[en] Travelling ionospheric disturbances (TID) in the lower thermosphere at heights of E_S layer formation in the mean-latitude ionosphere are studied. The parameters of medium-seale ad large-scale TIDs are given in histograms. At heights of the E region the TIDs of different time and spatial scales are detected

[en] It is known that travelling ionospheric disturbances are produced by gravity waves. During their movement from the F region downwards to the E region, gravity waves can produce thin layers called transients on ionograms and, if the wave motion persists, 'h-type Esub(S) can be produced. To investigate the problem, the continuity equations for both the E and F regions are solved for a perturbation, the motion of which is taken to be a gravity wave. Hitherto, N'/N⁰, the ratio of the disturbed to the undisturbed electron density, has been calculated by using only the Hall conductivity and ignoring the diffusion term for the F region. In the present calculations we have used Pedersan and Hall conductivities and calculated the N'/N⁰ ratio for both the E and F regions. Using CIRA standard atmosphere data we find for the F region that N' can exceed N⁰ by up to 4 percent, depending on the horizontal wind velocity. In the E region, N' reaches much higher values than in the F region. Thus at 120 km if we take a typical horizontal wind velocity of 80 m/sec (wavelength 150 km), N' is about twice as large as N⁰. From these results we see that the diffusion term is important for the E region. (author)

[en] Contributions to the studies of the normal E region, Sporadic E and the F region are reviewed and problems of measuring ionospheric movements discussed

No abstract available

[en] In order to interpret the direction of propagation of travelling ionospheric disturbances that have been observed from Valensole (43⁰ 48'' N, 6⁰E) in the ionospheric F region, the influence of thermospheric winds on the propagation of medium scale gravity waves between their sources and the point of observation is studied. At each height, the speed of wind requisite to reflect or to absorb gravity waves of different periods generated at two distinct heights is calculated. The speed of wind obtained is compared with the published data. The wind is shown to deeply modify the propagation of gravity waves in two slabs of height: between 30 and 80km and above about 200km. A particular circulation of winds between 30 and 80km is suggested to explain our results

No abstract available

[en] Medium-scale travelling ionospheric disturbances (MSTID) at ionosphere F-region altitudes in the region of Tbilisi in 1980-84 are investigated using three ionospheric stations of vertices of the measuring triangle with ∼50 km base. Continuous observations in 5-minute regime were performed during 12-15 days in every season of the year. It is shown that daily-seasonal changes of preferred MSTID motion directions are conditioned by neutral winds; disturbances mainly propagate against or across the wind. The main contribution to continuous variations of MSTID velocity is made by continuous and semi-continuous tide winds

[en] Two types of disturbances observed in the ionization density and the line-of-sight ion velocity data from the Worldwide Atmospheric Gravity Wave Study are analyzed and compared with theoretical studies. The study concentrates on the source-response relationship between auroral activities and gravity waves observed in the F-region. In the first section, the measured and derived wave parameters for a semiperiodic TID observed on October 18, 1985 during a moderately magnetically active period are shown to be consistent with predictions from wave theory. In the second section, the background wave spectra observed during several magnetically quiet days are analyzed. It is shown that the neutral vertical velocity spectrum can be modeled as a power law type spectrum. The overall kinetic energy of this spectrum is calculated and compared with the TID. 32 references

[en] The effects of travelling ionospheric disturbances (TIDs) on the observations of solar radio storms at meter and decameter wavelengths by the radioheliograph and the decameter array in Nancay (France) are used to derive basic parameters of atmospheric gravity waves. TIDs are modelled as one-dimensional lenses, which produce apparent shifts of the source position at meter wavelengths, and focusing at decameter wavelengths. For 21 common events observed on 8 days, we measure the direction of propagation, the horizontal wavelength of TIDs, and the amplitude of the vertical electron content fluctuation. The waves are probably of meteorological origin. We check that waves with such characteristics are able to propagate from tropospheric levels up to the F₂ ionospheric layer

[en] Electron density deviations from a basic variation with the solar zenith angle were investigated. A model study was conducted in which the effects of changes in neutral and relative densities of atomic and molecular oxygen on calculated electron densities were compared with incoherent scatter measurements in the height range 100--117 km at Arecibo, Puerto Rico. The feasibility of determining tides in the neutral atmosphere from electron density profiles was studied. It was determined that variations in phase between the density and temperature variation and the comparable magnitudes of their components make it appear improbable that the useful information on tidal modes can be obtained in this way. (Author)