Estimating uncertainties in the back-mapping of the fast solar wind

Abstract

Solar wind back-mapping is a combination of ballistic mapping and magnetic mapping. By examining the different model ingredients that can affect the derived back-mapped position, we aim to provide a more precise estimate of the source location and a measure of confidence in the mapping procedure. This can be used to improve the connection of remote sensing with in situ measurements. For the ballistic mapping we created custom velocity profiles. These profiles are constrained by observations of the fast solar wind close to the Sun and are used to examine the mapping uncertainty. The coronal magnetic field topology from the solar surface up to the source surface is modeled with a PFSS extrapolation. The sensitivity of the extrapolated field is examined by adding noise to the input magnetogram and performing a Monte Carlo simulation, where for multiple noise realizations we calculate the source position of the solar wind. Next, the effect of free parameters, like the height of the source surface, is examined and statistical estimates are derived. We used Gaussian Mixture clustering to group the back-mapped points, due to different sources of uncertainty, and provide a confidence area for the source location of the solar wind. Furthermore, we computed a number of metrics to evaluate the back-mapping results and assessed their statistical significance by examining 3 high speed stream events. Lastly, we explored the effect of corotation, close to the Sun, on the source region of the solar wind. Our results show that the height of the source surface produces the largest uncertainty in the source region of the fast solar wind, followed by the choice of the velocity profile and the noise in the input magnetogram. Additionally, we display the ability to derive a confidence area on the solar surface that represents the potential source region of the in-situ measured fast solar wind.