太陽風中旋轉不連續面及非線性艾爾文波之數值模擬研究

A Simulation Study of Rotational Discontinuities and Nonlinear Alfven Waves in the Solar Wind

陳敬中(Ching-Chung Chen)

指導教授 ： 呂凌霄 ； 蔡偉雄

國立中央大學/地球科學學院/太空科學研究所/碩士(2006年)

摘要

本論文研究利用電子-正離子雙流體模擬碼以及混合碼(流體電子與粒子形式的正離子)模擬研究不同初始條件下旋轉不連續面(RD)的演化過程，找出能形成穩定鉤狀RD的最佳初始條件。
本論文的研究結果顯示，當RD的初始厚度小於30 時，RD的過渡區中會放出很多大振幅的短波，並逐漸加寬過渡區的厚度，當RD初始厚度大於90 (正離子慣性長度)時，RD結構相對比較穩定，雖然仍會放出小振幅的波動，但是過渡區的厚度可大致維持不變。且形成很穩定的鉤狀旋轉不連續面。
本論文的研究成功模擬出穩定的雙鉤狀旋轉結構及δ型結構，此結果為過去模擬研究從未獲得的新結果，其中雙鉤型旋轉結構與過去太陽風中RD的觀測結果及非線性艾爾文波的理論解相符。

關鍵字

非線性艾爾文波 ； 雙流體碼數值模擬 ； 旋轉不連續面 ； 太陽風 ； 混合碼數值模擬

並列摘要

This thesis work studies rotational discontinuities (RDs) by means of electron-ion two-fluid simulation and hybrid simulation (fluid electrons and kinetic ions). We examine the evolution of RDs under different initial conditions. Our goal is to find the best initial conditions, which can yield the most stable RD structures.
The results of this research show that, when the initial width of the RD transition region is less than 30 , short-wavelength and large-amplitude waves will be emitted from the transition region. As a result, the transition region widens gradually with time. The RD structure is relatively steady when the initial width of the RD is more than 90 , although it can still emit small-amplitude waves to both up-stream and down-stream sides. The width of the transition region keeps constant and becomes a stable hook-shaped rotational structure.
Double-hook rotational structures and d-shaped rotational structures, which have never been obtained in the previous simulations, are found in this thesis study. The double-hook rotational structures obtained in this study are similar to the structures of RDs and Alfven waves observed in the solar wind.

並列關鍵字

nonlinear Alfven wave ； two-fluid simulation ； hybrid simulation ； solar wind ； rotational discontinuity

參考文獻

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Lin, Y., L. C. Lee, Magnetic field rotation and transition width in rotational discontinuities and Alfven wave trains, J. Geophys. Res., Volume 105, Issue A1, pp. 139-156, 2000.

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