Similar to Earth, Mercury's magnetotail experiences frequent dipolarization of the magnetic field. These rapid (~2 s) increases in the northward component of the tail field (ΔB_z ~ 30 nT) at Mercury are associated with fast sunward flows (~200 km/s) that enhance local magnetic field convection. Differences between the two magnetospheres, namely Mercury's smaller spatiotemporal scales and lack of an ionosphere, influence the dynamics of dipolarizations in these magnetotails. At Earth, the braking of fast dipolarization flows near the inner magnetosphere accumulates magnetic flux and develops the substorm current wedge. At Mercury, flow braking and flux pileup remain open topics. In this work, we develop an automated algorithm to identify dipolarizations, which allows for statistical examination of flow braking and flux pileup in Mercury's magnetotail. We find that near the inner edge of the plasma sheet, steep magnetic pressure gradients cause substantial braking of fast dipolarization flows. The dipolarization frequency and sunward flow speed decrease significantly within a region ~500 km thick located at ~900 km altitude above Mercury's local midnight surface. Due to the close proximity of the braking region to the planet, we estimate that ~10–20% of dipolarizations may reach the nightside surface of the planet. The remaining dipolarizations exhibit prolonged statistical flux pileup within the braking region similar to large‐scale dipolarization of Earth's inner magnetosphere. The existence of flow braking and flux pileup at Mercury indicates that a current wedge may form, although the limitations imposed by Mercury's magnetosphere require the braking of multiple, continuous dipolarizations for current wedge formation.

中文翻译：

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汞磁尾中两极流制动和磁通量堆积的MESSENGER观测：电流楔形成的证据

与地球相似，水星的磁尾经常经历磁场的双极化。这些快速（〜2秒）的增加在尾部字段向北组分（Δ乙_ž 水星处约30 nT）与快速向阳流（约200 km / s）有关，从而增强了局部磁场对流。两个磁层之间的差异，即水星较小的时空尺度和电离层的缺乏，会影响这些磁层中的双极化动力学。在地球上，快速双极化的制动在内部磁层附近流动，从而积累了磁通量并形成了亚暴电流楔形。在Mercury，流量制动和助焊剂堆积仍然是热门话题。在这项工作中，我们开发了一种自动算法来识别双极化，从而可以对水星磁尾中的流量制动和磁通堆积进行统计检查。我们发现在等离子片的内边缘附近，陡峭的磁压力梯度会导致快速的双极化流大量制动。在水星局部午夜表面上方约900 km的高度处约500 km的厚区域内，双极化频率和向阳流速明显降低。由于制动区域与行星非常接近，我们估计约10％至20％的双极化可能到达行星的夜表面。其余的双极化在制动区域内表现出延长的统计通量堆积，类似于地球内部磁层的大规模双极化。尽管Mercury磁层施加的限制要求制动多个，连续的双极化以形成电流楔，但Mercury处存在流量制动和磁通堆积的情况表明可能会形成电流楔。