近日，英国爱丁堡大学的Geoffrey M. Vasil及其研究团队取得一项新进展。经过不懈努力，他们证实太阳发电机在近地表开始运转。相关研究成果已于2024年5月22日在国际权威学术期刊《自然》上发表。

据悉，太阳的磁发电机周期展现出独特的模式：太阳黑子出现的传播区域多集中在纬度30°附近，随后每11年便在赤道附近消失。值得注意的是，与太阳黑子迁移紧密相关的纵向流动——即扭转振荡，它们无疑有着共同的成因。与某些关于这些现象深层起源的理论相悖，日震学研究精确地指出，低纬度的扭转振荡主要发生在太阳外层的5-10%范围内，即所谓的近地表剪切层。

这一区域内，向内逐渐增强的微分旋转与极向磁场的共同作用，强烈暗示了磁旋转不稳定性的存在。这种不稳定性在吸积盘理论中备受关注，也在实验室实验中得到了观察。因此，这两个事实共同引发了一个普遍问题：太阳发电机是否可能是由近地表的不稳定性所驱动的。

该研究团队获得了确凿的证据，与以往专注于更深速度界层的传统模型形成鲜明对比。通过简单的分析估算，近地表的磁旋转不稳定性有效地解释了扭转振荡的时空尺度以及推测的地下磁场振幅。最尖端的数值模拟进一步验证了这些估算，并成功复现了半球形磁流螺旋度定律。这一发现意味着发电机源自一个已被充分理解的近地表现象，为准确预测影响地球电磁基础设施的全磁周期和空间天气提供了更为乐观的前景。

附：英文原文

Title: The solar dynamo begins near the surface

Author: Vasil, Geoffrey M., Lecoanet, Daniel, Augustson, Kyle, Burns, Keaton J., Oishi, Jeffrey S., Brown, Benjamin P., Brummell, Nicholas, Julien, Keith

Issue&Volume: 2024-05-22

Abstract: The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating region of sunspot emergence appears around 30° latitude and vanishes near the equator every 11 years . Moreover, longitudinal flows called torsional oscillations closely shadow sunspot migration, undoubtedly sharing a common cause. Contrary to theories suggesting deep origins of these phenomena, helioseismology pinpoints low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface shear layer. Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the magneto-rotational instability, prominent in accretion-disk theory and observed in laboratory experiments. Together, these two facts prompt the general question: whether the solar dynamo is possibly a near-surface instability. Here we report strong affirmative evidence in stark contrast to traditional models focusing on the deeper tachocline. Simple analytic estimates show that the near-surface magneto-rotational instability better explains the spatiotemporal scales of the torsional oscillations and inferred subsurface magnetic field amplitudes. State-of-the-art numerical simulations corroborate these estimates and reproduce hemispherical magnetic current helicity laws. The dynamo resulting from a well-understood near-surface phenomenon improves prospects for accurate predictions of full magnetic cycles and space weather, affecting the electromagnetic infrastructure of Earth.

DOI: 10.1038/s41586-024-07315-1

Source: https://www.nature.com/articles/s41586-024-07315-1