Solar magnetic field strength and the “Sun's Shadow”

The angular displacement of the center of the observed Sun's shadow from the center of the optical solar disc tells us the information of average solar magnetic field strength in the space between the Sun and the Earth. We analyze the displacement of the Sun's shadow observed in 5 ~ 240 TeV cosmic-ray intensity with the Tibet-III air shower array during 10 years between 2000 and 2009, and compare with the MC simulations based on the coronal magnetic field model and Parker's spiral interplanetary magnetic field model. We find that the observed North-South displacement is significantly larger than the prediction of simulations. This result uniquely suggests the underestimation of the average field strength between the Sun and the Earth in our model. In this work, we will report the actual solar magnetic field strength evaluated from the observed Sun's shadow.