  One of the methods of detection and analysis of solar flares is observing the
time variations of certain solar spectral lines. During solar flares, a raise
of electron concentration occurs in Earth's ionosphere which results in
amplitude and phase variations of the recorded very low frequency (VLF) waves.
We compared the data obtained by the analysis of recorded VLF signals and line
spectra for different solar flares. In this paper we treated the DHO VLF signal
transmitted from Germany at the frequency of 23.4 kHz recorded by the AWESOME
system in Belgrade (Serbia) during solar flares in the period between 10:40 UT
and 13:00 UT on 2011 April 22.
