Space Sci. Revs., in press, 2001
Planar magnetic structures are regions of the solar wind where the magnetic field remains oriented parallel to a fixed plane for several hours or more. Discontinuities in the field direction may be encountered during these periods, the discontinuities' surfaces also being parallel to the plane within which the field is contained. A survey of Ulysses magnetic field data returned during 1990-1998 revealed that the solar wind's magnetic field was planar in nature for approximately 10% of the time. A survey is presented of planar magnetic structures encountered by Ulysses during two periods when the spacecraft was travelling south from the ecliptic to high southern heliographic latitudes, in 1992-1994 and 1998-2000. The characteristics of the planar magnetic structures encountered during these times are described, as well as their apparent relationships with large-scale structures such as coronal mass ejections, interplanetary shocks, heliospheric current sheet crossings and corotating interaction regions. Differences in the planar magnetic structures' characteristics between the declining and near-maximum phases of the solar activity cycle are described, and possible reasons for the differences are discussed.
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