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 EUV, FUV, and HENA,
and in situ observations by the DMSP F13 satellite provide a comprehensive
view of the coupled response of the inner magnetosphere and ionosphere. At
1900 UT a substorm onset initiated the event, causing a sunward convective
impulse which caused both a ring current injection and a plasmasphere
indentation. The motion of this impulse past the plasmasphere caused ripples
to propagate along the plasmapause, eastward and westward from pre-midnight
MLT. The MLT locations of the moving ripples agree 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, and in the second phase (1936 UT
to 2037 UT) this mild bulge was removed by an apparent westward flow that
stripped away the outer 1 RE of the duskside plasmasphere. The bulge
formation may have been caused by an E-field induced by local reduction of
the magnetic field by the ring current pressure increase. The second phase
was almost certainly due to the subauroral polarization stream (SAPS). The
SAPS effect was observed in the ionosphere by DMSP between about 1930 UT and
2000 UT. The SAPS flow channel was also evident in vector electric fields
inferred from the plasmapause motion. All the observations of this event
suggest strong coupling and interplay among the plasma populations of the
magnetosphere-ionosphere system. This event represents the first
identification of the directlyobserved effects on the plasmasphere of a
finite-speed propagating substorm-driven impulse, the SAPS flow channel, and
possibly, of the ring-current magnetic field reduction. 

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To be submitted to Journal of Geophysical Research, 2004