Antarctic cloud radiative forcing at the surface estimated from the ISCCP D2 and AVHRR Polar Pathfinder data sets, 1985-1993

Surface cloud radiative forcing was calculated using cloud and surface properties from the International Satellite Cloud Climatology Project (ISCCP) D-series product as input into a radiative transfer model. In addition, the newly extended AVHRR Polar Pathfinder (APP) data set, which includes surface cloud radiative forcing, was used in this 9-year (1985-1993) study. Spatial and temporal trends in the surface net cloud forcing for the Antarctic were examined in both the ISCCP-derived and APP data sets. Monthly means of the ISCCP-derived net cloud radiative forcing at the surface were found to be greater than zero all year-round poleward of 80°S. The APP net cloud forcing was found to exceed 10 W/m² south of 80°S every month of the year. The differences in the net cloud forcing between the two data sets largely occurs because of differing cloud amounts. Both the ISCCP and APP net surface fluxes were compared to fluxes measured at Neumayer Station. Errors in the monthly mean net all-wave surface flux of up to 50 W/m² were found for the ISCCP-derived product. The APP product errors were found not to exceed 13 W/m² at the monthly time scale.