Solar activity and space weather: challenges to geodesy

Abstract Solar activity presents a critical, modern threat to Geodesy, a discipline dependent on dedicated missions data and high-precision global navigation satellite system. This paper reviews key solar phenomena, as flares, coronal mass ejections, and high-speed solar wind streams, that perturb the near-Earth space environment. We analyze the resulting degradation across two key areas: satellite orbits and signal quality. First, very low and low Earth orbit satellites suffer significant orbital perturbations due to variable drag caused by fluctuations in solar radiation pressure and substantial solar ultraviolet and extreme-ultraviolet driven enhancements in thermospheric density. These effects are also relevant for high-precision geodetic missions operating far from Earth. Second, the integrity of the global navigation satellite system signal itself is compromised by ionospheric disturbances that induce scintillation, leading to severe positioning inaccuracies (signal loss, cycle slips), which are intolerable for millimeter-level geodetic applications. Ultimately, this work emphasizes the critical importance of utilizing observational data to capture solar activity. Sophisticated modeling of these complex, multi-scale solar effects is essential for ensuring the continued reliability and precision of modern geodetic solutions.