A forward-reverse shock pair in the solar wind driven by over-expansion of a coronal mass ejection: Ulysses observations
Balogh, A.; McComas, D. J.; Goldstein, B. E.; Bame, S. J.; Scime, E. E.; Phillips, J. L.; Gosling, J. T.; Pizzo, V. J.
United States
Abstract
A previously unidentified type of solar wind forward-reverse shock pair has been observed by Ulysses at 4.64 AU and S32.5°. In contrast to most solar wind forward-reverse shock pairs, which are driven by the speed difference between fast solar wind plasma and slower plasma ahead, this particular shock pair was driven purely by the over-expansion of a coronal mass ejection, CME, in transit from the Sun. A simple numerical simulation indicates that the overexpansion was a result of a high initial internal plasma and magnetic field pressure within the CME. The CME observed at 4.64 AU had the internal field structure of a magnetic flux rope. This event was associated with a solar disturbance in which new magnetic loops formed in the corona almost directly beneath Ulysses ∼11 days earlier. This association suggests that the flux rope was created as a result of reconnection between the “legs” of neighboring magnetic loops within the rising CME.