On the modulation of galactic cosmic ray intensity during solar activity cycles 19, 20, 21, 22 and early 23

Abstract

Cross‐plots of annual mean sunspot number against the annual mean intensity of galactic cosmic rays for the period 1953–1999 show a striking difference between such modulation loops for solar activity cycles 19 and 21 and those for cycles 20 and 22. The loops for cycles 19 and 21 are broad ovals whereas those for cycles 20 and 22 are nearly flat. A complementary feature of the data is that the cosmic ray intensity decreases more rapidly as the sunspot number increases following solar activity minima when the solar polar magnetic parameter A is negative than when A is positive. It is argued that these facts give some support to including gradient and curvature drifts in theories of the transport of cosmic rays in the heliosphere. Further development of the modulation loop for cycle 23 is awaited with special interest.