Physics of auroral phenomena : proceedings of the 35th Annual seminar, Apatity, 28 Februaru – 02 March, 2012 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2012. - 187 с. : ил., табл.

Experimental researches o fwave disturbances in the polar lower ionosphere liO-i 140- 3 130- J2 120 - -o ~ 110 - 100 - 90- 80 4 31.05.2011 21.5 UT, In s 20 lg(Ac ), ‘IB I ■ 70 P 6 0 i 50 45 40 H 35 30 UT, hrs Fig. 4. Amplitude of reflections of the ordinary wave in the control day and in the day of the solar eclipse. In the Figures it can be seen distinctly enough manifestation of signals scattered from irregularities of the polar mesosphere and the lower thermosphere. Observable echo exceeds a level of noise from the heights about 80 km, and grows, on the average, achieving the level of regular reflection at the heights of the E region. Reduction of intensity of reflections at all heights in the lower ionosphere and increase of heights of the reflecting layer also are well visible during the eclipse. The analysis of daily registration of amplitudes of partially scattered radio waves shows, that there are such time intervals of observations when reflections from irregularities in the lower ionosphere are absent, or their amplitude is sharply reduced. Recession and reduction of intensity of reflections are closely connected to splashes of observable riometric absorption. Increase of auroral absorption it is possible to explain by growth of the electron concentration the lower ionosphere as a result of precipitation of energetic electrons from magnetosphere. At the same time, the minimal frequency of regular reflection can become equal or more of the frequency of radiation and there will not be any reflections from the ionosphere. The behaviour of intensity of reflections from the lower ionosphere at quiet geophysical conditions on 31 May and during the day of the polar solar eclipse is submitted in Figure 4. According to our data the day of the eclipse differed from the near control days, 31 May and 2 June, only by presence of splashes of auroral absorption. In addition to the effects, mentioned above (decrease of intensity and increase at heights of reflections), isolines of amplitudes of reflections show clearly wavy changes after the maximal phase. Time variations of the electron concentration Ne during the day of the eclipse and the control days are shown in Figure 5. 16000 7 12000 8000 * 4000 0 Fig. 5. Time variations of the electron concentration at various heights during the solar eclipse (a continuous line) and for averaged values during the control days (a dashed line). It is clear, that for the day of the eclipse the electron concentration at the interval of time 20:55 - 21:10 UT gradually decreased and was lower than it was within the control days. Then during approximately 15 minutes there were not partial reflections during the eclipse because of strong auroral absorption and we could not estimate the electron concentration by the method of differential absorption. Since 21:30 UT (after beginning of the main phase of the eclipse) the electron concentration started to increase and come to its background value. It lasted about 15-20 minutes at the height of 87 km and about 50 minutes at the height near 90 km. In Figure 6 results of the wavelet analysis of partial reflections data, variations of the geomagnetic field and ionospheric absorption of space radio emission are submitted. Because of presence of a splash of auroral absorption 117