Driving dynamical inner-heliosphere models with in-situ solar-wind observations

Reconstruction of inner-heliosphere conditions is typically a three-step process. 1, the photospheric magnetic field is used to constrain a coronal model, which provides an estimate of the steady-state solar-wind at 0.1 AU; 2, coronagraph observations of Coronal Mass Ejections (CMEs) are used to characterise transient solar-wind disturbances at 0.1 AU; 3, a solar wind model propagates these structures out to Earth. A major limitation of this process is the accuracy of the ambient solar-wind estimate at 0.1 AU, which introduces significant uncertainty into reconstruction of the inner-heliosphere solar wind. Here, we demonstrate how an accurate estimate of the ambient solar wind at 0.1 AU can instead be produced from in-situ solar wind observations out at 1 AU. Using the fast CMEs (~1,500 km/s) in May 2024 as an example, we show that this process can accurately reproduce the solar-wind conditions at Earth and at Solar Orbiter, which was on the far side of the Sun. Solar-wind speed errors are reduced by more than 50% for this interval, though we stress that this is a reconstruction that has access to observations that would not be available to a genuine forecast. However, it is hoped that more accurate reconstructions of the ambient solar wind will lead to a better understanding of the properties of CMEs near the Sun and their subsequent propagation to Earth and other solar-system bodies.