On the long-term variation in the cosmic radiation

From an analysis of the cosmic-ray intensities recorded at Mt. Washington, Mt. Norikura, and Huancayo from 1954 to 1958, the long-term variation of intensity is interpreted as occurring in several sudden decreases rather than gradually. The largest changes of cosmic ray intensity and in the ratios of intensities recorded by the three detectors followed the occurrence of large Forbush-type decreases. The depressed intensity following the rapid decrease of July 11, 1959, further supports this interpretation. Frequency distributions of the changes in nucleonic intensity from day to day show the importance of the Forbush decreases to the long-term variation. These results are discussed in terms of possible solar modulating mechanisms.