[en] 10.12 1988 disturbed period from 14 up to 20 LT (45 deg E time) with two typical substorms, 14.30-15.30 and 18.30-19.30 LT and with magnetic variation between 15.10 and 18.30 LT, stand out at the background of the quiet magnetic field of the first half of Dec 1988

[en] To study the ionospheric gap considered is the anomalous ionization of the F2 region and decrease of its density in approximation of the gap zone according to the data of three ionospheric stations of the Arhangelskij proving ground. It is shown that under the moderately excited conditions a meridional chain of stations separated at the distance of approximately 100 km in subauroral zone permits to observe continuously the gap transfer and the transfer of the southern boundary of the anomalous ionization

[en] Altitude-latitudinal distribution of ionization in subauroral ionosphere for 19.03., 21.02., 25.01.1981 are plotted according to the data of synchronous measurements at the ''Interkosmos-19'' satellite and at three stations of vertical sounding on Archangelsk geophysical experimental range. Measurement results are compared with the observation data in Asian and American sectors. A comparison with modelling calculations is carried out as well. Description of three cases in subauroral ionosphere, presented, permits to make the following conclusions. Models of high-altitude ionosphere published, are in general agreement with presented experimental data: steep polar and more sloping equatorial wall of the main ionospheric trough (MJT), latitude position of MJT bottom, wedze at the MJT bottom in the evening sector under the conditions of geomagnetic disturbance. However several details and even sufficient features are not presented (or are presented inconsiderably), namely: step-like character of polar MJT wall, altitude MJT structure, electron concentration value in the trough and in a region of auroral peak, wedge at the bottom in the morning sector

[en] According to the data of terrestrial and satellite probing of the ionosphere the characteristic properties of the main ionospheric trough (MIT) in evenings during winter and equinoctial months under magnetic disturbances are described. On the basis of analysis of eleven substorms it is shown that in the considered height interval (800 km) the MIT depth decreases with the height increase, the MIT bottom position forms an angle with the line of equal invariant latitude, f₀F2 interruption occurs near the southern edge of the eastern electrojet, MIT development is followed by amplification of charged-particle precipitations revealing in E_s occurrence and absorption increase

[en] According to the data on electron concentration measurements taken by the Interkosmos-19 satellite the IMF effect on the main ionospheric through (MIF) location is considered. It is shown that the effect of B_Z and B_y IMF components is the contrary: the B_z increase and B_y decrease leads to increasing the MIT (Φ') latitude, and B_z decrease and B_y increase - to decreasing Φ'. When B_Z and B_y have different signs, the IMF effect is intensified, and at their equal signs the JMF effect weakens and under some conditions it is complitely levelled

[en] Variations of ionospheric trough depth are considered depending on helioglophysical conditions. In the perturbation periods the depth of the main ionospheric trough is maximum on hm under tranguil and slightly perturbed conditions the trough depth changes slighly along the height in the years of maximum solar activity while in the years of low solar activity a significant increase of trough depth with height is noted. A possible explanation of these variations in terms of known mechanisms of its formations is given

[en] Electron concentration height profiles in external ionosphere constructed, according to the data of the Interkosmos-19 and Kosmos-1809 satellites, are compared to the IRI-86 and SMI-85 models. Variations of discrepancies between the experimental data and summer models depending on the time of the day, height, latitude and solar activity, are considered. The conclusion is made that these models require considerable modification for adequate description of the electron concentration distribution in the external ionosphere

[en] The shifting of the main ionospheric gap during day-light ionospheric magnetic storms is considered. The gap depth and electron concentration gradints on the gap walls are determined. The shifting of the gap during the storm in the south-eastern direction has been found. The results agree with the theory elucidating the gap formation by the convective transport of an ionospheric plasma in the direction to the Sun

[en] Case studies results are considered of coordinated ground-based observations from the ionosondes in the Northern European part of the USSR together with the AUREOL-3 satellite conducted in the frame of the ARCAD-3 project. Directly measured positions are compared of the soft electron boundary, of the polar and equatorial walls of the main trough, and of the equatorial wall of the light ion trough. These are shown to be consistent with earlier results from the ARCAD-1 and ARCAD-2 coordinated ground-satellite experiments