通过二维数据同化表面通量传输和三维发电机模型的对比研究约束太阳表面磁场的径向衰减时间尺度
Constraining the radial decay timescale of solar surface magnetic field through a comparative study of data-assimilative 2D surface flux transport and 3D dynamo models
浏览论文内容
中文总结 AI 辅助
该研究通过对比二维表面通量传输模型和三维发电机模型，对太阳表面磁场径向衰减时间尺度进行自洽估计，经数据同化模拟及参数选择，得出使两模型表面动力学一致的$\tau$值，并发现其对不同角模式的影响。
中文摘要 AI 辅助
极向磁场是预测太阳活动周期振幅最可靠的先兆，二维表面通量传输（SFT）模型被广泛用于重构其演化。传统二维SFT模型无法捕捉表面场的表面-内部耦合，导致极向场反转延迟，通常通过添加衰减项$-B_r/\tau$来校正，但径向衰减时间尺度$\tau$约束不佳。本文通过对比二维SFT模型和三维运动发电机模型STABLE中的径向通量传输，对$\tau$进行自洽估计。保持两模型传输参数相同并假设表面-内部耦合为扩散性，极向场演化方程简化为特征值问题，得出$\tau$随角模式$l$增加而减小的谱。为捕捉现实的表面-内部耦合，进一步用真实磁图进行数据同化二维SFT模拟，并与数据同化三维STABLE模型结果比较以约束$\tau$和有效衰减模式。选择传输参数后，$\tau = 2$年使两模型表面动力学一致，此时间尺度对应自洽估计中的角模式$l = 8$。还用仅以大规模活动区为源的二维SFT模拟，发现$\tau = 7$年能准确捕捉偶极模式（$l = 1$）的径向衰减并消除极向场的长期漂移。
英文摘要
The polar magnetic field is the most reliable precursor for predicting the amplitude of the solar cycle, and the 2D surface flux transport (SFT) model is widely used to reconstruct its evolution. Traditional 2D SFT models can not capture the surface-interior coupling of the surface field, causing delays in polar field reversals. This deficiency is conventionally corrected by adding a decay term $-B_r/τ$ with a poorly constrained radial decay timescale $τ$. Here, we present a self-consistent estimate of $τ$ through a comparative study of radial flux transport in the 2D SFT model and the 3D kinematic dynamo model, STABLE. By keeping the same transport parameters for both models and assuming surface-interior coupling is diffusive, the poloidal field evolution equation reduces to an eigenvalue problem, which yields a spectrum of $τ$ that decrease with increasing angular modes $l$. To capture realistic surface-interior coupling, we further perform data-assimilated 2D SFT simulations with real magnetograms and compare those results with that of the data-assimilated 3D STABLE model to constrain $τ$ and effective decay modes. With our choice of transport parameters, a value of $τ=~2~\text{yr}$ keeps the surface dynamics of the two models consistent, and this timescale corresponds to the angular mode $l=8$ from our self-consistent estimate. We also perform 2D SFT simulations with only large-scale active regions, as the source. We find that $τ=7~\text{yr}$ accurately captures the radial decay of the dipole mode ($l=1$) and removes the secular drift in the polar fields.
