Coronal Magnetic Fields from the Effect of the Double Inversion of Circular Polarization of Radio Emission

Bogod, V. M.; Gelfreikh, G. B.; Ryabov, B. I.; Hafizov, S. R.

doi:10.1017/s0252921100029298

Cited by 3 publications

(3 citation statements)

References 1 publication

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“…If we consider the spectrum of Stokes V at a point in the limbward part of an active region, we expect inversion to occur at wavelengths longer than a critical value, where C ≥ 1 (note that the coupling coefficient goes like λ −4 , see Equation 31). In a number of cases a second inversion is observed at longer wavelengths (Bogod et al, 1993;Ryabov, 1998). This can be explained by the radiation crossing two TFRs on its way to the observer, something that may happen under complex morphologies of the magnetic field.…”

Section: Observationsmentioning

confidence: 99%

Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

Alissandrakis

Gary

2021

Front. Astron. Space Sci.

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The structure of the upper solar atmosphere, on all observable scales, is intimately governed by the magnetic field. The same holds for a variety of solar phenomena that constitute solar activity, from tiny transient brightening to huge Coronal Mass Ejections. Due to inherent difficulties in measuring magnetic field effects on atoms (Zeeman and Hanle effects) in the corona, radio methods sensitive to electrons are of primary importance in obtaining quantitative information about its magnetic field. In this review we explore these methods and point out their advantages and limitations. After a brief presentation of the magneto-ionic theory of wave propagation in cold, collisionless plasmas, we discuss how the magnetic field affects the radio emission produced by incoherent emission mechanisms (free-free, gyroresonance, and gyrosynchrotron processes) and give examples of measurements of magnetic filed parameters in the quiet sun, active regions and radio CMEs. We proceed by discussing how the inversion of the sense of circular polarization can be used to measure the field above active regions. Subsequently we pass to coherent emission mechanisms and present results of measurements from fiber bursts, zebra patterns, and type II burst emission. We close this review with a discussion of the variation of the magnetic field, deduced by radio measurements, from the low corona up to ~ 10 solar radii and with some thoughts about future work.

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Section: Observationsmentioning

confidence: 99%

Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

Alissandrakis

Gary

2021

Front. Astron. Space Sci.

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“…Double inversion of the circular polarization was detected for the first time by Bogod et al (1993a) in the spectral polarization observations with a new Panoramic Spectrum Analyzer (PAS, see Bogod et al 1993b) of the RATAN-600 radiotelescope on January 9-10, 1992. It was attributed to the electromagnetic mode coupling in the regions of the quasi-transverse propagation in the solar corona (hereafter, QT-regions) (Zheleznyakov 1970).…”

Section: Introductionmentioning

confidence: 98%

“…The detection by Bogod et al (1993a) of the double inversion in the centimeter wavelength range raises at least two questions: how one can verify the reality of the phenomenon and what is the multiplicity of the detectable inversions? Trying to verify if the multiple inversion is due to the wave mode coupling in QT-regions, in the present paper we compare the observed radio spectrum p v (A) of an AR with the theoretical spectrum (Section 3).…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Multiple Inversion of Circular Polarization in Solar Microwave Local Sources

Ryabov¹

1997

Open Astronomy

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Abstract. The multiple inversion of the sign of circular polarization in the microwave local source of an active region is interpreted as a result of the quasi-transverse propagation of microwaves. For further analysis of the inversion, mathematical restrictions on the degree of circular polarization are drawn using the wave mode coupling theory. The polarization depression at wavelengths, adjacent to the wavelength of zero circular polarization, is estimated for three active regions. Also, the dependence of multiple inversion on wavelength as a result of multiple crossing of the coronal QT-regions is verified. We suggest a hierarchy of coronal arches of active regions as a structure responsible for the multiple inversion of circular polarization of microwaves.

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Band-splitting of coronal and interplanetary type II bursts

Vršnak

Magdalenić

Auraß

et al. 2002

A&A

177

147

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Abstract. Type II radio bursts recorded in the metric wavelength range are excited by MHD shocks traveling through the solar corona. They often expose the fundamental and harmonic emission band, both frequently being split in two parallel lanes that show a similar frequency drift and intensity behaviour. Our previous paper showed that band-splitting of such characteristics is a consequence of the plasma emission from the upstream and downstream shock regions. Consequently, the split can be used to evaluate the density jump at the shock front and to estimate the shock Mach number, which in combination with the shock speed inferred from the frequency drift provides an estimate of the Alfvén velocity and the magnetic field in the ambient plasma. In this paper such a procedure is applied to 18 metric type II bursts with the fundamental band starting frequencies up to 270 MHz. The obtained values show a minimum of the Alfvén velocity at the heliocentric distance R ≈ 2 amounting to v A ≈ 400-500 km s −1 . It then increases achieving a local maximum of v A ≈ 450-700 km s −1 at R ≈ 2.5. The implications regarding the process of formation and decay of MHD shocks in the corona are discussed. The coronal magnetic field in the range 1.3 < R < 3 decreases as R −3 to R −4 , or H −1.5 to H −2 if expressed as a function of the height. The results are compared with other estimates of the coronal magnetic field in the range 1 < R < 10. Combined data show that below H < 0.3 the magnetic field is dominated by active region fields, whereas above H = 1 it becomes radial, behaving roughly as B = 2 × R −2 with a plausible value of B ≈ 5 nT at 1 a.u.

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Coronal Magnetic Fields from the Effect of the Double Inversion of Circular Polarization of Radio Emission

Cited by 3 publications

References 1 publication

Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

Analysis of the Multiple Inversion of Circular Polarization in Solar Microwave Local Sources

Band-splitting of coronal and interplanetary type II bursts

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