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Author:
Engwall, Erik (Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy)
Title:
Low-Energy Ion Escape from the Terrestrial Polar Regions
Department:
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy
Publication type:
Doctoral thesis, comprehensive summary (Other academic)
Language:
English
Place of publ.: Uppsala Publisher: Acta Universitatis Upsaliensis
Pages:
91
Series:
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214; 640
Year of publ.:
2009
URI:
urn:nbn:se:uu:diva-100650
Permanent link:
http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-100650
ISBN:
978-91-554-7512-3
Subject category:
Fusion, Plasma and Space Physics
SVEP category:
Geocosmophysics and plasma physics
Research subject:
Space and Plasma Physics
Keywords(en) :
space physics, ion outflow, polar wind, auroral upflows, atmospheric escape, magnetotail lobes, spacecraft wake, electric field measurements
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.

Public defence:
2009-05-20, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Degree:
degree of Doctor of Philosophy
Supervisor:
Eriksson, Anders I. , Dr. (Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division)
André, Mats, Professor (Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division)
Opponent:
Moore, Thomas, Professor (NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.)
Available from:
2009-04-28
Created:
2009-04-04
Last updated:
2009-04-30
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