Phase Jumps in Local Helioseismology |
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| Authors: | P S Cally |
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| Institution: | (1) Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, Monash University, Melbourne, Victoria, 3800, Australia |
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| Abstract: | Helioseismic rays trapped in a nonmagnetic acoustic cavity suffer a +90° phase jump at their lower (Lamb) turning point and
−90° 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 – for an isothermal model with uniform magnetic field – that the phase jump for fast magnetoacoustic
rays that penetrate the acoustic/Alfvénic equipartition level (c=a) is around −120°. 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. |
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| Keywords: | Waves magnetohydrodynamic Helioseismology theory |
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