Magnetosonic ULF Waves With Anomalous Plasma–Magnetic Field Correlations: Standing Waves and Inhomogeneous Plasmas

Ultra-low frequency (ULF) wave observations across the heliosphere often rely on the sign of correlations between plasma (density/pressure) and magnetic field perturbations to distinguish between fast and slow magnetosonic modes. However, the assumptions behind this magnetohydrodynamic result are no...

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Bibliographic Details
Published in:Geophysical research letters 2023-08, Vol.50 (16), p.n/a
Main Authors: Archer, M. O., Southwood, D. J., Hartinger, M. D., Rastätter, L., Nykyri, K.
Format: Article
Language:English
Subjects:
Advection
Compression
Correlation
Density
Diagnostic systems
Extremely low frequencies
Field strength
Fluid flow
Geomagnetic field
Heliosphere
Incompressible flow
inhomogeneous
Interference
Longitudinal waves
Magnetic field
Magnetic fields
magnetosonic
MHD waves
Modes
Perturbation
Planetary magnetospheres
Plasma
Plasma waves
Plasmas (physics)
Space Sciences (General)
Spacecraft
standing
Standing waves
Theories
Traveling waves
ULF waves
Wave propagation
Wavelength
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Summary:Ultra-low frequency (ULF) wave observations across the heliosphere often rely on the sign of correlations between plasma (density/pressure) and magnetic field perturbations to distinguish between fast and slow magnetosonic modes. However, the assumptions behind this magnetohydrodynamic result are not always valid, particularly within the magnetosphere which is inhomogeneous and supports standing waves along the geomagnetic field. Through theory and a global simulation, we find both effects can result in anomalous plasma–magnetic field correlations. The interference pattern in standing waves can lead both body and surface magnetosonic waves to have different cross-phases than their constituent propagating waves. Furthermore, if the scale of gradients in the background are shorter than the wavelength or the waves are near-incompressible, then advection by the wave of inhomogeneities can overcome the wave's inherent sense of compression. These effects need to be allowed for and taken into account when applying the typical diagnostic to observations.
ISSN:0094-8276
1944-8007
DOI:10.1029/2023GL104762