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arXiv 2604.04034astro-ph.SR
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不同双极近似方法对太阳表面磁场模拟的影响

Effects of Various Bipolar Approximations of Active Regions on Solar Surface Magnetic Field Simulations

School of Space and Earth Sciences, Beihang University（北京航空航天大学空间与地球科学学院）；Key Laboratory of Space Environment Monitoring and Information Processing of MIIT（工业和信息化部空间环境监测与信息处理重点实验室）

Yukun Luo, Jie Jiang, Ruihui Wang

备注：
11 pages, 6 figures, accepted for publication in ApJ
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AI总结：

本文研究了不同双极近似方法对太阳表面磁场模拟的影响，发现对称双极区域近似会系统性高估太阳活动极小期轴向偶极子强度，而形态不对称双极区域近似则与极性大小比密切相关。

摘要：

太阳表面磁场的演变对于理解太阳活动和其下动态过程至关重要。表面磁通输运（SFT）模型是用于模拟这一演变的广泛使用的有效工具。活跃区域被作为SFT模型的磁通源，但其配置通常被简化为对称或不对称双极磁区域（BMRs）。本文旨在定量和系统地评估此类磁通源近似对SFT结果的影响，并利用我们最近开发的SFT代码探索改进的近似方法。通过比较包含从太阳第23个周期到当前第25个周期的现实活跃区域配置的模拟，我们显示将活跃区域近似为对称BMRs会导致太阳极小期轴向偶极子强度的系统性高估。这一结果通过代数量化方法独立验证，该方法评估了单个活跃区域的轴向偶极子贡献。通过单调减少近似BMRs的大小可以部分减轻高估，但无法完全消除。当活跃区域被表示为形态不对称的BMRs时，模拟的轴向偶极子强度表现出与后极性和前极性大小比之间强且近似线性的负相关性。基于这些结果，我们提出了一种BMR大小和极性大小比的组合，使轴向偶极子演变与完全包含现实活跃区域配置所获得的结果相当。本研究为未来使用近似BMRs进行模拟提供了新的定量约束。

英文摘要：

The evolution of solar surface magnetic fields is essential for understanding solar activity and the underlying dynamic process. The surface flux transport (SFT) model is a widely used and effective tool for simulating this evolution. Active regions are incorporated as magnetic flux sources of the SFT model, but their configurations are usually simplified as symmetric or asymmetric bipolar magnetic regions (BMRs). Here, we aim to quantitatively and systematically assess how such flux source approximations affect SFT results and explore improved approximation methods using our recently developed SFT code. By comparing simulations that incorporate realistic active region configurations from solar cycle 23 through the ongoing cycle 25, we show that approximating active regions as symmetric BMRs leads to a systematic overestimation of the axial dipole strength at solar minimum. This result is independently confirmed using an algebraic quantification that evaluates the axial dipole contribution of individual active regions. The overestimation can be partially reduced by monotonically decreasing the size of the approximated BMRs, but it cannot be fully eliminated. When active regions are instead represented by morphologically asymmetric BMRs, the simulated axial dipole strength exhibits a strong and nearly linear negative dependence on the size ratio between the following and leading polarities. Based on these results, we propose a combination of BMR size and polarity size ratio that yields an axial dipole evolution comparable to that obtained with fully incorporated realistic active region configurations. This study provides a new quantitative constraint for improving future simulations with approximated BMRs.

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