Coronal Mass Ejections, the Tail of the Solar Wind Magnetic Field Distribution, and 11 Year Cosmic‐Ray Modulation at 1 AU

Abstract

Using a recent classification of the solar wind at 1 AU into its principal components (slow solar wind, high-speed streams, and coronal mass ejections [CMEs]) for 1972-2000, we show that the monthly averaged Galactic cosmic-ray intensity is anticorrelated with the percentage of time that the Earth is embedded in CME flows. We suggest that this anticorrelation results primarily from a CME-related change in the tail of the distribution function of hourly averaged values of the solar wind magnetic field (B) between solar minimum and solar maximum. The number of high B-values (≥10 nT) increases by a factor of ~3 from minimum to maximum (from 5% of all hours to 17%), with about two-thirds of this increase due to CMEs. On an hour-to-hour basis, average changes of cosmic-ray intensity at Earth become negative for solar wind magnetic field values ≥10 nT.