27-Day oscillation in the cosmic-ray intensity and shorter periodicities

Abstract

Average diurnal data of cosmic-ray intensity, recorded in the time intervals between July 1955 and December 1958 (maximum solar activity, IGY) and between November 1963 and April 1965 (minimum solar activity, IQSY) at Huancayo with one neutron monitor and one ionization chamber, and at Resolute Bay with one neutron monitor and one cubic telescope of G.M. counters, have been analysed with respect to the recurrent variations of the 27-day period and of shorter periods (approximately 12 days and 6 days). Results of the analysis are herein reported and discussed; it emerges that;a) the amplitude values obtained at the same time with different counters are of the same order of magnitude;b) in the period of maximum solar activity these values are much higher and more correlated (solar modulation effect) than in the period of minimum solar activity (local atmospheric effects).