Reduced Coronal Emission Above Large Isolated Sunspots

Ryabov, B. I.; Gary, Dale E.; Peterova, N. G.; Shibasaki, Κ.; Topchilo, N. A.

doi:10.1007/s11207-014-0634-3

Cited by 7 publications

(4 citation statements)

References 19 publications

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“…Their interpretation was that hot coronal plasma had been evacuated along the open field lines leaving a volume of cooler plasma that is seen as a depression in the microwave observations. Their work extends previous work by Ryabov et al (2015) where authors provided similar arguments to explain reduced microwave brightness at 17 GHz frequency in the peripheral areas of five other select sunspots.…”

Section: Introductionsupporting

confidence: 85%

“…Inspired by the EUV observations (Figure 1c), similar soft X-ray observations (not shown), and previous work by Ryabov et al (2015) and Ryabov and Shibasaki (2016), we pose the hypothesis that open magnetic field lines are present in the northern part of the sunspot. Due to increased plasma transport along these open field lines one could then expect reduced amounts of hot coronal plasma in the corresponding atmosphere volume.…”

Section: Model Setupsupporting

confidence: 78%

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Reduced Microwave Brightness Temperature in a Sunspot Atmosphere Due to Open Magnetic Fields

2021

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Motivated by dark coronal lanes in SOHO / EIT 284 Å EUV observations we construct and optimize an atmosphere model of the AR 8535 sunspot by adding a cool and dense component in the volume of plasma along open field lines determined using the Potential Field Source Surface (PFSS) extrapolation. Our model qualitatively reproduces the observed reduced microwave brightness temperature in the northern part of the sunspot in the VLA observations from 13 May 1999 and provides a physical explanation for the coronal dark lanes. We propose application of this method to other sunspots with such observed dark regions in EUV or soft X-rays and with concurrent microwave observations to determine the significance of open field regions. The connection between open fields and the resulting plasma temperature and density change is of relevance for slow solar wind source investigations.

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Section: Introductionsupporting

confidence: 85%

Section: Model Setupsupporting

confidence: 78%

Reduced Microwave Brightness Temperature in a Sunspot Atmosphere Due to Open Magnetic Fields

2021

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“…As a matter of fact, the NoRH o-mode images (R polarization for October 1011 and L for March 2016) show brightness depressions at the location of the spot (c.f. Topchilo, Peterova, and Borisevich, 2010;Bezrukov et al, 2011;Ryabov et al, 2015;Bogod et al, 2015). Sunspot-associated omode emission (2nd harmonic) started at at ∼11.9 GHz on October 2011 and ∼ 11.5 GHz on March 2016, which puts the magnetic field intensity at the base of the TR to ∼ 2150 and ∼ 2100 G respectively.…”

Section: Models Of the Radio Emissionmentioning

confidence: 99%

Modeling of the Sunspot-Associated Microwave Emission Using a New Method of DEM Inversion

et al. 2019

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We developed a method to compute the temperature and density structure along the line of sight by inversion of the differential emission measure (DEM), under the assumptions of stratification and hydrostatic equilibrium. We applied this method to the DEM obtained from AIA observations and used the results, together with potential extrapolations of the photosheric magnetic field, to compute the microwave emission of three sunspots, which we compared with observations from the RATAN-600 radio telescope and the Nobeyama Radioheliograph (NoRH). Our DEM based models reproduced very well the observations of the moderate-size spot on October 2011 and within 25% the data of a similar sized spot on March 2016, but predicted too low values for the big spot of April 14, 2016. The latter was better fitted by a constant conductive flux atmospheric model which, however, could not reproduce the peak brightness temperature of 4.7 × 10 6 K and the shape of the source at the NoRH frequency. We propose that these deviations could be due to low intensity non-thermal emission associated to a moving pore and to an opposite polarity light bridge. We also found that the double structure of the big spot at high RATAN-600 frequencies could be interpreted in terms of the variation of the angle between the magnetic field and the line of sight along the sunspot.

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“…Some authors (see [7], [8] for the reviews) have noted that the region of depressed coronal emission and open magnetic field lines at the edges of some ARs indicates the local source of the nascent slow solar wind. In some cases, the depressed soft X-ray coronal emission is accompanied by the depressed microwave emission at the periphery of the isolated sunspots [9], [10].…”

Section: Introductionmentioning

confidence: 99%

Low Brightness Temperature in Microwaves at Periphery of Some Solar Active Regions

Ryabov

Bezrukov

Kallunki

2017

Latvian Journal of Physics and Technical Sciences

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The microwave regions with low brightness temperature are found to overlap the regions of the depressed coronal emission and open field lines at the periphery of two solar active regions (ARs). The imaging microwave observations of the Sun with the Nobeyama Radio heliograph at 1.76 cm, the MRO-14 radio telescope of Metsähovi Radio Observatory at 0.8 cm, and the RT-32 of Ventspils International Radio Astronomy Centre in the range 3.2-4.7 cm are used. To reduce the noise in the intensity distribution of the RT-32 maps of the Sun, one wavelet plane of "à trous" wavelet space decomposition is subtracted from each map. To locate the open-field regions, the full-Sun coronal magnetic fields with the potential field source surface (PFSS) model for R SS = 1.8 R ʘ are simulated. We conclude that the revealed LTRs present narrow coronal hole-like regions near two ARs and imply an extra investigation on the plasma outflow.

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Reduced Coronal Emission Above Large Isolated Sunspots

Cited by 7 publications

References 19 publications

Reduced Microwave Brightness Temperature in a Sunspot Atmosphere Due to Open Magnetic Fields

Reduced Microwave Brightness Temperature in a Sunspot Atmosphere Due to Open Magnetic Fields

Modeling of the Sunspot-Associated Microwave Emission Using a New Method of DEM Inversion

Low Brightness Temperature in Microwaves at Periphery of Some Solar Active Regions

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