Authors: Nikolett Biro (University of Michigan), Andrea Opitz (HUN-REN Wigner RCP), Zoltan Nemeth (HUN-REN Wigner RCP), Akos Madar (HUN-REN Wigner RCP), Aniko Timar (HUN-REN Wigner RCP), Gergely Koban (University of Michigan)

The aim of this work is to determine the spatial variations in the background solar wind through multi-spacecraft data analysis, including recent missions, such as Parker Solar Probe and Solar Orbiter. By using ballistic propagation, we adjust for the radial and longitudinal time-lags between the different spacecraft, then compare their solar wind bulk velocity measurements. As an addition, we take into account the differential rotation of the Sun, and determine it to only have a small impact with spacecraft relatively close to the ecliptic plane. A statistical analysis is performed to evaluate propagation accuracy. In a case study, the effect of the latitudinal spacecraft separation on the observations is further investigated and backmapped to coronagraph imagery. As expected, propagated and in situ observed data deviate more at larger latitudinal spacecraft separations. We find that at latitudinal separations larger than four degrees this deviation starts to be important, so solar wind prediction accuracy decreases. These results will be useful for further analysis of inner heliospheric structures, for the improvement of propagation models, as well as to support the analysis of out-of-ecliptic solar wind observations.