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

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-sigma fluctuations in the hour averages and 48-s averages of the azimuthal and elevation angles being approximate to +/- 8 degrees and approximate to +/- 5 degrees, respectively). The average magnetic field strength was relatively large, B approximate to 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 approximate to 80 R-L, where R-L 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 R-L is of the same order of magnitude in the two locations, suggesting a common physical nature.