An assessment of the effect of day/night cloud overlap representation on longwave radiative flux estimates using NASA/GEWEX Surface Radiation Budget project and Calipso-CloudSat-CERES-MODIS Data Products

Clouds cover spatial and temporally most of the Earth surface and, therefore play an import role on the global energy budget and the hydrological cycle. In this challenge significant progress has been made in this field with satellite measurements. However, different instruments aboard EOS (Earth Observational System), their characteristics and operational modes (day/night) determine the cloud properties retrieved and therefore the radiative fluxes estimated at the TOA and surface. This study shows a global assessment of the cloud overlap representation and the longwave radiative fluxes estimated by the NASA/GEWEX Surface Radiation Budget (Release 3.1) and the CALIPSO-CloudSat-CERES-MODIS (hereafter CCCM Release B1) data products during the whole overlapping year of 2007. Since both data products have significantly different spatial and temporal resolution, a methodology was developed to combine all the collocated footprints from CCCM with SRB cloud properties (from ISCCP) and fluxes produced to a seasonal 2° latitude X 5° longitude) grid spanning from 82° N to 82° S. The results of this study quantify the agreement between the data products on a seasonal basis between day and night. The study also evaluates the origin of these differences between SRB and CCCM. The different cloud assumptions during day/night for the different properties (cloud fraction or cloud type) determine the cloud radiative forcing differences. The annual average cloud radiative forcing mean differences at TOA are +1 Wm-2 and -0.53 Wm-2 during the day and night respectively. At the surface those differences are about -0.9 Wm-2 (day time) and 1.7 Wm-2 (night time). This study also assesses these differences on a regional and seasonal basis for day and night cloud distributions.