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Particle-fluid simulation of the auroral current circuit
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2006 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 111, no A12201, 12- p.Article in journal (Refereed) Published
Abstract [en]

The incompatibility between stationary kinetic and dynamic fluid descriptions of auroral electron acceleration has been an outstanding problem in space physics for decades. In this study we introduce a new numerical simulation model that provides a unified picture by including electron temperature variations consistent with collisionless kinetic theory in the fluid description. We demonstrate that this new particle-fluid model can describe the partial reflection of Alfvén waves from the acceleration region, as well as the formation of a field-aligned potential drop proportional to the upward current. This study also suggests that for example ion dynamics and high-frequency waves must be added to the model before it properly can describe the return current region. Simulations based on the particle-fluid concept can be applied to various processes in space physics and astrophysics where strong currents flowing along an inhomogeneous magnetic field will cause temperature increases and field-aligned electric fields.

Place, publisher, year, edition, pages
Washington: American Geophysical Union. , 2006. Vol. 111, no A12201, 12- p.
Keyword [en]
Alfvén waves, auroral electron acceleration, electron heating
URN: urn:nbn:se:umu:diva-12004DOI: doi:10.1029/2006JA011826OAI: diva2:151675
Available from: 2007-03-18 Created: 2007-03-18 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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