Solar activity and transient decreases in cosmic-ray intensity

Abstract

The world-wide character of the intensity changes in meson and nucleon components is shown by a study of data from Ottawa, Churchill, and Resolute during the period October 1956 to December 1957. Further discussion is essentially restricted to the mean nucleonic component derived from the three stations. The investigation reveals an association between transient decreases in cosmic-ray intensity and the central meridian passage of active solar regions. On an average, the greater the activity rating of the regions, the larger is the cosmic-ray decrease. It is not possible, however, to discuss the relation specifically in terms of the characteristics of the regions, such as flares, sunspots, and the like. Further support for the relation comes from observation of geomagnetic data. Attention is drawn to the similarity between small as well as large transient decreases in intensity with regard to presence or absence of recurrence tendency. The study supports the view that both the 27-day variation and the Forbush events differ only in degree and could therefore be attributed to the same mechanism. It is possible to attribute the cosmic-ray decreases to beams of ionized rarified gas emitted from the sun and differing considerably in their characteristics.