Alfvenic velocity spikes and rotational flows in the near-Sun solar wind
Alfvenic velocity spikes and rotational flows in the near-Sun solar wind
复制标题
DOI：
10.1038/s41586-019-1813-z
复制
发表时间：
2019-12-12
期刊：
影响因子：
64.8
通讯作者：
Schwadron, N. A.
中科院分区：
文献类型：
--
作者：
Kasper, J. C.;Bale, S. D.;Schwadron, N. A.
超音速太阳风的预测（1）首先被地球附近的航天器证实（2，3），后来被日心距离小到62个太阳半径的航天器证实（4）。这些任务表明，等离子体从日冕中出现时会加速，这得益于不明过程，这些过程将能量从太阳向外输送，然后将其沉积在风中。阿尔夫文波动是这样一个过程的一个有希望的候选者，因为它们在日冕和太阳风中被看到，并且包含相当大的能量（5-7）。磁张力迫使日冕与太阳共同旋转，但迄今为止报道的远离太阳的任何剩余旋转都远远小于相互作用的风流的波动和偏转的幅度。在这里，我们报告的观测太阳风等离子体的日心距离约35太阳半径（9-11），以及在距离流的相互作用变得重要。我们发现，阿尔芬波组织成结构化的速度尖峰的持续时间长达几分钟，这是与传播的S-样弯曲的磁场线。我们探测到围绕太阳的太阳风流速的旋转分量不断增加，峰值为每秒35至50公里，大大高于波的振幅。这些流动超过了每秒几公里的经典速度预测，挑战了日冕环流模型，并质疑我们对恒星如何失去角动量和随着年龄的增长而自旋下降的理解。
The prediction of a supersonic solar wind(1) was first confirmed by spacecraft near Earth(2,3) and later by spacecraft at heliocentric distances as small as 62 solar radii(4). These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvenic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy(5-7). Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams(8). Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii(9-11), well within the distance at which stream interactions become important. We find that Alfven waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second-considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age(12-14).