Correlation between Solar Activity and the Sun’s Shadow Observed by the Tibet Air Shower Array

Abstract:

We analyze the solar cycle variation of the Sun’s shadow in 10 TeV cosmic ray intensity observed with the Tibet air shower array over an entire period of the Solar Cycle 23 between 1996 and 2008. The amplitude of the variation is as large as one half of the deficit intensity expected when all cosmic rays arriving from the direction of the optical Sun disk are excluded from the observation. The correlations between the deficit intensity in the Sun’s shadow and cosmic-ray modulation parameters are overall significant. Among those parameters, we find the highest correlation with the Heliospheric Current Sheet tilt-angle.

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