Effect of core electrical conductivity on core surface flow models
Abstract The electrical conductivity of the Earth’s core is an important physical parameter that controls the core dynamics and the thermal evolution of the Earth. In this study, the effect of core electrical conductivity on core surface flow models is investigated. Core surface flow is derived from...
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| Format: | Article |
| Language: | English |
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SpringerOpen
2020-11-01
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| Series: | Earth, Planets and Space |
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| Online Access: | http://link.springer.com/article/10.1186/s40623-020-01269-0 |
| _version_ | 1818930069422211072 |
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| author | Masaki Matsushima |
| author_facet | Masaki Matsushima |
| author_sort | Masaki Matsushima |
| collection | DOAJ |
| description | Abstract The electrical conductivity of the Earth’s core is an important physical parameter that controls the core dynamics and the thermal evolution of the Earth. In this study, the effect of core electrical conductivity on core surface flow models is investigated. Core surface flow is derived from a geomagnetic field model on the presumption that a viscous boundary layer forms at the core–mantle boundary. Inside the boundary layer, where the viscous force plays an important role in force balance, temporal variations of the magnetic field are caused by magnetic diffusion as well as motional induction. Below the boundary layer, where core flow is assumed to be in tangentially geostrophic balance or tangentially magnetostrophic balance, contributions of magnetic diffusion to temporal variation of the magnetic field are neglected. Under the constraint that the core flow is tangentially geostrophic beneath the boundary layer, the core electrical conductivity in the range from $${10}^{5} ~\mathrm{S}~{\mathrm{m}}^{-1}$$ 10 5 S m - 1 to $${10}^{7}~ \mathrm{S}~{\mathrm{m}}^{-1}$$ 10 7 S m - 1 has less significant effect on the core flow. Under the constraint that the core flow is tangentially magnetostrophic beneath the boundary layer, the influence of electrical conductivity on the core flow models can be clearly recognized; the magnitude of the mean toroidal flow does not increase or decrease, but that of the mean poloidal flow increases with an increase in core electrical conductivity. This difference arises from the Lorentz force, which can be stronger than the Coriolis force, for higher electrical conductivity, since the Lorentz force is proportional to the electrical conductivity. In other words, the Elsasser number, which represents the ratio of the Lorentz force to the Coriolis force, has an influence on the difference. The result implies that the ratio of toroidal to poloidal flow magnitudes has been changing in accordance with secular changes of rotation rate of the Earth and of core electrical conductivity due to a decrease in core temperature throughout the thermal evolution of the Earth. |
| first_indexed | 2024-12-20T03:54:50Z |
| format | Article |
| id | doaj.art-d20da7ca657a4d0ca9dceebe057c9260 |
| institution | Directory Open Access Journal |
| issn | 1880-5981 |
| language | English |
| last_indexed | 2024-12-20T03:54:50Z |
| publishDate | 2020-11-01 |
| publisher | SpringerOpen |
| record_format | Article |
| series | Earth, Planets and Space |
| spelling | doaj.art-d20da7ca657a4d0ca9dceebe057c92602022-12-21T19:54:22ZengSpringerOpenEarth, Planets and Space1880-59812020-11-0172111110.1186/s40623-020-01269-0Effect of core electrical conductivity on core surface flow modelsMasaki Matsushima0Department of Earth and Planetary Sciences, Tokyo Institute of TechnologyAbstract The electrical conductivity of the Earth’s core is an important physical parameter that controls the core dynamics and the thermal evolution of the Earth. In this study, the effect of core electrical conductivity on core surface flow models is investigated. Core surface flow is derived from a geomagnetic field model on the presumption that a viscous boundary layer forms at the core–mantle boundary. Inside the boundary layer, where the viscous force plays an important role in force balance, temporal variations of the magnetic field are caused by magnetic diffusion as well as motional induction. Below the boundary layer, where core flow is assumed to be in tangentially geostrophic balance or tangentially magnetostrophic balance, contributions of magnetic diffusion to temporal variation of the magnetic field are neglected. Under the constraint that the core flow is tangentially geostrophic beneath the boundary layer, the core electrical conductivity in the range from $${10}^{5} ~\mathrm{S}~{\mathrm{m}}^{-1}$$ 10 5 S m - 1 to $${10}^{7}~ \mathrm{S}~{\mathrm{m}}^{-1}$$ 10 7 S m - 1 has less significant effect on the core flow. Under the constraint that the core flow is tangentially magnetostrophic beneath the boundary layer, the influence of electrical conductivity on the core flow models can be clearly recognized; the magnitude of the mean toroidal flow does not increase or decrease, but that of the mean poloidal flow increases with an increase in core electrical conductivity. This difference arises from the Lorentz force, which can be stronger than the Coriolis force, for higher electrical conductivity, since the Lorentz force is proportional to the electrical conductivity. In other words, the Elsasser number, which represents the ratio of the Lorentz force to the Coriolis force, has an influence on the difference. The result implies that the ratio of toroidal to poloidal flow magnitudes has been changing in accordance with secular changes of rotation rate of the Earth and of core electrical conductivity due to a decrease in core temperature throughout the thermal evolution of the Earth.http://link.springer.com/article/10.1186/s40623-020-01269-0Core electrical conductivityCore surface flowTangentially geostrophic flowTangentially magnetostrophic flowElsasser number |
| spellingShingle | Masaki Matsushima Effect of core electrical conductivity on core surface flow models Earth, Planets and Space Core electrical conductivity Core surface flow Tangentially geostrophic flow Tangentially magnetostrophic flow Elsasser number |
| title | Effect of core electrical conductivity on core surface flow models |
| title_full | Effect of core electrical conductivity on core surface flow models |
| title_fullStr | Effect of core electrical conductivity on core surface flow models |
| title_full_unstemmed | Effect of core electrical conductivity on core surface flow models |
| title_short | Effect of core electrical conductivity on core surface flow models |
| title_sort | effect of core electrical conductivity on core surface flow models |
| topic | Core electrical conductivity Core surface flow Tangentially geostrophic flow Tangentially magnetostrophic flow Elsasser number |
| url | http://link.springer.com/article/10.1186/s40623-020-01269-0 |
| work_keys_str_mv | AT masakimatsushima effectofcoreelectricalconductivityoncoresurfaceflowmodels |