The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland

MHD solutions indicate that solar wind Alfvénic fluctuations striking the bow shock should launch a variety of disturbances into the magnetosheath, including both forward (antisunward) and reverse (sunward) propagating Alfvénic fluctuations. We present the first observational evidence of this prediction. This case study presents observations of the Wind spacecraft of Alfvénic fluctuations propagating antisunward along the away sector Parker spiral interplanetary magnetic field (IMF) on April 26 to 27, 1995. Simultaneous Geotail solar wind observations confirm the presence of Alfvénic fluctuations propagating along the spiral IMF, but Geotail magnetosheath observations indicate Alfvénic fluctuations propagating in the opposite direction relative to the draped, prenoon, magnetic field. The reversal in wave propagation direction at the bow shock provides striking evidence for the MHD model of wave-shock interaction.

Geophys. Res. Lett., 24, 3133-3136, 1997