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Observations of lower hybrid cavities in the inner magnetosphere by the Cluster and Viking satellites
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
2004 In: Annales Geophysicae, ISSN 0992-7689, Vol. 22, no 8, 2961-72 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2004. Vol. 22, no 8, 2961-72 p.
Identifiers
URN: urn:nbn:se:uu:diva-90684OAI: oai:DiVA.org:uu-90684DiVA: diva2:163129
Available from: 2003-09-05 Created: 2003-09-05Bibliographically approved
In thesis
1. Waves in space plasmas: Lower hybrid cavities and simple-pole distribution functions
Open this publication in new window or tab >>Waves in space plasmas: Lower hybrid cavities and simple-pole distribution functions
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Waves are a fundamental feature in many parts of physics, since they transport energy without transporting matter. This is the case also in space physics. Waves are responsible for energy transport both between different parts of space and between different particles in the space plasma. They are also useful for diagnostics of the space plasma itself. The present thesis considers two different parts of the large subject of space plasma waves: Lower hybrid cavities (LHCs) and simple-pole particle distribution functions.

The LHCs are localised density depletions that have been observed by several spacecraft. They have increased wave activity in the lower hybrid frequency range, and was previously found on altitudes up to 1750 km. New observations by the Viking and Cluster satellites show that they are common magnetospheric features, at least up to an altitude of 35,000 km. Theoretical results, assuming a cylindrically symmetric density depletion, show that even though the density depletion may decrease slowly with increasing radial distance, and thus be essentially infinite in extent, there is a maximum distance within which a trapped mode, with given wave number kz parallel to the geomagnetic field, may propagate. Furthermore, there is a local relation between the plasma density gradient and the lowest possible frequency that the trapped waves can have, for any monotonic density and given kz. The combined theoretical and observational results indicate that the length of the cavities is larger than the width by a factor of at least 200.

Simple-pole particle distribution functions are introduced because they can model high velocity tails of the particle distribution in a way that is not possible to do with Maxwellian distribution functions. These distributions also simplify the calculations. This gives new possibilities for the physical understanding, as well as the numerical calculations, of the dispersion relations of real space plasmas. The dispersion relations of plasmas described by simple-pole distributions are examined, both for unmagnetised and for magnetised plasmas. These examples show how particle populations with the same density and mean particle energy, but with somewhat different distribution functions, have different wave propagation properties that should be observable by existing spacecraft.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 61 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 869
Keyword
Space and plasma physics, space physics, plasma, waves, dispersion relations, lower hybrid cavities, Cluster, magnetosphere, Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-3527 (URN)91-554-5696-0 (ISBN)
Public defence
2003-09-26, 10132 (Häggsalen), Ångström Laboratory, Uppsala, 15:15
Opponent
Supervisors
Available from: 2003-09-05 Created: 2003-09-05Bibliographically approved

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