Existence of the Closed Magnetic Field Lines Crossing the Coronal Hole Boundaries

Abstract

Coronal holes (CHs) are regions with unbalanced magnetic flux and have been associated with open magnetic field (OMF) structures. However, it has been reported that some CHs do not intersect with OMF regions. To investigate the inconsistency, we apply a potential-field (PF) model to construct the magnetic fields of the CHs. As a comparison, we also use a thermodynamic magnetohydrodynamic (MHD) model to synthesize coronal images and identify CHs from the synthetic images. The results from both the potential-field CHs and synthetic MHD CHs reveal that there is a significant percentage of closed field lines extending beyond the CH boundaries and more than 50% (17%) of PF (MHD) CHs do not contain OMF lines. The boundary-crossing field lines are more likely to be found in the lower latitudes during active times. While they tend to be located slightly closer than the non-boundary-crossing ones to the CH boundaries, nearly 40% (20%) of them in PF (MHD) CHs are not located in the boundary regions. The CHs without open field lines are often smaller and less unipolar than those with open field lines. The MHD model indicates higher temperature variations along the boundary-crossing field lines than the non-boundary-crossing ones. The main difference between the results of the two models is that the dominant field lines in the PF and MHD CHs are closed and open field lines, respectively.

Source Region of the Solar Wind: Statistics of the Doppler Velocities at the Chromosphere

“…On the one hand, more statistical samples are necessary because the properties of different CHs and their evolutionary stages may also differ (Heinemann et al 2018), such as the characteristics of magnetic flux balance (Heinemann et al 2019). On the other hand, statistical analysis of open field lines derived from the global coronal models, including potential field source surface (e.g., Stansby et al 2020), non-force-free field (e.g., Wang et al 2020), and magnetohydrodynamics, would also be meaningful, as open field regions are channels for solar wind streams, although some CH regions have not found corresponding open magnetic field structures from the magnetic field model (Huang et al 2022). It is also promising to combine magnetic field models and in situ measurements to explore the source regions of solar wind in future studies.…”