Influence of Earth-directed Coronal Mass Ejections on the Sun’s Shadow Observed by the Tibet-III Air Shower Array

We examine the possible influence of Earth-directed coronal mass ejections(ECMEs) on the Sun's shadowin the 3~TeV cosmic-ray intensity observed by the Tibet-III air shower(AS) array. We confirm a clear solar-cyclevariation of the intensity deficit in the Sun's shadowduring ten years between 2000 and 2009. This solar-cyclevariation is overall reproduced by our Monte Carlo (MC) simulations of the Sun's shadowbased on the potential field model of the solar magnetic field averaged over each solar rotationperiod. We find, however, that the magnitude of the observed intensity deficit in the Sun's shadowis significantly less than that predicted by MC simulations, particularly during the period around solar maximumwhen a significant number of ECMEs is recorded. The $\chi^2$ tests of the agreement between the observations and the MC simulations show that the difference is larger during the periods when the ECMEs occur, and the difference is reduced if the periods of ECMEs are excluded from the analysis. This suggests the first experimental evidence of the ECMEs affecting the Sun's shadowobserved in the 3~TeV cosmic-ray intensity.