Электродинамические процессы в высоких широтах: материалы междунарордного симпозиума «Полярные геомагнитные явления», 25-31 мая 1986 г., Суздаль, СССР / Междунар. геодез. и геофиз. союз, Междунар. ассоц. геомагнетизма и аэрономии ; Акад. наук СССР, Кол. фил. им. С. М. Кирова, Поляр. геофиз. ин-т ; [редкол.: О. М. Распопов (отв. ред.). и др.]. - Апатиты : Кольский филиал АН СССР, 1988.

2) quasi-oaeillations (leaa regular but still mono-harmonic pulsations); 3) waves (sinusoidal pulsations of changing periods); 4) irregular pulsations of a multiharmonic spectrum. We have studied only санез 1,2 and 3 w i t h a period below 40 sec. They usually have a linear polarization. STATISTICAL STUDIES. Without m in i mizing euch a n important moment as the harmonic strusture dependence (in particular the period) on the geomagnetic latitude and longitude, wh ic h is one of the basic problems of the experiment carried out b y the KAPG project, we are basically investigating the depend ence of the amplitude (the frequency of occurrence, respectively) on the Dst index and its h ourly changes ДDst= D st ^ - Ds t ^ _^ . It is stressed on the high frequency part of the pulsation activity,i.e. Pc3 type w i t h a period T < 4 0 s. The pulsations wit h a period T > 40 s altogether are of a n irregular character of the type Pi2. The dependence of the frequency of occurrence is statisti cally analyzed depending on the local L T (universal UT) time a nd the differ ences дDst (see Figures 1 and 2). The dependence of the amplitudes jof the two components the north-south (H-S) and East-Wost (E-W) from дDst is given separately. While the dependence on UT is not an unexpected result (Pudovkin, йавророѵ and Kl e i m e n o v a , 1976) then the step-like increase of the occurrence frequency at positive variations of ДDst is an indication for the fact that the latter favour their propagation. Further analysis, however, геѵеаів the different behaviour of the two components from лDst; while the north- Bouth component is indifferent tov/ards the change in Dst, the east-west one shows little but monotonous dependence on A Dst without any leap at Dst=0 (Figures 3 and 4), This result obtained on the whole masBif of data per mo n t h does not correspond to the conclusion from F i g . 2. The detailed analysis shows that this effect is connected w i t h the substorm activity. Indeed during the storm from 21-24,09.1984 an abrupt increase of the amplitudes of the high frequen cy components is observed, where the amount of the negative variations are maximized, i.e. at the negative changes in Dst w h i c h characterize Dst decrease, the strong dependence of the pulsations amplitude fro m Dst itself is in fact manifested. The regression analysis made f or the stormy period on independent parameters: the h ourly averaged amplitude of the pulsations AE _w and A jj _ s and dependent parameters: a) Dst, дD s t ; b) H-change of the Figure 1. Universal time (UT) dependence of the high- frequency part of the middle- latitude geoelectric ULF pul sations, recorded at Preselent- si (PR). Shadowed area indicates the frequency of occurrence (above the line 0 ) and the frequency of non-detectability (below the line 0 ) of the continuous pulsations with period T b e l o w 40 seconds. UT 0 6 П /в Я ЮЗ