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Survey of cold ionospheric outflows in the magnetotail
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
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2009 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, no 8, 3185-3201 p.Article in journal (Refereed) Published
Abstract [en]

Low-energy ions escape from the ionosphere and constitute a large part of the magnetospheric content, especially in the geomagnetic tail lobes. However, they are normally invisible to spacecraft measurements, since the potential of a sunlit spacecraft in a tenuous plasma in many cases exceeds the energy-per-charge of the ions, and little is therefore known about their outflow properties far from the Earth. Here we present an extensive statistical study of cold ion outflows (0-60 eV) in the geomagnetic tail at geocentric distances from 5 to 19 R-E using the Cluster spacecraft during the period from 2001 to 2005. Our results were obtained by a new method, relying on the detection of a wake behind the spacecraft. We show that the cold ions dominate in both flux and density in large regions of the magnetosphere. Most of the cold ions are found to escape from the Earth, which improves previous estimates of the global outflow. The local outflow in the magnetotail corresponds to a global outflow of the order of 10(26) ions s(-1). The size of the outflow depends on different solar and magnetic activity levels.

Place, publisher, year, edition, pages
2009. Vol. 27, no 8, 3185-3201 p.
Keyword [en]
Cluster spacecraft, ion outflow, low-energy ions, polar wind, lobal wind, electric field measurements, atmospheric loss, magnetotail lobe
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
URN: urn:nbn:se:uu:diva-100649DOI: 10.5194/angeo-27-3185-2009ISI: 000269440700021OAI: oai:DiVA.org:uu-100649DiVA: diva2:210740
Available from: 2009-04-04 Created: 2009-04-04 Last updated: 2014-01-21Bibliographically approved
In thesis
1. Low-Energy Ion Escape from the Terrestrial Polar Regions
Open this publication in new window or tab >>Low-Energy Ion Escape from the Terrestrial Polar Regions
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The contemporary terrestrial atmosphere loses matter at a rate of around 100,000 tons per year. A major fraction of the net mass loss is constituted by ions, mainly H+ and O+, which escape from the Earth’s ionosphere in the polar regions. Previously, the outflow has only been measured at low altitudes, but to understand what fraction actually escapes and does not return, the measurements should be conducted far from the Earth. However, at large geocentric distances the outflowing ions are difficult to detect with conventional ion instruments on spacecraft, since the spacecraft electrostatic potential normally exceeds the equivalent energy of the ions. This also means that little is known about the ion outflow properties and distribution in space far from the Earth.

In this thesis, we present a new method to measure the outflowing low-energy ions in those regions where they previously have been invisible. The method is based on the detection by electric field instruments of the large wake created behind a spacecraft in a flowing, low-energy plasma. Since ions with low energy will create a larger wake, the method is more sensitive to light ions, and our measured outflow is essentially the proton outflow.

Applying this new method on data from the Cluster spacecraft, we have been able to make an extensive statistical study of ion outflows from 5 to 19 Earth radii in the magnetotail lobes. We show that cold proton outflows dominate in these large regions of the magnetosphere in both flux and density. Our outflow values of low-energy protons are close to those measured at low altitudes, which confirms that the ionospheric outflows continue far back in the tail and contribute significantly to the magnetospheric content. We also conclude that most of the ions are escaping and not returning, which improves previous estimates of the global outflow. The total loss of protons due to high-latitude escape is found to be on the order of 1026 protons/s.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 91 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 640
Keyword
space physics, ion outflow, polar wind, auroral upflows, atmospheric escape, magnetotail lobes, spacecraft wake, electric field measurements
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-100650 (URN)978-91-554-7512-3 (ISBN)
Public defence
2009-05-20, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Available from: 2009-04-28 Created: 2009-04-04 Last updated: 2009-04-30Bibliographically approved

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Eriksson, Anders I.André, Mats

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