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| Titel |
Secular variation and core-flow modelling with stable strafication at the top of the core |
| VerfasserIn |
Richard Holme, Bruce Buffett |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105377
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| Publikation (Nr.) |
 EGU/EGU2015-4897.pdf |
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| Zusammenfassung |
| Observed geomagnetic secular variation has been used for many years to provide an
observational constraint on the dynamics of the core through the modelling of its surface
flow. Recent results in both seismology and mineral physics provide strong evidence of a
stably stratified layer at the top of the core, which has substantial implications for the
calculation of such flows. It has been assumed for many years that the dynamic state at the
core surface is close to tangentially geostrophic, and pure stable stratification also requires a
flow to be toroidal. Combining these two conditions requires variations in flow that are
completely zonal toroidal, which are known not to provide an adequate explanation of the
observed secular variation.
However, a stably stratified layer can support flow instabilities of a more general
character. Buffett (2014) has recently provided a model in which zonal toroidal motions are
associated with the excitation of a zonal poloidal instability. This model is able to explain the
broad variation of the axial dipole over the past 100 years, and also to explain feature of
geomagnetic jerks that cannot be explained by purely torsional motions. This model has
inspired a new generation of core-flow models, with a substantial time-varying zonal
poloidal component, something that is absent from most models of core surface
flow.
Here, we present these new models, and consider to what extent this flow structure can
explain the details of secular variation. We also consider the implications for the connection
between core-surface flow and length-of-day variation - a stably stratified layer has
implications for the interpretation of core flow and the Earth’s angular momentum budget.
Finally, we consider the ability of core-surface flow models to probe the structure of the
stably- stratified layer.
Buffett (2014). Geomagnetic fluctuations reveal stable stratification at the top of the
Earth’s core, Nature 507, 484-487, doi:10.1038/nature13122 |
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