地球磁尾慢速震波之研究; A Study of Slow Shocks in the Earth’s Magnetotail

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Title:	地球磁尾慢速震波之研究;A Study of Slow Shocks in the Earth’s Magnetotail
Authors:	陳彥甫;Yen-Fu Chen
Contributors:	太空科學研究所
Keywords:	慢速震波;shock structure;jump conditions;slow shock
Date:	2004-03-26
Issue Date:	2009-09-22 09:46:12 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	Petschek 於1964年提出一磁力線重連理論模式，其中由X-line延伸出兩對的慢速震波。基於這樣的理論，在太空電漿環境中尋找慢速震波的存在對於磁力線重連的發生被視為是極重要的證據。過去許多的研究即是將人造衛星觀測資料，應用磁性流體力學的躍遷條件式來檢定有無慢速震波的特性。本文中將使用一套延伸自Hau and Sonnerup [1989] 所發展的震波躍遷方法，做為選定於地球磁尾所蒐集到的衛星觀測資料中之慢速震波與其上下游的狀態，並比較其他方法所得之結果。在七個穿越事件中有兩個案可確定是慢速震波。我們並進一步以霍爾磁性流體力學模式來分析此慢速震波案例之結構與物理特性。這些分析包括震波上下游兩端的定點特性，及經由積分非線性的霍爾磁性流體力學方程式而得的整個震波結構。研究顯示，當黏滯效應夠大時或足夠小的霍爾參數均可導致慢速震波下游波列結構的消失。 Petschek [1964] proposed a theoretical model for magnetic field line reconnection that involves two pairs of slow shocks. For this reason, search of slow shocks in the space plasma environment is important for the observational evidence of magnetic reconnection. Many researches have been carried out to compare the MHD jump conditions with the observational data to identify the characteristics of slow shocks. In the present study, a different method based on the formulation of Hau and Sonerrup [1989] is used to determine the upstream and downstream conditions of slow shocks from satellite data sampled in the geomagnetotail. Only two out of seven crossing events may be surely identified as slow shocks and the results are compared with those based on different methods. The characteristics of the slow shocks are further analyzed based on the resistive/viscous Hall-MHD models. In particular, linear fixed-point analysis is performed for the upstream and downstream states of the shocks while the shock structures are calculated from the numerical integration of nonlinear Hall-MHD equations. The study shows that the absence of wave trains acquires large values of viscosity and/or small Hall parameters.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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