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