Solar flares and active regions in the Hale sector boundary in Solar Cycle 24

Abstract

ABSTRACT Solar eruptions, such as flares and coronal mass ejections, have serious impacts on the Earth’s environment and human activity. Predicting the eruptions and therefore avoiding their damages is a main goal in the research community. Heliospheric current sheet (HCS), the boundary dividing the positive and negative magnetic fields that open up to the interplanetary space, is believed to be related with solar eruptions. The HCS consists of two types of boundaries: the Hale boundary and the non-Hale boundary, and the former is suggested in previous studies to be the region producing most of the solar flares. In this work, we explore relationships between Hale boundary, flares, and property of active regions (ARs). The HCS is determined from the magnetic field in the heliosphere calculated from the observed photospheric magnetic field using a potential field source surface model. We have analysed 8075 flares of C-class and above and 1652 ARs in the period from May 2010 to May 2019 in Solar Cycle 24. The following results are obtained: (1) 5957 flares ($74\pm 1~{{\ \rm per\ cent}}$) and 1212 ARs ($73\pm 2~{{\ \rm per\ cent}}$) are in the HCS; (2) among them, 70 per cent ($\pm 1~{{\ \rm per\ cent}}$) flares and 57 per cent ($\pm 3~{{\ \rm per\ cent}}$) ARs are in the Hale boundary; and (3) big ARs tend to emerge in the Hale boundary. We conclude that the HCS is related tightly to solar activity, and the Hale boundary is a region favoured to produce flares and to host large ARs.