Global distributions of CO2 volume mixing ratio in the middle and upper atmosphere from MIPAS high resolution spectra

Global distributions of the CO 2 vmr (volume mixing ratio) in the mesosphere and lower thermo sphere (from 70 km up to∼142 km) have been derived from high resolution mid-IR spectr a. This is the first time that the CO 2 vmr has been retrieved in the 120–140km range. The CO 2 vmrs have been retrieved using MIPAS daytime limb emission s pectra from the 4. 3μm region in its upper atmosphere (UA) mode (data version v5r_ CO2_622). The dataset spans from January 2005 until March 2012. The retrieval of CO 2 has been performed jointly with the line of sight (LOS) by usi ng a non-local thermo5 dynamic equilibrium (non-LTE) retrieval scheme. The non-L TE model incorporates the accurate vibrational-vibration al and vibrational-translational collisional rates recently de riv d from the MIPAS spectra. It also takes advantage of simu ltaneous MIPAS measurements of other atmospheric parameters, as the kinetic temperature (up to ∼100 km) from the CO2 15 μm region, the thermospheric temperature from the NO 5.3 μm emission, and the O 3 measurements (up to ∼100 km). The latter is very important for the calculations of the non-LTE populati ons because it strongly constrains the O( D) concentration below 10 ∼100 km. The estimated precision of the retrieved CO 2 vmr profiles varies with altitude ranging from ∼1% below 90 km, to 5% around 120 km and larger than 10% above 130 km. There are some l atitudinal and seasonal variations of the precision, which are mainly driven by the solar illumination conditions. The retrieved CO2 profiles have a vertical resolution of about 5–7 km below 120 km and between 10 and 20 km at 120–142km. We have show n t at the inclusion of the LOS as joint fit parameter improves the retrieval of CO 2, allowing a clear discrimination between the information o f CO2 concentration and the LOS 15 and also leading to significantly smaller systematic errors . The retrieved CO2 has a much better accuracy than previous limb emission measurements, because of the highly accurate rate coefficients recently derived from MIPAS, and the simultane ous MIPAS measurements of other key atmospheric parameters nee ded for the non-LTE modeling like the kinetic temperature an d the O3 concentration. The major systematic error source is the unc rtainty of the pressure/temperature profiles, inducing er rors of up to 15% above 100 km, and of ∼5% around 80 km at mid-latitude conditions. The errors due to uncertainties in the O( D) 20 and O(P ) profiles are within 3–4% in the 100–120km region, and those d u to uncertainties in the gain calibration and in the near-IR solar flux are within ∼2% at all altitudes. The retrieved CO 2 shows the major features expected and predicted by general circulation models. In particular, its abrupt decl ine above 80–90km and the seasonal change of the latitudinal distribution, with higher CO2 abundances in polar summer from 70 km up to ∼95 km and lower CO2 vmr in the polar winter. Above 1 Atmos. Meas. Tech. Discuss. , doi:10.5194/amt-2016-63, 2016 Manuscript under review for journal Atmos. Meas. Tech. Published: 15 March 2016 c © Author(s) 2016. CC-BY 3.0 License.