Possible evidence for coronal Alfvén waves

Hollweg, Joseph V.; Bird, M. K.; Volland, H.; Edenhofer, P.; Stelzried, C. T.; Seidel, B. L.

doi:10.1029/ja087ia01p00001

Cited by 122 publications

(108 citation statements)

References 13 publications

(11 reference statements)

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“…Examples of results which have been obtained with spacecraft transmitters are Stelzried et al (1970), Hollweg et al (1982), Pätzold et al (1987), Bird & Edenhofer (1990), Andreev et al (1997), Jensen et al (2013a,b), and Efimov et al (2015).…”

Section: Losmentioning

confidence: 99%

VLA Measurements of Faraday Rotation through Coronal Mass Ejections

et al. 2017

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Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the Sun that play an important role in space weather. Faraday rotation (FR) is the rotation of the plane of polarization that results when a linearly polarized signal passes through a magnetized plasma such as a CME and is proportional to the path integral through the plasma of the electron density and the line of sight component of the magnetic field.FR observations of a source near the Sun can provide information on the plasma structure of a CME shortly after launch; however, separating the contribution of the plasma density from the line of sight magnetic field is challenging.We report on simultaneous white-light and radio observations made of three CMEs in August 2012. We made sensitive Very Large Array (VLA) full-polarization observations using 1 − 2 GHz frequencies of a "constellation" of radio sources through the solar corona at heliocentric distances that ranged from 6 − 15R ⊙ . Of the nine sources observed, three were occulted by CMEs: two sources (0842+1835 and 0900+1832) were occulted by a single CME and one source (0843+1547) was occulted by two CMEs. In addition to our radioastronomical observations, which represent one of the first active hunts for CME Faraday rotation since Bird et al. (2007) and Jensen & Russell (2008), as well as previous CME FR observations by Bird et al. (1985).

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Section: Losmentioning

confidence: 99%

VLA Measurements of Faraday Rotation through Coronal Mass Ejections

et al. 2017

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“…In this case, the radio scintillation observations allow for an estimate of the turbulent magnetic field in the inner solar wind to be extracted, and we can use the procedures and arguments employed previously in the literature (e.g. Hollweg et al, 1982;Sakurai and Spangler, 1994;, to assess the viability of wave heating and acceleration mechanisms. The following discussion is also influenced by the arguments of Roberts (1989).…”

Section: Astrophysical Significance Of a Small Density Modulation Indexmentioning

confidence: 99%

“…It needs to be acknowledged that other remote sensing observations of the inner solar wind have been cited as evidence for δb/B 0 δn/n. Hollweg et al (1982) analyzed variations in Faraday rotation measure and radio phase of a spacecraft transmitter signal. Faraday rotation is proportional to the path integral of the plasma density and line-of-sight component of the magnetic field, and thus, contains information on the magnetic field and its fluctuations.…”

Section: Even If Similar Base Fluxes Are Injected In Open Andmentioning

confidence: 99%

“…The phase measurement is sensitive to the path integral of density alone. Hollweg et al (1982) examined the minimalist possibility that both Faraday rotation and phase variations could be accounted for by density fluctuations in a uniform magnetic field. They found that this extreme and nearly unphysical model could be excluded, since the required magnetic field would have to be about a factor of 5 higher than indicated by independent estimates.…”

Section: Even If Similar Base Fluxes Are Injected In Open Andmentioning

confidence: 99%

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The small amplitude of density turbulence in the inner solar wind

Spangler

2003

Nonlin. Processes Geophys.

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Abstract. Very Long Baseline Interferometer (VLBI) observations were made of radio sources close to the Sun, whose lines of sight pass through the inner solar wind (impact parameters 16-26 R ). Power spectra were analyzed of the interferometer phase fluctuations due to the solar wind plasma. These power spectra provide information on the level of plasma density fluctuations on spatial scales of roughly one hundred to several thousand kilometers. By specifying an outer scale to the turbulence spectrum, we can estimate the root-mean-square (rms) amplitude of the density fluctuations. The data indicate that the rms fluctuation in density is only about 10% of the mean density. This value is low, and consistent with extrapolated estimates from more distant parts of the solar wind. Physical speculations based on this result are presented.

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“…A comparison of the Faraday RMs of a sample of radio sources viewed through the solar corona to the RMs of the same sources observed far from the Sun reveals the presence of excess Faraday rotation that can be interpreted as originating in the solar corona. Prior work has involved monitoring the variation of linearly polarized S band (2.3 GHz) radio signals as they were occulted by the solar corona from interplanetary probes such as Pioneer VI (Stelzried et al 1970) and Helios (Hollweg et al 1982;Pätzold et al 1987). Double-frequency decimetric observations of the Faraday rotation of polarized extragalactic radio sources have also been exploited successfully (Sakurai & Spangler 1994;Mancuso & Spangler 1999Spangler 2005;Ingleby et al 2007) using the Very Large Array (VLA) radio telescope operated by the US National Radio Astronomy Observatory (NRAO).…”

Section: Introductionmentioning

confidence: 99%

Assessing the tilt of the solar magnetic field axis through Faraday rotation observations

Mancuso

Garzelli

2007

A&A

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Context. Faraday rotation measurements of extragalactic radio sources during coronal occultation allow assessment of both the electron density distribution and the three-dimensional magnetic field topology in the outer solar corona. Aims. We simulate the three-dimensional structure of both the coronal magnetic field and the electron density distribution in order to reproduce the excess Faraday rotation measures (RMs) of the occulted radio sources observed during solar activity minimum. In particular, we infer the tilt of the solar magnetic axis with respect to the rotation axis. Methods. We compare the output of the model with Very Large Array (VLA) radio polarimetric measurements of a sample of extragalactic sources observed in May 1997. Information on the magnetic field geometry can be retrieved by fine-tuning the set of model free parameters that best describe the observations. Results. We find that predicted and observed Faraday rotation measures are in excellent agreement, thus supporting the model. Our best-fitting model yields a tilt angle θ RB = 3.3 • of the solar magnetic axis with respect to the solar rotation axis around Carrington Rotation 1923. This result is consistent with analogous but independent estimates computed from the expansion coefficients of the photospheric field observed at the Wilcox Solar Observatory (WSO).

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Possible evidence for coronal Alfvén waves

Cited by 122 publications

References 13 publications

VLA Measurements of Faraday Rotation through Coronal Mass Ejections

VLA Measurements of Faraday Rotation through Coronal Mass Ejections

The small amplitude of density turbulence in the inner solar wind

Assessing the tilt of the solar magnetic field axis through Faraday rotation observations

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