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Earth’s ionospheric outflow dominated by hidden cold plasma
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: Nature Geoscience, ISSN 1752-0894, Vol. 2, no 1, 24-27 p.Article in journal (Refereed) Published
Abstract [en]

The Earth constantly loses matter, mostly in the form of H+and O+ ions, through various outflow processes from the upper atmosphere and ionosphere. Most of these ions are cold (below 1 eV in thermal energy), but can still escape and travel farther out along the magnetic field lines into the magnetospheric tail lobes. The outflow has previously beenmeasured close to the Earth. To understand what fraction does not return but instead escapes, the measurements should be conducted at larger geocentric distances. However, at high altitudes the cold ions are normally invisible to spacecraft measurements, because the potential of a sunlit spacecraft exceeds the equivalent energy of the ions. Here we show that cold ions dominate in both flux and density in the distant magnetotail lobes, using a new measurement technique on the Cluster spacecraft. The total loss of cold hydrogen ions from the planet is inferred to be of the order of 1026 s−1, which is larger than the previously observed more energetic outflow. Quantification and insight of the loss processes of the Earth’s atmosphere and ionosphere are also important for understanding the evolution of atmospheres on other celestial bodies.

Place, publisher, year, edition, pages
Nature Publishing Group , 2009. Vol. 2, no 1, 24-27 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-100647DOI: 10.1038/NGEO387ISI: 000262638500015OAI: oai:DiVA.org:uu-100647DiVA: diva2:210735
Available from: 2009-04-04 Created: 2009-04-04 Last updated: 2010-12-14Bibliographically 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)
Opponent
Supervisors
Available from: 2009-04-28 Created: 2009-04-04 Last updated: 2009-04-30Bibliographically approved

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