To search for signatures of Alfvénic waves in the solar photosphere, the authors analyze the oscillation amplitudes, phases and time-distance behavior between different observables in a sunspot umbra, its polarity inversion line, and surrounding area.
A surface flux-transport dynamo model assimilation shows that the long-lasting active-region complexes, which appeared in the Sun’s southern hemisphere during Cycle 24, played a crucial role in the pole’s polarity reversal and the field strength at the cycle minimum.
Through studying three homologous eruptive events in an active region, the authors conclude that shearing motions and magnetic flux cancellation play a dominant role leading to the recurrent eruptions, and are key processes forming the eruptive structures.
Analysis of magnetic helicity of eruptive and confined flaring events indicates that non-potential magnetic helicity is indicative to eruptive potentials of active regions.
Critical decay index is a measure of the rate at which background field intensity decreases with height over the flux ropes or erupting structures. The indices for 10 eruptive prominences are calculated, and their relations to the eruptions are discussed.
New HMI 96-minute vector magnetograms are now available. Deep averaging reduces noise and enhances long-lived magnetic structures.
A large sample statistical study of normalized Lorentz force and torques in emerging magnetic field shows that the photospheric magnetic field has a rather small Lorentz forces and torques, close to a force-free state.
An unsupervised machine-learning algorithm is used on selected features derived from the polarity inversion lines (PIL) mask and difference PIL mask. It is found these features are effective in predicting flaring occurrences.
The Sun’s poloidal and toroidal magnetic field components derived from synoptic magnetograms are assimilated into a mean-field dynamo model, and activity level for Cycle 25 is predicted based on this approach.
Electric current neutralization, which measures the ratio of direct current and return current inside active regions (ARs), is studied for a total of 30 AR samples. It is found that flare-productive ARs are more likely to exhibit non-neutralized currents than those flare-quiet ARs.