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Volume 11, issue 9 | Copyright

Special issue: Quadrennial Ozone Symposium 2016 – Status and trends...

Atmos. Meas. Tech., 11, 5125-5152, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Sep 2018

Research article | 10 Sep 2018

Validation of the IASI FORLI/EUMETSAT ozone products using satellite (GOME-2), ground-based (Brewer–Dobson, SAOZ, FTIR) and ozonesonde measurements

Anne Boynard1,2, Daniel Hurtmans3, Katerina Garane4, Florence Goutail1, Juliette Hadji-Lazaro1, Maria Elissavet Koukouli4, Catherine Wespes3, Corinne Vigouroux5, Arno Keppens5, Jean-Pierre Pommereau1, Andrea Pazmino1, Dimitris Balis4, Diego Loyola6, Pieter Valks6, Ralf Sussmann7, Dan Smale8, Pierre-François Coheur3, and Cathy Clerbaux1,3 Anne Boynard et al.
  • 1LATMOS/IPSL, Sorbonne Université, UVSQ, CNRS, Paris, 75252, France
  • 2SPASCIA, Ramonville-Saint-Agne, 31520, France
  • 3Atmospheric Spectroscopy, Service de Chimie Quantique et Photophysique, Université libre de Bruxelles, Brussels, 1050, Belgium
  • 4Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece
  • 5Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium
  • 6Institut für Methodik der Fernerkundung (IMF), Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
  • 7Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany
  • 8National Institute of Water and Atmospheric Research Ltd (NIWA), Lauder, New Zealand

Abstract. This paper assesses the quality of IASI (Infrared Atmospheric Sounding Interferometer)/Metop-A (IASI-A) and IASI/Metop-B (IASI-B) ozone (O3) products (total and partial O3 columns) retrieved with the Fast Optimal Retrievals on Layers for IASI Ozone (FORLI-O3; v20151001) software for 9 years (2008–July 2017) through an extensive intercomparison and validation exercise using independent observations (satellite, ground-based and ozonesonde). Compared with the previous version of FORLI-O3 (v20140922), several improvements have been introduced in FORLI-O3 v20151001, including absorbance look-up tables recalculated to cover a larger spectral range, with additional numerical corrections. This leads to a change of  ∼ 4% in the total ozone column (TOC) product, which is mainly associated with a decrease in the retrieved O3 concentration in the middle stratosphere (above 30hPa/25km). IASI-A and IASI-B TOCs are consistent, with a global mean difference of less than 0.3% for both daytime and nighttime measurements; IASI-A is slightly higher than IASI-B. A global difference of less than 2.4% is found for the tropospheric (TROPO) O3 column product (IASI-A is lower than IASI-B), which is partly due to a temporary issue related to the IASI-A viewing angle in 2015. Our validation shows that IASI-A and IASI-B TOCs are consistent with GOME-2 (Global Ozone Monitoring Experiment-2), Dobson, Brewer, SAOZ (Système d'Analyse par Observation Zénithale) and FTIR (Fourier transform infrared) TOCs, with global mean differences in the range of 0.1%–2% depending on the instruments compared. The worst agreement with UV–vis retrieved TOC (satellite and ground) is found at the southern high latitudes. The IASI-A and ground-based TOC comparison for the period from 2008 to July 2017 shows the long-term stability of IASI-A, with insignificant or small negative drifts of 1%–3%decade−1. The comparison results of IASI-A and IASI-B against smoothed FTIR and ozonesonde partial O3 columns vary with altitude and latitude, with the maximum standard deviation being seen for the 300–150hPa column (20%–40%) due to strong ozone variability and large total retrievals errors. Compared with ozonesonde data, the IASI-A and IASI-B O3 TROPO column (defined as the column between the surface and 300hPa) is positively biased in the high latitudes (4%–5%) and negatively biased in the midlatitudes and tropics (11%–13% and 16%–19%, respectively). The IASI-A-to-ozonesonde TROPO comparison for the period from 2008 to 2016 shows a significant negative drift in the Northern Hemisphere of −8.6±3.4%decade−1, which is also found in the IASI-A-to-FTIR TROPO comparison. When considering the period from 2011 to 2016, the drift value for the TROPO column decreases and becomes statistically insignificant. The observed negative drifts of the IASI-A TROPO O3 product (8%–16%decade−1) over the 2008–2017 period might be taken into consideration when deriving trends from this product and this time period.

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Short summary
In this paper, we perform a comprehensive validation of the IASI/Metop ozone data using independent observations (satellite, ground-based and ozonesonde). The quality of the IASI total and tropospheric ozone columns in terms of bias and long-term stability is generally good. Compared with ozonesonde data, IASI overestimates (underestimates) the ozone abundance in the stratosphere (troposphere). A negative drift in tropospheric ozone is observed, which is not well understood at this point.
In this paper, we perform a comprehensive validation of the IASI/Metop ozone data using...