Toward Optimal Closure of the Earth's Top-of-Atmosphere Radiation Budget

Abstract

Despite recent improvements in satellite instrument calibration and the algorithms used to determine reflected solar (SW) and emitted thermal (LW) top-of-atmosphere (TOA) radiative fluxes, a sizeable imbalance persists in the average global net radiation at the TOA from satellite observations. This imbalance is problematic in applications that use earth radiation budget (ERB) data for climate model evaluation, estimate the earth?s annual global mean energy budget, and in studies that infer meridional heat transports. This study provides a detailed error analysis of TOA fluxes based on the latest generation of Clouds and the Earth?s Radiant Energy System (CERES) gridded monthly mean data products [the monthly TOA/surface averages geostationary (SRBAVG-GEO)] and uses an objective constrainment algorithm to adjust SW and LW TOA fluxes within their range of uncertainty to remove the inconsistency between average global net TOA flux and heat storage in the earth?atmosphere system. The 5-yr global mean CERES net flux from the standard CERES product is 6.5 W m?2, much larger than the best estimate of 0.85 W m?2 based on observed ocean heat content data and model simulations. The major sources of uncertainty in the CERES estimate are from instrument calibration (4.2 W m?2) and the assumed value for total solar irradiance (1 W m?2). After adjustment, the global mean CERES SW TOA flux is 99.5 W m?2, corresponding to an albedo of 0.293, and the global mean LW TOA flux is 239.6 W m?2. These values differ markedly from previously published adjusted global means based on the ERB Experiment in which the global mean SW TOA flux is 107 W m?2 and the LW TOA flux is 234 W m?2.