# Re: question regarding OCMIP-2 CO2 code

• Subject: Re: question regarding OCMIP-2 CO2 code
• From: sabine@geo.Princeton.EDU (Chris Sabine)
• Date: Fri, 26 Feb 1999 13:01:31 -0500

```Keith,
I thought I should send this message out to all the OCMIP people
to clear up any confusion regarding our routines and the Abiotic HOWTO.
I think we have run into a problem with using the same notation to mean
different things. The problem lies in differing definitions of Kw. The
HOWTO defines Kw as the piston velocity [m/s] and we defined Kw as the
gas transfer coefficient [mole/(area*time*pressure)]. The gas transfer
coefficient is simply equal to the piston velocity times the solubility
[called alphaC in the HOWTO], so the flux equations in our README and the
Abiotic HOWTO (4a) are essentially equivalent with the exception that we
do everything in mass units and the abiotic HOWTO is in volume units.
As for the atmospheric pressure term in the flux calculation...as
you said, the decision to include that was made after we posted the
routines. Changes in atmospheric pressure will effect the flux. If that
is going to be included in the models then we will need to modify our
routines. As you said, co2starair would be xco2*ff*P, where P is the total
atmospheric pressure. Note that the Abiotic HOWTO is not exactly correct
in equation 5a. You must subtract the partial pressure of water vapor
from the total pressure. The water vapor correction is built into the
ff term in our routines. Equation 5a should read:

Csat = alphaC * xCO2atm * (P-pH2O)
where
alphaC is the C solubility for water vapor saturated air [mol/(kg*atm)
(same as in the HOWTO except we use mass units and correct for
nonideality of CO2 gas (fco2 vs pCO2))
xCO2atm is the mole fraction of CO2 in dry air * 10^6
P is total barometric pressure (atm)
pH2O is water vapor pressure at 100% humidity (atm)

I hope this helps. If anyone has further questions please let me know.

Chris

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