  A time series of soft X-ray emission observed on 1974-2007 years (GOES) is
analyzed. We show that in the periods of high solar activity 1977-1981,
1988-1992, 1999-2003 the energy statistics of soft X-ray solar flares for class
M and C is well described by a FARIMA time series with Pareto innovations. The
model is characterized by two effects. One of them is a long-range dependence
(long-term memory), and another corresponds to heavy-tailed distributions.
Their parameters are statistically stable enough during the periods. However,
when the solar activity tends to minimum, they change essentially. We discuss
possible causes of this evolution and suggest a statistical model for
predicting the flare energy statistics.
