aat Acta Astrophys. Tau. Acta Astrophysica Taurica 2712-925X Kiselev Nikolai Nikolaevich, Mosсow, settlement Moskovskii, Tat'yanin Park Str., 12, Moscow, Russia. RU 14 10.31059/aat.vol1.iss2.pp1-5 Research articles Sunspot magnetic fields: a comparison between the CrAO and SDO/HMI data Biktimirova Regina Abramenko Valentina Ural Federal University after the First Russian President B.N. Yeltsin, Ekaterinburg 620026, Sverdlovsk region, Russia Crimean Astrophysical Observatory, Nauchny, 298409 25 12 2020 1 2 1 5 21 12 2020 Copyright (c) 2020 Regina Biktimirova, Valentina Abramenko 2020 Regina Biktimirova, Valentina Abramenko The metadata for this submission is licensed under a Creative Commons Attribution 4.0 International License. Copyright and publishing rights for texts published in Acta Astrophysica Taurica is retained by the authors, with first publication rights granted to the journal.Texts are free to use with proper attribution and link to the licensing (Creative Commons Attribution 4.0 International).

We performed a digitization of maximum magnetic field measurements in sunspots. The original data were acquired as drawings at the Crimean Astrophysical Observatory of the Russian Academy of Sciences (CrAO RAS). About 1000 sunspots observed in 2014 have been analyzed. The data were compared to the corresponding measurements from the SDO/HMI instrument (with both the line-of-sight magnetic field B z ( HMI ) and the modulus of the magnetic field vector B ( HMI ) ). For the same sunspot, the maximum modulus of the magnetic field derived at CrAO was compared to the corresponding value from HMI. The Crimean data and the space-based data (of both types) were found to be in direct proportion to each other. A linear approximation over the entire range of measurements (1–4) kilogauss (kG) shows a Pearson correlation coefficient of 0.71 (with the 95 % confidence boundaries of 0.68–0.74) and a slope of linear regression of 0.65 ± 0.02 for both types of the space-based data. A linear approximation over the range of strong fields B ( CrAO ) > 1 . 8 kG gives a similar correlation, however the slope of linear regression is far closer to unity and constitutes 0.90 for the relationship ( B z ( HMI ) vs B ( CrAO ) ) and 0.84 for the relationship ( B ( HMI ) vs B ( CrAO ) ). In the range of weak fields B ( CrAO ) < 1 . 8 kG, a non-linear deviation (exceeding) of the space-based data is observed. Non-linearity can be explained, in part, by a specific routine of the magnetic field measurements at CrAO, however further investigations are needed to explore sources of possible non-linearity in the HMI data. The Crimean measurements of the maximum magnetic field in sunspots are concluded to be in good agreement with the corresponding SDO/HMI measurements, and therefore they can be used for scientific purposes.

Sun magnetic fields Liu Y., Hoeksema J.T., Scherrer P.H., et al., 2012. Solar Phys., vol. 279, pp. 295–316. Pevtsov A.A., Tlatova K.A., Pevtsov A.A., et al., 2019. Astron. Astrophys., vol. 628, id. A103. Plotnikov A.A., Kutsenko A.S., 2018. Izv. Krymsk. Astrofiz. Observ., vol. 114, no. 2, pp. 87–96. (In Russ.) Severnyi A.B., Stepanov V.E., 1956. Izv. Krymsk. Astrofiz. Observ., vol. 16, pp. 3–11. (In Russ.) Steshenko N.V., 1967. Izv. Krymsk. Astrofiz. Observ., vol. 37, pp. 21–28. (In Russ.) Schou J., Scherrer P.H., Bush R.I., et al., 2012. Solar Phys., vol. 275, pp. 229–259.