Meeting abstract

AGU Fall Meeting, San Francisco, 6-10 December 1998

Abstract: Planar magnetic structures (from hereon PMSs) are defined as events where the heliospheric magnetic field remains coplanar for periods of several hours or more, during which time several discontinuities (rotational and/or tangential) are seen in the field's direction. The results of a survey of PMS events detected by the Ulysses magnetometer, from the spacecraft's launch in 1990 to mid-1998, are presented. The survey was automated, to cope with the large dataset, as well as with the subjectivity inherent in searching for the features manually. To find periods of coplanarity, minimum variance analysis techniques were applied to the data. This method revealed the presence of numerous events which were coplanar after the mean field direction was subtracted, i.e. the field was confined to small circles in the spacecraft's field of view, as opposed to great circles seen during ``conventional'' PMSs. Such features are mostly undetectable during a manual survey. Changes in the nature of PMSs with heliographic latitude are described, as well as their relationships to other features encountered in the solar wind. The implications of the results in the context of the structures' origins are also briefly discussed.