Top-of-atmosphere shortwave and longwave broadband fluxes derived over ARM SGP using improved techniques

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Description

As part of an ongoing effort to provide a continuous satellite cloud and radiative property data set for climate studies over the ARM domains, the Visible Infrared Solar Split-Window Technique (VISST) satellite retrieval algorithm provides top-of-atmosphere (TOA) broadband shortwave (SW) and longwave (LW) fluxes from geostationary satellite data. These fluxes are currently calculated from empirically derived narrowband-to-broadband (NB-BB) conversion coefficients, derived from coincident geostationary satellite narrowband fluxes and Terra Clouds and the Earth's Radiant Energy Budget (CERES) broadband fluxes. The accuracy of these derived fluxes can be limited by a number of factors, including a lack of temporal and angular ranges in the coincident times, and the use of one representative narrowband wavelength to calculate broadband flux.

This study addresses some of the limitations inherent in the current NB-BB fits. While limited in data set length (January–August 1998), Tropical Rainfall Measuring Mission (TRMM) CERES data provide broadband fluxes along a precessing orbit, yielding diurnal variability in the data set. Terra, limited to two daily local observations, provides a wealth of data extending from March 2000 to the present. These two data sets are used to improve the derivation of SW and LW broadband fluxes from the Geostationary Operational Environmental Satellites (GOES) data. Additionally, a new 2-channel technique utilizing the 6.7 μm water vapor and 11 μm window channels (M. Sun et al. 2012) provides improvement in LW flux derivation. NB-BB fits are derived for GOES-8 and validated with CERES-Aqua observed broadband fluxes as well as modeled fluxes from Fu-Liou radiation code. These methods will be applied to other satellites and ARM domains.