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Electron pressure effects on driven auroral Alfvén waves
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2005 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 110, no A01214, 11- p.Article in journal (Refereed) Published
Abstract [en]

Fluid models for the auroral electron acceleration processes have almost exclusively been derived by assuming cold or isothermal electrons. The consequences of these assumptions have never been thoroughly analyzed. In this study we compare results from an isothermal simulation with those obtained when the pressure is calculated from a double adiabatic approximation and from stationary kinetic theory. We find that the reflection of shear Alfvén waves, as well as the current-voltage relation, is very sensitive to the description of the electron pressure variations. Using pressures calculated from steady-state kinetic theory, we find that driven shear Alfvén waves can build up auroral currents and fields that are consistent with a linear current-voltage relation.


Place, publisher, year, edition, pages
Washington: American Geophysical Union. , 2005. Vol. 110, no A01214, 11- p.
Keyword [en]
auroral electron acceleration Alfvén waves, electron pressure, nonlocal kinetic theory
URN: urn:nbn:se:umu:diva-12002DOI: doi:10.1029/2004JA010610OAI: diva2:151673
Available from: 2007-04-17 Created: 2007-04-17 Last updated: 2011-03-07Bibliographically approved
In thesis
1. Numerical modeling of auroral processes
Open this publication in new window or tab >>Numerical modeling of auroral processes
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

One of the most conspicuous problems in space physics for the last decades has been to theoretically describe how the large parallel electric fields on auroral field lines can be generated. There is strong observational evidence of such electric fields, and stationary theory supports the need for electric fields accelerating electrons to the ionosphere where they generate auroras. However, dynamic models have not been able to reproduce these electric fields. This thesis sheds some light on this incompatibility and shows that the missing ingredient in previous dynamic models is a correct description of the electron temperature. As the electrons accelerate towards the ionosphere, their velocity along the magnetic field line will increase. In the converging magnetic field lines, the mirror force will convert much of the parallel velocity into perpendicular velocity. The result of the acceleration and mirroring will be a velocity distribution with a significantly higher temperature in the auroral acceleration region than above. The enhanced temperature corresponds to strong electron pressure gradients that balance the parallel electric fields. Thus, in regions with electron acceleration along converging magnetic field lines, the electron temperature increase is a fundamental process and must be included in any model that aims to describe the build up of parallel electric fields. The development of such a model has been hampered by the difficulty to describe the temperature variation. This thesis shows that a local equation of state cannot be used, but the electron temperature variations must be descibed as a nonlocal response to the state of the auroral flux tube. The nonlocal response can be accomplished by the particle-fluid model presented in this thesis. This new dynamic model is a combination of a fluid model and a Particle-In-Cell (PIC) model and results in large parallel electric fields consistent with in-situ observations.

Place, publisher, year, edition, pages
Umeå: Fysik, 2007. 65 p.
space plasma physics, auroral acceleration region, auroral current circuit, Alfvén waves, parallel electric fields, equation of state, fluid simulation, PIC simulation
National Category
Fusion, Plasma and Space Physics
urn:nbn:se:umu:diva-1117 (URN)978-91-7264-294-2 (ISBN)
Public defence
2007-06-05, MA121, MIT-huset, Umeå University, 13:00
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2011-03-07Bibliographically approved

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Vedin, JörgenRönnmark, Kjell
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