The diurnal anisotropy of cosmic rays and the heliospheric transport parameters

Abstract

We review the data on long-term changes in the solar diurnal variation of cosmic rays, observed at Deep River with a neutron monitor and at Embudo with an underground muon telescope, during the period 1965–1976. We show that the model proposed by Erdos and Kota (1979, Sixteenth ICCR, Kyoto. Conference Papers 4, 45). cannot explain the systematic changes seen in our data during 1971–1976. An insight gained from the diffusion-convection model enables us to obtain a unique solution for K ‖ G r in terms of the parameters applicable to the solar wind and the diurnal anisotropy. This helps us calculate the rigidity ( R) dependence of the diffusion coefficient K ‖. We find that K ‖ = 1.37 × 10 18 R 0.6 m 2 s −1, where R is in gigavolts, and K ⊥ = 1.08 × 10 18 m 2 s −1. Our results are discussed.