We consider the physical origin of reconnection-related events in Saturn’s equatorial current sheet revealed by Cassini, specifically the dipolarization events discussed by Yao et al. (https://doi.org/10.1029/2018JA025837) that recur close to the ∼10.7 h planetary period oscillation (PPO) period. We argue that Yao et al.’s preferred recurrence explanation in terms of complete rotations of dipolarized field/current structures around the planet at close to the PPO period is highly implausible. All-mission observations of ion flows at relevant radial ranges ∼20–30 Saturn radii are essentially invariably sub-corotational, including reconnection-related hot ion injections, thus requiring implausible structure propagation at significant speeds through the plasma. We further show their assertion that the nightside events occur at PPO phases unfavorable for reconnection is incorrect. These events instead occur under PPO conditions associated with outward radial plasma displacement and/or a thinning plasma sheet with falling colatitudinal field, shown previously to be optimal for modulated reconnection bursts leading to dipolarizations and plasmoids. We instead suggest these events are related to well-documented Vasyliunas cycle disturbances, when two reconnection episodes happen to be triggered at similar favorable PPO phases on successive PPO cycles. Yao et al.’s dayside events do occur at phases unfavorable for recurrent reconnection, but may then simply be an effect of periodic field/plasma modulations during the regular PPO cycle combined with subcorotating small-scale structures often present in the plasma sheet. Both dayside and nightside events can thus be understood within existing knowledge of PPO modulations of the structure and dynamics of Saturn’s equatorial current sheet.

中文翻译：

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土星赤道等离子体片中周期性磁偶极化事件的物理起源

我们考虑了卡西尼号揭示的土星赤道电流表中重联相关事件的物理起源，特别是姚等人讨论的偶极化事件。(https://doi.org/10.1029/2018JA025837) 在接近 10.7 小时行星周期振荡 (PPO) 周期时重复出现。我们认为，Yao 等人在接近 PPO 时期，根据偶极场/电流结构在地球周围的完整旋转的首选递归解释是非常不可信的。对相关径向范围~20-30 土星半径的离子流的所有任务观测基本上都是次共转的，包括与重联相关的热离子注入，因此需要以显着速度通过等离子体进行难以置信的结构传播。我们进一步表明他们关于夜间事件发生在不利于重新连接的 PPO 阶段的断言是不正确的。相反，这些事件发生在 PPO 条件下，与向外径向等离子位移和/或具有下降横向场的变薄等离子片相关，先前表明对于导致偶极化和等离子团的调制重联爆发是最佳的。相反，我们建议这些事件与有据可查的 Vasyliunas 循环干扰有关，当两个重新连接事件碰巧在连续 PPO 循环的相似有利 PPO 阶段触发时。姚等人的白天事件确实发生在不利于反复重新连接的阶段，但可能只是在常规 PPO 循环期间周期性场/等离子体调制的影响，再加上通常存在于等离子体片中的次同向小尺度结构。因此，在土星赤道电流表的结构和动力学的 PPO 调制的现有知识中，可以理解白天和夜晚事件。