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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, 5895-5909, 2016
https://doi.org/10.5194/amt-9-5895-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 09 Dec 2016

Research article | 09 Dec 2016

Harmonisation and diagnostics of MIPAS ESA CH4 and N2O profiles using data assimilation

Quentin Errera1, Simone Ceccherini2, Yves Christophe1, Simon Chabrillat1, Michaela I. Hegglin3, Alyn Lambert4, Richard Ménard5, Piera Raspollini4, Sergey Skachko1, Michiel van Weele6, and Kaley A. Walker7,8 Quentin Errera et al.
  • 1Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
  • 2Istituto di Fisica Applicata “N. Carrara” (IFAC) del Consiglio Nazionale delle Ricerche (CNR), Firenze, Italy
  • 3University of Reading, Department of Meteorology, Reading, UK
  • 4Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
  • 5Air Quality Research Division, Environment and Climate Change Canada, Dorval, Canada
  • 6Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands
  • 7University of Toronto, Department of Physics, Toronto, Canada
  • 8University of Waterloo, Department of Chemistry, Waterloo, Canada

Abstract. This paper discusses assimilation experiments of methane (CH4) and nitrous oxide (N2O) profiles retrieved from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Here we focus on data versions 6 and 7 provided by the ESA processor. These data sets have been assimilated by the Belgian Assimilation System for Chemical ObsErvations (BASCOE). The CH4 and N2O retrieved profiles can oscillate, especially in the tropical lower stratosphere. Using the averaging kernels of the observations and a background error covariance matrix, which has previously been calibrated, allows the system to partly remedy this issue and provide assimilated fields that are more regular vertically. In general, there is a good agreement between the BASCOE analyses and independent observations from ACE–FTS (CH4 and N2O) and MLS (N2O), demonstrating the general good quality of CH4 and N2O retrievals provided by MIPAS ESA. Nevertheless, this study also identifies two issues in these data sets. First, time series of the observations show unexpected discontinuities due to an abrupt change in the gain of MIPAS band B, generally occurring after the instrument decontamination. Since the calibration is performed weekly, the abrupt change in the gain affects the measurements until the subsequent calibration is performed. Second, the correlations between BASCOE analyses and independent observations are poor in the lower stratosphere, especially in the tropics, probably due to the presence of outliers in the assimilated data. In this region, we recommend using MIPAS CH4 and N2O retrievals with caution.

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When this study started, its goal was to provide a reanalysis of the stratospheric composition of methane and nitrous oxide, two important sources of hydrogen and nitrogen species in the stratosphere that influence the ozone abundance. However, the goal changed when several issues in the assimilated observations were discovered. Finally, this study illustrates how data assimilation methods can be used to add value to the observations as well as to diagnose their limitations.
When this study started, its goal was to provide a reanalysis of the stratospheric composition...
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