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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-209
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-209
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 06 Jun 2019

Submitted as: research article | 06 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Impacts of H2O variability on accuracy of CH4 observations from MIPAS satellite over tropics

Temesgen Yirdaw Berhe1, Gizaw Mengistu Tsidu1,2, Thomas Blumenstock3, Frank Hase3, Thomas von Clarmann3, Justus Notholt4, and Emmanuel Mahieu5 Temesgen Yirdaw Berhe et al.
  • 1Department of Physics, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia
  • 2Department of Earth and Environmental Sciences, College of Science, Botswana International University of Technology and Science (BIUST), Priv.Bag 16, Palapye, Botswana
  • 3Institute of Meteorology and Climate Researchs (IMK-ASF), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 4Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 5Institut d’Astrophysique et de Géophysique, University of Liège (ULg), Liège, Belgium

Abstract. Uncertainties of tropical methane concentrations, retrieved from spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), MIPAS version V5R_CH4_220 are large. We explore the relation of these uncertainties with water vapour variability. We further show that these uncertainties have been reduced in MIPAS version V5R_CH4_224. Coincident measurements of CH4 by MIPAS, ground based FTIR and CH4 derived from EOS MLS coincident measurements of atmospheric water vapour (H2O), carbon monoxide (CO) and nitrous oxide (N2O) are used to estimate the standard uncertainty of MIPAS CH4 220, MIPAS CH4 224 and natural variability of H2O. Different methods such as bias evaluation, differential method and correlation coefficient are employed to explore the latitudinal variations of standard uncertainty of MIPAS CH4 220 and natural variability of water vapour as well as its reduction on MIPAS CH4 224. The averaged bias between MIPAS CH4 220 and ground-based FTIR measurements are −12.3 %, 8.4 % and 1.2 % for tropics, mid-latitudes and high latitudes, respectively. The standard deviations of the differences for these latitudinal bands are 5.9 %, 4.8 % and 4.7 %. More-over, the correlation coefficient between MIPAS CH4 220 and MIPAS V5R_N2O_220 is 0.32 in the upper troposphere and lower stratosphere over tropics and larger than the mod-est value 0.5 in mid and high latitudes. The poor correlation between MIPAS CH4 220 and MIPAS N2O 220 over tropics can indicate the large uncertainty of MIPAS CH4 220 over tropics that is related to water variability. Similarly, mean relative difference between MIPAS CH4 224 and ground-based FTIR measurements are 3.9 %, −2.6 % and −2.7 % in altitude 15–21 km and the average estimated uncertainty of MIPAS CH4 224 methane were obtained 2.4 %, 1.4 % and 5.1 % in altitude ranges of 15 to 27 km for tropics, mid and high latitudes, respectively. The estimated measurement uncertainty of MIPAS CH4 224 is different for the three latitude bands in the northern hemisphere, reflecting the latitudinal variation of uncertainties of MIPAS methane. However, the large reduction of uncertainty in MIPAS CH4 224 as com-pared to MIPAS CH4 220 has been confirmed for the tropical measurements. The correlation coefficients between the uncertainty of MIPAS CH4 220 and the variability of water vapour in lower stratosphere are strong (0.88) on monthly temporal scales. Similar methods were used for MIPAS CH4 224. It was found that the uncertainty in methane due to the variability of water vapor has been reduced.

Temesgen Yirdaw Berhe et al.
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Short summary
This study aims to assess the latitudinal variation of MIPAS version V5R_CH4_220 and V5R_CH4_224 uncertainty. Furthermore, we analyze the relationship between these uncertainties and the variability of water vapor. Mainly, the high uncertainty found in tropics for MIPAS CH4 220 is highly associated with variability of water vapour. However, this effect has been reduced in the new updated MIPAS CH4 224 datasets due to jointly fitted water profile with methane.
This study aims to assess the latitudinal variation of MIPAS version V5R_CH4_220 and ...
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