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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 is supported by DOE's Atmospheric
Radiation Measurement (ARM) program
and endorsed by the GEWEX Radiation
Panel (GRP) and 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.
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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