@phdthesis{oai:nagoya.repo.nii.ac.jp:00009446,
 author = {堀, 智昭},
 month = {Nov},
 note = {The plasma sheet, which is confined around the equatorial  region of the magnetosphere, is one of the most active site where the particle distribution consists of not only the thermal component (～several KeV) but also the suprathermal component (～several tens to hundreds of keV) as a result of various acceleration and transport processes.  These two components of magnetospheric plasma behave and affect plasma and field structures in the magnetosphere in different ways.  The thermal component is a major component of plasma in the plasma sheet and plays a main role in global interaction with the ambient magnetic and electric fields, hence their spatial distribution and also global transport processes are closely related to large-scale field structures of the plasma sheet.  On the other hand, the suprathermal component is a minor component and usually their abundance is negligibly small as compared to the thermal component.  However they are generated abundantly during geomagnetically disturbed periods such as substorms and transported into the inner region of the magnetosphere. These energetic particles generate a large-scale current system around the Earth and thereby cause significant variations in the geomagnetic field near the Earth.  Thus in order to understand dynamics of the magnetosphere comprehensively, it is essential to examine the contribution of both thermal and suprathermal plasmas to the formation of the magnetospheric plasma and field structures and also to the energization processes occurring in the plasma sheet.  Therefore, in this  dissertation, I investigate typical magnetospheric phenomena relating to the acceleration and transport processes for thermal and suprathermal components of plasmas, using the data obtained by the GEOTAIL spacecraft, and discuss the fundamental processes of plasma acceleration and subsequent transport in the magnetosphere. First I made a statistical study on ion flows, pressure, and the magnetic field directly observed in the plasma sheet and derived their large-scale structures.  It was shown that the average ion flow in the plasma sheet has a significant duskward component in the local midnight to dusk side regions, but is directed almost sunward on the dawn side.  Since this asymmetry probably resulted from the contribution of the ion pressure gradient drift, we estimated the true distribution of the convection electric field by correcting the observed V × B field by the observed ion pressure gradient.  The result is that, in addition to the duskward component of the electric field representing the sunward convection, the electric field has a significant sunward and anti-sunward (Ex) component on the dawn and dusk sides of the tail, respectively.  This means that the earthward convection has a tendency to bifurcate at the midnight meridian toward dawn and dusk in a relatively symmetric way.  It is also found that the magnitude of Ex is significant even at downtail distances of R> 15 R_E, showing that the bifurcation occurs at much greater distances than predicted by earlier models.  The important result is that there are significant differences between the convection patterns of ions (deduced from ion velocity) and magnetic flux (deduced from the electric field) in the near-Earth plasma sheet.  This difference suggests that the frozen-in condition does not hold for ions in the near-Earth plasma sheet and thus ions and magnetic fluxes are transported in different ways. Next, I studied the acceleration and transport processes of energetic particles by investigating spatial and temporal characteristics of flux enhancements of energetic particles and also their correlation with substorm activities on the basis of GEOTAIL HEP-LD observation.  I found that some of these flux enhancements exhibit either clear energy-dispersed or dispersionless features in temporal  variations of particle fluxes.  These characteristics give us import clues to estimate how far away the observation points are from the source of the energetic particles.  Using these clues, I examined properties of enhanced energetic particles during substorms.  I found that the dispersed events of energetic ions are distributed preferentially on the dusk side, while most of the dispersed electron events are found dawnward of the midnight meridian.  On the other hand, the dispersionless events are found only on the night side and are mostly distributed within R<15 R_E from the Earth.  From these results, it is interpreted that energetic particles forming such flux enhancements are generated on the night side, and subsequently drift azimuthally, and then reach the observation points.  A detailed analysis shows that ion dispersionless events are found more frequently than electron events.  This fact implies that the acceleration mechanism is less effective for electrons.  I also examined their correlation with substorm activities in detail. It was found that almost all the dispersionless and dispersed events are accosiated with substorms.   The dispersionless flux enhancements occurred within about +/-2 minutes of the corresponding substorm expansion onset, while all of the dispersed events are preceded by the onset probably due to  their finite transport time from the source region.  Duration of the observed energy dispersion is consistent with our test particle simulation with the source site assumed at local midnight in the near-Earth plasma sheet.  It was also found that some of the dispersed events have a long (～several tens of minutes) energy dispersion, indicating a possibility that energetic particles occasionally could make a closed drift path around the Earth even at radial distances exceeding the radial limit of the inner magnetosphere., 名古屋大学博士学位論文 学位の種類:博士(理学) (課程) 学位授与年月日:平成13年11月30日},
 school = {名古屋大学, Nagoya University},
 title = {Plasma Transport and Energization in the Earth's Magnetosphere},
 year = {2001}
}