Magnetic Fields in the Heliosheath and Distant Heliosphere:Voyager 1and2Observations During 2005 and 2006

Abstract

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 AE 0:0011) nT AU À1 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 %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 %3:7 AE 0:5 days for V1 and 2:5 AE 0:3 days for V2. On scales from 1-4 days, the autocorrelation function was a power law with exponent ¼ À0:440 AE 0:031 for V1 and ¼ À0:497 AE 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 ¼ 1:55 AE 0:05. V2 (at %S26 ) observed both positive and negative magnetic polarities throughout the interval from 2005.0 to 2006.9. There is evidence that V1 (at N34 ) 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. Subject headingg s: magnetic fields -MHD -solar wind -turbulence

Observations of the magnetic field and plasma in the heliosheath by Voyager 2 from 2007.7 to 2009.4

“…The data are plotted with a time delay corresponding to the propagation of the solar wind and frozen-in magnetic fields at a speed of 400 km/s from the sun to the positions of V1 and V2. Previous studies have shown that the latitudinal extent of the HCS changes little, O(10°), with increasing distance from the Sun out to 40 AU and even as far as the TS at ≈90 AU [Burlaga et al, 2007].…”

“…Figure 3 shows that the projected HCS moved past Voyager 1 (V1) after 2006.33 and was below the latitude of the V1 throughout the period discussed here. Voyager 1 observed negative polarity magnetic fields from the northern polar coronal hole throughout the interval from 2006.3 to 2006.9 [Burlaga et al, 2007]. It is surprising that V1 observed a large oscillation of B during this interval.…”

Turbulent Amplification of a Magnetic Field Driven by the Dynamo Effect at Rippled Shocks

“…For t τ the term proportional to v 2 A in the denominator is negligible and B grows exponentially (B/B 0 ∼ e t/τ ). For times t τ the term proportional to v 2 A dominates over the first term and the saturation is attained: field (Burlaga et al 2007), and the term rB 0 is no longer negligible with respect to B turb and a different analysis is needed.…”

The Phase Coherence of Interstellar Density Fluctuations

“…For instance, PCI, similar to Tsallis statistics, was first used for solar wind studies (Burlaga et al 2006(Burlaga et al , 2007(Burlaga et al , 2009. This is the case for the PCI.…”