The Ozone CCI - Overview of the Information Content and data Quality of Contributing Limb and Nadir O3 Profile Data Sets
Keppens, Arno1; Hubert, D.1; Verhoelst, T.1; Granville, J.1; Lambert, J.-L.1; Stuebi, R.2; Delcloo, A.3; Kivi, R.4; Godin-Beekmann, S.5; Siddans, R.6; Miles, G.6; van der A, R7; van Peet, J.7; Sofieva, V.8; Kyrola, E.8; Tamminen, J.8; Laeng, A.9; Stiller, G.9; von Clarmann, T.9; Raphoe, N.10; Weber, M.10
1Belgian Institute for Space Aeronomy (BIRA-IASB), BELGIUM; 2Federal Office of Meteorology and Climatology (MeteoSwiss), SWITZERLAND; 3Royal Meteorological Institute of Belgium (KMI-IRM), BELGIUM; 4Finnish Meteorological Institute – Arctic Research Centre (FMI-ARC), FINLAND; 5LATMOS, UVSQ, UPMC, CNRS, FRANCE; 6Rutherford Appleton Laboratory (RAL), UNITED KINGDOM; 7Royal Netherlands Meteorological Institute (KNMI), NETHERLANDS; 8Finnish Meteorological Institute – Earth Observation, FINLAND; 9Karlsruher Institut fur Technologie (KIT), GERMANY; 10Institute for Environmental Physics (IUP), University of Bremen, GERMANY

Atmospheric ozone has an important impact on the radiation budget of the Earth, through processes in the shortwave and the longwave spectral domains, and through its chemical influence on other radiatively active trace gases. Climate studies require accurate measurements of the horizontal and vertical distribution of ozone on the global scale and in the long term. To address this need and other research questions, several European atmospheric science missions were launched over the last 15 years. Ozone, considered as a major target, is retrieved from radiance data of various space-based sensors, observing with different viewing geometries in different spectral domains. In this paper we focus on the characterisation of ozone profile products from the European limb and nadir sensors, in the context of ESA’s Climate Change Initiative (CCI).

The Ozone_cci project aims at providing ozone data records suitable for climate studies by collecting, improving and merging observations from instruments aboard the European platforms ERS-2 (GOME), Envisat (GOMOS, MIPAS and SCIAMACHY) and MetOp-A (GOME-2). The first phase of the project is near completion, whose main goal was to produce several prototype data records: (1) a homogenized L2 data set of screened ozone profiles from each individual sensor and (2) temporally and zonally averaged (at various resolutions) L3 data sets for each sensor separately and for all sensors combined. Throughout the entire CCI programme and Ozone_cci in particular validation activities play an essential role. First to identify the most suitable retrieval algorithm for each instrument, and later to characterize the selected data sets. We hereby summarize the validation team's conclusions from phase one on the information content and data quality of L2 nadir ozone profile products from GOME, GOME-2 and SCIAMACHY, and of L2 limb ozone profiles from GOMOS, MIPAS and SCIAMACHY.

The spatial and temporal coverage of each L2 data set is documented, together with findings on information content studies from the vertical averaging kernels. We investigate aspects such as DFS (Degrees of Freedom of Signal), vertical sensitivity, vertical resolution and centroid offset, and their meridian and vertical variation. In the second part of the analysis we focus on the bias and spread of the L2 ozone profiles with respect to correlative ground-based measurements. Co-located observations from the well established NDACC/GAW networks of ozonesondes and stratospheric ozone lidars are used as a reference in a pseudo-global validation analysis from the ground up to about 47 km. We study the vertical and meridian structure of bias and spread, and, when possible, the drift. Finally, we briefly mention how these analyses contributed to the selection of the respective Ozone_cci retrieval algorithms for the nadir sensors GOME and GOME-2, and for the limb instrument MIPAS.