickly than Dst values in the recovery phase. AC components
are generally larger than DC components. These results would be useful in
future efforts to update the empirical electric field model in the inner
magnetosphere.