In the diffusion region of magnetotail reconnection, particle distributions are highly structured, exhibiting triangular shapes and multiple striations that deviate dramatically from the Maxwellian distribution. Fully kinetic simulations have been demonstrated to be capable of producing the essential structures of the observed distribution functions, yet are computationally not feasible for 3D global simulations. The fluid models used for large‐scale simulations, on the other hand, do not have the kinetic physics necessary for describing reconnection accurately. Our study aims to bridge fully kinetic and fluid simulations by quantifying the information required to capture the non‐Maxwellian features in the distributions underlying the closures used in the fluid code. We compare the results of fully kinetic simulations with observed electron velocity distributions in a magnetotail reconnection diffusion region and use the maximum entropy model to reconstruct electron and ion distributions using various numbers of moments obtained from the simulation. Our results indicate that using only local moments, the maximum entropy model can reproduce many of the features of the distributions: (1) the electron outflow distribution with a tilted triangular structure is reproduced with 21 or more moments in agreement with Ng et al. (2018, https://doi.org/10.1063/1.5041758) and (2) counterstreaming distributions can be captured with the 35‐moment model when the separation in velocity space between the populations is large.

中文翻译：

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磁尾重连接扩散区电子和离子分布函数的重构

在磁尾重连接的扩散区域中，粒子分布高度结构化，呈现出三角形形状和多个条纹，这些条纹与麦克斯韦分布明显不同。完全动力学模拟已被证明能够产生观察到的分布函数的基本结构，但是在计算上对于3D全局模拟是不可行的。另一方面，用于大规模仿真的流体模型不具有精确描述重新连接所必需的动力学物理学。我们的研究旨在通过量化捕获流体代码中使用的封闭所依据的分布中的非麦克斯韦特征所需的信息，从而在动力学和流体模拟之间建立桥梁。我们将完全动力学模拟的结果与在磁尾重连接扩散区域中观察到的电子速度分布进行比较，并使用最大熵模型，使用从模拟中获得的不同数量的矩来重建电子和离子分布。我们的结果表明，仅使用局部矩，最大熵模型就可以再现许多分布特征：（1）与Ng等人一致，具有倾斜三角形结构的电子流出分布可以再现21个或更多个矩。（2018，https://doi.org/10.1063/1.5041758）和（2）当群体之间速度空间的分隔较大时，可以使用35矩模型捕获逆流分布。