We present results of noon–midnight meridional plane global hybrid-Vlasov simulations of the magnetotail ion dynamics under a steady southward interplanetary magnetic field using the Vlasiator model. The simulation results show magnetotail reconnection and formation of earthward and tailward fast plasma outflows. The hybrid-Vlasov approach allows us to study ion velocity distribution functions (VDFs) that are self-consistently formed during the magnetotail evolution. We examine the VDFs collected by virtual detectors placed along the equatorial magnetotail within earthward and tailward outflows and around the quasi-steady X line formed in the magnetotail at $X\approx -\mathrm{14}{R}_{\mathrm{E}}$. This allows us to follow the evolution of VDFs during earthward and tailward motion of reconnected flux tubes as well as study signatures of unmagnetized ion motion in the weak magnetic field near the X line. The VDFs indicate actions of Fermi-type and betatron acceleration mechanisms, ion acceleration by the reconnection electric field, and Speiser-type motion of ions near the X line. The simulated VDFs are compared and show good agreement with VDFs observed in the magnetotail by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) spacecraft. We find that the VDFs become more gyrotropic but retain transverse anisotropy and counterstreaming ion beams when being convected earthward. The presented global hybrid-Vlasov simulation results are valuable for understanding physical processes of ion acceleration during magnetotail reconnection, interpretation of in situ observations, and for future mission development by setting requirements on pitch angle and energy resolution of upcoming instruments.

中文翻译：

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磁尾重联中的离子分布函数：全局混合 Vlasov 模拟结果

我们使用 Vlasiator 模型展示了在稳定的向南行星际磁场下磁尾离子动力学的中午 - 午夜子午面全局混合 Vlasov 模拟的结果。模拟结果显示了磁尾重联和向地和向尾快速等离子体流出的形成。混合 Vlasov 方法使我们能够研究在磁尾演化过程中自洽形成的离子速度分布函数 (VDF)。我们检查了由沿赤道磁尾放置的虚拟探测器收集的 VDF，位于向地和向尾流出中以及在磁尾中形成的准稳态X线周围。$X\approx ——\mathrm{14}{\mathrm{电阻}}_{\mathrm{乙}}$. 这使我们能够在重新连接的通量管向地和向后运动期间跟踪 VDF 的演变，以及研究X线附近弱磁场中未磁化离子运动的特征。VDF 指示费米型和电子加速器加速机制的作用、重联电场引起的离子加速以及X附近离子的 Speiser 型运动线。模拟的 VDF 与通过亚暴期间事件和宏观相互作用的时间历史 (THEMIS) 和月球与太阳相互作用的加速、重联、湍流和电动力学 (ARTEMIS) 航天器在磁尾中观察到的 VDF 进行了比较，并显示出良好的一致性。我们发现 VDF 变得更具回旋性，但在向地球对流时保留横向各向异性和逆流离子束。所呈现的全局混合 Vlasov 模拟结果对于理解磁尾重连期间离子加速的物理过程、解释原位观测以及通过设置对即将到来的仪器的俯仰角和能量分辨率的要求来进行未来的任务开发都很有价值。