TIME VARIATION AND STATISTICAL STUDIES OF MAGNETIC HELICITY INJECTION IN SOLAR MAGNETIC REGIONS

In this study, we analyzed the helicity injection in solar active regions statistically with the method proposed by Kusano et al. We investigated the variation in helicity injection as an active region evolves and the statistical distribution of helicity injection against the magnetic flux (Φ) and the latitude. The temporal evolution of active regions is divided into three phases ('emergence', 'active', and 'decay' phases). We studied one emergence-phase region, 13 active-phase regions, and five decay-phase regions. The total number of helicity injection rates we obtained is 1476. We found the following results. The dispersions (standard deviations) in the helicity injection rates are proportional to Φ-0.47 in the active-phase regions and to Φ-0.34 in the decay-phase regions. The dispersion for the emergence-phase region, 0.046 day-1, is larger than those for the active-phase regions, 0.004-0.03 day-1, and those for the decay-phase regions, 0.004-0.01 day-1. The average helicity injection rates of the active-phase regions show the latitude dependence, which is consistent with the 'hemispheric rule' of helical structures in the solar atmosphere, while those of the decay-phase regions are inconsistent with the hemispheric rule. The average helicity injection rates for the active-phase regions, 0.003-0.03 day-1, are larger than that for the emergence-phase region, 0.0045 day-1, and those for the decay-phase regions, <0.002 day-1. These dependences of the helicity injection rates give us clues on the generation mechanism of helicity and the evolution of the magnetic field in the solar convection zone.