CCI-Ozone Fundamental Climate Data Records: Evaluation of compliance with GCOS requirements and research needs

International audienceStarted in 2010 for a period of six years, ESA’s Climate Change Initiative aims at establishing Fundamental Climate Data Records (FCDRs) from satellite data for a list of Essential Climate Variables (ECVs). In this context, the Ozone_cci project provides FCDRs on atmospheric ozone from data acquired by ESA, EUMETSAT and Third Party Missions. Atmospheric ozone is an important ECV as it controls the radiation budget of the Earth, interacts with atmospheric dynamics and climate, and influences chemically other radiatively active species. Ozone data requirements were collected from the Global Climate Observing System (GCOS), from WMO rolling requirements, and from the climate research community involved in CCI activities through the Climate Modelling User Group. After a first phase of three years during which most of the contributing ozone retrieval algorithms were revisited, the project delivered a Climate Research Data Package (CRDP) with improved and harmonised ozone total column, nadir ozone profile and limb/occultation ozone profile FCDRs, from ERS-2 GOME, Envisat (GOMOS, MIPAS, SCIAMACHY), Odin (OSIRIS, SMR), SCISAT-1 ACE-FTS, and MetOp-A GOME-2. Extension to other satellite missions like Aura OMI and MetOp IASI, as well as further improvements in the UT/LS, in the troposphere and in the mesosphere are ongoing.In-depth characterisation and geophysical validation of FCDRs by independent teams play an essential role in the Ozone_cci project. First, in support to algorithm evolution and data improvement, e.g. via round-robin evaluation, to identify the most suitable retrieval algorithm or method for every ozone data set to be reprocessed. Later, to assess the quality of the reprocessed data sets and evaluate their compliance with user requirements. The objective of this paper is threefold: first, to show how the different categories of user requirements were translated into practical validation requirements; second, to provide an overview on the QA/validation system developed to meet objectives of the project and of the future Copernicus services; and third, to report on some already successful applications of the current ozone FCDRs in climate research. In particular, the current ozone FCDRs are shown to be well suited as core data sets for the evaluation of the climate and climate-chemistry models participating in CMIP6 and the next WMO ozone assessment. The paper concludes with a perspective on further developments of the project