Solar Physics

, 294:175 | Cite as

The Solar Radius at 37 GHz Through Cycles 22 to 24

  • Caius L. SelhorstEmail author
  • Juha Kallunki
  • C. Guillermo Giménez de Castro
  • Adriana Valio
  • Joaquim E. R. Costa


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).


Sun: radio radiation Solar cycle Sun: radius 



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.

Disclosure of Potential Conflicts of Interest

The authors declare that they have no conflicts of interest.


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.NAT – Núcleo de AstrofísicaUniversidade Cruzeiro do Sul/Universidade Cidade de São PauloSão PauloBrazil
  2. 2.Metsähovi Radio ObservatoryAalto UniversityKylmäläFinland
  3. 3.CRAAMUniversidade Presbiteriana MackenzieSão PauloBrazil
  4. 4.IAFEUniversidad de Buenos Aires/CONICETBuenos AiresArgentina
  5. 5.CEAInstituto Nacional de Pesquisas EspaciaisSão José dos CamposBrazil

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