Improved ARM-SGP TOA OLR Fluxes from GOES-8 IR Radiances Based on CERES Data

The radiation budget at the top of the atmosphere (TOA) is a quantity of fundamental importance to the Atmospheric Radiation Measurement (ARM) Program. Thus, it is necessary to measure the radiation budget components, broadband shortwave albedo and outgoing longwave radiation (OLR), as accurately as possible. Measurement of OLR over the ARM surface sites has only been possible since the advent of Clouds and the Earth’s Radiant Energy System (CERES; Wielicki et al. 1998) in 1998. Prior to CERES, it was necessary to infer the OLR from the infrared (IR; 10.8 μm) channel on the Geostationary Operational Environmental Satellite (GOES) imager by applying a narrowband-to-broadband (NB-BB) conversion (Minnis et al. 1995). Broadband OLR has been derived from GOES-7, GOES-8, and GOES10 data since 1994 (Khaiyer et al. 2002) as part of the NASA-Langley cloud and radiation products for the ARM Southern Great Plains (SGP) domain (available at: http://www-pm.larc.nasa.gov/SGP/armsgp.html or at the ARM data center). These GOES-derived broadband OLR data are based on an empirical relationship between April 1986 GOES-6 IR radiances and Earth Radiation Budget Experiment (ERBE) longwave (LW; 5-50 μm) fluxes and has an uncertainty of 7 Wm or 3% (Doelling et al. 1999). CERES measures LW radiation over a greater spectral band, has more accurate calibrations, and has a more robust radiance to flux conversion algorithm than ERBE (Loeb et al. 2003). Additionally, the IR-channel spectral filters and calibrations for the GOES imagers can vary with satellite and, therefore, the NB-BB relationship may also vary with each GOES instrument resulting in potential biases that depend on the particular GOES satellite. Thus, the NB-BB OLR relationship should be updated using CERES with contemporary GOES data to provide more accurate TOA LW fluxes for ARM. The objective of this study is to improve the NB-BB relationship so that the OLR derived from GOES can be used more confidently for energy budget, cloud forcing, and modeling studies over the ARM SGP.