Abstract
In studies of the temporal variations of the main internal geomagnetic field (the secular variation or SV), it is usual to consider separately the variations of the dipolar and non-dipolar parts which appear to have different time constants. The mechanism that is generally invoked to explain the generation of SV is the advection of the lines of force of the main field by the highly conducting fluid at the top of the core. Such a mechanism involves the main field as a whole and it is not clear a priori why its two parts should behave separately. I show here that the Coriolis force will probably dominate the force budget at the top of the core and that, in such a case, the motion of the fluid involves the two parts of the field in a different way; in particular, the existing axial dipolar component is not re-engaged in the process which builds up the SV.
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Le Mouël, J. Outer-core geostrophic flow and secular variation of Earth's geomagnetic field. Nature 311, 734–735 (1984). https://doi.org/10.1038/311734a0
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DOI: https://doi.org/10.1038/311734a0
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