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Abstract We investigate vertical and horizontal energy transport and associated heating in the thermosphere due to both upward propagating and in situ generated migrating and nonmigrating diurnal and semidiurnal tides over the solar cycle 24 (2009–2019). Upward propagating tidal fields are derived from wind and temperature observations from the TIDI and SABER instruments onboard the TIMED satellite, utilizing the Hough Mode Extension (HME) fitting approach. Using these observational tidal fields and fluid dynamic equations, we characterize both vertical and horizontal wave energy fluxes in the 80–250 km altitude range, providing a detailed view of how tidal energy varies throughout the thermosphere. Corresponding thermospheric heating rates are also derived from the observed tidal fields. To assess the contribution of in situ generated thermospheric tides to tidal energy and heat budget, we employ the same approach to the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) simulations for the same period and find that in situ generated tidal energy flux dominates the upper thermosphere. Our results reveal the temporal evolution of tidal energy fluxes across solar activity levels, as well as the complex interplay between vertical and horizontal energy redistribution, identifying regions of tidal energy sources and sinks. These findings improve our understanding of tidal energy transport in determining the dynamics and energetics in very low Earth orbit, the new frontier of space operations. 

Abstract This study examines how the breakdown of the stratospheric polar vortex influences lunar semidiurnal (M2) tides in F‐region electron density using Global Ionospheric Specification (GIS) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate‐2 (COSMIC‐2). During the 2020–2021 Sudden Stratospheric Warming (SSW) event—marked by an exceptionally disrupted polar vortex—we observe up to a 16% enhancement in the M2 lunar tide at low latitudes (equatorial ionization anomaly) around 300 km altitude relative to the mean state. The response of M2 in vertical plasma drifts measured by the ion velocity meter on board the Ionospheric Connection Explorer satellite shows similar variability. Whole‐atmosphere model simulations using the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (SD‐WACCM‐X) reproduce consistent M2 tidal signatures in E‐region zonal winds, F‐region vertical drifts, and electron density. To quantify the relative contributions of electrodynamics and neutral winds, we analyzed the ion continuity equation using the National Center for Atmospheric Research Thermosphere–Ionosphere–Electrodynamics General Circulation Model with SD‐WACCM‐X as the lower boundary. Results show M2 tides impact F‐region electron densities primarily through vertical plasma drifts, which increase by ∼114% during the SSW, while transport by neutral winds rises by ∼43%. These findings confirm that vertical drifts dominate lunar tide transport, with neutral winds providing a secondary contribution. 

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. 

Abstract This study investigates the relative importance of lower atmospheric versus in situ forcing in driving migrating and nonmigrating diurnal and semidiurnal tides in the thermosphere, as well as the impact of solar and geomagnetic activity on these tides. Our focus is the “thermospheric gap” region 110–250 km, where few observations are available but the tidal spectrum is known to change dramatically. We employ the Hough Mode Extension (HME) fitting approach to the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X) to separate upward‐propagating tides originating from tropospheric and stratospheric sources from those generated in situ within the thermosphere and calculate their ratio to quantify their relative importance. To assess the extent to which the solar and geomagnetic activity impact these thermospheric tides, we compare SD‐WACCM‐X simulations with control simulations in which geomagnetic (Kp) and solar (F10.7) activity are held at lower fixed values. Focusing on the year 2014, a period characterized by elevated solar and geomagnetic variability, we analyze how these external drivers modify tidal amplitudes as a function of latitude and season. The model simulations are validated by comparison with independent neutral density tide observations from the CHAllenging Minisatellite Payload data at approximately 390 km altitude from 2002 to 2004 (F10.7 = 140 sfu). The results highlight the critical role of both thermospheric and lower atmospheric forcings in shaping tidal dynamics, which has implications for forthcoming satellite missions targeting the space weather of the ionosphere‐thermosphere system and improving space operations in the very low Earth orbit. 

Abstract The ionosphere-thermosphere (IT) is a convergence point of energy and processes that interconnect Earth’s atmosphere with space. Processes generated by terrestrial weather in the lower atmosphere (i.e., troposphere and stratosphere, altitudes less than ~ 50 km) are recognized by the scientific community as sources of variability in both the structure and composition of the IT. Exposed to persistent wave forcing from terrestrial weather sources and solar and magnetic forcing, the IT is a domain of compelling scientific inquiry that connects thermodynamics, fluid dynamics, electrodynamics and plasma physics. Predicting its space weather is of significant national interest for space situation awareness including the very low earth orbit as the new frontier of space operations. Advancing the understanding of whole atmosphere interconnections between terrestrial and space weather requires coordinated modeling and observational efforts across different spatial and temporal scales. Toward this goal, the National Aeronautics and Space Administration (NASA), through the living with a star (LWS) program, established in 2022 a focused science topic (FST) to study the problem from various angles. In this manuscript we report on the vision, goals and status of the ongoing FST “Impact of Terrestrial Weather on the Ionosphere—Thermosphere”. Initial results show bigger impacts on the IT than hitherto thought and help to more clearly define the state-of-the-art in the context of future NASA missions such as EZIE, DYNAMIC and GDC. 

Abstract We implement a nudging module into the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) to identify effective techniques for incorporating global‐scale tides and medium‐scale gravity waves (GWs) that induce ionospheric variability. Nudging the full fields of basic state variables minimizes contamination from spectral aliasing and mode coupling, ensuring the most accurate reproduction of each tidal component. In contrast, nudging solely diurnal tides has substantial spectral leakage into semidiurnal tides, leading to underestimations of their own amplitudes and day‐to‐day variabilities (DTDVs). Nudging both diurnal and semidiurnal tides mitigates such underestimations, establishing a minimal requirement for reproducing tidal dynamics and ionospheric DTDVs. Lower boundary forcing (LBF) causes significant deviations of tidal amplitudes and DTDVs near the boundary, but only a ∼10% underestimation above it. The DTDV of vertical ion drift gradually increases with more wave components incorporated and shows a ∼10% underestimation with LBF. Constraining geopotential height (Z*) is critical in TIEGCM to properly add GWs at lower levels. Model runs withZ* constrained exhibit reduced sensitivity to nudging levels: one‐level nudging and LBF runs show 20%–30% underestimations of TID magnitudes compared to a four‐scale‐height nudging run. Conversely, whenZ* is unavailable and onlyU,V,Tare constrained, one‐level nudging and LBF lead to 80%–90% underestimations of TIDs, with LBF entirely missing wave features. Therefore, multi‐level nudging, especially withZ* unconstrained, is recommended to incorporate GWs. Overall, nudging provides a powerful tool to realistically incorporate observed or simulated waves across medium to global scales into ionosphere‐thermosphere models, offering a data‐driven perspective of variability for lower boundary conditions. 

Abstract We use the TIEGCM‐NG nudged by MAGIC gravity waves to study the impacts of a severe thunderstorm system, with a hundred tornado touchdowns, on the ionospheric and thermospheric disturbances. The generated waves induce a distinct concentric ring pattern on GNSS TIDs with horizontal scales of 150–400 km and phase speeds of 150–300 m/s, which is well simulated by the model. The waves show substantial vertical evolution in period, initially dominated by 0.5 hr at 200 km, shifting to 0.25 hr and with more higher‐frequency waves appearing at higher altitudes (∼400 km). The TADs reach amplitudes of 100 m/s, 60 m/s, 80 K, and 10% in horizontal winds, vertical wind, temperature, and relative neutral density, respectively. Significantly perturbations in electron density cause dramatic changes in its nighttime structure around 200 km and near the EIA crest. The concentric TIDs are also simulated in ion drifts and mapped from the Tornado region to the conjugate hemisphere likely due to neutral wind‐induced electric field perturbations. The waves manage to impact the ionosphere at altitudes of ICON and COSMIC‐2, which pass through the region of interest on a total of 8 separate orbits. In situ ion density observations from these spacecrafts reveal periodic fluctuations that frequently show good agreement with the TIEGCM‐NG simulation. The O⁺fraction observations from ICON indicate that the density fluctuations are the result of vertical transport of the ions in this region, which could result from either direct forcing by neutral winds or electrodynamic coupling. 

Abstract A new version of the US National Science Foundation National Center for Atmospheric Research (NSF NCAR) thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM) has been developed and released. This paper describes the changes and improvements of the new version (3.0) since its last major release (2.0) in 2016. These include: (a) increasing the model resolution in both the horizontal and vertical dimensions, as well as in the ionospheric dynamo solver; (b) upward extension of the model upper boundary to enable more accurate simulations of the topside ionosphere and neutral density in the lower exosphere; (c) improved parameterization for thermal electron heating rate; (d) resolving transport of minor species N(²D); (e) treating helium as a major species; (f) parameterization for additional physical processes, such as SAPS and electrojet turbulent heating; (g) including parallel ion drag in the neutral momentum equation; (h) nudging of prognostic fields near the lower boundary from external data; (i) modification to the NO reaction rate and auroral heating rate; (j) outputs of diagnostic analysis terms of the equations; (k) new functionalities enabling model simulations of certain recurrent phenomena, such as solar flares and eclipses. We present examples of the model validation during a moderate storm and compare simulation results by turning on/off new functionalities to demonstrate the related new model capabilities. Furthermore, the model was upgraded to comply with the new computer software environment at NSF NCAR for easy installation and run setup and with new visualization tools. Finally, the model limitations and future development plans are discussed. 

Abstract The statistics of day‐to‐day tidal variability within 35‐day running mean windows is obtained from Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (MIGHTI)/Ionospheric Connection Explorer (ICON) observations in the 90–107 km height region for the year 2020. Temperature standard deviations for 18 diurnal and semidiurnal tidal components, and for four quasi‐stationary planetary waves are presented, as function of latitude, altitude, and day‐of‐year. Our results show that the day‐to‐day variability (DTDV) can be as large as 70% of the monthly mean amplitudes, thus providing a significant source of variability for the ionospheric E‐region dynamo and hence for the F‐region plasma. We further validate our results with COSMIC‐2 ionospheric observations and present an approach to extend the MIGHTI/ICON results to all latitudes using Hough Mode Extension fitting, to produce global tidal fields and their statistical DTDV that are suitable as lower boundary conditions for nudging and ensemble modeling of TIE‐GCM. In the future, this will likely help to establish a data‐driven perspective of space weather variability caused by the tidal weather of the lower atmosphere. 

Abstract We provide observational evidence that the stability of the stratospheric Polar vortex (PV) is a significant driver of sub‐seasonal variability in the thermosphere during geomagnetically quiet times when the PV is anomalously strong or weak. We find strong positive correlations between the Northern Annular Mode (NAM) index and subseasonal (10–90 days) Global Observations of the Limb and Disk (GOLD) O/N₂perturbations at low to mid‐northern latitudes, with a largest value of +0.55 at ∼30.0°N when anomalously strong or weak (NAM >2.5 or < −2.1) vortex times are considered. Strong agreement for O/N₂variability and O/N₂‐NAM correlations is found between GOLD observations and the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) simulations, which is then used to delineate the global distribution of O/N₂‐NAM correlations. We find negative correlations between subseasonal variability in WACCM‐X O/N₂and NAM at high northern and southern latitudes (as large as −0.54 at ∼60.0°S during anomalous vortex times). These correlations suggest that PV driven upwelling at low latitudes is accompanied by corresponding downwelling at high latitudes in the lower thermosphere (∼80–120 km), which is confirmed using calculations of residual mean meridional circulation from WACCM‐X.