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Low-Energy Ion Escape from the Terrestrial Polar Regions
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- Engwall, Erik, 1977- (author)
- Uppsala universitet,Institutionen för fysik och astronomi
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- Eriksson, Anders I., Dr. (thesis advisor)
- Uppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen
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- André, Mats, Professor (thesis advisor)
- Uppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen
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- ISBN 9789155475123
- Uppsala : Acta Universitatis Upsaliensis, 2009
- English 91 s.
- Series: Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 ; 640
- Doctoral thesis (other academic/artistic)
Abstract
Subject headings
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- 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.
Subject headings
- NATURVETENSKAP -- Fysik -- Fusion, plasma och rymdfysik (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Fusion, Plasma and Space Physics (hsv//eng)
Keyword
- space physics
- ion outflow
- polar wind
- auroral upflows
- atmospheric escape
- magnetotail lobes
- spacecraft wake
- electric field measurements
- Geocosmophysics and plasma physics
- Geokosmofysik och plasmafysik
- Space and Plasma Physics
- rymd- och plasmafysik
Publication and Content Type
- vet (subject category)
- dok (subject category)
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