Long‐term variations of the cosmic ray north‐south anisotropy and the radial cosmic ray gradient at high rigidity

Abstract

Data from the Embudo underground cosmic ray muon telescope from 1965 to 1985 have been analyzed as a function of the polarity of the interplanetary magnetic field (IMF), B, to examine long‐term variations in the cosmic ray north‐south anisotropy, B × ▽NR, resulting from the interaction of B and ▽NR, the radial component of the heliocentric cosmic ray density gradient. The direction of the cosmic ray north‐south anisotropy is shown to be essentially constant over this period, and the extraterrestrial nature of the anisotropy is confirmed. The magnitude of the anisotropy is shown to be only weakly dependent on solar activity and to be independent of the magnetic polarity of the solar dipole which is the source of the IMF B. By inference, it is concluded that the radial heliocentric cosmic ray density gradient at high rigidity does not show a large variation with solar activity or with solar magnetic polarity.