Statistical Study on the Nature of Solar-Flux Emergence

Abstract

We studied 101 flux emergence events ranging from small ephemeral regions to large emerging flux regions that were observed with the Hinode Solar Optical Telescope filtergram. We investigated how the total magnetic flux of the emergence event controls the nature of emergence. To determine the modes of emergences, horizontal velocity fields of the global motion of the magnetic patches in the flux emerging sites were measured by local correlation tracking. Between two main polarities of the large emerging flux regions with more than around 2 × 10¹⁹ Mx, there were converging flows of anti-polarity magnetic patches. On the other hand, small ephemeral regions showed no converging flow, but a simple diverging pattern. When we looked into the detailed features in the emerging sites, irrespective of the total flux and the spatial size, all of the emergence events were observed to consist of single or multiple elementary emergence unit(s). The typical size of unitary emergence is 4 Mm, and consistent with simulation results. From a statistical study of the flux emergence events, the maximum spatial distance between two main polarities, the magnetic flux growth rate and the mean separation speed were found to follow the power-law functions of the total magnetic flux with indices of 0.27, 0.57, and -0.16, respectively. From a discussion on the observed power-law relations, we obtained a physical view of solar flux emergence, in which the emerging magnetic fields float and evolve while balancing to the surrounding turbulent atmosphere.