Solar cycle variation of cosmic-ray north-south anisotropy and radial gradient

Abstract

Cosmic ray data collected at Thule, Greenland and McMurdo, Antarctica covering the interval 1961-83 are analyzed to examine any anisotropies. The data were treated to eliminate contamination from systematic variations in the efficiencies of the detectors at each site and to calculate reliable error estimations. Account was also taken of the solar rotation period and the direction of the polarity of the interplanetary magnetic field for each measurement day. Yearly averages were then calculated for the north-south anisotropy. A continuous anisotropy was observed and attributed to a cosmic ray gradient caused by the B x grad n flux. An approximately 10 yr solar cycle variation of 0.28 percent was considered as the cause of a long term variation in the anisotropy with a magnitude of 0.053 percent. No correlation was found between the anisotropy and the polarity of the solar poloidal magnetic field. 38 references