A study of filament transition sheath from radio observations

Rao, A. Pramesh; Kundu, M. R.

doi:10.1007/bf00150882

Cited by 22 publications

(3 citation statements)

References 12 publications

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“…At the frequencies of about 1 − 30 GHz the filaments are expected to be optically thick, i.e., their observed brightness temperatures T b should be nearly equal to their kinetic temperatures T . This has been confirmed by observations: the typical observed brightness temperatures of the filaments in the mentioned frequency range are of order of 5 000 − 15 000 K both for the filaments on the disk and above the limb (Butz et al, 1975;Rao and Kundu, 1977;Kundu et al, 1978;Raoult, Lantos, and Fuerst, 1979;Kundu, 1985;Kundu, Melozzi, and Shevgaonkar, 1986;Hanaoka et al, 1994;Gopalswamy et al, 1997;Gopalswamy and Hanaoka, 1998;Uralov et al, 2002;Gopalswamy et al, 2003;Kundu et al, 2004;Golubchina et al, 2008;Alissandrakis et al, 2013, etc.). When multi-frequency observations of a particular filament are available, the brigthness temperature seems to be independent on the frequency.…”

Section: Microwave Observations Of Filaments and Flux Ropes 21 Filasupporting

confidence: 54%

“…Since the angular resolution in the radio range is in most cases insufficient to resolve directly the filament widths, these widths are estimated using deconvolution or forward-fitting when the observations are compared with the model images convolved with the instrument beam. The filament widths inferred from the microwave observations are variable: sometimes they are nearly the same as the widths observed in Hα (Butz et al, 1975;Raoult, Lantos, and Fuerst, 1979;Schmahl, Bobrowsky, and Kundu, 1981;Hanaoka et al, 1994, etc.), while sometimes they exceed the widths of the Hα filaments by a factor of about 1 − 5 (Kundu and McCullough, 1972;Chiuderi-Drago et al, 1975;Rao and Kundu, 1977;Kundu et al, 1978;Kundu, Melozzi, and Shevgaonkar, 1986;Irimajiri et al, 1995, etc. ); the observed widths of the radio filaments tend to decrease with the frequency.…”

Section: Microwave Observations Of Filaments and Flux Ropes 21 Filamentsmentioning

confidence: 97%

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Synthetic Radio Views of Simulated Solar Flux Ropes

2016

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In this paper, we produce synthetic radio views on simulated flux ropes in the solar corona, where finite-beta magnetohydrodynamic (MHD) simulations serve to mimic the flux rope formation stages, as well as their stable endstates. These endstates represent twisted flux ropes where balancing Lorentz forces, gravity and pressure gradients determine the full thermodynamic variation throughout the flux rope. The obtained models are needed to quantify radiative transfer in radio bands, and allow us to contrast weak to strong magnetic field conditions. Field strengths of up to 100 G in the flux rope yield the radio views dominated by optically thin free-free emission. The forming flux rope shows clear morphological changes in its emission structure as it deforms from an arcade to a flux rope, both on disk and at the limb. For an active region filament channel with a field strength of up to 680 G in the flux rope, gyroresonance emission (from the third-fourth gyrolayers) can be detected and even dominates over free-free emission at the frequencies of up to 7 GHz. Finally, we also show synthetic views on a simulated filament embedded within a (weak-field) flux rope, resulting from an energetically consistent MHD simulation. For this filament, synthetic views at the limb show clear similarities with actual observations, and the transition from optically thick (below 10 GHz) to optically thin emission can be reproduced. On the disk, its dimension and temperature conditions are as yet not realistic enough to yield the observed radio brightness depressions.

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Section: Microwave Observations Of Filaments and Flux Ropes 21 Filasupporting

confidence: 54%

Section: Microwave Observations Of Filaments and Flux Ropes 21 Filamentsmentioning

confidence: 97%

Synthetic Radio Views of Simulated Solar Flux Ropes

2016

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“…The dominant emission mechanism of quiescent prominences in microwaves is thermal bremsstrahlung. The free-free emission is often considered to be optically-thick at 17 GHz (Rao & Kundu 1977;Gretchnev et al 2006). In the opticallythick case, T b is assumed to be equal to the kinetic temperature.…”

Section: Analysis Of the Prominence Evolution In Microwave Norh Imagesmentioning

confidence: 99%

The early phases of a solar prominence eruption and associated flare: a multi-wavelength analysis

Chifor¹,

Mason²,

Tripathi³

et al. 2006

A&A

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Aims. We aim to examine the precursor phases and early evolution of a prominence eruption associated with a M4-class flare and a partial halo coronal mass ejection (CME) observed on 2005 July 27. Our main goal is to investigate the precursor eruption signatures observed in EUV, X-ray and microwave emission and their relation to the prominence destabilisation. Methods. We perform a multi-wavelength study of the prominence morphology and motion using high-cadence and spatial resolution EUV 171 Å images from the TRACE satellite. The high-temperature flare radiative emission in soft and hard X-rays are analysed through imaging and spectral modeling with RHESSI. Complementary microwave images (17 GHz and 34 GHz) from NoRH are also investigated.Results. The activation of the filament proceeds from one anchored footpoint. We observe "pre-eruption" brightenings in X-ray and EUV images, close to the erupting footpoint of the prominence, being temporally correlated to the point when the prominence first enters a slow-rise phase, and then an accelerated fast-rise phase. The brightness temperature (T b ) of the prominence at 34 GHz is increasing during the eruption. We also find very good correlation between the prominence height-time profile and the spatially integrated soft X-ray (SXR) emission. Conclusions. We discuss the observed precursor brightenings with respect to possible mechanisms that might be responsible for the prominence destabilisation and acceleration. Our observations suggest that reconnection events localised beneath the erupting footpoint may eventually destabilise the entire prominence, causing the eruption.

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Energy Balance in Prominence-Corona Transition Regions

Chiuderi¹,

Drago²

1990

Basic Plasma Processes on the Sun

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A study of filament transition sheath from radio observations

Cited by 22 publications

References 12 publications

Synthetic Radio Views of Simulated Solar Flux Ropes

Synthetic Radio Views of Simulated Solar Flux Ropes

The early phases of a solar prominence eruption and associated flare: a multi-wavelength analysis

Energy Balance in Prominence-Corona Transition Regions

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