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arXiv 2402.02486astro-ph.SR
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空间分辨率对太阳开放磁通量估计的影响

Spatial resolution effects on the solar open flux estimates

Ivan Milic, Rebecca Centeno, Xudong Sun, Matthias Rempel, Jaime de la Cruz Rodriguez

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To be published in A&A
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AI总结：

本研究通过端到端模拟与反演，发现望远镜空间分辨率降低会显著低估太阳开放磁通量，即使完全分辨时仍因光球表面波纹存在偏差，这对太阳活动周期建模有重要影响。

摘要：

用于推断太阳磁场的偏振光谱观测是在有限空间分辨率下获得的。这种有限分辨率对观测区域开放磁通量推断的影响尚未得到广泛研究。我们旨在通过一项端到端研究来表征平均磁通密度推断中产生的偏差，该研究包括合成数据的生成、其解释（反演）以及结果与原始模型的比较。我们基于最先进的太阳光球数值模拟，合成了中性铁在630纳米附近两条磁敏感谱线的偏振光谱。随后，我们进行了数据退化处理，以模拟有限角分辨率望远镜的影响，并使用米尔恩-埃丁顿偏振光谱反演代码对数据进行了解释（反演）。然后我们研究了推断参数对望远镜分辨率的依赖性。结果表明，随着望远镜分辨率的降低，平均磁通密度——与盘心观测到的开放磁通量相关——显著下降。原始净磁场通量被1米望远镜完全分辨，但20厘米孔径望远镜得到的结果小30%。即使在完全分辨的情况下，由于光球表面的波纹状结构，结果仍然存在偏差。当磁结构未被分辨时，即使是空间平均量，如观测区域的开放磁通量，也会被低估。其原因在于磁场推断过程中存在非线性。这种效应可能对大规模太阳磁场的建模产生影响；例如，与日冕洞或极区磁场相对应的那些，这些对于我们理解太阳活动周期具有重要意义。

英文摘要：

Spectropolarimetric observations used to infer the solar magnetic fields are obtained with a limited spatial resolution. The effects of this limited resolution on the inference of the open flux over the observed region have not been extensively studied. We aim to characterize the biases that arise in the inference of the mean flux density by performing an end-to-end study that involves the generation of synthetic data, its interpretation (inversion), and a comparison of the results with the original model. We synthesized polarized spectra of the two magnetically sensitive lines of neutral iron around 630\,nm from a state-of-the-art numerical simulation of the solar photosphere. We then performed data degradation to simulate the effect of the telescope with a limited angular resolution and interpreted (inverted) the data using a Milne-Eddington spectropolarimetric inversion code. We then studied the dependence of the inferred parameters on the telescope resolution. The results show a significant decrease in the mean magnetic flux density -- related to the open flux observed at the disk center -- with decreasing telescope resolution. The original net magnetic field flux is fully resolved by a 1m telescope, but a 20\,cm aperture telescope yields a 30\% smaller value. Even in the fully resolved case, the result is still biased due to the corrugation of the photospheric surface. Even the spatially averaged quantities, such as the open magnetic flux in the observed region, are underestimated when the magnetic structures are unresolved. The reason for this is the presence of nonlinearities in the magnetic field inference process. This effect might have implications for the modeling of large-scale solar magnetic fields; for example, those corresponding to the coronal holes, or the polar magnetic fields, which are relevant to our understanding of the solar cycle.

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