Evolution of high-m poloidal Alfvén waves in a dipole magnetic field
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
ISSN
2169-9380Type
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
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.
Related items
Showing items related by title, author, creator and subject.
-
The transport of Icelandic volcanic ash: insights from northern European cryptotephra records
Watson, E. J.; Swindles, G. T.; Stevenson, J. A.; Savov, I.; Lawson, I. T. (2016-10-30) - Journal articleFine ash produced during volcanic eruptions can be dispersed over a vast area, where it poses a threat to aviation, human health, and infrastructure. We analyze the particle size distributions, geochemistry, and glass shard ... -
An external telemetry system for recording resting heart rate variability and heart rate in free-ranging large wild mammals
Twiss, Sean D.; Brannan, Naomi; Shuert, Courtney R.; Bishop, Amanda M.; Pomeroy, Patrick. P.; Moss, Simon (2021-06-04) - Journal articleMeasures of heart rate variability (and heart rate more generally) are providing powerful insights into the physiological drivers of behaviour. Resting heart rate variability (HRV) can be used as an indicator of individual ... -
Twentieth-century poetry and science : science in the poetry of Hugh MacDiarmid, Judith Wright, Edwin Morgan, and Miroslav Holub
Gibson, Donald (University of St Andrews, 2015-12-14) - ThesisThe aim of this thesis is to arrive at a characterisation of twentieth century poetry and science by means of a detailed study of the work of four poets who engaged extensively with science and whose writing lives spanned ...