Global thermospheric density response to the May 2024 extreme storm: TianMu-1 constellation observations

In this study, we analyze the impact of the May 2024 geomagnetic storm on the thermospheric mass density by using TianMu-1 constellation satellite (TM02, TM06, TM07, TM11, TM15) observations. These observations reveal intense large-scale traveling atmospheric disturbances (TADs) originating at high latitudes and propagating equatorward. Observations by TM02 captured the evolution of a TAD structure: An initial amplitude of ~3.89 × 10^–12 kg/m³ at hundred-kilometer scale subsequently intensified to 4.78 × 10^–12 kg/m³, with the spatial extent expanding to the thousand-kilometer level. Significant hemispheric asymmetry was observed: the absolute density was higher predominantly in the northern hemisphere (TM02, TM06, TM07, TM11), whereas the difference in the relative density consistently showed greater enhancements in the southern hemisphere across all satellites, with the maximum north–south density differences exceeding 195%–640% above 60° latitude. In conjunction with SuperDARN (Super Dual Auroral Radar Network) observations, this striking hemispheric asymmetry can likely be attributed to disparities in plasma convection patterns between the two hemispheres. Furthermore, density perturbation characteristics exhibited strong local time (LT) dependence: Near noon (~10.7 LT, TM02 descending), the northern hemisphere onset preceded the southern onset. Conversely, near dusk (~17.6 LT, TM15 descending), the southern onset led the northern onset by approximately 3 hours. Ascending orbits (TM02, TM06, TM07, TM15) typically yielded larger global density enhancements compared with smaller southern-confined enhancements during descending orbits. Satellite TM11 showed comparable perturbations in both ascending and descending orbits. By leveraging its unique orbital architecture, the TianMu-1 constellation enables global near-simultaneous multi-LT sampling, providing a robust data foundation for both scientific research and engineering applications.