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The accidental reentry of 38 Starlink satellites occurred in early February 2022, associated with the occurrence of moderate magnetic storms. A poorly understood structure of Coronal Mass Ejections (CMEs) caused the magnetic storms at unexpected timing. Therefore, a better understanding of minor CME structures is necessary for the modern space weather forecast. During this event, the “up to 50%” enhancement of air drag force was observed at ~200 km altitude, preventing the satellites’ safety operations. Although the mass density enhancement predicted by the NRLMSIS2.0 empirical model is less than 25% under the present moderate magnetic storms, the real-time GAIA simulation showed a mass density enhancement of up to 50%. Further, the real-time GAIA simulation suggests that the actual thermospheric disturbances at 200 km altitude may occur with larger amplitude in a broader area than previously thought.

Understanding the morphology and dynamics of the thermosphere is key to understanding the Earth's upper atmosphere as a whole. Thermospheric winds play an important role in this process by transporting momentum and energy and affecting the composition, dynamics and morphology of not only the thermosphere but also of the ionosphere. The general morphology of the winds has been well established over the past decades, but we are only starting to understand its variability. In this process the lower atmosphere plays an important role due to direct penetration of waves from the lower atmosphere into the ionosphere/thermosphere, secondary waves generated on the way, or internal feedback mechanisms in the coupled ionosphere-thermosphere system. Therefore, knowledge about thermospheric variability and its causes is critical for an improved understanding of the global ionosphere-thermosphere system and its coupling to the lower atmosphere. We have used low-to mid-latitude zonal wind observations obtained by the Gravity Field and Steady-State Ocean Explorer (GOCE) satellite near 260 km altitude during geomagnetically quiet times to investigate the interannual and spatial zonal wind variability near dawn and dusk, during December solstice. The temporal and spatial variability is presented as a variation about the zonal mean values and decomposed into its underlying wavenumbers using a Fourier analysis. The obtained wave features are compared between different years and clear interannual changes are observed in the individual wave components, which appear to align with changes in the solar flux but do not correlate with variations in either El Nino Southern Oscillation or the Quasi Biennial Oscillation. The obtained wave features are compared and contrasted with results from the Climatological Tidal Model of the Thermosphere (CTMT) and revealed a very good agreement between CTMT and the 2009 and 2010 December GOCE zonal wind perturbations at dawn. However, during dusk, the CTMT zonal wind perturbations and in particular the zonal wave-1 component show significant differences with those observed by GOCE. [ABSTRACT FROM AUTHOR]

Thermosphere cooling is a known effect of increasing CO2 in the atmosphere. In this study, we explore the changes of thermosphere circulation and tides in the cooled thermosphere via a doubled CO2 numerical experiment using the Ground‐to‐topside Atmosphere Ionosphere model for Aeronomy (GAIA). The results reveal three major features. (1) The thermosphere cools about 10 K more around solstices than equinoxes, more at the summer pole than the winter pole. (2) The meridional circulation shifts downward and strongly accelerates by 5–15 m s−1. (3) The tidal activity experiences dramatic changes, with a 40–60% reduction in the semidiurnal tides (SW2) throughout the thermosphere but an 30–50% enhancement in diurnal tides (DW1) below 200 km altitude. The nonmigrating tide DE3 has only minor changes. These changes in temperature, meridional circulation, and tides are persistent features in all seasons and can profoundly affect the spatial distribution and diurnal cycles of the ionospheric responses to CO2 doubling via atmosphere composition and electrodynamics. Key Points: Thermosphere cooling is stronger around solstice than equinoxesThe meridional circulation is accelerated by 5–15 m/sSemidiurnal tides are strongly reduced [ABSTRACT FROM AUTHOR]