与近太阳太阳风中电子亏缺相关的准平行反日传播哨声波：粒子模拟
Quasi-parallel anti-sunward propagating whistler waves associated to the electron-deficit in the near-Sun solar wind: Particle-in-Cell simulation
AI总结：
本文利用粒子模拟研究近太阳太阳风电子速度分布中的电子亏缺如何触发波粒相互作用，从而驱动平行反日传播哨声波不稳定，并解释其与电子亏缺分布伴生观测的现象及非碰撞热流调节机制。
摘要：
太阳风的就位观测表明，电子速度分布函数（VDF）由一个准麦克斯韦核心（包含大部分电子群体）和两个较稀疏的成分组成：晕（halo），即超热且准各向同性的电子，以及一个逃逸束流群体，即strahl。最近的帕克太阳探针（PSP）和太阳轨道器（SO）观测为已知的非热特征增添了一个新成分——亏缺（deficit），即VDF向日侧区域的耗竭，这一特征已由外逸层模型预言，但从未被如此广泛地观测到。通过采用粒子模拟（Particle-in-Cell simulations），我们研究了再现内日球层典型观测到的电子VDF，并探讨电子亏缺是否可能促成动力学不稳定性的发生。先前研究和就位观测表明，strahl电子驱动斜向哨声波不稳定，而这些波反过来散射它们。结果，超热电子可以占据相空间中满足与平行传播哨声波共振条件的区域。超热电子损失动能，导致不稳定波的产生。VDF的向日侧最初缺乏电子，随着这一由亏缺本身触发的波粒相互作用过程的发生，逐渐被填充。我们的发现与当前PSP和SO观测进行了比较和验证：其中，我们的研究提供了一种机制，解释了日球层中经常观测到的平行反日哨声波的存在；提示了为什么这些波经常与呈现电子亏缺的分布同时被观测到；描述了一种非碰撞热流调节过程。
英文摘要：
In-situ observations of the solar wind have shown that the electron velocity distribution function (VDF) consists of a quasi-Maxwellian core, comprising most of the electron population, and two sparser components: the halo, which are suprathermal and quasi-isotropic electrons, and an escaping beam population, the strahl. Recent Parker Solar Probe (PSP) and Solar Orbiter (SO) observations have added one more ingredient to the known non-thermal features, the deficit-a depletion in the sunward region of the VDF, already predicted by exospheric models but never so extensively observed. By employing Particle-in-Cell simulations, we study electron VDFs that reproduce those typically observed in the inner heliosphere and investigate whether the electron deficit may contribute to the onset of kinetic instabilities. Previous studies and in-situ observations show that strahl electrons drive oblique whistler waves unstable, which in turn scatter them. As a result, suprathermal electrons can occupy regions of phase space where they fulfil resonance conditions with the parallel-propagating whistler wave. The suprathermal electrons lose kinetic energy, resulting in the generation of unstable waves. The sunward side of the VDF, initially depleted of electrons, is gradually filled, as this wave-particle interaction process, triggered by the depletion itself, takes place. Our findings are compared and validated against current PSP and SO observations: among others, our study provides a mechanism explaining the presence in the heliosphere of regularly observed parallel anti-sunward whistler waves; suggests why these waves are frequently observed in concomitant with distributions presenting an electron deficit; describes a non-collisional heat flux regulating process.
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