Reformed Solitary Kinetic Alfven Waves due to Dissipations and Auroral Electron Acceleration |
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摘 要: |
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关 键 词: | 极光电子加速 电磁流体力学 Alfven波 |
收稿时间: | 2000-07-07 |
Reformed Solitary Kinetic Alfvén Waves due to Dissipations and
Auroral Electron Acceleration |
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Authors: | WU De-Jin CHAO Jih-Kwin LEE Luo-Chuan and FENG Xue-Shang |
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Institution: | 1. Purple Mountain Observatory, The Chinese Academy of Sciences, Nanjing 210008, China
;2. National Astronomical Observatories, The Chinese Academy of Sciences, Beijing 100012, China
;3. Institute of Space Science, National Central University,
Taiwan, China
;4. College of Science, National Cheng Kung University,
Taiwan, China
;5. Center for Space Science and Application Research, The Chinese Academy of Sciences, Beijing 100080, China |
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Abstract: | The physical nature of the auroral electron acceleration has been an
outstanding problem in space physics for decades. Some recent observations
from the auroral orbit satellites, FREJA and FAST, showed that large
amplitude solitary kinetic Alfvén waves (SKAWs) are a common electromagnetic active phenomenon in the auroral magnetosphere. In a low-β (i.e., β/2<<me/mi<<1) plasma, the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions. This leads to instabilities and causes dissipations of SKAWs. In the present work, based on the analogy of classical particle motion in a potential well, it is shown that a shock-like structure can be formed from SKAWs if dissipation effects are included. The reformed SKAWs with a shock-like structure have a local density jump and a net field-aligned electric potential drop of order of mevA2/e over a characteristic width
of several λe. As a consequence, the reformed SKAWs can efficiently accelerate electrons field-aligned to the order of the local
Alfvén velocity. In particular, we argue that this electron acceleration mechanism by reformed SKAWs can play an important role in the auroral electron
acceleration problem. The result shows that not only the location of
acceleration regions predicted by this model is well consistent with the
observed auroral electron acceleration region of 1—2 RE above the auroral ionosphere, but also the accelerated electrons from this region can obtain an energy of several keV and carry a field-aligned current of several
μA/m2 which are comparable
to the observations of auroral electrons. |
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Keywords: | space plasma auroral electron acceleration solitary kinetic Alfvén wave |
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