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The changes listed in this table are with respect to the PI configuration.
| PMIP3 | Minimum solution | |
|---|---|---|
| Orbital parameters | [ ecc = 0.018994 ] - [ obl = 22.949° ] - [ peri-180° = 114.42° ] | |
| Date of vernal equinox | March 21 at Noon | |
| Trace gases | [ CO2 = 185 ppm ] - [ CH4 = 350 ppb ] - [ N2O = 200 ppb ] [ CFC = 0 ] - [ O3 = same as in PI ] | |
| Aerosols | Same as in CMIP5 PI (see Dust forcing note below) | |
| Solar constant | Same as in CMIP5 PI | |
| Vegetation | Same as in CMIP5 PI | |
| Ice sheets | Ice sheet extent and related changes in topography provided | |
| Land surface elevation and coastlines | Land-sea mask and elevation changes provided | Minimum changes (see below) |
| Ocean bathymetry | Up to groups, depending on the flexibility of their ocean model (see note below) | |
| River outflow | Modified according to a river pathway map (provided, see below) | Same as in CMIP5 PI |
| Ice sheet mass balance | Add excess LGM freshwater to ocean (see below) | Same as in CMIP5 PI |
| Mean ocean salinity | +1 PSU everywhere (to be added once at the beginning of the simulation) | |
| Mean atmospheric surface pressure | Global average equal to PI value (see below) |
Note that insolation should follows PMIP requirements. Please check it carefuly using the following tables (LGM insolation tables).
Check carefully the date of the Vernal equinox, because it has implications when we compare the paleo and PI seasonal cycles.
The ice sheet provided for PMIP3/CMIP5 LGM experiments is a blended product obtained by averaging three different ice sheets reconstructions: ICE-6G v2.0 provided by Dick Peltier, MOCA provided by Lev Tarasov and ANU provided by Kurt Lambeck. More information about this is available in the LGM ice-sheets description page.
Data files are available on the Files for PMIP3 experiments page.
Implementing the LGM ice-sheets implies changing the land-sea mask, the land surface elevation and the ocean bathymetry as described below. Groups having doubts about their setup should contact Masa Kageyama and Jean-Yves Peterschmitt.
This mask should be prescribed using the data provided in the LGM BC download page, where the sftlf variable is 0 (%) over the ocean and 100 (%) over land.
Make sure that the ocean model configuration keeps the following straits open:
The provided land-sea mask includes a Caspian Sea as defined, conservatively, by its modern day contour (the -29 m iso-altitude in this region in ICE-6G v2.0).
If implementing the land-sea mask proves difficult for a modelling group, the minimum implementation is to:
The change in surface elevation specified by the orog_diff variable provided in the LGM BC download page should be added to the present-day surface elevation, so that all the participating models will be perturbed in the same way.
Note: this specified change assumes that the surface elevation over present-day oceans is zero (m).
The ice-sheet extent should be prescribed using the data provided in the LGM BC download page, where the sftgif variable is 0 (%) where there is no ice-sheet, or 100 (%).
This mask includes ice shelves, which should be included in models that allow this feature.
sftgif and sftlf variables as areas where:sftgif == 100 and sftlf == 0The mean sea-level change corresponding to the ice-sheet reconstruction to be used in the PMIP3 LGM experiment is approximatively 116 m. A more complete description of the change in bathymetry can be computed from the Peltier ICE-6G v2.0 reconstruction.
The ocean bathymetry will be adapted by each group, depending on the flexibility of their ocean model.
Modelling groups should pay special attention to:
The river pathways and basins should be at least adjusted so that fresh water is conserved at the Earth's surface: care should be taken that rivers reach the ocean (due to the lower sea level at LGM, some river mouths have to be displaced towards the coast).
You can use the river routing provided by Lev Tarasov to change the routing scheme in your code, so that the river pathways is consistent with the presence of the ice-sheet. Please note that to our knowledge, so far, no group has attempted to introduce these changes in river runoff in their model configuration. We would appreciate some feedback from groups who who choose to use this data.
Data files are available on the Files for PMIP3 experiments page.
It is advised to ensure a closed fresh water balance at the Earth's surface: snow accumulating on the ice-sheets should be redistributed to the oceans, either globally or in the adjacent oceans.
The vegetation should be treated as in the CMIP5 PI experiment. The reason is that in CMIP5 we test the version of the model used for future climate projections. Since OA and ESM models will be considered, depending on the model used the vegetation will be
The simulations should be forced by the prescribed LGM CO2 concentrations. Please use the same protocol as in CMIP5 to store the diagnostic carbon fluxes and the variables needed for PCMIP (see PCMIP Project and CMIP5)
Some ESM have interactive aerosols. In that case compute dust and associated forcing online, as in PI. If this is not the case then the recommendation is to keep dust and aerosols as in PI (i.e. no change for 21 ka).
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