Abstract
Understanding the plasma transport process in space is a crucial issue in plasma physics.
In terms of magnetospheric physics, it is important not only for understanding theformation and maintenance of magnetosphere but also for space weather forecast. It is
widely known that transport of magnetosheath plasma into the magnetosphere acrossthe magnetopause becomes efficient under northward IMF conditions. This transport
makes not only the low-latitude boundary layer just inside the magnetopause at
low-latitudes, but also the cold-dense plasma sheet in the nightside magnetosphere.
When the cold-dense plasma of magnetosheath-origin is transferred deep into themagnetosphere, the stronger geomagnetic storm is induced. Although several transport
processes have been suggested, their relative importance was poorly understood.
The goal of this study is to unveil the mechanism of plasma transport across themagnetopause and in the magnetosphere under northward IMF conditions. Althoughseveral transport processes have been suggested, their relative importance is still notcompletely understood. Especially, the contribution of the following two transport
processes near the magnetopause is poorly understood: one is plasma transport acrossthe magnetopause induced by kinetic Alfvén wave (KAW) turbulence, and the other isplasma transport from the magnetopause toward the Earth induced by eddy turbulence
as is the case in an ordinary (Navier-Stokes) fluid. This is because there is no definite
observational evidence for their operation in space. In this dissertation, I challenge tofind their evidence by inspecting characteristic low energy charged particle signatureswith the use of multipoint observations from the THEMIS spacecraft and by making
comparisons between the observed signatures and the theoretical predictions. On thebasis of obtained results and previous knowledge, I aim at drawing a transparent pictureof plasma transport near the magnetopause under northward IMF conditions.
I start by developing the theory of plasma transport induced via KAW turbulence. The
KAW-induced transport is shown to be a selective transport depending on particle’senergy and surrounding environment. Focusing attention on its selective nature, I
propose a new data analysis method to identify the operation of the KAW-induced
transport on the basis of in situ plasma particle data. An event study of THEMIS
observations is performed applying the proposed method. From the analysis of ion
distribution functions obtained in front of and behind the dayside magnetopause, thecharacteristic ion signatures which are fairly consistent with the KAW-induced selective
transport are found. This study is first to show that KAW turbulence can indeed transfer

magnetosheath plasma into the magnetosphere across the magnetopause. In order tounderstand the quantitative contribution of the KAW-induced transport, a statistical
study of THEMIS observations is performed. By estimating the amount of ionstransferred across the magnetopause from simultaneous multipoint observations, it isshown that the KAW-induced transport can transfer only a small amount ofmagnetosheath plasma across the magnetopause. Synthesizing the obtained results, thenature of the KAW-induced transport is discussed.
In order to verify the plasma eddy diffusion in the magnetosphere, an event study of
THEMIS observations is performed. The spatial and time scales of the transport
signatures detected from simultaneous multipoint observations are shown to be in goodquantitative agreement with the numbers of the eddy diffusion coefficients. Thus, thisstudy is first to show the operation of plasma eddy diffusion.
New knowledge acquired in this dissertation is as follows: (1) collision-less spaceplasma is subject to cross-field diffusion in KAW turbulence; (2) the KAW-induced
transport is selective transport and may be effective for limited intervals when themagnetopause satisfies the specific conditions; (3) collision-less space plasma is subject
to eddy diffusion as is the case in an ordinary fluid, which can transfer plasma ofmagnetosheath origin in the magnetosphere.