地球磁層頂一維與二維結構分析;A Study of One and Two Dimensional Magnetopause Structure

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Title:	地球磁層頂一維與二維結構分析;A Study of One and Two Dimensional Magnetopause Structure
Authors:	周郁傑;Chou,Yu-Chieh
Contributors:	太空科學研究所
Keywords:	磁層頂;磁重聯;一維結構;二維結構;地球;1D structure;2D structure;Earth;Magnetopause;Reconnection
Date:	2012-10-14
Issue Date:	2012-11-12 14:26:49 (UTC+8)
Publisher:	國立中央大學
Abstract:	本論文研究地球磁層頂一維與二維結構，採用AMPTE/IRM衛星與THEMIS衛星之電漿與磁場資料。一維結構分析採用磁場最小差異量法(Minimum Variance Analysis, MVA)、DeHoffmann-Teller座標分析(HT)、與Wal?n Relation分析方法，針對328個地球磁層頂穿越事件，檢視MVA與HT分析結果及相關誤差分析，並依據Wal?n Relation結果判斷其結構為tangential discontinuity (TD) 或 rotational discontinuity (RD)結構。其中142個穿越事件同時具有良好的MVA與HT分析結果，且在良好的TD與RD事件中，不連續面法線方向磁場分量分別平均為4.4nT ( Bn/B=11%)與24nT ( Bn/B=31%)。我們並首次檢驗磁重聯現象(RD)與磁層頂電流片兩側電漿環境之相關性。根據Swisdak et al. [2010]提出之理論，當電流片兩側電漿環境 beta、磁場轉動角度 theta、與電流片特徵長度 L/di (其中di為離子的慣性長度)，符合delta_beta<2(L/di)tan(theta/2)條件時可發生磁重聯現象。透過檢測846個磁層頂穿越事件，在 delta-beta 相關性中，有93%的RD以及72%的TD符合可發生磁重聯之條件 ( L/di=1)。此結果顯示，地球磁層頂之電漿環境相當適合於磁重聯現象之發生，而磁重聯可發生於 delta_beta<2.8，且Swa~1 事件僅發生於deta_beta<1 。我們並發展二維Grad-Sharfanov (GS)重建模式，應用於地球磁層頂電流片之穿越事件，結果顯示，TD與RD皆具有相似之單一或多個X-line及磁島結構之磁重聯現象。A statistic study of one-dimensional (1D) and two-dimensional (2D) structure of Earth’s magnetopause is carried out by analyzing AMPTE/IRM and THEMIS plasma and magnetic field data. The analyses are based on the minimum variance analysis (MVA), the deHoffmann-Teller (HT) frame analysis and the Wal?n relation. A total of 328 magnetopause crossings are analyzed and error estimates associated with MVA and HT fame analyses. In 142 out of 328 events both MVA and HT frame analyses yield high quality results which are classified as either tangential-discontinuity (TD) or rotational-discontinuity (RD) structures based only on the Wal?n relation. For high quality events, the average normal magnetic field for TDs and RDs is 4.4nT ( Bn/B=11%) and 24nT ( Bn/B=31%), respectively. We have also examined for the first time the dependence of magnetic reconnection on plasma beta difference, delta_beta , and magnetic field shear angle, theta, across the current sheet based on the theoretical relation of (where L/di is the characteristic length of current sheet in units of ion inertial length) recently proposed by Swisdak et al. [2010] as the necessary condition for the occurrence of magnetic reconnection. The plasma conditions adjacent to Earth’s magnetopause are examined for 846 magnetopause crossing events from AMPTE and THEMIS spacecraft. It is found that 93% of RDs and 72% of TDs fall in the reconnection regime bounded by delta-beta curve. This result implies that the plasma condition of Earth’s magnetopause is in favor for reconnection. While RD events occur only for delta_beta<2.8 and events with Swa~1 occur only for delta_beta<1. Two-dimensional Grad-Shafranov (GS) reconstruction scheme is developed and applied to a large of number of TD and RD events which shows similar reconnection feature with single or multiple X-line accompanied with magnetic islands.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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