A reconnection layer associated with a magnetic cloud

We examine a 3-hour long interval on December 24, 1996, containing a magnetic hole associated with an interplanetary magnetic cloud. Two sets of perturbations are observed by the Wind spacecraft at 1 AU. In the first, the field and flow rotate at constant field strength, and the plasma is accelerated to the local Alfven speed. We show this to be a rotational discontinuity. In the second, observed 25 min later, the plasma is heated and the field decreases. We show this to be a slow shock. The whole structure is in pressure balance. We interpret the observations as MHD discontinuities arriving with varying delays from a reconnection site closer to the Sun. Energetic particle observations suggest further that ejecta material is present for many hours prior to the magnetic cloud observation and separated from it by the layer. This suggests that reconnection took place between field lines of a CME of which the magnetic cloud formed a part. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.