Assessment of Swarm Thermosphere Density Data

Kurzfassung

The increasing number of satellites in Low Earth Orbit (LEO) and the rapid advancement of satellite technology brought about significant progress in space-based applications, including telecommunications, Earth observation, navigation, and environmental monitoring. As satellite constellations expand, the challenges associated with maintaining orbital stability become more pronounced. One of the most critical issues facing satellites in LEO is atmospheric drag caused by the thermosphere, a region of Earth’s atmosphere located between 80 km and 1,000 km above the surface. Despite the thermosphere’s low density, its particles exert enough drag to gradually alter satellite orbits, leading to orbital decay and potential mission disruption. This study investigates thermospheric neutral density (TND) variability observed by the European Space Agency’s (ESA) Swarm satellites, covering the period from 2014 to 2023. The research focuses on examining the relationship between thermospheric density fluctuations and solar and geomagnetic activity, which are major drivers of variability in the upper atmosphere. Solar energy input into the thermosphere, particularly through extreme ultraviolet (EUV) radiation, plays a significant role in driving variations in thermospheric density, which in turn affects the drag experienced by satellites in LEO. This study investigates how changes in solar activity, quantified by indices such as the F10.7 solar radio flux index, influence thermospheric density at different altitudes and times of the day. Additionally, the research explores the impact of geomagnetic disturbances, which arise from solar wind interactions with Earth’s magnetosphere, particularly during geomagnetic storms driven by coronal mass ejections (CMEs) and other solar wind perturbations. The analysis stratifies data by solar local time and magnetic latitude, capturing both regional and diurnal variations in density response. Understanding these variations is essential for assessing how different regions of the thermosphere react to solar and geomagnetic inputs and how these responses affect satellites in various orbital positions. A key case study of the geomagnetic storm on 17 March 2015 is included to examine the thermosphere’s behavior during extreme geomagnetic events. This storm is used as a benchmark to evaluate the ability of the NRLMSIS-00 predictive model to replicate observed density variations under disturbed conditions. The study compares satellite-derived TND data with the model outputs to assess the model’s accuracy in forecasting thermospheric density. Statistical methods, including correlation analyses and scatter plot comparisons, are used to evaluate how well the model predicts density fluctuations during both quiet and disturbed geomagnetic periods. This assessment reveals the model’s strengths in predicting long-term trends but also highlights significant limitations, particularly its inability to capture rapid, transient density fluctuations during periods of intense geomagnetic activity. By analyzing a near-decade-long dataset from the Swarm mission, this research aims to advance the understanding of thermospheric dynamics, particularly the key drivers behind thermospheric variability. The findings provide critical insights that can improve the development of more accurate predictive models, which are essential for enhancing satellite orbit prediction, collision avoidance, and operational reliability in the increasingly crowded LEO environment. While many aspects of thermospheric dynamics are predictable, certain conditions remain challenging to model accurately. This research contributes to refining operational models, helping satellite operators better account for these complexities, and improving the overall reliability of thermospheric density forecasts. Specifically, this study enhances the characterization of density variations across different solar and geomagnetic conditions, thereby supporting more precise space weather impact assessments on satellite operations. Ultimately, these advancements contribute to a safer and more sustainable future for satellite technology.