Magnetic fields in the heliosheath and distant heliosphere:: Voyager 1 and 2 observations during 2005 and 2006

This paper examines the variability of daily averages of the magnetic field strength B in the heliosheath and in the distant solar wind measured by Voyager 1 (V1) and Voyager 2 (V2), respectively, from 2005.0 to 2006.9. In the heliosheath, a spatial gradient of (0.0023 +/- 0.0011) nT AU(-1) is observed, which constrains models of the inner heliosheath. This gradent is small compared to the expected average gradient of B across the entire heliosheath. In the heliosheath the profile of B is generally filamentary with numerous jumps, but a large-amplitude sine wave with a period of approximate to 200 days was observed by V1 at the end of the interval. The fluctuations of daily averages of B observed by V1 and V2 have a Gaussian distribution and lognormal distribution, respectively. The autocorrelation of B(t) from day of year (DOY) 1-512 was an exponential function with an e-folding time of approximate to 3.7 +/- 0.5 days for V1 and 2.5 +/- 0.3 days for V2. On scales from 1-4 days, the autocorrelation function was a power law with exponent alpha =-0.440 +/- 0.031 for V1 and alpha =-0.497 +/- 0.002 for V2. The distribution of differences of successive daily averages of B for both V1 and V2 is the Tsallis distribution of nonextensive statistical mechanics with the nonextensivity parameter q = 1.55 +/- 0.05. V2 (at approximate to S26 degrees) observed both positive and negative magnetic polarities throughout the interval from 2005.0 to 2006.9. There is evidence that V1 (at N34 degrees) might be entering a region of negative magnetic polarity as the latitudinal extent of the heliospheric current sheet decreases during the declining phase of solar cycle 23.