Infrasound Newtonian Noise Estimation at the Einstein Telescope Candidate Site Sos Enattos
We investigate the seasonal variability of atmospheric infrasound and its contribution to Newtonian noise (NN) at the Sos Enattos site, a leading candidate location for the Einstein Telescope (ET). Infrasound data recorded at three stations -- SOE0 (surface), SOE1 ($-84$ m), and SOE3 ($-160$ m) -- are analyzed over multiple seasons to characterize both temporal variability and the depth dependence of the acoustic field. The amplitude spectral density (ASD) at 1 Hz exhibits a clear seasonal modulation, with winter levels exceeding summer values by 10--15 dB, primarily driven by variations in wind conditions. Using the measured pressure spectra, we estimate the corresponding NN contribution within a standard atmospheric coupling framework. At the surface station (SOE0), the median characteristic strain reaches $\sim 10^{-22}$ at 1 Hz, whereas at the deepest underground station (SOE3) it decreases to $\sim 10^{-27}$, corresponding to a suppression of approximately five orders of magnitude. Across all stations and environmental conditions, the inferred NN remains well below the ET-D design sensitivity curve in the 1--10 Hz frequency band. These results demonstrate the strong attenuation of infrasound-induced NN with depth and confirm that atmospheric infrasound does not constitute a limiting noise source for underground gravitational-wave detectors at this site.