Mapping geomagnetic secular variation at the core-mantle boundary
Mapping geomagnetic secular variation at the core-mantle boundary
复制标题
绘制核幔边界处的地磁长期变化图
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
F. Bairstow
中科院分区：
文献类型：
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作者：
R. Holme;N. Olsen;F. Bairstow
摘要 最近卫星任务的数据极大地提高了地磁场模型及其一阶和二阶导数——长期变化（SV）和长期加速度（SA）的分辨率。 SV 和 SA 的光谱在核幔边界处都是“蓝色”，两者都与与 l(l + 1) 成比例的函数很好地拟合，其中 l 是球谐度。两个频谱的比率定义了所有可解析谐波度数大约 10 年的地磁变化的时间尺度。蓝色光谱应该阻止生成有意义的 SV 地图；尽管如此，调和度为 13 的地图的连贯性表明，可以从它们的检查中获得有用的见解。低SV在太平洋下得到证实，但在北大西洋和南极洲下也被发现。这些特征更容易通过热核幔耦合的发电机控制来解释，而不是通过电磁屏蔽。使用“综合模型”与最近卫星之前的测量地图进行比较表明，至少可追溯到 1970 年的模型足够好，可以直接比较 SV。
SUMMARY Data from recent satellite missions have vastly increased the resolution of models of the geomagnetic field, and itsfirst and second time derivatives – secular variation (SV) and secular acceleration (SA). The spectra of both SV and SA are ‘blue’ at the core–mantle boundary, both well-fit by functions proportional to l(l + 1) where l is the spherical harmonic degree. The ratio of the two spectra defines a timescale for geomagnetic variations of approximately 10 yrs for all resolvable harmonic degrees. The blue spectra should prevent meaningful maps of the SV being generated; nevertheless, the coherence of the maps up to harmonic degree 13 suggests that it is possible to obtain useful insight from their examination. Low SV is confirmed under the Pacific, but also revealed under the North Atlantic and Antarctica. These features are more readily explained in terms of dynamo control through thermal core–mantle coupling than by electromagnetic screening. Comparison with maps from measurements prior to the recent satellites, using the ‘Comprehensive Model’, suggests that models back to at least 1970 are sufficiently good to enable direct comparison of the SV.