Quasi‐Homologous Solar Flares and Impacts on Thermospheric Density and Satellite Orbital Drag

Abstract Quasi‐Homologous Flaring (QHF) activity from active regions on the Sun releases intense electromagnetic radiation in recurrent bursts over extended periods. In this letter, we present the effects of recurrent impulsive extreme ultraviolet (EUV) heating on thermospheric neutral density and the resulting atmospheric drag on satellites based on Swarm‐A measurements. Significant density enhancements up to 25%–30% and 50%–75% sustained for a few days, on both day and night sides, were observed at ∼460 km altitudes during QHF from AR4366 (February 2026) and AR3664 (May 2024), respectively. As a result, Swarm‐A orbital decay rate is increased from 79.43 to 96.28 m/day, and from 19.91 to 42.43 m/day during the AR4366 and AR3664 QHF events, respectively. Repeated EUV heating at intervals shorter than the typical thermospheric relaxation time during QHF flares is responsible for sustained density enhancements and therefore needs to be considered one of the important drivers of satellite drag.