Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Cluster Observations and Theoretical Explanations of Broadband Waves in the Auroral Region
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Broadband extremely low-frequency wave emissions below the ion plasma frequency have been observed by a number of spacecraft and rockets on auroral field lines. The importance of these broadband emissions for transverse ion heating and electron acceleration in the auroral regions is now reasonably well established. However, the exact mechanism(s) for mediating this energy transfer and the wave mode(s) involved are not well known. In this thesis we focus on the identification of broadband waves by different methods.

Two wave analysis methods, involving different approximations and assumptions, give consistent results concerning the wave mode identification. We find that much of the broadband emissions can be identified as a mixture of ion acoustic, electrostatic ion cyclotron and, ion Bernstein waves, which all can be described as different parts of the same dispersion surface in the linear theory of waves in homogeneous plasma.

A new result is that ion acoustic waves occur on auroral magnetic field lines. These are found in relatively small regions interpreted as acceleration regions without cold (tens of eV) electrons.

From interferometry we also determine the phase velocity and k vector for parallel and oblique ion acoustic waves. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength is around the proton gyro radius and always larger than the Debye length which is consistent with ion acoustic waves.

We have observed quasi-static parallel electric fields associated with the ion acoustic waves in regions with large-scale currents. Waves, in particular ion acoustic waves, can create an anomalous resistivity due to wave-particle interaction when electrons are retarded or trapped by the electric wave-field. To maintain the large-scale current, a parallel electric field is set up, which then can accelerate a second electron population to high velocities.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2005. , p. 42
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 55
Keywords [en]
Space and plasma physics, ion acoustic waves, auroral region, anomalous resistivity, Cluster
Keywords [sv]
Rymd- och plasmafysik
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-5809ISBN: 91-554-6258-8 (print)OAI: oai:DiVA.org:uu-5809DiVA, id: diva2:166467
Public defence
2005-06-01, Polhem, Ångströmslaboratoriet, Lägerhyddsv. 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2005-05-11 Created: 2005-05-11Bibliographically approved
List of papers
1. Identification of Broadband Waves Above the Auroral Acceleration Region: CLUSTER Observations
Open this publication in new window or tab >>Identification of Broadband Waves Above the Auroral Acceleration Region: CLUSTER Observations
Show others...
2004 In: Annales Geophysicae, ISSN 0992-7689, Vol. 22, no 12, p. 14-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-93091 (URN)
Available from: 2005-05-11 Created: 2005-05-11 Last updated: 2014-11-12Bibliographically approved
2. Cluster observations and theoretical identification of broadband waves in the auroral region
Open this publication in new window or tab >>Cluster observations and theoretical identification of broadband waves in the auroral region
Show others...
2005 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, no 12, p. 3739-3752Article 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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-93092 (URN)10.5194/angeo-23-3739-2005 (DOI)000235008400015 ()
Available from: 2005-05-11 Created: 2005-05-11 Last updated: 2017-12-14Bibliographically approved
3. Interferometric Identification of Ion Acoustic Broadband Waves in the Auroral Region: CLUSTER Observations
Open this publication in new window or tab >>Interferometric Identification of Ion Acoustic Broadband Waves in the Auroral Region: CLUSTER Observations
Show others...
2005 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 32, no 21Article in journal (Refereed) Published
Abstract [en]

[1] We determine the phase velocity and k vector for parallel and oblique broadband extremely low frequency, ELF, waves on nightside auroral magnetic field lines at altitudes around 4.6 RE. We use internal burst mode data from the EFW electric field and wave instrument onboard the Cluster spacecraft to retrieve phase differences between the four probes of the instrument. The retrieved characteristic phase velocity is of the order of the ion acoustic speed and larger than the thermal velocity of the protons. The typical wavelength obtained from interferometry is around the proton gyro radius and always larger than the Debye length. We find that in regions with essentially no suprathermal electrons above a few tens of eV the observed broadband waves above the proton gyro frequency are consistent with upgoing ion acoustic and oblique ion acoustic waves.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-93093 (URN)10.1029/2005GL022640 (DOI)
Available from: 2005-05-11 Created: 2005-05-11 Last updated: 2017-12-14Bibliographically approved
4. Direct Observations of Electric Fields and Particle Acceleration Caused by Anomalous Wave-Particle Resistivity in Space Plasmas
Open this publication in new window or tab >>Direct Observations of Electric Fields and Particle Acceleration Caused by Anomalous Wave-Particle Resistivity in Space Plasmas
Show others...
Manuscript (Other academic)
Identifiers
urn:nbn:se:uu:diva-93094 (URN)
Available from: 2005-05-11 Created: 2005-05-11 Last updated: 2010-01-13Bibliographically approved

Open Access in DiVA

fulltext(537 kB)1206 downloads
File information
File name FULLTEXT01.pdfFile size 537 kBChecksum MD5
2911728e10c0657cca45079e91075aa958fdb1cbc64a03c8d2338cc8b876f12e3b337fad
Type fulltextMimetype application/pdf
cover(170 kB)49 downloads
File information
File name COVER01.pdfFile size 170 kBChecksum MD5
b17457d698994490f9d93557f2d63efec7fd81e6f2b41acec3554d06aefbb0daaf3d948a
Type coverMimetype application/pdf
Buy this publication >>

By organisation
Department of Astronomy and Space Physics
Fusion, Plasma and Space Physics

Search outside of DiVA

GoogleGoogle Scholar
Total: 1206 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 2141 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf