2:00 PM - 2:15 PM
[PEM16-02] Long-term behavior and optimization of the source-surface radius in the potential-field source-surface extrapolation
Keywords:solar magnetic field, open magnetic flux, space weather
The PFSS (Potential Field Source Surface) method is a magnetic field extrapolation technique that assumes the magnetic field is potential up to a fixed distance from the solar center (source surface radius: Rss) and that all magnetic field lines open into interplanetary space beyond this point (r > Rss). The sole free parameter in the PFSS method, the source-surface radius (Rss), is commonly fixed at 2.5 solar radius, but previous studies suggest that its optimal value varies depending on solar activity. However, there is no consensus on how Rss should be adjusted. Some studies (Arden et al. 2014, Benavitz et al. 2024) argue that Rss should be relatively lower during solar maximum, while others (Huang et al. 2024) suggest that it should be reduced during solar minimum instead. These discrepancies arise from differences in (1) the magnetograms used as input for the PFSS method, (2) the analysis period, and (3) the reference model for validation. Therefore, to determine the optimal Rss, it is necessary to use a variety of magnetograms, extend the analysis period as much as possible, and ensure consistent validation criteria.
In this study, we aim to derive the optimal Rss and its scaling law using multiple magnetograms (KPVT, SOLIS/VSM, GONG, HMI, and their ADAPT realizations). By calculating the open flux from interplanetary magnetic field (IMF) observations near Earth and comparing it with the PFSS-derived open flux, we estimated the optimal Rss and investigated its dependence on solar activity and magnetic field parameters. Our results indicate that Rss increases during both solar maximum and minimum. This can be interpreted as follows: during solar maximum, the stronger magnetic field is less easily advected by the solar wind, while during solar minimum, the dipolar nature of the field allows it to maintain strength over larger spatial scales. Furthermore, we find that Rss can be fitted as a function of coronal magnetic field strength and dipole field strength. These findings suggest that Rss can be optimized based on observational data, potentially improving the space weather forecasting.
In this study, we aim to derive the optimal Rss and its scaling law using multiple magnetograms (KPVT, SOLIS/VSM, GONG, HMI, and their ADAPT realizations). By calculating the open flux from interplanetary magnetic field (IMF) observations near Earth and comparing it with the PFSS-derived open flux, we estimated the optimal Rss and investigated its dependence on solar activity and magnetic field parameters. Our results indicate that Rss increases during both solar maximum and minimum. This can be interpreted as follows: during solar maximum, the stronger magnetic field is less easily advected by the solar wind, while during solar minimum, the dipolar nature of the field allows it to maintain strength over larger spatial scales. Furthermore, we find that Rss can be fitted as a function of coronal magnetic field strength and dipole field strength. These findings suggest that Rss can be optimized based on observational data, potentially improving the space weather forecasting.