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CIRC:
Continual
Intercomparison of Radiation Codes
What is the rationale behind CIRC?
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 continued improvement of RT parameterizations.
CIRC
seeks to establish itself as the standard against which to document
code performance in scientific publications and in coordinated joint
modeling activities
such as GCM intercomparisons or ensemble climate change
predictions. While it is understood that the CIRC
reference calculations reflect current spectroscopic knowledge and may
themselves be imperfect, our intent is to update them when algorithmic
or database improvements become available and to expand them with new
cases as part of future phases of the effort. Feedback from
participants, users of the
dataset, and the atmospheric RT modeling community at large are
essential for
maintaining and enhancing the continuous nature of the CIRC effort.
A feature that distinguishes CIRC from previous intercomparisons such
as the Intercomparison of Radiation Codes in Climate Models (ICRCCM) is
that its pool of cases is largely based on observations. Atmospheric
and surface input, as well as radiative fluxes used for consistency
checks come primarily from the Atmospheric
Radiation Measurement (ARM)
Climate Research Facility measurements and satellite observations
that
are then compiled in the Broadband
Heating Rate Profile (BBHRP) product. Additonal 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, 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 cases and
homogeneous, single-layer overcast liquid cloud cases. Future phases
will add greater variety and complexity in the atmospheric description,
or
(depending on the lessons learned from Phase I and feedback from
participants) even include
simpler, perhaps synthetic, idealized experiments.
Model validation
The goal of CIRC at first stage is to document the performance of the
participating models relative to the LBL standards. Ultimately,
however, model performance should be critically evaluated in terms of
the accuracy needed to address operational GCM requirements for current
and future climate simulations and comparisons with observations. As
submissions come in and we start understanding better the details of
how the algorithms have processed the input provided to perform the
runs, we plan to define performance targets which can be used by
modelers to assess the performance of their models. Since the participating
algorithms may be tweaked
to accomodate CIRC input and output requirements, performance
evaluations may not reflect actual performance in typical operational
environment. It will therefore be valuable to receive multiple
submissions where different interpretations or processing of the
provided input are used (see also our
submission page).
Comments?
Please send to Lazaros
Oreopoulos your ideas and suggestions on how to evaluate model
performance with the CIRC dataset and how to make CIRC
succeed in meeting RT modeling needs.
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