Validation of the CERES Edition 2B Surface-Only Flux Algorithms

摘要

The Clouds and the Earth's Radiant Energy System (CERES) project uses two shortwave (SW) and two longwave (LW) algorithms to derive surface radiative fluxes on an instantaneous footprint basis from a combination of top-of-atmosphere fluxes, ancillarymeteorological data, and retrieved cloud properties. Since the CERES project examines the radiative forcings and feedbacks for Earth's entire climate system, validation of these models for a wide variety of surface conditions is paramount. The present validation effort focuses upon the ability of these surface-only flux algorithms to produce accurate CERES Edition 2B single scanner footprint data from the Terra and Aqua spacecraft measurements. To facilitate the validation process, high-quality radiometric surface observations have been acquired that were coincident with the CERES-derived surface fluxes. For both SW models, systematic errors range from -20 to -12 W m~(-2) (from -2.8% to — 1.6%) for global clear-sky cases, while for the all-sky SW model, the systematic errors range from 14 to 21 W m~(-2) (3.2%^.8%) for global cloudy-sky cases. Larger systematic errors were seen for the individual surface types, and significant random errors where observed, especially for cloudy-sky cases. While the SWmodels nearly achieved the 20 W m~(-2) accuracy requirements established for climate research, further improvements are warranted. For the clear-sky LW model, systematic errors were observed to fall within ±5.4 W m~(-2) (±1.9%) except for the polar case in which systematic errors on the order from -15 to —11 W m~(-2) (from —13% to —7.2%) occurred. For the all-sky LW model, systematic errors were less than ±9.2 W m~(-2) (±7.6%) for both the clear-sky and cloudy-sky cases. The random errors were less than 17 W m~(-2) (6.2%) for clear-sky cases and 28 W m~(-2) (13%) for cloudy-sky cases, except for the desert cases in which very high surface skin temperatures caused an overestimation in the model-calculated surface fluxes. Overall, however, the LW models met the accuracy requirements for climate research.