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On the Properties of Ionospheric Convection
KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
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: urn:nbn:se:kth:diva-10249ISBN: 978-91-7415-296-8 (print)OAI: oai:DiVA.org:kth-10249DiVA: diva2:212488
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
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, 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.

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 (Scopus ID)
Note
QC 20101029Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically 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, E-ISSN 2156-2202, 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 (Scopus ID)
Note
QC 20101028. Uppdaterad från Accepted till Published (20101028).Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically 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, E-ISSN 1944-8007, 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 (Scopus ID)
Note
QC 20101028. Uppdaterad från Submitted till Published (20101028).Available from: 2009-04-22 Created: 2009-04-22 Last updated: 2017-12-13Bibliographically approved

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