Measurement of the energy release rate and the reconnection rate in solar flares

By using the method presented by Isobe et al., the nondimensional reconnection rate v(in)/v(A) has been determined for the impulsive phase of three two-ribbon flares, where v(in) is the velocity of the reconnection inflow and v(A) is the Alfven velocity. The nondimensional reconnection rate is important to make a constraint on the theoretical models of magnetic reconnection. In order to reduce the uncertainty of the reconnection rate, it is important to determine the energy release rate of the flares from observational data as accurately as possible. To this end, we have carried out one-dimensional hydrodynamic simulations of a flare loop and synthesized the count rate detected by the Soft X-Ray Telescope (SXT) aboard the Yohkoh satellite. We found that the time derivative of the thermal energy contents in a flare arcade derived from SXT data is smaller than the real energy release rate by a factor of 0.3-0.8, depending on the loop length and the energy release rate. The results of the simulations are presented in the paper and used to calculate the reconnection rate. We found that the reconnection rate is 0.047 for the X2.3 flare on 2000 November 24, 0.015 for the M3.7 flare on 2000 July 14, and 0.071 for the C8.9 flare on 2000 November 16. These values are similar to that derived from the direct observation of the reconnection inflow by Yokoyama et al. and consistent with the fast reconnection models such as that of Petschek.