The Continual Intercomparison of Radiation Codes (CIRC) is intended as an evolving and regularly updated
permanent reference source for GCM-type radiative transfer (RT) code evaluation that will help in the improvement of
radiation parameterizations. CIRC seeks to establish itself as the standard against which code performance is documented
in scientific publications and coordinated joint modeling activities such as GCM intercomparisons. A feature that
distinguishes CIRC from previous intercomparisons is that its pool of cases is largely based on observations.
Atmospheric and surface input, as well as radiative fluxes used for consistency checks with the reference line-by-line
calculations come primarily from the Atmospheric Radiation Measurement (ARM) Climate Research Facility
measurements and satellite observations compiled in the Broadband Heating Rate Profile (BBHRP) product. Additional
datasets beyond BBHRP such as measurements from ARM field campaigns and spectral radiances from the AERI
instrument are also used to complete the set of desired cases and to ensure the quality of the input. For Phase I, launched
in June, CIRC aims to assess the baseline errors of GCM RT codes and therefore provides test cases that evaluate
performance under the least challenging conditions, i.e, well-understood clear-sky and homogeneous, single-layer
overcast liquid cloud cases.