Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state
Isotropic ion distribution functions triggered by consecutive solar wind bulk velocity jumps: a new equilibrium state
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DOI：
10.1051/0004-6361/201015619
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发表时间：
2011-03
影响因子：
6.5
通讯作者：
H. Fahr;M. Siewert
中科院分区：
文献类型：
--
作者：
H. Fahr;M. Siewert
上下文在整个日球层中，观测发现离子功率谱呈现出遵循幂律的超热尾。离子幂律谱虽然有很宽的谱指数范围4.4 ≤ γv ≤ 6.6，但似乎有速度幂指数γv ′（−5），这种现象在日球空间等离子体中或多或少都能找到。这可能是一个尚未确定的准平衡状态的无碰撞空间等离子体的指示。目标。我们开发的想法，这些形式的离子光谱可以产生一个连续的来回洗牌的风对流离子在连续跳跃从快到慢，反之亦然，批量速度制度。方法.如我们所示，由于这种洗牌和重新洗牌而出现的准平衡态自然会导致离子分布函数，这些函数是一系列加权麦克斯韦函数的叠加，从而导致幂律超过临界速度边界。因此，光谱强度与体积速度相关，但功率指数仅略微依赖于体积速度。结果然而，这里显示的完全发展的平衡态是由幂指数γv =（−3）的幂律来表征的，而不是4.4 ≤ γv ≤ 6.6。这些后一种状态，通常出现在观测中，因此可以表征我们在本文中讨论的非平衡态。
Context. Throughout the heliosphere, ion power spectra have been found in observations to exhibit suprathermal tails that follow power laws. Ion power-law spectra, though having a broad range of spectral indices 4.4 ≤ γv ≤ 6.6, perhaps favourably seem to have velocity power indices of γv � (−5), a phenomenon that can more or less ubiquitously be found in heliospheric space plasmas. This is probably indicative of an as yet unidentified quasi-equilibrium state of collisionless space plasmas. Aims. We develop the idea that these forms of ion spectra could be produced by a continuous back- and forth- shuffling of wind convected ions in consecutive jumps from fast to slow, and vice-versa, bulk velocity regimes. Methods. The appearance of a quasi-equilibrium state due to this shuffling and re-shuffling, as we show, naturally results in ion distribution functions that are superpositions of a series of weighted Maxwellians resulting into power laws beyond a critical velocity border. Spectral intensities thereby anticorrelate with bulk velocities, but power indices depend only slightly on bulk velocity. Results. The fully developed equilibrium state is shown here, however, to be characterized by a power law with power index γv = (−3), instead of 4.4 ≤ γv ≤ 6.6. These latter states, which generally show up in observations, thus may characterize an off-equilibrium state as we discuss in this paper.