A FORWARD-REVERSE SHOCK PAIR IN THE SOLAR-WIND DRIVEN BY OVER-EXPANSION OF A CORONAL MASS EJECTION - ULYSSES OBSERVATIONS

A previously unidentified type of solar wind forward-reverse shock pair has been observed by Ulysses at 4.64 AU and S32.5-degrees. 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 approximately 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.