The vertical and horizontal distribution of CO₂ densities in the upper mesosphere and lower thermosphere as measured by CRISTA

Abstract

[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.

A time-resolved model of the mesospheric Na layer: constraints on the meteor input function

“…For instance, this column abundance is predicted to result from a meteoroid mass input around 12 t d −1 , as estimated by the ISR observations (Sect. 2.3), combined with a low K zz value around 2×10 5 cm 2 s −1 , as predicted by gravity wave momentum deposition models (Kaufmann et al, 2002). But the same column abundance can be produced by the higher mass input estimated from conventional meteor radars (40-50 t d −1 ) (Hughes, 1978), if a larger value of K zz around 10 6 cm 2 s −1 is adopted, consistent with measured energy dissipation rates (Hocking, 1990).…”

“…While laboratory experiments appear to have placed the gas-phase chemistry on reasonably firm ground , there is currently uncertainty regarding the appropriate values of K zz to use for describing vertical transport in the MLT. Atmospheric models which include a parameterisation of gravity wave momentum deposition predict an average value for K zz between 80 and 90 km of (1−4)×10 5 cm 2 s −1 (Garcia and Solomon, 1994;Chabrillat et al, 2002;Kaufmann et al, 2002). In contrast, estimates based on measured energy dissipation rates in the MLT find values up to an order of magnitude greater (Hocking, 1990).…”

“…Since such large values of the eddy coefficient are greater than both experimental (Hocking, 1990) and theoretical (Kaufmann et al, 2002) estimates of K zz , it seems that the global mass input rate must be below 100 t d −1 . Furthermore, a recent modelling study of the significant decrease in the CO 2 mixing ratio above 80 km has demonstrated that the average K zz between 80 and 90 km needs to be less than about 3×10 5 cm 2 s −1 in order for molecular diffusion of CO 2 to compete with eddy diffusion, and hence produce some gravitational separation (Chabrillat et al, 2002).…”

“…It contains a full treatment of the odd oxygen and hydrogen chemistry in the MLT, with rate coefficients taken from the NASA/JPL compilation (DeMore et al, 1997). The vertical eddy diffusion coefficient is taken off-line from a 3D global model, TIME-GCM (Kaufmann et al, 2002 (Shimazaki, 1985;Brasseur and Solomon, 1998). The photolysis of O 2 in the Schumann-Runge bands is calculated using a recent formalism (Koppers and Murtagh, 1996).…”

CO<sub>2</sub>(ν<sub>2</sub>)-O quenching rate coefficient derived from coincidental SABER/TIMED and Fort Collins lidar observations of the mesosphere and lower thermosphere

“…The distributions agree within standard deviation limits (shown only for ACE-FTS for readability of the plot, the others are of the same order of magnitude). We did not consider CRISTA CO 2 distributions (Kaufmann et al, 2002) because there was no temporal overlap with the data sets used in the present study: almost 10 yr have passed since the CRISTA-2 operation.…”