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Title: Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2-D fluid model

Abstract

In this paper, progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. Simulations with parameters set to various ionospheric background conditions revealed properties of the gradient-drift and Farley-Buneman instabilities. Notably, sharper density gradients increase linear growth rates at all scales, whereas variations in cross-field E × B drift velocity only affect small-scale instabilities. A formalism defining turbulent fluctuation energy for the system is introduced, and the turbulence is analyzed within this framework. This exercise serves as a useful verification test of the numerical simulations and also elucidates the physics underlying the ionospheric turbulence. Various physical mechanisms involved in the energetics are categorized as sources, sinks, nonlinear transfer, and cross-field coupling. The physics of the nonlinear transfer terms is studied to identify their roles in producing energy cascades, which explain the generation of small-scale structures that are stable in the linear regime. The theory of two-step energy cascading to generate the 3 m plasma irregularities in the equatorial electrojet is verified for the first time in the fluid regime. Finally, in addition, the nonlinearity of the system allows the possibility of an inverse energy cascade, potentially responsible for generating large-scalemore » plasma structures at the top of the electrojet as found in different rocket and radar observations.« less

Authors:
ORCiD logo [1];  [2];  [2];  [3]
  1. Univ. of Texas, Austin, TX (United States). Inst. for Computational Engineering and Sciences (ICES); Ain Shams Univ., Cairo (Egypt). Dept. of Physics
  2. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies (IFS)
  3. Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies (IFS). Applied Research Lab. (ARL)
Publication Date:
Research Org.:
Univ. of Texas, Austin, TX (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1469341
Alternate Identifier(s):
OSTI ID: 1402383
Grant/Contract Number:  
FG02-04ER54742
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 9; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; equatorial electrojet; ionosphere instabilities; Farley-Buneman instability; gradient-drift instability; energy cascades; noncanonical Hamiltonian system

Citation Formats

Hassan, Ehab, Hatch, D. R., Morrison, P. J., and Horton, W. Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2-D fluid model. United States: N. p., 2016. Web. doi:10.1002/2016JA022671.
Hassan, Ehab, Hatch, D. R., Morrison, P. J., & Horton, W. Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2-D fluid model. United States. doi:10.1002/2016JA022671.
Hassan, Ehab, Hatch, D. R., Morrison, P. J., and Horton, W. Tue . "Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2-D fluid model". United States. doi:10.1002/2016JA022671. https://www.osti.gov/servlets/purl/1469341.
@article{osti_1469341,
title = {Multiscale equatorial electrojet turbulence: Energy conservation, coupling, and cascades in a baseline 2-D fluid model},
author = {Hassan, Ehab and Hatch, D. R. and Morrison, P. J. and Horton, W.},
abstractNote = {In this paper, progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. Simulations with parameters set to various ionospheric background conditions revealed properties of the gradient-drift and Farley-Buneman instabilities. Notably, sharper density gradients increase linear growth rates at all scales, whereas variations in cross-field E × B drift velocity only affect small-scale instabilities. A formalism defining turbulent fluctuation energy for the system is introduced, and the turbulence is analyzed within this framework. This exercise serves as a useful verification test of the numerical simulations and also elucidates the physics underlying the ionospheric turbulence. Various physical mechanisms involved in the energetics are categorized as sources, sinks, nonlinear transfer, and cross-field coupling. The physics of the nonlinear transfer terms is studied to identify their roles in producing energy cascades, which explain the generation of small-scale structures that are stable in the linear regime. The theory of two-step energy cascading to generate the 3 m plasma irregularities in the equatorial electrojet is verified for the first time in the fluid regime. Finally, in addition, the nonlinearity of the system allows the possibility of an inverse energy cascade, potentially responsible for generating large-scale plasma structures at the top of the electrojet as found in different rocket and radar observations.},
doi = {10.1002/2016JA022671},
journal = {Journal of Geophysical Research. Space Physics},
number = 9,
volume = 121,
place = {United States},
year = {Tue Sep 06 00:00:00 EDT 2016},
month = {Tue Sep 06 00:00:00 EDT 2016}
}

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