# Near-Real-Time Global Thermospheric Density Variations Unveiled by Starlink Ephemeris
## 4 Discussion
Figure 7 displays data from Shell 1, Shell 2, Shell 4, and Shell 5 from top to bottom. Shell 3 is excluded due to its significantly fewer available orbital planes compared to the other shells. In Shell 2, white bars in the colormaps indicate orbital planes that remain unpopulated. For each orbital plane in all the shells, we use the median mechanical energy loss of all satellites within the plane at each timestamp to represent the plane's data, thereby reducing errors and mitigating the impact of outliers. It is important to note that this approach reduces the dimensionality of the data by eliminating latitude variations, but it facilitates analysis from a constellation-wide perspective. Overall, the variation patterns of mechanical energy loss are similar across all shells. High-value regions gradually shift from lower-numbered to higher-numbered orbital planes over time, forming an upward-sloping band. This band corresponds to orbital planes where the ascending node crosses the equator around local noon. The apparent inconsistency between ascending and descending nodes within each shell arises from the 12-h LT difference between ascending and descending equator crossings, despite both belonging to the same orbital plane (determined by the RAAN and argument of latitude). This introduces a 180\({}^{\circ}\) phase difference. For example, in Shell 1, orbital plane 12 in the ascending nodes shares the same LT as orbital plane 48 in the descending nodes. Notably, all shells exhibit clear responses to the geomagnetic storm and the post-storm overcooling phenomenon, demonstrating that overcooling is observable across multiple altitudes. Further comparison reveals the following hierarchy of mechanical energy loss: Shell 1 > Shell 4 > Shell 5 > Shell 2. However, the orbital altitude ordering is Shell 4 < Shell 1 < Shell 5 < Shell 2. Generally, higher orbital altitudes result in lower mechanical energy loss due to reduced atmospheric drag, which explains the relationships among Shell 1, Shell 2, and Shell 5. However, Shell 1, despite its higher altitude, exhibits greater mechanical energy loss than Shell 4. We attribute this anomaly to differences in satellite versions between the two shells, as listed in Table 2. Shell 1, deployed much earlier, consists of Starlink v1.0 satellites, while the subsequent shells primarily use the updated Starlink v1.5 design. The v1.0 satellites are comparatively bulkier, potentially experiencing greater atmospheric drag. Additionally, the v1.0 satellites feature visors to reduce albedo by blocking sunlight reflection, while visors were removed for the v1.5 satellites. This design evolution implies uneven solar radiation pressure effects between the two versions, further contributing to the observed anomaly in mechanical energy loss. The above results generally reflect the variation in thermospheric density at the global scale. Should precise orbital data from Starlink satellites become accessible, they would substantially enhance the spatiotemporal resolution and multi-altitude coverage of thermo  
Figure 7: Mechanical energy loss of Starlink satellites across different orbital shells. Panels from top to bottom represent **(a,b)** Shell 1, **(c,d)** Shell 2, **(e,f)** Shell 4, and **(g,h)** Shell 5. Left panels correspond to ascending nodes, while right panels depict descending nodes. **(i,j)** The Dst index is provided for reference. spheric density measurements. This advancement could enable more refined atmospheric characterization and significantly improve our understanding of thermospheric dynamics.