Ионосферные явления-80: материалы наблюдений Поляр. геофиз. ин-та по проекту Междунар. исслед. магнитосферы за 1980г. (оперативно-информационный материал). Апатиты, 1986.

5 connected with sharp variations of aolar radioemiaelono during the period considered which dscreaeed greatly in Maroh end August. The aharp decrease of activity in March 13Ё0 can be seen during rotation 2004 on the Calendar data in Fig,1. The recurrent sequences of the disturbances, usually clearly seen in 27 days calendars, are nearly absent, in any case during the first half of the year. In the second half of the year the aotivity is a little nigher, but the recurrent tendency laetei to be rather weak (Fig, 1 ), The previous investigations showed that during minimum solar activity in the first and second half of the year, x-eepectivaly, the negative and positive sectors of the IMF assisted to growth of the activity and that tho beginning of a new active period coincides with a change of the sign of the sector structure. Лв seen the first affirmation 1 b conserved in the year- the active period in the firat half of the year lasts longer during the negative IMP intervals and shorter during the positive ones. Besides, it is very diffucult to say anything definite about the second affirmation taking into account great variability of the sector structure. Changes of illumination of the ionosphere determine eleotron density in D, E, .FI lower ionospheric layers; gradually changing density reaches its maximum near noon (10 UT). These layers disappear during quiet winter nights. Disturbances creat addition^] ionization registered as appearance of sporadic E-layer as well as increase oi absorption. K.g.3a~e presents fo ]?2 variations for 1980 as well as for the previous years dv.ri.ng quiet days. Tue days without magnetic disturbances 15 nT) with smooth foP 2 variations and without continuous disturbances in the lower ionosphere were considered >ao quiet and are listed in Table 1. In winter fo J?2 variation itself is characterized by sharp increase of morning ionization, gaining the maximum near noon, which is followed by gradual fall towards night and morning hours. The number of days taken for determining veriacione was not large, hence the effect of disturb- aneea wtts not eliminated completely. In particular, this influence is observed in growing of night ionization marked on several plots in Fig.li. The width of day-time maximum increases together with growth of the duration of luminosity period towards summer. Daily fo I’2 values reduce whereas night ones grow. In summer time fo F2 diurnal variations of quiet days practioally disappear. Increase o.i activity, appearance of geomagnetic disturbances lead to growth of electron density in F-layere during night hours as well as appearance of additional reflection (F-spread). Electron density is reduced during day hours at periods after prolonged magnetic storms end intensive nighttime substorms. Transformation of ordinary conditions and gradual growth of daily ionization last for several days* In summer time reduce of ordinery ionization by intensive disturbance!) to some extend, restores diurnal variations and differences between day and night, since disturbances appear mainly at night and are accompanied by reducing of iort.i aation, A definite FCA event was observed on 18.07-20.07. The Russian text presents the analysis of the ionospheric behaviour for each month of the year.