| Summary: | 碩士 === 國立中央大學 === 太空科學研究所 === 87 === Magnetopause structures can be classified as tangential and rotational discontinuities ( TD and RD, respectively ). TDs are usually associated with the closed model of Earth's magnetosphere where Bn=0 and un=0 . (Bn is the component of the magnetic field normal to the magnetopause and un is the flow component across the current layer.) While RDs are linked with the field line reconnection model of the open magnetosphere where the solar wind IMF (Interplanetary Magnetic Field) and Earth's magnetospheric magnetic field are connected to each other and Bn≠0 ,un≠0 .
Identifing the two structures - TD and RD at Earth's magnetopause has been carried out through analyzing the plasma and magnetic field data of the AMPTE/IRM ( Active Magnetospheric Particle Tracer Explorers / Ion Release Module ) satellite passing across the current layer. We show that the conventional way of distinguishing the two structures by using the minimum variance analysis ( MVA ) to determine whether there is a net normal magnetic field component across the layer may be misleading. In other words, the absence or presence of Bn cannot be used as a sole criterion for distinguishing the TDs from RDs. In this study, TDs and RDs are distinguished from detailed analyses of the deHoffmann-Teller velocity and Walen relation. The analysis of a total of 171 magnetopause crossings shows that the occurrences of TDs and RDs are about 75% and 15% , respectively; while the other 10% cannot be identified with certainty.
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