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Evolution of high-m poloidal Alfvén waves in a dipole magnetic field

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Elsden_2020_Evolution_of_high_m_JGR_SP_e2020JA028187.pdf (9.997Mb)
Date
08/2020
Author
Elsden, Thomas
Wright, Andrew
Funder
Science & Technology Facilities Council
Grant ID
ST/N000609/1
Keywords
Alfven waves
high-m
magnetosphere
MHD
simulation
ULF waves
GE Environmental Sciences
QB Astronomy
QC Physics
Aquatic Science
Forestry
Soil Science
Geophysics
Oceanography
Ecology
Water Science and Technology
Atmospheric Science
Geochemistry and Petrology
Earth-Surface Processes
Earth and Planetary Sciences (miscellaneous)
Palaeontology
Space and Planetary Science
DAS
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Abstract
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.
Citation
Elsden , T & Wright , A 2020 , ' Evolution of high-m poloidal Alfvén waves in a dipole magnetic field ' , Journal of Geophysical Research: Space Physics , vol. 125 , no. 8 , e2020JA028187 . https://doi.org/10.1029/2020JA028187
Publication
Journal of Geophysical Research: Space Physics
Status
Peer reviewed
DOI
https://doi.org/10.1029/2020JA028187
ISSN
2169-9380
Type
Journal article
Rights
Copyright © 2020 American Geophysical Union. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the final published version of the work, which was originally published at https://doi.org/10.1029/2020JA028187.
Description
Funding: Leverhulme Trust. Grant Number: ECF‐2019‐155; UKRI Science and Technology Facilities Council (STFC) Grant Number: ST/N000609/1.
Collections
  • University of St Andrews Research
URI
http://hdl.handle.net/10023/21457

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