SOLAR ACTIVITY AND 11-YEAR MODULATION OF COSMIC RAYS

The cosmic-ray intensity during the 18th and 19th solar cycles is examined in the light of Gnevyshev's suggestion of the presence of two maxima in each solar cycle. The 18th solar cycle (1944-54) has two prominent and widely separated cosmic-ray minima corresponding in phase with the two maxima in Bartel's Ap index. For the 19th solar cycle the existence of two minima is less prominent than for the 18th solar cycle. The maximum at higher solar latitudes is more effective in reducing cosmic-ray intensity than the maximum at the lower latitudes. Ap, however, has a larger maximum during the lower latitude solar maximum. A relation between Ap and cosmic-ray intensity is obtained. This relationship is shown to be consistent with Parker's solar-wind theory of the modulation of cosmic rays. © 1969 D. Reidel Publishing Company.