Solar-Terrestrial Physics Solar-Terrestrial Physics Solar-Terrestrial Physics 2500-0535 39472 10.12737/stp-63202002 Results of current research Results of current research Results of current research Low-power solar flares of optical and X-ray wavelengths for solar cycles 21–24 Low-power solar flares of optical and X-ray wavelengths for solar cycles 21–24 https://orcid.org/0000-0001-5725-8262 Боровик Александр Васильевич Borovik Aleksandr Vasil'evich aborovik@iszf.irk.ru

кандидат физико-математических наук;

candidate of physical and mathematical sciences;

 https://orcid.org/0000-0002-9563-1360 Жданов Антон Андреевич Zhdanov Anton Andreevich kick.out@mail.ru Институт солнечно-земной физики СО РАН Иркутск Россия Institute of Solar Terrestrial Physics SB RAS Irkutsk Russian Federation Институт солнечно-земной физики СО РАН Иркутск Россия Institute of Solar Terrestrial Physics SB RAS Irkutsk Russian Federation 6 3 16 22 https://naukaru.ru/en/nauka/article/39472/view

Using data obtained in optical and X-ray wavelengths, we have analyzed solar flare activity for cycles 21–24. Over the last three cycles, solar activity is shown to decrease significantly. As compared to solar cycle 21 (the most active over the last 50 years), in cycle 24 2–4-class large optical flares are 4.4 times rarer; 1-class flares, 8.2 times; and S-class small flares, 4.1 times. The number of X-class flares decreased 3.7 times; M-class flares, 3.2 times. This confirms that secular solar activity trends affect peak values of 11-year cycles. It is shown that optical low-power flares can be accompanied by proton fluxes and X-ray bursts of different intensity, including X-class ones. Ranges of small flare emission in soft X-rays largely overlap with emission ranges of flares of high optical classes. We have confirmed that X-ray emission from solar flares appears on average 2 min before the optical emission. The X-ray maximum for small optical flares and 1-class flares occurs approximately 1 min later; for 2–4-class flares, 2 min.

Using data obtained in optical and X-ray wavelengths, we have analyzed solar flare activity for cycles 21–24. Over the last three cycles, solar activity is shown to decrease significantly. As compared to solar cycle 21 (the most active over the last 50 years), in cycle 24 2–4-class large optical flares are 4.4 times rarer; 1-class flares, 8.2 times; and S-class small flares, 4.1 times. The number of X-class flares decreased 3.7 times; M-class flares, 3.2 times. This confirms that secular solar activity trends affect peak values of 11-year cycles. It is shown that optical low-power flares can be accompanied by proton fluxes and X-ray bursts of different intensity, including X-class ones. Ranges of small flare emission in soft X-rays largely overlap with emission ranges of flares of high optical classes. We have confirmed that X-ray emission from solar flares appears on average 2 min before the optical emission. The X-ray maximum for small optical flares and 1-class flares occurs approximately 1 min later; for 2–4-class flares, 2 min.

 solar activity solar flares solar activity solar flares

Altyntsev A.T., Banin V.G., Kuklin G.V., Tomozov V.M. Solnechnye vspyshki [Solar Flares]. Moscow, Nauka Publ., 1982, 246 p. (In Russian). Altyntsev A.T., Banin V.G., Kuklin G.V., Tomozov V.M. Solnechnye vspyshki [Solar Flares]. Moscow, Nauka Publ., 1982, 246 p. (In Russian). Culhane J.L., Phillips K.J.H. Solar X-ray bursts at energies less than 10 keV observed with OSO-4. Solar Phys. 1970, vol. 11, iss. 1, pp. 117-144. DOI: 10.1007/BF00156556. Culhane J.L., Phillips K.J.H. Solar X-ray bursts at energies less than 10 keV observed with OSO-4. Solar Phys. 1970, vol. 11, iss. 1, pp. 117-144. DOI: 10.1007/BF00156556. Drake J.F. Characteristics of soft solar X-ray bursts. Solar Phys. 1971, vol. 16, iss. 1, pp. 152-185. DOI: 10.1007/ BF00154510. Drake J.F. Characteristics of soft solar X-ray bursts. Solar Phys. 1971, vol. 16, iss. 1, pp. 152-185. DOI: 10.1007/ BF00154510. Fletcher L., Dennis B.R., Hudson H.S., Krucker S., Phillips K., Veronig A., Battaglia M., et al. An observational overview of solar flares. Space Sci. Rev. 2011, vol. 159, iss. 1-4, pp. 19-106. DOI: 10.1007/s11214-010-9701-8. Fletcher L., Dennis B.R., Hudson H.S., Krucker S., Phillips K., Veronig A., Battaglia M., et al. An observational overview of solar flares. Space Sci. Rev. 2011, vol. 159, iss. 1-4, pp. 19-106. DOI: 10.1007/s11214-010-9701-8. Kurt V.G. Electrons and X-ray emission of solar flares. Basic Plasma Processes on the Sun: Proc. 142th Symposium of the International Astronomical Union. 1990, pp. 409-413. DOI: 10.1017/S007418090008832X. Kurt V.G. Electrons and X-ray emission of solar flares. Basic Plasma Processes on the Sun: Proc. 142th Symposium of the International Astronomical Union. 1990, pp. 409-413. DOI: 10.1017/S007418090008832X. Pearce G.A., Harrison R.A. Statistical analysis of the soft X-ray profiles of solar flares. Astron. Astrophys. 1988, vol. 206, no. 1, pp. 121-128. Pearce G.A., Harrison R.A. Statistical analysis of the soft X-ray profiles of solar flares. Astron. Astrophys. 1988, vol. 206, no. 1, pp. 121-128. Smit G., Smit E. Solnechnye vspyshki [Solar Flares]. Moscow, Mir Publ., 1966, 426 p. (In Russian). English edition: Smith H.J., Smith E.P. Solar Flares. New York, Macmillan; London, Collier-Macmillan, 1963, 322 p. Smit G., Smit E. Solnechnye vspyshki [Solar Flares]. Moscow, Mir Publ., 1966, 426 p. (In Russian). English edition: Smith H.J., Smith E.P. Solar Flares. New York, Macmillan; London, Collier-Macmillan, 1963, 322 p. Sotnikova R.T., Moskalenko A.V. The Sun in X-rays. Trudy VII simpoziuma po solnechno-zemnoi fizike Rossii i stran SNG [Proc. VIIth Symposium on Solar-Terrestrial Physics for Russia and CIS Countries]. Troitsk, 1999, pp. 156-161. (In Russian). Sotnikova R.T., Moskalenko A.V. The Sun in X-rays. Trudy VII simpoziuma po solnechno-zemnoi fizike Rossii i stran SNG [Proc. VIIth Symposium on Solar-Terrestrial Physics for Russia and CIS Countries]. Troitsk, 1999, pp. 156-161. (In Russian). Temmer M., Veronig A., Hanslmeier A., Otruba W., Messerotti M. Statistical analysis of solar Hα flares. Astron. Astrophys. 2001, vol. 375, no. 3, pp. 1049-1061. DOI: 10.1051/ 0004-6361:20010908. Temmer M., Veronig A., Hanslmeier A., Otruba W., Messerotti M. Statistical analysis of solar Hα flares. Astron. Astrophys. 2001, vol. 375, no. 3, pp. 1049-1061. DOI: 10.1051/ 0004-6361:20010908. Thomas R.J., Teske R.G. Solar soft X-rays and solar activity. II: Soft X-ray emission during solar flares. Solar Phys. 1971, vol. 16, iss. 2, pp. 431-453. DOI: 10.1007/BF00162486. Thomas R.J., Teske R.G. Solar soft X-rays and solar activity. II: Soft X-ray emission during solar flares. Solar Phys. 1971, vol. 16, iss. 2, pp. 431-453. DOI: 10.1007/BF00162486. Veronig A., Temmer M., Hanslmeier A., Otruba W., Messerotti M. Temporal aspects and frequency distributions of solar soft X-ray flares. Astron. Astrophys. 2002, vol. 382, no. 3, pp. 1070-1080. DOI: 10.1051/0004-6361:20011694. Veronig A., Temmer M., Hanslmeier A., Otruba W., Messerotti M. Temporal aspects and frequency distributions of solar soft X-ray flares. Astron. Astrophys. 2002, vol. 382, no. 3, pp. 1070-1080. DOI: 10.1051/0004-6361:20011694. URL: http://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-flares/h-alpha/events/ (accessed September 19, 2019). URL: http://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-flares/h-alpha/events/ (accessed September 19, 2019). URL: https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-flares/x-rays/goes/xrs/ (accessed September 19, 2019). URL: https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-flares/x-rays/goes/xrs/ (accessed September 19, 2019). URL: https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-flares/documentation/readme_solar-features_solar-flares.pdf (accessed September 19, 2019). URL: https://www.ngdc.noaa.gov/stp/space-weather/solar-data/solar-features/solar-flares/documentation/readme_solar-features_solar-flares.pdf (accessed September 19, 2019). URL: https://sidstation.loudet.org/solar-activity-en.xhtml (accessed September 19, 2019). URL: https://sidstation.loudet.org/solar-activity-en.xhtml (accessed September 19, 2019). URL: https://umbra.nascom.nasa.gov/SEP/ (accessed September 19, 2019). URL: https://umbra.nascom.nasa.gov/SEP/ (accessed September 19, 2019).