Because helioseismology uses surface signals to calculate subsurface characteristics the behaviour of surface acoustic oscillations in sunspots is important in interpreting helioseismic results. SOHO-MDI Doppler velocity analysis of AR9026 and AR9033 at 3, 4, and 5 mHz, using helioseismic holography, show that the amplitude and the phase in the correlation of the acoustic ingression with the observed surface velocity are found to be sensitive to the relative line-of-sight angle in the penumbra of both sunspots. This is consistent with a conversion of vertically propagating acoustic waves into magneto-acoustic waves with motion described by ellipses.
Solar MHD Theory and Observations: A High Spatial Resolution Perspective
- Pub Date:
- December 2006