The objective of the ESA CCI Clouds project is to provide long-term coherent cloud property datasets, exploiting the opportunities for synergy of various earth observation missions. This provides a greater degree of accuracy with enhanced temporal and spatial sampling than can be obtained from cloud property datasets that stem from a single source.

The ESA CCI Clouds project is designed to maximise the growing synergistic potential of past, current and future European and US satellite missions in order to meet the increasing demands for coherent long-term cloud property datasets within the scientific community. The primary objectives of the ESA CCI Cloud project are:

• The development of intercalibrated radiance datasets (Fundamental Climate Data Records) for ESA instruments and those of other organisations in a programme of international cooperation: firstly, by fully utilising the results of the WMO Global Space-based Inter-Calibration System (GSICS) as a main end-user, and secondly, by introducing complementary methods to further enhance the potential of GSICS.
• The development of a coherent physical retrieval framework for the Global Climate Observing System (GCOS) Essential Climate Variables (ECVs) on cloud properties, i.e. cloud cover, cloud height and temperature, and liquid and ice water content. The ECV retrieval framework is freely available to the public and for use by the scientific community.
• The development of two global datasets lasting several years for the GCOS cloud property ECVs, which will include uncertainty estimates based on carefully calibrated and intercalibrated radiances.
• Validation of the cloud property products as compared to ground-based and other satellite-based measurements, taking into consideration the respective error structures of the individual observations.
• Provision of a common database and the requisite evaluation of cloud datasets, as in the context of the Global Energy and Water Cycle Experiment (GEWEX).
• The development of a comprehensive Europe-wide processing system that will further strengthen the operational production of cloud property datasets after the ESA CCI programme has ended.
• The promotion of a strategy for dataset construction and datasets for the global scientific and operational community. This involves active collaboration with the Climate Modelling User Group (CCI CMUG) consortium.

Objectives for MeteoSwiss's participation in the ESA CCI Clouds project Phase 2 (2014-2016)

Climate monitoring applications: Characterisation stability and homogeneity of the CCI Cloud dataset: The potential of homogeneous long-term observations of cloud cover by satellites to complement long-term ground-based observations will only be significant when they are able to be estimated with a stability of around 1% or better over several decades. In spite of advances in retrieval algorithms, satellite-based cloud cover climatology is hampered by issues with technical artefacts, such as changes in satellite sensors, radiometric and geometric calibration problems, unwanted effects of optical angles or shifts in the diurnal overpass time. For this reason, MeteoSwiss has introduced the following research tasks into the ESA CCI Clouds project:

• Evaluation of climatological stability and homogeneity of the AVHRR and MODIS cloud cover over central Europe with the help of SYNOP in terms of the monthly and annual timescales

• Analysis of the diurnal cycle of the AVHRR and MODIS cloud cover with the help of the Meteosat (CM SAF) cloud climatology as well as SYNOP central European data

• Generation of a de-trended and de-biased cloud cover climatology resolving the diurnal cycle of cloud cover over central Europe, with statistical reconstruction of the night-time cycle.

Integration of Cloud CCI into a flagship project for national GFCS activities: MeteoSwiss plays an active role in preparing the Cloud CCI data, and communicating it and making it available to the interested user community. The climate information user group recently expanded from a 'purely' scientific community of climate specialists into one which encompasses a wide range of users, such as social scientists, decision-makers, resource managers, health officials, reinsurance officials etc. This means that climate data providers share the responsibility not only for generating optimum quality data, but also for preparing the climate monitoring information in ways that make it useful for a wide range of users In the context of this remit, it is proposed that the final, validated Cloud CCI data retrieved over a 30+ year period be used in a national climate monitoring showcase project for Switzerland.

Phase 1 (2010-2013) Validation of cloud products in mountainous and polar regions

As part of this remit, MeteoSwiss provided validation activities with a particular focus on mountainous and polar regions: Such areas are most sensitive to climate fluctuations and change, and therefore require high quality data recording for the purposes of climate analysis. Furthermore, it is important from a scientific perspective that such an evaluation is conducted independently of the dataset producers.
The role of MeteoSwiss was to evaluate the ESA CCI cloud cover data derived from the AVHRR and MODIS sensors in comparison with the in-situ data for the relevant weather conditions in mountainous and polar regions (Antarctica, Spitzbergen and Greenland). In addition to reporting on the overall accuracy of the CCI cloud cover for these regions, this study also focused on finding the major inaccuracies between the satellite-based cloud cover and surface-based observations, in order to identify the main limitations of the satellite-based cloud cover retrieval algorithm. The identification of these limitations proved to be beneficial to the algorithm developers in the second phase of the CCI Clouds project, helping them to improve the cloud recognition methods.

The Ozone CCI project is part of the ESA Global Monitoring of Essential Climate Variables (ECVs) programme, more commonly known as the Climate Change Initiative (CCI), the second phase of which was begun in 2010 for a period of six years.

The CCI programme is intended to make a contribution to the databases that collect ECVs as required by the United Nations Framework Convention on climate change (UNFCCC) and the International Panel on Climate Change (IPCC).
Specifically, the ESA CCI Ozone project involves the following tasks:

• Analysis of the climate researchers' requirements for ozone data
• Providing satellite-derived ozone measurements in a form suitable for use by climate researchers
• Utilisation of available ozone data in the ESA Earth observation archive and the ozone measurements of Third Party Missions (TPM).
  

Three main product lines are being developed:

• Total ozone from nadir UV backscatter sensors
• Ozone profiles from nadir UV backscatter sensors
• Ozone profiles from limb and occultation sensors
  

The following diagram explains the concept:

Before the data is produced, the following questions have to be answered:

• What kind of data do the climate scientists require as input data for their coupled chemistry-climate models? (These are models which predict future climatic developments.)
• What is the level of quality required for these data (precision and accuracy)?

The scientists at MeteoSwiss have therefore produced a document containing the users' requirements.