Fast Quasi-Geostrophic Magneto-Coriolis Modes in the Earth's core

TL;DR

This paper introduces a hybrid quasi-geostrophic model for Earth's core that identifies fast, equatorially localized Magneto-Coriolis modes, offering insights into rapid magnetic field changes and core magnetic structure probing.

Contribution

It develops a novel hybrid QG model with columnar flows and 3D magnetic fields, revealing high-frequency modes relevant to Earth's core dynamics.

Findings

Modes with periods of a few years identified

Energy localized in the equatorial region

Potential explanation for observed geomagnetic features

Abstract

Fast changes of Earth's magnetic field could be explained by inviscid and diffusion-less quasi-geostrophic (QG) Magneto-Coriolis modes. We present a hybrid QG model with columnar flows and three-dimensional magnetic fields and find modes with periods of a few years at parameters relevant to Earth's core. For the simple poloidal magnetic field that we consider here they show a localization of kinetic and magnetic energy in the equatorial region. This concentration of energy near the equator and the high frequency make them a plausible mechanism to explain similar features observed in recent geomagnetic field observations. Our model potentially opens a way to probe the otherwise inaccessible magnetic field structure in the Earth's outer core.