The Continual Intercomparison of Radiation Codes (CIRC) - GEWEX

The Continual Intercomparison of 

Radiation Codes (CIRC) 

Lazaros Oreopoulos 1 , Eli Mlawer 2 , 

Jennifer Delamere 2 , Timothy Shippert 3 

With contibutions from: T. Charlock, B. Fomin, M. Iacono, Z. Jin, S. 

Kato, D. Kratz, J. Manners, P. Raisanen, and F. Rose 

1 

NASA-GSFC, Greenbelt, MD, USA 

2 

AER, Lexington, MA, USA 

3 

PNNL, Richland, WA, USA

Historical Perspective (1) 

ICRCCM-I (1984 - 1991): InterComparison of Radiation Codes for 

Climate Models, WCRP/IRC) 

- LW: Ellingson and Fouquart (1991) 

-~60 idealized cases (mostly cloudless) 

- SW: Fouquart et al. (1991) 

-~60 idealized cases (again, mostly cloudless) 

- LBL vs. approximate models 

Overall message : for cloudless skies, errors can be alarmingly large 

LW


•ICRCCM-II (1991): SPECTRE (FIRE II) 

Emphasis on LW and cloudless skies 

Ellingson and Wiscombe (BAMS, 1996) 

Overall message : using observations to 

assess models can be fruitful, but is HARD 

... Genesis of the ARM program.


ICRCCM-III SW: (Barker et al. 2003) 

- Interpretation and handling of unresolved clouds 

- CSRM domains; benchmarks set by 3D MC codes 

-Compares 3D with PPH and ICA 

-Overall message : standard assumptions are often 

inadequate and no 1D single method is adequate for all.


ICRCCM-III LW: (IRC; Ellingson et al., ongoing) 

- Interpretation and handling of unresolved clouds 

-CSRM domains; benchmarks set by a 3D MC code 

-Compares 3D with PPH and ICA 

Overall message : TBD; So far, proven the inadequacy of 

standard overlap assumptions 

solid: ICA 

dashed: MRO 

dotted: RO


RTMIP (RT Model Intercomparison Project, Collins et al., 2006 

- Focusing on well-mixed greenhouse gases 

- RT codes of IPCC AR4 GCMs 

- SW and LW with several LBL references 

Take home message : LBL codes agree, means of GCM codes 

good, but spread too wide (worse at the SFC for SW) 

2xCO2 forcing

So, what is the Continual Intercomparison of 

Radiation Codes (CIRC)? 

• RT model intercomparison aspiring to become the standard for 

documenting the performance of RT codes used in Large-Scale Models 

• Supported by DOE’s ARM program and endorsed by GRP and IRC 

• Goal is to have RT codes of GCMs (incl. IPCC) report performance 

against CIRC 

• Phase I was launched on June 4, 2008 

How CIRC differs from previous intercomparisons: 

• Observation-tested (LW) LBL calculations are used as radiative benchmarks 

• Benchmark results are publicly available 

• Observationally-based input (from an ARM product named BBHRP, mostly) 

• Flexible structure and longer lifespan than previous intercomparisons

CIRC website 

http://www.circ-project.org 

http://circ.gsfc.nasa.gov

Challenges we faced 

• For input and reference calculations to be credible, a reasonable level of 

agreement with observations is desirable 

• Our designated data source (ARM BBHRP v.1.4.1) is small; very few 

BBHRP cases satisfy our criteria: 

homogeneous* (1D) 

closure at both SFC and TOA for both SW and LW 

• LBL calculations are not standard in BBHRP 

• Input for LBL calculations is not necessarily available from BBHRP (e.g., 

spectral surface albedo) 

• Validation of LBL calculations 

• We nevertheless came up with a bunch of (semi-validated) cases 

* See also SPECTRE paper by Ellingson and Wiscombe (BAMS 1996)

CIRC’s main data source: 

BBHRP at SGP March 2000-February 2001 

daytime datapoints with TOA and SFC fluxes: 

375 

overcast liquid clouds: 

8 

appropriate for CIRC 

(homogeneous, closure) 

1 

25 

SGP SW total at SFC 

Clear-sky cases: 150 

(~60 % have SZA > 60°) 

number of datapoints 

20 

15 

10 

5 

mean≈ – 2.5 

sdev≈ 6 

Direct component is for normal surface 

0 

-20 -15 -10 -5 0 5 10 15 20 

residual=obs-RRTM

CIRC Phase I cases 

Case 

SZA 

PWV 

(cm) 

τ aer 

LWP 

(gm -2 ) 

LW SFC 

obs - LBL (%) 

LW TOA 

SW SFC 

SW TOA 

(1) SGP 9/25/00 

47.9° 

1.23 

0.04 

0.5 

-0.9 

0.5 

-3.1 

(2) SGP 7/19/00 

64.6° 

4.85 

0.18 

0.6 

-1.4 

-1.1 

8.4 

(3) SGP 5/4/00 

40.6° 

2.31 

0.09 

1.0 

-1.2 

-0.1 

-8.7 

(4, 5) NSA 

5/3/04 2xCO 2 

) 

55.1° 

0.29 

0.13 

1.2 

-0.6 

-0.8 

0.7 

(6) SGP 3/17/00 

45.5° 

1.90 

0.24 

263.4 

1.1 

-3.0 

4.9 

-0.9 

(7) PYE 7/6/05 

41.2° 

2.42 

39.1 

0.2 

0.6 

-0.4 

-0.1

LW QC: LBLRTM spectral comparisons with AERI 

10 

AERI-LBLRTM, Case 2 

radiance difference 

mW/(m -2 sr cm -1 ) 

5 

0 

-5 

-10 

600 700 800 900 1000 1100 1200 1300 1400 

wavenumber (cm -1 ) 

errors < 1 Wm -2

SW QC: Spectral comparison with RRTM 

sum ( 

) 

≈ 0.14 Wm -2 

downwelling SFC 

sum ( ) 

≈ 1.18 Wm -2 

upwelling TOA & SFC 

7/19/2000, SGP: Warm and moist

CIRC modus operandi (Phase I) 

• Input & output (TOA and SFC fluxes at 1 cm -1 ) and instructions on how to 

run the cases are openly available at the CIRC website 

• Only registered users (considered as formal participants) have privileges 

such as: 

e-mail notifications about changes, updates, and corrections to the CIRC 

dataset. 

priority to participate in workshops and publications 

• Registered users may have to submit results within predetermined 

deadlines. 

• Submitted results and intercomparison analysis will be posted on website 

• Implementation details and performances of participating codes will be 

documented and evaluated

Phase I launch 

• Mass e-mail on June 4, 2008 (text available at CIRC website) 

• 17 requests to register as participants (7 USA, 2 Brazil, 2 

France, 2 Russia, 1 Australia, 1 Canada, 1 UK, 1 Finland) 

• 8 submissions received so far (a few more in the pipeline) 

• Feedback: 

o At IRC business meeting: absorb ICRCCM 

o Should not have publicized the reference results 

o More synthetic cases, please 

o SW heating rates, please 

o Remove aerosols 

o Separate species 

• Still fine-tuning and clarifying things 

• Please advertise, and if you have a code, participate!

Phase I initial results, flux errors 

% difference from LBL calculations 

10 

5 

0 

-5 

obs 

GSFC 

FLCKKR 

COART 

ES 

FMI 

LW downwelling flux at surface 

Case1 Case2 Case3 Case4 Case5 Case6 Case7 


4 

2 

0 

-2 

-4 

LW upwelling flux at TOA 


-10 

10 

10 

SW upwelling flux at TOA 


5 

0 

-5 

Case1 Case2 Case3 Case4 Case 5 Case6 Case7 


5 

0 

-5 

Case1 Case2 Case3 Case4 Case 5 Case6 Case7 

-10 

SW total downwelling flux at SFC 

31% 

-10 

FLCKKR (= Fu, Liou Charlock, Kato, Kratz, Rose), submitted by Rose and Charlock 

COART (= Coupled Ocean-Atmosphere Radiative Transfer), submitted by Jin and Charlock 

ES (= Edwards-Slingo), submitted by Manners 

FMI (=Finnish Meteorological Institute), submitted by Räisänen

CAM3 RT vs. RRTMG 

5 

4 

LW down SFC 

obs 

CAM 

RRTMG 

2 

1 

% deviation from LBLRTM 

3 

2 

1 

% deviation from LBLRTM 

0 

-1 

-2 

-3 

0 

-4 

-1 


-5 

LW up TOA 


8 

SW down SFC 

10 

% deviation from CHARTS 

6 

4 

2 

0 

% deviation from CHARTS 

5 

0 

-5 

-2 

Case1 Case2 

Case3 Case4 Case 5 Case6 Case7 

-10 

Case1 Case2 

SW up TOA 

Case3 Case4 Case 5 Case6 Case7

Phase I preliminary results, heating rates 

p(hPa) 

0.1 

1 

10 

100 

LW, case2, moist 

1000 

-15 -10 -5 0 5 

heating rate (K/day) 

0.1 

SW, case2 

p(hPa) 

1 

10 

100 

RRTM 

LBLf 

1000 

0 5 10 15 20 


p(hPa) 

p(hPa) 

0 

200 

400 

600 

800 

RRTM 

LBLf 

LBLRTM 

LW, case6, thick cloud 

1000 -15 -10 -5 0 5 

0 

200 

400 

600 

800 


SW, case6 

1000 0 5 10 15 20 


Note: No reference SW HR available from CHARTS

Importance of spectral surface albedo 

CHARTS weighted-SSF weighted sfc. albedo 

CHARTS-R sfc 

NIR 

(3)=0.299 

SSF-R sfc 

NIR 

(3)=0.274 

CHARTS-R sfc 

NIR 

(4)=0.514 

SSF-R sfc 

NIR 

(4)=0.471 

flux difference (Wm -2 ) 

15 

10 

5 

0 

TOA upwelling 

GSFC 

CAM 

ES 

} 

Resolve sfc 

albedo into 

2 bands 

Resolves 

sfc albedo 

into 6 bands 

-5 

Case1 Case2 

Case3 Case4 Case 5 Case6 Case7

Phase I initial results, CO 2 forcing of dry atmospheres 

SW or LW forcing (Wm -2 ) 

4 

3 

2 

1 

0 

-1 

-2 

-3 

-4 

LBL 

SW 

LW 

GSFC 

CAM 

FLCKKR 

COART 

FMI 

ES 

SFC 

RRTMG 

CHARTS-R sfc 

NIR 

(4)=0.514 

CHARTS-R sfc 

NIR 

(5)=0.516 

FLCKKR and COART 

have fixed CO 2 

in SW 

SW or LW forcing (Wm -2 ) 

2 

1.5 

1 

0.5 

0 

-0.5 

TOA 

-1 

Case4-Case5 (double CO2 experiment)

CO 2 forcing net flux profile differences 

0 

SW 

0 

LW 

200 

200 

p(hPa) 

400 

600 

p(hPa) 

400 

600 

800 

1000 

800 

1000 

CAM 

GSFC 

ES 

RRTM 

-0.5 0 0.5 1 1.5 2 2.5 

flux difference (Wm -2 ) 

0 1 2 3 4 5 

flux difference (Wm -2 )

CO 2 spectral forcing 

TOA or SFC forcing (Wm -2 /cm -1 ) 

0.04 

0.02 

0 

-0.02 

Case4-Case5 

TOA up 

SFC down 

thermal 

-0.04 

2xCO 

2 

spectral forcing 

SFC forcing (Wm -2 /cm -1 ) 

0.005 

0.004 

0.003 

0.002 

0.001 

600 800 1000 1200 1400 

wavenumber (cm -1 ) 

Case4-Case5, down SFC 

solar 

0 

2000 4000 6000 8000 1 10 4 

wavenumber (cm -1 )

CIRC activities and future 

• Talks at IRS’08 and ARM’08 WG meetings 

• Extended abstract to appear in IRS’08 proceedings 

• Short (“Nowcast”) BAMS article submitted 

• ARM proposal seeking funding for Phase II (ice clouds, SW 

spectral closure) pending 

• “Pristine” and “cloudless” (Cases 6 & 7) versions will soon be 

released 

• Would like to see submission from RT codes used for global 

flux datasets 

• Workshop within 2009 (after GRC on Radiation & Climate?) 

• Standards, certification, funding?

The Continual Intercomparison of Radiation Codes (CIRC) - GEWEX

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