- Title
- Multi-satellite observations of ULF waves in the Earth's magnetosphere
- Creator
- Liu, Yonghua
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2011
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- ULF waves (0.001-5 Hz) in the Earth's magnetosphere are highly related to magnetospheric structure and field and plasma composition embedded in the magnetosphere. They also have a close relationship with solar wind conditions and IMF parameters as well as their variations on both time and space. In this thesis we use wave field and particle data from the Cluster constellation of 4 satellites to study EMIC and ULF waves in the middle magnetosphere and cusp regions. An extensive analysis of three typical EMIC wave events indicates that the outer plasmasphere/plasmapause around the equator is an important source region for these waves which were confined to the narrow shell of the plasmapause. The polarization of the waves depends on their location relative to the plasmapause, with left hand polarization around the equatorial region and inside the plasmapause and right hand polarization near the outer boundary on the equator at higher latitudes. The wave energy mainly propagated away from the equator suggesting the bouncing wave packet (BWP) model may not be valid, instead long period Pc5 wave modulation may play a role in amplification of the EMIC waves. These waves were excited under three conditions, ion temperature anisotropy, moderate cold plasma density (plasmasphere) and hot plasma fiux (ring current), which lead to the plasmapause around the equator as a favorable wave source region. A ULF wave event in the Pc2 band seen in the outer magnetosphere near noon and also on the ground was identified as an EMIC wave, with dominantly left hand polarization and wave energy guided by the magnetic field direction and the ionospheric waveguide. The energy source is considered to be plasma sheet keV protons convected from the magnetotail to the dayside outer magnetosphere. Three ULF wave events in the Pc3-4 band were seen by the Cluster satellites in the outer magnetosphere near the boundary layer. Ground observations show these waves occurred over a wide range of latitude but were confined to the morning and early afternoon. These waves were mainly left hand polarized and the wave energy propagated along the magnetic field direction. The full wave vector of the Pc3-4 waves was nearly perpendicular to the geomagnetic field. The phase velocity of the waves propagated westward in the morning and eastward in afternoon. These Pc3-4 waves (10-60 mHz) were guided Alfvenic mode waves at high latitude and field line resonances at middle and low latitudes, having a source upstream in the solar wind. The accompanying Pc4-5 waves (2-10 mHz) were related to field line resonances. The coherency of the Pc3 waves between the satellites is highly related to the alignment of satellite pairs with respect to the geomagnetic field direction. This provides a transverse scale size of the geomagnetic Pc3 ULF waves near the exterior cusp at about 900 km or 0.14 Re when the coherency is set as 0.65. A statistical study in the Pc2-5 wave band around the noon-midnight sector using three months of data shows that Pc5 had significant occurrence in both the dayside magnetosphere and the high latitude boundary layer near the exterior cusp, while the Pc2-4 waves dominantly occurred in the dayside magnetosphere. The wave power for the Pc2, Pc3 and Pc4 waves significantly increased with increasing solar wind dynamic pressure, increasing solar wind density, and decreasing solar wind velocity. This suggests that the Pc2-4 waves were not infuenced by the Kelvin-Helmholtz instability. The 22-50 mHz Pc3 waves have a source in the upstream solar wind while Pc4 waves may be excited via the magnetospheric cavity mode and the Pc2 waves by the ion cyclotron instability. Pc5 wave occurrence peaked at the high latitude boundary, near 86.7° invariant latitude (L ≈ 300) and GSM z < -8 Re and were associated with IMF Bx < -4nT suggesting they may be generated by Bx-based magnetic reconnection near the exterior cusp.
- Subject
- ULF waves; magnetosphere; solar winds
- Identifier
- http://hdl.handle.net/1959.13/929825
- Identifier
- uon:10692
- Rights
- Copyright 2011 Yonghua Liu
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Abstract | 325 KB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Thesis | 9 MB | Adobe Acrobat PDF | View Details Download |