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

TL;DR

This study explores how radially decreasing electrical conductivity in planetary cores affects dynamo processes, revealing significant impacts on flow and magnetic field characteristics, with implications for understanding Mercury's weak magnetic field.

Contribution

It introduces a model with radially variable electrical conductivity and demonstrates its effects on planetary dynamo behavior, a novel approach compared to previous homogeneous conductivity models.

Findings

Radially decreasing conductivity alters flow and magnetic field dynamics.

The flow is influenced by the balance of Coriolis and Lorentz forces.

A low conductivity layer near Mercury's core explains its weak magnetic field.

Abstract

The transition from liquid metal to silicate rock in the cores of the terrestrial planets is likely to be accompanied by a gradient in the composition of the outer core liquid. The electrical conductivity of a volatile enriched liquid alloy can be substantially lower than a light-element-depleted fluid found close to the inner core boundary. In this paper, we investigate the effect of radially variable electrical conductivity on planetary dynamo action using an electrical conductivity that decreases exponentially as a function of radius. We find that numerical solutions with continuous, radially outward decreasing electrical conductivity profiles result in strongly modified flow and magnetic field dynamics, compared to solutions with homogeneous electrical conductivity. The force balances at the top of the simulated fluid determine the overall character of the flow. The relationship between Coriolis and Lorentz forces near the outer boundary controls the flow and magnetic field intensity and morphology of the system. Our results imply that a low conductivity layer near the top of Mercury's liquid outer core is consistent with its weak magnetic field.