Polarization of fundamental type III radio bursts

Wentzel, Donat G.

doi:10.1007/bf00153791

Cited by 18 publications

(10 citation statements)

References 24 publications

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“…Effects such as mode coupling due to magnetic fields (e.g. Zheleznyakov & Zlotnik, 1964), and scattering due to low-frequency waves (Wentzel, 1984;Melrose, 1989a), or kinetic Alfven waves (Sirenko et al, 2002) during propagation are certainly able to reduce the degree of polarisation but cannot explain why fully polarised emission is never seen. Wentzel (1984) therefore proposed that the emission was depolarised to some extent within the source region itself, and that this was inherent to the emission process.…”

Section: Polarisationmentioning

confidence: 99%

“…Zheleznyakov & Zlotnik, 1964), and scattering due to low-frequency waves (Wentzel, 1984;Melrose, 1989a), or kinetic Alfven waves (Sirenko et al, 2002) during propagation are certainly able to reduce the degree of polarisation but cannot explain why fully polarised emission is never seen. Wentzel (1984) therefore proposed that the emission was depolarised to some extent within the source region itself, and that this was inherent to the emission process. For harmonic emission, it was initially thought that the Langmuir waves involved would coalesce head on, and therefore Melrose & Sy (1972); Melrose et al (1978) and the correction by Melrose et al (1980) concluded that harmonic emission must be weakly O-mode polarised.…”

Section: Polarisationmentioning

confidence: 99%

See 1 more Smart Citation

A review of solar type III radio bursts

Reid

Ratcliffe

2014

Res. Astron. Astrophys.

335

217

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Solar type III radio bursts are an important diagnostic tool in the understanding of solar accelerated electron beams. They are a signature of propagating beams of nonthermal electrons in the solar atmosphere and the solar system. Consequently, they provide information on electron acceleration and transport, and the conditions of the background ambient plasma they travel through. We review the observational properties of type III bursts with an emphasis on recent results and how each property can help identify attributes of electron beams and the ambient background plasma. We also review some of the theoretical aspects of type III radio bursts and cover a number of numerical efforts that simulate electron beam transport through the solar corona and the heliosphere.

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Section: Polarisationmentioning

confidence: 99%

Section: Polarisationmentioning

confidence: 99%

A review of solar type III radio bursts

Reid

Ratcliffe

2014

Res. Astron. Astrophys.

335

217

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show abstract

“…Since lower intrinsic polarization can occur only if the initial frequency exceeds the x-mode cutoff frequency (f x cut ), the previous expectation that LMC and nonlinear processes would produce only o-mode radiation meant that depolarization theories were mainly investigated. These include mode coupling [29], scattering by low frequency waves [30,31], and reflection at density inhomogeneities [32]. However, Mjølhus [20] showed that an incident xmode wave perpendicular to B 0 can undergo LMC into an ES wave and a reflected x-mode wave at ionospheric density irregularities.…”

Section: Introductionmentioning

confidence: 99%

Mode Conversion of Langmuir to Electromagnetic Waves with Parallel Inhomogeneity in the Solar Wind and the Corona

Kim¹,

Cairns²,

Robinson³

2008

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Linear mode conversion of Langmuir waves to radiation near the plasma frequency at density gradients is potentially relevant to multiple solar radio emissions, ionospheric radar experiments, laboratory plasma devices, and pulsars. Here we study mode conversion in warm magnetized plasmas using a numerical electron fluid simulation code with the density gradient parallel to the ambient magnetic field B0 for a range of incident Langmuir wavevectors. Our results include: (1) Both oand x-mode waves are produced for Ω ∝ (ωL) 1/3 (ωc/ω) 1, contrary to previous ideas. Only o mode is produced for Ω 1.5. Here ωc is the (angular) electron cyclotron frequency, ω the angular wave frequency, and L the length scale of the (linear) density gradient. (2) In the unmagnetized limit, equal amounts of o-and x-mode radiation are produced. (3) The mode conversion window narrows as Ω increases. (4) As Ω increases the total electromagnetic field changes from linear to circular polarization, with the o-and x-mode signals remaining circularly polarized. (5) The conversion efficiency to the x mode decreases monotonically as Ω increases while the o-mode conversion efficiency oscillates due to an interference phenomenon between incoming and reflected Langmuir/z modes. (6) The total conversion efficiency for wave energy from the Langmuir/z mode to radiation is typically less than 10%, but the corresponding power efficiencies differ by the ratio of the group speeds for each mode and are of order 50 − 70%. (7) The interference effect and the disappearance of the x mode at Ω 1 can be accounted for semiquantitatively using a WKB-like analysis. (8) Constraints on density turbulence are developed for the x mode to be generated and be able to propagate from the source. (9) Standard parameters for the corona and the solar wind near 1 AU suggest that linear mode conversion should produce both o-and x-mode radiation for solar and interplanetary radio bursts. It is therefore possible that linear mode conversion under these conditions might explain the weak total circular polarizations of type II and III solar radio bursts.

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“…Wang & Li (1991) have shown that the nonlinear coupling of radio waves with whistlers or ion sound waves explains the nature of the millisecond oscillations in the decimetric radio spike bursts. The conversion of radio emission as o-mode waves into x-mode waves via scattering on ion-sound and whistler waves has been considered by Wentzel (1984) and by Melrose (1988). This mechanism has been used for explaining the weak polarization of radio-bursts of type II and III at metric wavelengths.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear interaction of kinetic Alfvén waves and radio waves in the solar corona

Sirenko

Voitenko

Goossens

2002

A&A

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Abstract. This paper investigates the nonlinear interaction of short wavelength kinetic Alfvén waves (KAWs) with extraordinary (x-) and ordinary (o-) mode radio waves using two fluid magnetohydrodynamics. The focus is on the interaction of a preexistent KAW with an ordinary electromagnetic wave, giving rise to an extraordinary electromagnetic wave. The equation governing the time evolution of the amplitude of the excited x-mode is derived. The growth time of the x-mode wave is determined and the corresponding interaction distance is computed for active regions in the low corona and for high corona. The nonlinear coupling appears to be quite efficient for reasonable amplitudes of KAWs in the corona, B A /B 0 = 0.02-0.2. We suggest that this process provides a new possibility for the detection and remote sensing of coronal kinetic Alfvén waves by means of radio observations.

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Polarization of fundamental type III radio bursts

Cited by 18 publications

References 24 publications

A review of solar type III radio bursts

A review of solar type III radio bursts

Mode Conversion of Langmuir to Electromagnetic Waves with Parallel Inhomogeneity in the Solar Wind and the Corona

Nonlinear interaction of kinetic Alfvén waves and radio waves in the solar corona

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