2006 Fiscal Year Final Research Report Summary
Correlation between magnetic and density fluctuations in the foreshock MHD turbulence
| Project/Area Number |
17540423
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | Kyushu University |
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Principal Investigator |
HADA Tohru Kyushu University, Interdisciplinary Graduate School of Engineering Sciences, Associate Professor (30218490)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUKIYO Shuichi KYUSHU UNIVERSITY, Interdisciplinary Graduate School of Engineering Sciences, Assistant Professor (00380709)
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| Project Period (FY) |
2005 – 2006
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| Keywords | MHD waves / MHD turbulence / Nonlinear waves / foreshock / foreshock waves |
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| Research Abstract |
We have conducted the research mainly on the following topics.
1.Magnetic and density fluctuations associated with parametric instabilities: effects of incoherent parent waves Many theoretical and numerical simulation studies of Alfven wave parametric instabilities assume a presence of monochromatic (coherent) parent wave initially, although not consistent with observations. When the initial parent waves are given as incoherent turbulence with finite width in the wave number, we find that density fluctuations at small wave numbers are triggered instantaneously due to the beating among the Alfven waves. Due to this effect, the modulational, rather than the decay type parametric instabilities are preferentially driven unstable.
2. Magnetic and density fluctuations associated with parametric instabilities: effects of incoherent parent waves Parametric instabilities of parallel Alfven waves are studied, using a framework of Vlasov description for ions in the longitudinal direction and fluid
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description of transverse directions. The longitudinal ion kinetic effects play essential roles in the parametric instabilities.
3. Nonlinear evolution of a system with Alfven and sound waves which are nearly degenerate The quasi-linear Alfven and the sound waves in the solar wind and the foreshock plasma should be considered degenerate (propagate with nearly equal velocities) since the plasma beta ratio is near unity, and the Alfven wave magnetic field amplitude is large compared with the background field. We have included the ion kinetic effects to the above model and discussed within this model the relationship between the magnetic and the density perturbations.
4. Development of a method to analyze turbulence data obtained by multiple-spacecraft experiments By using the capon and the linear prediction method, frequently used for determination of the wave numbers and the power spectra analysis for array signal data, we are developing a method to evaluate bi-spectrum (and bi-coherence) of large amplitude MHD waves typically observed in the foreshock region of the earth's bowshock. Less
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