湍流空间等离子体中无各向同性假设的惯性区能量传输
Inertial-Range Energy Transfer Free from Isotropic Assumption in Turbulent Space Plasma
AI总结：
本文系统比较了方向平均法和滞后多面体导数系综法在测量惯性区三维能量传输中的表现，揭示了各向异性对能量级联测量的影响，为多航天器任务提供了关键指导。
摘要：
惯性区能量级联的概念常被用于湍流空间等离子体中以估算能量耗散率。控制惯性区三阶结构函数行为的定律，即三阶定律，是少数量化跨尺度能量传输的严格理论结果之一。广泛使用的基于三阶定律的耗散率假设各向同性，这与空间等离子体的各向异性本质根本冲突。关于如何使用多航天器星座量化这种各向异性能量级联的基本问题仍然存在。随着日球层学界越来越多地推进多航天器、多尺度星座（如等离子体观测站和HelioSwarm），我们重新审视了与精确测量惯性区能量传输相关的这些关键问题。在这里，我们对两种方法进行了系统比较：方向平均法和滞后多面体导数系综法，以确定跨尺度能量传输的全三维依赖性。我们发现，DA表现出极向和方位角依赖性，但对航天器配置不敏感。相比之下，LPDE受到航天器间距和四面体形状的强烈影响，而对采样轨迹相对不敏感。我们的发现对当前和未来的多航天器任务具有直接意义。DA和LPDE都将提供关于空间和天体物理学中湍流性质的关键信息。
英文摘要：
The idea of an energy cascade in the inertial range is often invoked in turbulent space plasmas to estimate the energy dissipation rate. Laws governing the behavior of third-order structure functions in the inertial range, so-called third-order laws, are among the few rigorous theoretical results quantifying cross-scale energy transfer. The widely used third-order-law derived rate assumes isotropy, which fundamentally conflicts with the anisotropic nature of space plasmas. Elementary questions persist regarding how such anisotropic energy cascades can be quantified using multi-spacecraft constellations. As the heliospheric community increasingly progresses towards multi-spacecraft, multi-scale constellations, such as Plasma Observatory and HelioSwarm, we revisit these crucial issues pertinent to accurately measuring the inertial-range energy transfer. Here we make a systematic comparison between two methods: direction-averaging (DA) and lag polyhedral derivative ensemble (LPDE) to determine the full three-dimensional (3D) dependence of cross-scale energy transfer. We find that DA exhibits both polar and azimuthal dependence, but is insensitive to spacecraft configuration. By contrast, LPDE is strongly affected by spacecraft separation and tetrahedral shape, while being comparatively insensitive to the sampling trajectory. Our findings have direct implications for current and future multi-spacecraft missions. Both DA and LPDE will provide crucial information on the nature of turbulence in space and astrophysics.
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