Using a multipoint method of detecting internal gravity waves (IGW), an analysis is made of 92 sessions of observations of the variations in the intensity of the left bracket 01 right bracket 5577 A night airglow in Ashkhabad. Criteria for selecting frequency harmonics caused by IGW are established, and the seasonal variations of IGW parameters are studied. It is found that the directions of propagation of IGW vary especially greatly from winter to summer. The seasonal-azimuthal distribution of the chosen indices of dynamic activity of the lower atmosphere, together with the seasonal variation of the filter effect of the upper stratosphere - lower mesosphere jetstream, can explain the seasonal variation of the dominant directions of propagation of IGW observed over Ashkabad at heights of the left bracket OI right bracket 5577 A night airglow.