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

This work analyses polar cap ionospheric variability and predictive modelling using EISCAT Svalbard Radar (ESR) data from March 2007 to February 2008 during solar minimum. Over four million ESR measurements were combined with ionosonde observations and space weather indices to characterize high-latitude dynamics and assess polar cap foF2 forecasting ability. Under quiet conditions, foF2 shows strong diurnal and seasonal modulation reflecting extreme polar illumination cycles. Geomagnetic disturbances produce systematic altitude-dependent responses including F-region density depletion, enhanced ion temperatures, and storm-time flow variations. Cross-correlation analysis revealed rapid thermal responses (<1 h) and delayed density recoveries (12–48 h) at different coupling timescales. Multi-instrument validation showed moderate ESR–ionosonde correlation with systematic bias, which is the first year-long uncertainty assessment of polar cap foF2 variability with space weather indices. Agreement was highest in spring/autumn and degraded under disturbed conditions. Predictive modelling showed empirical models failed to provide reliable forecasts, while a physics-informed model incorporating persistence, lagged geomagnetic drivers, and convection effects achieved robust short-term skill (R² ≈ 0.73, r ≈ 0.88). Operational assessment demonstrated excellent nowcasting skill (0–2 h) and reliable short-term forecasts (2–6 h). These results extend previous high-latitude studies to become the first year-long systematic characterization of polar cap ESR response, storm-time lags, and predictive limits. This work provides key benchmarks for high-latitude ionospheric modelling, demonstrates physics-informed approach value, and highlights opportunities and constraints for operational space weather forecasting in polar regions.