Magnetic boundary layers in numerical dynamos with heterogeneous outer boundary heat flux
| Autor: | Filipe Terra-Nova, Hagay Amit |
|---|---|
| Přispěvatelé: | Université de Sao Paulo (USP) et PUC-SP, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS) |
| Jazyk: | angličtina |
| Rok vydání: | 2023 |
| Předmět: |
010504 meteorology & atmospheric sciences
Physics and Astronomy (miscellaneous) Magnetic Reynolds number Boundary (topology) Astronomy and Astrophysics Geometry 010502 geochemistry & geophysics Boundary layer thickness 01 natural sciences Magnetic flux Outer core Physics::Geophysics Magnetic field Geophysics Heat flux 13. Climate action Space and Planetary Science [SDU]Sciences of the Universe [physics] Astrophysics::Earth and Planetary Astrophysics Physics::Atmospheric and Oceanic Physics Geology ComputingMilieux_MISCELLANEOUS 0105 earth and related environmental sciences Dynamo |
| Zdroj: | XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) Physics of the Earth and Planetary Interiors Physics of the Earth and Planetary Interiors, Elsevier, 2021, 309, pp.106589. ⟨10.1016/j.pepi.2020.106589⟩ |
| ISSN: | 0031-9201 |
| DOI: | 10.1016/j.pepi.2020.106589⟩ |
| Popis: | It has been proposed that magnetic flux expulsion due to outer core fluid upwellings may affect the geomagnetic secular variation on the core-mantle boundary (Bloxham, 1986). In this process intense horizontal field lines are concentrated below the outer boundary, introducing small radial length scales and consequently strong radial diffusion. We explore such magnetic boundary layers in numerical dynamo simulations with heterogeneous outer boundary heat flux inferred from a tomographic model of lower mantle seismic shear waves velocity anomalies. Our scheme associates magnetic boundary layers to peak horizontal magnetic fields at the top of the shell. In our models mean magnetic boundary layer thickness ranges ≈200-400 km and decreases with increasing magnetic Reynolds number. Extrapolation or interpolation to Earth's core conditions based on total core flow amplitude or its poloidal part gives mean magnetic boundary layer thickness of ≈220 and ≈260-330 km, respectively. We find magnetic boundary layers associated with the azimuthal field at the equatorial region, whereas magnetic boundary layers associated with the meridional field are found at mid latitudes. Negative outer boundary heat flux anomalies yield preferred locations of expulsion of azimuthal field below Africa and the Pacific (at low latitudes of the Northern Hemisphere.), while positive outer boundary heat flux anomalies yield preferred locations of expulsion of meridional field below the Americas and East Asia. Our results suggest that the local diffusion time is on the order of several kyr and the local magnetic Reynolds number is on the order of ≈10, both much smaller than classical estimates. The 28th IUGG General Assembly (IUGG2023) (Berlin 2023) |
| Databáze: | OpenAIRE |
| Externí odkaz: |
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