Statistical Study of the Reconnection Rate in Solar Flares Observed withYohkohSXT

We report a statistical study of flares observed with the Soft X-rayTelescope (SXT) onboard Yohkoh in the year of 2000. We measure physicalparameters of 77 flares, such as the temporal scale, the size, and the magneticflux density and find that the sizes of flares tend to be distributed morebroadly as the GOES class becomes weaker and that there is a lower limit ofmagnetic flux density that depends on the GOES class. We also examine therelationship between these parameters and find weak correlation betweentemporal and spatial scales of flares. We estimate reconnection inflowvelocity, coronal Alfven velocity, and reconnection rate using above observedvalues. The inflow velocities are distributed from a few km/s to several tenskm/s and the Alfven velocities in the corona are in the range from 10^3 to 10^4km/s. Hence the reconnection rate is 10^-3 - 10^-2. We find that thereconnection rate in a flare tends to decrease as the GOES class of the flareincreases. This value is within one order of magnitude from the theoreticalmaximum value predicted by the Petschek model, although the dependence of thereconnection rate on the magnetic Reynolds number tends to be stronger thanthat in the Petschek model.Comment: 21 pages, 8 figures, accepted for publication in Ap