抄録
Amplitudes and phases of the annual and semiannual components in the geomagnetic disturbance field and its constituents are derived at each local hour of the day for Alibag and Hermanus. The annual variations at Alibag and Hermanus are nearly in phase. The variations at the same station for intervals 12hr apart are nearly in phase opposition. It is shown that the local time variation in the annual component is predominantly due to the modulation in the asymmetric part (SD) and that in semiannual component is due primarily to the symmetric part (DR) of the disturbance field. The semiannual modulation of symmetric and asymmetric parts of the disturbance field are in phase opposition during morning hours and in phase in the evening hours leading to a marked forenoon/evening asymmetry in its amplitude. The results obtained here explain the local time variation in annual and semiannual modulations of horizontal intensity derived from observations on all days earlier by BHARGAVA (1972b, c).
