Gyroresonant acceleration of electrons in the magnetosphere by superluminous electromagnetic waves
Gyroresonant acceleration of electrons in the magnetosphere by superluminous electromagnetic waves
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DOI：
10.1029/2000ja000309
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发表时间：
2001-06
影响因子：
--
通讯作者：
D. Summers;R. Thorne;F. Xiao
中科院分区：
文献类型：
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作者：
D. Summers;R. Thorne;F. Xiao
超光极光千米辐射起源于地球磁层的极光空洞，作为右手异常模式（R-X）发射，左手普通模式（L-O）和左手异常模式（L-X）也有额外的贡献。这三种模式可以传播到外辐射带，并在广泛的外磁层范围内与捕获的高能电子发生回旋共振相互作用。我们建立了准线性扩散的一般理论，并在速度空间中构造了每一种超光波模式的共振扩散曲线。随机电子加速的潜力是由波的色散特性和电子回旋频率与等离子体频率之比控制的。研究发现，R-X、L-O和L-X模式都能在参数空间的各个区域产生显著的电子加速度。L-O模式被发现有可能在从极光腔到高纬度（bbb30°）外辐射带的空间区域内，在很宽的波法向角范围内，将电子从~ 10 keV加速到~ MeV。R-X模式对于加速磁层电子似乎不太有效，因为加速到显著能量（~ MeV）需要非常小的波法向角（<10°）。L-X模式波在磁层中产生显著电子加速的可能性主要受到高的最小能量要求的限制，例如，在外辐射带中需要400 keV。为了评估超光波模式是否对地磁风暴期间相对论性电子的随机加速有显著贡献，目前的研究需要通过射线追踪分析和结合波能数据的能量扩散系数计算来补充。
Superluminous auroral kilometric radiation originates in the auroral cavity of the Earth's magnetosphere as right-hand extraordinary (R-X) mode emissions, with additional contributions from the left-hand ordinary (L-O) and left-hand extraordinary (L-X) modes. The three modes can propagate into the outer radiation belt and undergo gyroresonant interaction with trapped energetic electrons over a broad extent of the outer magnetosphere. We develop a general theory of quasi-linear diffusion and construct resonant diffusion curves in velocity space for each superluminous wave mode. The potential for stochastic electron acceleration is controlled by the dispersive properties of the waves and the ratio between the electron gyrofrequency and plasma frequency. It is found that each of the R-X, L-O, and L-X modes can produce significant acceleration of electrons over individual regions of parameter space. The L-O mode is found to have the potential for accelerating electrons from ∼10 keV to ∼MeV energies, over a broad range of wave normal angles, in spatial regions extending from the auroral cavity to the high-latitude (>30°) outer radiation belt. The R-X mode appears to be less effective for accelerating magnetospheric electrons, since acceleration to significant energies (∼MeV) requires very small wave normal angles (<10°). The potential for significant electron acceleration in the magnetosphere by L-X mode waves is restricted not least by the requirement of high minimum energies, e.g., 400 keV in the outer radiation belt. To assess whether the superluminous wave modes contribute significantly to the stochastic acceleration of relativistic electrons during geomagnetic storms, the present study needs to be supplemented by ray-tracing analyses and the calculation of energy diffusion coefficients incorporating data on wave power.