Investigation of Source Surface Height Variations in EUHFORIA and Their Impact on Solar Wind Predictions

Solar wind modeling with the 3D MHD model EUHFORIA (EUropean Heliospheric FORecasting Information Asset; Pomoell & Poedts, 2018) revealed discrepancy with in situ observations by the Parker Solar Probe (PSP) at near-Sun distances . The default coronal model employed in EUHFORIA consists of the potential field source surface extrapolation (PFSS), Schatten current sheet (SCS) model and semi-empirical WSA model, which simulate the plasma and magnetic conditions at the inner boundary (0.1 AU). Parameters such as the PFSS source surface height (R_SS), which is the outer boundary of PFSS, and the inner boundary of SCS model influence the modelled coronal hole areas and the associated open flux areas. A default R_SS value of 2.6 R_⊙, as per McGregor et al. (2008), is used in EUHFORIA for solar wind simulations. Lowering the R_SS value has been reported to better capture coronal hole areas (Asvestari et al., 2019), improve the reconstruction of small-scale features (Badman et al., 2020), and more accurately reflect coronal magnetic field topologies during different phases of solar cycles (Lee et al., 2011; Arden et al., 2014).

In this parameter study we investigate the possible systematic effects of changing the outer boundary of the PFSS model and the inner boundary of the SCS model, while keeping default values for other parameters. The resulting solar wind simulations are compared to those obtained using all default parameters in the model, by evaluating their agreement with the in situ observations from PSP for its first ten perihelion encounters. Although we found improved modeling accuracy for several time intervals, first results do not show clear systematic improvements in the accuracy of the modeled solar wind.