Hour-scale response of low-Earth-orbit satellite altitude to extreme geomagnetic storms revealed by the NinjaSat CubeSat during the 2024 solar maximum

Extreme geomagnetic storms accelerate low-Earth-orbit satellite decay by inflating the thermosphere, yet the hour-scale pathway from solar-wind energy to atmospheric heating is poorly understood. Using the GNSS receiver of the NinjaSat CubeSat ( ~ 500 km, 97^∘ sun-synchronous), we tracked orbital altitude through solar-maximum 2024 and cross-correlated the storm-time altitude-change rate with geomagnetic indices during the two largest storms of the year. The EUV-corrected residual correlates with the polar-cap (PC) index at r 0.8 , PC leading or coincident with the response by up to ~ 3 h, as do the auroral electrojet indices AE and AL. It also correlates with the Dst index ( r≈ 0.82 - 0.84 ), but the altitude drop precedes the Dst minimum by ~ 3 h, attributing this to a common solar-wind driver rather than ring-current heating. XRISM ( 31^∘ , ~ 560 km) shows the storm-induced density enhancement reached low latitudes in May 2024 but not in October 2024, consistent with a shorter electrojet duration despite comparable peak intensity. Polar Joule heating, indexed by PC, is thus the dominant storm-time drag driver, providing a natural forecasting window of up to ~ 3 h.