K. Sigsbee, C. A. Cattell
(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455)
F. Mozer (Space Sciences Laboratory, University of California, Berkeley, CA 94720)
D. Fairfield (NASA/GSFC, Laboratory for Extraterrestrial Physics, Code 695, Greenbelt, MD 20771)
K. Tsuruda and T. Yamamoto (ISAS, Sagamihara 229, Japan)
S. Kokubun (STELAB, Nagoya University, Toyokawa 442, Japan)
On April 26, 1995 a substorm onset occurred at about 0750 UT as
identified by auroral kilometric radiation, ground magnetometers
and data from several spacecraft(Fairfield et al., Paper
Presented at ICS 3, 1996). During this event, Geotail was in
the near equatorial region around 13 Re and 1300 LT. Instruments
on board the Geotail spacecraft observed intense DC electric fields
of 50 mV/m in conjunction with some of the largest high speed
earthward flows ever detected at 13 Re. We will present time-series
analysis of low frequency waves observed during the April 26, 1995
substorm event. The observed waves are extremely intense, bursty
and often associated with large spiky fields. At frequencies below
a few Hz, the dominant power is at frequencies comparable to the
lower hybrid frequency. At lower frequencies, a brief compression
in the Pi2 range is observed, as well as waves at higher frequencies.
Similar waves are observed in association with other onsets in
the inner magnetotail. Statistical comparisons to waves observed
during other events will be made. The dominant wave modes will be
identified and their implications for relevant substorm processes
will be discussed.