Earth's Thermosphere Research Articles

Evening Solar Terminator Waves in Earth's Thermosphere: Neutral Wind Signatures Observed by ICON‐MIGHTI

AbstractThe moving solar terminator (ST) generates atmospheric disturbances, broadly termed solar terminator waves (STWs). Despite theoretically recurring daily, STWs remain poorly understood, partially due to measurement challenges near the ST. Analyzing Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) data from NASA's Ionospheric Connection Explorer (ICON) observatory, we present observations of STW signatures in thermospheric neutral winds, including the first reported meridional wind signatures. Seasonal analysis reveals STWs are most prominent during solstices, when they intersect the ST about ∼20° latitude from the equator in the winter hemisphere and have phase fronts inclined at a ∼40° angle to the ST. We also provide the first observed STW altitude profiles, revealing large vertical wavelengths above 200 km. Comparing these observations to four different models suggests the STWs likely originate directly or indirectly from waves from below 97 km. STWs may play an under‐recognized role in the daily variability of the thermosphere‐ionosphere system, warranting further study.

Wavelike Oscillations in High Latitude Thermospheric Doppler Temperature and Line‐Of‐Sight Wind Observed Using All‐Sky Imaging Fabry‐Perot Spectrometers

AbstractMultiple years of thermospheric wind and temperature data were examined to study gravity waves in Earth's thermosphere. Winds and temperatures were measured using all‐sky imaging optical Doppler spectrometers deployed at two sites in Alaska, and three in Antarctica. For all sites, oscillatory perturbations were clearly present in high‐pass temporally filtered F‐region line‐of‐sight (LOS) winds for the majority of the clear‐sky nights. Oscillations were also discernible in E‐region LOS wind and F‐region Doppler temperature, albeit less frequently. Oscillation amplitudes correlated strongly with auroral and geomagnetic activity. Observed wave signatures also correlated strongly between geographically nearby observing sites. Amplitudes of LOS wind oscillations were usually small when viewed in the zenith and increased approximately with the sine of the zenith angle—as expected if the underlying motion is predominantly horizontal. Scanning Doppler Imager instruments observe in many look directions simultaneously. Phase relationships between perturbations observed in different look directions were used to identify time intervals when the oscillations were likely to be due to traveling waves. However, a number of instances were noted in which the oscillations had characteristics suggesting geophysical mechanisms other than traveling waves—a recognition that was only possible because of the large number of look directions. Lomb‐Scargle analysis was used on a representative subset of days to resolve the spectral distributions of the wind and temperature oscillations. F‐region wind oscillations on days analyzed this way exhibited periods typically ranging from 60 min and above. By contrast, E‐region wind oscillation periods were as short as 30 min.

Solar‐Synchronous Tides in Mars Thermosphere CO2, Ar, and N2 Densities From MAVEN

AbstractMeasurements of CO2, Ar and N2 densities from the Neutral Gas and Ion Mass Spectrometer on the Mars Atmosphere and Volatile Evolution Mission (MAVEN) between 150 and 200 km altitude during 2015–2022 are analyzed to reveal diurnal (DW1), semidiurnal (SW2) and terdiurnal (TW3) solar‐synchronous tides in Mars thermosphere. Multi‐year‐mean tidal perturbations on a diurnal‐ and zonal‐mean background, corrected for solar flux variations, are reported as a function of latitude (48°S–48°N), altitude and solar longitude (Ls). The DW1, SW2 and TW3 amplitudes at for example, 180 km altitude are of order 90%–120%, 15%–20%, and ≲10% for CO2 and Ar, and roughly 2/3 these values for N2, the latter presumably due to the difference in molecular weight from the other species. Through examination of vertical phase progressions, DW1 is concluded to be mainly excited in situ, but SW2 and TW3 contain significant contributions from tides propagating upward from lower altitudes. By analogy with studies for Earth's thermosphere, the DW1 amplitudes and phases are thought to reflect the combined influences of thermal expansion and vertical winds. Points of agreement and disagreement with DW1, SW2, and TW3 amplitudes and phases derived from the Mars Climate Database are noted and interpreted.

The Effects of a Small Geomagnetic Storm on Earth's Thermosphere and Ionosphere: ICON Observations of the 25 January 2021 Disturbance

AbstractIsolated geomagnetic storms during solar minimum offer the opportunity to observe the effects of solar wind on Earth's atmosphere without interference from other background changes in the ionosphere‐thermosphere system. Here, we observe the effects of a minor storm on the ionosphere at middle and low latitudes, where disturbances in thermospheric winds and composition can produce storm‐time changes in ionospheric densities. Using data from the NASA Ionospheric Connection Explorer (ICON), we investigate the competing effects of composition changes and neutral wind disturbances in modifying the ionosphere during the 25 January 2021 storm. Large enhancements in plasma densities are seen across the dayside late on 25 January, associated with large changes in meridional winds and significant high‐latitude electric current enhancements as measured by the auroral electrojet index. At the same time, we find evidence of rapid transport of heated air from the southern auroral zone to the equator in the East‐Asian sector with the appearance of deeply reduced O/N2 in the morning sector and storm‐time northward winds prior to its appearance. We observe significant, rapid erosion of the high plasma densities in the sector where thermospheric disturbance appears over 5 hr of observation. The noon‐time plasma density enhancements are short‐lived and we observe no westward perturbation in the low‐middle latitude, dayside zonal winds over a 5‐day period including the storm. Thus, we attribute the ionospheric changes to prompt penetration and meridional wind forcing, while ruling out the presence of a storm‐time disturbance dynamo and its related ionospheric effects.

Potential Stratospheric Ozone Depletion Due To Iodine Injection From Small Satellites

AbstractWe use the 3‐D Whole Atmospheric Community Climate Model to investigate stratospheric ozone depletion due to the launch of small satellites (e.g., CubeSats) with an iodine propulsion system. The model considers the injection of iodine from the satellites into the Earth's thermosphere and suggests a 4‐yr timescale for transport of the emissions down to the troposphere. The base case scenario is 40,000 small satellite launches per year into low orbit (100–600 km), which would inject 8 tons I yr−1 above 120 km as I+ ions and increase stratospheric inorganic iodine by ∼0.1 part per trillion (pptv). The model shows that this scenario produces a negligible impact on global stratospheric ozone (∼0.05 DU column depletion). In contrast, a 100‐fold increase in the launch rate, and therefore thermospheric iodine injection, is predicted to result in modeled ozone depletion of up to 14 DU (approximately 2%–7%) over the polar regions.

Solar EUV‐Enhancement and Thermospheric Disturbances

AbstractThe increase of energetic electromagnetic flux during solar flares and particle precipitation during geomagnetic activity are among the most important sources of neutral density disturbances to the Earth's thermosphere. However, disentangling the role of X and EUV radiation during solar flares is difficult due to the rarity of sufficiently isolated EUV‐enhancements. Past work investigating the role of EUV‐enhancements has been based on simulations only. This study focuses on the analysis of the response of the thermosphere to relatively long‐lasting (between 1 and 2 days) EUV‐enhancements. These events take place in isolation from coronal mass ejections, but often occur during the recovery phase of flare events. Using the Gravity Recovery and Climate Experiment and Challenging Minisatellite Payload accelerometer‐derived density datasets, we show that the EUV‐enhancements slow the thermosphere's recovery from a flare, and maintain a high level density perturbation “plateau” lasting several hours. The level of disturbance was found to be between 30% and 70% compared to the thermosphere's density without any disturbance. The duration of this plateau is long enough that it may be important for estimating satellite drag. Over the duration of the EUV‐enhancements, Dst drops are also observed, indicating ring current activity. The proposed physical mechanism driving the Dst changes is linked to the increased production of O+ ions of ionospheric origin, which may occur over the EUV‐enhancement period.

Attenuation of evanescent acoustic-gravity modes in the Earth thermosphere

Attenuation of evanescent acoustic-gravity modes in the Earth thermosphere

PROBA2 LYRA Occultations: Thermospheric Temperature and Composition, Sensitivity to EUV Forcing, and Comparisons With Mars

AbstractA method for retrieving temperature and composition from 150 to 350 km in Earth's thermosphere using total number density measurements made via extreme ultraviolet (EUV) solar occultations by the Project for OnBoard Autonomy 2/Large Yield Radiometer (PROBA2/LYRA) instrument is presented. Systematic and random uncertainties are calculated and found to be less than 5% for the temperature measurements and 5%–20% for the composition measurements. Regression coefficients relating both temperature and the [O]/[N2] abundance ratio with EUV irradiance at 150, 275, and 350 km are reported. Additionally, it is shown that the altitude where [O] equals [N2] decreases with increasing solar EUV irradiance, an effect attributed to thermal expansion. Temperatures from 2010 to 2017 are compared with estimates from the MSIS empirical model and show good agreement at the dawn terminator but LYRA is markedly cooler at the dusk terminator, with the MSIS‐LYRA temperature difference increasing with solar activity. Anthropogenic cooling can explain this discrepancy at periods of lower solar activity, but the divergence of temperature with increasing solar activity remains unexplained. LYRA measurements of the exospheric temperature sensitivity to EUV irradiance are compared with contemporaneous measurements made at Mars, showing that the exospheric temperature at Mars is approximately half as sensitive to EUV variability as that of Earth.

The Thermospheric Column O/N2 Ratio.

More than 2 decades ago, D. J. Strickland and colleagues proposed use of the O/N2 column number density ratio as a new geophysical quantity to interpret thermospheric processes recorded in far ultraviolet (FUV) images of the Earth. This concept has enabled multiple advances in understanding the global behavior of Earth's thermosphere. Nevertheless, confusion remains about the conceptual meaning of the column density ratio, and in the application of this integral quantity. This is so even though it is now a key thermospheric measurement made by current and planned far ultraviolet remote sensing missions in pursuit of new understanding of thermospheric processes and variability. The intent here is to review the historical context of the O/N2 column density ratio, clarify its physical meaning, and resolve misunderstandings evident in the literature. Simple examples elucidate its original derivation for extracting column O/N2 ratios from measurements of the OI 135.6 nm/N2 Lyman-Birge-Hopfield (LBH) emission based on an algorithmic synthesis of model precomputations. These are organized in the form of a table lookup of column density ratio as a function of observed radiance ratios. To accommodate generalized solar-geophysical and viewing conditions, the table required to specify the number of needed parameters becomes large. Proposed as an alternative is a simplified, first principles approach to obtaining the column density ratio from the emission ratio. This new methodology is now being applied successfully to FUV measurements made from onboard the Ionospheric CONnection satellite and will be applied retrospectively to the Global Ultraviolet Imager data.

Thermospheric Neutral Winds Above the Oukaimeden Observatory: Effects of Geomagnetic Activity

AbstractIn the context of space weather, we investigate the effect of geomagnetic activity on Earth's thermosphere above the Oukaimeden Observatory in Morocco (geographic coordinates: 31.206°N, 7.866°W; magnetic latitude: 22.77°N) over 3 years from 2014 to 2016. The observatory is equipped with a Fabry‐Perot interferometer (FPI) that provides measurements of thermospheric wind speed. In this study 41 disturbed nights (with SYM‐H ≤ −50 nT, Kp ≥ 5) were identified and analyzed. We have characterized the meridional and zonal winds variability and dependence on the solar cycle, during both quiet and disturbed conditions. We have classified the storm time meridional neutral winds into three types of variation. The first type is characterized by traveling atmospheric disturbance (TAD)‐induced circulation: the first TAD coming from the north and the second TAD being transequatorial, coming from the south. This type of storm with TAD‐induced circulation accounts for 59% of the cases. The second type exhibits only slight discrepancies between the disturbed and quiet night flows. These cases account for 33% of the cases. The third type is characterized by the transequatorial wind in whole the night. This last type accounts for 8% of the cases. Finally, we apply a superposed epoch analysis method on the FPI data, and the effect of each phase of the geomagnetic storm on the wind flow and vertical total electron content VTEC has been quantified.

Exploring Thermospheric Variations Triggered by Severe Geomagnetic Storm on 26 August 2018 Using GRACE Follow‐On Data

AbstractWith the successful launch of the satellite mission Gravity Recovery and Climate Experiment (GRACE) Follow‐On in May 2018 the opportunity arises to resume the analysis of accelerometer data regarding space weather induced perturbations of the Earth's thermosphere. On 21 August 2018 a complex interplanetary coronal mass ejections occurred on the Sun, which subsequently triggered an unexpected large geomagnetic storm on 26 August. We present a detailed analysis of the interplanetary coronal mass ejection eruption and explore the occurred perturbation of the neutral mass density in the upper Earth's atmosphere. Due to the heating and the subsequent expansion of the thermosphere also the drag force acting on the spacecraft is enhanced. This leads to an additional storm‐induced orbit decay, which we calculate by means of variations in the semimajor axis. The evaluation is based on the utilization of accelerometer measurements from GRACE Follow‐On. For the reduction of disturbing nongravitational forces we implemented a physical shadow function, which incorporates the Earth's oblateness and the atmospheric refraction and extinction. Additionally, the estimation of Earth's reradiation is now based on hourly measurements by the Clouds and the Earth's Radiant Energy System. The resulting atmospheric densities and orbit decays are compared with predictions from our preliminary thermospheric forecasting tool, which is based on the study by Krauss et al. (2018, https://doi.org/10.1029/2018JA025778). The evaluation shows that the maximum estimated orbit decay triggered by the geomagnetic storm on 26 August is in the order of approximately 8.2 m and thus in good accordance with the forecasted value (9.5 m)—predicted with a lead time of about 60 min.

Global‐Scale Observations of the Limb and Disk Mission Implementation: 1. Instrument Design and Early Flight Performance

AbstractThe Global‐scale Observations of the Limb and Disk (GOLD) is a National Aeronautics and Space Administration mission of opportunity designed to study how the Earth's ionosphere‐thermosphere system responds to geomagnetic storms, solar radiation, and upward propagating atmospheric tides and waves. GOLD employs an instrument with two identical ultraviolet spectrographs that make observations of the Earth's thermosphere and ionosphere from a commercial communications satellite owned and operated by Société Européenne des Satellites (SES) and located in geostationary orbit at 47.5° west longitude (near the mouth of the Amazon River). They make images of atomic oxygen 135.6 nm and N2 Lyman‐Birge‐Hopfield (LBH) 137–162 nm radiances of the entire disk that is observable from geostationary orbit and on the near‐equatorial limb. They also observe occultations of stars to measure molecular oxygen column densities on the limb. Here, we provide an overview of the instrument and compare its prelaunch and early flight measurement performance. Direct comparison of LBH spectra of an electron lamp taken before launch with spectra on orbit provides evidence that both cascade and direct excitation are important sources of thermospheric LBH emission.

Global‐Scale Observations of the Limb and Disk Mission Implementation: 2. Observations, Data Pipeline, and Level 1 Data Products

AbstractThe Global‐scale Observations of the Limb and Disk (GOLD) is a National Aeronautics and Space Administration mission of opportunity designed to study how the Earth's ionosphere‐thermosphere system responds to geomagnetic storms, solar radiation, and upward propagating atmospheric tides and waves. GOLD employs two identical ultraviolet spectrographs that make observations of the Earth's thermosphere and ionosphere from a commercial communications satellite owned and operated by Société Européenne des Satellites (SES) and located in geostationary orbit at 47.5° west longitude (near the mouth of the Amazon River). They make images of atomic oxygen 135.6 nm and N2 Lyman‐Birge‐Hopfield radiances from the entire disk that is observable from geostationary orbit and on the near‐equatorial limb. They also observe occultations of stars to measure molecular oxygen column densities on the limb. Here we describe the algorithms and science data processing that convert downlinked data to spectral‐spatial image cubes and occultation spectra, calibrated in geophysical units. These Level 1 data products include disk and near‐equatorial limb images of spectra acquired on a 30‐min cadence beginning at 06:10 Coordinated Universal Time and ending at 23:10. Nighttime images of the disk, covering regions east of the terminator, begin at 20:10 Coordinated Universal Time and also continue until 00:40 the next day. During the day, some limb images are replaced by time series of stellar spectra that exhibit absorption by molecular oxygen as the star is occulted by the Earth's atmosphere. Instrumental artifacts that occasionally appear in the released data are discussed.

A New Data Set of Thermospheric Molecular Oxygen From the Global‐scale Observations of the Limb and Disk (GOLD) Mission

AbstractThe Global‐scale Observations of the Limb and Disk (GOLD) instrument was launched on 25 January 2018 onboard the SES‐14 commercial communications satellite and began nominal science operations in October 2018. Operating from geostationary orbit at 47.5°W longitude, GOLD images the Earth's thermosphere and ionosphere in the far‐ultraviolet (132–162 nm), measuring critical geophysical parameters by continuously scanning the Earth's disk and limb 18 hours per day. GOLD also performs stellar occultation measurements using bright type O and B stars. Up to 10 occultations per day are obtained at latitudes ranging from 60°S to 45°N and two fixed longitudes, ~33°E and ~128°W. The occultation data provide a direct measurement of atmospheric absorption in the O2 Schumann Runge continuum, which is used to retrieve the O2 density profile from 130‐ to 200‐km altitude. This paper describes the GOLD occultation measurement technique and the operational retrieval algorithm used to derive the Level 2 O2DEN data product. The spatial, temporal, and local time sampling of the GOLD O2 data product is summarized, and the data quality, retrieval errors, and validation plans are discussed. Occultations are observed under both daytime and nighttime conditions, providing the O2 density over a complete range of local times. GOLD retrievals have an estimated precision of 10% and a vertical resolution of 5–10 km, depending on altitude. The data have sufficient accuracy and resolution to provide scientifically useful constraints on the O2 abundance and variability. Initial comparisons show qualitative agreement, but also notable differences, between the GOLD O2 data and the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Radar (NRLMSISE‐00) empirical model predictions.

Determining the thermomechanical image shift for the MIGHTI instrument on the NASA-ICON satellite.

The Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI) instrument on NASA's Ionospheric Connection Explorer's mission will measure neutral winds in the Earth's thermosphere. We investigate how thermal changes to the instrument's optical bench affect the relative position of the image recorded by the camera. The thermal shift is measured by fitting the image of a series of reference notches and determining their current position on the camera with subpixel precision. Analyzing ground-based calibration data, we find that the image position is not affected within the uncertainty of the analysis for the applied thermal changes. We also address the question of the analysis uncertainty with signal-to-noise ratio.

Multiple Satellite Analysis of the Earth's Thermosphere and Interplanetary Magnetic Field Variations Due to ICME/CIR Events During 2003–2015

AbstractWe present a refined statistical analysis based on interplanetary coronal mass ejections (ICMEs) as well as corotating interaction regions (CIRs) for the time period 2003–2015 to estimate the impact of different solar wind types on the geomagnetic activity and the neutral density in the Earth's thermosphere. For the time‐based delimitation of the events, we rely on the catalog maintained by Richardson and Cane and the corotating interaction region lists provided by S. Vennerstrom and Jian et al. (2011, https://doi.org/10.1007/s11207‐011‐9737‐2). These archives are based on in situ measurements from the Advanced Composition Explorer and/or the Wind spacecraft. On this basis, we thoroughly investigated 196 Earth‐directed ICME and 195 CIR events. To verify the impact on the Earths thermosphere we determined neutral mass densities by using accelerometer measurements collected by the low‐Earth‐orbiting satellites Gravity Recovery and Climate Experiment and Challenging Minisatellite Payload. Subsequently, the atmospheric densities are related to characteristic ICME parameters. In this process a new calibration method has been examined. Since increased solar activity may lead to a decrease of the satellites orbital altitude we additionally assessed the orbital decay for each of the events and satellites. The influence of CIR events is in the same range of magnitude as the majority of the ICMEs (186 out of 196). Even though, the extended investigation period between 2011 and 2015 has a lack of extreme solar events the combined analysis reveals comparable correlation coefficients between the neutral densities and the various ICME and geomagnetic parameters (mostly >0.85). The evaluation of orbit decay rates at different altitudes revealed a high dependency on the satellite actual altitude.

Τhe observational and empirical thermospheric CO2 and NO power do not exhibit power-law behavior; an indication of their reliability

In this paper we investigate the evolution of the energy emitted by CO2 and NO from the Earth's thermosphere on a global scale using both observational and empirically derived data. In the beginning, we analyze the daily power observations of CO2 and NO received from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) equipment on the NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite for the entire period 2002–2016. We then perform the same analysis on the empirical daily power emitted by CO2 and NO that were derived recently from the infrared energy budget of the thermosphere during 1947–2016. The tool used for the analysis of the observational and empirical datasets is the detrended fluctuation analysis, in order to investigate whether the power emitted by CO2 and by NO from the thermosphere exhibits power-law behavior. The results obtained from both observational and empirical data do not support the establishment of the power-law behavior. This conclusion reveals that the empirically derived data are characterized by the same intrinsic properties as those of the observational ones, thus enhancing the validity of their reliability.

New Calibration Method of Accelerometers in GRACE Satellites Based on Precise Solar Radiation Model

Adopting the precise radiation pressure model, we compute the real perturbation force caused by the solar radiation on the GRACE satellites and estimate the scale factors of accelerometer's y axis and z axis. Setting these scale factors constant and using the dynamical orbit determination (OD), we estimate the rest four calibration parameters, i.e. the scale factor of the x axis and the biases of three axes. On this basis, we obtain the daily calibration parameters from 2002 to 2014. The average values and standard deviations of scale factors of the x, y and z axes are 0.9435 ± 0.0187, 0.9393 ± 0.0444, 1.0371 ± 0.0391 for GRACE-A, and 0.9313 ± 0.0170, 0.9488 ± 0.0452, 1.0274 ± 0.0446 for GRACE-B, respectively. Compared with our previous work, this new method constrains the scale factors of the y and z axes with the precise radiation pressure model, which can reduce the influence of data errors on the weak-signal axes (y, z), as well as reduce the correlation between scale factors and biases, and eventually improve the stability of calibration parameters. Taking the y and z axes of GRACE-A as an example, the standard deviations of scale factors with this new method are about 0.0391–0.0444, while the previous results obtained by the unconstrained dynamical orbit determination were about 0.21–0.31. It is shown that the standard deviations of scale factors in this paper have been reduced by more than 78%, and those of biases have been reduced by more than 85%. Therefore, the calibration parameters estimated with the new method are more stable and will be of particular interest for the study on the rotation speed and wind field of the Earth's thermosphere.

Trajectories of thermospheric air parcels flowing over Alaska, reconstructed from ground‐based wind measurements

AbstractIt is widely presumed that the convective stability and enormous kinematic viscosity of Earth's upper thermosphere hinders development of both horizontal and vertical wind shears and other gradients. Any strong local structure (over scale sizes of several hundreds of kilometers) that might somehow form would be expected to dissipate rapidly. Air flow in such an atmosphere should be relatively simple, and transport effects only slowly disperse and mix air masses. However, our observations show that wind fields in Earth's thermosphere have much more local‐scale structure than usually predicated by current modeling techniques, at least at auroral latitudes; they complicate air parcel trajectories enormously, relative to typical expectations. For tracing air parcels, we used wind measurements of an all‐sky Scanning Doppler Fabry‐Perot interferometer and reconstructed time‐resolved two‐dimensional maps of the horizontal vector wind field to infer forward and backward air parcel trajectories over time. This is the first comprehensive study to visualize the complex motions of thermospheric air parcels carried through the actual observed local‐scale structures in the high‐latitude winds. Results show that thermospheric air parcel transport is a very difficult observational problem, because the trajectories followed are very sensitive to the detailed features of the driving wind field. To reconstruct the actual motion of a given air parcel requires wind measurements everywhere along the trajectory followed, with spatial resolutions of 100 km or less, and temporal resolutions of a few minutes or better. Understanding such transport is important, for example, in predicting the global‐scale impacts of aurorally generated composition perturbations.

Influence of parameterized small‐scale gravity waves on the migrating diurnal tide in Earth's thermosphere

AbstractEffects of subgrid‐scale gravity waves (GWs) on the diurnal migrating tides are investigated from the mesosphere to the upper thermosphere for September equinox conditions, using a general circulation model coupled with the extended spectral nonlinear GW parameterization of Yiğit et al. (). Simulations with GW effects cut off above the turbopause and included in the entire thermosphere have been conducted. GWs appreciably impact the mean circulation and cool the thermosphere down by up to 12–18%. GWs significantly affect the winds modulated by the diurnal migrating tide, in particular, in the low‐latitude mesosphere and lower thermosphere and in the high‐latitude thermosphere. These effects depend on the mutual correlation of the diurnal phases of the GW forcing and tides: GWs can either enhance or reduce the tidal amplitude. In the low‐latitude MLT, the correlation between the direction of the deposited GW momentum and the tidal phase is positive due to propagation of a broad spectrum of GW harmonics through the alternating winds. In the Northern Hemisphere high‐latitude thermosphere, GWs act against the tide due to an anticorrelation of tidal wind and GW momentum, while in the Southern high‐latitudes they weakly enhance the tidal amplitude via a combination of a partial correlation of phases and GW‐induced changes of the circulation. The variable nature of GW effects on the thermal tide can be captured in GCMs provided that a GW parameterization (1) considers a broad spectrum of harmonics, (2) properly describes their propagation, and (3) correctly accounts for the physics of wave breaking/saturation.