抄録
The solar cycle line has been resolved in the horizontal force by power spectrum analysis using 120 years' data of Colaba-Alibag. Having established the presence of a large signal, the variation and phase in relation to solar cycle have been computed from the data of eight observatories by the application of an appropriately designed band-pass numerical filter. The response in the horizontal force has been found to be larger and more uniform than estimated earilier. At most of the stations, the response was still greater during peaks of odd solar cycles suggesting a 22-year variation in the field. An unexpected 17 to 18 year cyclic variation has also been noticed in the autocorrelation function of the data series of Colaba-Alibag. The data of this station, after removal of the secular variation, also suggest the presence of an 80 year cycle in the horizontal force.
