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Only one Clouds and Earth's Radiant Energy System (CERES) instrument is onboard the Suomi National Polar-orbiting Partnership (NPP) and it has been\udplaced in cross-track mode since launch; it is thus not possible to construct\uda set of angular distribution models (ADMs) specific for CERES on NPP.\udEdition 4 Aqua ADMs are used for flux inversions for NPP CERES measurements.\udHowever, the footprint size of NPP CERES is greater than that of Aqua CERES,\udas the altitude of the NPP orbit is higher than that of the Aqua orbit.\udFurthermore, cloud retrievals from the Visible Infrared Imaging Radiometer\udSuite (VIIRS) and the Moderate Resolution Imaging Spectroradiometer\ud(MODIS), which are the imagers sharing the spacecraft with NPP CERES and Aqua CERES,\udare also different. To quantify the flux uncertainties due to the footprint\udsize difference between Aqua CERES and NPP CERES, and due to both the\udfootprint size difference and cloud property difference, a simulation is\uddesigned using the MODIS pixel-level data, which are convolved with the\udAqua CERES and NPP CERES point spread functions (PSFs) into their respective\udfootprints. The simulation is designed to isolate the effects of footprint\udsize and cloud property differences on flux uncertainty from calibration and\udorbital differences between NPP CERES and Aqua CERES. The footprint size\uddifference between Aqua CERES and NPP CERES introduces instantaneous flux\uduncertainties in monthly gridded NPP CERES measurements of less than 4.0 W m−2\udfor SW (shortwave) and less than 1.0 W m−2 for both daytime and nighttime\udLW (longwave). The global monthly mean instantaneous SW flux from simulated NPP CERES\udhas a low bias of 0.4 W m−2 when compared to simulated\udAqua CERES, and the root-mean-square (RMS) error is 2.2 W m−2\udbetween them; the biases of daytime and nighttime LW flux are close to zero\udwith RMS errors of 0.8 and 0.2 W m−2. These uncertainties are\udwithin the uncertainties of CERES ADMs. When both footprint size and cloud\udproperty (cloud fraction and optical depth) differences are considered, the\uduncertainties of monthly gridded NPP CERES SW flux can be up to\ud20 W m−2 in the Arctic regions where cloud optical depth\udretrievals from VIIRS differ significantly from MODIS. The global\udmonthly mean instantaneous SW flux from simulated NPP CERES has a high bias\udof 1.1 W m−2 and the RMS error increases to\ud5.2 W m−2. LW flux shows less sensitivity to cloud property\uddifferences than SW flux, with uncertainties of about 2 W m−2\udin the monthly gridded LW flux, and the RMS errors of global monthly mean daytime\udand nighttime fluxes increase only slightly. These results highlight the\udimportance of consistent cloud retrieval algorithms to maintain the accuracy\udand stability of the CERES climate data record

atmospheric measurement techniques

The effects of different footprint sizes and cloud algorithms on the top-of-atmosphere radiative flux calculation from the Clouds and Earth's Radiant Energy System (CERES) instrument on Suomi National Polar-orbiting Partnership (NPP)