The Effect of Fast Normal Mode Structure and Magnetopause Forcing on FLRs in a 3‐D Waveguide

Elsden, T.; Wright, Andrew N.

doi:10.1029/2018ja026222

Cited by 17 publications

(21 citation statements)

References 40 publications

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“…This is particularly clear in panel (c), which corresponds to the second radial harmonic that is symmetric about noon (Figures a and b) and was discussed at the start of this subsection. These results confirm the mode structure reported by Elsden and Wright () for a 2‐D dipole (namely, that waveguide modes have a standing nature near noon, but propagating nature on the flanks) carries over to a 3‐D dipole with flared flanks.…”

Section: Simulation Resultssupporting

confidence: 91%

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

Wright

Elsden

2020

JGR Space Physics

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A novel simulation grid is devised that is optimized for studying magnetohydrodynamic (MHD) wave coupling and phase mixing in a dipole‐like magnetic field. The model also includes flaring on the dawn and dusk flanks. The location of the magnetopause is quite general. In particular, it does not have to coincide with a coordinate surface. Simulations indicate the central role of global fast waveguide modes. These switch from being azimuthally standing in nature at noon, to propagating antisunward on the flanks. The field line resonances (FLRs) seen in the simulation results are three dimensional and not strictly azimuthally polarized. When a plume is present, the FLRs cross a range of 2 in L shell, and have a polarization that is midway between toroidal and poloidal.

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Section: Simulation Resultssupporting

confidence: 91%

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

Wright

Elsden

2020

JGR Space Physics

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“…The model used has been described at length in many previous studies (e.g., Elsden & Wright, 2017, 2018, 2019; Wright & Elsden, 2016; Wright et al, 2018) and will therefore only briefly be summarized here.…”

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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“…These modes will depend upon the magnetic field structure, plasma mass density variation and the size and shape of the magnetospheric waveguide and will therefore result in a broad spectrum of permissible frequencies. The particular fast waveguide modes excited will further depend upon the temporal/spatial structure of the solar wind driving (Elsden & Wright, 2019).…”

Section: Discussionmentioning

confidence: 99%

Modeling the Varying Location of Field Line Resonances During Geomagnetic Storms

et al. 2022

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Previous observational studies have shown that the natural Alfvén frequencies of geomagnetic field lines vary significantly over the course of a geomagnetic storm, decreasing by up to 50% from their quiet time values outside the plasmasphere. This was recently demonstrated statistically using ground magnetometer observations across 132 geomagnetic storm events (Wharton et al., 2020). This then brings into question where field line resonances (FLRs) will form in storm‐time conditions relative to quiet times. With storm‐time radiation belt dynamics depending heavily upon wave‐particle interactions, understanding how FLR locations change over the course of a storm will have important implications for this area. Using 3D magnetohydrodynamic (MHD) simulations, we investigate how changes in the Alfvén frequency continuum of the Earth's dayside magnetosphere over the course of a geomagnetic storm affect the fast‐Alfvén wave coupling. By setting the model Alfvén frequencies consistent with the observations, and permitting a modest change in the plasmapause/magnetopause locations consistent with storm‐time behavior, we show that FLR locations can change substantially during storms. The combined effects of higher fast waveguide frequencies and lower Alfvén frequencies during storm main phases, act together to move the FLR locations radially inwards compared to quiet times. FLRs outside of the plasmasphere are moved radially inward by 1.7 Earth radii for the cases considered.

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The Effect of Fast Normal Mode Structure and Magnetopause Forcing on FLRs in a 3‐D Waveguide

Cited by 17 publications

References 40 publications

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

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

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

Modeling the Varying Location of Field Line Resonances During Geomagnetic Storms

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