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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 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 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 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. 

We quantify the short-term (<30 day) variability of column O/N 2 measured by GOLD from January 2019 to August 2022 for various geomagnetic activity conditions. We find enhanced variabilities at high latitudes during active (Kp ≥ 3.0) times and weak but statistically significant variabilities at low latitudes. For active times, the largest absolute variability of O/N 2 ratio is 0.14 and the largest relative variability is 20.6% at ∼60.0°N in Fall, which are about twice those of quiet times. The variability at higher latitudes can be larger than that of lower latitudes by a factor of 5–8. We further quantify contributions of magnetospheric forcing to O/N 2 variability in the Ionosphere-Thermosphere region by correlating O/N 2 perturbations with Dst. During geomagnetic active times, positive correlations as large as +0.66 and negative correlations as large as −0.65 are found at high and low latitudes, respectively, indicative of storm-induced O and N 2 upwelling at high latitudes and down welling at low latitudes. During quiet times, correlations between O/N 2 perturbations and Dst become insignificant at all latitudes, implying a more substantial contribution from below. O/N 2 variabilities maximize in Fall and decrease towards Summer, while correlations maximize in Spring/Summer and decrease in Winter/Spring, which may be related to seasonal variations of geomagnetic activity and mean circulation.