Impact of geomagnetic storm intensity on thermospheric density and orbital decay of LEO satellites: a G1–G5 per-event analysis

Geomagnetic storms enhance thermospheric density and increase atmospheric drag on low-Earth-orbit (LEO) satellites, accelerating their orbital decay, as illustrated by the loss of 38 Starlink satellites in February 2022. Prior multi-event analyses have characterized this response primarily through superposed epoch analyses (SEA). Here we apply a per-event approach: for each of 22 storms spanning G1 to G5 (2003–2024), including the May 2024 Gannon storm, we compare the storm-peak orbit of Gravity Recovery and Climate Experiment (GRACE) or GRACE-Follow On (-FO) with a matched quiet-time reference orbit. The mean orbital decay rate enhancement generally increases with storm intensity (77.2%, 98.5%, 138.1%, 149.6%, and 166.5% from G1 to G5), although the scatter within each category is large. Operation altitude is also important: low-altitude events produce strong drag responses even under weak geomagnetic forcing. An empirical multiple linear regression model using quiet-time decay rate, maximum Kp, and operation altitude reproduces the storm-time decay rate (R² = 0.91; root mean square error, RMSE = 12.3 m/day; leave-one-out RMSE = 15.1 m/day). Replacing Kp with the open-ended Hp30 index gives similar results. These per-event benchmarks complement SEA-based analyses, provide a reference for empirical thermospheric models, and support storm-time orbit prediction for LEO satellites.