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Variations of Upper Cut-off Rigidity Of Cosmic Ray Diurnal Anisotropy

Ambika Singh, Divya Dubey, Rukmani Pratap Singh & Anil Kumar Tiwari

Using the experimental data of the high counting rate neutron monitor, the solar diurnal anisotropy of galactic cosmic rays has been investigated for the period 1986-2006.The most probable value of the upper cut-off rigidity of the diurnal variation shows a 22- years magnetic cycle variations with the lowest value at the sunspot minima of A>0 phase. Upper cut-off rigidity in solar cycle 22 and 23 is found to vary between 40 GV to about 100 GV. This is derived by using the minimum variance analysis between a few high and low latitude stations by including the set of variation coefficients. The derived amplitude of the diurnal anisotropy (in space) varies with a period of one solar activity (11-year cycle, whereas, the phase of the diurnal anisotropy displays an obvious 22-year magnetic cycle