Ионосферные явления-77: материалы наблюдений Поляр. геофиз. ин-та по проекту Междунар. исслед. магнитосферы за 1977г. (оперативно-информационный материал). Апатиты, 1978.

5 calender are noted the days, when the activity exeedes the level of previous day. In the middle part of the year the activity decreases and it is on very low level during June. In the second half-year C-sector almost dieappeares, В-sector becomes very wide, D-sector is the most active^ the highest activity is connected with positive sectors. In the end of the year some unusual events arises the ECA and the storms with unusual behaviour of geophysical phenomena. The common state of auroral ionosphere is disturbed one* the quiet days are rare. Most of the disturbances are connected with the magnetospheric substorms. For the disturbances which begin at afternoon hours in equinox or winter seasons it is typical the break of daily variation of fQF2, the appearance of sporadic E-layer and additional formations in F-region and the presence simultaneously with them of the positive magnetic bays and hydrogen aurora. The disturbances which arise in early afternoon hours usually are accompanied by the absor­ ption increasings. Later such increasings become rare and the positive geomagnetic bays in late evening hours often are not accompanied by absorption. At the night hours the disturbances become the most intense} they are accompanied by the sharp negative bays, by the aetive forms of aurora, the appearance of dense sporadic layers and the absorption increasings. In morning the intensity of geomagnetic bays registered by auroral stations decreases, for morning disturbances the deep and long lived absorption increasings are typical. The absorption events can be observed at daytime also, but then at the evening hours they disappeared. The apperance of increased absorption and E e~layer is often observed,'during daytime also, but they do not break the normal fQF2 variation and hence the sunlit ionosphere seems to be less disturbed than in dark periods. In summer the daily variation of fQF2 becomes small, but the daily variation of the disturbance occurence remains remarkable, the dense sporadic Ear and E Ba-layers appear mostly during night hours. In summer often E 0^—layer appeares, which is not correlated with magnetic activity. During strong disturbances the smooth changes of ionospheric parameters often become broken by strong absorption (blackout) or by the very dense sporadic layers. The daily variation of f0^2 is also changed; when the disturbance arise in the day time, the value of fQF2 may both increase and decrease. If the disturbance began early, during previous night, the value of fQF2 always decreases. In the beginning of the year the value of fQF2 is relatively low even in daytime. The disturbance occur often and develop in the dense EB at night and in the absorption increasing. The dense E 0 appear almost every night and its density changes in accordance with magnetic disturbances. With every new magnetic bay both f^Eg and the electron density of P-region increase. If the disturbance is not appeared at evening hours during quiet days fQP2 can decrease till the limit of ionosonde scale, the ionosphere "dieappeares". During very quiet nigbt 21-22.01 the ionosphere is not observed from 16UT till 06.30UT. With the approach to the spring the density of F-layer becomes higher during longer time and is not disappeared during night. In March during quiet periods the P-layer is seen all day continuously. In the middle of March when the disturbed days alternate with quiet ones, it is seen that the daytime f q P2 are higher in caee of quiet and lower in case of disturbed previous day. With the increasing of sunlit period E and F1 layers are seen during more longer time, since the end of May - all day continuously. In June the activity is very low. The variation of layer frequencies is small. Often (e.g. 30.0V, 9.VI and 10.VI) E0^- layer with high f^Sg appeares during magnetic quiet period. The sensitivity of the iono­ sphere to the magnetospheric activity is high» ionosphere is often disturbed in days with almost quiet magnetic field. During quiet periods the critical frequencies gradually increase. In the end of June the daily variation is almost absent. In July and August ionosphere remains sunlit, but the activity is higher than in June. The variation often is complicated by the appearance of dense E 0 , and the absorption. During most of the time E sf exists, but its density is not high. The first decade of