Department of Image Processing

A new time-evolution diagnostics of solar flares was developped. We use the high-order statistical moments (3rd order - skewness and 4th order - kurtosis) of the active region histograms. They are computed from the Halpha images during solar flares from their initial phases up to their maxima. The shape of the curve is compared with that of the quiet region. The curves are also compared with the soft X-ray curves by GOES satellite by means of cross-correlation and Kendall rank correlation. These moments are very sensitive to pre-flare activities. We used them for a determination of "the flare starting time" and for the study of the pre-flare quasi-periodic processes.