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6ka Experimental Design

This was a BC development page (see discussion panel at the end of the page)

Make sure you use the final version of the 6k BC!

Boundary conditions

Summary of 6ka boundary conditions

PMIP3/CMIP5 Minimum solution
Orbital parameters [ ecc = 0.018682 ] - [ obl = 24.105° ] - [ peri-180° = 0.87° ]
Date of vernal equinox March 21 at noon
Trace gases [ CO2 = 280 ppm ] - [ CH4 = 650 ppb ] - [ N2O = 270 ppb ] - [ CFC = 0 ] - [ O3 = same as PI ]
Aerosols Same as PI
Solar constant 1365 W/m2 As in PI
Vegetation prescribed or interactive as in CMIP5 PI
Ice sheets Remnant Laurentide ice-sheet (provided*) Same as PI
Topography and coastlines Modification of Hudson Bay coastlines (provided*) Same as PI

*For the ice-sheet reconstruction, see discussion on LGM wiki page

Please use the discussion panel to comment this table!


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

  • prescribed to PI (which means both vegetation types and LAI are prescribed )
  • Prescribed to PI with interactive LAI (models with interactive carbone cycle, but no vegetation dynamics)
  • Computed by the model (models with dynamic vegetation)

There are still questions concerning the possibility to have a 6ka reconstructed vegetation from a combination of model output and data analyses that could be used for sensitivity experiments. Please tell if you are interested by such a map and what would be the best variables (pft?) that should be provided (see comment from B. Otto-Bliesner in the discussion pannel).

For Earth System Models with interactive carbone cycle

The simulations are forced by CO2 concentrations. Please use the same protocol as in CMIP5 to store the carbone fluxes and the variables needed for PCMIP (see list here)


Note that insolation should follows PMIP requirements. Please check it carefully using the following tables (6ka BP insolation tables)

Initial conditions

PMIP3 Alternative solution
Initial conditions Branch off PI after adjustement Same as in PI
Model spin up Same as in PI

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PMIP3 Guest Login,, 2009/02/21 19:00

For orbital parameters, include how to set orbital year for those models that have that option.

Pascale Braconnot, , 2009/07/21 15:24

Finally I am not sure I understand this comment. The PI is 1950 AD, 6ka is 6kyr BP calendar, Orbital parameters are from Berger(1978). Insolation tables are provided for 360 and 365 day year. Do you think we should push the groups to use a celestial calendar to compute 6ka monthly means? There is already so many things to fix in the different models to produce the CMIP5 output that I am not sure that this will not add too much constraint on the groups.

PMIP3 Guest Login,, 2009/07/21 19:26

No I didn't mean that we should push groups to use the celestial calendar.

What I would like is to include in the table heading: “orbital parameters”, a description of the orbital year. That is, in our model and possibly other models, we use code that allows us to set orb_year to -4050 (i.e. 1950 minus 6000) for 6ka. This is easier than setting eccentricity, obliquity, and perihelion (this latter can be tricky).

PMIP3 Guest Login,, 2009/02/21 19:03

Another alternative solution for modification of Hudson Bay coastlines might be to allow users to specify some percentage of appropriate land grid squares as lakes.

Pascale Braconnot, , 2009/07/21 15:27

I have the feeling that the implementation is really model dependant (some have % ocean for example), and that it will be impossible to make sure everybody does the same.

PMIP3 Guest Login,, 2009/02/21 19:07

A vegetation map for 6ka reconstructed from a combination of model output and data analyses would be very useful for modeling groups that will not be using interactive vegetation in their PI and 20th century runs. We could query groups on the best format. For CCSM, a pft vegetation map would be best.

PMIP3 Guest Login,, 2009/07/21 19:29

For solar constant, do we want to specify under the PMIP3/CMIP5 “prescribed as in CMIP5 PI”?

John Hughes, Met Office Hadley Centre, 2009/11/24 14:25

CMIP5 CO2 pre-industrial concentrations are 285 ppmv for 1850, 286 ppmv for 1860. HadGEM2ES PI control is getting spun up to 286 ppmv, so I would plan on using 286 for the 6k too.

pa&cale Braconnot , LSCE, 2009/11/24 21:01

I recommand that you use the trace gazes listed for 6ka in your 6k simulations. I should be able to circulate the new protocol soon. The control should be your CMIP5 pre-industrial Similarly use the same solar constant as in your PI.

pmip3/design/6k/index.txt · Last modified: 2010/09/16 12:35 by jypeter