A Model for the Sources of the Slowly Varying Component of Microwave Solar Radiation.

Kakinuma, Takakiyo; Swarup, G.

doi:10.1086/147450

Cited by 166 publications

(43 citation statements)

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“…The bright (106K) sunspot-associated cores, which were intepreted in terms of gyroradiation at the second and third harmonics of the gyrofrequency, were thought to play an important role in the emission of solar bursts, while the weaker (10 5K) halo emission was associated with the thermal bremsstrahlung of chromospheric plage. Additional support for this composite core-halo model with two radiation mechanisms was independently provided 25 by Kakinuma and Swarup who showed that gyroresonant absorption can explain the apparent peak in the spectrum of the S component at wavelengths A -6-12 cm, as well as the observed decrease in circular polarization with increasing wavelength.…”

Section: Introductionmentioning

confidence: 78%

Three Dimensional Structure and Time Development of Radio Emission from Solar Active Regions.

Lang¹

1983

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Section: Introductionmentioning

confidence: 78%

Three Dimensional Structure and Time Development of Radio Emission from Solar Active Regions.

Lang¹

1983

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“…The remarkable correlation between S-component fluxes and measures of sunspots early investigated (cf., e.g., Kruger et al 1964) can be explained by the fact that magnetic fields play a dominating role in the basic emission mechanism of the S-component. This mechanism is due to thermal gyroresonance absorption which was first suggested by Zheleznyakov (1962) and Kakinuma & Swarup (1962). Based on this mechanism, models have been put forward interpreting observations of high angular resolution and providing a tool for plasma diagnostics of coronal magnetic fields and other physical parameters (Zlotnik 1968a, b;Lantos 1968;Gelfreikh & Lubyshev 1979;Alissandrakis et al 1980;Kruger et al 1985;Lee et al 1995;Gopalswamy et al 1996).…”

Section: Introductionmentioning

confidence: 97%

Are short‐time variations of the solar S‐component emission identical with microwave bursts?

et al. 1997

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Extended time series (time resolution about 2-3 min) of spatially resolved observations (2 17 arcsec) in one dimension of solar S-component sources obtained at the Siberian Solar Radio Telescope (SSRT) at 5.2 cm wavelength allow the detection of evolutional features of the growth and decay of active regions in the solar corona. Characteristic slow flux variations with timescales of about 1-2 hours occurring during the decay phase of the radio emission in the low corona above plages and sunspots are compared with recently detected step-like flux increases on timescales of about 10-20 min followed by quasi-constant periods appearing in the initial phase of the development of active regions. Superimposed on this basic behaviour, also fluctuations at shorter timescales (or even periodic oscillations) have been observed. As it is well known from emission-model calculations, the variations of the S-component radiation can be due to variations of the magnetic field and/or changes of the energy of the radiating particles, which is basically the same emission mechanism as for microwave bursts. Since the "S-component" is originally defined by its long timescale behaviour derived from whole-Sun flux density measurements, the presently detected small-timescale features in S-component sources require either a revised definition of S-component emission or must be considered as "burst-like" .

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“…The X and O modes generally propagate independently of one other, and hence the polarization is unchanged during propagation. However, coupling between the two modes may occur when they pass through the region of magnetic fields orthogonal to the line of sight, called quasi-transverse (QT) layer (Kakinuma & Swarup 1962). One particular outcome of the mode coupling is the complete depolarization of the emission which depends on the frequency, magnetic field, and density (Cohen, 1960).…”

Section: Introductionmentioning

confidence: 99%

“…The (x, y) coordinates are geocentric coordinates in the west and the south, respectively, and x and y increase toward the west and the south, respectively. (from Lee et al 1998) in deriving one of these quantities (e.g., Kundu and Alissandrakis 1984, Alissandrakis & Chiuderi Drago 1994, Alissandrakis et al 1996, Ryabov et al 1999. In this paper, we instead focus on the location of the depolarization strip as an important constraint on models for the large scale coronal magnetic field structure.…”

Section: Introductionmentioning

confidence: 99%

Microwave Depolarization above Sunspots

Lee

White

2010

Proc. IAU

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Abstract. Microwave emissions from sunspots are circularly polarized in the sense of rotation (right or left) determined by the polarity (north or south) of coronal magnetic fields. However, they may convert into unpolarized emissions under certain conditions of magnetic field and electron density in the corona, and this phenomenon of depolarization could be used to derive those parameters. We propose another diagnostic use of microwave depolarization based on the fact that an observed depolarization strip actually represents the coronal magnetic polarity inversion line (PIL) at the heights of effective mode coupling, and its location itself carries information on the distribution of magnetic polarity in the corona. To demonstrate this diagnostic utility we generate a set of magnetic field models for a complex active region with the observed line-of-sight magnetic fields but varying current density distribution and compare them with the 4.9 GHz polarization map obtained with the Very Large Array (VLA). The field extrapolation predicts very different locations of the depolarization strip in the corona depending on the amount of electric currents assumed to exist in the photosphere. Such high sensitivity of microwave depolarization to the coronal magnetic field can therefore be useful for validating electric current density maps inferred from vector magnetic fields observed in the photosphere.

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A Model for the Sources of the Slowly Varying Component of Microwave Solar Radiation.

Cited by 166 publications

References 0 publications

Three Dimensional Structure and Time Development of Radio Emission from Solar Active Regions.

Three Dimensional Structure and Time Development of Radio Emission from Solar Active Regions.

Are short‐time variations of the solar S‐component emission identical with microwave bursts?

Microwave Depolarization above Sunspots

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