Comparison of Empirical and Theoretical Models of the Thermospheric Density Enhancement During the 3-4 February 2022 Geomagnetic Storm

On 3 February 2022, at 18:13 UTC, SpaceX launched and a short time later deployed 49 Starlink satellites at an orbit altitude between 210 and 320 km. The satellites were meant to be further raised to 550 km. However, the deployment took place during the main phase of a moderate geomagnetic storm, and another moderate storm occurred on the next day. The resulting increase in atmospheric drag led to 38 out of the 49 satellites reentering the atmosphere in the following days. In this work, we use both observations and simulations to perform a detailed investigation of the thermospheric conditions during this storm. Observations at higher altitudes, by Swarm-A (& SIM;438 km, 09/21 Local Time [LT]) and the Gravity Recovery and Climate Experiment Follow-On (& SIM;505 km, 06/18 LT) missions show that during the main phase of the storms the neutral mass density increased by 110% and 120%, respectively. The storm-time enhancement extended to middle and low latitudes and was stronger in the northern hemisphere. To further investigate the thermospheric variations, we used six empirical and first-principle numerical models. We found the models captured the upper and lower thermosphere changes, however, their simulated density enhancements differ by up to 70%. Further, the models showed that at the low orbital altitudes of the Starlink satellites (i.e., 200-300 km) the global averaged storm-time density enhancement reached up to & SIM;35%-60%. Although such storm effects are far from the largest, they seem to be responsible for the reentry of the 38 satellites. On 3 February 2022, at 18:13 UTC, the 38 out of the 49 Starlink satellites reentered the atmosphere during a moderate geomagnetic storm that occurred on current and the next day. The storm-time enhanced thermospheric density is the cause of an enhanced atmospheric drag effect on the LEO satellites and space debris. In this work, the whole thermosphere neutral mass density conditions are investigated in detail by a combination of the observations and the model simulations. The results show that & SIM;110%-120% storm-time increase in the upper thermospheric density (e.g., & SIM;400-500 km), and the storm-time density increase reached & SIM;35%-60% at the orbit altitude of the Starlink satellites, that is, 200-300 km. Although such storm effects are far from the largest, they seem to be responsible for the reentry of the 38 satellites. Observations by Swarm-A (& SIM;438 km) and Gravity Recovery and Climate Experiment Follow-On (& SIM;505 km) missions show 110% and 120% storm-time increase in the thermospheric densityBoth empirical and numerical models captured the observed storm-time density enhancements, however simulated results differ by up to 70%Simulations show that the storm-time density increase reached 35%-60% at the orbit altitude of the Starlink satellites, that is, 200-300 km