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Plasma Heating and Flow in an Auroral Arc

机译:极光弧中的等离子体加热和流动

摘要

We report direct observations of the three-dimensional velocity distribution of selected topside ionospheric ion species in an auroral context between 500 and 550 km altitude. We find heating transverse to the local magnetic field in the core plasma, with significant heating of 0(+), He(+), and H(+), as well as tail heating events that occur independently of the core heating. The 0(+) velocity distribution departs from bi-Maxwellian, at one point exhibiting an apparent ring-like shape. However, these observations are shown to be aliased within the auroral arc by temporal variations that arc not well-resolved by the core plasma instrument. The dc electric field measurements reveal superthermal plasma drifts that are consistent with passage of the payload through a series of vortex structures or a larger scale circularly polarized hydromagnetic wave structure within the auroral arc. The dc electric field also shows that impulsive solitary structures, with a frequency spectrum in the ion cyclotron frequency range, occur in close correlation with the tail heating events. The drift and core heating observations lend support to the idea that core ion heating is driven at low altitudes by rapid convective motions imposed by the magnetosphere. Plasma wave emissions at ion frequencies and parallel heating of the low-energy electron plasma are observed in conjunction with this auroral form; however, the conditions are much more complex than those typically invoked in previous theoretical treatments of superthermal frictional heating. The observed ion heating within the arc clearly exceeds that expected from frictional heating for the light ion species H(+) and He(+), and the core distributions also contain hot transverse tails, indicating an anomalous transverse heat source.
机译:我们报告了在500至550 km高度的极光环境中选定的顶侧电离层离子物种的三维速度分布的直接观察。我们发现横向于核心等离子体中局部磁场的加热,具有显着的0(+),He(+)和H(+)加热,以及尾部加热事件,这些事件独立于核心加热而发生。 0(+)速度分布偏离bi-Maxwellian,在某一点上表现出明显的环形形状。但是,这些观测结果显示,由于核心等离子仪器无法很好解决的时间变化,在极光弧内造成了混淆。直流电场测量揭示了超高温等离子体漂移,该漂移与有效负载通过极光弧内的一系列涡旋结构或较大规模的圆极化水电磁波结构相一致。直流电场还表明,脉冲孤子结构的频谱在离子回旋加速器频率范围内,与尾部加热事件密切相关。漂移和岩心加热的观测结果支持了这样一个想法,即岩心离子加热是由磁层施加的快速对流运动在低空驱动的。结合这种极光形式,可以观察到在离子频率下的等离子体波发射和低能电子等离子体的平行加热。但是,该条件比以前的超热摩擦加热理论处理中通常调用的条件复杂得多。电弧内观察到的离子加热明显超过了轻离子物质H(+)和He(+)的摩擦加热所预期的范围,并且芯分布还包含热的横向尾部,表明横向热源异常。

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