Simulations of MHD Wave Propagation and Coupling in a 3‐D Magnetosphere

Wright, Andrew N.; Elsden, T.

doi:10.1029/2019ja027589

Cited by 27 publications

(59 citation statements)

References 24 publications

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“…2 , showing excellent agreement across all spacecraft in the equatorial plane (panel a). These observations show MSE do not conform to the typical ULF wave paradigm of tailward propagation 9 , 20 (waveguide modes’ Poynting fluxes are directed tailward or have no net azimuthal component 37 – 39 ; Kelvin–Helmholtz generated surface waves travel tailward and radiate energy into the magnetosphere 40 , 41 ). The wave energy density (Fig.…”

Section: Resultsmentioning

confidence: 90%

“…Figure 5 shows cuts along the terminator. This reveals, in addition to the surface waves, the presence of a quarter wavelength waveguide mode 39 , 48 (at the magnetopause there is a δ v r antinode and δ B ∥ node; δ B ∥ exhibits nodal structure radially). The waveguide mode couples to a toroidal Alfvén mode 50 at Y G S M ~11.5 R E ( δ v ϕ antinode).…”

Section: Resultsmentioning

confidence: 95%

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Magnetopause ripples going against the flow form azimuthally stationary surface waves

et al. 2021

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Surface waves process the turbulent disturbances which drive dynamics in many space, astrophysical and laboratory plasma systems, with the outer boundary of Earth’s magnetosphere, the magnetopause, providing an accessible environment to study them. Like waves on water, magnetopause surface waves are thought to travel in the direction of the driving solar wind, hence a paradigm in global magnetospheric dynamics of tailward propagation has been well-established. Here we show through multi-spacecraft observations, global simulations, and analytic theory that the lowest-frequency impulsively-excited magnetopause surface waves, with standing structure along the terrestrial magnetic field, propagate against the flow outside the boundary. Across a wide local time range (09–15h) the waves’ Poynting flux exactly balances the flow’s advective effect, leading to no net energy flux and thus stationary structure across the field also. Further down the equatorial flanks, however, advection dominates hence the waves travel downtail, seeding fluctuations at the resonant frequency which subsequently grow in amplitude via the Kelvin-Helmholtz instability and couple to magnetospheric body waves. This global response, contrary to the accepted paradigm, has implications on radiation belt, ionospheric, and auroral dynamics and potential applications to other dynamical systems.

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Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 95%

Magnetopause ripples going against the flow form azimuthally stationary surface waves

et al. 2021

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“…A note on the choice of the 2‐D dipole as opposed to similar but more sophisticated 3‐D dipole numerical magnetospheric models which now exist (Wright & Elsden, 2020). The aim of this paper is to elucidate a fundamental plasma physics process numerically for the first time.…”

Section: Numerical Modelmentioning

confidence: 99%

Evolution of High‐m Poloidal Alfvén Waves in a Dipole Magnetic Field

Elsden

Wright

2020

JGR Space Physics

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We investigate how initially high‐m, poloidal Alfvén waves evolve using a numerical model solving the ideal, cold, linear magnetohydrodynamic (MHD) equations in a 2‐D dipole coordinate system. The curved magnetic geometry provides a key difference between the poloidal and toroidal Alfvén frequencies of any one field line. A polarization rotation from poloidal toward toroidal predicted from the Cartesian box model theory still occurs but now with the waves following contours of Alfvén frequency, which moves the Alfvén wave across field lines. The structure of these contours depends on the harmonic mode along the field line and the equilibrium. We find that the amplitude peak of the poloidal mode moves significantly radially outward in time. When the typically observed azimuthal phase motion of such waves is included, hodograms show a polarization rotation from purely poloidal to a mixed poloidal/toroidal polarization at all locations. Such features could be used to help interpret satellite observations of Pc4‐5 poloidal ultralow frequency (ULF) waves in Earth's magnetosphere.

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“…With frequencies much smaller than ion cyclotron frequencies, ULF perturbations have been commonly modeled by single‐fluid MHD equations in curved dipole magnetic field (Radoski, 1967; Radoski & Carovillano, 1966). In MHD simulations (e.g., Leonovich et al, 2016; Nakariakov et al, 2016), propagation of ULF perturbations can be well resolved, which essentially depends on scales and dynamics of the perturbation source (e.g., Klimushkin et al, 2019; Wright & Elsden, 2020). Magnetopause dynamics (Hartinger et al, 2013; Plaschke, 2016) or plasmasheet injections (Liu et al, 2017; Runov et al, 2014) can act as the source for ULF perturbations.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Whistler Waves by Ultra‐Low‐Frequency Perturbations: The Importance of Magnetopause Location

et al. 2020

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Ultra-low-frequency (ULF, 0.001-1 Hz) perturbations are important aspect of the dynamics in the inner magnetosphere: They are responsible for radial transport (diffusion) of high-energy electrons and for energizing the ionosphere with field-aligned currents. This study is devoted to properties of ULF perturbations generated at the magnetopause, their propagation into the inner magnetosphere, and their modulation of whistler-mode very-low-frequency (VLF) waves. Taking advantage of the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission configuration in 2019, we investigate ULF perturbations simultaneously captured by three spacecraft at different distances from the magnetopause. Combining ground-based and THEMIS measurements of ULF perturbations to separate temporal and spatial variations of their properties, we show that their intensity decays exponentially with distance from the magnetopause as close as the geostationary orbit. Near the magnetopause ULF perturbations can modulate whistler-mode (VLF) waves effectively: Close to the magnetopause, VLF wave bursts have the same periodicity as the ULF perturbations. Our results demonstrate that almost the entire outer magnetosphere (from the geostationary orbit to L ∼ 12), including the outer radiation belts, is significantly influenced by ULF perturbations excited by magnetopause dynamic responses to the solar wind.

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Simulations of MHD Wave Propagation and Coupling in a 3‐D Magnetosphere

Cited by 27 publications

References 24 publications

Magnetopause ripples going against the flow form azimuthally stationary surface waves

Magnetopause ripples going against the flow form azimuthally stationary surface waves

Evolution of High‐m Poloidal Alfvén Waves in a Dipole Magnetic Field

Modulation of Whistler Waves by Ultra‐Low‐Frequency Perturbations: The Importance of Magnetopause Location

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