| dc.date.accessioned |
2017-05-29T06:43:17Z |
und |
| dc.date.accessioned |
2017-10-24T12:04:20Z |
|
| dc.date.available |
2017-05-29T06:43:17Z |
und |
| dc.date.available |
2017-10-24T12:04:20Z |
|
| dc.date.issued |
2017-05-29T06:43:17Z |
|
| dc.identifier.uri |
http://radr.hulib.helsinki.fi/handle/10138.1/6032 |
und |
| dc.identifier.uri |
http://hdl.handle.net/10138.1/6032 |
|
| dc.title |
Mirror mode waves in coronal mass ejection-driven sheath regions |
en |
| ethesis.discipline |
Theoretical Physics |
en |
| ethesis.discipline |
Teoreettinen fysiikka |
fi |
| ethesis.discipline |
Teoretisk fysik |
sv |
| ethesis.discipline.URI |
http://data.hulib.helsinki.fi/id/C29de80f-21cd-424a-b706-b564d642b058 |
|
| ethesis.department.URI |
http://data.hulib.helsinki.fi/id/3acb09b1-e6a2-4faa-b677-1a1b03285b66 |
|
| ethesis.department |
Institutionen för fysik |
sv |
| ethesis.department |
Department of Physics |
en |
| ethesis.department |
Fysiikan laitos |
fi |
| ethesis.faculty |
Matematisk-naturvetenskapliga fakulteten |
sv |
| ethesis.faculty |
Matemaattis-luonnontieteellinen tiedekunta |
fi |
| ethesis.faculty |
Faculty of Science |
en |
| ethesis.faculty.URI |
http://data.hulib.helsinki.fi/id/8d59209f-6614-4edd-9744-1ebdaf1d13ca |
|
| ethesis.university.URI |
http://data.hulib.helsinki.fi/id/50ae46d8-7ba9-4821-877c-c994c78b0d97 |
|
| ethesis.university |
Helsingfors universitet |
sv |
| ethesis.university |
University of Helsinki |
en |
| ethesis.university |
Helsingin yliopisto |
fi |
| dct.creator |
Ala-Lahti, Matti |
|
| dct.issued |
2017 |
|
| dct.language.ISO639-2 |
eng |
|
| dct.abstract |
Mirror mode waves arise from the antiphase, low frequency fluctuations of the magnetic field and plasma density when the energy is conserved and a sufficient temperature anisotropy is present in the plasma. These waves are linearly polarized and they are frequently observed in heliospheric plasma, in particular in different sheath structures. They are the most widely studied in the planetary magnetosheaths, but also found in cometosheaths and in the heliosheath. In addition, mirror mode waves are reported to also occur in CME-driven sheaths. The knowledge of mirror modes in CME-driven sheaths is, however, very limited despite of the fact that they might contribute to regulating the CME sheath plasma on a global scale, and also a ect the geoeffectivity of CME-driven sheaths as well as the modulation and acceleration of energetic particles. As of yet, no statistical studies of mirror modes in CME-driven sheaths exist.
In this thesis, a background to the basic physical plasma phenomena and structures in the heliosphere is given by briegly discussing the solar wind, interplanetary shocks and sheath regions. The central focus of this thesis is however on CME-driven sheath regions and the mirror mode wave occurrence in them. CME-driven sheaths are turbulent plasma regions between the CME ejecta and its preceding interplanetary shock. This thesis discusses the differences between CME-driven sheaths and other heliospheric sheaths. In addition, mirror modes are considered in detail by presenting the theory of mirror instability in both fluid and kinetic descriptions and by discussing the fundamental features of mirror modes in other heliospheric sheaths regions. The previous studies of mirror modes and the methods applied in them are also widely presented.
A program that identifies mirror mode structures from the magnetic field data of a spacecraft is constructed for this thesis. In the identification process, the program applies the linear polarization of mirror modes and the knowledge of the angular change of the magnetic field direction across a mirror mode structure. This new, almost fully automatic program combines previous mirror mode identification methods in a novel way, thus creating a new method for detecting and studying mirror modes in CME-driven sheath regions, as well as in other sheath regions.
In this thesis, the constructed program is applied to perform a statistical study of mirror mode waves in CME-driven sheaths. Mirror modes were discovered to be common structures, but similar to the planetary magnetosheaths. They occupy only a relatively small part of the CME sheath. The results show that in CME-driven sheaths mirror modes are generally low amplitude structures that typically occur as trains of two or three mirror mode waves. In addition, the sheath plasma was noted to have notable temperature anisotropies, being generally mirror unstable when mirror modes were detected. The properties of the preceding shock of a CME-driven sheath were deduced to a ect mirror mode occurrence and the shock compression was concluded to provide a source of free energy. |
en |
| dct.language |
en |
|
| ethesis.language.URI |
http://data.hulib.helsinki.fi/id/languages/eng |
|
| ethesis.language |
English |
en |
| ethesis.language |
englanti |
fi |
| ethesis.language |
engelska |
sv |
| ethesis.thesistype |
pro gradu-avhandlingar |
sv |
| ethesis.thesistype |
pro gradu -tutkielmat |
fi |
| ethesis.thesistype |
master's thesis |
en |
| ethesis.thesistype.URI |
http://data.hulib.helsinki.fi/id/thesistypes/mastersthesis |
|
| dct.identifier.urn |
URN:NBN:fi-fe2017112251961 |
|
| dc.type.dcmitype |
Text |
|
