Uncertainty in L1 Measurements and its Effect on Geomagnetic Response

Solar wind measurements at the L1 Lagrange point provide an uncertain estimate of the electromagnetic and plasma parameters driving the magnetosphere, as these measurements are taken far from the critical magnetopause reconnection site. This uncertainty leads to underestimating the Earth's response to extreme space weather. Previous research has observed that with increasing solar wind strength, Earth's response appears to saturate, rather than scale proportionally. Over the past four decades, numerous theoretical explanations for this saturation effect have been proposed. However, we explain how this phenomenon might be a misinterpretation arising from unaccounted uncertainty in measurements of the solar wind that impact the magnetosphere. Estimating these uncertainties and correcting for them is crucial to advancing our field. In particular, it will enhance our understanding of solar wind–magnetosphere coupling, improve global magnetospheric simulations, and refine space weather forecasting. Moreover, we demonstrate that this issue has broader implications for any correlation studies: random measurement errors can cause a system's linear response to be perceived as non-linear. In the coming decade, the advent of novel multi-spacecraft missions will play a pivotal role in addressing these uncertainties by systematically filling critical gaps in our understanding, enabling more accurate interpretations and predictions of the geospace environment.