Middle Atmosphere General Circulation Model Research Articles

Mean-Flow Effects of Thermal Tides in the Mesosphere and Lower Thermosphere

Abstract This study addresses the heat budget of the mesosphere and lower thermosphere with regard to the energy deposition of upward-propagating waves. To this end, the energetics of gravity waves are recapitulated using an anelastic version of the primitive equations. This leads to an expression for the energy deposition of waves that is usually resolved in general circulation models. The energy deposition is shown to be mainly due to the frictional heating and, additionally, due to the negative buoyancy production of wave kinetic energy. The frictional heating includes contributions from horizontal and vertical momentum diffusion, as well as from ion drag. This formalism is applied to analyze results from a mechanistic middle-atmosphere general circulation model that includes energetically consistent parameterizations of diffusion, gravity waves, and ion drag. This paper estimates 1) the wave driving and energy deposition of thermal tides, 2) the model response to the excitation of thermal tides, and 3) the model response to the combined energy deposition by parameterized gravity waves and resolved waves. It is found that thermal tides give rise to a significant energy deposition in the lower thermosphere. The temperature response to thermal tides is positive. It maximizes at polar latitudes in the lower thermosphere as a result of poleward circulation branches that are driven by the predominantly westward Eliassen–Palm flux divergence of the tides. In addition, thermal tides give rise to a downward shift and reduction of the gravity wave drag in the upper mesosphere. Including the energy deposition in the model causes a substantial warming in the upper mesosphere and lower thermosphere.

Southern Hemisphere Extratropical Gravity Wave Sources and Intermittency Revealed by a Middle-Atmosphere General Circulation Model

Abstract Southern Hemisphere extratropical gravity wave activity is examined using simulations from a free-running middle-atmosphere general circulation model called Kanto that contains no gravity wave parameterizations. The total absolute gravity wave momentum flux (MF) and its intermittency, diagnosed by the Gini coefficient, are examined during January and July. The MF and intermittency results calculated from the Kanto model agree well with results from satellite limb and superpressure balloon observations. The analysis of the Kanto model simulations indicates the following results. Nonorographic gravity waves are generated in Kanto in the frontal regions of extratropical depressions and around tropopause-level jets. Regions with lower (higher) intermittency in the July midstratosphere become more (less) intermittent by the mesosphere as a result of lower-level wave removal. The gravity wave intermittency is low and nearly homogeneous throughout the SH middle atmosphere during January. This indicates that nonorographic waves dominate at this time of year, with sources including continental convection as well as oceanic depressions. Most of the zonal-mean MF at 40°–65°S in January and July is due to gravity waves located above the oceans. The zonal-mean MF at lower latitudes in both months has a larger contribution from the land regions but the fraction above the oceans remains larger.

A parameterization of gravity waves emitted by fronts and jets

AbstractBased on the theoretical and experimental facts that gravity waves (GWs) can be spontaneously emitted during the evolution of a near‐balanced flow, a stochastic parameterization of GWs linked to fronts and jets is proposed. Although the spontaneous adjustment theory used predicts “exponentially” small GW fields, it is shown that it is sufficient to produce realistic GW drag at mesospheric levels. Off‐line tests using reanalyzed meteorological fields are conducted and show that the GWs emitted present a strong annual cycle following that of the sources. Also, the GW momentum fluxes in the lower stratosphere are qualitatively realistic in terms of intermittency. Online tests in a middle atmosphere general circulation model show that the scheme can potentially perform as well as highly tuned existing GW schemes.

Dynamics of polar vortices at cloud top and base on Venus inferred from a general circulation model: Case of a strong diurnal thermal tide

Polar vortices in the presence of a thermal tide are investigated using a Venusian middle atmosphere general circulation model. Around the cloud top, where the warm polar region is maintained by the thermal wind associated with a high latitude jet, the temperature contrast forms the polar vortex pattern. The cold collar and hot oval (monopole) near the pole are enhanced by the polar diurnal tide, and unstable vortices form the hot dipole and tripole. The centroid of the hot oval is displaced from the pole to around 80° by the diurnal tide. The hot dipole appears and breaks up into a tripole when transient vortical and divergent eddies with zonal wavenumbers 2 and higher are predominant within the polar hot oval region. Because the divergence and temperature are a quarter cycle out of phase with the eddy vorticity, the vortical eddies transport heat toward the cold region. Thus, the cloud-top polar vortices are mainly formed by a combination of the diurnal tide and transient baroclinic wave. At the cloud base, isotherms are almost zonally uniform and the eddy temperature structure is not apparent. In contrast, divergence and vorticity have large amplitudes within this region. The vortical eddies have a comma-shaped pattern, which is stably maintained and rotates with a period of about 5 days. The divergence and vorticity might be important in controlling cloud morphology at the cloud base via material transport.

The SOCOL version 3.0 chemistry–climate model: description, evaluation, and implications from an advanced transport algorithm

Abstract. We present the third generation of the coupled chemistry–climate model (CCM) SOCOL (modeling tools for studies of SOlar Climate Ozone Links). The most notable modifications compared to the previous model version are (1) the dynamical core has been updated with the fifth generation of the middle-atmosphere general circulation model MA-ECHAM (European Centre/HAMburg climate model), and (2) the advection of the chemical species is now calculated by a mass-conserving and shape-preserving flux-form transport scheme instead of the previously used hybrid advection scheme. The whole chemistry code has been rewritten according to the ECHAM5 infrastructure and transferred to Fortran95. In contrast to its predecessors, SOCOLvs3 is now fully parallelized. The performance of the new SOCOL version is evaluated on the basis of transient model simulations (1975–2004) with different horizontal (T31 and T42) resolutions, following the approach of the CCMVal-1 model validation activity. The advanced advection scheme significantly reduces the artificial loss and accumulation of tracer mass in regions with strong gradients that was observed in previous model versions. Compared to its predecessors, SOCOLvs3 generally shows more realistic distributions of chemical trace species, especially of total inorganic chlorine, in terms of the mean state, but also of the annual and interannual variability. Advancements with respect to model dynamics are for example a better representation of the stratospheric mean state in spring, especially in the Southern Hemisphere, and a slowdown of the upward propagation in the tropical lower stratosphere. Despite a large number of improvements model deficiencies still remain. Examples include a too-fast vertical ascent and/or horizontal mixing in the tropical stratosphere, the cold temperature bias in the lowermost polar stratosphere, and the overestimation of polar total ozone loss during Antarctic springtime.

Stratospheric ozone and the morphology of the northern hemisphere planetary waveguide

A middle atmosphere general circulation model is used to examine the effects of zonally asymmetric ozone (ZAO) on the Northern Hemisphere planetary waveguide (PWG) during winter (December–February). The morphology of the PWG is measured by a refractive index, Eliassen‐Palm flux vectors, the latitude of the subtropical zero wind line, and the latitude of the subtropical jet. ZAO causes the PWG to contract meridionally in the upper stratosphere, expand meridionally in the lower stratosphere, and expand vertically in the upper stratosphere and lower mesosphere. The ZAO‐induced changes in the PWG are the result of increased upward and poleward flux of planetary wave activity into the extratropical stratosphere and lower mesosphere. These changes cause an increase in the Eliassen‐Palm flux convergence at high latitudes, which produces a warmer and weaker stratospheric polar vortex and an increase in the frequency of stratospheric sudden warmings. The ability of ZAO to alter the flux of planetary wave activity into the polar vortex has important implications for accurately modeling wave‐modulated and wave‐driven phenomena in the middle atmosphere, including the 11‐year solar cycle, stratospheric sudden warmings, and the phase of the Northern Hemisphere annular mode.

Gravity Wave Characteristics in the Southern Hemisphere Revealed by a High-Resolution Middle-Atmosphere General Circulation Model

AbstractGravity wave characteristics in the middle- to high-latitude Southern Hemisphere are analyzed using simulation data over 3 yr from a high-resolution middle-atmosphere general circulation model without using any gravity wave parameterizations. Gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere, while the gravity wave energy is generally weak in summer. The wave energy distribution in winter is not zonally uniform, but it is large leeward of the southern Andes and Antarctic Peninsula. Linear theory in the three-dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector. Results of ray-tracing and cross-correlation analyses are consistent with this theoretical expectation. The leeward energy propagation extends to several thousand kilometers, which explains part of the gravity wave distribution around the polar vortex in winter. This result indicates that orographic gravity waves can affect the mean winds at horizontal locations that are far distant from the source mountains. Another interesting feature is a significant downward energy flux in winter, which is observed in the lower stratosphere to the south of the southern Andes. The frequency of the downward energy flux is positively correlated with the gravity wave energy over the southern Andes. Partial reflection from a rapid increase in static stability around 10 hPa and/or gravity wave generation through nonlinear processes are possible mechanisms to explain the downward energy flux.

Analysis of fast and ultrafast Kelvin waves simulated by the Kyushu-GCM

Properties of fast and ultrafast Kelvin waves from the lower stratosphere to the mesosphere and lower thermosphere (MLT) region simulated by the Kyushu University Middle Atmosphere General Circulation Model (Kyushu-GCM) have been investigated based on a single-year dataset. Eastward-propagating components with zonal wavenumber s=1 have been shown to exhibit Kelvin wave structures. These waves are fast and ultrafast Kelvin waves in the lower mesosphere and the MLT region, respectively. Signatures of Kelvin wave structures are recognized throughout the region from the lower stratosphere to the lower thermosphere. Vertical wavelengths of fast and ultrafast Kelvin waves are identified in the altitude range from 15 to 20km and between 30 and 60km, respectively. Wave amplitudes increase with increasing height, where the growth rate nearly conserves the wave energy density, which is consistent with theoretical predictions and observational results. Eastward-tilting phase lines show upward energy and downward phase propagation. Eastward-tilting vertical structures, vertically growing wave amplitudes, and upward Eliassen–Palm (EP) flux vectors show that the Kelvin waves propagate vertically, implying that they are excited in the troposphere. Dissipation of ultrafast Kelvin waves in the MLT region is highly visible at heights of 90–100km. The zonal accelerations caused by this wave dissipation fluctuate over time and are characterized by values between 8 and −0.5ms−1day−1, while the annual average is approximately 1ms−1day−1 at 100km height.

Venusian middle-atmospheric dynamics in the presence of a strong planetary-scale 5.5-day wave

The middle atmospheric dynamics on Venus are investigated using a middle atmosphere general circulation model. The magnitude of the superrotation is sensitive to the amplitude of the planetary-scale waves. In particular, the critical level absorptions of the forced planetary-scale waves might contribute to the maintenance of the superrotation near the cloud base. In the case of strong 5.5-day wave forcing, the superrotation with zonal wind speed higher than 100 m s −1 is maintained by the forced wave. Four-day and 5.5-day waves are found near the equatorial cloud top and base, respectively. The planetary-scale waves have a Y-shaped pattern maintained by the amplitude modulation in the presence of strong thermal tides. The polar hot dipole is unstable and its dynamical behavior is complex near the cloud top in this model. The dipole merges into a monopole or breaks up into a tripole when the divergent eddies with high zonal wavenumbers are predominant in the hot dipole region. A cold collar is partly enhanced by a cold phase of slowly propagating waves with zonal wavenumber 1. Although such a complex dipole behavior has not been observed yet, it is likely to occur under a dynamical condition similar to the present simulation. Thus, the dynamical approach using a general circulation model might be useful for analyzing Venus Express and ground-based observation data.

A simple model for the interhemispheric coupling of the middle atmosphere circulation

The interhemispheric coupling of the middle atmosphere general circulation is characterized by a global anomaly pattern of the zonal-mean temperature. This pattern reflects an anomalous stratospheric and mesospheric residual circulation, in which a weaker (stronger) stratospheric winter circulation is linked to an upward (downward) shift of its upper mesospheric branch reaching from the summer to the winter pole. This phenomenon is robust in observational data and several middle atmosphere general circulation models. In the present study, the recently proposed mechanism of the interhemispheric coupling is unequivocally proven within the framework of a zonally symmetric model that excludes any additional effects due to resolved waves and non-zonally propagating gravity waves. Two simulations are conducted that differ in the strength of the polar vortex. A weaker polar vortex results in a downward shift of the winter mesospheric gravity wave drag. This leads to changes also in the summer upper mesosphere via a feedback solely between gravity wave breaking and the zonal-mean state. The accompanying temperature anomaly reproduces the pattern of the interhemispheric coupling.

Simulation of the eastward 4‐day wave in the Antarctic winter mesosphere using a gravity wave resolving general circulation model

The eastward moving 4‐day wave in the Antarctic winter mesosphere is investigated using a high‐resolution middle atmosphere general circulation model that directly simulates the spontaneous generation, propagation, and dissipation of gravity waves. The results are also compared with the simulated seasonal march of the meridional structures of the westerly jet streams in the Southern Hemisphere upper stratosphere and mesosphere in order to investigate baroclinic/barotropic instability as a possible excitation mechanism for the 4‐day wave. The model successfully reproduces the dynamically unstable double‐jet structure of the mesospheric westerly winds. The simulated 4‐day wave develops in association with the baroclinic and barotropic instability of the mesospheric mean flows and has similar characteristics to those observed at 50–60°S near the stratopause. The 4‐day wave has strong equatorward heat flux associated with strong baroclinicity in the Antarctic winter mesosphere, mainly attributable to poleward overturning circulation driven by gravity wave forcing. Eastward forcing due to the 4‐day wave occurs within the double‐jet structure and offsets part of the westward forcing due to gravity waves. Such an effect partially acts to stabilize the unstable mean flow structure in the Antarctic winter mesosphere.

Consistent Scale Interaction of Gravity Waves in the Doppler Spread Parameterization

Abstract The standard Doppler spread parameterization of gravity waves, which was proposed by C.-O. Hines and has been applied in a number of middle atmosphere general circulation models, is extended by the inclusion of all effects associated with vertical diffusion. Here the Wentzel–Kramers–Brillouin (WKB) approximation is employed to calculate the vertical propagation of the wave spectrum in the presence of wave damping. According to the scale interaction between quasi-stationary turbulence and the larger nonturbulent flow, all vertical diffusion applied to the resolved flow should damp the parameterized gravity waves as well. Hence, the unobliterated part of the gravity wave spectrum is subject to diffusive damping by the following processes: 1) the background diffusion derived from the model’s boundary layer vertical diffusion scheme, which may extend into the middle atmosphere, 2) molecular diffusion, and 3) the turbulent diffusion resulting from the truncation of the gravity wave spectrum by Doppler spreading, which thus feeds back on the unobliterated gravity waves. The extended Doppler spread parameterization is examined using perpetual July simulations performed with a mechanistic general circulation model. For reasonable parameter settings, the convergence of the potential temperature flux cannot be neglected in the sensible heat budget, especially in the thermosphere. Less gravity wave flux enters the model thermosphere when vertical diffusion is included, thus avoiding the need for artificial means to control the parameterized gravity waves in the upper atmosphere. The zonal wind in the tropical middle and upper atmosphere is found to be especially sensitive to gravity wave damping by diffusion.

Modeling the effects of gravity wave momentum deposition on the general circulation above the turbopause

A nonlinear spectral gravity wave (GW) drag parameterization systematically accounting for breaking and dissipation in the thermosphere developed by Yiğit et al. (2008) has been implemented into the University College London Coupled Middle Atmosphere‐Thermosphere‐2 (CMAT2) general circulation model (GCM). The dynamical role of GWs propagating upward from the lower atmosphere has been studied in a series of GCM tests for June solstice conditions. The results suggest that GW drag is not only nonnegligible above the turbopause, but that GWs propagate strongly into the upper thermosphere, and, upon their dissipation, deposit momentum comparable to that of ion drag, at least up to 180–200 km. The effects of thermospheric GW drag are particularly noticeable in the winter (southern) hemisphere, where weaker westerlies and stronger high‐latitude easterlies are simulated well, in agreement with the empirical Horizontal Wind Model (HWM93). The dynamic response in the F region is sensitive to the variations of the source spectrum. However, the spectra commonly employed in middle atmosphere GCMs reproduce the circulation both in the lower and upper thermosphere reasonably well.

General aspects of a T213L256 middle atmosphere general circulation model

A high‐resolution middle atmosphere general circulation model (GCM) developed for studying small‐scale atmospheric processes is presented, and the general features of the model are discussed. The GCM has T213 spectral horizontal resolution and 256 vertical levels extending from the surface to a height of 85 km with a uniform vertical spacing of 300 m. Gravity waves (GWs) are spontaneously generated by convection, topography, instability, and adjustment processes in the model, and the GCM reproduces realistic general circulation in the extratropical stratosphere and mesosphere. The oscillations similar to the stratopause semiannual oscillation and the quasi‐biennial oscillation (QBO) in the equatorial lower stratosphere are also spontaneously generated in the GCM, although the period of the QBO‐like oscillation is short (15 months). The relative roles of planetary waves, large‐scale GWs, and small‐scale GWs in maintenance of the meridional structures of the zonal wind jets in the middle atmosphere are evaluated by calculating Eliassen‐Palm diagnostics separately for each of these three groups of waves. Small‐scale GWs are found to cause deceleration of the wintertime polar night jet and the summertime easterly jet in the mesosphere, while extratropical planetary waves primarily cause deceleration of the polar night jet below a height of approximately 60 km. The meridional distribution and propagation of small‐scale GWs are shown to affect the shape of the upper part of mesospheric jets. The phase structures of orographic GWs over the South Andes and GWs emitted from the tropospheric jet stream are discussed as examples of realistic GWs reproduced by the T213L256 GCM.

Global estimates of gravity wave momentum flux from High Resolution Dynamics Limb Sounder observations

High Resolution Dynamics Limb Sounder (HIRDLS) temperature profiles are analyzed to derive global properties of gravity waves. We describe a wavelet analysis technique that determines covarying wave temperature amplitude in adjacent temperature profile pairs, the wave vertical wavelength as a function of height, and the horizontal wave number along the line joining each profile pair. The analysis allows a local estimate of the magnitude of gravity wave momentum flux as a function of geographic location and height on a daily basis. We examine global distributions of these gravity wave properties in the monthly mean and on an individual day, and we also show sample instantaneous wave events observed by HIRDLS. The results are discussed in terms of previous satellite and radiosonde observational analyses and middle atmosphere general circulation model studies that parameterize gravity wave effects on the mean flow. The high vertical and horizontal resolution afforded by the HIRDLS measurements allows the analysis of a wider range of wave vertical and horizontal wavelengths than previous studies and begins to show individual wave events associated with mountains and convection in high detail. Mountain wave observations show clear propagation to altitudes in the mesosphere.

A three-dimensional modelling study of the processes leading to mid latitude nitric oxide increases in the lower thermosphere following periods of high geomagnetic activity

The processes leading to enhancements in mid latitude nitric oxide (NO) densities following geomagnetic storms have been investigated using the University College London (UCL) Coupled Middle Atmosphere and Thermosphere (CMAT) general circulation model. A comparison of calculated storm time and quiet time NO densities at 110 km altitude reveals the presence of aurorally produced NO at both high and mid latitudes for several days after subsidence of activity. At 150 km, the NO enhancements are shorter lived and remain for up to approximately 2 days after the storm. By separating the contribution of chemical production and loss, horizontal and vertical advection, and molecular and eddy diffusion in the calculation of NO densities, we show that at 150 km altitude, horizontal transport must be taken into consideration if post-storm mid latitude enhancements are to be reproduced. Chemical production of NO at high latitudes continues for up to 2 days after subsidence of a storm at altitudes of around 150 km. We show that equatorward winds at this altitude are sufficiently strong to transport the aurorally produced NO to mid latitudes. Vertical diffusion transports NO from altitudes of 150 km and above, to lower altitudes where it is longer lived. At 110 km altitude, chemical, diffusive and advective terms must all be included in the calculation of NO density in order to simulate realistic mid latitude enhancements. We propose that it is the combined effects of increased chemical production, downward diffusion from altitudes of 150 km and above, and transport by winds that lead to increases in mid latitude NO density at altitudes of around 110 km. This is the first detailed study of the causes of post-storm mid latitude NO enhancements to use a three-dimensional general circulation model.

3-D GCM modelling of thermospheric nitric oxide during the 2003 Halloween storm

Abstract. Numerical modelling of thermospheric temperature changes associated with periods of high geomagnetic activity are often inaccurate due to unrealistic representation of nitric oxide (NO) densities and associated 5.3-μm radiative cooling. In previous modelling studies, simplistic parameterisations of NO density and variability have often been implemented in order to constrain thermospheric temperature predictions and post storm recovery timescales during and following periods of high auroral activity. In this paper we use the University College London (UCL) 3-D Coupled Thermosphere and Middle Atmosphere (CMAT) General Circulation Model to simulate the 11-day period from 23 October to 3 November 2003, during which the Earth experienced some of the largest geomagnetic activity ever recorded; the so called "Halloween storm". This model has recently been updated to include a detailed self consistent calculation of NO production and transport. Temperatures predicted by the model compare well with those observed by the UCL Fabry Perot Interferometer at Kiruna, northern Sweden, when changes in solar and auroral activity are taken into account in the calculation of NO densities. The spatial distribution of predicted temperatures at approximately 250-km altitude is also discussed. Simulated NO densities at approximately 110 km are presented. Large quantities of NO are found to be present at to the equator, one to two days after the most intense period of geomagnetic activity. This is the first 3-D GCM simulation of NO production and transport over the 2003 Halloween storm period.

Simulations of anthropogenic change in the strength of the Brewer–Dobson circulation

The effect of climate change on the Brewer–Dobson circulation and, in particular, the large-scale seasonal-mean transport between the troposphere and stratosphere is compared in a number of middle atmosphere general circulation models. All the models reproduce the observed upwelling across the tropical tropopause balanced by downwelling in the extra tropics, though the seasonal cycle in upwelling in some models is more semi-annual than annual. All the models also consistently predict an increase in the mass exchange rate in response to growing greenhouse gas concentrations, irrespective of whether or not the model includes interactive ozone chemistry. The mean trend is 11 kt s−1 year−1 or about 2% per decade but varies considerably between models. In all but one of the models the increase in mass exchange occurs throughout the year though, generally, the trend is larger during the boreal winter. On average, more than 60% of the mean mass fluxes can be explained by the EP-flux divergence using the downward control principle. Trends in the annual mean mass fluxes derived from the EP-flux divergence also explain about 60% of the trend in the troposphere-to-stratosphere mass exchange rate when averaged over all the models. Apart from two models the interannual variability in the downward control derived and actual mass fluxes were generally well correlated, for the annual mean.

Three‐dimensional GCM modeling of nitric oxide in the lower thermosphere

The coupled middle atmosphere and thermosphere (CMAT) general circulation model has been used to predict the global distribution of nitric oxide (NO) in the lower thermosphere. This three‐dimensional (3‐D) model incorporates a complex ion and neutral chemical scheme, high‐resolution solar flux data and variable auroral energy inputs. Comparison of simulated NO densities with those observed by the Student Nitric Oxide Explorer (SNOE) show that the CMAT model is able to recreate large‐scale features in the observed NO distribution under differing geophysical conditions. While previous studies have used 1‐D photochemical models to speculate on the latitudinal extent of aurorally produced NO, we have simulated NO production and transport in three dimensions under both geomagnetically stable and disturbed conditions. We have shown that the spatial and temporal distribution of aurorally produced NO is highly variable with location and local time. CMAT simulations suggest that under moderate geomagnetic conditions, the most equatorward geographic latitudes to be influenced by aurorally produced NO are 30°S and 45°N. Under conditions of high geomagnetic activity, aurorally produced NO is present at latitudes poleward of 15°S and 28°N. The asymmetry in latitudinal extent is attributed to the greater offset between geographic and geomagnetic poles in the southern hemisphere. NO density maxima are predicted to occur between 14 and 48 hours after a period of high geomagnetic activity, their spatial and temporal distribution depending on location with respect to the auroral oval and local time at which auroral forcing occurs.

A study into the effects of gravity wave activity on the diurnal tide and airglow emissions in the equatorial mesosphere and lower thermosphere using the Coupled Middle Atmosphere and Thermosphere (CMAT) general circulation model

Momentum deposition by gravity wave breaking is known to affect the amplitude and phase of the diurnal tide. Modelling studies of this interaction have produced some conflicting results and as yet, the exact nature of this interaction is not fully understood. In this study, the effects of parameterised gravity wave momentum deposition on the diurnal tide and subsequently on green line airglow from atomic oxygen during equinox are investigated using the Coupled Middle Atmosphere and Thermosphere (CMAT) general circulation model. The effects of gravity wave drag calculated by two different parameterisations, Meyer [1999. Gravity wave interactions with the diurnal propagating tide. Journal of Geophysical Research 104, 4223–4239] and Medvedev and Klaassen [2000. Parameterisation of gravity wave momentum deposition based on non-linear wave interactions: basic formulation and sensitivity tests. Journal of Atmospheric and Terrestrial Physics 62, 1015–1033], are compared in the low latitude MLT region between 70 and 120 km, where the amplitude of the diurnal tide and green line volume emission rates maximise. Results indicate that momentum sources from both gravity wave parameterisations act to reduce the mid-latitude zonal jets and advance the phase of the diurnal tide, such that the peak amplitude at a given height occurs at an earlier time of day. Gravity wave momentum deposition as parameterised by Meyer [1999. Gravity wave interactions with the diurnal propagating tide. Journal of Geophysical Research 104, 4223–4239] results in a reduction of the amplitude of the diurnal tide in the MLT region, whereas the tidal amplitude is increased when the Medvedev and Klaassen [2000. Parameterisation of gravity wave momentum deposition based on non-linear wave interactions: basic formulation and sensitivity tests. Journal of Atmospheric and Terrestrial Physics 62, 1015–1033] parameterisation is used. Both parameterisations affect the local time variability of the simulated airglow, and the magnitude of the peak emission rate. When using gravity wave momentum sources from the Medvedev and Klaassen [2000. Parameterisation of gravity wave momentum deposition based on non-linear wave interactions: basic formulation and sensitivity tests. Journal of Atmospheric and Terrestrial Physics 62, 1015–1033] parameterisation, the magnitude and morphology of CMAT tidal winds and O( 1S) 557.7 nm emission rates are in agreement with recent satellite observations.