[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*Subject*: two things*From*: najjar@essc.psu.edu (Ray Najjar)*Date*: Tue, 12 May 1998 10:39:20 -0400 (EDT)

US OCMIP participants: Two of you mentioned you had difficulty reading the attached postscript file describing my proposal for CFC modeling protocols. You can try accessing this file, or an ADOBE PDF version, by anonymous ftp to ftp.essc.psu.edu; cd to the directory /pub/meteo/najjar. Let me know if you still have trouble or if you have other ideas about how I can get such files to you. I use FrameMaker for my word processing, so it would be easy for me to make a FrameMaker file available. I don't think I can easily make a Microsoft Word file available-- sorry. A second point that I would like to open up for discussion is gas exchange in OCMIP. Niki Gruber found the use of model SST for computing solubility and observed SST for computing the Schmidt number inconsistent. Jim Orr thinks we should stick with OCMIP-1 protocols for gas exchange. If I understand correctly, everyone in OCMIP-1 used the same gas transfer *coefficient* (K) for CO2 gas exchange. Thus the flux was parameterized by F = K(pw-pa) where F is the upward CO2 flux, pw is the partial pressure of CO2 in water and pa is the partial pressure of CO2 in the atmosphere. Everyone used the same fields of K, computed with observed SSTs and winds. (Recall that K = alpha*kw where alpha is the solubility of CO2 and kw is the gas transfer velocity for CO2. kw was taken from Wanninkhof, 1992.) Everyone also used the same value of pa, but, of course, values of pw varied from model to model. pw is a diagnostic quantity that must be computed from prognostic variables in the model (DIC and Alk), but it is not clear to me what SSTs were used to compute pw. Either way, I see problems. If model SSTs were used for computing pw, then essentially two different SST data sets were used to compute the CO2 solubility: model SSTs for computing alpha for pw and observed SSTs for computing alpha for K. If observed SSTs were used for computing pw, then there is inconsistency between the model circulation field and the temperatures used for computing pw. This is more important than it may seem. It's reasonable to assume that deep water will form in regions with very specific T-S characteristics, and therefore, to the extent that surface waters equilibrate, very specific gas concentrations. It seems to me that you want consistency here so that, for example, if deep water sources are very cold that they be characterized by very high gas concentrations. Because of the long equilibration time for CO2, this may not be a big problem, but I think it could be disastrous for oxygen and CFCs. My suggestion, therefore, is that only model SSTs are used for computing gas solubilities. In other words, I propose that all OCMIP-2 gas exchange (CO2, O2 and CFCs) is parameterized using F = kw(C - alpha*pa), where C is the surface gas concentration computed by your model, alpha is computed with model SSTs and pa is specified to be the same for all groups. The question, which Niki brought up, is whether the Schmidt number (imbedded in kw) should be computed with model or observed SSTs. I am ambivalent on this issue. On the one hand, we might want everyone to use the same value of kw; on the other we might want internal model consistency (only one set of SSTs are used, period). I guess I am more inclined to agree with Niki. Let me know your thoughts so we can come to some agreement soon. Ray

- Prev by Date:
**standard biological model** - Next by Date:
**CFC model (fwd)** - Prev by thread:
**standard biological model** - Next by thread:
**CFC model (fwd)** - Index(es):