2023-06-07 カリフォルニア大学バークレー校(UCB)
◆研究チームは、高エネルギー粒子のストリームを検出し、これが超顆粒流と一致することを報告しました。これは、いわゆる「高速」太陽風の起源であることを示唆しています。太陽風の起源を理解することは、地球の衛星や電力網に被害をもたらす可能性のある太陽嵐を予測するのに役立ちます。
＜関連情報＞
- https://news.berkeley.edu/2023/06/07/parker-solar-probe-flies-into-the-fast-solar-wind-and-finds-its-source/
- https://www.nature.com/articles/s41586-023-05955-3
コロナホール内の高速太陽風の発生源としての交流再接続 Interchange reconnection as the source of the fast solar wind within coronal holes
S. D. Bale,J. F. Drake,M. D. McManus,M. I. Desai,S. T. Badman,D. E. Larson,M. Swisdak,T. S. Horbury,N. E. Raouafi,T. Phan,M. Velli,D. J. McComas,C. M. S. Cohen,D. Mitchell,O. Panasenco & J. C. Kasper
Nature Published:07 June 2023
DOI:https://doi.org/10.1038/s41586-023-05955-3
Abstract
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 heating1,2 and interchange reconnection3,4,5. 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) spacecraft6 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’7,8 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.
