The IPCC Data Distribution Centre Accessing the GCM Data

Appendix: Specifications for GCM Data Requested by the IPCC DDC

Integrations (using the same model):

• Long, multi-century control runs.
• Perturbed runs using historic forcing up to 1990 followed by a forcing scenario over a period up to 2100.
• Ensemble runs where completed
• High resolution time-slice experiments where completed

The forcing scenarios of interest to us are those with historic greenhouse gas (GHG) forcing from a "pre-industrial" period to 1990 (with and without sulphate aerosol forcing), and future forcing scenarios which approximate to equivalent GHG forcing of about 1% and 0.5% per annum from 1990 onwards (with and without associated sulphate aerosol forcing approximating the IS92a sulphur scenario).

Variables

We divide the requested variables (monthly mean data) into a "core" set (i.e., essential) and an optional set. We envisage that a large majority of impact studies will be accessing only the core variables, and the IPCC Task Group rightly gave priority to recommending that these variables be available through the DDC. For a smaller number of impact studies some of the optional variables may also be requested. You may therefore like to consider making these also available to the DDC, or at least having them potentially available to users through your own centre.

Core List

• Mean surface air temperature (2m equivalent)
• Mean maximum surface air temperature
• Mean minimum surface air temperature
• Total precipitation
• Total incident solar radiation
• Mean scalar wind speed (derived from daily or hourly components)
• A measure of humidity (mixing ratio, vapour pressure, etc.)
• Mean sea-level pressure
• Global-mean sea-level change due to thermal expansion (decade-mean data would be sufficient)

Optional List

• Daily mean temperature variance
• Daily precipitation variance
• Surface skin temperature (i.e., SST over water)
• Soil moisture
• Large-scale (frontal) precipitation
• Convective precipitation
• 850, 500 and 200hPa height and height variance, temperature, relative humidity and wind fields

Timesteps

The data we request to be lodged with the DDC are complete monthly mean time series data from the relevant integrations. If you are unable to supply the full time series until later, but have partial datasets already available, we would still appreciate receiving these now (and the full data later). If only decade-mean monthly averages are available we would consider whether these might still be useful. For the optional variables, decade-mean monthly data would generally be sufficient.

With regard to the equivalent daily timestep data, and for monthly variables not held by the DDC, we are suggesting that requests to the DDC for such data be directed to the relevant modelling centre. We therefore need to know from you whether daily data would be made available to such users by you, and if so which of the above variables and integrations and for which timeslices.

Other information

We request model data at their original resolution and precise information about the model grid co-ordinates. Also:

• Land-sea mask
• Model gridbox elevation
• The exact forcing scenarios used
• Meta data relating to the identification, processing and transfer of the relevant climate model data

A brief description of the model and experiments, or else references to reports and scientific literature which contain such information. We would also like reference to publications that contain results of validation or model intercomparison studies involving the version of the model supplied to the DDC.