A Global Simulation of the Dynamo, Zonal Jets, and Vortices on Saturn

TL;DR

This paper presents a high-resolution simulation of Saturn's interior dynamics that reproduces key features like jet streams, vortices, and magnetic field characteristics, emphasizing the role of a stably stratified layer.

Contribution

First self-consistent simulation to simultaneously reproduce Saturn's atmospheric and magnetic features, highlighting the importance of a stably stratified layer in planetary dynamics.

Findings

Reproduces polar cyclones and jet streams in the molecular layer.

Shows interaction between jet streams and magnetic field.

Replicates Saturn's magnetic energy spectrum features.

Abstract

The fluid dynamics in planet Saturn gives rise to alternating east-west jet streams, large cyclonic and anticyclonic vortices, and a dipole-dominant magnetic field which is highly axisymmetric about the planetary rotation axis. Modelling these features in a self-consistent manner is crucial for understanding the dynamics of Saturn's interior and atmosphere. Here we report a turbulent high-resolution dynamo simulation in a spherical shell which produces these features simultaneously for the first time. A crucial model ingredient is a long-hypothesised stably stratified layer (SSL), sandwiched between a deep metallic hydrogen layer and an outer low-conductivity molecular layer, born out of limited solubility of Helium inside metallic Hydrogen at certain depths. The model spontaneously produces polar cyclones and significant low and mid latitude jet stream activities in the molecular layer. The off-equatorial low-latitude jet streams partially penetrate into the SSL and interact with the magnetic field. This helps to axisymmetrize the magnetic field about the rotation axis and convert some of the poloidal magnetic field to toroidal field, which appears as two global magnetic energy rings surrounding the deeper dynamo region. The simulation also mimics a distinctive dip in the fifth spherical harmonic in Saturn's magnetic energy spectrum as inferred from the Cassini Grand Finale measurements. Our model highlights the role of an SSL in shaping the fluid dynamical and magnetic features of giant planets, as exemplified at Saturn.