Faraday-rotation fluctuations from radio-sounding measurements of the circumsolar plasma using polarized signals from the HELIOS-1 and HELIOS-2 space probes

Ефимов, А. И.; Луканина, Л. А.; Rogashkova, A. I.; Samoznaev, L. N.; Чашей, И. В.; Bird, M. K.; Paëtzold, M.

doi:10.1134/s1063772915040022

Cited by 8 publications

(16 citation statements)

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“…Efimov et al . [] reported an FRF spectral index (here presented as a negative value) of −2.4 + 0.2 at 2 R ⊙ and a trend of decreasing magnitude with increasing distance. Our determination of α = − 2.64 seems a credible extension of their spectral index curve to solar offset ~1.6–1.9 R ⊙ .…”

Section: Discussionmentioning

confidence: 79%

“…The power spectral index can give clues on the presence of temporal‐spatial turbulence in the plasma and may indicate the development of an energy cascade that underlies wave turbulence models of coronal heating. FRF spectra from the HELIOS missions have shown power spectra over the ~1–10 mHz range with a about −1.6 at 6 R ⊙ with spectral steepening to −2.4 at 2 R ⊙ [ Efimov et al ., , ]. We therefore sought to confirm the presence of a power spectrum in the millihertz frequency range and obtain the spectral indices below solar offset 2 R ⊙ .…”

Section: Observations and Data Processingmentioning

confidence: 99%

“…Recent reviews by Efimov et al . [, ] illustrate a broad range of FRF frequencies, from milliHertz (mHz) scales extending into the sub‐mHz range.…”

Section: Introductionmentioning

confidence: 99%

“…Lowfrequency FR fluctuations with time scales up to hours are believed to represent Alfvén waves [Hollweg et al, 1982] and have been implicated in the overall process of energy transport required for heating and acceleration of the solar wind [Chashei, 1989;Hollweg et al, 2010]. Recent reviews by Efimov et al [2015aEfimov et al [ , 2015b illustrate a broad range of FRF frequencies, from milliHertz (mHz) scales extending into the sub-mHz range.…”

Section: Introductionmentioning

confidence: 99%

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Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

et al. 2017

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Faraday rotation (FR) of transcoronal radio transmissions from spacecraft near superior conjunction enables study of the temporal variations in coronal plasma density, velocity, and magnetic field. The MESSENGER spacecraft 8.4 GHz radio, transmitting through the corona with closest line‐of‐sight approach 1.63–1.89 solar radii and near‐equatorial heliolatitudes, was recorded soon after the deep solar minimum of solar cycle 23. During egress from superior conjunction, FR gradually decreased, and an overlay of wave‐like FR fluctuations (FRFs) with periods of hundreds to thousands of seconds was found. The FRF power spectrum was characterized by a power law relation, with the baseline spectral index being −2.64. A transient power increase showed relative flattening of the spectrum and bands of enhanced spectral power at 3.3 mHz and 6.1 mHz. Our results confirm the presence of coronal FRF similar to those described previously at greater solar offset. Interpreted as Alfvén waves crossing the line of sight radially near the proximate point, low‐frequency FRF convey an energy flux density higher than that of the background solar wind kinetic energy, but only a fraction of that required to accelerate the solar wind. Even so, this fraction is quite variable and potentially escalates to energetically significant values with relatively modest changes in estimated magnetic field strength and electron concentration. Given the uncertainties in these key parameters, as well as in solar wind properties close to the Sun at low heliolatitudes, we cannot yet confidently assign the quantitative role for Alfvén wave energy from this region in driving the slow solar wind.

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Section: Discussionmentioning

confidence: 79%

Section: Observations and Data Processingmentioning

confidence: 99%

“…Recent reviews by Efimov et al . [, ] illustrate a broad range of FRF frequencies, from milliHertz (mHz) scales extending into the sub‐mHz range.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

et al. 2017

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“…These FR fluctuations are of interest in the study of coronal Alfvén and magnetosonic waves, and turbulence, but not evaluated here. See works by Wexler et al (2017) and for investigation of the FR fluctuations in these MESSSENGER data and reports on earlier FR observations by others (Andreev et al, 1997;Chashei et al, 2000;Efimov et al, 2015;Hollweg et al, 1982Hollweg et al, , 2010.…”

Section: Observational Datamentioning

confidence: 91%

Radio Occultation Observations of the Solar Corona Over 1.60–1.86 R_⊙: Faraday Rotation and Frequency Shift Analysis

et al. 2019

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The study of coronal energy transport, central to the solar wind acceleration problem, relies upon accurate representation of magnetic fields and plasma electron densities. This information is difficult to obtain in middle‐to‐lower coronal regions that may contain complex magnetic structures. Faraday rotation (FR) solar radio occultation observations, which reveal line‐of‐sight (LOS) integrated product of the coronal magnetic field and electron density, can help characterize the coronal environment and constrain magnetic field strengths. Global magnetohydrodynamic (MHD) models use specified synoptic solar surface magnetograms and may be used to facilitate FR interpretation by estimating detailed magnetic field properties along the radio LOS. We present a hybrid FR analysis incorporating magnetic field solutions from an MHD coronal model, and an electron density radial profile conforming to radio frequency shift observations. The FR modeled by the hybrid method is compared to MErcury Surface, Space ENvironment, GEochemistry and Ranging spacecraft radio FR observations through a coronal region of low heliolatitudes and radial distance 1.60–1.86 R⊙ from the heliocenter, collected during a state of relative solar quiescence. The hybrid model reasonably reproduces the form, polarity, and magnitude of the observed FR. For this specific coronal region, the calculated radial profile of electron concentrations and varied magnetic field strengths indicate Alfvén wave speeds below 50 km/s close to the point of closest approach but near 400 km/s in adjacent regions along the sounding LOS. The new approach of combining MHD models with radio sounding observations supports study of MHD wave processes in the challenging middle‐coronal magneto‐ionic environment.

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Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

Beardsley

Johnston‐Hollitt

Trott

et al. 2019

Publ. Astron. Soc. Aust.

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The Murchison Widefield Array (MWA) is an open access telescope dedicated to studying the low frequency (80-300 MHz) southern sky. Since beginning operations in mid 2013, the MWA has opened a new observational window in the southern hemisphere enabling many science areas. The driving science objectives of the original design were to observe 21 cm radiation from the Epoch of Reionisation (EoR), explore the radio time domain, perform Galactic and extragalactic surveys, and monitor solar, heliospheric, and ionospheric phenomena. All together 60+ programs recorded 20,000 hours producing 146 papers to date. In 2016 the telescope underwent a major upgrade resulting in alternating compact and extended configurations. Other upgrades, including digital back-ends and a rapid-response triggering system, have been developed since the original array was commissioned. In this paper we review the major results from the prior operation of the MWA, and then discuss the new science paths enabled by the improved capabilities. We group these science opportunities by the four original science themes, but also include ideas for directions outside these categories.

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Faraday-rotation fluctuations from radio-sounding measurements of the circumsolar plasma using polarized signals from the HELIOS-1 and HELIOS-2 space probes

Cited by 8 publications

References 16 publications

Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

Radio Occultation Observations of the Solar Corona Over 1.60–1.86 R_⊙: Faraday Rotation and Frequency Shift Analysis

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

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Faraday-rotation fluctuations from radio-sounding measurements of the circumsolar plasma using polarized signals from the HELIOS-1 and HELIOS-2 space probes

Cited by 8 publications

References 16 publications

Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

Radio Occultation Observations of the Solar Corona Over 1.60–1.86 R⊙: Faraday Rotation and Frequency Shift Analysis

Science with the Murchison Widefield Array: Phase I results and Phase II opportunities

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Resources

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Radio Occultation Observations of the Solar Corona Over 1.60–1.86 R_⊙: Faraday Rotation and Frequency Shift Analysis