Changes in Amplitude of the Cosmic-Ray 27-Day Intensity Variation with Solar Activity

Abstract

Both cosmic-ray neutron and ionization-chamber intensity observations reveal that the amplitude of the 27-day recurring intensity variation has been changing over an interval of several years. A method for studying this phenomenon using ionization chamber data for the period 1936-1946 and neutron intensity data for 1951-1953 is described which not only selects preferentially the 27-day variations but also selects the variations which are world wide.The amplitude of the 27-day intensity variation over these years displays minima and a maximum closely related in time to the minima and maxima of the approximately 11-year cycle in general solar activity. Thus, these results provide additional, and independent, evidence that solar active regions are responsible for producing the mechanism which controls the 27-day cosmic-ray primary intensity variations.