Abstract. We use a newly developed global Hall MHD code to investigate how reconnection drives magnetotail asymmetries in small magnetospheres. Here, we consider a scaled-down, Earth-like magnetosphere where the ion inertial length (δ_i) is artificially inflated to one planetary radius (the real Earth's δ_i ≈ 1/15–1/20 R_E in the magnetotail). This results in a magnetotail width on the order of 30 δ_i, slightly smaller than Mercury's tail and much smaller than Earth's. At this small size, we find that the Hall effect has significant impact on the global flow pattern, changing from a symmetric, Dungey-like convection under resistive MHD to an asymmetric pattern similar to that found in previous Hall MHD simulations of Ganymede's subsonic magnetosphere as well as other simulations of Mercury's using multi-fluid or embedded kinetic physics. We demonstrate that the Hall effect is sufficient to induce a dawnward asymmetry in observed dipolarization front locations and find quasi-periodic global scale dipolarizations under steady, southward solar wind conditions. On average, we find a thinner current sheet dawnward; however, the measured thickness oscillates with the dipolarization cycle. During the flux-pileup stage, the dawnward current sheet can be thicker than the duskward sheet. This could be an explanation for recent observations that suggest Mercury's current sheet is actually thicker on the duskside: a sampling bias due to a longer-lasting "thick" state in the sheet.

中文翻译：

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小型类地磁层中的磁尾重联不对称性

摘要。我们使用新开发的全球霍尔 MHD 代码来研究重联如何驱动小磁层中的磁尾不对称。在这里，我们考虑按比例缩小的类似地球的磁层，其中离子惯性长度 ( δ _i ) 被人为地膨胀到一个行星半径（磁尾中真实地球的δ _i  ≈ 1/15–1/20 R _E）。这导致磁尾宽度约为 30 δ _i，比水星的尾巴略小，比地球的尾巴小得多。在这个小尺寸下，我们发现霍尔效应对全球流动模式有显着影响，从电阻 MHD 下的对称、类 Dungey 对流变为类似于之前对木卫三亚音速磁层的霍尔 MHD 模拟中发现的不对称模式，如以及使用多流体或嵌入式动力学物理学的其他水星模拟。我们证明霍尔效应足以在观测到的偶极锋位置引起黎明不对称，并在稳定的南向太阳风条件下发现准周期性全球尺度偶极化。平均而言，我们发现黎明前的电流片较薄；然而，测量的厚度随着偶极周期而波动。在助焊剂堆积阶段，黎明电流片可以比黄昏片厚。这可能是对最近的观察结果的解释，即水星当前的表层实际上在黄昏时更厚：由于表层中更持久的“厚”状态导致的采样偏差。