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Production of small-scale Alfvén waves by ionospheric depletion, nonlinear magnetosphere-ionosphere coupling and phase mixing

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Wright_2013_JGRSP_Production.pdf (825.5Kb)
Date
03/04/2013
Author
Russell, A. J. B.
Wright, Andrew Nicholas
Streltsov, A. V.
Funder
Science & Technology Facilities Council
Grant ID
ST/K000950/1
Keywords
Magnetosphere-ionosphere coupling
Small-scale Alfven waves
Ionospheric depletion
Phase mixing
Magnetosphere-ionosphere waves
Ionospheric feedback instability
Quiet auroral arcs
Field-line resonances
Dynamic magnetosphere
Electric fields
Model
Acceleration
Cavity
QC Physics
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Abstract
Rockets and satellites have previously observed small-scale Alfven waves inside large-scale downward field-aligned currents, and numerical simulations have associated their formation with self-consistent magnetosphere-ionosphere coupling. The origin of these waves was previously attributed to ionospheric feedback instability; however, we show that they arise in numerical experiments in which the instability is excluded. A new interpretation is proposed in which strong ionospheric depletion and associated current broadening (a nonlinear steepening/wave-breaking process) form magnetosphereionosphere waves inside a downward current region and these oscillations drive upgoing inertial Alfven waves in the overlying plasma. The resulting waves are governed by characteristic periods, which are a good match to previously observed periods for reasonable assumed conditions. Meanwhile, wavelengths perpendicular to the magnetic field initially map to an ionospheric scale comparable to the electron inertial length for the low-altitude magnetosphere, but become shorter with time due to frequency-based phase mixing of boundary waves (a new manifestation of phase mixing). Under suitable conditions, these could act as seeds for the ionospheric feedback instability.
Citation
Russell , A J B , Wright , A N & Streltsov , A V 2013 , ' Production of small-scale Alfvén waves by ionospheric depletion, nonlinear magnetosphere-ionosphere coupling and phase mixing ' , Journal of Geophysical Research: Space Physics , vol. 118 , no. 4 , pp. 1450-1460 . https://doi.org/10.1002/jgra.50168
Publication
Journal of Geophysical Research: Space Physics
Status
Peer reviewed
DOI
https://doi.org/10.1002/jgra.50168
ISSN
2169-9402
Type
Journal article
Rights
©2013. American Geophysical Union. All Rights Reserved.
Description
The authors acknowledge the International Space Science Institute (Switzerland) for funding the program that inspired this work. AJBR is grateful to the Royal Commission for the Exhibition of 1851 for present support and acknowledges an STFC studentship that funded part of this work.
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  • University of St Andrews Research
URI
http://hdl.handle.net/10023/5150

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