Equatorial Rossby waves are detected using the HMI’s time-distance subsurface flow fields. It is also found that the power of the Rossby waves show a positive correlation with the sunspot number, while the frequency of the waves shows an anti-correlation with the sunspot number.
Magnetic flux loss from the solar interior due to flux emergence explains why all solar cycles decline in the same way.
Quasi-biennial oscillations are found in the Sun’s interior rotation-rate residuals. They appear differently at different depths and latitudes, and evolve with time.
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.
Using the solar axial magnetic dipole moment obtained prior to the solar minimum, the author predicts that the maximum sunspot number of Solar Cycle 25 is about 128.
A novel approach is developed to reconstruct the surface magnetic helicity density for the Sun or sun-like stars. The method is applied on the SDO/HMI-observed vector field synoptic data to study the temporal evolution of the Sun’s magnetic helicity density during Solar Cycle 24.
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.
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.
Long-term migration of the Sun’s open magnetic flux is studied, and its relation with the sunspot numbers is discussed.