论文标题
黑子中空间相关的波动对与磁扭转有关的指标的影响
Impact of spatially correlated fluctuations in sunspots on metrics related to magnetic twist
论文作者
论文摘要
黑子上方的磁场的扭曲是太阳能物理学中的重要数量。例如，磁扭转在耀斑和冠状质量弹出（CME）的启动中起作用。已经使用均匀扭曲的通量管模型发现了上方扭曲的各种代理，并根据单光球形磁力图常规计算。一类代理基于$α_z$，垂直电流与垂直磁场的比率。另一类代理基于所谓的扭曲密度$ Q $，该密度取决于方位角场与垂直场的比率。但是，这些代理对磁场的时间波动的敏感性尚未得到很好的表征。我们旨在确定扭曲代理对磁场中时间波动的敏感性，如SDO/HMI矢量磁场映射的时间序列所估计。为此，我们介绍了一个黑子模型，其峰值垂直字段在光电状态下为2370高斯，均匀的扭曲密度$ q = -0.024 $ mm $ $^{ - 1} $。我们添加了与SDO/HMI观测值一致的磁场的时间波动的实现，包括空间相关。使用蒙特 - 卡洛方法，我们确定不同代理对时间波动的鲁棒性。磁场的三个组件的时间波动与最高1.4毫米的空间分离相关（从点扩散函数比预期的要多）。蒙特 - 卡洛方法使我们能够证明磁场扭曲的几个代理在每个单个磁力图中都没有偏置。代理上关联的随机错误的标准偏差在$ 0.002 $和$ 0.006 $ mm $^{ - 1} $之间，该范围比平均值$ q $的平均值小约一个数量级。
The twist of the magnetic field above a sunspot is an important quantity in solar physics. For example, magnetic twist plays a role in the initiation of flares and coronal mass ejections (CMEs). Various proxies for the twist above the photosphere have been found using models of uniformly twisted flux tubes, and are routinely computed from single photospheric vector magnetograms. One class of proxies is based on $α_z$, the ratio of the vertical current to the vertical magnetic field. Another class of proxies is based on the so-called twist density, $q$, which depends on the ratio of the azimuthal field to the vertical field. However, the sensitivity of these proxies to temporal fluctuations of the magnetic field has not yet been well characterized. We aim to determine the sensitivity of twist proxies to temporal fluctuations in the magnetic field as estimated from time-series of SDO/HMI vector magnetic field maps. To this end, we introduce a model of a sunspot with a peak vertical field of 2370 Gauss at the photosphere and a uniform twist density $q= -0.024$ Mm$^{-1}$. We add realizations of the temporal fluctuations of the magnetic field that are consistent with SDO/HMI observations, including the spatial correlations. Using a Monte-Carlo approach, we determine the robustness of the different proxies to the temporal fluctuations. The temporal fluctuations of the three components of the magnetic field are correlated for spatial separations up to 1.4 Mm (more than expected from the point spread function alone). The Monte-Carlo approach enables us to demonstrate that several proxies for the twist of the magnetic field are not biased in each of the individual magnetograms. The associated random errors on the proxies have standard deviations in the range between $0.002$ and $0.006$ Mm$^{-1}$, which is smaller by approximately one order of magnitude than the mean value of $q$.
