An interplanetary planar magnetic structure oriented at a large (∼ 80 deg) angle to the Parker spiral

Magnetic field structures in the solar wind, characterised by a variation of the field vectors within a plane inclined to the ecliptic (‘Planar Magnetic Structures’, PMS's), were reported recenty (Nakagawa et al., 1989). These PMS's have the property that the plane of variation of the field also contains the nominal Parker spiral direction. We report here an observation of a PMS where the direction of the line of intersection of the plane of field variation with the ecliptic plane makes a large (∼80 deg) angle to the Parker spiral direction. Furthermore, the angular variables of the field, θ B (elevation) and φ B (azimuth) (a) vary over a restricted range, and (b) are linearly related. We show the latter property to be related to the former. We argue that currently proposed models for the origin of PMS's, in as much as they require field configurations which retain strict alignment with the Parker spiral direction from formation to observation, are probably incomplete.