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Abstract We investigate Ionosphere‐Thermosphere (IT) responses to the March 2023 geomagnetic storm using GOLD and PFISR observations, along with TIEGCM simulations driven by data‐assimilated aurora and electric fields. A Lattice Kriging approach is implemented to assimilate auroral electron flux and characteristic energy from ground‐based (THEMIS/ASIs) and satellite (DMSP/SSUSIs) measurements, and the empirical model (Zhang & Paxton, 2008,https://doi.org/10.1016/j.jastp.2008.03.008). Electric field assimilation uses SuperDARN ion drifts, PFISR, and the SuperDARN SHF potential model. Compared to the default run, the assimilated simulation better captures GOLD observations, including an O/N₂depletion by ∼0.5, and a neutral temperature enhancement of ∼170 K relative to a quiet day. These changes are primarily driven by enhanced Joule heating from assimilated aurora and electric fields, and the resultant upwelling. Results from different model runs implies that aurora modestly increases temperature, while electric fields further enhance it and modulate its spatial structure. The assimilated run also captures the local PFISR observations, including (a) F‐region elevated ion and electron temperatures (∼4000 K); (b) a negative ionospheric storm phase with ∼60% F‐region electron density reduction; and (c) E‐region electron density enhancements by 50%, relative to a quiet day. Electric fields more strongly elevate ion temperature and reduce F‐ region electron density, whereas aurora drives E‐region electron density enhancements. The combined effect of both drivers produces the largest height‐integrated Joule heating at the Poker Flat, reaching ∼120 mW/m². Overall, we demonstrate that assimilating high‐latitude drivers into TIEGCM significantly improves its capability to simulate storm‐time IT dynamics with richer spatial structures and increased variability. 

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 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 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. 

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 The Madden–Julian Oscillation (MJO), a recurring intraseasonal (30–96 days) disturbance in the troposphere, strongly influences the E‐region and F‐region ionosphere through its modulation of atmospheric tides. Among these, the diurnal eastward wave number 3 (DE3) tide, driven by MJO‐modulated latent heating, carries MJO signals upward into the E‐region. However, coupling into the F‐region remains poorly understood due to the lack of direct thermospheric neutral wind observations. To address this, we investigate MJO propagation from the E‐region to the F‐region using simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) nudged with outputs from the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere ionosphere Extension (SD‐WACCM‐X). The results show that DE3 amplitudes in F‐region electron density (∼300 km, 15°N) vary by about ∼ 20%. The simultaneous response of E‐region zonal winds, F‐region vertical drifts, and electron density highlights the role of the E‐region dynamo. Controlled simulations reveal that ∼ 73% of DE3 MJO perturbations are transported by vertical drifts, with the remainder by neutral winds. The semidiurnal eastward wave number 2 (SE2) tide contributes about 65% of its variability transmitted via field‐aligned neutral winds. While SE2 plays a secondary role (∼10%, half of DE3), DE3 dominates the tidal variability, emphasizing the E‐region dynamo's control over the ionospheric response. The MJO further modulates zonal mean F‐region electron density by 4%–5%, primarily through semidiurnal westward (SW2) migrating tides. These results highlight how MJO–tide interactions shape ionospheric variability, with potential impacts on satellite drag, navigation, and communication systems. 

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 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 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.