Influence of Nonuniform Distribution of Acoustic Wavefield Strength on Time-Distance Helioseismology Measurements
Influence of Nonuniform Distribution of Acoustic Wavefield Strength on Time-Distance Helioseismology Measurements
复制标题
声波场强度不均匀分布对时距日震测量的影响
DOI：
10.1086/533495
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
A. Kosovichev
中科院分区：
文献类型：
--
作者：
K. Parchevsky;Junwei Zhao;A. Kosovichev
通过对数值模拟的太阳振荡数据的分析，研究了声波振幅的不均匀分布、声源强度和声速的扰动对时距日震学方法测量的声波走时漂移的影响。结果表明，在较短的距离内，黑子声源的不均匀分布对平均旅行时移的贡献可能与黑子声速扰动的贡献相当(但小于)，而与声速效应的贡献相反。这种效应可能会导致对太阳黑子表面以下负声速扰动的低估，这在以前的时间-距离日震学推论中被发现。这种影响不能通过人为增加太阳黑子振荡的幅度来纠正。对于大时距环空，波场的不均匀分布对平均走时影响不大，从而对声速反演结果影响不大。用于确定太阳黑子下质量流的测量旅行时差也可以因这种效应而系统地移动，但幅度不大。
By analyzing numerically simulated solar oscillation data we study the influence of nonuniform distribution of acoustic wave amplitude, acoustic source strength, and perturbations of the sound speed on the shifts of acoustic travel times measured by the time-distance helioseismology method. It is found that for short distances, the contribution to the mean travel-time shift caused by nonuniform distribution of acoustic sources in sunspots may be comparable to (but smaller than) the contribution from the sound-speed perturbation in sunspots, and that it has the opposite sign to the sound-speed effect. This effect may cause some underestimation of the negative sound-speed perturbations in sunspots just below the surface, which was found in previous time-distance helioseismology inferences. This effect cannot be corrected by artificially increasing the amplitude of oscillations in sunspots. For large time-distance annuli, the nonuniform distribution of wavefields does not have significant effects on the mean travel times, and thus the sound-speed inversion results. The measured travel-time differences, which are used to determine the mass flows beneath sunspots, can also be systematically shifted by this effect, but only by an insignificant magnitude.