Investigation of the structure of traveling ionospheric disturbances on the basis of tomographic experiments

A tomographic reconstruction of the ionosphere at latitudes of 40 degrees -60 degrees for the daytime conditions of December 1993, is demonstrated. The two-dimensional sections show the high-latitude structure of the ionosphere with quasi-periodical variations in the electron density along a given latitude with a characteristic scale of similar to 300 km. An analysis of the spatial structure of the observed inhomogeneities indicates that these structures are related to the propagation of medium-scale traveling ionospheric disturbances (TID) with periods of 15-20 min, It is assumed that the TID considered are caused by internal gravity waves (IGW) with amplitudes of the velocity meridional components of similar to 100 m/s propagating in the thermosphere at altitudes of the ionospheric F2 layer An analysis of the structure of TID and corresponding IGW indicates that, under the given geophysical conditions, the terminator may be a possible source of the disturbances observed.