[1] The polar summer thermal structure, with its cold mesopause and steep temperature gradients, both below and above the mesopause, produces the largest non-LTE effects in the CO 2 n 2 mode manifold states. In this paper we focus on validating the non-LTE model applied for operational temperature retrievals from the SABER 15 mm limb radiance observations for these extreme conditions. We demonstrate that accounting for the redistribution of n 2 quanta among various CO 2 isotopes shifts the retrieved summer 2002 polar mesopause altitude upwards by 2 to 4 km. It brings the SABER temperature measurements into a better agreement with those of falling sphere experiments, lidar observations, as well as with climatological data.

[1] The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured the global distribution of CO 2 4.3 mm infrared emissions in the mesosphere and lower thermosphere during two Space Shuttle missions in November 1994 and August 1997. The daytime radiances have been inverted to CO 2 number densities in the 60-130 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved CO 2 number densities was carried out. The O( 1 D) excitation mechanism and model parameters constitute the most important uncertainties of retrieved CO 2 , typically 10-20%. The inaccuracy due to uncertainties in other atmospheric parameters is usually less than 10%. The CO 2 volume mixing ratio (VMR) deviates from being well mixed between 70 and 80 km, which is significantly lower than indicated by previous rocket-borne mass spectrometer data and model calculations but is in good agreement with the data obtained by other 4.3 mm emission and absorption experiments. The global distribution of CRISTA-2 CO 2 density shows significant longitudinal and latitudinal structures. The zonal mean CO 2 densities are increasing toward polar summer latitudes below 90 km and above 115 km. Between 90 and 115 km, the latitudinal gradient is reversed. At 100 km, the gradient is mostly pronounced, reaching up to 50% difference between low and high latitudes. These variations are compared with results obtained by the Thermosphere/Ionosphere/Mesosphere Electrodynamics General Circulation Model (TIME-GCM), showing very good agreement for the latitudinal distribution. Below 110 km, this variation is mostly due to the change in total density rather than to the CO 2 VMR.

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The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite has been measuring the limb radiance in 10 broadband infrared channels over the altitude range from ~ 400 km to the Earth's surface since 2002. The kinetic temperatures and CO2 volume mixing ratios (VMRs) in the mesosphere and lower thermosphere have been simultaneously retrieved using SABER limb radiances at 15 and 4.3 µm under nonlocal thermodynamic equilibrium (non‐LTE) conditions. This paper presents results of a validation study of the SABER CO2 VMRs obtained with a two‐channel, self‐consistent temperature/CO2 retrieval algorithm. Results are based on comparisons with coincident CO2 measurements made by the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE‐FTS) and simulations using the Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD‐WACCM). The SABER CO2 VMRs are in agreement with ACE‐FTS observations within reported systematic uncertainties from 65 to 110 km. The annual average SABER CO2 VMR falls off from a well‐mixed value above ~80 km. Latitudinal and seasonal variations of CO2 VMRs are substantial. SABER observations and the SD‐WACCM simulations are in overall agreement for CO2 seasonal variations, as well as global distributions in the mesosphere and lower thermosphere. Not surprisingly, the CO2 seasonal variation is shown to be driven by the general circulation, converging in the summer polar mesopause region and diverging in the winter polar mesopause region.

[1] The global distribution of mesospheric and lower thermospheric ozone 9.6 mm infrared emissions was measured by the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment during two Space Shuttle missions in November 1994 and August 1997. The radiances measured by CRISTA have been inverted to O 3 number densities in the 50-95 km range by using a nonlocal thermodynamic equilibrium model. A detailed sensitivity study of retrieved O 3 number densities has been carried out. The ozone abundance profiles show volume mixing ratios of 1-2 ppmv at the stratopause, 0.5 ppmv or less around 80 km, and typically 1 ppmv during daytime and 10 ppmv during nighttime at the secondary maximum. The agreement with other experiments is typically better than 25%. The global distribution of upper mesospheric ozone shows significant latitudinal gradients and an enhancement in the equatorial upper mesosphere. At the polar night terminator a third ozone maximum is observed. Three-dimensional model results indicate that the latitudinal gradients are significantly influenced by solar tides.

[1] The paper presents a new grid point global general circulation model (GCM) for the Martian atmosphere with the vertical domain extending from the surface into the lower thermosphere (around 130 km). The model contains the comprehensive physical parameterizations relevant to this altitude range, including a novel CO 2 15 mm band radiation scheme for the non-LTE. The performance of the model is shown in the zonal mean fields simulated for several seasons. The comparison demonstrates a good agreement with the temperature measurements by the Thermal Emission Spectrometer below 40 km and an overall agreement with the results from other Martian GCMs. The model was used to demonstrate that the global meridional transport during solstices is forced primarily by eddies and that the ability of the model to simulate the winter polar warming depends on the ability to resolve the longitudinal disturbances, both topographically and radiatively generated.

The National Aeronautics and Space Administration (NASA) Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) Sounding of the Atmosphere using Broadband Radiometry (SABER) instrument performs near‐global measurements of the vertical kinetic temperature (Tk) profiles and volume mixing ratios of various trace species (including O3, CO2, and H2O), with data available from 2002 to present. In this work, the first comparative study of the latest publically available SABER version 2.0 operational retrieval is reported in order to assess the performance of satellite Tk profiles relative to high‐resolution ground‐based lidar profiles. Collocated multiyear seasonal average Tk profiles were compared at nine different locations, representing a variety of different latitudes. In general, the SABER v2.0 and lidar mean seasonal Tk profiles agree well, with the smallest absolute values of ΔTk (z) (SABER minus lidar) found between 85 and 95 km, where the respective SABER and lidar uncertainties were smallest. At altitudes ≥100 km, the SABER Tk (z) typically exhibited warmer temperatures relative to the lidar Tk (z) profiles, whereas for altitudes ≤85 km, SABER Tk (z) was cooler. Relative to lidar, SABER tends to exhibit a warm bias during high‐latitude summertime, with the reasons for this currently still unclear. Overall, SABER was able to reproduce the general latitude‐ and season‐specific variations in the lidar Tk profiles and shown to be statistically similar for most seasons, at most locations, for the majority of altitudes, and with no overall bias.