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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.
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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