Observation of Earth's Orbital Motion Using Cosmic-Ray Compton-Getting Effect at Matsushiro Underground Station.

Abstract

The Earth's motion Compton-Getting effect on the solar diurnal variation of cosmic ray intensity, has been examined by using observed data at Matsushiro underground station located at the effective vertical depth of 220m.w.e. underground (threshold energy -7.1010eV, median primary energy≥7.1011eV) for the period 1980-1990. In the analysis, to eliminate the atmospheric effects on the muon intensity, the differences of the observed intensity between two-directional telescopes; the east-pointing (E-) and the west-pointing (W-) telescope, are used. Also the analysis is made for two different periods of the solar activity; the quiet period for averaged sunspot numbers Z 60 (1980-1984 and 1988-1989). It is shown that for the quiet period, the difference E-W diurnal vector has the phase of 22.5±1.3hr LT and the amplitude of 0.030±0.007%. With a clockwise rotation of this E-W vector by the right angle, we may compare it with that expected from the Earth's motion Compton-Getting effect. It is found that the observed (0.030±0.007% in 4.5±1.3hr LT) and the expected vector (-0.021% in -6hr LT) are in fair agreement with each other. It is also found that for the active period, the observed E-W diurnal vector seems likely to show some contribution from the solar diurnal anisotropy, in addition to the Compton-Getting effect on it. This suggests that for the last solar active period the upper cut-off energy of solar diurnal anisotropy might be as high as that (several 1011eV) for the threshold (-7.1010eV) of 220m.w.e. depth underground.