Ion distributions in large magnetic holes in the fast solar wind

Abstract

Magnetic holes are isolated localized depressions in the magnitude of the interplanetary magnetic field. Six examples of long-duration (9 to 30 min) magnetic holes observed by the Ulysses spacecraft at high heliographic latitudes near 3 AU are studied in detail. Each of the holes was in pressure balance with its surroundings. The proton-proton and alpha-proton differential streaming typically observed in the fast solar wind dropped to very low levels within the holes. The ion temperatures perpendicular to the magnetic field also increased, leading to marginal mirror-mode stability. Possible causes of these high-latitude magnetic holes are discussed. A new method of deconvolving the three-dimensional angular distributions of the protons and alpha particles from the ion instrument's angular response is described in an appendix.