Definition of physical parameters of 8 X-class solar flares

We observed top 8 X-class solar flares registered in the period May 1998 – May 2015. We measure physical parameters of 8 solar flares, such as the temporal scale, size, and magnetic flux density, and find that the sizes of flares tend to be distributed more broadly as the GOES class becomes weaker and that there is a lower limit of magnetic flux density that depends on the GOES class. We also made a brief analysis of solar flares registered in these days, also has shown the duration of time and peak of solar flares in Universal time. We have identified several physical quantities of solar flares and estimated reconnection rate of solar flares. To determine the physical parameters we used images taken with the AIA instrument on board SDO satellite at wavelengths 131 A, 174 A, 193 A, 211 A, 335 A, 1600 A, 1700 A, 4500 A, SXT - pictures, HMI Magnetogram, SOLIS Chromospheric Magnetogram, GOES XRT-data. Using the observed values, we calculate reconnection inflow velocity, coronal Alfven velocity, and reconnection rate. The inflow velocities vary from a few kilometers per second to several tens of kilometers per second, and the Alfven velocities in the corona are in the range of 103 to 104 kilometers per second. As a result, the rate of reconnection is 10-3. We find that the reconnection rate in a flare tends to decrease as the GOES class of the flare increases.