Abstract
To better understand the influence of the activity cycle on the solar atmosphere, we report the time variation of the radius observed at 37 GHz (\(\lambda=8.1\mbox{ mm}\)) obtained by the Metsähovi Radio Observatory (MRO) through Solar Cycles 22 to 24 (1989 – 2015). Almost 5800 maps were analyzed, however, due to instrumental setup changes the dataset showed four distinct behaviors, which required a normalization process to allow for the whole interval analysis. When the whole period was considered, the results showed a positive correlation index of 0.17 between the monthly means of the solar radius at 37 GHz and solar flux obtained at 10.7 cm (F10.7). This correlation index increased to 0.44, when only the data obtained during the last period without instrumental changes were considered (1999 – 2015). The solar radius correlation with the solar cycle agrees with the previous results obtained at mm/cm wavelengths (17 and 48 GHz), nevertheless, this result is the opposite of that reported at submillimeter wavelengths (212 and 405 GHz).
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Andrei, A.H., Boscardin, S.C., Chollet, F., Delmas, C., Golbasi, O., Jilinski, E.G., Kiliç, H., Laclare, F., Morand, F., Penna, J.L., Reis Neto, E.: 2004, Comparison of CCD astrolabe multi-site solar diameter observations. Astron. Astrophys.427, 717. DOI . ADS .
Bachurin, A.F.: 1983, Variation in solar radio radius with the phase of the solar activity cycle at wavelengths of 2.25 and 3.5 cm. Izv. Ordena Trud. Krasn. Znam. Krym. Astrofiz. Obs.68, 68. ADS .
Basu, D.: 1998, Radius of the Sun in relation to solar activity. Solar Phys.183, 291. ADS .
Battaglia, M., Hudson, H.S., Hurford, G.J., Krucker, S., Schwartz, R.A.: 2017, The solar X-ray limb. Astrophys. J.843(2), 123. DOI . ADS .
Bush, R.I., Emilio, M., Kuhn, J.R.: 2010, On the constancy of the solar radius. III. Astrophys. J.716, 1381. DOI . ADS .
Chapman, G.A., Dobias, J.J., Walton, S.R.: 2008, On the variability of the apparent solar radius. Astrophys. J.681, 1698. DOI . ADS .
Costa, J.E.R., Silva, A.V.R., Makhmutov, V.S., Rolli, E., Kaufmann, P., Magun, A.: 1999, Solar radius variations at 48 GHz correlated with solar irradiance. Astrophys. J. Lett.520, L63. DOI . ADS .
Emilio, M., Leister, N.V.: 2005, Solar diameter measurements at São Paulo Observatory. Mon. Not. Roy. Astron. Soc.361, 1005. DOI . ADS .
Emilio, M., Kuhn, J.R., Bush, R.I., Scherrer, P.: 2000, On the constancy of the solar diameter. Astrophys. J.543, 1007. DOI . ADS .
Gilliland, R.L.: 1981, Solar radius variations over the past 265 years. Astrophys. J.248, 1144. DOI . ADS .
Giménez de Castro, C.G., Varela Saraiva, A.C., Costa, J.E.R., Selhorst, C.L.: 2007, The solar radius in the EUV during the cycle XXIII. Astron. Astrophys.476, 369. DOI . ADS .
Kallunki, J., Tornikoski, M.: 2018, Measurements of the quiet-Sun level brightness temperature at 8 mm. Solar Phys.293, 156. DOI . ADS .
Kilic, H., Golbasi, O.: 2011, Comparison of long-term trend of solar radius with sunspot activity and flare index. Astrophys. Space Sci.334, 75. DOI . ADS .
Kosovichev, A., Rozelot, J.-P.: 2018a, Cyclic changes of the Sun’s seismic radius. Astrophys. J.861(2), 90. DOI . ADS .
Kosovichev, A.G., Rozelot, J.P.: 2018b, Solar cycle variations of rotation and asphericity in the near-surface shear layer. J. Atmos. Solar-Terr. Phys.176, 21. DOI . ADS .
Kuhn, J.R., Bush, R.I., Emilio, M., Scherrer, P.H.: 2004, On the constancy of the solar diameter. II. Astrophys. J.613, 1241. DOI . ADS .
Laclare, F., Delmas, C., Coin, J.P., Irbah, A.: 1996, Measurements and variations of the solar diameter. Solar Phys.166, 211. DOI . ADS .
Lefebvre, S., Bertello, L., Ulrich, R.K., Boyden, J.E., Rozelot, J.P.: 2006, Solar radius measurements at Mount Wilson Observatory. Astrophys. J.649, 444. DOI . ADS .
Menezes, F., Valio, A.: 2017, Solar radius at subterahertz frequencies and its relation to solar activity. Solar Phys.292, 195. DOI . ADS .
Noël, F.: 2004, Solar cycle dependence of the apparent radius of the Sun. Astron. Astrophys.413, 725. DOI . ADS .
Rozelot, J.P.: 1998, The correlation between the Calern solar diameter measurements and the solar irradiance. Solar Phys.177, 321. ADS .
Rozelot, J.P., Kosovichev, A., Kilcik, A.: 2015, Solar radius variations: an inquisitive wavelength dependence. Astrophys. J.812, 91. DOI . ADS .
Scargle, J.D.: 1982, Studies in astronomical time series analysis. II – Statistical aspects of spectral analysis of unevenly spaced data. Astrophys. J.263, 835. DOI . ADS .
Selhorst, C.L., Silva, A.V.R., Costa, J.E.R.: 2004, Radius variations over a solar cycle. Astron. Astrophys.420, 1117. ADS .
Selhorst, C.L., Giménez de Castro, C.G., Válio, A., Costa, J.E.R., Shibasaki, K.: 2011, The behavior of the 17 GHz solar radius and limb brightening in the spotless minimum XXIII/XXIV. Astrophys. J.734, 64. DOI . ADS .
Selhorst, C.L., Simões, P.J.A., Brajša, R., Valio, A., Giménez de Castro, C.G., Costa, J.E.R., Menezes, F., Rozelot, J.P., Hales, A.S., Iwai, K., White, S.: 2019, Solar polar brightening and radius at 100 and 230 GHz observed by ALMA. Astrophys. J.871(1), 45. DOI . ADS .
Acknowledgements
C.L.S. acknowledges financial support from the São Paulo Research Foundation (FAPESP), grant number 2019/03301-8. C. L. S. and C. G. G. C. are thankful to CNPq by the support through grants 306638/2018-5 and 305203/2016-9, respectively. The authors also thank Niko Lavonen for help with the data reduction.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Disclosure of Potential Conflicts of Interest
The authors declare that they have no conflicts of interest.
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
About this article
Cite this article
Selhorst, C.L., Kallunki, J., Giménez de Castro, C.G. et al. The Solar Radius at 37 GHz Through Cycles 22 to 24. Sol Phys 294, 175 (2019). https://doi.org/10.1007/s11207-019-1568-6
Received:
Accepted:
Published:
DOI: https://doi.org/10.1007/s11207-019-1568-6