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.

As another example ofthe meridional profile of Pel pulsations associated with the SI weshowthe observations made on 22 March, 1979 in Fig. 2. There is a wave activity at about 1 Hz at Nurmijarvi before the SI at 08.26 UT. The SI results in small increaseofthe frequency of these pulsations. At more n o r thern stations (Oulu and Sodankyla) Pel pulsations occur in quite different frequency bands. In conclusion, these two examples illustrate that the SI induces great changes in the spectrum ofongoing Pel pulsations. Changes are most prominent at auroral latitudes. The characteristics of the spectrum seem to be more L- dependent than incaseofordinary Pel pulsation events. GENERATION OF IPDP PLASMA WAVES AFTER THE ONSET OF SUBSTORM. The charact eristic feature of IPDP pulsation events which are associated with the sub storm activity is an upward sweep of frequency of pulsations, typically from 0.1 to 1 Hz in 0*5 t 2 h (see, e.g. Pikkarainen et al.,1983). Pikkarainen et al. (1983) have shown that the slope of typical high-latitude events is smaller than that of low-latitude events. Kangas et al.(1976) showed two examples where Pel pulsations were obser ved before the onset of the IPDP event. They reported that IPDP pulsations KEVO 15 DECEMBER 1984 UT 2000 2100 OULU 15 DECEMBER 190A Fig. 3. Sonograms of magnetic pulsations observed at Kevo and Oulu on 15 December, 1984» л 98