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| Titel |
Numerical simulations of thermo-chemically driven convection and geodynamos |
| VerfasserIn |
Tobias Trümper, Martin Breuer, Ulrich Hansen |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250055836
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| Zusammenfassung |
| Our numerical study focuses on convection and magnetic field generation in a rotating
spherical shell with the objective to model combined thermal and compositional convection
as proposed for the Earth’s core. Since the core of the Earth is cooling, a thermal gradient is
established, which can drive thermal convection. Simultaneously, the advancing
solidification of the inner core releases latent heat and increases the concentration
of the light constituents of the liquid phase, e.g., sulphur, oxygen, and silicon, at
the inner core boundary. Thus, buoyancy is created by both thermal and chemical
heterogeneities. Typically, the molecular diffusivities of both driving components
differ by some orders of magnitude indicating that one has to consider two separate
transport equations in the numerical solution. In our double-diffusive convection
model, we assume that the thermal diffusivity κT exceeds the compositional one
κC by a factor of ten (κT-κC=10). The core mantle boundary is supposed to be
impermeable for the light component. The freezing inner core, however, provides a certain
flux of light material at the inner core boundary. Therefore, appropriate Neumann
boundary conditions are implemented in the numerical scheme. The ratio of thermal to
chemical forcing in the Earth’s core is still rather uncertain. As a joint action of both
buoyancy sources is most likely we investigated core convection in a range of varying
thermal to chemical forcing ratios. We find that the patterns of spatial flow structures
like differential rotation and helicity depend significantly on the particular driving
scenario. Additionally, we compare our results to equivalent simulations with Dirichlet
boundary conditions thus assessing the influence of the different types of boundary
conditions on the convective flow. We also studied the linear onset of convection
in terms of both the chemical and thermal Rayleigh number at different Ekman
numbers and diffusivity ratios. Furthermore, we investigated the effect of different
thermo-chemical driving scenarios on the process of magnetic field generation of the
MHD geodynamo. It turns out that the distribution of magnetic energy inside and
outside the tangent cylinder varies as a function of the thermal to chemical forcing
ratio. |
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