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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 12 | Copyright
Atmos. Meas. Tech., 9, 6081-6100, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Dec 2016

Research article | 20 Dec 2016

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

Á. Aythami Jurado-Navarro1, Manuel López-Puertas1, Bernd Funke1, Maya García-Comas1, Angela Gardini1, Francisco González-Galindo1, Gabriele P. Stiller2, Thomas von Clarmann2, Udo Grabowski2, and Andrea Linden2 Á. Aythami Jurado-Navarro et al.
  • 1Instituto de Astrofísica de Andalucía, CSIC, Granada, Spain
  • 2Institute for Meteorology and Climate Research (IMK-ASF), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Abstract. Global distributions of the CO2vmr (volume mixing ratio) in the mesosphere and lower thermosphere (from 70 up to  ∼ 140km) have been derived from high-resolution limb emission daytime MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) spectra in the 4.3µm region. This is the first time that the CO2vmr has been retrieved in the 120–140km range. The data set spans from January 2005 to March 2012. The retrieval of CO2 has been performed jointly with the elevation pointing of the line of sight (LOS) by using a non-local thermodynamic equilibrium (non-LTE) retrieval scheme. The non-LTE model incorporates the new vibrational–vibrational and vibrational–translational collisional rates recently derived from the MIPAS spectra by [Jurado-Navarro et al.(2015)]. It also takes advantage of simultaneous MIPAS measurements of other atmospheric parameters (retrieved in previous steps), such as the kinetic temperature (derived up to  ∼ 100km from the CO2 15µm region of MIPAS spectra and from 100 up to 170km from the NO 5.3µm emission of the same MIPAS spectra) and the O3 measurements (up to  ∼ 100km). The latter is very important for calculations of the non-LTE populations because it strongly constrains the O(3P) and O(1D) concentrations below  ∼ 100km. The estimated precision of the retrieved CO2vmr profiles varies with altitude ranging from  ∼ 1% below 90km to 5% around 120km and larger than 10% above 130km. There are some latitudinal 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 5–7km below 120km and between 10 and 20km at 120–140km. We have shown that the inclusion of the LOS as joint fit parameter improves the retrieval of CO2, allowing for a clear discrimination between the information on CO2 concentration and the LOS and also leading to significantly smaller systematic errors. The retrieved CO2 has an improved accuracy because of the new rate coefficients recently derived from MIPAS and the simultaneous MIPAS measurements of other key atmospheric parameters (retrieved in previous steps) needed for non-LTE modelling like kinetic temperature and O3 concentration. The major systematic error source is the uncertainty of the pressure/temperature profiles, inducing errors at midlatitude conditions of up to 15% above 100km (20% for polar summer) and of  ∼ 5% around 80km. The errors due to uncertainties in the O(1D) and O(3P) profiles are within 3–4% in the 100–120km region, and those due to uncertainties in the gain calibration and in the near-infrared solar flux are within  ∼ 2% at all altitudes. The retrieved CO2 shows the major features expected and predicted by general circulation models. In particular, its abrupt decline above 80–90km and the seasonal change of the latitudinal distribution, with higher CO2 abundances in polar summer from 70 up to  ∼ 95km and lower CO2vmr in the polar winter. Above  ∼ 95km, CO2 is more abundant in the polar winter than at the midlatitudes and polar summer regions, caused by the reversal of the mean circulation in that altitude region. Also, the solstice seasonal distribution, with a significant pole-to-pole CO2 gradient, lasts about 2.5 months in each hemisphere, while the seasonal transition occurs quickly.

Publications Copernicus
Short summary
We present global distributions of CO2 concentrations in the upper atmosphere (70–140 km) derived from high-resolution 4.3 µm MIPAS spectra from 2005 to 2012. CO2 relative abundances have been measured at 120–140 km for the first time. The data have an unprecedented accuracy. CO2 shows a strong seasonal behaviour. CO2 largely controls the temperature of the upper atmosphere and its measurement is very important for understanding the impact of climate change in this region.
We present global distributions of CO2 concentrations in the upper atmosphere (70–140 km)...