Lunar daily variation of geomagnetic horizontal intensity at Alibag

Abstract

Following the mathematical development of Chapman and Miller, Tschu has described a practical method of determining the lunar daily variation of geophysical elements. By application of the Chapman-Miller method as described by Tschu, the lunar semidiurnal variation of geomagnetic horizontal intensity at Alibag is worked out for the equinoctial season by making use of the hourly values of the element for the period 1940 to 1944. The expression L(H)=1.2 sin(2τ+62°)±0.3 where L(H) is the amplitude of the lunar variation in the horizontal intensity H and τ is the lunar time reckoned from lower transit of mean moon at Alibag is obtained for lunar semidiurnal variation. L(H) is a maximum when the lunar time is 2 lunar hours past midnight or noon. The solar diurnal variation is also determined up to 4 harmonics. A comparison of these results with similar results for Kodaikanal suggests that solar and lunar variations are independent of each other.