MagNetZ with Jenny Wong (2021/09/08) - Dynamo simulations with a stably-stratified F-layer
Channel: MagNetZ
Date: 2021-09-08

Dynamo simulations with a stably-stratified F-layer at the base of Earth’s outer core

The video is also available for download at: https://earthref.org/ERDA/2482/
and can be referenced with the doi: 10.7288/V4/ERDA/2482

Title: Dynamo simulations with a stably-stratified F-layer at the base of Earth’s outer core
Author: Jenny Wong from ISTerre, Université de Grenoble-Alpes, France
Author Website: https://jnywong.netlify.app/

Seismic observations reveal a slowdown in the P wave velocity at the base of the Earth’s outer core attributed to the presence of a stably-stratified layer, also known as the F-layer. In this talk, we focus on the impact of the F-layer on the geodynamo process that generates the Earth’s magnetic field. Field generation is mainly powered by thermal and compositional convection in the liquid bulk of the core, and the dynamics can be divided into two distinct regions inside and outside the tangent cylinder: this is conventionally defined as a cylinder tangent to the inner core boundary and aligned with the rotation axis. Using numerical dynamo models with core-mantle coupling, we simulate a stably stratified layer at the base of the core with varying degrees of stratification that effectively increases the size of the tangent cylinder and alters the dynamics thereof. We find that zonal flows beneath the CMB are significantly enhanced by the F-layer while jets emanating from the tangent cylinder become detached due to the rearrangement of the thermal wind balance caused by the shift in electromagnetic and gravitational torques. We evaluate the magnetic field at the core surface and determine a possible geomagnetic signature of the F-layer from our simulations independent of the degree of stratification, in which the location of the maximal radial field strength associated with the envelope of a polar magnetic minimum seen in the geomagnetic data is shifted by several degrees in latitude.