Research Article

The state of mid-latitude thermosphere retrieved from ionosonde and Swarm satellite observations during geomagnetic storms in February 2022

¹ Istituto Nazionale di Geofisica e Vulcanologia (INGV), Roma 00143, Italy
² Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow 108840, Russia

^* Corresponding author: loredana.perrrone@ingv.it

Received: 25 June 2024
Accepted: 28 December 2024

Abstract

This analysis of the impact of geomagnetic storms on the Thermosphere-Ionosphere system provides critical insights into the complex interplay between geomagnetic activity and the upper atmosphere dynamics. On February 3, 2022, SpaceX launched 49 Starlink satellites into orbits at altitudes ranging between 210 and 320 km. Unfortunately, 38 of these satellites were lost due to the effects of two moderate geomagnetic storms, which caused a significant increase in neutral density in the thermosphere, resulting in higher atmospheric drag. To study the impact of these geomagnetic storms on the Thermosphere-Ionosphere system, F-layer Ne(h) profiles from ground-based ionosondes, located in different longitudinal sectors of both hemispheres, along with Swarm-C neutral density observations, were analyzed using an original method called THERION (THERmospheric parameters from IONosonde observations). The analysis revealed that during the daytime in mid-latitude regions, the thermosphere exhibited relatively small neutral density perturbations of less than 50% at an altitude of 250 km. However, significant disturbances in thermospheric and ionospheric parameters were identified in the longitudinal sectors over America and Australia. In the Northern Hemisphere’s winter, the largest increase in atomic oxygen [O] was revealed, ranging between 30% and 50%, which significantly contributed to the rise in neutral density at 250 km (ρ₂₅₀). This seasonal increase in [O] was a key factor driving the observed neutral density changes. Conversely, in the summer hemisphere, atomic oxygen [O] decreased by 20–40%, reducing its contribution to neutral density. Instead, the rise in ρ₂₅₀ was primarily attributed to an increase in molecular nitrogen [N₂], which was driven by elevated neutral temperatures (Tex) caused by the geomagnetic storms. In the Northern Hemisphere’s winter, the combined effects of atomic oxygen [O] downwelling and an increase in molecular nitrogen [N₂], driven by higher neutral temperatures (Tex), acted in phase. This synergy resulted in a 35–45% rise in neutral density at 250 km. In contrast, during the Southern Hemisphere’s summer, the opposing effects of [O] (which decreased) and [N₂] (which increased) largely cancelled each other out. As a result, the overall impact on ρ₂₅₀ was minimized, showing limited changes in neutral density. This contrast illustrates the seasonal dependence of thermospheric composition and temperature responses to geomagnetic disturbances. The European longitudinal sector exhibited behavior similar to the American longitudinal sector but with less intensity. Here, a 16–35% storm-time increase in neutral density at 250 km was primarily driven by a rise in atomic oxygen [O]. In the winter Japanese sector, neutral density perturbations were modest, with increases of less than 21%, primarily attributed to elevated neutral temperatures (Tex). These findings indicate that while the overall impact of the two February 2022 geomagnetic storms on the Thermosphere-Ionosphere system was moderate, it was significant enough to cause the loss of 38 satellites. This underscores the critical need for continuous monitoring of the thermosphere to better predict and mitigate the effects of geomagnetic activity on satellite operations.