Alfvén Waves, Density Cavities and Electron Acceleration Observed from the FAST Spacecraft
Alfvén Waves, Density Cavities and Electron Acceleration Observed from the FAST Spacecraft
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从 FAST 航天器观测到的阿尔芬波、密度空腔和电子加速
DOI：
10.1238/physica.topical.084a00064
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发表时间：
2000
期刊：
影响因子：
2.9
通讯作者：
J. Mcfadden
中科院分区：
文献类型：
--
作者：
C. Chaston;C. Carlson;R. Ergun;J. Mcfadden
从FAST(Fast Auronal Snapshot)航天器上观测到了在极光电子加速区传播的惯性Alfvén波，整个高度范围(350-4180公里)。这些电子集肤深度大小的场结构是色散的，并携带与地磁场平行的电场分量，导致各种非线性效应，包括形成磁场排列的密度空穴和电子加速。高分辨率测量表明，脉冲波场包络或密度腔内的电子分布由一个冷电离层分量和一个加速加热场向分量组成，该分量由下行和反射的电离层和磁鞘(太阳风)电子组成。在大振幅情况下，波内等离子体可能由加速分量主导，腔内等离子体耗尽接近100%。将观测到的密度耗尽与有质动力密度空穴形成与电子加热相关的预测进行比较，显示出很好的一致性。此外，模拟表明，加速分量的大部分观测特征可以通过冷电离层和磁鞘电子与惯性Alfvén波在高度相关的密度剖面中传播时的Landau共振来解释。
Inertial Alfvén waves propagating in regions of auroral electron acceleration are observed from the FAST (Fast Auroral Snapshot) spacecraft over its entire altitude range (350–4180 km). These electron skin depth sized field structures are dispersive and carry an electric field component parallel to the geomagnetic field leading to a variety of non-linear effects including the formation of magnetic field-aligned density cavities and electron acceleration. High resolution measurements show that the electron distribution inside the impulsive wave field envelope or density cavity consists of a cold ionospheric component and an accelerated and heated field-aligned component comprised of downgoing and reflected ionospheric and magnetosheath (solar wind like) electrons. In large amplitude examples the plasma within the wave may be dominated by the accelerated component and the depletion of plasma within the cavity approaches 100%. Comparison of the observed density depletion with the predictions of ponderomotive density cavity formation in association with electron heating shows good agreement. Furthermore, simulations show that most of the observed features of the accelerated component can be explained through Landau resonance of the cold ionospheric and magnetosheath electrons with the inertial Alfvén wave as it propagates through an altitude dependent density profile.