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The Kelvin-Helmholtz instability at Mercury: An assessment
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
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2010 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 58, no 11, 1434-1441 p.Article in journal (Refereed) Published
Abstract [en]

The Kelvin-Helmholtz instability is believed to be an important means for the transfer of energy, plasma, and momentum from the solar wind into planetary magnetospheres, with in situ measurements reported from Earth, Saturn, and Venus. During the first MESSENGER flyby of Mercury, three periodic rotations were observed in the magnetic field data possibly related to a Kelvin-Helmholtz wave on the dusk side magnetopause. We present an analysis of the event, along with comparisons to previous Kelvin-Helmholtz observations and an investigation of what influence finite ion gyro radius effects, believed to be of importance in the Hermean magnetosphere, may have on the instability. The wave signature does not correspond to that of typical Kelvin-Helmholtz events, and the magnetopause direction does not show any signs of major deviation from the unperturbed case. There is thus no indication of any high amplitude surface waves. On the other hand, the wave period corresponds to that expected for a Kelvin-Helmholtz wave, and as the dusk side is shown to be more stable than the dawn side, we judge the observed waves not to be fully developed Kelvin-Helmholtz waves, but they may be an initial perturbation that could cause Kelvin-Helmholtz waves further down the tail. (C) 2010 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
2010. Vol. 58, no 11, 1434-1441 p.
Keyword [en]
Mercury, Kelvin-Helmholtz, Finite Larmor radius, Magnetopause
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-26806DOI: 10.1016/j.pss.2010.06.008ISI: 000281368500002Scopus ID: 2-s2.0-77955550841OAI: oai:DiVA.org:kth-26806DiVA: diva2:375822
Note
QC 20101209Available from: 2010-12-09 Created: 2010-11-29 Last updated: 2017-12-11Bibliographically approved
In thesis
1. New Perspectives on Solar Wind-Magnetosphere Coupling
Open this publication in new window or tab >>New Perspectives on Solar Wind-Magnetosphere Coupling
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The streaming plasma in the solar wind is a never ending source of energy, plasma, and momentum for planetary magnetospheres, and it continuously drives large-scale plasma convection systems in our magnetosphere and over our polar ionosphere. This coupling between the solar wind and the magnetosphere is primarily explained by two different processes: magnetic reconnection at high latitudes, which interconnects the interplanetary magnetic field (IMF) with the planetary dipole field, and low-latitude dynamos such as viscous interaction, where the streaming plasma in the solar wind may trigger waves and instabilities at the flanks of the magnetosphere, and thereby allow solar wind plasma to enter into the system.This work aims to further determine the nature and properties of these driving dynamos, both by statistical studies of their relative importance for ionospheric convection at Earth, and by assessment and analysis of the Kelvin-Helmholtz instability at Mercury, utilizing data from the MESSENGER spacecraft's first and third flyby of the planet.It is shown that the presence of the low-latitude dynamos is primarily dependent on the IMF direction: the driving is close to non-existent when the IMF is southward, but increases to the order of a third of the total ionospheric driving when the IMF turns northward (here, the magnitude of the driving is also shown to be dependent on the viscous parameters in the solar wind). The work also discusses the saturation of the reconnection generated potential, and shows that the terrestrial response follows a non-linear behavior for strong solar wind driving both when the IMF is southward and northward.Comparative studies of different magnetospheres provide an excellent path for increasing our understanding of space-related phenomena. Here, study of the Kelvin-Helmholtz instability at Mercury allows us to investigate how the different parameters of the system affect the mass, energy, and momentum transfer at the flanks of the magnetosphere. The large ion gyro radius expected is shown to develop a dawn-dusk asymmetry in the growth rates, with the dawn side as the more unstable of the two. This effect should be particularly visible when the planet is close to perihelion. Mercury's smaller scale size combined with the relatively high spacecraft velocity is also shown to provide excellent opportunities for studying the spatial structure of the waves, and a vortex reconstruction that can explain all the large-scale variations in the Kelvin-Helmholtz waves observed during MESSENGER's third Mercury flyby is presented.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. viii, 77 p.
Series
Trita-EE, ISSN 1653-5146 ; 2011:027
Keyword
magnetosphere, ionosphere, mercury, kelvin-helmholtz
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-32070 (URN)978-91-7415-939-4 (ISBN)
Public defence
2011-04-15, F3, Lindstedtsvägen 26, Stockholm, 13:15 (English)
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Note
QC 20110405Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2011-04-13Bibliographically approved

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