Recurrent X-Class Flare Activity from NOAA Active Region 4366 and Its Weak Geoeffective Response: A Case Study of the Solar-Terrestrial Event (1–6 February 2026)

Abstract

Aims: To characterise the exceptionally dense sequence of X-class solar flares produced by NOAA Active Region 4366 and to examine why this energetic eruption sequence produced only a minor geomagnetic response at Earth. Study Design: A bulletin-based observational case study synthesising publicly issued space-weather reports. Place and Duration of Study: Data were compiled from bulletins issued by NOAA's Space Weather Prediction Center (SWPC), the Solar Influences Data Analysis Center (SIDC, Belgium), and NASA for the period 1–6 February 2026. Methodology: Flare timing, magnitude, and active-region attribution were drawn from operational SWPC and SIDC bulletins and NASA Solar Dynamics Observatory imagery. Geomagnetic storm classification was based on the SIDC’s real-time planetary Kp index and the Belgian local K-index (K_BEL). A reproducible data-source table and an X-class event chronology table are provided. Causal language has been aligned with the bulletin-based nature of the dataset. Results: AR 4366 produced six X-class flares, including an X8.1 event at 23:57 UT on 1 February 2026, which was among the strongest of Solar Cycle 25, together with 21 C-class and 38 M-class flares between 1 and 5 February 2026. Despite this activity, the associated magnetic cloud produced only a minor geomagnetic storm (planetary Kp = 5) on 4–5 February 2026, with no visible aurora reported from Belgium under the cited SIDC conditions. Conclusion: The observed mismatch between eruptive intensity and geoeffectiveness is consistent with the established understanding that CME propagation geometry and solar-wind/IMF coupling strongly influence the geomagnetic response rather than flare X-ray class alone. This finding underscores the continued need for coronagraphic CME tracking and upstream L1 solar-wind monitoring in operational space-weather forecasting.