Abstract The interplanetary magnetic field (IMF) measured near Earth can be up to 2 times greater than that derived from models using remote solar observations. We investigate this discrepancy by modeling the IMF using a potential field source surface (PFSS) model using synoptic maps of the photospheric magnetic field from 2010 May to 2024 April. Five types of radial field synoptic maps are used in this work: the B r synoptic maps from vector magnetic field data, the M r synoptic maps from the line-of-sight field data, the rescaled M r synoptic maps rescaled from the M r maps by a center-to-limb distance dependent rescaling factor of B r / M r , and composite and rescaled composite synoptic maps comprised of a combination of strong-field pixels from the B r maps and the rest from either the original M r or rescaled M r maps. The modeled IMFs from all five types of synoptic maps agree with each other well in the solar maximum phase, when they are about 2 times smaller than in situ measurements. The IMF calculated from the B r and both composite and rescaled composite synoptic maps match well with in situ observations during solar minimum from 2017 to 2022. The IMF values modeled from both the M r and rescaled M r synoptic maps are still significantly smaller in this time interval. This suggests that (1) the B r maps represent the radial field better than the M r ; and (2) the PFSS model is appropriate to model the heliospheric magnetic field in solar minimum, but has limitations when used near solar maximum.
Liu et al. (Tue,) studied this question.