Work

Superposition of Doppler‐Shifting Magnetopause Kelvin‐Helmholtz Modes Through Dynamic Mode Decomposition of a Global MHD Simulation

Year: 2026

Type: article

Abstract: The Kelvin‐Helmholtz instability (KHI) mediates the viscous‐like solar‐terrestrial interaction by generating magnetopause surface waves that quickly become non‐linear. Basic theory predicts the locally most‐unstable linear wave dominates. However, Kelvin‐Helmholtz is a broad, convective instability that also amplifies waves originating upstream. We address this conundrum by applying dynamic mode decomposition to a Gorgon global magnetohydrodynamic simulation of the KHI. While distinct modes quickly grow at points along the magnetopause, signaling local generation, their energy continues to slowly grow downtail. Thus, a superposition is present along the magnetopause, where the dominant mode is not always the locally fastest‐growing. Each mode's wavelength elongates downtail, correlating with the boundary layer flow speed due to the accelerating advective flow around the magnetosphere Doppler shifting the fixed‐frequency waves. This may explain why longer wavelengths are observed in the tail than theory predicts and motivates further exploration of tangential inhomogeneities in basic Kelvin‐Helmholtz theory.

Source: Geophysical Research Letters

DOI: 10.1029/2025gl120284

Authors: H. M. Kelly, M. O. Archer, J. P. Eastwood, M. Heyns, J. W. B. Eggington, J. P. Chittenden

Institutions: Met Office, Imperial College London, EDF Energy (United Kingdom)

Language: English

Topic: Ionosphere and magnetosphere dynamics

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,190