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3D Magnetic Nulls and Regions of Strong Current in the Earth's Magnetosphere
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, Department of Physics and Astronomy.
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Plasma, a gas of charged particles exhibiting collective behaviour, can be found everywhere in our vast Universe. The characteristics of plasma in very distant parts of the Universe can be similar to characteristics in our solar system and near-Earth space. We can therefore gain an understanding of what happens in astrophysical plasmas by studying processes occurring in near Earth space, an environment much easier to reach.

Large volumes in space are filled with plasma and when different plasmas interact distinct boundaries are often created. Many important physical processes, for example particle acceleration, occur at these boundaries. Thus, it is very important to study and understand such boundaries. In Paper I we study magnetic nulls, regions of vanishing magnetic fields, that form inside boundaries separating plasmas with different magnetic field orientations. For the first time, a statistical study of magnetic nulls in the Earth’s nightside magnetosphere has been done by using simultaneous measurements from all four Cluster spacecraft. We find that magnetic nulls occur both in the magnetopause and the magnetotail. In addition, we introduce a method to determine the reliability of the type identification of the observed nulls. In the manuscript of Paper II we study a different boundary, the shocked solar wind plasma in the magnetosheath, using the new Magnetospheric Multiscale mission. We show that a region of strong current in the form of a current sheet is forming inside the turbulent magnetosheath behind a quasi-parallel shock. The strong current sheet can be related to the jets with extreme dynamic pressure, several times that of the undisturbed solar wind dynamic pressure. The current sheet is also associated with electron acceleration parallel to the background magnetic field. In addition, the current sheet satisfies the Walén relation suggesting that plasmas on both sides of the current region are magnetically connected. We speculate on the formation mechanisms of the current sheet and the physical processes inside and around the current sheet.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 32 p.
Keyword [en]
Magnetic Nulls, Particle Acceleration, Current sheets, Magnetic reconnection, Magnetosphere
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
URN: urn:nbn:se:uu:diva-292742OAI: oai:DiVA.org:uu-292742DiVA: diva2:926581
Presentation
2016-05-27, Polhelmsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 2013-4309
Available from: 2016-05-16 Created: 2016-05-09 Last updated: 2016-05-16Bibliographically approved
List of papers
1. Statistics and accuracy of magnetic null identification in multispacecraft data
Open this publication in new window or tab >>Statistics and accuracy of magnetic null identification in multispacecraft data
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2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, 6883-6889 p.Article in journal (Refereed) Published
Abstract [en]

Complex magnetic topologies are ubiquitous in astrophysical plasmas. Analyzing magnetic nulls, regions of vanishing magnetic field, is one way to characterize 3-D magnetic topologies. Magnetic nulls are believed to be important in 3-D reconnection and turbulence. In the vicinity of a null, plasma particles become unmagnetized and can be accelerated to high energies by electric fields. We present the first statistical study of the occurrence of magnetic nulls and their types in the Earth's nightside magnetosphere. We are able to identify the nulls both in the tail and in the magnetopause current sheets. On average, we find one null for every few current sheet crossings. We show that the type identification of magnetic nulls may be sensitive to local fluctuations in the magnetic field. We develop and demonstrate a method to estimate the reliability of the magnetic null type identification.

National Category
Geophysics Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-267334 (URN)10.1002/2015GL064959 (DOI)000363411200002 ()
Funder
Swedish Research Council, 2013-4309
Available from: 2015-11-24 Created: 2015-11-20 Last updated: 2017-12-01Bibliographically approved
2. Kinetic Study of Thin Current Sheet in Magnetosheath Jet
Open this publication in new window or tab >>Kinetic Study of Thin Current Sheet in Magnetosheath Jet
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(English)Manuscript (preprint) (Other academic)
Keyword
Current sheet, Particle acceleration, Magnetosheath
National Category
Fusion, Plasma and Space Physics
Research subject
Physics with specialization in Space and Plasma Physics
Identifiers
urn:nbn:se:uu:diva-292738 (URN)
Funder
Swedish Research Council, 2013-4309
Available from: 2016-05-09 Created: 2016-05-09 Last updated: 2016-05-16

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Eriksson, Elin

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