Аскаплоты советских станций за 1976 год : (оперативно-информационный материал) / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : Кольский филиал АН СССР, 1989.

13 PA index variation leads to better coincidence of auroral and magnetic activity variation (see, "Ascaplots for 1975", /5/). Figure 4a ia a scetch of seasonal variations of geo- and helio-physical parame ters. The reading was taken off from the mean values of the corresponding parameter for the given year. Similar to the previous year only the magnetic activity displayed distinct seasonal variation. The equinoxial maximum was observed in March and September, whereas the minimum was marked in winter and summer for the northern hemisphere. Some asymmetry is observed, i.e. the spring maximum is significantly higher than the autumn one and the summer minimum is much more deeper than the winter one. Seasonal variation is practically absent for auroral and solar activity. PA index variations had three small rises in January-December and April-March and in August. Figure 4 6 displays seasonal variation of the same parameters averaged for 1972-1976. Similar to variations in 1976 distinct seasonal variation is marked only for magnetic activity with the same features but with the lower amplitude. There is practically no seasonal variation for solar and auroral activity. Figure 4 b presents the monthly difference between variations in 1976 (Fig.4a) and mean values (Fig.4 6 ) for the same three parameters of the activity. Since this year coincides with the minimum of solar activity the differences appear to be mainly negative. Cycle variations of geophysical activity for 1972-1980 are recorded in the issue of ascaplots for 1980 /6/.