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Depressed emission between magnetic arcades near a sunspot  

Boris Ryabov   Submitted: 2016-11-07 02:13

The locations of the depressed emission in microwaves, EUV, and soft X-rays are compared with each other and with the location of the plasma outflow in the active region (AR) 8535. We found that two open-field regions overlap the regions of depressed emission near the ARs sunspot. These two open-field regions are simulated with the potential-field source-surface (PFSS) model under radial distances Rss = 1.8 R⊙ and Rss = 2.5 R⊙. Each open-field region locates between the arcades of the loops of the same magnetic polarity. The former open-field region covers the region of the plasma outflow, which is thus useful for the tests on connection to the heliosphere. The utmost microwave depression of the intensity in ordinary mode (the Very Large Array 15 GHz observations) overlaps the region of the plasma outflow as well and thus indicates this outflow. The lasting for 8 days depression in soft X-rays and the SOHO EIT 2.84x10-8m images is attributed to the evacuation of as hot coronal plasma as T≥ 2x106K from the extended in height (''open'') magnetic structures. We conclude that the AR 8535 presents the sunspot atmosphere effected by the large-scale magnetic fields.

Authors: B.I. Ryabov, K. Shibasaki
Projects:

Publication Status: Baltic Astronomy (published)
Last Modified: 2016-12-07 12:16
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Reduced Coronal Emission above Large Isolated Sunspots  

Boris Ryabov   Submitted: 2014-11-21 12:52

We analyse specific regions of reduced soft X-ray and microwave emission in five large isolated sunspots. The Nobeyama Radioheliograph 17 GHz observations reveal a local depression of microwave brightness in the peripheral area of the sunspots. The depression regions appear light (weak absorption) in the He 10830 Å line in areas with extended (''open'') field lines as indicated by potential field source surface model (PFSS) extrapolations up to 1.5 R. The observed depressions of 3 - 8% in ordinary mode at 17 GHz is interpreted as resulting from free-free emission under a decrease of 5 - 10% in plasma density. Our model estimates show that it is the decrement of density in both coronal and lower layers above the depression region that accounts for the depression. We believe that such depression regions are good candidates for marking the location of outward plasma motions.

Authors: B. I. Ryabov, D. E. Gary, N. G. Peterova, K. Shibasaki, and N. A. Topchilo
Projects: None

Publication Status: accepted for publication in Solar Physics doi: 10.1007/s11207-014-0634-3
Last Modified: 2014-12-03 15:05
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Coronal Magnetography of Solar Active Region 8365 with the SSRT and NoRH Radio Heliographs  

Boris Ryabov   Submitted: 2006-04-10 02:08

Microwave maps of solar active region NOAA 8365 are used to derive the coronal magnetograms of this region. The technique is based on the fact that the circular polarization of a radio source is modified when microwaves pass through the coronal magnetic field transverse to the line of sight. The observations were taken with the Siberian Solar Radio Telescope (SSRT) on October 21 - 23 and with the Nobeyama Radio Heliograph (NoRH) on October 22 - 24, 1998. The known theory of wave mode coupling in quasi-transverse (QT) region is employed to evaluate the coronal magnetograms in the range of 10 - 30 G at the wavelength 5.2 cm and 50 - 110 G at 1.76 cm, taking the product of electron density and the scale of coronal field divergence to be constant of 1018 cm-2. The height of the QT-region is estimated from the force-free field extrapolations as 6.2 109 cm for the 20 G and 2.3 109 cm for 85 G levels. We find that on large spatial scale, the coronal magnetograms derived from the radio observations show similarity with the magnetic fields extrapolated from the photosphere.

Authors: Ryabov, B.I., Maksimov, V.P., Lesovoi, S.V., Shibasaki, K., Nindos, A., Pevtsov, A.
Projects:

Publication Status: Solar Phys. v.226, 223, 2005
Last Modified: 2006-04-12 13:23
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Depressed emission between magnetic arcades near a sunspot
Reduced Coronal Emission above Large Isolated Sunspots
Coronal Magnetography of Solar Active Region 8365 with the SSRT and NoRH Radio Heliographs

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