Helicity injection by the continued shear and converging flows contributes to a sigmoid’s sustenance, its core field twist, ans its eventual eruption.
To minimize cross-talk effect from vertical flows and sound-speed perturbations, a new inversion code is developed to invert for flows and sound-speed perturbations simultaneously from time-distance travel-time measurements. The code is validated using numerical simulation data.
Magnetic flux of opposite polarities belonging to two different emerging/emerged bipoles inside multipolar magnetic regions, can experience “collisional shearing”, a process resulting in strong shearing and fast cancellation of magnetic flux near the polarity inversion line. This type of flux cancellation is found to be the cause of a succession of major flares and CMEs in complex active regions.
Through analyzing simultaneous HMI’s visible-light observations and AIA’s ultraviolet observations, the authors show that a significant amount of acoustic waves with frequencies lower than the theoretical cutoff frequency can channel up along less inclined magnetic field from the photosphere to the chromosphere.
Both magnetic flux emergence and shearing flows occurred before the X9.3 flare on 2017 September 6. This analysis shows that shearing flows played a more significant role in leading to the helicity and electric currents buildup before the major eruption.
An analysis of zonal flow acceleration/deceleration inside the Sun reveals patterns of dynamo waves, and suggests that the primary seat of the dynamo is located in a high-latitude zone of the tachocline.
Observations of 10 coronal jetlets show that flux cancelation is usually a necessary condition for buildup and triggering of UV/EUV coronal network jetlets, and that network jetlets are plausibly small-scale versions of larger coronal jets.
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.