Climate studies of clouds, radiation and atmospheric water vapour - Climate Monitoring SAF (CM SAF)

The CM SAF project is generating, evaluating and archiving high-quality cloud products from satellite data. The products allow detailed analyses of cloud conditions and cloud properties, atmospheric radiation (radiation budget components at surface and at top of atmosphere) and the atmospheric content of water vapour. SMHI focuses on CM SAF cloud products for which we have a supervising and coordinating role within the project.

Monitoring of cloud conditions is important for understanding the role of clouds in the climate system and for studying potential changes of cloudiness and cloud properties as a consequence of a changed climate. The SMHI meteorological research group uses primarily data from polar orbiting meteorological satellites for studies over Europe and the Arctic. Recently also global cloud processing has been started.

Generation of cloud climate statistics

CM SAF computes monthly means of various cloud parameters with a horizontal resolution of 15 km. The computations are based on cloud products derived from the AVHRR (Advanced Very High Resolution Radiometer) instrument onboard polar orbiting satellites and from the SEVIRI (Spinning Enhanced Visible and InfraRed Imager) instrument on the geostationary satellites. The following cloud parameters are covered:

  • Total cloud amount or cloud fractional cover (CFC)
  • Contributions from the following cloud type (CTY) groups: Low-level clouds, Medium-level clouds, High-level thick clouds, High-level thin clouds and Fractional (broken or sub-pixel) clouds
  • Cloud top height (CTH)

In addition to these basic cloud parameters CM SAF also derives three cloud parameters describing microphysical properties of clouds:

  • Cloud phase (CPH): Defining the contribution from pure water clouds, pure ice clouds and mixed phase clouds
  • Cloud optical thickness (COT): A measure of the opacity of clouds (related to cloud albedo)
  • Cloud water path (CWP): Defining the total amount of cloud water in an atmospheric column

The covered region is Europe, Africa and large parts of the Atlantic Ocean and products are available since 2004. Over Sweden a precursor climatology (named the SCANDIA climatology) has been defined for the period 1991-2000 having a horizontal resolution of 4 km. In 2009 CM SAF also started cloud product generation over the Arctic region.

European cooperation

The CM SAF project is based upon a cooperation between several European meterological institutes. The managing host of the project is the German weather service (Deutscher Wetterdienst – DWD). Besides SMHI other partners are the Dutch meteorological institute (KNMI), the Finnish meteoroligal institute (FMI), the Swiss meteorological institute (MeteoSwiss) and the Belgian meteorological institute (RMI).