Acceleration of Suprathermal Tails in the Solar Wind
Acceleration of Suprathermal Tails in the Solar Wind
复制标题
太阳风中超热尾的加速
DOI：
10.1086/591543
复制
发表时间：
2008
期刊：
影响因子：
--
通讯作者：
G. Gloeckler
中科院分区：
文献类型：
--
作者：
L. Fisk;G. Gloeckler
在太阳风中，超热粒子无处不在，其能量通常从~1 keV的核子- 1到~几个MeV的核子- 1。值得注意的是，过热粒子在许多不同的情况下表现出共同的光谱形状；分布函数是粒子速度的幂律，谱指数为-5。观测结果不能用传统的随机加速度来解释，因为随机加速度产生的谱取决于动量扩散系数等，因此在不同的情况下，谱预计会有所不同。提出了粒子在热隔离压缩湍流中加速的理论。热隔离在太阳风的空间均匀条件下是有效的，如果应用得当，产生的超热尾总是具有所需的光谱形状。该理论描述了谱的时间演化到其平衡形式，并预测了加速度的高速截止。高速的截止点被证明与地球上的安静时间光谱的观测结果很好地一致，并且与整个外日球层的观测结果一致。
Suprathermal particles are ubiquitously present in the solar wind, with energies typically from ~1 keV nucleon−1 to ~a few MeV nucleon−1. Remarkably, the suprathermal particles exhibit a common spectral shape in many different circumstances; the distribution function is a power law in particle speed, with spectral index of –5. The observations cannot be explained by traditional stochastic acceleration, which yields spectra that depend on, e.g., the momentum diffusion coefficient, and thus the spectra are expected to be different in different circumstances. A theory is presented in which the particles are accelerated in thermally isolated compressional turbulence. Thermal isolation is valid in spatially homogeneous conditions in the solar wind, and when properly applied, yields suprathermal tails that always have the required spectral shape. The theory describes the time evolution of the spectrum to its equilibrium form and predicts the high-speed cutoff on the acceleration. The high-speed cutoff is shown to be in good agreement with observations of quiet-time spectra at Earth and is consistent with observations throughout the outer heliosphere.