GCOS Atmospheric Upper Air ECV: Cloud Properties
Contributing Networks & Status

Cloud feedback is considered to be one of the most uncertain aspects of future climate projections and is responsible for much of the wide range of estimates of climate sensitivity from models. The accurate measurement of cloud properties is exceedingly difficult. The WCRP International Satellite Cloud Climatology Project (ISCCP) has developed a continuous record of infrared and visible radiances since 1983 utilizing both geostationary and polar orbiting satellite data, but the record suffers from inhomogeneities. Reprocessing the data to account for orbital drift and other issues has helped reduce uncertainties in the observations. Long-term datasets of the AVHRR (Advanced Very High Resolution Radiometer) should be reprocessed to obtain records relating to cloud microphysics. The comprehensive global operational cloud products from MODIS (Moderate Resolution Imaging Spectroradiometer) and MISR (Multiangle Imaging Spectroradiometer) serve as reference for an extended period of time (almost a decade as of this writing). High-resolution infrared and microwave soundings (e.g., from HIRS (High-Resolution Infrared Sounder)) also have been contributing to better understanding of cloud properties, with a considerable length of record. Actions should be taken to avoid gaps in these advanced cloud products by using other available satellite systems (e.g., Fengyun (FY)-3) and by upgrading future sensors to capabilities equivalent to these systems. Because of the importance of the observation of cloud amount, microphysical characteristics and radiative properties, and their variation in time, continued research on improving observational capabilities is required.  
 
The effect on cloud formation and cloud lifetime of aerosol is one of the largest uncertainties in climate modelling. Detailed measurements of cloud microphysics in combination with aerosol measurements are needed to improve current estimates. Besides the cloud observations described above and the aerosol observations described for the atmospheric composition domain, combined LIDAR (Light Detection and Ranging)-RADAR (Radio Detection and Ranging measurements (ground-based, aircraft and satellite) are needed to study the aerosol-cloud interaction for research. Detailed field campaigns jointly measuring in situ cloud condensation nuclei and aerosol size and distribution are needed to study the atmospheric processes of the indirect aerosol effect. 

(Source: WMO/IOC Implementation Plan for the Global Observing System for Climate in Support of the UNFCCC (2010 Update) GCOS-138, GOOS-184, GTOS-76, WMO-TD/No. 1523)

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