Unexpected space weather causing the reentry of 38 Starlink satellites in February 2022

The accidental reentry of 38 Starlink satellites occurred in early February, 2022, associated with the occurrence of moderate magnetic storms. Poorly understood structure of coronal mass ejections (CMEs) caused the magnetic storms at unexpected timing. Better understanding of minor CME structures is therefore necessary for modern space weather forecast. The "up to 50%" enhancement of air drag force was observed at ~200 km altitude, preventing the satellites from their safety operations. Although the mass density enhancement predicted by the NRLMSIS2.0 empirical model is less than 25 % under the present moderate magnetic storms, the real-time GAIA simulation showed the mass density enhancement of up to 50%. Further, the GAIA simulation suggests that the actual thermospheric disturbances at 200 km altitude may occur with larger amplitude in the wider area than previously thought.