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"ecCKD" is a free software tool for generating CKD gas optics models. It requires a limited amount of user input, primarily to specify the required band structure, an error tolerance, the minimum pressure down to which heating rates are required and the range of greenhouse-gas concentrations that need to be simulated. From this it generates a CKD model in the form of look-up tables stored in a single self-describing CKD definition file in NetCDF format. This can be read in by the free ecRad radiation scheme (currently only the ecckd branch), but the nature of the look-up table is simple enough that it could in principle be incorporated into any other radiation scheme. It is quite data intensive, requiring the 1 TB700 GB CKDMIP line-by-line gas absorption database to be available on disk. A particular innovation is the ability to generate full-spectrum correlated-k (FSCK) models, first investigated for atmospheric applications by Pawlak et al. (2004) in the shortwave and Hogan (2010) in the longwave. The gas optics models generated tend to be both accurate and efficient. Their speed is characterized by the total number of "k-terms", i.e. the total number of pseudo-monochromatic radiative transfer calculations that need to be performed to compute broadband longwave or shortwave flux profiles.
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