  The light curves of solar flares in the impulsive phase are complex in
general, indicating that multiple physical processes are involved in. With the
GOES (Geostationary Operational Environmental Satellite) observations, we find
that there are a subset of flares, whose impulsive phases are dominated by a
period of exponential growth of the emission measure. The flares occurred from
January 1999 to December 2002 are analyzed, and the results from the
observations made with both GOES 8 and GEOS 10 satellites are compared to
estimate the instrumental uncertainties. Their mean temperatures during this
exponential growth phase have a normal distribution. Most flares within the
1\sigma\ range of this temperature distribution belong to the GOES class B or
C, with the peak fluxes at the GOES low-energy channel following a log-normal
distribution. The growth rate and duration of the exponential growth phase also
follow a lognormal distribution, in which the duration is distributed in the
range from half a minute to about half an hour. As expected, the growth time is
correlated with the decay time of the soft X-ray flux. We also find that the
growth rate of the emission measure is strongly anti-correlated with the
duration of the exponential growth phase, and the mean temperature increases
slightly with the increase of the growth rate. The implications of these
results on the study of energy release in solar flares are discussed in the
end.
