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Energization and Acceleration of Dayside Polar Outflowing Oxygen
Umeå University, Faculty of Science and Technology, Space Science.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with energetic oxygen ions (i.e. single-charged atomic oxygen ions, O+) at altitudes higher than 5 Earth radii (RE) and at latitudes above 75 (toward 90) degrees invariant latitude (deg ILAT) in the dayside polar magnetosphere observed by Cluster. The instrument used in this study is CIS (Cluster Ion Spectrometry experiment) / CODIF (a time-of-flight ion COmposition and DIstribution Function analyser), which covers an energy range from »10 eV up to 38 keV. Cluster detected O+ with energies more than 1 keV (hereafter termed “keV O+”), indicating that energization and/or acceleration process(es) take place in the dayside high-altitude (inside magnetopause) and high-latitude region. These O+ are outflowing (precisely, upward-going along the geomagnetic field lines), and these outflowing keV O+ show a heated (or energized) signature in the velocity distribution as well.

First, outflowing O+ are observed at the poleward cusp and/or the mantle formed a partial shell-like configuration seen in the velocity distribution. Second, the latitudinal distribution of outflowing O+ (most of them have energies less than 1 keV statistically) observed below 7 RE is consistent with velocity filter effect by the polar convection, while the latitudinal distribution of outflowing keV O+ observed above 7 RE cannot be explained by velocity filter effect only, i.e. this indicates that additional energization and/or acceleration takes place at higher altitudes in the dayside polar region. Thirdly, a tendency to observe outflowing keV O+ for during different geomagnetic conditions is studied. The keV O+ above 9 RE is more often for K p¸5 rather than for K p•3. However the energy of O+ is not dependent on ASY /SYM indices.

Finally, the dependence on the solar wind conditions is also studied. The energization and/or acceleration of outflowing O+ is controlled by both solar wind moments (except solar wind electric field) and strong southward interplanetary magnetic field (IMF) at the time scale of tens of minutes at only higher altitudes. Further examination shows that solar wind dependence is different at three regions: one is the poleward cusp, another is the low-altitude polar cap, and finally the high-altitude polar cap, combining all the results. There is (a) new energization and/or acceleration process(es) at the high-altitude polar cap. On the other hand, flux enhancement of O+ observed above 5 RE is also controlled by solar wind moments (e.g. solar wind electric field) and strong southward IMF, however the ionospheric changes play a more important role on the flux enhancement of O+.

Place, publisher, year, edition, pages
Umeå: Fysik , 2005. , 56 p.
Series
IRF Scientific Report, ISSN 0284-1703 ; 287
Keyword [en]
Solar wind-magnetosphere interactions, Magnetosphere-ionosphere coupling, O+ energization/acceleration, O+ outflow
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:umu:diva-647ISBN: 91-7305-963-3 (print)OAI: oai:DiVA.org:umu-647DiVA: diva2:144126
Public defence
2005-11-11
Available from: 2005-11-28 Created: 2005-11-28Bibliographically approved
List of papers
1. Shell-like configuration in O+ ion velocity distribution at high altitudes in the dayside magnetosphere observed by Cluster/CIS
Open this publication in new window or tab >>Shell-like configuration in O+ ion velocity distribution at high altitudes in the dayside magnetosphere observed by Cluster/CIS
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2004 In: Annales Geophysicae, Vol. 22, 2473–2483- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4862 (URN)
Available from: 2005-11-28 Created: 2005-11-28Bibliographically approved
2. Statistics of high-altitude and high-latitude O+ ion outflows observed by Cluster/ CIS
Open this publication in new window or tab >>Statistics of high-altitude and high-latitude O+ ion outflows observed by Cluster/ CIS
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2005 In: Annales Geophysicae, Vol. 23, 1909–1916- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4863 (URN)
Available from: 2005-11-28 Created: 2005-11-28Bibliographically approved
3. Statistical study of relationships between dayside high-altitude and high-latitude O+ ion outflows, solar winds, and geomagnetic activity
Open this publication in new window or tab >>Statistical study of relationships between dayside high-altitude and high-latitude O+ ion outflows, solar winds, and geomagnetic activity
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2005 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 23, 1909-1916 p.Article in journal (Refereed) Published
Abstract [en]

The persistent outflows of O+ ions observed by the Cluster CIS/CODIF instrument were studied statistically in the high-altitude (from 3 up to 11 RE) and high-latitude (from 70 to ~90 deg invariant latitude, ILAT) polar region. The principal results are: (1) Outflowing O+ ions with more than 1keV are observed above 10 RE geocentric distance and above 85deg ILAT location; (2) at 6-8 RE geocentric distance, the latitudinal distribution of O+ ion outflow is consistent with velocity filter dispersion from a source equatorward and below the spacecraft (e.g. the cusp/cleft); (3) however, at 8-12 RE geocentric distance the distribution of O+ outflows cannot be explained by velocity filter only. The results suggest that additional energization or acceleration processes for outflowing O+ ions occur at high altitudes and high latitudes in the dayside polar region.

Keyword
Magnetospheric physics, Magnetospheric configuration and dynamics, Solar wind-magnetosphere interactions
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-4864 (URN)10.5194/angeo-23-1909-2005 (DOI)
Available from: 2005-11-28 Created: 2005-11-28 Last updated: 2012-05-04Bibliographically approved
4. structure of high altitude O+ energization and outflows: a case study
Open this publication in new window or tab >>structure of high altitude O+ energization and outflows: a case study
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2004 In: Annales Geophysicae, Vol. 22, 2497–2506- p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4865 (URN)
Available from: 2005-11-28 Created: 2005-11-28Bibliographically approved

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