Prediction of the Temporal Evolution of Solar X-Ray Flares

A solar flare is an explosive release of stored magnetic energy on the Sun. Much of this energy is converted into x-ray photons which escape into space. As a solar flare begins, the 1-8 x-ray photon flux at Earth's orbit, as measured by the GOES satellite, rapidly increases. It quickly reaches a peak and slowly decays. A plot of this flux exhibits an approximate lognormal shape. A lognormal function becomes a normal, symmetric, function when the logarithm of the independent variable is taken. Once the peak flux is reached, this symmetry is used to make a prediction of the flare end time. Examining over 1300 flares, an improvement in the flare end time prediction over the current climatological method is demonstrated. Predictions of the evolution of the flux prior to reaching the peak flux are also made beginning five minutes after flare onset. An effort to predict the temporal evolution prior to the peak is made using a fourth order least squares fit to the rise-phase flux alone and the rise-phase flux plus an estimate of the decay flux. Using both methods, accurate predictions of the x-ray flux evolution are made when the rise phase averages 65% complete.