Ohmic and viscous damping of inner core translational oscillations

TL;DR

This study uses simulations to quantify viscous and Ohmic damping of Earth's inner core oscillations, finding Ohmic dissipation dominates and allows modes to persist for years, explaining their non-detection.

Contribution

The paper derives scaling laws for damping mechanisms of Earth's inner core oscillations, highlighting the dominance of Ohmic dissipation over viscous effects.

Findings

Ohmic dissipation causes decay times of 3-16 years.

Viscous effects are negligible, confined to a thin boundary layer.

Equatorial modes damp at least twice as fast as polar modes.

Abstract

Large earthquakes can trigger translational oscillations of Earth's inner core (Slichter modes), yet their damping remains uncertain. Using simulations, we quantify viscous and Ohmic dissipation in the fluid outer core. Earth's rotation splits the motion into one polar and two equatorial modes. We explore all three and derive scaling laws for the quality factor with each dissipation mechanism. Viscous effects are negligible, confined to a thin layer at the inner core boundary. Ohmic dissipation dominates, with decay times of 3-16 years. Equatorial modes damp at least twice as fast as the polar mode. Our results suggest that Slichter modes can persist for years. Their continued non-detection is therefore more likely due to weak excitation than rapid damping.