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1. Non‐Migrating Structures in the Northern Midlatitude Thermosphere During December Solstice Using ICON/MIGHTI and FPI Observations

   https://doi.org/10.1029/2023JA031468  

   Navarro, L. A.; Makela, J. J.; Forbes, J. M.; Harding, B. J.; Englert, C. R.; Harlander, J. M.; Marr, K. D.; Kerr, R.; Noto, J.; Wu, Q.; et al (September 2023, Journal of Geophysical Research: Space Physics)

   Abstract Midlatitude thermospheric wind observations from the Michelson Interferometer for Global High‐resolution Thermospheric Imaging on board the Ionospheric Connections Explorer (ICON/MIGHTI) and from the ground‐based Boulder, Urbana, Millstone Hill and Morocco Fabry‐Perot interferometers (FPIs) are used to study a distinct solar local time (SLT) evolution in the nighttime wind field around the December solstice period. Our results show, to the best of our knowledge for the first time, strong non‐migrating tides in midlatitude thermospheric winds using coincident from different observing platforms. These observations exhibited a structure of strong (∼50–150 m/s) eastward and southward winds in the pre‐midnight sector (20:00–23:00 SLT) and in the post‐midnight sector (02:00–03:00 SLT), with a strong suppression around midnight. Tidal analysis of ICON/MIGHTI data revealed that the signature before midnight was driven by diurnal (D0, DE1, DE2, DW2) and semidiurnal (SE2, SE3, SW1, SW4) tides, and that strong terdiurnal (TE2, TW1, TW2, TW5) and quatradiurnal (QW2, QW3, QW6) tides were important contributors in the mid‐ and post‐midnight sectors. ICON/MIGHTI tidal reconstructions successfully reproduced the salient structures observed by the FPI and showed a longitudinal dual‐peak variation with peak magnitudes around 200°–120°W and 30°W–60°E. The signature of the structure extended along the south‐to‐north direction from lower latitudes, migrated to earlier local times with increasing latitude, and strengthened above 30°N. Tidal analysis using historical FPI data revealed that these structures were often seen during previous December solstices, and that they are much stronger for lower solar flux conditions, consistent with an upward‐propagating tidal origin. 

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2. Tidally Driven Intra‐Seasonal Oscillations in the Thermosphere From TIEGCM‐ICON and Connections to the Madden‐Julian Oscillation

   https://doi.org/10.1029/2024JA033178  

   Gasperini, Federico; Maute, Astrid; Wang, Houjun; McClung, Owen; Aggarwal, Deepali; Kumari, Komal (January 2025, Journal of Geophysical Research: Space Physics)

   Recent evidence has revealed that strong coupling between the lower atmosphere and the thermosphere (100 km) occurs on intra‐seasonal (IS) timescales ( 30–90 days). The Madden‐Julian Oscillation (MJO), a key source of IS variability in tropical convection and circulation, influences the generation and propagation of atmospheric tides and is believed to be a significant driver of thermospheric IS oscillations (ISOs). However, limited satellite observations in the “thermospheric gap” (100–300 km) and challenges faced by numerical models in characterizing this region have hindered a comprehensive understanding of this connection. This study uses an Ionospheric Connection Explorer (ICON)‐adapted version of the Thermosphere Ionosphere Electrodynamics General Circulation Model, incorporating lower boundary tides from Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) observations, to quantify the impact of the upward‐propagating tidal spectrum on thermospheric ISOs and elucidate connections to the MJO. Thermospheric zonal and diurnal mean zonal winds exhibit prominent ( 20 m/s) tidally driven ISOs throughout 2020–2021, largest at low latitudes near 110–150 km altitude. Correlation analyses confirm a robust connection between thermospheric ISOs, tides, and the MJO. Additionally, Hovmöller diagrams show eastward tidal propagation consistent with the MJO and concurrent Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. This study demonstrates that vertically propagating tides play a crucial role in linking IS variability from the lower atmosphere to the thermosphere, with the MJO identified as a primary driver of this whole‐atmosphere teleconnection. Understanding these connections is vital for advancing our knowledge in space physics, particularly regarding the dynamics of the upper atmosphere and ionosphere 

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3. Relative Contributions of Lower‐Atmosphere Tidal and Solar‐Magnetospheric Forcings to the Day‐to‐Day Variability of F‐Region Electron Density

   https://doi.org/10.1029/2025JA034717  

   Lu, Xian; Oberheide, Jens; Aggarwal, Deepali (May 2026, Journal of Geophysical Research: Space Physics)

   Abstract We use Thermosphere Ionosphere Electrodynamics General Circulation Model simulations nudged to realistic tides and their statistical day‐to‐day variabilities (DTDVs), derived from Michelson Interferometer for Global High‐Resolution Thermospheric Imaging/Ionospheric Connection Explorer observations, to estimate the relative importance of tidal and solar‐geomagnetic (solar and magnetospheric (SM)) forcings in driving F‐region electron density (Ne) variability. Ne is decomposed into mean and tidal components for diagnosis. The simulations show excellent agreements with COSMIC‐2 observations in reproducing 2–35‐day Ne DTDVs, proving that the dominant sources for DTDVs are realistically captured. Under solar minimum conditions (F10.7 = 70), tides contribute ∼56% of the absolute Ne DTDVs across all components, while SM forcing contributes ∼33%. As solar activity rises (F10.7 = 80–110), the tidal contribution decreases to ∼37%, while the SM contribution increases to ∼49%. Their summed contributions of less than one suggest a role of nonlinear dynamics in dictating the overall variability. The tidal and SM contributions to relative DTDVs (absolute DTDVs divided by background Ne) are ∼77% and ∼58%, respectively, indicating the stronger role of tides in determining short‐term relative fluctuations. The increased SM contribution with rising solar activity, combined with the dominant role of tides in relative DTDVs, implies that part of the SM contribution to absolute DTDVs stems from modifying the background Ne. The relative importance of tidal and SM forcings varies significantly by component: tides consistently dominate DE3 and SW2, while SM dominates DW1; for the Ne mean, the dominant driver changes as solar activity changes. These observationally constrained and validated simulations enable more realistic quantifications of the forcing contributions from above and below, providing valuable guidance for advancing Ionosphere‐Thermosphere predictability. 

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4. Tidally Driven Wavenumber‐3 and ‐4 Structures in the Ionosphere‐Thermosphere Observed by ICON and Comparison of Their Coupling Mechanisms

   https://doi.org/10.1029/2025JA034470  

   Martinez, B C; Lu, Xian (December 2025, Journal of Geophysical Research: Space Physics)

   Abstract We analyze fixed local time, longitudinal wavenumber‐3 (WN3) and wavenumber‐4 (WN4) structures in the low‐latitude F‐region ionosphere using ICON‐IVM observations of ion drifts, temperatures, and densities from Jan 2020 to Jun 2022. These ionospheric wave patterns are compared to non‐migrating tides and stationary planetary waves in the Mesosphere and Lower Thermosphere (MLT) zonal winds from ICON‐MIGHTI. We find relative amplitudes of ionospheric WN4 are highly correlated with WN4 in MLT zonal winds (cc = 0.80), and particularly with DE3 (cc = 0.77). WN4 shows the strongest correlation with DE3 near ∼110 km altitude and ∼15° magnetic latitude, where MLT winds are approximately field‐aligned with the ionospheric measurements and E‐region conductivities peak. Phase analysis further supports the E‐region dynamo as the dominant mechanism coupling MLT and ionospheric WN4. In contrast, no such evidence is found for WN3, suggesting alternative coupling mechanisms dominate. The relative amplitudes of ionospheric WN3 show correlations with WN3 in MLT zonal winds but with a weaker coefficient (cc = 0.55, and cc = 0.50 with DE2). Variability in ionospheric WN3 is also significantly influenced by the stationary planetary wave SPW3 (cc = 0.30). To test whether thermospheric composition changes contribute to the generation of ionospheric WN3/4, we correlate O/N₂wave amplitudes with ionospheric wave amplitudes. We find a significant correlation between ionospheric and O/N₂WN3 (cc = 0.41) but only a weak correlation for WN4 (cc = 0.19) consistent with a greater role for composition‐driven coupling in WN3 than WN4. 

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5. Ionosphere-thermosphere coupling via global-scale waves: new insights from two-years of concurrent in situ and remotely-sensed satellite observations

   https://doi.org/10.3389/fspas.2023.1217737  

   Gasperini, Federico; Harding, Brian J; Crowley, Geoffrey; Immel, Thomas J (September 2023, Frontiers in Astronomy and Space Sciences)

   Growing evidence indicates that a selected group of global-scale waves from the lower atmosphere constitute a significant source of ionosphere-thermosphere (IT, 100–600 km) variability. Due to the geometry of the magnetic field lines, this IT coupling occurs mainly at low latitudes ( $<$ 30°) and is driven by waves originating in the tropical troposphere such as the diurnal eastward propagating tide with zonal wave number s = −3 (DE3) and the quasi-3-day ultra-fast Kelvin wave with s = −1 (UFKW1). In this work, over 2 years of simultaneousin situion densities from Ion Velocity Meters (IVMs) onboard the Ionospheric Connection Explorer (ICON) near 590 km and the Scintillation Observations and Response of the Ionosphere to Electrodynamics (SORTIE) CubeSat near 420 km, along with remotely-sensed lower (ca. 105 km) and middle (ca. 220 km) thermospheric horizontal winds from ICON’s Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) are employed to demonstrate a rich spectrum of waves coupling these IT regions. Strong DE3 and UFKW1 topside ionospheric variations are traced to lower thermospheric zonal winds, while large diurnal s = 2 (DW2) and zonally symmetric (D0) variations are traced to middle thermospheric winds generatedin situ. Analyses of diurnal tides from the Climatological Tidal Model of the Thermosphere (CTMT) reveal general agreement near 105 km, with larger discrepancies near 220 km due toin situtidal generation not captured by CTMT. This study highlights the utility of simultaneous satellite measurements for studies of IT coupling via global-scale waves. 

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