Gewex Cloud Assesment Database

Scientific background

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 record of the state of the atmosphere over the entire globe. Satellite cloud data records are now over 25 years old; however, climatologies compiled from different satellite data sets may have systematic biases.
The Global Energy and Water Cycle Experiment (GEWEX) Cloud Assessment, launched in 2005 by the GEWEX Radiation Panel and finalised in 2012, provides the first coordinated intercomparison of publicly available global cloud products (gridded, monthly statistics) obtained from multi-spectral imager, IR sounder and lidar measurements.

The objective of GEWEX Cloud Assessment is to :

Compare the cloud properties of different satellite products for the study of climate (cloud) evolution and the evaluation of climate models

The first version of GEWEX Cloud Assessment database, created by the participating teams, contains many cloud properties: their monthly means, variability and distributions in 1° latitude x 1° longitude grid boxes and is available here.

In addition to the self-assessments (Annex I of Stubenrauch et al. 2012) that show the maturity of the different datasets, the analyses have shown how cloud properties are perceived by instruments measuring different parts of the electromagnetic spectrum and how the averages and distributions of cloud properties are affected by the choice of instruments as well as by certain methodological decisions.

Since then, several teams have improved their datasets and new long-term global datasets have emerged.

Therefore, the GEWEX Data and Analysis Group is planning an update of this cloud database, which is currently under preparation and will be available soon. The first version of the database has a maximum temporal coverage from 1982 to 2010. The cloud database will be updated once a year. Corrections to the rendering algorithms will be made as well as the temporal extension of the datasets. New data sets from new instruments will also be available.

The products

The available products are level 3 satellite products from different instruments and put on a common grid. This concerns 11 cloud products from different parameters:

-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 maximum temporal coverage is from 1982 to 2010

AERIS is involved in the production of 2 of the 11 level 3 products (AIRS and IASI) and is in charge of the publication and distribution of the 2nd version of the GEWEX-CA database.