GEWEX Cloud Assessment

Assessment of global cloud datasets from satellites

Clouds cover about 70% of the Earth's surface and play a dominant role in the energy and water cycle of our planet. Only satellite observations provide a continuous survey of the atmospheric state over the entire globe. Satellite cloud data records now exceed more than 25 years; however, climatologies compiled from different satellite datasets can exhibit systematic biases.

The Global Energy and Water cycle Experiment (GEWEX) Cloud Assessment, initiated in 2005 by the GEWEX Radiation Panel and finalized in 2012, provides the first coordinated intercomparison of publically available, global cloud products (gridded, monthly statistics) retrieved from measurements of multi-spectral imagers, IR sounders, and lidar.

Cloud amount (CA)

Effective CA (CAE)

Cloud pressure (CP)

Cloud temperature (CT)

Cloud altitude (CZ)

Cloud optical depth (COD)

Cloud IR emissivity (CEM)

Cloud phase (ice/water)

Ice water path (CIWP)

Liquid water path (CLWP)

Effective particle radius:
CREI (ice), CREW (water)

The WCRP report of the cloud assessment is available in the Publications section. In general, the datasets agree well, within the retrieval uncertainties. Differences in average cloud properties are mostly explained by the inherent instrument capability for detecting and/or identifying optically thin cirrus.

The Level-3 monthly averaged and gridded data can be accessed through the Database section where they can be selected based on any combination of three criteria: instruments, variables, and years. These data are intended to facilitate climate studies, climate model evaluations, and other assessments.