Observations of coronal holes with the Siberian Radio Heliograph by Altyntsev et al. – Group of European Photo voltaic Radio Astronomers

Coronal holes (CHs) are areas of decreased brightness in photo voltaic disk photographs in excessive ultraviolet (EUV) or tender X-ray emissions similar to configurations with open magnetic area traces. Knowledge on their space and depth of brightness despair is utilized in forecasts of photo voltaic wind parameters within the neighborhood of Earth.

Common two-dimensional observations of CHs in microwaves with a spatial decision to 10–20“ started within the Nineteen Nineties at frequencies of 5.7 GHz (SSRT) and 17 GHz (NoRH). At 5.7 GHz, there was typically a brightness temperature despair in CHs to eight·10³ Okay with a brightness temperature of the quiet Solar 16·10³ Okay. At 17 GHz, the distinction between CH and the quiet Solar is imperceptible, however in lots of instances sources of elevated radio brightness had been seen inside and on CH boundaries. Numerous causes for the looks of such heterogeneities at 17 GHz have been mentioned: 1) microflares within the chromospheric community resulting in power launch at CH bases; 2) focus of open magnetic area traces within the chromosphere, which correspond to their elevated divergence within the corona.

The aim of this work is to research multiwave CH observations with the Siberian Radio Heliograph. We now have examined traits of microwave buildings inside the boundaries of the CH noticed in EUV emission within the central a part of the photo voltaic disk on April 25 and September 20, 2023.

Observations

The complete photo voltaic disk maps on April 25, 2023 obtained with the Siberian Radio Heliograph [Lesovoi et al., 2017; Altyntsev et al., 2020] at ~ 06:14 UT. Radio maps had been constructed mechanically in routine mode at 20 frequencies from 2.8 as much as 9.4 GHz with sign accumulation time of 4 s at each frequency. To scale back noise, we moreover averaged photographs obtained at adjoining receiving frequencies.

Determine 1. Microwave maps averaged at frequencies of two.8 GHz and three.0 GHz (a), 9.0 GHz and 9.4 GHz (c). Background photographs had been reworked by equalization and smoothing with 30″ window. White contours (panel a) present the depressions with ranges 0.7T_QS and 0.9T_QS. Yellow contours present the EUV depressions at 0.5 degree of the imply brightness of the SDO/AIA picture within the 211 Å line. Panel b is an EUV picture within the 211 Å channel. The brightness is cropped from above at 0.6 of the brightness common over the disk to focus on buildings contained in the CH. Panel d presents longitudinal area magnetograms reworked by equalization and smoothing with a window of 30″. Pink traces point out the cross-section for establishing brightness temperature profiles in Determine 2. Squares denote the areas for which the radio brightness histograms had been analyzed.

Determine 2. Brightness temperature profiles in depth (R+L, black stable line; R-L, pink stable line) (a–c), plotted alongside the photo voltaic disk cross-sections depicted in Figures 1. Black dotted, dashed, and pink dotted traces are the quiet Solar ranges T_QS, 0.9T_QS, 0.7T_QS. Panel d portrays brightness profiles within the 211 and 193 Å traces. Vertical dash-dot traces in all panels are the CH boundaries decided from by the EUV emission within the 193 Å channel; black and pink dotted traces correspond to half the brightness within the corresponding channel. All profiles are smoothed by a 30″ window. Panel e presents the SDO/HMI magnetogram profile.

In Determine 3 we will see microwave spectrum on 25 April occasion (asterisks). The vertical bars present the boundaries of the pixel brightness scatterings contained in the sq. bins in Determine 1. There are additionally proven spectra of the quiet Solar, and two CHs on 23 September.

Determine 3.  Spectrum of radio emission of the quiet Solar T_QS (stable line) and brightness temperatures averaged over CH. Asterisks with bars point out the spectrum of the April 25, 2023 CH. The bars present T_max and T_min contained in the CH sq.. Lilac diamonds mark RATAN-600 measurements [Borovik et al., 1990]. Pink and blue curves are the imply brightness temperatures recorded into two CHs on September 20, 2023.

Dialogue and Conclusion

 SRH radio maps enable us to confidently detect radio brightness depressions related to CHs. In form and measurement, the EUV emission despair areas are the closest to the microwave ones with brightness about 0.7T_QS at frequencies ~3–4 GHz. Every day observations with SRH can be utilized, equally to extra-atmospheric EUV photographs, to determine CHs on the photo voltaic disk.

Take a look at observations with the Siberian Radio Heliograph have confirmed the outcomes of CH observations obtained from multiwave one-dimensional scans from RATAN-600 and two-dimensional maps from SSRT (5.7 GHz) and the Nobeyama Radio Heliograph (17 GHz).

It follows from Determine 1 that the buildings of decreased brightness with scales >100“ may be traced within the microwave vary from 2.8 to 10 GHz. These buildings don’t clearly correlate with the distribution of the longitudinal magnetic area element. There are virtually no marked spatial heterogeneities in EUV emission (see Determine 2). Pixel-to-pixel evaluation of the brightness temperature in CH exhibits the presence of small-scale (a number of arcsec) heterogeneities. The pixel-to-pixel brightness scatterings at a frequency of two.8 GHz reaches T_max/T_min=2.5, and with growing frequency it decreases right down to 1.3 at ~10 GHz.

Depressions manifest themselves at low frequencies, at which the contribution of the coronal layer is giant, and are attributed to ~1.5 time decrease plasma density and temperature within the corona above CH relative to the quiet Solar [Borovik et al., 1999].

The microwave radiation of the quiet Solar and CHs is generated by the bremsstrahlung mechanism and consists, within the first approximation, of radiation from two layers: the optically thick chromosphere and the optically skinny corona. Depressions manifest themselves at low frequencies, at which the contribution of the coronal layer is giant, and are attributed to ~1.5 time decrease plasma density and temperature within the corona above CH relative to the quiet Solar [Borovik et al., 1999].

Take a look at observations of coronal holes with two antenna arrays in 3–6 and 6–12 GHz ranges have proven the excessive diagnostic potential of the Siberian Radio Heliograph. Spectral observations with SRH will present distinctive details about the dynamics and construction of the photo voltaic ambiance over CHs from the chromosphere to the decrease corona, in addition to in regards to the bodily nature of heterogeneities inside CHs, together with options of magnetic area distribution.

The usage of common mapping of the photo voltaic disk in utilized issues of forecasting photo voltaic wind variations is promising. SRH observations can present the principle CH parameters employed in forecasting (location and form of despair areas, depth of despair, flare exercise at CH boundaries, brightness heterogeneities in CHs), that are presently obtained from extra-atmospheric observations of EUV emission.

Primarily based on the current paper: Altyntsev, A. T., Globa M.V., Meshalkina, N. S., Sych R.A. Observations of coronal holes with the Siberian Radio Heliograph: 2024,  Photo voltaic-Terrestrial Physics, 10 (3), P.3-10, DOI: 10.12737/stp-103202401.

*Full record of authors: Altyntsev¹, A. T., Globa¹, M.V., Meshalkina¹, N. S., Sych¹, R. A.

¹Institute of Photo voltaic-Terrestrial Physics SB RAS, Lermontov St. 126A, Irkutsk 664033, Russia

References

1. AltyntsevT., Lesovoi S.V., Globa M.V. et al.: Photo voltaic-Terr. Phys., 2020, 6 ( 2), 30.
2. BorovikN., Kurbanov M.S., Livshits M.A. et al.: Soviet Astronomy, 1990, 34(5), 522.
3. Borovik V.N., Medar V.G., Korzhavin A.N.: Lett. 1999, 25(4), 250.