Numerical Modelling of Zonal Winds on Gas Giants
von Paula Naomi Wulff
Datum der mündl. Prüfung:2023-10-25
Erschienen:2023-12-22
Betreuer:Prof. Dr. Ulrich Christensen
Gutachter:Prof. Dr. Ulrich Christensen
Gutachter:Prof. Dr. Andreas Tilgner
Dateien
Name:Thesis_Wulff_corr.pdf
Size:27.6Mb
Format:PDF
Zusammenfassung
Englisch
The outer regions of both Jupiter and Saturn host strong, alternately eastward and westward zonal winds. These are essentially steady in time and cover all latitudes, albeit diminished in amplitude at the mid-to-high latitudes. Gravity measurements have revealed that the jets observed on the surface must extend deep into the planets’ convective regions, from the surface to around 3,000 km and 9,000 km in Jupiter and Saturn respectively. Numerical simulations have had difficulties in reproducing winds that form at the higher latitudes and are quenched at these inferred depths, in the same models. This work addresses this conundrum and shows that the key structural element is a stably stratified layer, located below the outer convective region where zonal winds form. In this layer, radial flows are inhibited and convection is quenched which leads to a damping of zonal winds and a decoupling from underlying conducting regions. It is found that wider jets penetrate further into the stable layer and the structures are no longer invariant with respect to the axis of rotation, as they are in the rotationally dominated convective envelope. Furthermore, magnetic effects, quantified by the electrical conductivity and the internal magnetic field, can reduce the penetration depth of the jets. Our simulations suggest that the presence of stable stratification that reaches upwards into a region of weak conductivity is essential for maintaining strong winds at mid-to-high latitudes, that drop off at a depth that is consistent with constraints from the measured gravity and magnetic fields.
Keywords: Rotating Magnetohydrodynamics; Rotating Hydrodynamics; Gas Giants; Zonal Flows; Saturn; Jupiter