Cross and magnetic helicity in the outer heliosphere from Voyager 2 observations

Iovieno, Michele; Gallana, Luca; Fraternale, Federico; Richardson, J. D.; Opher, M.; Tordella, Daniela

doi:10.1016/j.euromechflu.2015.08.009

Cited by 13 publications

(13 citation statements)

References 36 publications

(69 reference statements)

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“…METHODS FOR SPECTRAL ANALYSIS Computing power spectra over a broad range of frequencies in the outer heliosphere is challenging because of the sparsity of the 48 s data (70% of magnetic field are missing). Fraternale et al (2016), Gallana et al (2016), Iovieno et al (2016) and Fraternale (2017) have demonstrated that a careful application of different, independent, techniques makes it possible to recover the spectrum with proper accuracy (e.g., with the accuracy of 10% or lower in the spectral index. The techniques description and numerical codes have been provided in the above references.…”

Section: Appendixmentioning

confidence: 99%

Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium

Fraternale

Pogorelov

Richardson

et al. 2019

ApJ

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The understanding of inertial-scale dynamics in the heliosheath is not yet thorough. Magnetic field fluctuations across the inner heliosheath and the local interstellar medium are here considered to provide accurate and highly resolved statistics over different plasma conditions between 88 and 136 AU. By using the unique in situ 48-s measurements from the Voyager Interstellar Mission, we investigate different fluctuation regimes at the magnetohydrodynamic (MHD) scales, down to the MHD-to-kinetic transition. We focus on a range of scales exceeding five frequency decades (5 × 10 −8 < f < 10 −2 Hz), which is unprecedented in literature analysis. A set of magnetic field data for eight intervals in the inner heliosheath, in both unipolar and sector regions, and four intervals in the local interstellar medium is being used for the analysis. Results are set forth in terms of the power spectral density, spectral compressibility, structure functions and intermittency of magnetic field increments. In the heliosheath, we identify the energy-injection regime displaying a ∼ 1/f energy decay, and the inertial-cascade regime. Here, the power spectrum is anisotropic and dominated by compressive modes, with intermittency that can reach kurtosis values up to ten. In the interstellar medium the structure of turbulence is anisotropic as well, with transverse fluctuations clearly prevailing after May 2015. Here, we show that intermittent features occur only at scales smaller than 10 −6 Hz.

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Section: Appendixmentioning

confidence: 99%

Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium

Fraternale

Pogorelov

Richardson

et al. 2019

ApJ

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“…However, the case studies of D'Amicis & Bruno (2015) andD'Amicis et al (2016) hint that when heavy ion measurements are not available the Alfvénicity of the solar wind fluctuations may be a more reliable proxy for solar wind origin than speed. The problem with using Alfvénicity as a categorisation variable is that the solar wind becomes systematically less Alfvénic with distance (Roberts et al 1987;Bruno et al 2007;Iovieno et al 2016), due to both small scale turbulent evolution and large scale velocity shears and interaction regions (Bruno et al 2006). This means not all solar wind that started off Alfvénic near the sun is still Alfvénic when it is measured at 1 AU.…”

Section: Introductionmentioning

confidence: 99%

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Stansby

Horbury

Matteini

2018

Monthly Notices of the Royal Astronomical Society

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Robustly identifying the solar sources of individual packets of solar wind measured in interplanetary space remains an open problem. We set out to see if this problem is easier to tackle using solar wind measurements closer to the Sun than 1 AU, where the mixing and dynamical interaction of different solar wind streams is reduced. Using measurements from the Helios mission, we examined how the proton core temperature anisotropy and cross helicity varied with distance. At 0.3 AU there are two clearly separated anisotropic and isotropic populations of solar wind, that are not distinguishable at 1 AU. The anisotropic population is always Alfvénic and spans a wide range of speeds. In contrast the isotropic population has slow speeds, and contains a mix of Alfvénic wind with constant mass fluxes, and non-Alfvénic wind with large and highly varying mass fluxes. We split the in-situ measurements into three categories according these observations, and suggest that these categories correspond to wind that originated in the core of coronal holes, in or near active regions or the edges of coronal holes, and as small transients form streamers or pseudostreamers. Although our method by itself is simplistic, it provides a new tool that can be used in combination with other methods for identifying the sources of solar wind measured by Parker Solar Probe and Solar Orbiter.

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“…High data sparsity represents one of the major challenges to spectral analysis. A targeted breakthrough is to provide a simple and efficient way to obtain spectral information on the full frequency range contained in long, gappy temporal data sets in the many different plasma regimes sampled by the Voyager mission, see, e.g., two preliminary works by our group Fraternale et al [] and Iovieno et al []. This advancement may in the intermediate term prepare the ground for the analysis of V2 local interstellar medium plasma data and in the long term to prepare a spectral analysis standard for observational data coming from future scientific space missions inside the interstellar medium.…”

Section: Methods For Spectral Analysis Of Gapped Datamentioning

confidence: 99%

Voyager 2 solar plasma and magnetic field spectral analysis for intermediate data sparsity

et al. 2016

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The Voyager probes are the furthest, still active, spacecraft ever launched from Earth. During their 38 year trip, they have collected data regarding solar wind properties (such as the plasma velocity and magnetic field intensity). Unfortunately, a complete time evolution of the measured physical quantities is not available. The time series contains many gaps which increase in frequency and duration at larger distances. The aim of this work is to perform a spectral and statistical analysis of the solar wind plasma velocity and magnetic field using Voyager 2 data measured in 1979, when the gap density is between the 30% and 50%. For these gap densities, we show the spectra of gapped signals inherit the characteristics of the data gaps. In particular, the algebraic decay of the intermediate frequency range is underestimated and discrete peaks result not from the underlaying data but from the gap sequence. This analysis is achieved using five different data treatment techniques coming from the multidisciplinary context: averages on linearly interpolated subsets, correlation without data interpolation, correlation of linearly interpolated data, maximum likelihood data reconstruction, and compressed sensing spectral estimation. With five frequency decades, the spectra we obtained have the largest frequency range ever computed at five astronomical units from the Sun; spectral exponents have been determined for all the components of the velocity and magnetic field fluctuations. Void analysis is also useful in recovering other spectral properties such as micro and integral scales.

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Cross and magnetic helicity in the outer heliosphere from Voyager 2 observations

Cited by 13 publications

References 36 publications

Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium

Magnetic Turbulence Spectra and Intermittency in the Heliosheath and in the Local Interstellar Medium

Diagnosing solar wind origins usingin situmeasurements in the inner heliosphere

Voyager 2 solar plasma and magnetic field spectral analysis for intermediate data sparsity

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