Evidence of nonlinear signatures in the solar wind proton density at the L1 Lagrange point

Context. The solar wind is a medium characterized by strong turbulence and significant field fluctuations on various scales. Recent observations have revealed that magnetic turbulence exhibits a self-similar behavior. Similarly, high-resolution measurements of the proton density have shown comparable characteristics, prompting several studies of the multifractal properties of these density fluctuations. Aims. This work aims to investigate whether low-resolution measurements of the solar wind proton density exhibit nonlinear and multifractal structures. We also aim to interpret these features within the framework of non-extensive statistical mechanics. Methods. We performed a systematic analysis of hourly resolution proton density data obtained from various spacecraft located at the Lagrange point L1, recorded over 17 years. We analyzed the multifractal nature of the fluctuations and tested for consistency with the q-triplet formalism from non-extensive statistical mechanics. Results. We find that low-resolution solar wind proton density data also display nonlinear and multifractal signatures. Our analysis provides a validation of the q-triplet predicted by non-extensive statistical theory. To the best of our knowledge, this represents the most rigorous and systematic validation to date of the q-triplet in the solar wind.