Time variations of Alibag K-indices ( 1946-1965)

Abstract

Results of analysis of time variations of Alibag K-indices for the period 1946 to 1965 confirm the occurrence of day-time maximum in summer and night-time maximum in the equinoxes and winter. Average magnitude of K-index at each of the 3-hour intervals, for which K-indices are scaled, depicts semi-annual trend with equinoctial maxima. This semi-annual variation is particularly prominent around midnight. Annual trends in equivalent daily range amplitude, At, for Alibag show clear equinoctial maxima for both IQ and m days of the years 1952-54. No clear semi-annual variation in At is seen during sunspot active periods of 1955-57 and 1958.60. Power spectra of At depicts also rotation periodicities for the years around the sunspot minimum year 1954. This periodicity is much less prominent during the years around sunspot maximum. The observed features are discussed.