Observations of quiet solar features with the SSRT and NoRH

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Observations of quiet solar features with the
SSRT and NoRH
Relatively

• V.V. Grechnev SSRT team
• Institute of Solar-Terrestrial Physics,
• Irkutsk, Russia

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Observations of quiet solar features with the
SSRT and NoRH

• V.V. Grechnev SSRT team
• Institute of Solar-Terrestrial Physics,
• Irkutsk, Russia

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Outline

• Advantages of Observations with Two
  Radioheliographs
• Filaments Prominences
• Coronal Holes
• Coronal Bright Points
• Coronal Arcades
• Magnetic Field Measurements
• Importance of Observations with two
  Radioheliographs

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Nobeyama Radioheliograph, NoRH

• T-shaped interferometer, 84 antennas
• Operating frequencies 17 34 GHz
• Sensitivity 400 K
• Angular resolution 10? 5?
• Temporal resolution 1 s (0.1 s)
• Synthesizing telescope

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Siberian Solar Radio Telescope, SSRT

• Cross-shaped equidistant interferometer 128  128
  antennas, diameter of 2.5 m, stepped by 4.9 m in
  EW NS directions (baselines of 622.3 m)
• Frequency range 56755787 MHz (?  5.2 cm)
• 2D imaging full solar disk 2 min, active
  region 40 s and,
• simultaneously,
• Fast 1D mode 14 ms/scan
• Angular resolution in 2D mode 21?, in 1D mode
  15?
• Sensitivity 1500 K
• Directly imaging telescope

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Advantages of Observations with Two
Radioheliographs

• Two-frequency observations
• 10 times different optical thickness
• Overlapping in time
• Different imaging principles
• Despite of relatively poor spatial resolution

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SSRT NoRH Images Compared with Other
Observations
October 6, 1997

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Filaments Prominences
October 6, 1997
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Coronal Bright Points
October 6, 1997
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Coronal Bright Points

• Coronal Bright Points at 1.5-17 GHz are due to
  optically thin bremsstrahlung.
• Some Coronal Bright Points visible in other
  emissions are not pronounced in NoRH maps due to
  CLEAN routine.

? Everywhere ? Not all counterparts ? No
counterparts
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Coronal Holes

• Coronal holes are inhomogeneous.
• T5.7 correlate with T17 in
• coronal bright points diffuse brightenings,
• filaments.
• T5.7 anticorrelate with T17 in radial features
  that are darkest at 5.7 GHz, but not pronounced
  in 195 Å or H? images.
• Favorable heating mechanism in those features is
  dissipation of Alfvén waves.
• Criterion Dark feature at both 5.7 17 GHz ?
  filament (channel).
• See poster by Maksimov et al.

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Coronal Arcades, also Posteruptive

• Ne 1010 cm-3, Te 6 MK (soft X-rays
  microwaves).
• Long-living giant hot structures in the corona at
  100 Mm B gt 20 G or ? gt1?
• Dark lanes likely due to falling remnants of a
  filament can contribute to mass supply
  equilibrium conditions.
• See poster by Grechnev et al.

2001/10/22
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Coronal Arcades, also Posteruptive

• Large-scale coronal magnetic configurations are
  revealed, in accord with magnetograms and
  extrapolated magnetic fields.
• Due to nonthermal contributions, magnetic fields
  can be well overestimated.
• See poster by Grechnev et al.

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Magnetic Field Estimates

• High-sensitivity NoRH data (20 K)
• Microwave spectrum combined with RATAN-600
• Non-radial observations
• See also talk by Ryabov

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Projection effect quiet AR 487,
sunspot-associated source _at_ 5.7 GHz
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Method of extrapolated Br magnetograms allows

• avoiding projection effects in B? magnetograms
• identification of the type of microwave source in
  NoRH maps
• Results
• Neutral Line associated Sources (NLS) are
  widespread at 17 GHz
• NLS birth or displacement precedes powerful
  flares CMEs.

Color 17 GHz I, Contours extrapolated Br
See poster by Uralov Rudenko
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? Radio Source Type Identification

• NLS at 17 GHz are indistinguishable from
  sunspot-associated gyroresonance sources in the
  degree of polarization, which can vary for
  sources of both type from small values to 100
• Extrapolated Br magnetograms allow their
  identification
• See poster by Uralov Rudenko

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Importance of Observations with two
Radioheliographs

• Observations at several radio frequencies only
  assure
• Identification of emission mechanisms
• Correct estimates of magnetic fields in the
  corona
• Free-free diagnostics measuring magnetic fields
• New research areas
• Detection of flare-productive sites
• Coronal magnetography (Ryabov)
• Non-local diagnostics (coronal holes)
• etc

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Conclusion

• Putting additional constraints on physical
  conditions based on the observed quantities,
  microwave imaging data crucially enhance the
  reliability of results and consistency of
  interpretations. This is why microwave imaging
  data is a necessary constituent of observational
  data sets on solar phenomena.
• The results presented here have been possible due
  to the usage of microwave imaging data obtained
  with the solar dedicated radioheliographs NoRH
  and SSRT operating without interruption for over
  a decade.

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Acknowledgments

• We thank
• Pulkovo and Nobeyama Solar Groups and,
  especially, Prof. H. Nakajima and Prof. G.
  Gelfreikh for fruitful discussions and assistance
• Nobeyama Solar Group for the opportunity to
  participate this meeting and the hospitality