Авроральные явления - 79 : результаты работ по программе Международного года исследований магнитосферы : материалы наблюдений Полярного геофизического института за 1979 г. : (оперативно-информационный материал) / Акад. наук СССР, Кол.фил. им. С. М. Кирова, Поляр. геофиз. ин-т ; [отв. ред. Б. Е. Брюнелли].

5 High geomagnetic activity in spring ia аіво seen from diurnal variation of mean r^ (Pig.4a). Variation is asymmetric, at morning hours activity is higher than at the evening ones. This is caused by asymmetry of time distribution of great magn etic storms in April. Ionospheric disturbances are maximum at night when the contrib ution of corpuscular ionization is greater than the UV one; as for seasons disturb ances are the highest in winter and spring. The maximum near the midnight is typical о о for luminosity of auroral 4278 and 5577 A emissions. Hydrogen emissions and 6300 A- line have their maxima at evening hours; precipitation of hydrogen and soft plasma mainly takes place at these hours also. Calendar (Fig.2) shows that the periods of high and low activity last for several days begining with sharp increase and are followed by gradual fall. During the last years of Solar Cycle the onsets of active periods formed distinct recurrent sequencies. Thia year falls on the growth phase and the tendency to form recurrent sequencies is less pronounced than earlier. Calendar (Pig.2) shows that at the begining of the year days of high activity are placed on the first three quarters of the Bartelto rotation period, more quiet days constitute the last quarter, Further, quiet days appear at the begining of the rotation period; duration of high activity period gradually decreased. The plot of high activity region is wedge like narrowing towards summer, Recurrentness in the second half of the year is even more weakly pronounced than in the first one. The level of activity can also be estimated from mean diurnal values of r^ (Fig.5). The days with considerably increased r^ values are marked. Distribution of days is not quite casual: the daya can form recurrent sequences though the way of organizing them is not unique and the recurrents, as mentioned, are indistinct. Connection between the distribution of high-latitude geomagnetic activity and sector structure of the Interplanetary Magnetic Field (IMF) was demonstrated in our previous volume with the data on minimum solar activity. It was noted that the begining of an active period often coincides with the moment of IMF sign change. Futher development of activity depends on the sector sign. Since positive В pro duces northward (with respect to the Eartn's magnetic axis) component during the first half of the year, increase of activity in spring may be associated with existence of IMS’negative sector and positive one in autumn. IMF sector sign distr ibution in 1979 according to /17/ is also given in Fig.5. At the begining of the year IMF is negative throughout the main part of Bartel's rotation. Positive IMF appears at the end of the rotation. Then it turns up at the begining too; its duration gradually grows while the duration of the negative one decreases. Transi tion to the other sector is not straight and is accompanied by repeated changes of the field-sign. During the second half of the year the sector structure is almost indistinguished. Changes of the magnetic field seem to be more evenly near the Sun as seen from the Stanford Solar Observatory data /15/ for 1979 presented in Fig.6. She position of the sector boundary is confirmed, however repeated changes of the sign near the sector boundary are not marked here. Mean values of гц and activity according to Calendar (Fig,2) separately for the daya with positive and negative IMF have been calculated in order to test the i n fluence of the sector structure. The days were selected according to the data by Mansurov (Fig. 5) /17/ and the measurements near the Sun (Pig. 6) /15/. Flg.7a,b~d presents the results of calculations. It is seen that the days with negative IMF formed the spring maximum whereas the August maximum is formed by the days with both IMS1 signs. Calendar (Pig, 2) and the given magnetograma show that during the first half of the year the duration of the active periods is longer in the negative sector than in the positive one. During the second half of the year an opposite correlation is not observed, the results are indistinct because of low level of activity.