Characterising mesoscale magnetopause surface waves within magnetosphere--ionosphere--ground
coupling
coupling
File(s)
Published version
Author(s)
Archer, Martin
Southwood, David
Zhang, Song
Sun, Qiran
Heyns, Mike
Type
Journal Article
Abstract
Disturbances to the magnetopause location driven by upstream pressure variations or flow shear instabilities may be described as surface waves, which act as localised sources of field-aligned currents coupling the magnetosphere to the ionosphere. However, their impacts on the ionosphere and ground across representative ranges of wave and system properties are poorly understood. We, therefore, develop a simple numerical model for dispersionless mesoscale magnetopause surface waves within the coupled magnetosphere–ionosphere–ground system to gain insight into how their amplitudes and spatial scales throughout the system might vary with conditions. In general, the impacts of finite wave packets can be decomposed into periodic fluctuations (with matching wavelength to that directly above in the magnetosphere) along with slowly-varying trends that result from finite wave effects. Finite wave packets act in the far-field like a string of alternating field-aligned currents well described both in the ionosphere and on the ground as a two-dimensional current dipole. In the ionosphere, near-field periodic fluctuations exponentially decay over the reduced wavelength latitudinally away from the projected magnetopause boundary layer flux tubes, which may limit how well they can be resolved by radar. The relationship between the magnetic field above and below the ionosphere becomes more complicated for surface waves than infinite plane Alfvén waves due to the additional spatial structure, which introduces interference across the spectrum of wavenumbers present. This modifies how the ionosphere screens, rotates, and spatially smears magnetic field perturbations across all three components in different ways. For mesoscale wavelengths this importantly results in latitudinal scales of amplitude and polarisation variation smaller than typical ground magnetometer spacings, motivating the need for denser networks. A range of effective skin depths in the ground are applicable to surface waves, meaning ground induction can vary between a near-perfect insulator to a good conductor, affecting both observable ground magnetic fields and resulting geoelectric fields. The predicted peak amplitudes of surface waves' impacts suggest they may act as significant sources of ionospheric/thermospheric Joule heating and geoelectric fields in the ground, thereby contributing to space weather impacts. These are, however, highly localised latitudinally when considering typical mesoscale waves. Our results provide key insight into interpreting ground-based observations, of particular timeliness with the rollout of new digital ionospheric radars and the SMILE mission's planned conjugate ground–space campaigns.
Date Issued
2027-07-07
Date Acceptance
2026-06-24
Citation
Annales Geophysicae, 2027, 44 (2), pp.595-630
ISSN
0992-7689
Publisher
Copernicus Publications
Start Page
595
End Page
630
Journal / Book Title
Annales Geophysicae
Volume
44
Issue
2
Copyright Statement
© Author(s) 2026. This work is distributed under the Creative Commons Attribution 4.0 License.
License URL
Identifier
10.5194/angeo-44-595-2026
Publication Status
Published