Comprehensive study of the magnetospheric response to a hot flow anomaly

We present a comprehensive observational study of the magnetospheric respon se to an interplanetary magnetic field (IMF) tangential discontinuity, whic h first struck the postnoon bow shock and magnetopause and then swept past the prenoon bow shock and magnetopause on July 24, 1996. Although unaccompa nied by any significant plasma variation, the discontinuity interacted with the bow shock to form a hot flow anomaly (HFA), which was observed by Inte rball-1 just upstream from the prenoon bow shock. Pressures within and Eart hward of the HFA were depressed by an order of magnitude, which allowed the magnetopause to briefly (similar to 7 min) move outward some 5 R-E beyond its nominal position and engulf Interball-1. A timing study employing nearb y Interball-1 and Magion-4 observations demonstrates that this motion corre sponded to an antisunward and northward moving wave on the magnetopause. Th e same wave then engulfed Geotail, which was nominally located downstream i n the outer dawn magnetosheath. Despite its large amplitude, the wave produ ced only minor effects in GOES-8 geosynchronous observations near local daw n. Polar Ultraviolet Imager (UVI) observed a sudden brightening of the afterno on aurora, followed by an even more intense transient brightening of the mo rning aurora. Consistent with this asymmetry, the discontinuity produced on ly weak near-simultaneous perturbations in high-latitude postnoon ground ma gnetometers but a transient convection vortex in the prenoon Greenland grou nd magnetograms. The results of this study indicate that the solar wind int eraction with the bow shock is far more dynamic than previously imagined an d far more significant to the solar wind-magnetosphere interaction.