Observations of Spotless Solar Flares in Baikal Astrophysical Observatory of the ISTP SB RAS and their Interpretation
Five spotless solar flares were analyzed using chromospheric observations in the Hα line. The flares were registered in Baikal Astrophysical Observatory ISTP SD RAS on March 16, 1981, June 28, 2001 (two flares), May 28, 2002 and June 5, 2002. We also used the photospheric observational data from other observatories and magnetic field data from the Kitt Peak Observatory (USA) and SOHO/MDI. The flare of March, 16 1981 was used to study the active region evolution and preflare chromospheric activations were studied in details. Noteworthy is the fact of appearance of S-type the vortex structure close to the polarity reversal line before this flare. In details it was studied the structure and development of some spotless flares. We established a close connection of flare ribbons and nodes with boundaries of chromospheric and magnetic networks, with magnetic hills having a high magnetic field values. The majority of examined flares were shown to appear at the magnetic field rise phase in magnetic hills of active regions. We explain the appearance and structural evolution of spotless flares using the state-of-the-art solar flare models.