Solar-cycle periodicity in secular variation of H at Alibag

Abstract

Quiet-day monthly mean values of H at midday and midnight of Alibag for the period 1906 to 1967 are examined for cyclic variations of sunspot cycle periodicity after elimination of the secular variation by the method of polynomial regression and the technique of numerical filteration. The cyclic component is observed both in the midday and midnight series, with prominent amplitudes from about 1930 to 1955. For most of the solar-cycles during the period of data the component variation is nearly in phase with the sunspot cycle and its amplitude for the midday series is almost twice that for the midnight series. Since the two data series differed only in respect of the magnitude of Sq (H) in them, it is construed that in addition to other causes Sq (H) also contributes to the solar-cycle variation in H.