Структура и динамика полярных токовых систем : материалы международного симпозиума «Полярные геомагнитные явления», 25-31 мая, Суздаль, СССР / Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т. – Апатиты : [б. и.], 1988.

Вц.аг (»Т) Fig. 11. Effects of the positive Pig. 12. Distribution of time and negative reversals of В component delays of ground response to sharp IMP obtained by the superposed y epoch discontinuities passage through the method for winter and summer seasons reference point at the nose of a bow (Troshichev et al.,1985). shock: (a)- for increase of polar cap convection against southward reversal of B 2 ; (b) - for decrease of polar cap convection against the northward reversal of В ; (с) - for an isolated onset of Pi2 train against a positive change of IMP В . The total number of studied cases is given in circles (Sergeev et al.,1986). The turning of B y from the negative to the positive direction does not seem to play a significant role in magnetic activity. The time lag between a sharp reversal in the IMF and a triggered substorm may be very small or even negative (Sergeev et al.,1986j Troshichev et al., 1985). A special study of this problem carried out by Sergeev et al.(1986) using the satellite information on зо1аг wind parameters and data on P12 onsets shows that the substorm expansion is triggered by the contact of the solar wind discontinuity with the bow shock. In case of strongly inclined directional discontinuity fronts this contact will take place at first on the flanks of the magnetoephore and only after that on its nose. As a result the triggered substorm onsets are usually observed before the polar cap electric field response to the corresponding IMF discontinuity (Fig.12). According to Dmitrieva and Sergeev (1985) geoefficiency of impulses in the solar wind pressure does not depend so much on changes in plasma parame ters as on the IMF variations accompanying them. Consequently even large changes of the solar wind parameters (strong SC) are not responsible for trig gering of the expansive phase without IMF changes. The mechanisms of the substorm triggering remain undetermined. In the framework of existing hypotheses the influence of the northward reversal in B z component ie either connected with the appropriate changes in the magneto sphere etruoture or with a breakdown of the system of the magnetospheric conv ection been established. However these hypotheses can not explain the effects of the IMP aaimuthal component on the substorm development. I27