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The Juno mission is delivering spectacular data of Jupiter's magnetic field, while the gravity measurements finally allow constraining the depth of the winds observed at cloud level. However, to which degree the zonal winds contribute to the planet's dynamo action remains an open question. Here we explore numerical dynamo simulations that include a Jupiter‐like electrical conductivity profile and successfully model the planet's large‐scale field. We concentrate on analyzing the dynamo action in the Steeply Decaying Conductivity Region (SDCR) where the high conductivity in the metallic Hydrogen region drops to the much lower values caused by ionization effects in the very outer envelope of the planet. Our simulations show that the dynamo action in the SDCR is strongly ruled by diffusive effects and is therefore quasi‐stationary. The locally induced magnetic field is dominated by the horizontal toroidal field, while the locally induced currents are dominated by the latitudinal component. The simple dynamics can be exploited to yield estimates of surprisingly high quality for both field and currents. These could potentially be exploited to predict the dynamo action of the zonal winds in Jupiter's SDCR but also in other planets. The Juno mission is delivering spectacular data of Jupiter's magnetic field, while the gravity measurements finally allow constraining the depth of the winds observed at cloud level. However, to which degree the zonal winds contribute to the planet's dynamo action remains an open question. Here we explore numerical simulations of Jupiter's internal dynamics that successfully model the planet's large‐scale field. We concentrate on analyzing the dynamo action in the Steeply Decaying Conductivity Region (SDCR) where the high conductivity in the metallic Hydrogen region drops to the much lower values in the outer envelope of the planet. Our simulations show that the dynamo action in the SDCR is strongly ruled by diffusive effects and is therefore rather simple. The simple dynamics can be exploited to yield estimates of surprisingly high quality for both the induced field and the electric currents in the SDCR. These will allow predicting the dynamo action of the zonal winds in Jupiter's SDCR but also in other planets. Numerical simulations of Jupiter's dynamo are analyzed, concentrating on the outer steeply decaying conductivity regionWe find that the dynamo dynamics in this region is dominated by Ohmic dissipation and can thus be reasonably estimatedThe estimates can be applied to Jupiter or other planets, to reveal the possible dynamo action of zonal winds or other flow contributions

Context. We present a purely-radiative hydrodynamical model of the κ-mechanism that sustains radial oscillations in Cepheid variables.

Spacecraft data reveal a very Earth‐like Jovian magnetic field. This is surprising since numerical simulations have shown that the vastly different interiors of terrestrial and gas planets can strongly affect the internal dynamo process. Here we present the first numerical dynamo that manages to match the structure and strength of the observed magnetic field by embracing the newest models for Jupiter's interior. Simulated dynamo action primarily occurs in the deep high electrical conductivity region, while zonal flows are dynamically constrained to a strong equatorial jet in the outer envelope of low conductivity. Our model reproduces the structure and strength of the observed global magnetic field and predicts that secondary dynamo action associated to the equatorial jet produces banded magnetic features likely observable by the Juno mission. Secular variation in our model scales to about 2000 nT per year and should also be observable during the 1 year nominal mission duration. First model that reproduces Jupiter's magnetic fieldRely on up‐to‐date ab initio structure modelsPrediction testable against future Juno's measurements

Context. We study the ?-mechanism that excites radial oscillations in Cepheid variables.Aims. We address the mode couplings that manage the nonlinear saturation of the instability in direct numerical simulations (DNS).Methods. We project the DNS fields onto an acoustic subspace built from the regular and adjoint eigenvectors that are solutions to the linear oscillation equations.Results. We determine the time evolution of both the amplitude and kinetic energy of each mode that propagates in the DNS. More than 98% of the total kinetic energy is contained in two modes that correspond to the linearly-unstable fundamental mode and the linearly-stable second overtone. Because the eigenperiod ratio is close to 1/2, we discover that the nonlinear saturation is due to a 2:1?resonance between these two modes. An interesting application of this result concerns the reproduction of Hertzsprung's progression observed in Bump Cepheids.

Context.In Cepheids close to the red edge of the classical instability strip, a coupling occurs between the acoustic oscillations and the convective motions close to the surface. The best topical models that account for this coupling rely on 1-D time-dependent convection (TDC) formulations. However, their intrinsic weakness comes from the large number of unconstrained free parameters entering into the description of turbulent convection.Aims.We compare two widely used TDC models with the first 2-D non-linear direct numerical simulations (DNS) of the convection-pulsation coupling in which the acoustic oscillations are self-sustained by the κ-mechanism.Methods.The free parameters appearing in the Stellingwerf and Kuhfuß TDC recipes are constrained using a χ2-test with the time-dependent convective flux that evolves in nonlinear simulations of highly-compressible convection with the κ-mechanism.Results.This work emphasises some inherent limits to TDC models, that is, the temporal variability and non-universality of their free parameters. More importantly, within these limits, Stellingwerf’s formalism is found to give better spatial and temporal agreements with the nonlinear simulation than Kuhfuß’s one. It may therefore be preferred in 1-D TDC hydrocodes or stellar evolution codes.

Context.We study the convection-pulsation coupling that occurs in cold Cepheids close to the red edge of the classical instability strip. In these stars, the surface convective zone is supposed to stabilise the radial oscillations excited by the κ-mechanism.