Ionospheric response characterization during geomagnetic disturbances: EISCAT Svalbard Radar analysis (2007)

Polar-cap ionospheric variability and foF2 predictability are characterized using 12 months of EISCAT Svalbard Radar (ESR) data during the 2007–2008 solar minimum. Over four million altitude-resolved measurements were analyzed to establish a baseline and quantify storm responses. Quiet-time foF2 exhibits strong solar-driven modulation (~ 1.4–2.8 MHz). Geomagnetic disturbances cause systematic F2-region depletions (~ 39%) and rapid E-region heating. Cross-comparison against the Tromsø Dynasonde reveals a systematic bias of approx. − 1.7 MHz and weak correlation (r=0.27), physically attributable to the ~ 950 km separation between the polar cap and auroral oval. Empirical models based solely on indices (Kp, AE) failed (R 2 < 0), whereas a physics-informed Ridge regression model incorporating persistence and lagged drivers achieved robust skill (R 2 =0.73) for 0–4 h forecasts. These results establish a solar-minimum benchmark, demonstrating that short-term persistence dominates predictability in the polar cap.