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arXiv 2007.16168astro-ph.SR
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磁膨胀因子与日冕伪流观测到的太阳风速度的关系

On the Relationship between Magnetic Expansion Factor and Observed Speed of the Solar Wind from Coronal Pseudostreamers

Samantha Wallace, Charles N. Arge, Nicholeen M. Viall, Ylva Pihlstrom

备注：
18 pages, 7 figures, 2 tables, appendix with 3 additional tables
发表信息：
Published in 2020, The Astrophysical Journal, Volume 898, Number 1
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摘要：

在过去的30多年里，磁膨胀因子（$f_s$）已被用于经验关系，以预测1 AU处的太阳风速度（$v_{obs}$），基于这两个量之间的反比关系。日冕单极拖缆（即伪拖缆）经历有限的场线扩展，导致$f_s$依赖关系，以预测与这些结构相关的快风。然而，案例研究表明，在现场观察到的伪流光太阳风比$f_s$派生慢得多。为了进一步研究这一点，我们进行了统计分析，以确定是否$f_s$和$v_{obs}$是负相关的一个大样本的时期，在多个1天文单位的航天器（即ACE，STEREO-A/B）观察到伪流光风。我们使用Wang-Sheeley-Arge（WSA）模型驱动的空军数据同化光球通量传输（ADAPT）光球场地图，以确定38个时期，当航天器观察伪流光风。我们比较了膨胀因子的最后一个开放的领域线的任何一方的pseudostreamer尖点与相应的现场测量的太阳风速度。我们发现只有慢风（$v_{obs}$ $<$ 500 km/s）与伪流有关，并且对于这些场线，$f_s$和$v_{obs}$之间没有显著的相关性。这表明，伪流光的开-闭边界附近的磁力线不受沿$f_s$ - $v_{obs}$关系中假设的连续开放通量管的稳态加速度的影响。一般来说，在开放和封闭的场线之间的边界处的动力学，如交换重联，将使这种关系的稳态假设无效。

英文摘要：

For the past 30+ years, the magnetic expansion factor ($f_s$) has been used in empirical relationships to predict solar wind speed ($v_{obs}$) at 1 AU, based on an inverse relationship between these two quantities. Coronal unipolar streamers (i.e. pseudostreamers) undergo limited field line expansion, resulting in $f_s$-dependent relationships to predict fast wind associated with these structures. However, case studies have shown that in situ observed pseudostreamer solar wind was much slower than that derived with $f_s$. To investigate this further, we conduct a statistical analysis to determine if $f_s$ and $v_{obs}$ are inversely correlated for a large sample of periods when pseudostreamer wind was observed at multiple 1 AU spacecraft (i.e. ACE, STEREO-A/B). We use the Wang-Sheeley-Arge (WSA) model driven by Air Force Data Assimilative Photospheric Flux Transport (ADAPT) photospheric field maps to identify 38 periods when spacecraft observe pseudostreamer wind. We compare the expansion factor of the last open field lines on either side of a pseudostreamer cusp with the corresponding in situ measured solar wind speed. We find only slow wind ($v_{obs}$ $<$ 500 km/s) is associated with pseudostreamers, and that there is not a significant correlation between $f_s$ and $v_{obs}$ for these field lines. This suggests that field lines near the open-closed boundary of pseudostreamers are not subject to the steady-state acceleration along continuously open flux tubes assumed in the $f_s$-$v_{obs}$ relationship. In general, dynamics at the boundary between open and closed field lines such as interchange reconnection will invalidate the steady-state assumptions of this relationship.

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