In section 9. The Sun
Spiral-shaped wavefronts in a sunspot umbra
Sunspots are large concentrations of magnetic field at the surface of the Sun. In this paper, the authors identify a two-armed spiral wavefront in a sunspot through the analysis of the (vertical) Doppler motions. These can be interpreted as the signature of magneto-acoustic waves propagating upward along the magnetic field. As such, they might provide new insight into how sunspots are anchored inside the Sun.