aat Acta Astrophys. Tau. Acta Astrophysica Taurica 2712-925X Kiselev Nikolai Nikolaevich, Mosсow, settlement Moskovskii, Tat'yanin Park Str., 12, Moscow, Russia. RU 100 Magnetism and Activity of the Sun - 2022 Conference proceedings Low-power solar flares in the Hα line: research results Borovik Alexander Institute of Solar-Terrestrial Physics SB RAS, Irkutsk 24 12 2024 5 4 17 28 14 12 2024 Copyright (c) 2024 Alexander Borovik 2024 Alexander Borovik 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).

The paper summarizes the results of long-term studies of low-power flares in the Hα line (optical class S) obtained using data from the international flare patrol, observational materials in the 6563 Å line of the Baikal Astrophysical Observatory of the ISTP SB RAS and GONG telescopes, observations from the SDO, SOHO, and Kitt Peak Observatory. As a result of the performed studies, the refined, statistically reliable and most complete to date data on the spatiotemporal parameters of solar flares have been obtained, and their total energy in the optical wavelength range has been estimated. Low-power flares were found to form dense clusters on the Sun, which are centers of flare activity (CFA) associated with regions of emerging magnetic fluxes. It was also found that such flares occur near the local small-scale short-lived polarity inversion lines (LPIL) of the longitudinal magnetic field. One of the identified regularities of their occurrence is the increase in the magnetic field gradient in certain sections of the LPIL in the flare region. The duration of growth is from 40 minutes to 1.5 hours. The magnetic field reaches its maximum gradient (1.3-1.5 G/km) at the time of flare occurrence. The results of the study show that low-power flares have development scenarios similar to large flares: they are accompanied by activation and eruption of filaments, have an explosive phase, are accompanied by radiation of different power in the X-ray and radio ranges as well as by proton fluxes. Among them there are flares that cover the sunspot umbrae, two-ribbon and white-light flares. The results obtained can be used to construct physical models, diagnose nonstationary processes on the Sun, and predict solar activity and geoeffective solar events.

solar flares magnetic fields The work was carried out within the framework of the state assignment II.16 and supported by the RFBR grant 19-52-45002. Altyntsev A.T., Banin V.G., Kuklin G.V., Tomozov V.M., 1982. Solar flares, M.: Nauka. (In Russ.) Bogachev S.A. et al., 2020. Uspekhi fizicheskikh nauk, vol. 190, no. 8, pp. 838–858. (In Russ.) Borovik A.V., 1989. Issled. po geomagnetizmu, aeronomii i fizike Solnca, vol. 87, pp. 154–166. (In Russ.) Borovik A.V., 1990. Issled. po geomagnetizmu, aeronomii i fizike Solnca, vol. 91, pp. 63–73. (In Russ.) Borovik A.V., Myachin D.Yu., 2002. Solar Phys., vol. 205, pp. 105–116. Borovik A.V., Zhdanov A.A., 2017a. Solar-Terrestrial Physics, vol. 3, no. 1, pp. 40–56. Borovik A.V., Zhdanov A.A., 2017b. Solar-Terrestrial Physics, vol. 3, no. 4, pp. 5–16. Borovik A.V., Zhdanov A.A., 2018a. Solar-Terrestrial Physics, vol. 4, no. 3, pp. 3–12. Borovik A.V., Zhdanov A.A., 2018b. Solar-Terrestrial Physics, vol. 4, no. 2, pp. 8–16. Borovik A.V., Zhdanov A.A., 2019. Solar-Terrestrial Physics, vol. 5, no. 4, pp. 3–9. Borovik A.V., Zhdanov A.A., 2020. Solar-Terrestrial Physics, vol. 6, no. 3, pp. 16–22. Borovik A.V., Zhdanov A.A., 2022. Solar-Terrestrial Physics, vol. 8. no. 1, pp. 19–23. Borovik A.B., Grigoryev V.M., Kargapolova N.N., et al., 1986. Contributions of the astronomical observatory Skalnate Pleso, vol. 15, pp. 211–242. (In Russ.) Borovik A.V., Myachin D.Yu., Tomozov V.M., 2014. Izvestiya IGU. Ser. Nauki o Zemle, vol. 7, no. 1, pp. 23–45. (In Russ.) Borovik A.V., Mordvinov A.V., Golubeva E.M., and Zhdanov A.A., 2020. Astron. Rep., vol. 64, no. 6, pp. 540–546. Dodson H.W., Hedeman E.R., 1970. Solar Phys., vol. 13, no. 2, pp. 401–419. Falciani R., Rigutti M., 1972. Solar Phys., vol. 26, pp. 114–116. Fletcher L. et al., 2011. Space Sci. Rev., vol. 159, no. 1–4, pp. 19–106. Heyvaerts J., Priest E.R., Rust D.M., 1977. Solar Phys., vol. 53, no. 1, pp. 255–258. Howard R, Harvey J.W., 1964. Astrophys. J., vol. 139, no. 5, pp. 1328–1335. Kurochka L.N., Rossada V.M., 1981. Solnechnye dannye, no. 7., pp. 95–100. (In Russ.) Neupert W.M., 1968. Astrophys. J., vol. 153, pp. L59–L64. Prist E., 1985. Solar magnetic hydrodynamics, M.: Mir. (In Russ.) Severnyi A.B., Shaposhnikova E.F., 1961. Izv. Krymsk. Astrofiz. Observ., vol. 24, pp. 235–257. (In Russ.) Simon G.W., Leighton R.B., 1964. Astrophys. J., vol. 140, pp. 1120–1147. Smit G., Smit E., 1966. Solar flares, M.: Mir. (In Russ.) Somov B.V., 1992. Physical processes in solar flares, Dordrecht, Boston: Kluwer Academic Publishers. Svestka Z., 1975. In Shea M.A., Smart D.F. (Eds.), Results obtained during the campaign for integrated observations of solar flares (CINOF). Special reports, AFCRL-TR-75-0437. Air Force Cambridge Research Labs., no. 193, pp. 9–23. Svestka Z. et al., 1982. Solar Phys., vol. 75, no. 1–2, pp. 305–329.