Influence of the large-scale inhomogeneities on the Intercosmos-19 topside sounding ionograms in the region of the main ionospheric trough

The complex ionograms of the topside sounding onboard the Intercosmos-19 satellite in the main iono-
spheric trough region were observed on November 26, 1980. The two additional traces more distant than the
main traces were recorded on these ionograms. All the traces become more diffuse, when closing in and finally
merge into one, strongly diffusive trace when the satellite approaches to the trough minimum. The increase
of the diffusivity (F-spread) on all the traces is related to the growth of the small-scale inhomogeneities when
approaching to the trough minimum. The interpretation of the complex ionograms by the means of ray tracing
was carried out. The 2D version of the ray tracing on the base of the method of the characteristics was used.
The calculations show that the additional traces are related to the large-scale inhomogeneity which stretches
along the magnetic meridian in the horizontal plane above the F2-layer maximum. The calculations allow us to
estimate the inhomogeneity parameters: intensity dNe/Ne = 0.20, the length, width and height are about 1000
km, 100 km and 300 km correspondingly.