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| Titel |
Double-diffusive inner core convective translation |
| VerfasserIn |
Renaud Deguen, Thierry Alboussière, Stephane Labrosse |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250131426
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| Publikation (Nr.) |
 EGU/EGU2016-11833.pdf |
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| Zusammenfassung |
| The hemispherical asymmetry of the inner core has been interpreted as resulting form a
high-viscosity mode of inner core convection, consisting in a translation of the inner core.
With melting on one hemisphere and crystallization on the other one, inner core
translation would impose a strongly asymmetric buoyancy flux at the bottom of
the outer core, with likely strong implications for the dynamics of the outer core
and the geodynamo. The main requirement for convective instability in the inner
core is an adverse radial density gradient. While older estimates of the inner core
thermal conductivity favored a superadiabatic temperature gradient and the existence
of thermal convection, the much higher values recently proposed makes thermal
convection very unlikely. Compositional convection might be a viable alternative
to thermal convection: an unstable compositional gradient may arise in the inner
core either because the light elements present in the core are predicted to become
increasingly incompatible as the inner core grows (Gubbins et al. 2013), or because
of a possibly positive feedback of the development of the F-layer on inner core
convection. Though the magnitude of the destabilizing effect of the compositional field
is predicted to be similar to or smaller than the stabilizing effect of the thermal
field, the huge difference between thermal and chemical diffusivities implies that
double-diffusive instabilities can still arise even if the net density decreases upward.
We propose here a theoretical and numerical study of double diffusive convection
in the inner core that demonstrate that a translation mode can indeed exist if the
compositional field is destabilizing, even if the temperature profile is subadiabatic, and
irrespectively of the relative magnitude of the destabilizing compositional gradient and
stabilizing temperature field. The predicted inner core translation rate is similar to the
mean inner core growth rate, which is more consistent with constraints from the
geomagnetic field morphology and secular variation (Aubert et al., 2013) than the higher
translation rate predicted for a thermally driven translation (Alboussière et al., 2010). |
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