Canadian Middle Atmosphere Model Research Articles

The Impact of Stratospheric Model Configuration on Planetary-Scale Waves in Northern Hemisphere Winter

Abstract The impact of stratospheric model configuration on modeled planetary-scale waves in Northern Hemisphere winter is examined using the Canadian Middle Atmosphere Model (CMAM). The CMAM configurations include a high-lid (0.001 hPa) and a low-lid (10 hPa) configuration, which were each run with and without conservation of parameterized gravity wave momentum flux. The planetary wave structure, vertical propagation, and the basic state are found to be in good agreement with reanalysis data for the high-lid conservative configuration with the exception of the downward-propagating wave 1 signal. When the lid is lowered and momentum is conserved, the wave characteristics and basic state are not significantly altered, with the exception of the downward-propagating wave 1 signal, which is damped by the act of conservation. When momentum is not conserved, however, the wave amplitude increases significantly near the lid, and there is a large increase in both the upward- and downward-propagating wave 1 signals and a significant increase in the strength of the basic state. The impact of conserving parameterized gravity wave momentum flux is found to be much larger than that of the model lid height. The changes to the planetary waves and basic state significantly impact the stratosphere–troposphere coupling in the different configurations. In the low-lid configuration, there is an increase in wave-reflection-type coupling over zonal-mean-type coupling, a reduction in stratospheric sudden warming events, and an increase in the northern annular mode time scale. Conserving gravity wave momentum flux in the low-lid configuration significantly reduces these biases.

On the consistency of model, ground‐based, and satellite observations of tidal signatures: Initial results from the CAWSES tidal campaigns

Comparisons between tidal wind signatures diagnosed from satellite and ground‐based observations and a general circulations model for two (September–October 2005, March–April 2007) of the four Climate and Weather of the Sun‐Earth System (CAWSES) Global Tidal Campaign observation periods are presented (CAWSES is an international program sponsored by Scientific Committee on Solar‐Terrestrial Physics). Specific comparisons are made between model (extended Canadian Middle Atmosphere Model), satellite (Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)), meteor, MF and incoherent scatter radar (ISR), and lidar tidal signatures in the mesosphere and lower thermosphere. The satellite and ground‐based signatures are in good agreement and demonstrate for the first time that the tidal wind fields observed by both types of observations are consistent with each other. This is the first time that such agreement has been reported and effectively resolves the long‐standing issue between ground‐based radar and satellite optical measurements of winds. This level of agreement, which has proved elusive in the past, was accomplished by superposing the significant tidal components from the satellite analyses to reconstruct the fields observed by the ground stations. Particularly striking in these comparisons is the extent to which the superposed fields show strong geographic variability. This variability is also seen in the component superpositions generated from the extended Canadian Middle Atmosphere Model (eCMAM), although differences in the geographic patterns are evident.

First multi-year occultation observations of CO<sub>2</sub> in the MLT by ACE satellite: observations and analysis using the extended CMAM

Abstract. This paper presents the first global set of observations of CO2 in the mesosphere and lower thermosphere (MLT) obtained by the ACE-FTS instrument on SCISAT-I, a small Canadian satellite launched in 2003. The observations use the solar occultation technique and document the fall-off in the mixing ratio of CO2 in the MLT region. The beginning of the fall-off of the CO2, or "knee" occurs at about 78 km and lies higher than in the CRISTA-1 measurements (~70 km) but lower than in the SABER 1.06 (~80 km) and much lower than in rocket measurements. We also present the measurements of CO obtained concurrently which provide important constraints for analysis. We have compared the ACE measurements with simulations of the CO2 and CO distributions in the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). Applying standard chemistry we find that we cannot get agreement between the model and ACE CO2 observations although the CO observations are adequately reproduced. There appears to be about a 10 km offset compared to the observed ACE CO2, with the model "knee" occurring too high. In analyzing the disagreement, we have investigated the variation of several parameters of interest (photolysis rates, formation rate for CO2, and the impact of uncertainty in turbulent eddy diffusion) in order to explore parameter space for this problem. Our conclusions are that there must be a loss process for CO2, about 2–4~times faster than photolysis that will sequester the carbon in some form other than CO and we have speculated on the role of meteoritic dust as a possible candidate. In addition, from this study we have highlighted a possible important role for unresolved vertical eddy diffusion in 3-D models in determining the distribution of candidate species in the mesosphere which requires further study.

The effect of nonlinearity in CO<sub>2</sub> heating rates on the attribution of stratospheric ozone and temperature changes

Abstract. An analysis of the attribution of past and future changes in stratospheric ozone and temperature to anthropogenic forcings is presented. The analysis is an extension of the study of Shepherd and Jonsson (2008) who analyzed chemistry-climate simulations from the Canadian Middle Atmosphere Model (CMAM) and attributed both past and future changes to changes in the external forcings, i.e. the abundances of ozone-depleting substances (ODS) and well-mixed greenhouse gases. The current study is based on a new CMAM dataset and includes two important changes. First, we account for the nonlinear radiative response to changes in CO2. It is shown that over centennial time scales the radiative response in the upper stratosphere to CO2 changes is significantly nonlinear and that failure to account for this effect leads to a significant error in the attribution. To our knowledge this nonlinearity has not been considered before in attribution analysis, including multiple linear regression studies. For the regression analysis presented here the nonlinearity was taken into account by using CO2 heating rate, rather than CO2 abundance, as the explanatory variable. This approach yields considerable corrections to the results of the previous study and can be recommended to other researchers. Second, an error in the way the CO2 forcing changes are implemented in the CMAM was corrected, which significantly affects the results for the recent past. As the radiation scheme, based on Fomichev et al. (1998), is used in several other models we provide some description of the problem and how it was fixed.

Impact of Climate Change on Stratospheric Sudden Warmings as Simulated by the Canadian Middle Atmosphere Model

Abstract The dynamics of Northern Hemisphere major midwinter stratospheric sudden warmings (SSWs) are examined using transient climate change simulations from the Canadian Middle Atmosphere Model (CMAM). The simulated SSWs show good overall agreement with reanalysis data in terms of composite structure, statistics, and frequency. Using observed or model sea surface temperatures (SSTs) is found to make no significant difference to the SSWs, indicating that the use of model SSTs in the simulations extending into the future is not an issue. When SSWs are defined by the standard (wind based) definition, an absolute criterion, their frequency is found to increase by ∼60% by the end of this century, in conjunction with a ∼25% decrease in their temperature amplitude. However, when a relative criterion based on the northern annular mode index is used to define the SSWs, no future increase in frequency is found. The latter is consistent with the fact that the variance of 100-hPa daily heat flux anomalies is unaffected by climate change. The future increase in frequency of SSWs using the standard method is a result of the weakened climatological mean winds resulting from climate change, which make it easier for the SSW criterion to be met. A comparison of winters with and without SSWs reveals that the weakening of the climatological westerlies is not a result of SSWs. The Brewer–Dobson circulation is found to be stronger by ∼10% during winters with SSWs, which is a value that does not change significantly in the future.

Sensitivity of Simulated Climate to Conservation of Momentum in Gravity Wave Drag Parameterization

Abstract The Canadian Middle Atmosphere Model is used to examine the sensitivity of simulated climate to conservation of momentum in gravity wave drag parameterization. Momentum conservation requires that the parameterized gravity wave momentum flux at the top of the model be zero and corresponds to the physical boundary condition of no momentum flux at the top of the atmosphere. Allowing momentum flux to escape the model domain violates momentum conservation. Here the impact of momentum conservation in two sets of model simulations is investigated. In the first set, the simulation of present-day climate for two model-lid height configurations, 0.001 and 10 hPa, which are identical below 10 hPa, is considered. The impact of momentum conservation on the climate with the model lid at 0.001 hPa is minimal, which is expected because of the small amount of gravity wave momentum flux reaching 0.001 hPa. When the lid is lowered to 10 hPa and momentum is conserved, there is only a modest impact on the climate in the Northern Hemisphere; however, the Southern Hemisphere climate is more adversely affected by the deflection of resolved waves near the model lid. When momentum is not conserved in the 10-hPa model the climate is further degraded in both hemispheres, particularly in winter at high latitudes, and the impact of momentum conservation extends all the way to the surface. In the second set of simulations, the impact of momentum conservation and model-lid height on the modeled response to ozone depletion in the Southern Hemisphere is considered, and it is found that the response can display significant sensitivity to both factors. In particular, both the lower-stratospheric polar temperature and surface responses are significantly altered when the lid is lowered, with the effect being most severe when momentum is not conserved. The implications with regard to the current round of Intergovernmental Panel on Climate Change model projections are discussed.

Sensitivity of climate to dynamically‐consistent zonal asymmetries in ozone

Previous investigations into the effect of zonal asymmetries in ozone on climate have compared simulations with prescribed 3‐D ozone, in which the ozone is not necessarily consistent with the model dynamics, to simulations with prescribed zonal mean ozone. We assess the impact of zonal asymmetries in ozone by comparing a control simulation of a coupled chemistry version of the Canadian Middle Atmosphere Model (CMAM) in which the ozone and model dynamics are consistent, with a simulation in which only the zonal mean of the ozone is passed to the radiative transfer scheme. These simulations reveal a robust stratospheric zonal‐mean temperature and geopotential height response to zonal asymmetries in ozone that is consistent with that identified in previous studies and of a magnitude comparable to observed trends. These results suggest that the inclusion of zonal asymmetries in ozone may be essential for the accurate simulation of future stratospheric temperature trends.

A new method of assessing filtering schemes in data assimilation systems

AbstractA new statistical diagnostic is proposed to assess the impact of externally applied filters in data assimilation systems with high‐lid atmospheric models. The diagnostic involves comparing the variances of 6 h differences of 6 h forecasts with those of a free model simulation. It was applied to the Canadian Middle Atmosphere Model Data Assimilation System (CMAM‐DAS) to choose among various filtering options. The variances of 6 h difference fields are shown to suppress long time‐scales and highlight short ones. This explains their sensitivity to a variety of filters considered and their relative insensitivity to the choice of initial conditions used for the time series. The method was used to quantify the extent to which a digital filter applied to the full state reduced the desired level of variability, as well as to determine objectively the most appropriate filter for our system from among several incremental analysis updating schemes. The method should be especially useful for models extending to the stratosphere and mesosphere, where short time‐scales represent significant contributions to the energy spectrum. Copyright © 2009 Royal Meteorological Society and Crown in the Right of Canada

Simulated Anthropogenic Changes in the Brewer–Dobson Circulation, Including Its Extension to High Latitudes

Abstract Recent studies using comprehensive middle atmosphere models predict a strengthening of the Brewer–Dobson circulation in response to climate change. To gain confidence in the realism of this result it is important to quantify and understand the contributions from the different components of stratospheric wave drag that cause this increase. Such an analysis is performed here using three 150-yr transient simulations from the Canadian Middle Atmosphere Model (CMAM), a Chemistry–Climate Model that simulates climate change and ozone depletion and recovery. Resolved wave drag and parameterized orographic gravity wave drag account for 60% and 40%, respectively, of the long-term trend in annual mean net upward mass flux at 70 hPa, with planetary waves accounting for 60% of the resolved wave drag trend. Synoptic wave drag has the strongest impact in northern winter, where it accounts for nearly as much of the upward mass flux trend as planetary wave drag. Owing to differences in the latitudinal structure of the wave drag changes, the relative contribution of resolved and parameterized wave drag to the tropical upward mass flux trend over any particular latitude range is highly sensitive to the range of latitudes considered. An examination of the spatial structure of the climate change response reveals no straightforward connection between the low-latitude and high-latitude changes: while the model results show an increase in Arctic downwelling in winter, they also show a decrease in Antarctic downwelling in spring. Both changes are attributed to changes in the flux of stationary planetary wave activity into the stratosphere.

Past and future conditions for polar stratospheric cloud formation simulated by the Canadian Middle Atmosphere Model

Abstract. We analyze here the polar stratospheric temperatures in an ensemble of three 150-year integrations of the Canadian Middle Atmosphere Model (CMAM), an interactive chemistry-climate model which simulates ozone depletion and recovery, as well as climate change. A key motivation is to understand possible mechanisms for the observed trend in the extent of conditions favourable for polar stratospheric cloud (PSC) formation in the Arctic winter lower stratosphere. We find that in the Antarctic winter lower stratosphere, the low temperature extremes required for PSC formation increase in the model as ozone is depleted, but remain steady through the twenty-first century as the warming from ozone recovery roughly balances the cooling from climate change. Thus, ozone depletion itself plays a major role in the Antarctic trends in low temperature extremes. The model trend in low temperature extremes in the Arctic through the latter half of the twentieth century is weaker and less statistically robust than the observed trend. It is not projected to continue into the future. Ozone depletion in the Arctic is weaker in the CMAM than in observations, which may account for the weak past trend in low temperature extremes. In the future, radiative cooling in the Arctic winter due to climate change is more than compensated by an increase in dynamically driven downwelling over the pole.

Impact of tropospheric and stratospheric data assimilation on mesospheric prediction

Numerical experiments are used to assess the potential benefit of the assimilation of tropospheric and stratospheric observations on mesospheric prediction. A simulated atmosphere, taken as truth, is created using the Canadian Middle Atmosphere Model (CMAM). The truth is sampled at the locations of the measurements from the actual observing system to produce observations, which are then assimilated with theCMAM-DAS (Data Assimilation System). Obtained forecasts are compared with the truth, and error statistics are calculated. An assessment based on predictability shows that upward propagation of information resulting from the assimilation of tropospheric and stratospheric observations improves the mesosphere in the largest scales (with horizontal wavenumbers less than approximately 10). At the same time, the principal inability of the system to predict mesospheric small scales is demonstrated.Numerical experiments are used to assess the potential benefit of the assimilation of tropospheric and stratospheric observations on mesospheric prediction. A simulated atmosphere, taken as truth, is created using the Canadian Middle Atmosphere Model (CMAM). The truth is sampled at the locations of the measurements from the actual observing system to produce observations, which are then assimilated with theCMAM-DAS (Data Assimilation System). Obtained forecasts are compared with the truth, and error statistics are calculated. An assessment based on predictability shows that upward propagation of information resulting from the assimilation of tropospheric and stratospheric observations improves the mesosphere in the largest scales (with horizontal wavenumbers less than approximately 10). At the same time, the principal inability of the system to predict mesospheric small scales is demonstrated.

Impact of tropospheric and stratospheric data assimilation on mesospheric prediction

Numerical experiments are used to assess the potential benefit of the assimilation of tropospheric and stratospheric observations on mesospheric prediction. A simulated atmosphere, taken as truth, is created using the Canadian Middle Atmosphere Model (CMAM). The truth is sampled at the locations of the measurements from the actual observing system to produce observations, which are then assimilated with theCMAM-DAS (Data Assimilation System). Obtained forecasts are compared with the truth, and error statistics are calculated. An assessment based on predictability shows that upward propagation of information resulting from the assimilation of tropospheric and stratospheric observations improves the mesosphere in the largest scales (with horizontal wavenumbers less than approximately 10). At the same time, the principal inability of the system to predict mesospheric small scales is demonstrated.

Technical Note: The CCCma third generation AGCM and its extension into the middle atmosphere

Abstract. The Canadian Centre for Climate Modelling and Analysis third generation atmospheric general circulation model (AGCM3) is described. The discussion summarizes the details of the complete physics package emphasizing the changes made relative to the second generation version of the model. AGCM3 is the underlying model for applications which include the IPCC fourth assessment, coupled atmosphere-ocean seasonal forecasting, the first generation of the CCCma earth system model (CanESM1), and middle-atmosphere chemistry-climate modelling (CCM). Here we shall focus on issues related to an upwardly extended version of AGCM3, the Canadian Middle-Atmosphere Model (CMAM). The CCM version of CMAM participated in the 2006 WMO/UNEP Scientific Assessment of Ozone Depletion and issues concerning its climate such as the impact of gravity-wave drag, the modelling of a spontaneous QBO, and the seasonality of the breakdown of the Southern Hemisphere polar vortex are discussed here.

Odin stratospheric proxy NO<sub>y</sub> measurements and climatology

Abstract. Five years of OSIRIS (Optical Spectrograph and InfraRed Imager System) NO2 and SMR (Sub-millimetre and Millimetre Radiometer) HNO3 observations from the Odin satellite, combined with data from a photochemical box model, have been used to construct a stratospheric proxy NOy data set including the gases: NO, NO2, HNO3, 2×N2O5 and ClONO2. This Odin NOy climatology is based on all daytime measurements and contains monthly mean and standard deviation, expressed as mixing ratio or number density, as function of latitude or equivalent latitude (5° bins) on 17 vertical layers (altitude, pressure or potential temperature) between 14 and 46 km. Comparisons with coincident NOy profiles from the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) instrument were used to evaluate several methods to combine Odin observations with model data. This comparison indicates that the most appropriate merging technique uses OSIRIS measurements of NO2, scaled with model NO/NO2 ratios, to estimate NO. The sum of 2×N2O5 and ClONO2 is estimated from uncertainty-based weighted averages of scaled observations of SMR HNO3 and OSIRIS NO2. Comparisons with ACE-FTS suggest the precision (random error) and accuracy (systematic error) of Odin NOy profiles are about 15% and 20%, respectively. Further comparisons between Odin and the Canadian Middle Atmosphere Model (CMAM) show agreement to within 20% and 2 ppb throughout most of the stratosphere except in the polar vortices. The combination of good temporal and spatial coverage, a relatively long data record, and good accuracy and precision make this a valuable NOy product for various atmospheric studies and model assessments.

Sensitivity of simulated climate to conservation of momentum in gravity wave drag parameterization

The Canadian Middle Atmosphere Model is used to examine the sensitivity of simulated climate to conservation of momentum in gravity wave drag parameterization. Momentum conservation requires that the parameterized gravity wave momentum flux at the top of the model be zero and corresponds to the physical boundary condition of no momentum flux at the top of the atmosphere. Allowing momentum flux to escape the model domain violates momentum conservation. Here the impact of momentum conservation in two sets of model simulations is investigated. In the first set, the simulation of present-day climate for two model-lid height configurations, 0.001 and 10 hPa, which are identical below 10 hPa, is considered. The impact of momentum conservation on the climate with the model lid at 0.001 hPa is minimal, which is expected because of the small amount of gravity wave momentum flux reaching 0.001 hPa. When the lid is lowered to 10 hPa and momentum is conserved, there is only a modest impact on the climate in the Northern Hemisphere; however, the Southern Hemisphere climate is more adversely affected by the deflection of resolved waves near the model lid. When momentum is not conserved in the 10-hPa model the climate is further degraded in both hemispheres, particularly in winter at high latitudes, and the impact of momentum conservation extends all the way to the surface. In the second set of simulations, the impact of momentum conservation and model-lid height on the modeled response to ozone depletion in the Southern Hemisphere is considered, and it is found that the response can display significant sensitivity to both factors. In particular, both the lower-stratospheric polar temperature and surface responses are significantly altered when the lid is lowered, with the effect being most severe when momentum is not conserved. The implications with regard to the current round of Intergovernmental Panel on Climate Change model projections are discussed.

Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model

Observations of noctilucent clouds have revealed a surprising coupling between the winter stratosphere and the summer polar mesopause region. In spite of the great distance involved, this inter-hemispheric link has been suggested to be the principal reason for both the year-to-year variability and the hemispheric differences in the frequency of occurrence of these high-altitude clouds. In this study, we investigate the dynamical influence of the winter stratosphere on the summer mesosphere using simulations from the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). We find that for both Northern and Southern Hemispheres, variability in the summer polar mesopause region from one year to another can be traced back to the planetary-wave flux entering the winter stratosphere. The teleconnection pattern is the same for both positive and negative wave-flux anomalies. Using a composite analysis to isolate the events, it is argued that the mechanism for inter-hemispheric coupling is a feedback between summer mesosphere gravity-wave drag (GWD) and zonal wind, which is induced by an anomaly in mesospheric cross-equatorial flow, the latter arising from the anomaly in winter hemisphere GWD induced by the anomaly in stratospheric conditions.

Summertime stratospheric processes at northern mid-latitudes: comparisons between MANTRA balloon measurements and the Canadian Middle Atmosphere Model

Abstract. In this paper we report on a study conducted using the Middle Atmospheric Nitrogen TRend Assessment (MANTRA) balloon measurements of stratospheric constituents and temperature and the Canadian Middle Atmosphere Model (CMAM). Three different kinds of data are used to assess the inter-consistency of the combined dataset: single profiles of long-lived species from MANTRA 1998, sparse climatologies from the ozonesonde measurements during the four MANTRA campaigns and from HALOE satellite measurements, and the CMAM climatology. In doing so, we evaluate the ability of the model to reproduce the measured fields and to thereby test our ability to describe mid-latitude summertime stratospheric processes. The MANTRA campaigns were conducted at Vanscoy, Saskatchewan, Canada (52° N, 107° W) in late August and early September of 1998, 2000, 2002 and 2004. During late summer at mid-latitudes, the stratosphere is close to photochemical control, providing an ideal scenario for the study reported here. From this analysis we find that: (1) reducing the value for the vertical diffusion coefficient in CMAM to a more physically reasonable value results in the model better reproducing the measured profiles of long-lived species; (2) the existence of compact correlations among the constituents, as expected from independent measurements in the literature and from models, confirms the self-consistency of the MANTRA measurements; and (3) the 1998 measurements show structures in the chemical species profiles that can be associated with transport, adding to the growing evidence that the summertime stratosphere can be much more disturbed than anticipated. The mechanisms responsible for such disturbances need to be understood in order to assess the representativeness of the measurements and to isolate long-term trends.

Normal mode Rossby waves and their effects on chemical composition in the late summer stratosphere

Abstract. During past MANTRA campaigns, ground-based measurements of several long-lived chemical species have revealed quasi-periodic fluctuations on time scales of several days. These fluctuations could confound efforts to detect long-term trends from MANTRA, and need to be understood and accounted for. Using the Canadian Middle Atmosphere Model, we investigate the role of dynamical variability in the late summer stratosphere due to normal mode Rossby waves and the impact of this variability on fluctuations in chemical species. Zonal wavenumber 1, westward travelling waves are considered with average periods of 5, 10 and 16 days. Time-lagged correlations between the temperature and nitrous oxide, methane and ozone fields are calculated in order to assess the possible impact of these waves on the chemical species. Using Fourier-wavelet decomposition and correlating the fluctuations between the temperature and chemical fields, we determine that variations in the chemical species are well-correlated with the 5- and 10-day waves between 30 and 60 km, although the nature of the correlations depend strongly on altitude. Interannual variability of the waves is also examined.

Vertical propagation of information in a middle atmosphere data assimilation system by gravity‐wave drag feedbacks

The mesospheric response to the 2002 Antarctic Stratospheric Sudden Warming (SSW) is analysed using the Canadian Middle Atmosphere Model Data Assimilation System (CMAM‐DAS), where it represents a vertical propagation of information from the observations into the data‐free mesosphere. The CMAM‐DAS simulates a cooling in the lowest part of the mesosphere which is accomplished by resolved motions, but which is extended to the mid‐ to upper mesosphere by the response of the model's non‐orographic gravity‐wave drag parameterization to the change in zonal winds. The basic mechanism is that elucidated by Holton consisting of a net eastward wave‐drag anomaly in the mesosphere during the SSW, although in this case there is a net upwelling in the polar mesosphere. Since the zonal‐mean mesospheric response is shown to be predictable, this demonstrates that variations in the mesospheric state can be slaved to the lower atmosphere through gravity‐wave drag.

Detection of migrating diurnal tide in the tropical upper troposphere and lower stratosphere using the Challenging Minisatellite Payload radio occultation data

The atmospheric limb sounding technique making use of radio signals transmitted by the Global Positioning System (GPS) has already proven to be a promising approach for global atmospheric measurements. In this study, we assess for the first time the potential of GPS radio occultation soundings for detecting the migrating diurnal tide. Retrieved temperatures between 10 and 30 km in the tropics from the Challenging Minisatellite Payload (CHAMP) occultation observations during May 2001 to August 2005 are analyzed using space‐time spectrum analysis to isolate diurnal waves. Because of incomplete local time (LT) coverage of the monthly CHAMP occultation data in any given year, data from all available years are merged to obtain complete 24‐h LT coverage. The effects of aliasing associated with uneven data sampling and measurement noise are estimated using synthetic data. The results show the feasibility of determining tidal structures from the composite CHAMP occultation data, and the vertical, seasonal, and latitudinal structures of the diurnal tide are presented. The estimated diurnal amplitude generally increases with altitude, exhibiting a maximum of order 1 K at 30 km. The estimated phase indicates an upward propagating mode above 14 km with a vertical wavelength about 20 km. The observed diurnal tide at 30 km exhibits a distinct seasonal‐latitudinal variation. Comparison of the observed diurnal tide to the simulated tide in the extended Canadian Middle Atmosphere Model (CMAM) and Global‐Scale Wave Model Version 2 (GSWM02) indicates that CMAM overestimates the amplitude but reproduces the seasonal‐latitudinal variation of the diurnal tide while GSWM02 simulates well the annual mean amplitude but lacks the seasonal‐latitudinal variation of the diurnal tide.