Coupled response of the inner magnetosphere and ionosphere on 17 April 2002

J. Goldstein, J. L. Burch, B. R. Sandel, S. B. Mende, P. C:son Brandt, and 
M. R. Hairston


We present an observational study of the global dynamics of the plasmasphere,
aurora, ring current, and subauroral ionosphere on 17 April 2002, during a
substorm. Global observations by IMAGE and in situ observations by DMSP F13
provide a comprehensive view of the coupled response of the inner magnetosphere
and ionosphere. At 1900 UT a substorm onset initiated a sunward convective
impulse which caused a ring current injection. The motion of this impulse past
the plasmasphere caused ripples to propagate along the plasmapause, eastward
and westward from pre-midnight MLT. The motion of the ripples agrees
exceptionally well with the motion of the aurora and the ring current, implying
strong coupling. The westward-moving ripple (on the duskside) participated in a
two-phase plasmapause undulation effect. In the first phase (1915 UT to 1936
UT), a mild 0.4Ð0.5 RE bulge formed near 2000 MLT, probably caused by an
E-field induced by local reduction of the magnetic field by the ring current
pressure increase. In the second phase (1936 UT to 2037 UT) this mild bulge was
removed by a sub-auroral polarization stream (SAPS) westward flow that stripped
away the outer 1 RE of the duskside plasmasphere. The SAPS effect was observed
in the ionosphere by DMSP between about 1930 UT and 2000 UT, and evident in
vector E-fields inferred from plasmapause motion. All the observations of this
event suggest strong coupling among the plasma populations of the
magnetosphere-ionosphere system. This event represents the first identification
of the directly-observed global plasmaspheric effects of a substorm-driven
impulse, the SAPS flow channel, and of the ring-current magnetic field
reduction.

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Journal of Geophysical Research, 110, A03205, doi:10.1029/2004JA010712, 2005.