Abstract
The association of the geomagnetic lunar daily variation (L) in the horizontal component with the polarity of the interplanetary magnetic field (IMF), first detected in the geomagnetic data from an Indian equatorial electrojet station, Trivandrum, is examined with more extensive data of Huancayo, a South American observatory in the equatorial electrojet belt. Seven sets of 4 consecutive years each during the period 1926-61 are selected and the first four harmonics of L are determined separately for days of A and C polarities of IMF in each of the sets, confining the data to the four d-months, November to February, when the signal to noise ratio is largest. In the four sets during high solar activity, C-polarity days show larger L than A-polarity days in the odd solar cycles and vice versa in the even solar cycles which has been noticed earlier in similar results from Trivandrum. The change in response is neither consistent nor significant in the sets during low solar activity. From these results a quasi-stationary double solar cycle, or solar magnetic cycle, in the response of L to the changes in IMF polarity is inferred. The physical mechanisms that may possibly bring about the observed modulation are discussed.
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