World-wide cosmic ray variations, 1937-1952

Annual means from continuous registration of cosmic-ray ionization at four stations from 1937 to 1952 show a variation of nearly four per cent, which is similar at all stations and which is negatively correlated with sunspot numbers. This variation in cosmic-ray intensity is quite similar for the annual means of all days, international magnetic quiet days, and international magnetic disturbed days, which indicates that it is not due to transient decreases accompanying some magnetic storms. Although the cosmic-ray intensity at some stations is affected by meteorological conditions, it is shown that on the average the cosmic-ray changes observed at Huancayo agree well with those at other stations. From an analysis of the variability of daily means at Huancayo and a sample comparison with Simpson's neutron data, it is concluded that the cosmic-ray ionization at Huancayo is very little affected by meteorological effects. Through a comparison with Neher's balloon observations, evidence is provided to indicate the reliability of cosmic-ray results at Huancayo over long periods of time. The relation between cosmic-ray decreases and some measures of geomagnetic activity is indicated, and it is shown that the major transient decreases in cosmic-ray intensity occur during magnetic disturbance. Graphs are included which depict the daily means of cosmic-ray intensity at Huancayo for all available data, 1937–1953.