Additional Information for and Requests of Modeling Groups

Last updated 25 April 2005

Request for documentation of models and simulations

Request for time-correspondence information

Request for CO2 radiative forcing information (from Taylor, Boer, and Webb)

Formal invitation to submit IPCC simulations


Request for documentation of models and simulations (1/31/05)

The links immediately below lead to forms that should be filled out to provide some basic model documentation in uniform format.  The information asked for on the attached document clearly does not constitute full model documentation, but it should answer many of the common questions that arise when analyzing output from multiple models.  A number of scientists have helped in preparing this form, including IPCC chapter 8 lead authors, other lead authors, and PCMDI scientists. Please enter information for your model into one of these two forms electronically and return it to

Request for time-correspondence information (2/17/05)

From the metadata contained in the model output files, it is not always clear at what point in the control run, the perturbation run was initiated.  Sometimes this data can be found in the global attributes, but even then we have found ambiguities.  To avoid any misinterpretation, we have posted on our web site this information from groups who have already contributed model output to the archive (in 3 different formats: web page, Excel spread sheet, pdf file). 

New contributors of data should enter the information from their model into the one of the following forms:

Please do this as soon as possible.  There is also an instructions and example file that you should read.

Request for CO2 radiative forcing information (from Taylor, Boer, and Webb) 

30 December 2004
Dear colleagues,

We represent two of the projects registered to analyze IPCC model output archived at PCMDI. Our interest is in understanding differences in model climate sensitivity and feedbacks in these simulations. It is important for the IPCC to move beyond simply reporting the range of global climate sensitivities as was the case in past Reports. This is the primary reason that radiative forcing fields were requested as part of the IPCC standard output (see

We are unable to proceed with these projects without first obtaining the model radiative forcing fields (on your global grid), and we are writing to ask for your assistance. We limit our request to the 2xCO2 case. The additional calculations required are very modest and result in monthly mean 2xCO2 radiative forcing, resolved into four components:

1. longwave clear-sky radiative forcing.
2. longwave all-sky radiative forcing
3. shortwave clear-sky radiative forcing
4. shortwave all-sky radiative forcing

The analysis will be most straight-forward if you report the 2xCO2 forcing for the 4 components listed above at 200 mb (or the tropopause) and if you calculate these fluxes

1.  both before and after stratospheric adjustment (i.e., the instantaneous and adjusted forcing).
or, if you are unable to do this,
2.  before stratospheric adjustment (i.e., the instantaneous forcing).

Although "adjusted" forcing is preferred on theoretical grounds, some groups may not be able to perform this calculation, so option 2 is also acceptable.  The groups who perform both the "instantaneous" and "adjusted" calculations will facilitate both understanding of the feedbacks and also comparisons with those models where option 2 is followed.  Further technical details and guidance are provided in notes at the end of this email and one method of computing the adjusted radiative forcing for CO2 is described in Tett et al. 2002 (JGR VOL 107, No. D16, 10.1029/2000JD000028).

The deadline for analyzing IPCC model output is distressingly near since analyses must be submitted for publication by May. We ask for your assistance in providing this radiative forcing data as soon as possible.

Please let us know ( <>, <>, <>) if you are willing to provide this data, when it might be available, and if we can be of any assistance.

Best regards,
Karl Taylor (USA), George Boer (Canada), and Mark Webb (UK)

Notes on calculation of radiative forcing

As explained in the list of IPCC standard output document (, the four components of the forcing fields should be provided as a function of longitude and latitude for each of the 12 months of the year. Traditionally, the calculation is based on a control climate basic state in which two radiation calculations are performed each time step, one with 1xCO2 (i.e., the control), and the second with CO2 doubled.  The result of each of these calculations is separately accumulated and archived each month, while integrating the model through a single annual cycle.  Only the set of fluxes calculated with 1xCO2 is actually "seen" by the model itself (i.e., these are the fluxes that contribute to diabatic heating).  The difference between the two fluxes is the radiative forcing.

To summarize:

Let S and L be the shortwave and longwave radiative fluxes, respectively, at 200 mb (or the tropopause).

For the control simulation (1xCO2) retain:
- all sky components So and Lo
- corresponding clear sky components
- monthly means at 200 mb (tropopause) on the grid for 1 year

For the control simulation, do a second diagnostic call to the radiation code with 2xCO2 but with all other variables unchanged. Retain:
- all sky components S*, L*
- corresponding clear sky components
- monthly means at 200 mb (tropopause) on the grid for 1 year

The instantaneous 200mb (tropopause) forcing is given by the difference between the two calculations (S*-So, L*-Lo, and similarly for clear-sky components).

The above description neglects treatment of stratospheric adjustment. Several different methods for calculating the stratospherically adjusted forcing have been used.  Upon request, options for computing stratospheric adjustment will be discussed in a future correspondence.

Formal invitation to submit IPCC simulations

Original description of requested simulations (22 August 2003)

Information on simulations and analysis procedure (8 December 2003)

Letter from WGCM Climate Simulation Panel establishing further requirements (28 January 2004)