地球磁層頂二維結構之研究; A study of two-dimensional structure of earth's magnetopause

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题名:	地球磁層頂二維結構之研究;A study of two-dimensional structure of earth's magnetopause
作者:	鄭偉良;Wai-Leong Teh
贡献者:	太空科學研究所
关键词:	磁層頂;磁流體力學;Magnetopause;Magnetohydradynamics (MHD)
日期:	2003-05-19
上传时间:	2009-09-22 09:46:03 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	在日地交互作用中，地球磁層頂扮演著很重要的角色。磁層頂的內部結構，由磁流體力學觀點，有簡單的一維模式：切線不連續面和旋轉不連續面。前者為封閉的磁層模式，沒有磁層頂法向之磁場分量；而後者為開放的磁層模式，具有磁層頂法向分量的磁場，通常伴隨著行星際磁場與地球磁場重連的發生。對於磁層頂的二維結構，Hau和Sonnerup [1999] 已發展出利用單一人造衛星穿過磁層頂所收集的電漿和磁場資料，來重建磁層頂的二維切線不連續面結構。這些作者發現磁層頂內充滿珍珠似磁島(magnetic island)結構，是磁重連撕裂模不穩性的產物。由於此種結構須滿足特定之物理假設，目前僅有少數的觀測個案。本篇論文之目的為尋找此種電漿結構於磁層頂發生的證據。我們利用兩年AMPTE/IRM人造衛星通過地球磁層頂所收集的磁場和電漿資料來分析判斷可能產生此結構之事件。此論文所用的分析方法有： Minimum Variance Analysis (MVA); Minimization of Faraday Residue (MFR); DeHoffmann-Teller Velocity Analysis; Bootstrap Method;及 Analytical Error Estimate for MVA。利用這些分析結果來篩選適當的磁層頂穿越事件，並應用Hau and Sonnerup之重建方法，我們找到了磁層頂內磁島發生的進一步證據。本論文將比較兩個具有一串磁島之磁層頂二維結構的案例。此倆事件分別發生於赤道面的dawn和dusk之地球磁層頂側翼，而磁島的寬度約為500 公里，以每秒約200公里的速度向磁尾移動。 Magnetopause plays an important role in the interaction between the solar wind and earth’s magnetosphere. Conventionally the magnetopause current layer is described by two simple one-dimensional magnetohydrodynamic (MHD) models that are tangential discontinuity (TD) and rotational discontinuity (RD) associated with the closed and open models of the magnetosphere. Hau and Sonnerup [1999] have developed a new technique to reconstruct the 2D tangential-discontinuity like magnetopause structure by using the single satellite data obtained during magnetopause crossings. These authors found that a series of pearl like magnetic islands are embedded within the magnetopause that is presumably caused by the tearing mode instability. Due to the physics constraints and hypotheses required to reconstruct such self-consistent plasma structures, only a few of these cases have been found to date. The purpose of this paper is to seek for further evidence of magnetic island structure at the magnetopause. We have surveyed the two-year AMPTE/IRM plasma and magnetic field data during the magnetopause crossings based on the analysis methods of Minimum Variance Analysis (MVA), Minimization of Faraday Residue (MFR), DeHoffmann-Teller Velocity Analysis, and Analytical Error Estimate as well as Bootstrap Method for MVA. Using these analysis results along with the reconstruction method of Hau and Sonnerup [1999], we have identified two events that show a series of magnetic island structure within the magnetopause with island width of about 500 km. These two events occur at the dawn and dusk sides of the magnetopause flank and are convecting tailward with high speed of ~200 km/s.
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