Phase Jumps in Local Helioseismology
Phase Jumps in Local Helioseismology
复制标题
当地日震学中的相位跳跃
DOI：
10.1007/s11207-008-9290-9
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发表时间：
2009
期刊：
影响因子：
2.8
通讯作者：
P. Cally
中科院分区：
文献类型：
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作者：
P. Cally
捕获在非磁性声腔中的日震射线在其下部(LAMB)转折点经历+90°的相位跳跃，在上部(声学截止)反射点经历90°的−跳跃。这两个相消使得日震学家可以有效地假设该相位沿着连接两个表面点的射线路径局部连续。然而，在强表面磁场中，如在太阳黑子中发现的那样，对于均匀磁场的等温模型，快磁声射线穿透声学/AlfvéNic均分能级(c=a)的相位跳跃约为−12 0°。此外，在上行和下行支路ATC=a上还存在进一步的负相位跳跃，这增加了净相变。忽视这些影响可能会导致在旅行时移方面对日震数据的误解。
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 atc=athat add to the net phase change. Neglecting these effects can lead to a misinterpretation of helioseismic data in terms of travel-time shifts.