: Contents: Results of observations made during the IGY; Frequency-separated reception and its combination with spatial separation; Method of complete correlation analysis; Volumetric correlation analysis.

Irregularity structure and movement in the ionosphere (selected passages)

Solar activities including solar radiations affects not only the electron content of the ionosphere but also the various frequencies used in telecommunications. The alternating voltages of the frequency modulation (FM) in Ahamdu Bello University radio station was obtained during the period of three months from July to September 2019. The variation of all prominent peaks of the electron density begins during sunrise and sunset, where most of the peaks shows weak signal strength during the daytime i.e. at 16,000N/m3 compared to night time and morning time at 0.00N/m3 and 0.00N/m3 respectively. The results showed that this station have all day signal strength, while night time show variability in signal strength. This observation may be attributed to the solar activity in the atmosphere. We calculated the critical frequency and hence find the Maximum Usable Frequency (MUF) and conclude that solar radiation factor give the minimum significant effect to radio signals.

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The effect of solar radiation on the signal strength of a.b.u. samaru radio station

The analysis of the MF radar data shows an existence of the repeated phenomenon of a backscattered signal intensity decrease for the period of 0.5 - 4 hrs in evening. A comparison with the fluxes of the particles reveals an intercoupling of the considered processes. One of an assumption explaining the lower ionosphere dynamics peculiarity for the viewed periods is discussed.

Behaviour peculiarity of mf signal backscatted by polar ionosphere in evening

The lower polar ionosphere research are carried out by the modified measuring complex of the observatory Tumanny (69.0 degree(s)N, 35.7 degree(s)E) since 1999. It were performed an analysis of the dynamical processes caused by the neutral gas motion, preliminary investigation of statistical and spectral characteristics of the backscattered waves and, furthermore, variations of the electron density were calculated. The areas, where the electron density irregularities with scales more than 100 m at heights from 70 till 99 km were groped, were detected by the spaced sensors measurements of the backscattered waves. During the solar eclipse of 1999 August 11 for the short time the increased radioecho intensity was observed at the heights near the mesopause.

Lower polar ionosphere research by the partial radioreflections technique

MF radar observations of mesospheric backscatter were carried out during summer - winter 1999 in Tumanny (69.0 degree(s)N, 35.7 degree(s)E) using PGI radar of the vertical sounding. The measurements indicated the presence of strong radar returns from altitudes between about 74 and 99 km. Usually, the reflection region looks like as 2 or 3 distinct layers, which are located at heights 74 - 82, 82 - 89 and 89 - 99 km. The features of MF waves backscattered from a height range of 82 - 89 km are very similar to VHF radar measurements of Polar Mesospheric Summer Echoes (PMSE). A distinctive feature of these measurements is a registration of sharp gradients of the electron density at the heights where the backscattered waves amplitudes were more intensive. An analysis of the digital ionograms obtained in Loparskaya (68.6 degree(s)N, 33.3 degree(s)E) have shown that the intensive sporadic E-layers are observed during the strong MF radar returns from the mesopause region.

M. V. Yakimov

Papers

Lower polar ionosphere research by the partial radioreflections technique

MF radar sounding of the polar mesophere for the experiment of 1999