Авроральные явления - 80 : результаты работ по программе Международного года исследований магнитосферы : материалы наблюдений Полярного геофизического института за 1980 г. : (оперативно-информационный материал) / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т ; [отв. ред. Б. Е. Брюнелли].

The calendar in Figure 2 contains evaluation of activity for every hour of the year. Diurnal variation with decreaBing activity in the day-time (middle of every row) and its anomalously low level in March, rotation 2004 are clearly distinguished. The tendency for recurrent sequencies is manifested as weak as in the previous year. All active formations in this year are cut off by the mentioned rotation 2004. The seasonal variation of all activities is also presented in Figure 3. It is seen that rH gains its maximum in June; in the considered year there are no equinoctial maxima which are distinctly displayed on the plot of mean values for 11 years. It is seen that all monthly mean Гдvalues, except June, are less than the value averaged for 11 years. Anomalous manifestations of activity began in 1979. In /11/ it was marked that a usually observed rise of activity near the equinox was broken by a decrease the autumnal maximum did not occur, and .the period of low activity continued in spring 1980. Comparison with the plot of solar radioeraission variation shows that this unusual decrease of geomagnetic activity coincides with deep oscillations of the radioemission flux. Solar activity is unstable in 1980. On the background of a generally high level there appear deep falls which can be compared with anomal ous manifestations of geomagnetic activity and its decrease instead of an expected rise. Examinations of the plots in Figures 1 and 2 enables to conclude that the well кпотеі statement concerning an increase of activity during the equinoctial seasons is true only for the cases when solar activity does not suffer any essential changes throughout the year. Occurence of such changes can lead to a sharp alteration of geomagnetic activity variations and even to disappearence of its typical features. The diurnal variation of activity from geomagnetic, ionospheric and optical observations for every season of the year is presented in Figure 4. Thus, low activity in spring is confirmed.. The growth of activity towaras night during all the seasons, as well as broadening of the maximum in winter with increasing of darkness of the day is clearly seen. Comparison of daily mean values of hourly range, r^ with the sector signs of IMF is carried out in Figure 5« The days with increases geomagnetic activity determined by either rH increasing, magnetograma or notation of a magnetic storm occurence in information issues /15-16/ are marked. Figure 6 presents the distribution of such active days in comparison with Dst variation averaged for 4 hour intervals. The tendency for formation of recurrent sequenoies is proved to be poorly manifested. The regions of increases activity in the figure is shifted towards more later dayaj the recurrency, if any, is realized in more than 27 days. According to the data of the previous years /4-11/ two types of relationship between active periods ware marked. Occurence of active periods tends to be connected with the reversal of the IMF sign because if the commencement of magnetic storms is due to arrival of new high speed corpuscular fluxes then, probably, the magnetic field of the new flux will differ from the field of the previous one. Moreover, the sign of the sector influences the intensity of the осcuring active period, via. in the first half of the year a more high level is expected to correspond to the negative sector of IMF, whereas it corresponds