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Highly structured slow solar wind emerging from an equatorial coronal hole

机译：从赤道冠状孔涌出的高度结构化的缓慢太阳风

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During the solar minimum, when the Sun is at its least active, the solar wind(1,2) is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvenic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind(3) of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain(4); theories and observations suggest that they may originate at the tips of helmet streamers(5,6), from interchange reconnection near coronal hole boundaries(7,8), or within coronal holes with highly diverging magnetic fields(9,10). The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfven-wave turbulence(11,12), heating by reconnection in nanoflares(13), ion cyclotron wave heating(14) and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe(15) at 36 to 54 solar radii that show evidence of slow Alfvenic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities(10,16) that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind.
机译：在太阳最低峰期间，当太阳处于最低活动状态时，在高纬度观测到的太阳风（1,2）主要是快速的（每秒超过500公里），是高度Alfvenic稀疏的等离子体流，来自深处冠状孔。靠近黄道平面时，太阳风散布着变化不大的慢风（3），风速小于每秒500公里。慢风流的确切来源尚不确定（4）；理论和观察表明，它们可能起源于头盔彩带的尖端（5,6），来自冠状孔边界（7,8）附近或具有高度发散磁场的冠状孔内的互换重连接（9,10）。尽管可能的候选机制包括Alfven波湍流（11,12），纳米喇叭口中的重新连接加热（13），离子回旋波加热（14）以及通过热梯度加速1，但仍未解决驱动太阳风所需的加热机制。在一个天文单位的距离处，风混合并放出，因此这些源和过程的许多诊断结构已经丢失。在这里，我们从帕克太阳探测器（15）的太阳半径为36到54处观察到，这表明从小赤道日冕孔涌现出缓慢的Alfvenic太阳风。测得的磁场表现出大的，间歇性的反转，这些反转与等离子流和增强的Poynting通量有关，并散布在更平滑且湍流较小的近径向磁场中。此外，等离子波测量表明存在与等离子体加热和热化过程相关的电子和离子速度空间微不稳定性（10,16）。我们的测量结果表明，太阳风的激发有一种冲动机制，微观不稳定性在加热中起作用，我们提供的证据表明低纬度的日冕气孔是缓慢的太阳风的关键来源。

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