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

TL;DR

This study investigates how Earth-directed coronal mass ejections influence the Sun's shadow in cosmic-ray observations, providing evidence that ECMEs reduce the shadow's intensity during solar maximum periods.

Contribution

It presents the first experimental evidence that ECMEs affect the Sun's shadow in cosmic-ray data, highlighting discrepancies between observations and simulations during active solar periods.

Findings

Observed solar-cycle variation in Sun's shadow intensity.

Discrepancy between observed and simulated shadow magnitudes during ECMEs.

ECMEs significantly influence cosmic-ray shadow measurements.

Abstract

We examine the possible influence of Earth-directed coronal mass ejections (ECMEs) on the Sun's shadow in the 3~TeV cosmic-ray intensity observed by the Tibet-III air shower (AS) array. We confirm a clear solar-cycle variation of the intensity deficit in the Sun's shadow during ten years between 2000 and 2009. This solar-cycle variation is overall reproduced by our Monte Carlo (MC) simulations of the Sun's shadow based on the potential field model of the solar magnetic field averaged over each solar rotation period. We find, however, that the magnitude of the observed intensity deficit in the Sun's shadow is significantly less than that predicted by MC simulations, particularly during the period around solar maximum when 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 shadow observed in the 3~TeV cosmic-ray intensity.