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atmospheric CO2 used by radiative and by biogeochemical flux computations

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ludwig.lierhamm...
atmospheric CO2 used by radiative and by biogeochemical flux computations

How much is the global and the tropical atmospheric CO2 content used by radiative and by biogeochemical flux computations for the CESM1-BGC piControl and 1pctCO2 experiments in CMIP5?

 

klindsay

Generally, there are 2 options for CO2 in radiative and biogeochemical flux computations in CESM1(BGC). One option is diagnostic, where the CO2 is a specified concentration that doesn't vary in space, but can vary in time. The other option is prognostic, where radiative computations use the local column average of the prognostically computed CO2 and the biogeochemical flux computations use the bottom layer concentration of the prognostically computed CO2.

The piControl experiment uses the diagnostic CO2 option. All radiative and biogeochemical flux computations use the 1850 reference CO2 value of 284.7 ppmv. There is no spatial or termporal variation in the CO2 being used.

Note that this is different from the esmControl, which uses the prognostic CO2 option. This has spatial and temporal variations.

The 1pctCO2 experiment uses the diagnostic CO2 option. All radiative and biogeochemical use the CO2 values arising from the imposed 1% ramp. There is no spatial variation in the CO2 being used. The only temporal variation is from the gradual ramp. In particular, there is no season cycle.

Note that all of the CESM1(BGC) experiments do prognostically compute a spatially and temporally varying atmospheric CO2 concentration. The subtlety is that this concentration is not used when the diagnostic CO2 option is used. Its presence when it is not used can be admittedly confusing.

Hope this helps, Keith

 

ludwig.lierhamm...

Many thanks for this in detail info.

You helped me a lot.

Best wishes,

Ludwig

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