The Earth's magnetic field: Which geometry?
The Earth's magnetic field: Which geometry?
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地球磁场：哪种几何形状？
DOI：
10.1029/91eo00260
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
J. Mouël
中科院分区：
文献类型：
--
作者：
V. Courtillot;J. Valet;G. Hulot;J. Mouël
如果没有太阳风的存在，地球的内禀磁场--如果从足够远的太空中观察--看起来几乎是完美的偶极，偶极轴目前相对于旋转轴倾斜约10°。在地球表面，轴向偶极项占主导地位，除其他用途外，它还作为古地磁学的指南针定向和板块构造应用的基础。人们可能会问，如果从核幔边界的源点上方观测到的磁场，这种偶极优势是否会保持。答案是确实如此（图1），尽管偶极部分的振幅相对于高阶（较短波长）项有所减小。这些高阶项与平坦的、类似白噪声的功率谱兼容。这意味着在各种谐波项中存储有相似量的能量（例如，参见Constable和帕克[1988]），尽管“粉红色”光谱（即，在较长波长处的功率略高）是合理的[Hulot等人，1992年]。超过13度和13阶（即波长短于1500 km）的术语被地壳和岩石圈（即表面静力学）场所污染。
Were it not for the presence of a solar wind, the intrinsic magnetic field of the Earth—if observed from far enough out in space—would appear to be almost perfectly dipolar, with the axis of the dipole presently tilted by some 10° with respect to the rotation axis. At the Earth's surface, the axial dipolar term is dominant, which serves among other uses as a basis for both orientation with a compass and plate-tectonic applications of paleomagnetism. One can ask whether this dipolar dominance would hold were the field observed from just above its source at the core-mantle boundary. The answer is that indeed it does (Figure 1), although of course the dipolar part is reduced in amplitude relative to the higher-order (shorter wavelength) terms. These higher-order terms are compatible with a flat, white-noise-like, power spectrum. This implies that there are similar amounts of energy stored in the various harmonic terms (see, for example,Constable and Parker [1988]), although a “pink” spectrum (that is, slightly more power at the longer wavelengths) is as plausible [Hulot et al., 1992]. Terms beyond degree and order 13 (that is, wavelengths shorter than 1500 km) are contaminated by crustal and lithospheric (that is, surficial static) fields.