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A linear auroral current-voltage relation in fluid theory
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
2004 (Engelska)Ingår i: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 22, nr 5, s. 1719-1728Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Progress in our understanding of auroral currents and auroral electron acceleration has for decades been hampered by an apparent incompatibility between kinetic and fluid models of the physics involved. A well established kinetic model predicts that steady upward field-aligned currents should be linearly related to the potential drop along the field line, but collisionless fluid models that reproduce this linear current-voltage relation have not been found. Using temperatures calculated from the kinetic model in the presence of an upward auroral current, we construct here approximants for the parallel and perpendicular temperatures. Although our model is rather simplified, we find that the fluid equations predict a realistic large-scale parallel electric field and a linear current-voltage relation when these approximants are employed as nonlocal equations of state. This suggests that the concepts we introduce can be applied to the development of accurate equations of state for fluid simulations of auroral flux tubes.

Ort, förlag, år, upplaga, sidor
Paris: Gauthier-Villars , 2004. Vol. 22, nr 5, s. 1719-1728
Identifikatorer
URN: urn:nbn:se:umu:diva-12001DOI: 10.5194/angeo-22-1719-2004OAI: oai:DiVA.org:umu-12001DiVA, id: diva2:151672
Tillgänglig från: 2007-04-17 Skapad: 2007-04-17 Senast uppdaterad: 2018-06-09Bibliografiskt granskad
Ingår i avhandling
1. Numerical modeling of auroral processes
Öppna denna publikation i ny flik eller fönster >>Numerical modeling of auroral processes
2007 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Umeå: Fysik, 2007. s. 65
Nyckelord
space plasma physics, auroral acceleration region, auroral current circuit, Alfvén waves, parallel electric fields, equation of state, fluid simulation, PIC simulation
Nationell ämneskategori
Fusion, plasma och rymdfysik
Identifikatorer
urn:nbn:se:umu:diva-1117 (URN)978-91-7264-294-2 (ISBN)
Disputation
2007-06-05, MA121, MIT-huset, Umeå University, 13:00
Opponent
Handledare
Tillgänglig från: 2007-05-08 Skapad: 2007-05-08 Senast uppdaterad: 2018-06-09Bibliografiskt granskad

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