A strong limb flare observed simultaneously by the SDO/AIA and SDO/HMI, which is very rare, allows the authors to study the emission mechanism for white-light flare loops, as well as estimate the electron densities along the flare loop.
A total of 90 circular-ribbon flares are identified in 8 years of SDO observations, and 33 of them are found associated with white-light enhancements, a rate higher than non-circular-ribbon flares. It is thus suggested that the fan-spine magnetic field topology and the total amount of energy release plays roles in causing white-light flares.
Physical parameters, including sunspots tilt angles, total magnetic flux, polarity pole separations, and magnetic areas, are measured for most sunspot groups in solar cycles 23 and 24. Differences between Hale and anti-Hale sunspots in separate hemispheres and cycles are studied statistically.