Equatorial electro et effects on geomagnetic pulsations

Magnetic pulsation signals (in the period range 20-150 sec) observed during 1976 at the two stations - Choutuppal (geogr. lat., 17.5deg N; geomag. lat. 7.5deg), a station outside the electrojet, and Etaiyapuram (geogr. lat. 9.2deg N; geomag. lat.-0.6deg), a station at the dip equator, under the electrojet - are examined to compare their relative strengths at the two stations. The signal strength in Hsub(x)-component for Pc3, Pc4 pulsations at Etaiyapuram shows a clear enhancement relative to that at Choutuppal around noon hours. During the afternoon sector (after about 1500 hr LT), however, there appears to be a transition in the relative strengths of the signal in that the signal at Choutuppal tends to be larger and this trend continues through the night. The results on Pc3, Pc4 pulsations are seen to indicate a definite influence of the equatorial electrojet on the signal strength of these pulsations and thus suggest the possible existence of ionospheric current systems oscillating at these frequencies. (auth.)