Study Cosmic Ray Forbush Decrease Using The Yangbajing Observation Station

The Yangbajing(YBJ) observation station ,which located in Tibet at 4300m a.s.l, is famous cosmic-ray observation station in the worldwide.Nowadays, YBJ-ARGO experiment is operating normally. Especially, the single particle technique (SPT) data of this experiment can give count rate of secondly particles of EAS according different energy range (multiplicity greater than 1,2,3 and 4, respectively, i.e.) and can be used to study the solar modulation of cosmic ray at E>10GeV.In this thesis, the single particle technique data from January 15th to 27th 2005 are analyzed, and the cosmic ray flux Forbush decrease after some class X solar flares has been observed, moreover all the detailed structures of the light curves are similar to the results from neutron monitors. The maximum amplitudes of FD are about -5%, -4%,-2% and 0% with multiplicity greater than 1,2,3 and 4, respectively, i.e. the maximum amplitudes of FD decrease as the energy of cosmic ray increase. These are the first results of FD at the same site with different energy.More meteorological parameters data had been recorded by ARGO-SPT experiment since November of 2005. In this thesis, the data of environment parameters in December of 2005 are analyzed using the method of multivariate correlation analysis. It has been found that in the system consisting of SPT count rate, pressure, temperature of outdoor and temperature of indoor, pressure and temperature of outdoor effect the SPT count rate positively, while temperature of indoor does negatively. At same time, the results indicate that pressure is primary part of environment parameters which influences the SPT count rate.Due to the solar modulation and other factors, the cosmic ray flux has some changes which maybe induce some variability of the Earth's climate, such as cloudiness. It is possible effective way to research connection between cosmic ray and cloud through studying effect on cloudiness of galactic cosmic ray flux associated with Forbush decrease (FD) events, because climate variability, especially cloudiness, operate with similar temporal characteristics as FD events.Twelve FD events had been recorded at Yangbajing neutron monitor during years from October of 2003 to October of 2005. Variation of cloudiness following ten of twelve FD events over the regions of Yangbajing cosmic ray observation also has been observed by infrared radiometer. By statistically analyzing the FD events, it has been found that significant increase of cloud cover during FD events. The results indicate cloudiness increase at lower latitudes in regions of thinner cloud, which is consistent with results at this lower latitudes found by other investigators.