Authors: Claire L. Liu (Los Gatos High School, Los Gatos, CA), Junwei Zhao (Stanford University)

Solar eruptions, such as flares and Coronal Mass Ejections (CMEs), have shown serious impacts on the Earth’s environment and human daily activity. Predicting the eruptions and therefore helping to avoid their damages are one of the main goals in the research community. The 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 activity and eruptions. The HCS consists of two types of boundary: the Hale boundary that separates the magnetic field whose polarity follows the Hale law, and the non-Hale boundary that is against the Hale law. The Hale boundary is suggested in previous studies to be the region producing most of the solar flares. In this work, we explore this relationship using better methodology and newly acquired data, especially the magnetic field data for active regions. The HCS is determined from the magnetic field in the heliosphere calculated from the observed magnetic field on the solar surface using a Potential Field Source Surface model (PFSS). The observed data are taken by the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). We have analyzed 7290 C-class and above flares and 1486 active regions (ARs) in the time period from May 2010 to May 2019 in Solar Cycle 24. We obtained the following results: (1) 5284 flares (72\% $\pm 1\%$) and 1097 ARs (74\% $\pm 2\%$) are in the HCS; (2) among them, 69\% ($\pm 1\%$) flares and 57\% ($\pm 3\%$) ARs are in the Hale boundary; and (3) big ARs tend to emerge in the Hale boundary. We conclude that (1) the HCS is related tightly to solar activity, and (2) the Hale boundary is a region favored to produce flares, supportive of the previous study.