Lunar tidal oscillations in horizontal magnetic intensity at Kodaikanal during periods of low and high sunspots

Abstract

The paper describes the lunar daily (L) variations at fixed lunar ages and the lunar monthly (M) variations at fixed solar hours in horizontal magnetic intensity (.H) at Kodaikanal for the low sunspot period, Jan, 1951 to Dec, 1955; and for the high sunspot period Jan. 1956 to Dec, 1960. The lunar daily variations at any of the seasons or solar activity epochs are found to follow Chapman's phase law: L=Cn sin [n~+(.n-2)v+an]. With the increase of solar activity the phase of Ls wave remains constant for each of the seasons, but the amplitude increases during D. and E. months and slightly decreases during the months, The lunar semi monthly (.M2) waves at fixed solar hours vary with the solar time in the same way as the electrojet current, i.e., the amplitude starts increasing with sunrise reaches a maximum near noon and decreases to a low value by sunset. The ratio of lunar semidiurnal (LB} wave to the solar semidiurnal (82) wave for any of the seasons decreases with solar activity. The amplitudes of LB or M2 wave at Kodaikanal are much smaller than the corresponding values at Huancayo indicating the longitudinal variation in the lunar daytime effects in H along the magnetic equator. The lunar semimonthly tides for the daytime hours are predominantly under the control of lunar time during the D. months and of lunar age during the J .months.