Andriiets O. Magnetic fields in weak solar flares on the levels of photosphere and chromosphere.

The thesis contains new results concerning the structure of the magnetic field diagnostics in weak solar flares. It was found that the magnetic field in the weak solar flare of July 18, 2000 increased up to approximately 0.05 T at the bottom and up to 0.08-0.1 T at the high photosphere, while its altitude gradient decreased from 0.0012 to 0.0008 T/km during the flare. The filling factor decreased during the flare. The magnetic field has decreased about 0.03 T after 20 minutes. At the first moment of flare observation, 3 minutes before its peak, in the lower layers of the photosphere there were upflows, and in the upper - downflows. The downflow velocity significantly decreased in the main phase of the flare. The results of this study indicate the spread of disturbance of the upper layers of the solar atmosphere in the lower and the rapid changes in the magnetic field in the flare. It was shown, that weak solar flare of July 28, 2004 has some specific features of the magnetic field, typical for more power flares. In particular, the altitude gradient of magnetic field was found close to zero. Photospheric thermodynamical parameters have changed during the 8 minutes of observations for 1h 50 m before the C1 class flare of May 24, 2012. But these changes were smoother than for the flare. According to the two received semiempirical models it is found some layers with the temperature enhancement. The magnetic field of the photosphere was gradually decreasing with height before flare, unlike in the flare photosphere. In most models, its value was about 0.2 T in the lower photosphere and 0.13 T - in the upper photosphere. The angle of the magnetic field vector in the models varied in the range of 90 deg in the lower to 120-140 degs in the upper photosphere.