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.

180° Pig. 6. The eastward and westward electrojets in the current systems D P 12 (a) and DP.J .j (b) according to Troshichev et al.(1974). autunm (Ohl and Ohl,1977; Sohreiber, 1977 1 Lundstedt et al.,1981) get more evidence. 2) When B a > 0 the probability of geomagnetic disturbances drops drasti cally. Table 1 shows the relation of a number of disturbances under В > 0 to a number of disturbances under B z < 0 for various values of angle 9 . One can see from this table that occurence of disturbances under B z> 0 is obviously dependent on the ratio of the IMP vertical component to azimuthal one: when |By/ > |BZ I , the frequence of disturbances is several times higher than when |By | < |BZ |. The higher the westward electrojet intensity the less the number of disturbances under B z >0. 3) The role of the azimuthal component is especially large in the distur bance modes (a) and (b). The evident relation of amplitude t<S disturbance occurence is revealed when the Russell-McPherron mechanism effects are exclu ded from examination. This relation ie maximal in summer and minimal in winter. This means that the influence of |By | connected usually with intensification of the transpolar conveotion is displayed to full extent in the lighted polar ionosphere where conductivity is maximum. 4) Along with the |By | and Russ ell-McPherron effects the influence of the negative azimuthal component is also seen when the magnetic activity is low. This influence is especially noticeable for disturbances with prevalent eastward electrojet (mode "a") and may be connected with intensification of a conveotion flow in the evening sector of the northern polar cap under В < 0 (Troehiohev, 1984). 5) The disturbances with the predominant westward electrojet are least affected by the azimuthal component. They are developed almost exclusively under the IMP southward component being maximum in the winter season. This means that the westward electrojet defining the substorm explosive phase is most pronounced in the winter polar ionosphere, the background conductivity of which is minimal. The e x a m in e d data show at least three effects of the azimuthal component I2I