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

Abstract

Abstract. This paper presents the first global set of observations of CO 2 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 CO 2 in the MLT region. The beginning of the fall-off of the CO 2 , 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 CO 2 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 CO 2 observations although the CO observations are adequately reproduced. There appears to be about a 10 km offset compared to the observed ACE CO 2 , 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 CO 2 , 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 CO 2 , 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 candi-

The use of IASI data to identify systematic errors in the ECMWF forecasts of temperature in the upper stratosphere

“…It is usually assumed that CO 2 is well mixed in the atmosphere. However, there is strong evidence (Shia et al, 2006; IASI data to evidence ECMWF temperature biases Carlotti et al, 2007;Beagley et al, 2010) that this assumption leads to an overestimation of the CO 2 mixing ratio in the stratosphere. Consequently, in this paper we analyze the effect of overestimating the CO 2 profile in the stratosphere.…”

Stratospheric warming influence on the mesosphere/lower thermosphere as seen by the extended CMAM

“…The extended CMAM (Beagley et al, 2000;Fomichev et al, 2002;McLandress et al, 2006;Beagley et al, 2010) is one of the first ground-to-thermosphere general circulation models in the world and is based on the regular version of the CMAM described by Beagley et al (1997). The primary rationale for the extended CMAM is to examine the nature of the physical and dynamical processes in the mesosphere/lower thermosphere region without the artificial effects of an imposed sponge layer which can modify the circulation in an unrealistic manner.…”

“…Molecular diffusion and gas separation occur with the increase of height in the atmosphere. The model also has comprehensive stratospheric chemistry and a simplified ion chemistry scheme (Beagley et al, 2010) ) and electrons, and it employs 102 neutral, 27 ion and 49 photolysis reactions. The nitrogen chemistry in the extended CMAM is based on the stratospheric CMAM nitrogen chemistry and expanded.…”

“…It gave the capability of modelling the physics and dynamics of the atmosphere from the ground to approximately 250 km, thus providing a powerful tool for comparisons with satellite observational data like those from the Upper Atmosphere Research Satellite (UARS) and the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED). The most recent version of the extended CMAM (Beagley et al, 2010) has incorporated neutral and simplified ion chemistry, actively simulating 99 % of the atmosphere's constituents except for noble gases which are specified.…”

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

“…In Fig. 3a we show the average vertical distributions of CO 2 , which were calculated in WACCM model (Garcia et al, 2007;Smith et al, 2011), retrieved from SABER V1.07 in (Rezac, 2011), and retrieved from the ACE-FTS occultation observations (Beagley et al, 2010). 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).…”