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.