The Variation Of Solar Magnetic Field And The Correlation Between It And The Cosmic-Ray Shadow Of The Sun

Solar magnetic field means the magnetic field in the solar atmosphere. The solar mean magnetic field (SMMF) represents the magnetic disequilibrium of the whole magnetic flux seen in the visible solar hemisphere. The sun is the nearest fixed star from the earth. It affects our daily life a lot. The solar activity has great impact on the earth, and most of the solar activities, such as sunspot, solar flare and prominence, are dominated by the solar magnetic field. Thus, the research of the periodicity of solar magnetic field is of great importance.The short-term periodicity of SMMF is analyzed in this paper. Wilcox Solar Observatory (WSO) has been built at Stanford University in1975. Sun-as-a-star integrated light measurements of the mean solar magnetic field have been made daily since May1975. The typical measurement error of the daily data of SMMF from WSO is less than0.05G. The periodicity of SMMF varies as the level of the solar activity changes. The periodicity of SMMF is quite complex during the transition period between the solar maximum and minimum. Thus, we analyzed the periodicity of the solar mean magnetic field in each solar maximum and minimum.Using the data observed by Wilcox Solar Observatory from1975to2010, the short-term periodicity of the SMMF in each solar maximum and minimum is analyzed with the Lomb-Scargle Periodogram. The result shows that SMMF has main periods about9days,13.5days,27days. During the solar maximum, the SMMF has the most dominant period near27days. However, in solar minimum, the13.5-day periodicity is most significant except in1984-1986. These results show that the solar active region distribution in the solar maximum is quite different from that in solar minimum.The ARGO-YBJ collaboration has observed the cosmic ray at Yangbaijing for a long time. Because of the shelter of the sun, the distribution of particle counts on the sky shows a deficit corresponding to the location of the sun shadow. Since almost all the cosmic rays are charged, the cosmic particles will be bend under the influence of the solar magnetic field and interplanetary magnetic field, and the cosmic-ray shadow of the sun will be shifted from the apparent solar position. Thus, observation of the cosmic-ray shadow of the sun may provide us new information of the solar magnetic field and the interplanetary magnetic field.This paper analyzed the observation data of ARGO-YBJ experiment from2008to2010. We found that the displacement of the cosmic-ray shadow of the sun in west-east direction correlates with the solar polar magnetic field significantly. This result will benefit the further analysis of the solar magnetic field.