الفهرس 
acknowledgmentOnly 14 pages are availabe for public view
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Abstract
The intensity of the nucleonic component of cosmic rays observed at twelve
neutron monitor stations are used to study the diurnal variations of cosmic rays during
Forbush Decrease (FO) events. This observation data cover a wide range of threshold
cut-off rigidities (1.02 GV < R, < 13.65 GV), and a period of one magnetic cycle
(1965-1987). FO’s events have been classified according to the shape of the shock
waveinto two types (sharp and slow) .
The harmonic analysis technique has been used to calculate the diurnal
variations of cosmic ray. The superposed Epoch method has been applied to study the
effect of Forbush Decreases on the first two harmonics of solar diurnal variations. It
was found that the amplitude of solar diurnal variation (SOV) during the sharp FO’s is
maller than that during the slow decreases. The time of maximum of the diurnal
variation during the sharp decrease events is earlier than that during the slow
decreases.FO’s doesn’t affect the second harmonics of solar diurnal variations.
The amplitude of cosmic ray anisotropy in free space has been calculated
usingtwo different techniques: the Variance Analysis and the Least Square Method.
It was found that the amplitude of anisotropy in free space shows a periodic behavior
through the solar magnetic cycle. It is also independent on the primary magnetic
rigidity up to a limiting value which depends on the solar activity. The direction of
diurnal anisotropy shows 22-year variation. The upper cut-off rigidity Rc, above
which the anisotropy vanishes. varies from about 30 GV during minimum solar
activityup to 100 GV during maximum solar activity.