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 (ref. ¹). Moreover, longitudinal flows called torsional oscillations closely shadow sunspot migration, undoubtedly sharing a common cause². 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^3,4. Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the magneto-rotational instability^5,6, prominent in accretion-disk theory and observed in laboratory experiments⁷. 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 models⁸ 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 amplitudes⁹. State-of-the-art numerical simulations corroborate these estimates and reproduce hemispherical magnetic current helicity laws¹⁰. 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.

太阳的磁发电机周期具有独特的模式：太阳黑子出现的传播区域出现在纬度 30° 附近，每 11 年在赤道附近消失（参考文献 ¹ ）。此外，称为扭转振荡的纵向流密切影响太阳黑子的迁移，无疑具有共同的原因 ² 。与暗示这些现象的深层起源的理论相反，日震学将低纬度扭转振荡精确定位到太阳外部 5-10%，即近地表剪切层 ^3,4 。在该区域内，向内增加的差动旋转与极向磁场的结合强烈暗示了磁旋转不稳定性 ^5,6 ，这在吸积盘理论中很突出，并在实验室实验中观察到 ⁷ 。这两个事实共同提出了一个普遍问题：太阳发电机是否可能是近地表不稳定性。在这里，我们报告了强有力的肯定证据，与专注于更深层次速跃层的传统模型 ⁸ 形成鲜明对比。简单的分析估计表明，近地表磁旋转不稳定性更好地解释了扭转振荡的时空尺度和推断的地下磁场振幅 ⁹ 。最先进的数值模拟证实了这些估计并再现了半球磁流螺旋定律 ¹⁰ 。由一种众所周知的近地表现象产生的发电机改善了准确预测完整磁周期和空间天气的前景，影响地球的电磁基础设施。