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Isolated magnetic field structures in Mercury's magnetosheath as possible analogues for terrestrial magnetosheath plasmoids and jets
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0003-1270-1616
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0002-9164-0761
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.ORCID iD: 0000-0002-0349-0645
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2016 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 129, 61-73 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated MESSENGER magnetic field data from the Mercury magnetosheath and near solar wind, to identify isolated magnetic field structures (defined as clear, isolated changes in the field magnitude). Their properties are studied in order to determine if they may be considered as analogues to plasmoids and jets known to exist in Earth's magnetosheath. Both isolated decreases of the magnetic field absolute value ('negative magnetic field structures') and increases ('positive structures') are found in the magnetosheath, whereas only negative structures are found in the solar wind. The similar properties of the solar wind and magnetosheath negative magnetic field structures suggests that they are analogous to diamagnetic plasmoids found in Earth's magnetosheath and near solar wind. The latter have earlier been identified with solar wind magnetic holes. Positive magnetic field structures are only found in the magnetosheath, concentrated to a region relatively close to the magnetopause. Their proximity to the magnetopause, their scale sizes, and the association of a majority of the structures with bipolar magnetic field signatures identify them as flux transfer events (which generally are associated with a decrease of plasma density in the magnetosheath). The positive magnetic field structures are therefore not likely to be analogous to terrestrial paramagnetic plasmoids but possibly to a sub-population of magnetosheath jets. At Earth, a majority of magnetosheath jets are associated with the quasi-parallel bow shock. We discuss some consequences of the findings of the present investigation pertaining to the different nature of the quasi-parallel bow shock at Mercury and Earth.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 129, 61-73 p.
Keyword [en]
Mercury, Magnetosheath, Bow shock, MESSENGER, Plasmoids, Magnetosheath jets
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-192709DOI: 10.1016/j.pss.2016.06.002ISI: 000381323800006Scopus ID: 2-s2.0-85006710378OAI: oai:DiVA.org:kth-192709DiVA: diva2:974404
Note

QC 20160926

Available from: 2016-09-26 Created: 2016-09-20 Last updated: 2017-11-21Bibliographically approved
In thesis
1. Structures and processes in the Mercury magnetosphere
Open this publication in new window or tab >>Structures and processes in the Mercury magnetosphere
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The mechanisms involved in the transfer of mass and energy from the solar wind to any planetary magnetosphere is considered an important topic in space physics. With the use of the Mercury spacecraft MESSENGER's data, it has been possible to study these processes in an environment different, yet similar, to Earth's. These data have resulted in new knowledge advancing not only the extraterrestrial space plasma research, but also the general space physics field.

 

This thesis aims to investigate mechanisms for the transfer of mass and energy into Mercury’s magnetosphere, and magnetospheric regions affected by, and processes directly driven by, these. The work includes the Kelvin-Helmholtz instability (KHI) at the magnetopause, which is one of the main drivers for mass and energy transfer on Earth, the low-latitude boundary layer (LLBL), which is in direct connection to the magnetopause and proposed to be affected by the KHI, magnetospheric ultra-low frequency (ULF) waves driven by the KHI, and isolated magnetic field structures in the magnetosheath as possible analogues to the Earth magnetosheath plasmoids and jets.

 

Kelvin-Helmholtz waves (KHW) and the LLBL are identified and characterized. The KHWs are observed almost exclusively on the duskside magnetopause, something that has not been observed on Earth. In contrast, the LLBL shows an opposite asymmetry. Results suggest that the KHI and LLBL are connected, possibly by the LLBL creating the asymmetry observed for the KHWs.

 

Isolated changes of the total magnetic field strength in the magnetosheath are identified. The similar properties of the solar wind and magnetosheath negative magnetic field structures suggest that they are analogues to diamagnetic plasmoids found on Earth. No clear analogues to paramagnetic plasmoids are found.  

 

Distinct magnetospheric ULF wave signatures are detected frequently in close connection to KHWs. Results from the polarization analysis on the dayside ULF waves indicate that the majority of these are most probably driven by the KHI. In general, likely KHI driven ULF waves are observed frequently in the Hermean magnetosphere. 

Although similar in many aspects, Mercury and Earth show fundamental differences in processes and structures, making Mercury a highly interesting planet to study to increase our knowledge of Earth-like planets.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 53 p.
Series
TRITA-EE, ISSN 1653-5146 ; 2017:029
Keyword
Mercury, MESSENGER, magnetosphere, processes, structures
National Category
Fusion, Plasma and Space Physics
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-207173 (URN)978-91-7729-349-1 (ISBN)
Public defence
2017-06-15, Kollegiesalen, Brinellvägen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish National Space Board, 122/11
Note

QC 20170519

Available from: 2017-05-19 Created: 2017-05-18 Last updated: 2017-05-19Bibliographically approved

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