  In this paper, we study the influence of solar flares on electron
concentration in the terrestrial ionospheric D-region by analyzing the
amplitude and phase time variations of very low frequency (VLF) radio waves
emitted by DHO transmitter (Germany) and recorded by the AWESOME receiver in
Belgrade (Serbia) in real time. The rise of photo-ionization rate in the
ionospheric D-region is a typical consequence of solar flare activity as
recorded by GOES-15 satellite for the event on March 24, 2011 between 12:01 UT
and 12:11 UT. At altitudes around 70 km, the photo-ionization and recombination
are the dominant electron gain and electron loss processes, respectively. We
analyze the relative contribution of each of these two processes in the
resulting electron concentration variation in perturbed ionosphere.
