Modulation of Galactic Cosmic Rays and Changes in the Solar Magnetic Field
H.V. Cane1,2, I.G. Richardson1,3, T.T. von Rosenvinge1, G. Wibberenz4

1 NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
2 University of Tasmania, Hobart, Tasmania, Australia
3 University of Maryland, College Park, MD 20742, USA
4 University of Kiel, D-24118 Kiel, Germany

We discuss the modulation of galactic cosmic rays over more than a 22-year magnetic cycle (solar cycles 20-23). We suggest that the cosmic ray intensity profile can be decomposed into a gradual component with superimposed medium-term modulation events with durations of the order of one year. The inverted profile of the cosmic ray intensity tracks rather well the interplanetary magnetic field (IMF) strength as observed near 1 AU. Coupling between the IMF strength (B) and the cosmic ray transport parameters leads to a conceptually simple modulation model in which the modulation process is linked to global variations of B. We also study the correlation between cosmic ray intensity and tilt angle. The slopes of the cosmic ray response to variations in tilt angle are similar for both magnetic polarities for tilt angles between about 25 degrees and 60 degrees. Systematic differences between polarity A > 0 and A < 0 epochs are found around solar minimum for small tilt angles, in principal agreement with the existence of drift effects.