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Estimating properties of concentrated parallel electric fields from electron velocity distributions
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
2007 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 34, no 16, L16107Article in journal (Refereed) Published
Abstract [en]

Information about the magnitude of the field-aligned potential drop along auroral field lines is usually derived from the velocity distribution of the particles. When the electrons are accelerated by a strong double layer their velocity distribution will have features different from those produced by a weak, spread-out, electric field. Quantifying these features, we obtain information about the strength and thickness of the double layer.

Place, publisher, year, edition, pages
Washington: American Geophysical Union (AGU), 2007. Vol. 34, no 16, L16107
Keyword [en]
auroral acceleration region, particle
National Category
Geosciences, Multidisciplinary
Identifiers
URN: urn:nbn:se:umu:diva-16550DOI: 10.1029/2007GL030162ISI: 000249334400002OAI: oai:DiVA.org:umu-16550DiVA: diva2:156223
Available from: 2007-10-05 Created: 2007-10-05 Last updated: 2017-12-14Bibliographically 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.
Keyword
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
Identifiers
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
Opponent
Supervisors
Available from: 2007-05-08 Created: 2007-05-08 Last updated: 2017-03-27Bibliographically approved

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