Intermittency and q-Gaussian Distributions in the Magnetic Field of the Very Local Interstellar Medium (VLISM) Observed by Voyager 1 and Voyager 2

Abstract

Voyager 1 (V1) observed q-Gaussian distributions of 1 hr increments of the components the magnetic field B throughout the very local interstellar medium (VLISM) on scales on the order of 1 year, from 2013 through 2019, excluding the disturbed regions near two shocks. The intermittency of the components of B is described by q from the q-Gaussian distributions of 1 hr increments B as well as by the kurtosis K derived from the time series of the increments of B. Farther than ∼5 au from the heliopause, Voyager 1 observed larger intermittency in the fluctuations of the predominantly transverse component B N and in the nearly longitudinal component B T of B. The average values of q for the B N component and transverse B T component for these data in the VLISM are q=1.32±0.03 and q=1.22±0.03, respectively. The corresponding average values of the kurtosis are K=7.2 and K=4.9. Voyager 2 (V2) crossed the heliopause on 2018 November 5. Near the heliopause, in 2019, V2 observed large intermittency in 1 hr increments of the compressive component B T and smaller intermittency in B N . The Voyager 2 observations give q=1.51±0.06 and q=1.17±0.06 for the B N and B T components of B, respectively, as well as K=7.2 and K=12.3, respectively. The intermittency in B T and B N , observed by V2 near the heliopause was significantly larger than that observed by V1 when it was near the heliopause.

Magnetic Field Observations in the Very Local Interstellar Medium by Voyagers 1 and 2

“…Following the Jump in B ("sh") during 2020 at Voyager 2 In addition to the relatively long wavelength fluctuations described in the previous section, V2 observed small-scale intermittency in the VLISM (Burlaga et al 2020b). In this section we show that intermittency was observed during 2020 in the VLISM at ∼4−7 au from the heliopause.…”

“…V1 observed transverse (Alfvénic) fluctuations of B between 131.40 and 135.98 au at latitudes 34°.6-34°.7 N (∼10-14 au beyond the heliopause) from 2015/DOY 145 to 2016/DOY 248 (Burlaga et al 2018). The most recent V1 observations continued to show the presence of transverse fluctuations of B in the VLISM from 141.44 to 146.01 au at 34°.7-34°.8 N (∼20-24 au from the heliopause) between 2018/DOY 5 and 2019/DOY 178 (Burlaga et al 2020b). Zank et al (2017) developed an interpretation that only compressible fast magnetosonic modes can be transmitted from the inner heliosheath across the heliopause and into the VLISM, thus providing an explanation for the observations of Burlaga et al ( , 2015.…”

Exploring turbulence from the Sun to the local interstellar medium: Current challenges and perspectives for future space missions

“…The magnetic compressibility, as defined by the ratio of the power spectrum of |B| and the trace power spectrum, decays with distance (Burlaga et al, 2018;Zank et al, 2019;Burlaga et al, 2020b;Zhao et al, 2020;Fraternale and Pogorelov, 2021), but surprisingly remains large at fine scales, at V1 (Fraternale and Pogorelov, 2021). Intermittency of VLISM fluctuations and fine-scale features (0.01 ≲ k ⊥ d i ≲ 1) have been observed only recently by Fraternale et al (2019a); Fraternale et al (2020b); Burlaga et al (2020a). This results suggest that local processes may operate at scales below the proton-proton Coulomb-collisional mean free path (∼0.3-5 AU, for temperature values between ∼7,500 and ∼40,000 K).…”

Turbulence in the Outer Heliosphere

“…As discussed by Burlaga et al (2020a), there is no compelling direct evidence in Voyager data for magnetic reconnection, even in the distant IHS. On the other hand, observations alone are not sufficient to conclude that magnetic reconnection does not occur and, arguably, reconnection cannot really be separated from turbulence (Lazarian and Vishniac 1999;Eyink et al 2011;Eyink 2015).…”

“…Intermittency in the VLISM has been observed by Fraternale et al (2019a), and a detailed investigation of quiet intervals was carried out by Burlaga et al (2020a) using 1 h increments. They have shown that the intermittency in the transverse component is dominant in the VLISM beyond several AU from the HP.…”