Effects of a radially varying electrical conductivity on 3D numerical dynamos

Pérez, Nelly Diego; Heimpel, Moritz

doi:10.1016/j.pepi.2010.03.006

Cited by 28 publications

(32 citation statements)

References 48 publications

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“…A super-exponential increase in the molecular layer until about 0.9R smoothly transitions into a much shallower gradient in the metallic layer. Since the superexponential increase causes numerical difficulties, we use several simplified conductivity profiles with a constant interior conductivity branch that is matched to an exponentially decaying outer branch via a polynomial that assures a continuous first derivative (Gómez-Pérez et al, 2010):…”

Section: Background Statementioning

confidence: 99%

Physical conditions for Jupiter-like dynamo models

Duarte

Wicht

Gastine

2018

Icarus

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The Juno mission will measure Jupiter's magnetic field with unprecedented precision and provide a wealth of additional data that will allow us to constrain the planet's interior structure and dynamics. Here we analyse 66 different numerical simulations in order to explore the sensitivity of the dynamo-generated magnetic field to the planets interior properties. Jupiter field models based on pre-Juno data and up-to-date interior models based on ab initio simulations serve as benchmarks. Our results suggest that Jupiter-like magnetic fields can be found for a number of different models. These complement the steep density gradients in the outer part of the simulated shell with an electrical conductivity profile that mimics the low conductivity in the molecular hydrogen layer and thus renders the dynamo action in this region largely unimportant. We find that whether we assume an ideal gas or use the more realistic interior model based on ab initio simulations makes no difference. However, two other factors are important. A low Rayleigh number leads to a too strong axial dipole contribution while the axial dipole dominance is lost altogether when the convective driving is too strong. The required intermediate range that yields Jupiter-like magnetic fields depends on the other system properties. The second important factor is the convective magnetic Reynolds number radial profile Rm c (r), basically a product of the non-axisymmetric flow velocity and electrical conductivity. We find that the depth where Rm c exceeds about 50 is a good proxy for the top of the dynamo region. When the dynamo region sits too deep, the axial dipole is once more too dominant due to geometric reasons. Extrapolating our results to Jupiter and the result suggests that the Jovian dynamo extends to 95% of the planetary radius. The zonal flow system in our simulations is dominated by an equatorial jet which remains largely confined to the molecular layer. Where the jet reaches down to higher electrical conductivities, however, it gives rise to a secondary αΩ dynamo that modifies the dipole-dominated field produced deeper in the planet. This secondary dynamo can lead to strong magnetic field patches at lower latitudes that seem compatible with the pre-Juno field models.

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Section: Background Statementioning

confidence: 99%

Physical conditions for Jupiter-like dynamo models

Duarte

Wicht

Gastine

2018

Icarus

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“…For convenience we also define the relative transition radius in percentage: χ m = r m /r o . This profile has first been used by Gómez-Pérez et al (2010) and it seems a fair first approximation to the results from ab initio calculations by French et al (2012). The super-exponential increase of electrical conductivity over the molecular layer is not feasible to model numerically (see Fig.…”

Section: Variable Conductivitymentioning

confidence: 99%

Anelastic dynamo models with variable electrical conductivity: An application to gas giants

Duarte

Gastine

Wicht

2013

Physics of the Earth and Planetary Interiors

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The observed surface dynamics of Jupiter and Saturn are dominated by a banded system of fierce zonal winds. The depth of these winds remains unclear but they are thought to be confined to the very outer envelopes where hydrogen remains molecular and the electrical conductivity is small. The dynamo maintaining the dipole-dominated magnetic fields of both gas giants, on the other hand, likely operates in the deeper interior where hydrogen assumes a metallic state.Here, we present numerical simulations that attempt to model both the zonal winds and the interior dynamo action in an integrated approach. Using the anelastic version of the MHD code MagIC, we explore the effects of density stratification and radial electrical conductivity variations. The electrical conductivity is mostly assumed to remain constant in the thicker inner metallic region and it decays exponentially towards the outer boundary throughout the molecular envelope.Our results show that the combination of a stronger density stratification and a weaker conducting outer layer is essential for reconciling dipole dominated dynamo action and a fierce equatorial zonal jet. Previous simulations with homogeneous electrical conductivity show that both are mutually exclusive, with solutions either having strong zonal winds and multipolar magnetic fields or weak zonal winds and dipole-dominated magnetic fields. All jets tend to be geostrophic and therefore reach right through the convective shell in our simulations.The particular setup explored here allows a strong equatorial jet to remain confined to the weaker conducting outer region where it does not interfere with the deeper seated dynamo action. The flanking mid to high latitude jets, on the other hand, have to remain faint to yield a strongly dipolar magnetic field. The fiercer jets on Jupiter and Saturn only seem compatible with the observed dipolar fields when they remain confined to a weaker conducting outer layer.

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“…The conductivity and further material properties along the Jovian adiabat were calculated by French et al [186]. These data will serve as a more realistic input in future dynamo simulations for planetary magnetic fields [187] that so far assume a superexponential behavior of the electrical conductivity (orange line in Fig. 16).…”

Section: Interior Models For Jupiter and Saturnmentioning

confidence: 94%

“…It is in perfect agreement with the semiconductor model of Liu et al [183] (red dashed line) based on experimental data. Also shown is a model of Gomez-Perez et al [187] used in dynamo simulations of Jupiter's magnetic field for a given P-T value. It intersects the isentrope just in the region where it flattens.…”

Section: Interior Models For Jupiter and Saturnmentioning

confidence: 99%

Frontiers and Challenges in Warm Dense Matter

2014

Lecture Notes in Computational Science and Engineering

187

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Effects of a radially varying electrical conductivity on 3D numerical dynamos

Cited by 28 publications

References 48 publications

Physical conditions for Jupiter-like dynamo models

Physical conditions for Jupiter-like dynamo models

Anelastic dynamo models with variable electrical conductivity: An application to gas giants

Frontiers and Challenges in Warm Dense Matter

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