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Cluster observations of the electric potential at the Earth's quasi-parallel bow shock
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
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2005 In: Annales Geophysicae, ISSN 0992-7689Article in journal (Refereed) Submitted
Place, publisher, year, edition, pages
URN: urn:nbn:se:uu:diva-93712OAI: oai:DiVA.org:uu-93712DiVA: diva2:167278
Available from: 2005-11-24 Created: 2005-11-24Bibliographically approved
In thesis
1. Dissipation at the Earth's Quasi-Parallel Bow Shock
Open this publication in new window or tab >>Dissipation at the Earth's Quasi-Parallel Bow Shock
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Earth's bow shock is a boundary where the solar wind becomes decelerated from supersonic to subsonic speed before being deflected around the Earth. This thesis presents measurements by the Cluster spacecraft upstream and at the Earth's quasi-parallel bow shock where the angle between the upstream magnetic field and the bow shock normal is less than 45 degrees. An intrinsic feature of quasi-parallel shocks is the ability of ions, that are reflected off the shock in a specular manner, to propagate far upstream and to interact with the incident solar wind. This leads to the generation of a variety of plasma waves, e.g., Ultra-Low Frequency (ULF) waves, which in their turn interact with the different ion populations. Some of the ULF waves are thought to steepen into so-called Short Large-Amplitude Magnetic Structures (SLAMS).

This thesis studies the impact of SLAMS on the incident solar wind. SLAMS are thought to play an important role in terms of 1) returning shock-reflected ions back to the shock where they can eventually contribute to downstream thermalisation and 2) local pre-dissipation of the solar wind.

The first electric field measurements of SLAMS showed a strong electric field rotation over SLAMS in association with the rotation of the magnetic field. This often leads to a local change from quasi-parallel to quasi-perpendicular conditions. In addition, short-scale electric field features were observed, e.g., spiky electric field structures associated with the leading edge of SLAMS and solitary electric field structures on Debye length scales, which are suggested to represent ion phase space holes.

Using the abilitiy of the four Cluster satellites to obtain propagation vectors of SLAMS and the high-resolution electric field measurements, the electric potential over SLAMS was studied. These structures are associated with a significant potential on the order of a few hundred to thousand Volt. Comparing these findings with data from the ion spectrometer, it was found that the bulk flow is locally significantly decelerated and moderately deflected and heated. In addition, SLAMS reflect incident ions on both the leading and trailing edge. The flux of so-called gyrating ions show a clear maximum in association with SLAMS. This indicates that SLAMS indeed play an important role for pre-dissipation of the solar wind upstream of the shock.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. vii + 49 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 116
Space and plasma physics, collisionless shocks, wave-particle interactions, nonlinear phenomena, cross-shock potential, Cluster spacecraft, Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
urn:nbn:se:uu:diva-6123 (URN)91-554-6391-6 (ISBN)
Public defence
2005-12-16, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Available from: 2005-11-24 Created: 2005-11-24Bibliographically approved

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