aat Acta Astrophys. Tau. Acta Astrophysica Taurica 2712-925X Kiselev Nikolai Nikolaevich, Mosсow, settlement Moskovskii, Tat'yanin Park Str., 12, Moscow, Russia. RU 93 Magnetism and Activity of the Sun - 2022 Conference proceedings Pre-impulsive flare energy release according to sub-terahertz and X-ray solar observations Smirnova Viktoriya V. Tsap Yurii T. Ryzhov Vladimir S. Crimean Astrophysical Observatory, Nauchny 298409 Crimean Astrophysical Observatory, Nauchny 298409 Bauman Moscow State Technical University, 2nd Baumanskaya str. 5, Moscow, 105005, Russia 24 12 2024 5 4 35 38 13 11 2024 Copyright (c) 2024 Viktoriya V. Smirnova, Yurii T. Tsap, Vladimir S. Ryzhov 2024 Viktoriya V. Smirnova, Yurii T. Tsap, Vladimir S. Ryzhov 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 study time delays between X-ray and sub-terahertz emission at the initial phase of solar flares to clarify the nature of heating of the transition region and upper chromosphere of the Sun. Analysis of a series of events showed that hard X-ray emission is delayed relative to sub-THz emission at the onset of flares by 3–6 minutes for some considered events. The electron thermal conductivity of the coronal plasma cannot ensure the effective heating of the transition region and solar chromosphere. This suggests the heating of the chromospheric plasma in situ during the pre-impulsive phase of solar flares.

Sun solar flares sub-terahertz radio emission chromosphere This work was supported by the RFBR grant No. 20-52-26006 Czech_a (V.V. Smirnova), the RSF grant No. 22-12-0030 (Yu.T. Tsap), and the Ministry of Education and Science research project No. 1021051101548-7- 1.3.8 (Yu.T. Tsap, V.V. Smirnova). Altyntsev A.A., Fleishman G.D., Lesovoi S.V., Meshalkina N.S., 2012. Astrophys. J., vol. 758, no. 2, p. 138. Charikov Yu.E., 2000. Phys. Chem. Earth Part C: Solar, Terrestrial and Planetary Science, vol. 25, iss. 5–6, p. 407. Fernandes L.O.T., Kaufmann P., Correia E., et al., 2017. Solar Phys., vol. 292, no. 1, p. 21. Fleishman G.D., Martinez O.H.C., Landi E., Glesener L., 2022. Front. Astron. Space Sci., vol. 9, id. 966444. Harrison R.A., Waggett P.W., Bentley R.D., et al., 1985. Solar Phys., vol. 97, iss. 2, pp. 387–400. Hudson H.S., Simoes P.J.A., Fletcher L., Hayes L.A., Hannah I.G., 2021. Mon. Not. Roy. Astron. Soc., vol. 501, no. 1, pp. 1273–1281. Kaufmann P., Trottet G., Giménez de Castro C.G., et al., 2000. Solar Phys., vol. 197, no. 2, pp. 361–374. Kaufmann P., Trottet G., Giménez de Castro C.G., et al., 2009. Solar Phys., vol. 255, no. 1, pp.131–142. Kontar E.P., Motorina G.G., Jeffrey N.L.S., et al. 2018. Astron. Astrophys., vol. 620, p. A95. Lüthi T., Magun A., Miller M., 2004. Astron. Astrophys., vol. 415, pp. 1123–1132. Morgachev A.S., Tsap Yu.T., Smirnova V.V., Motorina G.G., 2018. Geomagnetism and Aeronomy, vol. 58, no. 8, pp. 1113–1122. Priest E.R., 1982. Solar Magnetohydrodynamics. Dordrecht: D. Riedel. Smirnova V.V., Tsap Yu.T., Morgachev A.S., Motorina G.G., Bárta M., 2021. Geomagnetism and Aeronomy, vol. 61, no. 7, pp. 993–1000. Tappin S.J., 1991. Astron. Astrophys. Suppl. Ser., vol. 87, no. 2, pp. 277–302. Tsap Yu.T., Smirnova V.V., Morgachev A.S., et al., 2016. Adv. Space Res., vol. 57, iss. 7, pp. 1449–1455. Tsap Yu.T., Smirnova V.V., Motorina G.G., et al., 2018. Solar Phys., vol. 293, no. 3, p. 50.