| The time variation of the cosmic ray flux is one of crucial problems in the field of cosmic ray physics, solar geophysics and astrophysics, etc. The origin, propagation and modulation of cosmic ray can be studied through its variation. However, it lacked significance of statistical to study the time variation of the cosmic ray with even high energy before, because the cosmic ray flux with even high energy is very low.The development of EAS with ultrahigh energy reaches about its maximum at the altitude of the Yangbajing Cosmic Ray Observation Station Tibet AS_γ array where the density of shower particles is high, the threshold energy is low, and the trigger rate is high. Tibet AS_γ array has been running for more than ten years, and there is large numbers of data . Therefore, it is propitious to study the time variation of cosmic ray with even high energy. Tibet AS_γ array also records some meteorological parameters, such as atmospheric pressure, temperature of the AS control room, temperature of outside, temperature of cable drain. The meteorological effect of cosmic ray can be corrected by using multianalysis. And then the variation of the cosmic ray flux without meteorological effect can be studied.In this thesis, cosmic ray flux recored between 1994-2004 is collected and tided. The annual variation of the data is obvious. Meteorological parameters of 1994-2004 are also tidied in the thesis. The annual variation of each meteorological parameter likes cosmic ray flux. There is obvious correlation existing between cosmic ray and each meteorological parameter. After the meteorological effect of cosmic ray being corrected by using multianalysis, there is no annual variation of cosmic ray. Then the cosmic ray flux after corrected is analysed with wavelet transform. Statistical result of data after analysed shows that there are more 4 diurnal and 6 diurnal variations of the cosmic ray, the next are 5 diurnal, 7 diurnal and 8 diurnal.The sidereal diurnal variation of cosmic ray ties up with the most basic and important problem in cosmic ray physics such as the origin, propagation and theacceleration mechanisms of cosmic ray. In this thesis the simulated signals are analysed with epoch folding methods for distinguishing sidereal diurnal (0.997 diural) variation and solar diurnal (1.0 diural) variation. The results show that the length of interval among data doesn't effect distinguishing the two variations. To distinguish sidereal diurnal variation and solar diurnal variation, we need data of three years by analyzing distribution of period and phase, but of six point seven years only by analyzing distribution fig of period.The data of cosmic ray flux obtained by Tibet ASy experiment is of ten years. It is enough to distinguish sidereal diurnal variation and solar diurnal variation. The cosmic ray flux of 1994-2003 after corrected is analysed for studying its short variations. The 1.0 diurnal variation is detected with signal-noise ratio 46.3, with amplitude 0.48 and phase 0. 82 (19. 7h).It has practical significance to analyse the time variation of the cosmic ray with data obtained by Tibet ASy array for 1994-2003, for the first time. |
