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ABSTRACT The Earth's ionosphere plays a critical role in radio wave transmission, reflection, and scattering, directly affecting communication, navigation, and positioning systems. However, the comprehensive impacts of space weather remain to be fully established in cases where the ionosphere experiences strong disturbances during geomagnetic storms. We reported unprecedented observational evidence of extreme ionospheric electron density depletion and its hemispheric asymmetry during the May 10–12, 2024 super geomagnetic storm, utilizing multi-instrument ground-based and spaceborne in-situ observations. The ionospheric electron density significantly decreased, with a maximum reduction of 98% over the whole northern hemisphere for more than 2 days, causing backscatter echo failures in multiple ionosondes within the Chinese Meridian Project (CMP) monitoring network. In contrast, mid-to-low latitude regions in the southern hemisphere exhibited electron density enhancements. Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) simulations demonstrated strong consistency with northern hemispheric observations. The vertical drift and the column integrated ratio of O and N2 (ΣO/N2) from observations and simulations indicated the deep reduction of total electron content (TEC) mainly generated by severe ion recombination associated with neutral composition changes that interacted with the disturbed electric field. The summer to winter neutral wind and asymmetry of O/N₂ were possibly responsible for the asymmetry in electron density between the northern and southern hemispheres. These results advance understanding of ionospheric storm physics by establishing causal links between magnetosphere-thermosphere coupling processes and extreme electron density variations, while providing critical observational constraints for space weather model refinement. 

Abstract The 12‐year continuous observation of gravity wave momentum fluxes (GWMFs) estimated by the Mohe meteor radar (53.5°N, 122.3°E) revealed prominent intraseasonal variability around the extratropical mesopause (82–94 km) during boreal winters. Composite analysis of the December‒January‒February (DJF) season according to the Madden‒Julian Oscillation (MJO) phases revealed that the zonal GWMFs notably increased in MJO Phase 4 (P4) by ∼2–4 m²/s², and a Monte Carlo test was designed to examine the statistical significance. The response in zonal winds lags behind the GWMF response by two MJO phases (i.e., 1/2π), indicating a “force‒response” interaction between them. Additionally, time‐lagged composites revealed that strengthened westward GWMFs occurred ∼25–35 days after MJO P4, coincident with the MJO impact on the zonal winds in the stratosphere. The analysis results also suggested that the mechanism of MJO by which the MJO influences the stratospheric circulation might involve poleward propagating effects of stationary planetary waves with zonal wavenumber one. This work emphasizes the importance of GW intraseasonal variability, which impacts tropical sources from the troposphere to the extratropical mesopause. 

Abstract The strongest geomagnetic storm in the preceding two decades occurred in May 2024. Over these years, ground‐based observational capabilities have been significantly enhanced to monitor the ionospheric weather. Notably, the newly established Sanya incoherent scatter radar (SYISR) (Yue, Wan, Ning, & Jin, 2022,https://doi.org/10.1038/s41550‐022‐01684‐1), one of the critical infrastructures of the Chinese “Meridian Project,” provides multiple parameter measurements in the upper atmosphere at low latitudes over Asian longitudies. Unique ionospheric changes on superstorm day 11 May were first recorded by the SYISR experiments and the geostationary satellite (GEO) total electron content (TEC) network over the Asian sector. The electron density or TEC displayed wavelike structures rather than a regular diurnal pattern. Surprisingly, two humps, a common feature in the daytime equatorial ionization anomaly structure, disappeared. The SYISR observations revealed that multiple wind surges accompanied the downward phase propagation caused by atmospheric gravity waves (AGWs) originating from auroral zones. Meanwhile, strong upward and large downward drifts were respectively observed in the daytime and around sunset. The Thermosphere‐Ionosphere Electrodynamics Global Circulation Model (TIEGCM) simulations demonstrated that abnormal ionospheric changes were attributed to meridional wind disturbances associated with AGWs and recurrent penetration electric fields corresponding to largerB_zsouthward excursions and disturbance dynamo. The complicated interplay between AGWs and disturbance electric fields contributed to this unique ionospheric variation. 

Abstract 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 (∼438 km, 09/21 Local Time [LT]) and the Gravity Recovery and Climate Experiment Follow‐On (∼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 ∼35%–60%. Although such storm effects are far from the largest, they seem to be responsible for the reentry of the 38 satellites. 

Climate change is characterized by global surface warming associated with the increase of greenhouse gas population since the start of the industrial era. Growing evidence shows that the upper atmosphere is experiencing appreciable cooling over the last several decades. The seminal modeling study by Roble and Dickinson (1989) suggested potential effects of increased greenhouse gases on the ionosphere and thermosphere cooling which appear consistent with some observations. However, several outstanding issues remain regarding the role of CO 2 , other important contributors, and impacts of the cooling trend in the ionosphere and thermosphere: for example, (1) what is the regional variability of the trends? (2) the very strong ionospheric cooling observed by multiple incoherent scatter radars that does not fit with the prevailing theory based on the argument of anthropogenic greenhouse gas increases, why? (3) what is the effect of secular changes in Earth’s main magnetic field? Is it visible now in the ionospheric data and can it explain some of the regional variability in the observed ionospheric trends? (4) what is the impact of long-term cooling in the thermosphere on operational systems? (5) what are the appropriate strategic plans to ensure the long-term monitoring of the critical space climate?