The solar dynamo cycle, a process responsible for solar activity and magnetic fields in the Sun, is believed to be located deep inside the Sun, within the tachocline — a boundary between the outer convective and inner radiative zones. Recently Geoffrey Vasil and colleagues reported their results from state-of-the-art simulations, which support the idea of the solar dynamo originating near (the outer 5–10% of) the Sun’s surface. The underlying mechanism is that a magneto-rotational instability (MRI) operates in the near-surface shear layer (NSSL) and is responsible for driving the solar dynamo.

The authors are inspired by the idea of MRI of plasma flows in accretion disks and apply it to understand the solar dynamo. They solve the linearized anelastic magnetohydrodynamic equations for the physical environment of the NSSL to find the role of density stratification on the Alfvén velocities. The estimated Alfvén speed is within the range of the internal magnetic field that is necessary to drive the MRI. Dedalus code is used to model the initial phase of the solar cycle and as the cycle evolves the toroidal field undergoes several possible MHD instabilities (including MRI) contributing to poloidal-field regeneration. The overall analysis supports the existence of unstable modes leading to hemispherical magnetic current helicity laws and growth of the MRI.

太阳发电机周期是负责太阳活动和太阳磁场的过程，据信位于太阳深处的速跃层（外部对流区和内部辐射区之间的边界）内。最近，Geoffrey Vasil 及其同事报告了他们最先进的模拟结果，这些结果支持了太阳发电机起源于太阳表面（外部 5-10%）附近的想法。其根本机制是磁旋转不稳定性（MRI）在近地表剪切层（NSSL）中运行并负责驱动太阳发电机。

作者受到吸积盘中等离子体流 MRI 的启发，并将其应用于理解太阳发电机。他们求解了 NSSL 物理环境的线性滞弹性磁流体动力学方程，以找出密度分层对阿尔文速度的作用。估计的阿尔文速度在驱动 MRI 所需的内部磁场范围内。 Dedalus 代码用于模拟太阳周期的初始阶段，随着周期的发展，环形场会经历几种可能的 MHD 不稳定性（包括 MRI），从而导致极向场再生。总体分析支持不稳定模式的存在，导致半球磁流螺旋定律和 MRI 的增长。