Helioseismic rays trapped in a nonmagnetic acoustic cavity suffer a +90A? phase jump at their lower (Lamb) turning point and a??90A? at the upper (acoustic cutoff) reflection point. That the two cancel allows helioseismologists to effectively assume that phase is locally continuous along a ray path joining two surface points. However, in strong surface magnetic field, as found in sunspots, it is shown a?? for an isothermal model with uniform magnetic field a?? that the phase jump for fast magnetoacoustic rays that penetrate the acoustic/Alfv??nic equipartition level (c=a) is around a??120A?. Moreover, there are further negative phase jumps on the upgoing and downgoing legs at c=a that add to the net phase change. Neglecting these effects can lead to a misinterpretation of helioseismic data in terms of travel-time shifts.
|Pages (from-to)||241 - 257|
|Number of pages||17|
|Publication status||Published - 2009|