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The importance of waves in space plasmas: Examples from the auroral region and the magnetopause
Umeå University, Faculty of Science and Technology, Physics.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis discusses the reasons for space exploration and space science. Space plasma physics is identified as an essential building block to understand the space environment and it is argued that observation and analysis of space plasma waves is an important approach.

Space plasma waves are the main actors in many important processes. So-called broadband waves are found responsible for much of the ion heating in the auroral region. We investigate the wave properties of broadband waves and show that they can be described as a mixture of electrostatic wave modes. In small regions void of cold electrons the broadband activity is found to be ion acoustic waves and these regions are also identified as acceleration regions. The identification of the wave modes includes reconstructions of the wave distribution function. The reconstruction technique allow us to determine the wave vector spectrum, which cannot be measured directly. The method is applied to other wave events and it is compared in some detail with a similar method.

Space plasma wave are also sensitive tools for investigations of both the fine-structure and the dynamics of space plasmas. Studies of whistler mode waves observed in the boundary layer on the magnetospheric side of the magnetopause reveal that the plasma is organized in tube-like structures moving with the plasma drift velocity. The perpendicular dimension of these tubes is of the order of the electron inertial length. We present evidence that each tube is linked to a reconnection site and argue that the high density of tube-like structures indicates patchy reconnection.

Place, publisher, year, edition, pages
Umeå: Fysik , 2005. , 28 p.
Keyword [en]
Space and plasma physics, Plasma waves, magnetospheric physics, magnetopause, auroral region, wave distribution function, space exploration, reconnection, current tubes
Keyword [sv]
Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
Research subject
Space Physics
Identifiers
URN: urn:nbn:se:umu:diva-538ISBN: 91-7305-872-6 (print)OAI: oai:DiVA.org:umu-538DiVA: diva2:143758
Public defence
2005-06-03
Available from: 2005-05-13 Created: 2005-05-13Bibliographically approved
List of papers
1. Wave mode identification via wave distribution function analysis
Open this publication in new window or tab >>Wave mode identification via wave distribution function analysis
2001 In: Physics and Chemistry of the Earth, 26, 229–235, 2001., Vol. 26, 229-235 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4593 (URN)
Available from: 2005-05-13 Created: 2005-05-13Bibliographically approved
2. Investigating wave data from the FAST satellite by reconstructing the wave distribution function
Open this publication in new window or tab >>Investigating wave data from the FAST satellite by reconstructing the wave distribution function
2002 In: Journal of Geophysical Research, Vol. 107, doi:10.1029/2001/2001JA900154- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4594 (URN)
Available from: 2005-05-13 Created: 2005-05-13Bibliographically approved
3. Cluster observations and theoretical explanations of broadband waves in the auroral region
Open this publication in new window or tab >>Cluster observations and theoretical explanations of broadband waves in the auroral region
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2005 (English)In: Annales Geophysicae, Vol. 23, 3739-3752 p.Article in journal (Refereed) Published
Abstract [en]

 Broadband waves are common on auroral field lines. We use two different methods to study the polarization of the waves at 10 to 180 Hz observed by the Cluster spacecraft at altitudes of about 4 Earth radii in the nightside auroral region. Observations of electric and magnetic wave fields, together with electron and ion data, are used as input to the methods. We find that much of the wave emissions are consistent with linear waves in homogeneous plasma. Observed waves with a large electric field perpendicular to the geomagnetic field are more common (electrostatic ion cyclotron waves), while ion acoustic waves with a large parallel electric field appear in smaller regions without suprathermal (tens of eV) plasma. The regions void of suprathermal plasma are interpreted as parallel potential drops of a few hundred volts.

Place, publisher, year, edition, pages
Copernicus Publications, 2005
Identifiers
urn:nbn:se:umu:diva-4595 (URN)10.5194/angeo-23-3739-2005 (DOI)
Available from: 2005-05-13 Created: 2005-05-13 Last updated: 2012-05-04Bibliographically approved
4. Electron-scale sheets of whistlers close to the magnetopause
Open this publication in new window or tab >>Electron-scale sheets of whistlers close to the magnetopause
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2005 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 12, 3715-3725 p.Article in journal (Refereed) Published
Abstract [en]

Whistler emissions close to the magnetopause on the magnetospheric side are investigated using the four Cluster spacecraft. The waves are found to be generated in thin (electron-scale) sheets moving with the plasma drift velocity. A feature in the electron data coincides with the waves; hot magnetospheric electrons disappear for a few satellite spins. This produces or enhances a temperature anisotropy, which is found to be responsible for the generation of the whistler mode waves. The high energy electrons are thought to be lost through the magnetopause and we suggest that the field lines, on which the waves are generated, are directly connected to a reconnection diffusion region at the magnetopause.

Place, publisher, year, edition, pages
Göttingen: Copernicus gesellschaft, 2005
Keyword
magnetospheric physics, magnetopause, cusp and boundary layers, space plasma physics, magnetic reconnection, waves and instabilities
National Category
Astronomy, Astrophysics and Cosmology Geology Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:umu:diva-4596 (URN)10.5194/angeo-23-3715-2005 (DOI)000235008400013 ()
Available from: 2005-05-13 Created: 2005-05-13 Last updated: 2017-01-20Bibliographically approved
5. Electron-scale structures indicating patchy reconnection at the magnetopause?
Open this publication in new window or tab >>Electron-scale structures indicating patchy reconnection at the magnetopause?
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(English)Manuscript (preprint) (Other academic)
National Category
Meteorology and Atmospheric Sciences Astronomy, Astrophysics and Cosmology Geology
Identifiers
urn:nbn:se:umu:diva-4597 (URN)
Available from: 2005-05-13 Created: 2005-05-13 Last updated: 2017-01-20Bibliographically approved

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