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CIRC:
Continual
Intercomparison
of
Radiation Codes
What is CIRC?
CIRC is in many respects the successor to
the seminal ICRCCM
(Intercomparison
of Radiation Codes in Climate Models)
effort that spanned the late 80's - early
00's. CIRC distinguishes itself from ICRCCM
by its emphasis on using observations to
build its catalog of cases. It is intended
as an evolving and regularly updated
reference source for GCM-type radiative
transfer (RT) code evaluation, and similar
to ICRCCM, its goal is to contribute to the
improvement of solar and thermal RT
parameterizations. CIRC has received support
by DOE's Atmospheric
Radiation
Measurement (ARM) program and is a
project of GEWEX's
GDAP
and GASS
panels as well as a working group within IAMAS's International
Radiation Commission (IRC). More
information on the rationale behind CIRC can
be found here.
The invitation letter that launched Phase I
on June 4, 2008 is available in this page.
Register as a CIRC participant
While anybody can download the input files
needed for the radiative transfer runs and
the reference
output results, we urge users of this
website to register as "CIRC participants".
Registered CIRC participants will enjoy
benefits such as:
- Updates via e-mail about improvements,
additions, and corrections to the
reference dataset and the accompanying
documentation.
- An opportunity to have their results
compared to those of other participants.
- Invitation to workshops on CIRC.
- Invitation to coauthor scientific
papers on CIRC.
Please register as a CIRC
participant by sending your name,
affiliation and e-mail address to Lazaros
Oreopoulos.
What we provide and what we request
The CIRC Phase I cases, with one
exception, are based on ARM BBHRP
cases satisfying preset criteria that make
them appropriate for the purposes of the
intercomparison. The main criterion was:
- satisfactory radiative closure at the
surface and TOA (for both the solar and
thermal part of the spectrum),
while for the cloudy cases additional
criteria were:
- overcast conditions
- the presence of only one water phase
(liquid)
- cloud homogeneity (as indicated by
small variability in the observed
surface irradiances),
and for the clear sky cases
additional criteria were:
- a wide range of precipitable water
loadings
- a significant range of aerosol
loadings
- a significant range of solar
geometries
We provide all the input typically needed
by a GCM-type radiative transfer algorithm
to calculate profiles of radiative fluxes
and heating rates, namely profiles of
atmospheric pressure, temperature, gas
concentrations, aerosol single scattering
properties, cloud fraction/water
path/effective particle size, and surface
albedo. A comprehensive list of these
quantities and details about how they were
specified or derived can be found here, while
the input data themselves can be
downloaded from here.
The reference
output consists of surface and TOA
fluxes resolved at 1 cm-1
resolution and broadband longwave (LW)
flux and heating rate profiles. The
longwave results were obtained with the
line-by-line radiation code LBLRTM,
while the shortwave (SW) results were
obtained with the doubling-adding code CHARTS (Code
for High-Resolution Accelerated
Radiative Transfer with Scattering)
which uses LBLRTM gaseous absorption
optical depths. CHARTS output is
currently limited to radiative fluxes at
the boundaries of the atmospheric column
(TOA and surface), but fluxes at
additional atmospheric levels may be
provided in the future. The output
requested from CIRC participants consists
of broadband
SW and LW flux and heating rate profiles.
Phase I Cases
CIRC Phase I consists of seven cases,
five cloud-free, and two with overcast
liquid clouds. The cloudless cases come
from BBHRP Southern
Great
Plains (SGP) cases (three), and from
one BBHRP Northern
Slope
of Alaska (NSA) case which spawns
two experiments, one with nominal and one
with doubled carbon dioxide. The
cloudy cases come from a BBHRP SGP case
and from a Pt.
Reyes, CA ARM
Mobile Facility (AMF) deployment
case . In early 2010, runs for new
simplified "subcases" were requested in
order to aid the interpretation of Phase I
submissions. The detailed list of cases
with description and links to download the
corresponding input and output is provided
here.
4xCO2 cases
In late 2014 Robert
Pincus led an effort to evaluate
approximate RT codes with respect to
forcing performance under 4xCO2
conditions. The CIRC Phase I cloud-free
pristine (no-aerosol) subcases with
spectrally flat surface albedo (for SW)
were used. The effort provided the
opportunity to evaluate updated versions
of the RT codes that participated in CIRC
Phase I, as well as codes that had not yet
participated in CIRC both under nominal as
well as quadrupled CO2
concentrations. The most important results
of the exercise are described in this paper.
The article contains information on how to
download input and output data relevant to
the exercise.
Contact information
For more information on CIRC please
contact Lazaros
Oreopoulos. For questions on BBHRP,
LBLRTM and CHARTS contact Eli Mlawer.
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