H J Singer
On October 18, 1995 a magnetic cloud was observed in the solar wind by the WIND spacecraft just before it encountered the Earth's magnetosphere. Many of the features associated with the cloud, such as the shock, changes in the solar wind density, and changes in the IMF Bz component, affected the magnetic field observed at geosynchronous orbit through changes in various magnetospheric current systems. These effects will be described, with particular attention on an interval when the magnetic field at GOES 9, located at about 1620 LT, became severely distorted so as to have a southward orientation, which is usually interpreted as a magnetopause crossing at geosynchronous orbit. However, this disturbance occurred at a time when the solar wind dynamic pressure was insufficient to move the magnetopause in to the geosynchronous location. The conditions that produced this extreme distortion of the geosynchronous magnetic field will be described, and comparisons of GOES magnetic field observations will be made with ground magnetometer data from the Canadian CANOPUS magnetometer network as well as magnetic field models. In addition, fieldaligned currents derived from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) model and projected from the ionosphere to the magnetospheric equatorial plane will be compared to the observed magnetic field perturbations.
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