  The perturbations from the solar terminator in the range of acoustic-gravity
waves (AGWs) periods from 5 minutes to 1 hour were analysed with the use of
measurements of VLF radio signals amplitudes on the European radio path
GQD--A118 (Great Britain--France). These observations provide information on
the propagation of waves at altitudes near the mesopause ($\sim$ 90 km), where
VLF radio waves are reflected. On the considered radio path a systematic
increase in fluctuations in the amplitudes of radio waves was observed within a
few hours after the passage of the evening terminator. For April, June, October
2020 and February 2021 events, the distribution of the number of wave
perturbations with large amplitudes over AGWs time periods has been studied.
Our results show that the evening terminator for different seasons is dominated
by waves in the range of periods of 15--20 minutes. The amplitudes of the AGWs
from the terminator at the heights of the mesosphere (fluctuations in the
concentration of neutral particles, velocity components and vertical
displacement of the volume element) are approximately determined by the
fluctuations of the amplitudes of the VLF radio signals. The amplitudes of the
AGWs on the terminator are 12--14\% in relative concentration fluctuations,
which correspond to the vertical displacement of the atmospheric gas volume of
1.1--1.3 km. Based on the analysis of the AGW energy balance equation, it was
concluded that the waves predominantly propagate in a quasi-horizontal
direction at the terminator. The possibility of studying the long-term changes
in the mesosphere parameters using fluctuations in the amplitudes of VLF radio
waves at the terminator is shown.
