Physics Department, University of California, Berkeley, CA, USA.
Space Sciences Laboratory, University of California, Berkeley, CA, USA.
Nature. 2023 Jun;618(7964):252-256. doi: 10.1038/s41586-023-05955-3. Epub 2023 Jun 7.
The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called 'coronal holes'. The energy source responsible for accelerating the plasma is widely debated; however, there is evidence that it is ultimately magnetic in nature, with candidate mechanisms including wave heating and interchange reconnection. The coronal magnetic field near the solar surface is structured on scales associated with 'supergranulation' convection cells, whereby descending flows create intense fields. The energy density in these 'network' magnetic field bundles is a candidate energy source for the wind. Here we report measurements of fast solar wind streams from the Parker Solar Probe (PSP) spacecraft that provide strong evidence for the interchange reconnection mechanism. We show that the supergranulation structure at the coronal base remains imprinted in the near-Sun solar wind, resulting in asymmetric patches of magnetic 'switchbacks' and bursty wind streams with power-law-like energetic ion spectra to beyond 100 keV. Computer simulations of interchange reconnection support key features of the observations, including the ion spectra. Important characteristics of interchange reconnection in the low corona are inferred from the data, including that the reconnection is collisionless and that the energy release rate is sufficient to power the fast wind. In this scenario, magnetic reconnection is continuous and the wind is driven by both the resulting plasma pressure and the radial Alfvénic flow bursts.
填充日球层的高速太阳风起源于太阳上称为“冕洞”的开放磁场深处。负责加速等离子体的能源源广泛存在争议；然而，有证据表明它本质上是磁场，候选机制包括波加热和交换重联。日冕表面附近的磁场结构与“超米粒”对流单元有关，其中下降流产生强烈的磁场。这些“网络”磁场束中的能量密度是风的候选能量源。在这里，我们报告了帕克太阳探测器（PSP）航天器测量的高速太阳风流，这些测量结果为交换重联机制提供了有力证据。我们表明，日冕底部的超米粒结构仍然在近太阳太阳风中留下印记，导致磁“折返”的不对称斑块和突发的高速风流，具有幂律状的高能离子能谱，超过 100keV。交换重联的计算机模拟支持观测的关键特征，包括离子能谱。从数据中推断出低日冕中交换重联的重要特征，包括重联是无碰撞的，并且能量释放率足以为高速风提供动力。在这种情况下，磁重联是连续的，风由等离子体压力和径向阿尔芬波爆发产生的径向阿尔芬波驱动。
