Clear-Sky scene has different algorithms depending on the product ERBE-like, Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF), or Energy Balanced and Filled (EBAF). ERBE-like clear-sky scene is determined from CERES footprints that were crudely identified as clear using the ERBE scene id algorithm which uses climatological, zonal LW thresholds and appropriate SW thresholds based on 12 scene ids.
EBAF & SSF clear-sky scenes are determined from CERES footprints that are 99% clear as identified by CERES-MODIS clear-sky mask from the MODIS pixels contained within the CERES footprint. SSF clear-sky products contain many cloudy regions that may have no clear-sky observations for one particular month with no attempts to fill these regions. The EBAF clear-sky products filled all non-observed clear-sky regional fluxes for a complete clear-sky global map, and all temporal and spatial domains should have clear-sky fluxes.
quantify atmosphere-surface energy exchanges. In climate
research, detailed investigations of the influence of diverse
atmospheric conditions on radiative fluxes ask for a welldefined distinction between clear-sky and cloudy-sky situations. Effects of clouds, the so called “cloud forcing”, can
only be determined by explicitly separating clear-sky from
all-sky radiation measurements. A Clear-Sky Index (CSI)
to separate clear-sky from cloudy-sky situations has therefore been introduced, using accurate atmospheric longwave
radiation in conjunction with air temperature and humidity measurements at the was tested and first used on measurements of the Alpine Surface Radiation Budget (ASRB) network, and was of prime
importance for the determination of the altitude dependence
of cloud forcing and greenhouse effect over the Alps.
station. This clear-sky index, which
has the important advantage to be applicable 24 hours a day.