Linear magnetic holes in a unipolar region of the heliosheath observed by Voyager 1

Abstract

Voyager 1 (V1) observed a unipolar interval in the heliosheath from day of year (DOY) 146–204, 2006, in which the magnetic field B was directed toward the Sun nearly along the spiral field direction. The direction of B was nearly constant in this interval (the 1‐σ fluctuations in the hour averages and 48‐s averages of the azimuthal and elevation angles being ≈±8° and ≈±5°, respectively). The average magnetic field strength was relatively large, B ≈ 0.21 nT. The fluctuations in both the hour averages and 48‐s averages of B were non‐Gaussian, being skewed toward small values of B, primarily by the presence of numerous linear magnetic holes. The magnetic holes moved past V1 at a rate of the order of 2/day. The characteristics of nine magnetic holes were analyzed by fitting the magnetic field strength profiles to a Gaussian distribution. The radial extent of the magnetic holes was of the order of 650,000 km, which is ≈80 RL, where RL is the Larmor radius of the pickup protons in the heliosheath. Although the magnetic holes in the heliosheath are much larger than those at 1 AU, the size in units of RL is of the same order of magnitude in the two locations, suggesting a common physical nature.