Thermosphere-ionosphere-mesosphere-electrodynamics General Circulation Model Research Articles

Thermospheric density enhancements in the dayside cusp region during strong BY conditions

Tri‐axial accelerometer data from the Challenging Minisatellite Payload (CHAMP) satellite have revealed the thermospheric density and its variability in unprecedented detail. The data often contain regions of high density located in the cusp sector at high latitudes. In this paper we provide the first detailed explanation of a high latitude density enhancement observed by CHAMP, focusing on the August 24, 2005 interval. The Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIMEGCM) was driven by high‐fidelity high‐latitude inputs specified by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) algorithm, and reproduced the main features of the density enhancements. The TIMEGCM and AMIE provide a global framework for interpretation of the CHAMP densities. Our simulations reveal that the observed density enhancement in the dayside cusp region resulted from unexpectedly large amounts of energy entering the Ionosphere‐Thermosphere system at cusp latitudes during an interval of strong (+20 nT) BY.

Comparison of CHAMP and TIME‐GCM nonmigrating tidal signals in the thermospheric zonal wind

Four years (2002–2005) of continuous accelerometer measurements taken onboard the CHAMP satellite (orbit altitude ∼400 km) offer a unique opportunity to investigate the thermospheric zonal wind on a global scale. Recently, we were able to relate the longitudinal wave‐4 structure in the zonal wind at equatorial latitudes to the influence of nonmigrating tides and in particular to the eastward propagating diurnal tide with zonal wave number 3 (DE3). The DE3 tide is primarily excited by latent heat release in the tropical troposphere in deep convective clouds. In order to investigate the mechanisms that couple the tidal signals to the upper thermosphere, we undertook a comparison with the thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) developed at the National Center for Atmospheric Research (NCAR). We ran the model for a day in March, June, September, and December and applied the same processing steps to the model output as was done for the CHAMP tidal analysis. The main results of the comparison can be summarized as follows: (1) TIME‐GCM simulations do not correctly reproduce the observed intra‐annual variations of DE3 and the eastward propagating diurnal tide with zonal wave number 2 (DE2). (2) Simulations of DE3 for June are more successful. Both TIME‐GCM and CHAMP show an increase in DE3 amplitudes with decreasing solar flux level. (3) The amplitudes of the simulated westward propagating diurnal tide with zonal wave number 2 (DW2) and the standing diurnal tide (D0) increase with increasing solar flux in June. The predicted dependence of DW2 and DO on solar flux is also observed by CHAMP.

Day-by-day modelling of the ionospheric F2-layer for year 2002

The thermosphere–ionosphere–mesosphere-electrodynamics general circulation model (TIME-GCM) has been run for the year 2002. Its version 1.2 features include day-by-day input of solar irradiance, geomagnetic energy input parameterized by the 3-h Kp index, and global lower boundary conditions from the National Centres for Environmental Prediction (NCEP) data. In addition, it includes tidal forcing from the global-scale wave model (GSWM) and parameterized gravity waves from below. The computed day-by-day values of noon peak electron density NmF2 agree well with ionosonde data for five northern sites and two southern mid-latitude sites, and closely follow the day-by-day modelled concentration ratio of atomic oxygen to molecular nitrogen. Seasonal and hemispheric patterns appear in the model with some, though not full, success. The model's day-to-day patterns show an impressive degree of variability, with simulations of total variability both above and below those observed.

Short‐term variation of the s = 1 nonmigrating semidiurnal tide during the 2002 stratospheric sudden warming

In this study, the NCAR Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME‐GCM) is used to examine short‐term changes in the global structure of the migrating and s = 1 nonmigrating semidiurnal tides in a model run approximating the 2002 Southern Hemisphere stratospheric sudden warming. The TIME‐GCM is found to resolve an s = 1 nonmigrating semidiurnal tide with latitudinal structure similar to that of prior studies and with global structure in the MLT region strongly correlated with Southern Hemisphere planetary wave 1 (PW1) wave events, prior to equinox. Comparison with a control run with no planetary wave activity, Eliassen‐Palm flux, and correlation analysis of the s = 1 semidiurnal tide structure suggest that the wave propagates from the source region in the winter hemisphere stratosphere into both the summer and winter lower thermospheres. The amplitudes of the migrating semidiurnal tide in the Southern Hemisphere are anticorrelated with the nonmigrating tide, suggesting significant energy loss due to nonmigrating tidal generation, a result not previously seen. The amplitude of the s = 1 nonmigrating semidiurnal tide from TIME‐GCM is also compared with data from the South Pole meteor radar system. While the observations show bursts of nonmigrating tidal activity correlated to PW1 activity of comparable amplitudes to the model results, these events do not always appear at the same times as those in the model. This suggests that while the processes generating the nonmigrating tide in TIME‐GCM are realistic, the TIME‐GCM run itself displays differences in time evolution compared to the observations during this time.

Seasonal variations of the nighttime O(1S) and OH airglow emission rates at mid‐to‐high latitudes in the context of the large‐scale circulation

The seasonal climatology of the O(1S) and OH nighttime airglow in the mesosphere and lower thermosphere (MLT) for the mid‐to‐high latitude region is explored in the context of the large‐scale general circulation. Multiple years of the Wind Imaging Interferometer (WINDII) satellite data from November 1991 to August 1997 are monthly averaged to depict the global patterns of the seasonal variations of the airglow volume emission rates for various altitudes and local times. These observations are compared with the simulations of the Thermosphere‐Ionosphere‐Mesosphere Electrodynamics General Circulation Model (TIME‐GCM). Both the WINDII and the TIME‐GCM results display the semi‐annual and annual variations of the O(1S) and OH airglow emission rates for specific altitudes and local times. The TIME‐GCM reproduces most of the emission variation signatures observed by WINDII, but provides additional information on vertical advection and downward mixing of atomic oxygen. The study indicates that vertical advection associated with the tides and the large‐scale circulation plays a major role in the airglow seasonal variations. The annual influence of the large‐scale circulation appears more clearly in the mesosphere than in the lower thermosphere, while the semi‐annual variation occurs only in the lower thermosphere.

Climatology of mesopause region temperature, zonal wind, and meridional wind over Fort Collins, Colorado (41°N, 105°W), and comparison with model simulations

Between May 2002 and April 2006, many continuous observations of mesopause region temperature and horizontal wind, each lasting longer than 24 h (termed full‐diurnal‐cycle observations), were completed at the Colorado State University Na Lidar Facility in Fort Collins, Colorado (41°N, 105°W). The combined data set consists of 120 full‐diurnal‐cycle observations binned on a monthly basis, with a minimum of 7 cycles in April and a maximum of 18 cycles in August. Each monthly data set was analyzed to deduce mean values and tidal period perturbations. After removal of tidal signals, monthly mean values are used for the study of seasonal variations in mesopause region temperature, zonal and meridional winds. The results are in qualitative agreement with our current understanding of mean temperature and wind structures in the midlatitude mesopause region with an observed summer mesopause of 167 K at 84 km, summer peak eastward zonal wind of 48 m/s at 94 km, winter zonal wind reversal at ∼95 km, and peak summer (pole) to winter (pole) meridional flow of 17 m/s at 86 km. The observed mean state in temperature, zonal and meridional winds are compared with the predictions of three current general circulation models, i.e., the Whole Atmosphere Community Climate Model version 3 (WACCM3) with two different simulations of gravity wavefields, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), and the 2003 simulation of the Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics General Circulation Model (TIME‐GCM). While general agreement is found between observation and model predictions, there exist discrepancies between model prediction and observation, as well as among predictions from different models. Specifically, the predicted summer mesopause altitude is lower by 3 km, 8 km, 3 km, and 1 km for WACCM3 the two WACCM runs, HAMMONIA, and TIME‐GCM, respectively, and the corresponding temperatures are 169 K, 170 K, 158 K, and 161 K. The model predicted summer eastward zonal wind peaks to 71 m/s at 102 km, to 48 m/s at 84 km, to 75 m/s at 93 km, and to 29 m/s at 94 km, in the same order. The altitude of the winter zonal wind reversal and seasonal asymmetry of the pole‐to‐pole meridional flow are also compared, and the importance of full‐diurnal‐cycle observations for the determination of mean states is discussed.

Connections between deep tropical clouds and the Earth's ionosphere

We report on a series of simulations with the National Center for Atmospheric Research (NCAR) thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) which were designed to replicate and facilitate the interpretation of the longitudinal structure discovered in IMAGE satellite airglow observations of the equatorial ionization anomaly (EIA) at the far‐ultraviolet (FUV) 135.6‐nm wavelength during March–April 2002 equinox. Our TIME‐GCM results indicate that the four‐peaked longitudinal variation in the EIA observed by IMAGE‐FUV near 20:00 local solar time can be explained by the effects of an eastward propagating zonal wavenumber‐3 diurnal tide (DE3) that is excited by latent heat release associated with raindrop formation in the tropical troposphere.

Comparative study of short‐term diurnal tidal variability

The wind and temperature measurements from an unusually long period operation of the sodium lidar at Colorado State University (41°N, 105°W) around September equinox 2003 showed significant short‐term tidal variability. Coincident with the large tidal changes, a strong temperature inversion layer was also observed above 90 km. Examination of the simultaneous temperature measurement from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, not only confirms the existence of the inversion layer but also reveals the global nature of the inversion, suggesting the presence of a transient planetary wave in the mesosphere. The large tidal variability, therefore, is probably a consequence of the interaction between the transient planetary wave and tides. This possibility is investigated by using the NCAR thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) and by comparing model results with the lidar, SABER, and TIMED Doppler Interferometer (TIDI) measurements. With a large transient planetary wave specified at the model lower boundary, the model is able to produce strong diurnal tidal variability comparable to that from the lidar observation, and the modeled temperature inversion is similar to that from the SABER measurement. The model results suggest that the planetary/tidal wave interaction excites nonmigrating tides and modulates the gravity modes and/or the rotational modes of the diurnal migrating tide. Among the nonmigrating tides, the diurnal zonally symmetric (S = 0) component is the strongest, and its interaction with the planetary wave leads to a strong diurnal eastward wave number 1 component.

A climatology of nonmigrating semidiurnal tides from TIMED Doppler Interferometer (TIDI) wind data

With the launch of the TIMED satellite in December 2001, continuous temperature and wind data sets amenable to MLT tidal analyses became available. The wind measuring instrument, the TIMED Doppler Interferometer (TIDI), is operating since early 2002. Its day- and nighttime capability allows to derive tidal winds over a range of MLT altitudes. This paper presents climatologies (June 2002–June 2005) of monthly mean amplitudes and phases for six nonmigrating semidiurnal tidal components between 85 and 105 km altitude and between 45°S and 45°N latitude (westward propagating wave numbers 4, 3, 1; the standing oscillation s0; and eastward propagating wave numbers 1, 2) in the zonal and meridional wind directions. Amplitude errors are 15–20% (accuracy) and 0.8 m/s (precision). The phase error is 2 h. The TIDI analysis agrees well with 1991–1994 UARS results at 95 km. During boreal winter, amplitudes of a single component can reach 10 m/s at latitudes equatorward of 45°. Aggregate effects of nonmigrating tides can easily reach or exceed the amplitude of the migrating tide. Comparisons with the global scale wave model (GSWM) and the thermosphere–ionosphere–mesosphere–electrodynamics general circulation model (TIME-GCM) are partly inconclusive but they suggest that wave–wave interaction and latent heat release in the tropical troposphere both play an important role in forcing the semidiurnal westward 1, westward 3, and standing components. Latent heat release is the leading source of the eastward propagating components.

An ion drag contribution to the lower thermospheric wind in the summer polar region

Using the European incoherent scatter (EISCAT) Svalbard radar located in Longyearbyen (78.2°N, 16.0°E) and with the EISCAT UHF radar located in Tromsø (69.6°N, 19.2°E), we have analyzed the data obtained for six consecutive days from 1000 UT on 1 July 1999 to 1000 UT on 7 July 1999 to investigate the importance of ion drag on the lower thermospheric wind dynamics in the summer polar region. The electric field observed at Longyearbyen exhibited a stable diurnal variation primarily occurring throughout the first 3 days of observations, while, during the latter 3 days, the diurnal variation was not clearly identified. The electric field observed at Tromsø did not exhibit such a stable variation. On the basis of the difference of the electric field variation observed at Longyearbyen, we divided the data sets into two intervals with a length of 3 days each. We compared the horizontal velocities of the ions and the neutral gases. At upper heights (∼110–120 km) on the first 3 days, the difference between the ion and neutral motion was clearly identified at Longyearbyen, while it was not at Tromsø. We compared the diurnal tidal amplitudes and phases of the two intervals derived from the Longyearbyen data. The amplitude of the meridional diurnal tide for the first 3 days was larger than that of the latter 3 days over the height region between 100 and 118 km at Longyearbyen. Furthermore, we compared ion drag accelerations with total accelerations. We concluded that the ion drag played an important role in the diurnal amplitude at Longyearbyen on the first 3 days of the observations. In addition, we compared the National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) predictions with the observations. The TIME‐GCM predictions also indicated that the diurnal tide is influenced by the convection electric field.

The impact of stormtime changes in the non-auroral conductance upon the low- and mid-latitude electric field

The interaction between the ionosphere and magnetosphere that generates the subauroral electric field is complex. In general, the magnetosphere provides the currents and the ionosphere and thermosphere provide the resistance. During geomagnetic storms, the subauroral electric field intensifies. At the same time, the stormtime energy input generates changes to the thermosphere that alter the ionospheric conductivity. These ionospheric changes are slow-forming and long-lasting. For this reason, two very similar sets of solar wind drivers, separated in time by a few days, may generate different electric field behavior. This study examines the impact of negative phase preconditioning upon the subauroral electric field development. The prompt-penetration component of the subauroral electric field is calculated by the Rice Convection Model (RCM) using ionospheric conductances calculated from runs of the Thermosphere–Ionosphere–Mesosphere Electrodynamics General Circulation Model. A simple step-function in the convection electric field drives the RCM simulations. The results show that the preconditioned conductances produce significant effects in the predawn sector. However, the negative storm phase did not significantly impact the electric field outside of this region. In addition, the negative phase conductance causes only a minor decrease in the initial strength of the penetration electric field.

Diurnal nonmigrating tides from TIMED Doppler Interferometer wind data: Monthly climatologies and seasonal variations

TIMED Doppler Interferometer (TIDI) measurements of zonal and meridional winds in the mesosphere/lower thermosphere are analyzed for diurnal nonmigrating tides (June 2002 to June 2005). Climatologies of monthly mean amplitudes and phases for seven tidal components are presented at altitudes between 85 and 105 km and latitudes between 45°S and 45°N (westward propagating wave numbers 2, 3, and 4; the standing diurnal tide; and eastward propagating wave numbers 1, 2, and 3). The observed seasonal variations agree well with 1991–1994 UARS results at 95 km. Comparisons between the TIDI results and global scale wave model (GSWM) and thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) tidal predictions indicate that the large eastward propagating wave number 3 amplitude is driven by tropical tropospheric latent heat release alone. In contrast, latent heating and planetary wave/migrating tidal interactions are equally important to westward 2 and standing diurnal tidal forcing. There is good quantitative agreement between TIDI and the model predictions during equinox, but the latter tend to underestimate the westward 2 and standing diurnal tide during solstice. Neither model reproduces the observed seasonal variations of the eastward propagating components.

Mesospheric surf zone and temperature inversion layers in early November 1994

Carbon monoxide, temperature, and potential vorticity data (November, 1994) from the cryogenic infrared spectrometers and telescopes for the atmosphere (CRISTA) experiment are used to analyze the relationship between the mesospheric surf zone in the winter hemisphere and simultaneously observed thermal inversions just above. The observed upward propagating planetary waves rapidly decay when they approach the critical wind line in the upper mesosphere and a distinct surf zone is formed between 60–75 km. Above 85 km, the planetary wave activity increases again revealing an out-of-phase behavior with the waves below. This is likely due to momentum forcing associated with breaking gravity waves that have been filtered by the stratospheric and lower mesospheric planetary waves. The abrupt vertical phase shift of the planetary waves thus induces a strong vertical geopotential curvature that is sufficiently large, through hydrostatic equilibrium, to invert the thermal structure around 80 km. The CRISTA observations and their interpretation are consistent with simulations of the thermosphere–ionosphere–mesosphere-electrodynamics general circulation model (TIME-GCM) that was run for the same time period. Both the observation and the model results rather point to a more indirect, though essential, role of the gravity waves in the formation of the mesospheric inversion layers in early winter 1994.

Observations of the 5-day wave in the mesosphere and lower thermosphere

The 5-day wave is the gravest symmetric Hough mode of westward propagating zonal wavenumber 1. This wave is observed using the SABER instrument aboard the TIMED satellite during the first three years of the spacecraft mission (2002–2004). Supporting measurements were made with mesospheric radar systems. To better interpret the observations, the NCAR thermosphere–ionosphere–mesosphere–electrodynamics general circulation model (TIME-GCM) simulation of year 2003 is used for comparative analysis. For the simulation the lower boundary was specified using NCEP data. The climatology from SABER shows a May maximum in the amplitude of the 5-day wave, which is consistent with the seasonal dependence found in earlier studies. A particularly strong wave with a ∼6 day period was observed in May 2003 and is studied in some detail. There is considerable evidence from both data and model in our study that a major source for this wave was in the southern (winter) hemisphere. Cross-equatorial ducting allowed the wave to propagate into the northern (summer) hemisphere, where it was amplified by baroclinic instability.

Non-migrating diurnal tides as measured by the TIMED Doppler interferometer: Preliminary results

Preliminary meridional wind data from the TIMED Doppler Interferometer (TIDI) onboard the TIMED satellite are analyzed for nonmigrating diurnal tides. Tidal definitions are given for the most pronounced westward, eastward and standing oscillations (w2, e3, s0). The analysis interval is March 2002 to June 2004 and covers the altitude range 85-105 km. Monthly tidal wind fields from 40 � S-40 � N are presented. TIDI tides compare favorably with previously reported 95 km HRDI results. Nonmigrating diurnal tidal wind speeds larger than 30 m/s are observed thus emphasizing the important role of nonmigrating tides in middle atmosphere coupling. A comparative analysis with the Global Scale Wave Model (GSWM) and the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) indicates that both latent heat release in the tropical troposphere and non-linear Planetary Wave / migrating tide interaction are important sources of nonmigrating tides in the mesosphere and lower thermosphere.

The 6.5‐day wave and its seasonal variability in the middle and upper atmosphere

The zonal wave number 1 planetary wave of period near 6.5 days is a robust feature in the mesosphere and lower thermosphere (MLT) region with prominent seasonal variability as revealed by ground based and satellite observations. This wave and its seasonal variability are well reproduced in a recent one model year run of the National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere‐electrodynamics general circulation model (TIME‐GCM) with its lower boundary specified according to the National Centers for Environmental Prediction analysis (year 1993). Wavelet analysis of the model output shows that in the MLT region the wave maximizes before and after the equinoxes and minimizes at solstices. The wave amplitudes at the equinoxes are smaller than the peaks before and after but are still larger than the wave amplitudes at solstices. However, at the lower boundary near 30 km the wave peaks are predominantly between fall and the following spring. By examining the episodes of maximum and minimum wave amplitude and by conducting additional control experiments using the TIME‐GCM, the structure of this planetary wave and the factors determining the wave characteristics and seasonal variability are studied in detail. It is found that the wave source, mean wind structure, instability, and the critical layers of the wave can all affect the wave response in the MLT region and can have a strong seasonal dependence. Before and after equinox, the wave follows the waveguide and propagates from the stratosphere to the summer mesosphere/mesopause, where it may amplify due to baroclinic/barotropic instability. Such instability is usually absent from the equinoctial atmosphere, so that there is no wave amplification at equinox. At solstice the wave decays significantly when propagating away from its winter source due to the strong eastward winter stratospheric jet. In the summer side the westward jet is also strong, and the meridional and vertical extension of the critical layer of the wave is large enough to enclose the instability in the summer mesosphere/mesopause at middle to high latitudes. The wave is thus reflected away and prevented from reaching and amplifying at the unstable region. The seasonal variation of the quasi‐two‐day wave, which has zonal phase speed similar to the 6.5‐day wave, is also studied using similar diagnostics. It is further shown that within certain seasonal “window” periods, the variability in the MLT, especially the summer MLT, may closely track the lower atmospheric variability associated with these waves.

Gravity Wave Induced Fluctuation of OH Airglow Profile

AbstractA model for the effect of nonlinear propagating gravity wave on OH airglow profile is set up by using the Full Implicit Continuous Eulerian (FICE) scheme and the Thermosphere‐Ionosphere‐Mesosphere Electrodynamics General Circulation Model (TIME‐GCM). Analysis shows that the shorter vertical wavelength gravity wave significantly influences the peak layer of OH volume emission rate when the gravity wave propagates through the emission layer. In some cases it induces a double‐peak structure in OH volume emission rate profile, suggesting that the non‐linear propagation of gravity wave is a direct cause to the double‐peak structure of OH airglow. In addition, the profile of OH airglow is sensitive to the breaking of gravity wave at mesospause. These results can explain some observations, and can provide a good indication for studying the characteristic of nonlinear gravity wave by using OH airglow measurement.

A global view of tidal temperature perturbations above the mesopause: Preliminary model/observation intercomparison

Migrating and nonmigrating diurnal tides in the temperature data from the satellite borne, Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment are compared to model predictions from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME-GCM) and from the Global Scale Wave Model (GSWM). The comparative model/observation analysis is performed between 75–120 km altitude and at 7.5°N. The results suggest that interactions between quasi-stationary planetary waves and radiative and latent heat forced tidal components may play an important role in generating the thermal tidal structure above the mesopause though more extended model studies are necessary.

Lidar studies of interannual, seasonal, and diurnal variations of polar mesospheric clouds at the South Pole

Polar mesospheric clouds (PMC) were observed by an Fe Boltzmann temperature lidar at the South Pole in the 1999–2000 and 2000–2001 austral summer seasons. We report the study of interannual, seasonal, and diurnal variations of PMC using more than 430 h of PMC data. The most significant differences between the two seasons are that in the 2000–2001 season, the PMC mean total backscatter coefficient is 82% larger and the mean centroid altitude is 0.83 km lower than PMC in the 1999–2000 season. Clear seasonal trends in PMC altitudes were observed at the South Pole where maximum altitudes occurred around 10–20 days after summer solstice. Seasonal variations of PMC backscatter coefficient and occurrence probability show maxima around 25–40 days after summer solstice. Strong diurnal and semidiurnal variations in PMC backscatter coefficient and centroid altitude were observed at the South Pole with both in‐phase and out‐of‐phase correlations during different years. A significant hemispheric difference in PMC altitudes was found, that the mean PMC altitude of 85.03 km at the South Pole is about 2–3 km higher than PMC in the northern hemisphere. Through comparisons with the NCAR Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics General Circulation Model (TIME‐GCM), the hemispheric difference in PMC altitude is attributed to the hemispheric differences in the altitudes of supersaturation region and in the upwelling vertical wind, which are mainly caused by different solar forcing in two hemispheres that the solar flux in January is 6% greater than the solar flux in July due to the Earth's orbital eccentricity. Gravity wave forcing also contributes to these differences.

Tidal signatures and aliasing in temperature data from slowly precessing satellites

Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME‐GCM) data are used to simulate tidal patterns in satellite‐borne observations of the mesosphere and lower thermosphere (MLT) region. The results are given for the measurement geometry of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument, though the technique is applicable to any satellite‐based instrument. TIME‐GCM tides are sampled along the instrument measurement track and analyzed in terms of ascending/descending orbit node differences. Our simulations show a significant aliasing, e.g., of migrating and nonmigrating diurnal and semidiurnal components into tidal fields of observed zonal wavenumbers s′ ≥ 0. Above the mesopause, the model tides induce a 10 K bias in daily means of zonally averaged temperatures. An estimate of the tide‐induced vertical displacement of air parcels is given, assuming tidal motions are adiabatic. Corresponding signatures are expected to be present in MLT observations of chemical species. Addressing tidal‐sampling issues is of general interest for comparing satellite observations with models, climatologies, and other measurements.