MAGNETIC FIELD STRENGTH FLUCTUATIONS IN THE HELIOSHEATH:VOYAGER 1OBSERVATIONS DURING 2009

Abstract

We analyze the "microscale fluctuations" of the magnetic field strength B on a scale of several hours observed by Voyager1 (V1) in the heliosheath during 2009. The microscale fluctuations of B range from coherent to stochastic structures. The amplitude of microscale fluctuations of B during 1 day is measured by the standard deviation (SD) of 48 s averages of B. The distribution of the daily values of SD is lognormal. SD(t) from day of year (DOY) 1 to 331, 2009, is very intermittent. SD(t) has a 1/f or "pink noise" spectrum on scales from 1 to 100 days, and it has a broad multifractal spectrum f(α) with 0.57 α 1.39. The time series of increments SD(t + τ ) − SD(t) has a pink noise spectrum with α = 0.88 ± 0.14 on scales from 1 to 100 days. The increments have a Tsallis (q-Gaussian) distribution on scales from 1 to 165 days, with an average q = 1.75 ± 0.12. The skewness S and kurtosis K have Gaussian and lognormal distributions, respectively. The largest spikes in K(t) and S(t) are often associated with a change in B across a data gap and with identifiable physical structures. The "turbulence" observed by V1 during 2009 was weakly compressible on average but still very intermittent, highly variable, and highly compressible at times. The turbulence observed just behind the termination shock by Voyager 2 was twice as strong. These observations place strong constraints on any model of "turbulence" in the heliosheath.

MAGNETIC FIELD STRENGTH FLUCTUATIONS AND THEq-TRIPLET IN THE HELIOSHEATH:VOYAGER 2OBSERVATIONS FROM 91.0 TO 94.2 AU AT LATITUDE 30° S

“…The parameter q is called the "non-extensivity index", and it is often denoted q stat (Tsallis 2009). The observed value of q is in good agreement with the value q = 1.67 observed in the heliosheath by V1 during 2009 (Burlaga & Ness 2012a), and it is the same as that observed by V1 during 2011 (Burlaga & Ness 2012b). The value q = 1.75 (which is consistent with q = 1.7) was found by Burlaga & Viñas (2005) and Burlaga et al (2007) in the distant supersonic solar wind.…”

“…Thus, we obtain α min = 0.73 ± 0.03 and α max = 1.35 ± 0.03. These results are similar to those obtained in the heliosheath by Burlaga & Ness (2012a). A narrower multifractal spectrum was observed just behind the termination shock, with α min = 0.84 ± 0.02 and α max = 1.18 ± 0.02 which are the basic parameters describing the multifractal spectrum (Burlaga & Ness 2010).…”

“…In the supersonic solar wind, the large-scale fluctuations of B have correlations on various scales. A multifractal structure on scales from one to several days was observed at all distances between 1 AU and the termination shock (Burlaga 1991a(Burlaga , 1991b, in the disturbed heliosheath just behind the termination shock (Burlaga et al 2006;Macek 2007;Macek & Szczepaniak (2008, and deep into the heliosheath Burlaga & Ness 2012a).…”

“…The hourly and daily averages are derived from 48 s component averages. The method used to prepare "clean" 48 s averages and the associated hour and daily averages of the magnetic field is discussed briefly by Burlaga & Ness (2012a).…”

Cosmic ray anisotropies near the heliopause

“…Moreover, Burlaga & Ness (2012) report that the turbulence conditions in the heliosheath are drastically different from those in the supersonic solar wind. This may cause "traditional" diffusion coefficients, such as the FLRW coefficient, to become inaccurate close to the HP.…”