Observations of quiet solar features with the SSRT and NoRH V.V. Grechnev & SSRT team Institute of Solar-Terrestrial Physics, Irkutsk, Russia Relatively

Observations of quiet solar features with the SSRT and NoRH V.V. Grechnev & SSRT team Institute of Solar-Terrestrial Physics, Irkutsk, Russia

3 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

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

5 Siberian Solar Radio Telescope, SSRT Cross-shaped equidistant interferometer antennas, diameter of 2.5 m, stepped by 4.9 m in E–W & N–S directions (baselines of m) Frequency range 5675–5787 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

6 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…

7 SSRT & NoRH Images Compared with Other Observations October 6, 1997

8 Filaments & Prominences F F F F F F October 6, 1997

9 CBP  Coronal Bright Points

/06/ GHz, 02:09 17 GHz, 02:08 SXR, 02:08 Coronal Bright Points Coronal Bright Points at 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

11 Coronal Holes Coronal holes are inhomogeneous. T 5.7 correlate with T 17 in  coronal bright points & diffuse brightenings,  filaments. T 5.7 anticorrelate with T 17 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. 1998/04/20-26

12 Coronal Arcades, also Posteruptive Ne ~10 10 cm -3, Te ~6 MK (soft X-rays & microwaves). Long-living giant hot structures in the corona at 100 Mm: B > 20 G or  >1? 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

/11/23 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. 2001/10/22

14 Magnetic Field Estimates High-sensitivity NoRH data (20 K) Microwave spectrum – combined with RATAN-600 Non-radial observations See also talk by Ryabov

15 Projection effect: quiet AR 487, sunspot- associated 5.7 GHz Color :B Contours: I 5.7 Color: V 5.7 Contours: I 5.7 Color: extrapolated B r Contours: I 5.7 Oct. 27  -  -7  +  0  Oct. 31 Nov. 4

Method of extrapolated B r 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. See poster by Uralov & Rudenko Day: 28 October 28 Oct., 2 hr. later 29 October 30 October Before flares: X 17.2 М 3.5, X 10 М 1.5 Caused by: NLS birth NLS displacement NLS birth M i d d l e r e s o l u t i o n Low resolution Color: 17 GHz I, Contours: extrapolated B r

17  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 B r magnetograms allow their identification See poster by Uralov & Rudenko

18 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…

19 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.

20 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