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New Perspectives on Solar Wind-Magnetosphere Coupling
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
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 [en]
magnetosphere, ionosphere, mercury, kelvin-helmholtz
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-32070ISBN: 978-91-7415-939-4OAI: oai:DiVA.org:kth-32070DiVA: diva2:408523
Public defence
2011-04-15, F3, Lindstedtsvägen 26, Stockholm, 13:15 (English)
Opponent
Supervisors
Note
QC 20110405Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2011-04-13Bibliographically approved
List of papers
1. Statistical analysis of the sources of the cross-polar potential for southward IMF, based on particle precipitation characteristics
Open this publication in new window or tab >>Statistical analysis of the sources of the cross-polar potential for southward IMF, based on particle precipitation characteristics
2008 (English)In: Geophysical Research Letters, ISSN 0094-8276, Vol. 35, no 8, L08103- p.Article in journal (Refereed) Published
Abstract [en]

There are several proposed physical processes which may contribute to the cross-polar potential and thus drive ionospheric convection around the polar caps. It is generally believed that magnetic reconnection is the dominant process, however dynamos such as viscous interaction and impulsive penetration are other possible contributors. A comprehensive statistical study has been conducted using data from the DMSP F13 satellite for passages along the northern hemisphere dawn-dusk meridian, with focus on typical two-cell convection patterns during times of steady southward IMF conditions. The results show that the low-latitude dynamo (viscous interaction or reconnection in the LLBL) on average accounts for only 1–2 kV of the total potential drop, values lower than those previously predicted. At rare occasions this dynamo can be a significant source of energy, however, contributing to more than 20 kV of the cross-polar potential.

Keyword
Astrophysics, Atmospherics, Electric generators, Energy management, Flow interactions, Geophysics, Hypersonic flow, Interactive devices, Magnetic fields, Magnetism, Precipitation (chemical), Statistical methods, Theorem proving
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-10246 (URN)10.1029/2008GL033383 (DOI)000255458700005 ()2-s2.0-48249140716 (ScopusID)
Note
QC 20101029Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2011-04-05Bibliographically approved
2. The Reverse Convection Potential:  A Statistical Study of the General Properties of Lobe Reconnection and Saturation Effects During Northward IMF
Open this publication in new window or tab >>The Reverse Convection Potential:  A Statistical Study of the General Properties of Lobe Reconnection and Saturation Effects During Northward IMF
2009 (English)In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 114, no 6, A06205- p.Article in journal (Refereed) Published
Abstract [en]

The saturation tendency of the cross-polar potential for southward interplanetary magnetic fields has been the subject of numerous studies, however, the behavior of the reverse convection potential when the IMF is northward remains less clear. In this study, we present a thorough statistical analysis of the 4-cell convection pattern associated with northward IMF and lobe reconnection, based on a large set of DMSP F13 satellite data. Results show a behavior much similar to the southward IMF case, with a clear saturation tendency of the reverse convection potential for strong solar wind electric fields both seen in the data and validated in the statistical analysis. The saturated potential level reaches a limit of about 60 kV, on the order of a fourth of the saturated potential seen for dayside reconnection during southward IMF.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-10247 (URN)10.1029/2008JA013838 (DOI)000267003700003 ()2-s2.0-70349439089 (ScopusID)
Note
QC 20101028. Uppdaterad från Accepted till Published (20101028).Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2011-04-05Bibliographically approved
3. Properties of the Boundary Layer Potential for Northward Interplanetary Magnetic Field
Open this publication in new window or tab >>Properties of the Boundary Layer Potential for Northward Interplanetary Magnetic Field
2009 (English)In: Geophysical Research Letters, ISSN 0094-8276, Vol. 36, no 11, L11104- p.Article in journal (Refereed) Published
Abstract [en]

We present a method for estimating the portion of the ionospheric high-latitude potential that maps to the magnetospheric boundary layer during steady northward IMF and global ionospheric 4-cell convection patterns associated with lobe reconnection, together with the results of a statistical study based on DMSP F13 data from 1996-2004. In comparison with a previous study for steady southward IMF by Sundberg et al. [2008], the results show significantly larger boundary layer potentials, with a mean value of 10 kV for the 271 events studied, corresponding to roughly 30-35% of the potential generated by the solar wind interaction. In a statistical analysis, the boundary layer potential is also shown to depend significantly on viscous parameters such as the solar wind velocity, density and pressure.

 

Keyword
Convection patterns, Interplanetary magnetic fields, Magnetospheric boundary layers, Mean values, Northward IMF, Solar wind interactions, Solar wind velocity, Statistical analysis, Statistical study
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-10248 (URN)10.1029/2009GL038625 (DOI)000267000000008 ()2-s2.0-68949107317 (ScopusID)
Note
QC 20101028. Uppdaterad från Submitted till Published (20101028).Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2011-04-05Bibliographically approved
4. The Kelvin-Helmholtz instability at Mercury: An assessment
Open this publication in new window or tab >>The Kelvin-Helmholtz instability at Mercury: An assessment
Show others...
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.

Keyword
Mercury, Kelvin-Helmholtz, Finite Larmor radius, Magnetopause
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:kth:diva-26806 (URN)10.1016/j.pss.2010.06.008 (DOI)000281368500002 ()2-s2.0-77955550841 (ScopusID)
Note
QC 20101209Available from: 2010-12-09 Created: 2010-11-29 Last updated: 2011-04-05Bibliographically approved
5. Reconstruction of propagating Kelvin-Helmholtz vortices at Mercury's magnetopause
Open this publication in new window or tab >>Reconstruction of propagating Kelvin-Helmholtz vortices at Mercury's magnetopause
Show others...
2011 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 59, no 15, 2051-2057 p.Article in journal (Refereed) Published
Abstract [en]

A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin-Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.

Keyword
Mercury, Kelvin-Helmholtz, Magnetopause, MESSENGER
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-32067 (URN)10.1016/j.pss.2011.05.008 (DOI)000298722800021 ()2-s2.0-82455187989 (ScopusID)
Note
QC 20120206Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2012-02-06Bibliographically approved

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