Geomagnetic storm enhancement of Schumann resonance amplitude: a dose-response analysis using the Sierra Nevada ELF archive

I report a monotonic dose-response relationship between geomagnetic storm intensity and Schumann resonance (SR) amplitude using four years of continuous measurements from the Sierra Nevada ELF station (March 2013 through February 2017). Daily mean Mode 1 SR amplitude increases from 0.345 arbitrary units during geomagnetically quiet periods (Kp < 5) to 0.351 during moderate storms (Kp 5-6.7, +1.7%) and 0.366 during strong storms (Kp ≥ 7, +6.2%). The trend is statistically significant after correction for autocorrelation (Newey-West t = 4.09, p = 4.4 × 10− 5 ) and survives controls for seasonal variation (p = 1.8× 10− 5 ), global lightning activity (p = 6.2 × 10− 7 ), and solar radio flux. Both magnetic channels show the same amplitude enhancement, while the frequency shift is field-component dependent, carried by the north-south channel (Spearman ρ = 0.22, p < 10− 6 ) and absent in the east-west channel. The geomagnetic index and global lightning activity are nearly uncorrelated (ρ = −0.06), indicating a magnetospheric contribution to SR variability distinct from the tropospheric lightning source. The study period spans the maximum and declining phase of solar cycle 24, when geomagnetic storms are frequent. A self-contained reproduction script is provided.