Magnetic field strength fluctuations and temperature in the heliosheath

Abstract

We analyze high-resolution observations of the magnetic field strength B made by Voyager 2 (V2) in the heliosheath behind the termination shock from 2007 day of year 245-301. The magnetic field strength is highly variable during intervals of several hours, with large jumps in B on scales of minutes to a few hours. The distributions of increments of B are kurtotic on scales from 48 s to 1.7 hr owing to large tails produced by the jumps in B, and they are approximately Gaussian on the scale of 6.8 hr. The distributions of increments of B are described accurately by the q-Gaussian distribution of nonextensive statistical mechanics on scales of 48 s to 6.8 hr. The entropic index q is a function of scale, and it has a broad peak between 192 and 3072 s centered at ≈770 s. The characteristic width of the jumps in B(t) in four intervals is L ≈ 150,000 km, consistent with the scale of the maximum value of the entropic index. The characteristic width L is a multiple n of the pickup proton gyroradius, where 1 ≤ n ≤ 17, approximately. From L we estimate that the pickup proton temperature T in the post-shock flow is of the order of 2.5 × 106 K if n=9 or 1.3 x 107 K if n=4. Given more accurate estimates of n, it will be possible to use this method to estimate T in the heliosheath as a function of time and distance. © 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A.