Time Variations of Cosmic Rays

Abstract

Amplitudes and phases of the solar diurnal variations (SOY) of nucleonic component of cosmic rays observed at 12 neutron monitor stations were computed. It was found that Forbush Decrease events (FD's) affect the amplitude and direction of the first harmonic of the solar diurnal variations. While, there is no effect for FD's events on the second harmonic of solar diurnal variations.

The amplitude and direction of anisotropy in free space have been calculated using observation of data from 8 neutron monitor stations. The rigidity exponent (y) and the upper cut-off rigidity (R,) for the diurnal anisotropy are found to change over the solar magnetic cycle ( 1965- 1987). The upper cut-off rigidity was found to change with the solar

activity from a value of 30 GY during minimum solar activity up to a value of I 00 GY during maximum solar activity. The direction of diurnal anisotropy exist in two distinct states during the solar magnetic cycle ( 1965-1987) .