Radial heliospheric magnetic fields detected by Ulysses

Abstract

The magnetometer aboard the Ulysses spacecraft has recorded numerous examples of heliospheric magnetic fields orientated in near-radial directions for periods of several hours or more. These fields are unusual, as their existence is contrary to the predictions of classical theories concerning solar wind production and propagation. The magnetic field data gathered by Ulysses up to the end of 1997 were searched for all instances of radial fields of significant duration. Here, arising from that study, an overview of the detected radial field periods is given; including their latitudinal occurrence, their coincidence with other solar wind features, and some of their phenomenology. A particularly persistent radial field was recorded in early January 1997; this highly unusual event is described in greater depth. The implications and possible causes of radial field periods are discussed.