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Statistical analysis of the sources of the cross-polar potential for southward IMF, based on particle precipitation characteristics
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
2008 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, 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.

Place, publisher, year, edition, pages
2008. Vol. 35, no 8, L08103- p.
Keyword [en]
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: urn:nbn:se:kth:diva-10246DOI: 10.1029/2008GL033383ISI: 000255458700005Scopus ID: 2-s2.0-48249140716OAI: oai:DiVA.org:kth-10246DiVA: diva2:212466
Note
QC 20101029Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically approved
In thesis
1. On the Properties of Ionospheric Convection
Open this publication in new window or tab >>On the Properties of Ionospheric Convection
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The solar wind interaction with the magnetosphere-ionosphere system continuously drives plasma convection in the polar regions of the ionosphere. The flow velocity and the shape of the convection pattern are closely dependent on the interplanetary conditions, in particular the direction of the interplanetary magnetic field (IMF). The main driver of the system is considered to be magnetic reconnection between the IMF and the terrestrial field, a process that is most efficient during southward IMF when the magnetic fields at the dayside magnetopause are anti-parallell, and less efficient but still present when the IMF is northward. Additional driving may be caused by waves at the magnetopause flanks, where viscous effects can lead to an energy, momentum and plasma exchange across the boundary.

In this work, we make use of the characteristics of the ionospheric convection and particle precipitation to investigate the nature of the driving dynamos, and large statistical data sets for steady solar wind conditions are used to derive the general behavior of the driving processes and their dependence on interplanetary conditions. The results show that the primary dynamo responsible for the convection in the boundary layer is closely dependent on the sign of the IMF Bz component, the average potential over the boundary layer region increases from <1 kV for steady southward IMF up to the order of 10kV for strictly northward conditions with reconnection poleward of the cusps, whereas the magnitude of magnetic field only has a minor influence at most. This could for example indicate that the magnetopause is more unstable to Kelvin-Helmholtz waves for parallel rather than anti-parallel magnetic fields, or that magnetic reconnection on the dayside suppresses other processes.

It is well known that the ionospheric potential drop saturates during strong driving conditions and southward IMF. The results presented here also show that the same phenomenon occurs when the IMF is northward. This gives additional information on the physics governing the solar wind-magnetosphere-ionosphere interaction, and may impose new restrictions on the theories explaining the saturation.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. x, 41 p.
Series
Trita-EE, ISSN 1653-5146 ; 2009:020
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-10249 (URN)978-91-7415-296-8 (ISBN)
Presentation
2009-05-11, Seminarierummet, Alfvénlaboratoriet, Teknikringen 31, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2009-05-06 Created: 2009-04-22 Last updated: 2010-10-29Bibliographically approved
2. 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)
Opponent
Supervisors
Note
QC 20110405Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2011-04-13Bibliographically approved

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