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Hybrid-Kinetic Modelling of Space Plasma with Application to Mercury
- Author / Creator
- Paral, Jan
A planet's magnetosphere is often very dynamic, undergoing large
topological changes in response to high speed (~400 km/s) solar wind
intervals, coronal mass ejections, and naturally excited plasma wave modes.
Plasma waves are very effective at transporting energy throughout the
magnetosphere, and are therefore of interest in the context of the coupling
between solar wind and magnetosphere. Of relevance to this thesis is
Kelvin-Helmholtz macro-instability. Kelvin-Helmholtz instability (KHI) is
excited by shear of the flows. KHI is commonly observed at equatorial
regions of the magnetopause where fast flowing magnetosheath plasma may
interact with slow bulk velocities of magnetospheric plasma. The instability
is responsible for exciting shear Alfv'en waves which (at Earth) may be
detected using the ground based magnetometers located at latitude of excited
field lines. This thesis uses numerical modelling to understand and to
explain the generation and propagation of the KHI in Mercury's magnetosphere.
The instability is initiated close to the planet and convectively grows while
being transported along the tail. When the wave amplitude reaches a
nonlinear stage, the structure of the wave becomes complex due to the
wrapping of the plasma into the vortex. A vortex structure is typical for
KHI and it is used for identifying the wave in the data from satellites. The
instability commonly occurs at the dawn or dusk flank magnetopause (MP) of
Earth with approximately the same probability. But the data from NASA's
MESSENGER spacecraft, currently in the orbit of the planet Mercury, suggest a
strong asymmetry in the observations of KHI. It is shown that the KHI
initiated near the subsolar point evolves into large-scale vortices
propagating anti-sunward along the dusk-side MP. The simulations are in
agreement with the third flyby of the MESSENGER spacecraft, where saw-tooth
oscillations in the plasma density, flow, and magnetic field were observed.
The observed asymmetry in the KHI between dawn and dusk is found to be
controlled by the finite gyro-radius of ions, and by MP pressure gradients
and the large-scale solar wind convection electric field.
- Graduation date
- Spring 2013
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.