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.
Newly developed time-distance helioseismic imaging method, which includes more multiskip acoustic waves, is proved to be more reliable in mapping the Sun’s far-side active regions.
This study explores the magnetic triggers of recurrent active region jets. Both widely debated triggers, namely, flux cancellation and flux emergence, are associated alternatively to the apparently homologous jets.
Of three consecutive flares that occurred in a same active region within 4 hours, why were two non-eruptive and one eruptive? Non-linear force-free modeling suggest that breakout reconnection during the first two flares weakened the overlying field, allowing the flux rope to erupt in the third.
In an MHD simulation of flux emergence, a δ-sunspot is formed spontaneously by a collision of areas with opposite polarities. Driven by convective flows and counter-streaming flows, sheared polarity inversion lines form and flux ropes are created above.
Subsurface meridional flows from ring-diagram analysis showed a clear hemispheric asymmetry in last 18 years. Interestingly, this flow asymmetry leads the magnetic flux and sunspot number asymmetry by 3.1 – 3.6 years.
Features of the Shannon entropy transfer between solar magnetic modes are described and analyzed. It is confirmed that solar magnetic modes can be separated into three groups: entropy sources, entropy transmitters, and entropy targets.
Photospheric magnetic properties for a set of coronal holes are investigated using HMI magnetograms, and it is found that the overall unbalanced magnetic flux of the coronal holes arises from long-lived magnetic elements with a lifetime longer than 40 hours.
What excites the sunspot umbral oscillations? Through analyzing two sunspots observed by FeI line, the authors found that the 3-minute umbral oscillations are likely excited by internal small-scale magnetoconvection associated with umbral dots.
A number of sunquake events were detected in the photosphere after the X9.3 flare of 6 September 2017. This analysis reported the first detection of the chromspheric response to the sunquake events using CaII and Hα observations made by the Swedish 1-meter Solar Telescope.