A correlation between IMF and the limiting primary rigidity for the cosmic ray diurnal anisotropy

A plausible explanation is provided for the existence of the subsidiary maximum in the annual mean cosmic ray diurnal anisotropy, observed during the declining phase (1982-85) of the solar activity cycle 21. For this period, the values of the limiting primary rigidity (Rc), applicable to the steady state diurnal anisotropy, are quite large. Also, the annual mean magnitudes (B) of the interplanetary magnetic field (IMF) are very high. The data for Rc and B are reviewed for 1964-1987 period. A correlation is found to exist between the two parameters.