Surface magnetic field effects in local helioseismology

Using helioseismic holography strong evidence is presented that the phase (or equivalent travel-time) of helioseismic signatures in Dopplergrams within sunspots depend upon the line-of-sight angle in the plane containing the magnetic eld and vertical directions. This is shown for the velocity signal in the penumbrae of two sunspots at 3, 4 and 5 mHz. Phasesensitive holography demonstrates that they are signicantly affected in a strong, moderately inclined magnetic eld. This research indicates that the effects of the surface magnetic eld are potentially very signicant for local helioseismic analysis of active regions.