Heliospheric plasma sheets as small-scale transients

Abstract

Ulysses plasma and magnetic field data from the ecliptic plane near 1 AU signaling multiple heliospheric plasma sheets across a sector boundary are analyzed in order to determine their geometrical configuration. The plasma sheets coincided with a region of sporadic heat flux dropouts and planar magnetic structure. The plane of the structure was inclined to the ecliptic plane by 56° and nearly orthogonal to the Parker spiral. Pronounced flow deflections within the plasma sheets were closely aligned with the magnetic structure plane. Geometrical constraints and the lack of correlation between the highly variable magnetic fields in the planar structure and the flow deflections preclude a single, wavy plasma sheet interpretation. The flow deflections were nested in similar, larger-scale deflections on the downslope of a pressure wave. The observations are consistent with spacecraft passage through the flanks of a transient disturbance which distorted the sector boundary plane. We interpret the planar magnetic structure with its embedded plasma sheets as a layer of small-scale, intertwined flux ropes with varying degrees of helicity, flattened into sector-boundary-aligned sheets by kinematic distention and compression. The sporadic dropout of heat flux may have signaled flux-rope detachment from the Sun or particle scattering, possibly owing to the high variability of plasma parameters across the plasma sheets.