To assess the impact of active regions to the axial dipole moment, the authors isolate the contribution of individual regions for Cycles 21, 22, and 23 using a surface flux transport model, and find that although the top ~10% of contributors tend to define sudden large variations in the dipole moment, the cumulative contribution of many weaker regions cannot be ignored.
New helioseismic analysis of the Sun’s subsurface zonal flows shows the equator-migrating branch of the faster-than-average rotation, a sign of the Solar Cycle 25.
The Sun’s seismic radius, measured from the frequencies of f modes, is determined using both MDI and HMI data, covering a total of 21 years. It is found that the seismic radius is reduced by 1-2 km during the maxima, but the largest change of the radius happens at about 5 Mm beneath the surface.
HMI-observed vector magnetic-field maps were lowered to a resolution of lmax=5, so that a comparison between solar and stellar magnetic field is possible.
Waves of magnetic-field variations were observed associated with the sunquake waves that were excited by the X9.3 flare on 2017 September 6. The nature and cause of the magnetic waves are discussed after the phase relations and power distributions of the magnetic waves and Doppler-observed sunquake waves are investigated.
Ring-diagram analysis is applied on the HMI-observed sunspots of about 3 years. The attenuation of wave amplitudes near sunspots, rotational speed of sunspots, and subsurface flows around sunspots are discussed.
A deep learning code is developed to enhance HMI continuum intensity images and line-of-sight magnetic field for a better spatial resolution.
Employing an updated Babcock–Leighton dynamo model, this study finds that the model with scattered tilt angles, which are around the Joy’s Law but with a standard deviation of 15°, is able to reproduce the observed variations of solar cycles.
Long-term migration of the Sun’s open magnetic flux is studied, and its relation with the sunspot numbers is discussed.
Heat flux delivered by magnetic reconnection is calculated based on a model using magnetic field observations, and the calculation is then compared with AIA EUV observations.