On the Differences in the Ambient Solar Wind Speed Forecasting Caused by Using Synoptic Maps from Different Observatories

We consider the problem of forecasting the solar wind speed using not only well-known magnetic field data sets, such as the Wilcox Solar Observatory (WSO) and the Global Oscillations Network Group (GONG) but others, such as the Infrared Magnetograph (IRmag) at the National Astronomical Observatory of Japan and the Solar Telescope for Operative Prediction (STOP) in Russia. We use these observations to study Carrington rotation (CR) 2164 (21 May – 17 June 2015). Our initial calculations are based on the Wang-Sheeley-Arge (WSA) model and include determining the coronal magnetic field using the potential field source surface (PFSS) approximation. The speed of the ambient solar wind near the Sun is calculated using an empirical equation that considers the flux tube expansion factor (FTEF) and the distance of the flux tube footpoint from the coronal hole boundary (DCHB) at the photospheric level. The solar wind bulk speed at the Earth’s orbit is calculated using the Heliospheric Upwind eXtrapolation (HUX) model. It is shown that the discrepancies in the speed values from four different data sets could reach ≈ 200 km s −1 , which is significant. We compare our predictions with in situ data from the Advance Composition Explorer (ACE) and demonstrate that a better coincidence between calculated and empirical results, accounting for the magnetic field strength in coronal holes, can be achieved.