A Parametric Study to Constrain Empirically-based Models of the Ambient Solar Wind

Current empirically-based models, driven by various features of the coronal magnetic field often perform relatively well, (1) in the absence of obvious transient phenomena, and (2) when the ambient solar configuration remains relatively stable over several or more rotations. However, even under these conditions, the models can sometimes fail dramatically. Currently, there are three primary techniques for predicting, in particular, solar wind speed at 1 AU based on synoptic maps of the photospheric magnetic field. The original Wang-Sheeley (WS) model uses an observed negative correlation between solar wind speed and the expansion factor of the solar magnetic field. The Predictive Science “Distance from the Coronal Hole Boundary” (DCHB) model specifies speed in the photosphere based on the perpendicular distance from the coronal hole boundary and maps this speed out to 30 solar radii. And finally, the Wang-Sheeley-Arge (WSA) model combines the WS and DCHB prescriptions. In this study, we compare these three approaches for a set of carefully chosen Carrington rotations. For each, we ran a suite of solutions using a range of input parameters. We also generated solutions driven by synoptic magnetograms from different observatories, since we have found that they can significantly affect the resultant solutions. To directly compare the model solutions with 1 AU in situ measurements at ACE, Wind, STEREO A and B, and assess the potential impact of modeling stream evolution, we used two global heliospheric models (Enlil and MAS). We also employed an alternative and potentially more revealing approach of dynamically mapping the in situ measurements back to a reference surface at 30 solar radii and comparing them with the model maps.