Geomagnetic field analysis—III. Magnetic fields on the core—mantle boundary
David Gubbins,Jeremy Bloxham +1 more
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In this paper, the stochastic inversion method was applied to the main field data for the first time to obtain a finite lower bound on the Ohmic heating in the core, which provides strong prior information and gives finite error estimates at the core.Abstract:
Summary. The method of stochastic inversion, previously applied to secular variation data, is applied to main field data. Adaptations to the method are required: non-linear, as well as linear, data are used; allowance is made for crustal components in the observatory data; and the prior information is specified differently. The requirement that the models should satisfy a finite lower bound on the Ohmic heating in the core provides strong prior information and gives finite error estimates at the core—mantle boundary.
The new method is applied to data from the epochs 1969.5 and 1980.0. The resulting field models are very much more complex than other models, such as the IGRF models extrapolated to the core, and show considerable small-scale detail which, on the basis of the error analysis, can be believed.
The flux integral over the northern hemisphere is computed at each epoch; the difference between the two epochs is approximately one standard deviation, suggesting that the question as to whether the decay of the dipole is consistent with the frozen-flux hypothesis has been resolved in favour of the hypothesis.read more
Citations
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Four centuries of geomagnetic secular variation from historical records
TL;DR: In this article, the authors present a new model of the magnetic › eld at the core{mantle boundary for the interval 1590{1990] to 1990, called gufm1, which is based on a massive new compilation of historical observations.
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The secular variation of Earth's magnetic field
TL;DR: In this paper, a model of the magnetic field at the core-mantle boundary at selected epochs from 1715.0 to 1980.0 reveal novel features in the field at core.
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Geomagnetic Secular Variation
TL;DR: In this paper, the authors analyse over 175,000 magnetic observations from an interval spanning 1695-1980 to produce a sequence of maps of the magnetic field at the core-mantle boundary; they find that even the earlier data enable them to determine reliable maps.
Journal ArticleDOI
Time-dependent mapping of the magnetic field at the core-mantle boundary
Jeremy Bloxham,Andrew Jackson +1 more
TL;DR: In this paper, the problem of constructing a time-dependent map of the magnetic field at the core-mantle boundary was considered and the smoothest solution compatible with the observations was proposed.
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Numerical modelling of the geodynamo: a systematic parameter study
TL;DR: In this article, the authors analyse 50 3D numerical calculations of hydrodynamic dynamos driven by convection in a spherical shell, with rigid and stress-free boundaries, with Prandtl number 1, magnetic Prandttl numbers in the range 0.5-5, Ekman numbers E=10− 3−10−4 and Rayleigh numbers to 15 times critical.
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