Variations of the atmospheric electric field in the near-pole region related to the interplanetary magnetic field

Variations in the atmospheric, near-surface vertical electric field compone nt E (z) measured at the Russian Antarctic station Vostok in 1998 are analy zed in conjunction with changes of the interplanetary magnetic field (IMF). A total of 134 days were selected which satisfied the "fair weather" condi tions, that is, days with absence of high winds, falling or drifting snow, clouds, and electric field "pollution" from the station's power plant. It i s shown that the average diurnal variation of E (z) for these days follows the global geoelectric field "fair - weather" diurnal variation: the "Carne gie" curve, which describes the global electric circuit formed by the thund erstorm activity occurring mostly over equatorial regions. The E-z diurnal variation shows strong seasonal dependence: it is maximal (similar to 40% o f the average daily magnitude) in summer but gradually reduces through the equinoctial months and is almost negligible during the austral winter. E (z ) at Vostok is strongly affected by variations in both the IMF B-y and B-z components. The influence of B-y is dominant during geomagnetic daytime hou rs (1 100-1400 UT at Vostok): E (z) increases with B-y in the range from -1 0 to +10 nT. The IMF B-z effect is mainly seen at dawn (E (z) decreases wit h B-z) and dusk (E (z) increases with B-z).