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OM paper (fwd)


Good news
I've just received the comments from the reviewver of the CFC paper.
The comments are good, and the paper is recommanded for publication after
minor revision.

I will do these minor changes rapidly and resubmit it soon for
publication. I won't be able to do it before too weeks, I am now in
vacation for renovating my house. 
If you have some comments on the review (see below) or any suggestion,
please send it to me before I answer to the editor.


- -------------------------------------------------------------------------
Jean-Claude DUTAY

Laboratoire de Modelisation du Climat et de l'Environnement 
DSM, Orme des Merisiers, Bat 709
CE Saclay
91191 Gif sur Yvette Cedex
Tel : 33-1-69 08 31 12
Fax : 33-1-69 08 77 16

email : dutay@lmce.saclay.cea.fr
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- ---------- Forwarded message ----------
Date: Thu, 9 Nov 2000 10:44:57 +0000 (GMT)
From: Ocean Modelling Editors <omod@soc.soton.ac.uk>
To: dutay@lsce.saclay.cea.fr
Subject: OM paper

Dear Dr. Dutay et al,
Below are the referee comments on your OM paper "Evaluation of ocean model ..."
from which you will see that both referees liked your paper a lot. Not 
surprisingly, they did have some suggestions, mostly fairly minor, which will 
need addressing.
When you resubmit, please include a letter detailing how you handled these 
concerns. I may or may not send the paper out again depending on my reading of 
the letter and the paper.
I hope to hear from you shortly!
Peter Killworth

P.S. Referee 1 explains why the refereeing time was longer than I like. Non
mea culpa!

Referee 1:
- ---------
Review of "Evaluation of ocean model ventilation with CFC-11:
comparison of 13 global ocean models" by J.-C. Dutay et al.

First an apology from this reviewer regarding the delay in this
response.  Since I received this paper to review several weeks ago, I
have made four trips covering 16 time zones.  The Editor tried his
best, but I was unable to write this review earlier.

I have a number of comments about this manuscript which range in
importance from minor to moderately major:

1)  The manuscript is not carefully prepared.  I realize that the first
author is not a native English speaker, but many of the errors should
be found by an English spelling checker.  Failing that, many of the
co-authors are native English speakers, and any of them who actually
read the paper could have easily made it more readable.  The errors
include unmatched parentheses, one of the authors' names spelled with
an "0" instead of an "O", authors' names in the references or citations
misspelled,  US states misspelled, "CO2" without the subscript or with
an "0" instead of an "O", mixed British and US spelling such as
"modelled" versus "modeled", etc.  Water mass names such as Circumpolar
Deep Water should be capitalized.  Also, manuscripts without page
numbers should not be accepted for review because they make it very
difficult to identify the passages cited in the reviewer's comments.
In this case, I have numbered my copy by hand and I will use these
numbers in this review.

2)  Page 2, last line, and page 9, first line:  It is likely that the
Southern Ocean (note capitalization) is the region of largest
anthropogenic CO2 uptake, but I don't believe that there is any
observational evidence to support this supposition.  Indeed, the
oceanic radiocarbon evidence suggests that carbon exchange in this
region is limited, perhaps by ice cover in winter and by a fresh water
cap in summer.  One might look at the recent work of Sabine, Gruber and
others for some direct evidence of this uptake rate, but it would be
wiser not to make such a definite statement.  Surely to use model
calculations to come to this conclusion would be unwise in the light of
the main thrust of this paper.

3)  It would be helpful to cite original data references for the CFC
data used in these model comparisons.  In many cases there are
published data reports which should be cited (and their "metadata" read
by the data users).

4)  Page 7, Equations 1 and 2:  There is a problem with the treatment
of water vapor in Equation 1.  If "alpha" is indeed the solubility
coefficient, then the vapor pressure of water at the interface (Pw,
normally taken as the vapor pressure of seawater at the potential
temperature and salinity of the water parcel) needs to be included in
the equation by replacing "P/P0" with "(P-Pw)/P0".  Alternatively if
"alpha" is really the solubility function "F" (see Warner and Weiss,
1985) that includes the water vapor term, then the formulation is
correct but "alpha" should be "F".  Also, the manuscript is
inconsistent in using both "k" and "kw" for the transfer velocity or
exchange coefficient.

5)  Page 7, paragraph 1:  The Walker et al. atmospheric source function
is published (JGR,105, 14,285, 2000).  Also, the values are based on
simple modeling of industrial production and release data plus
measurements in the recent part of the record.  The records are not

6)  Figure 1:  Change "f11" to "CFC-11" and "f12" to "CFC-12" in the
legend of the top panel.  Why include CFC-12 in the top panel anyway,
since CFC-12 is not discussed in this paper?  Also, change "pptv" to
"ppt" because the values are given in mole fractions and these are not
equivalent to volume ratios if the gases in question are not ideal
(CFC-11 is very non-ideal -- it is a liquid at standard conditions).
Finally, if CFC-12 is not shown, the title at the top of the top panel
should be "CFC-11 Atmospheric Mole Fractions".  These are not partial
pressures!  Change the figure caption accordingly, as well.

7)  Page 10, line 3, and Figures 4, 6, 11 and 11bis:  I am bothered by
the units of the "Pcfc inventory" in the middle panels of these plots.
If I integrate pressure I get units of pressure times length.  Thus it
could be "atm m" (x 10^-12), but definitely not "ppt mm" (or "pptv. mm"
as written).  This should be sorted out.

8)  Page 13, last paragraph, line 3:  The Ajax prime meridian section
was measured in 1983-84.

9)  Page 19:  The discussion of Southern Ocean ventilation processes is
written without recognition of the importance of shelf-edge processes
in the formation of deep and bottom waters in this region (e.g. Carmack
and Foster, 1975; Foster and Carmack, 1976).  It is my understanding
that since the models generally lack the resolution to resolve these
processes, they must resort to open-ocean convective processes to
simulate ventilation and mixing that is actually driven by very cold
and saline waters flowing off the continental shelves and descending
into the abyss.  This is bound to give a distorted picture of deep
water ventilation.


   This is an interesting and important contribution.  The
distributions of CFCs in the real ocean obviously provide the means of
critically diagnosing the ability of GCMs to simulate (or in the case
of the adjoint approach, reproduce) mean ventilation processes in the
real ocean.  People who are not modelers (and some who are) need a way
to calibrate themselves concerning the ability of these models to
simulate and ultimately predict the behavior of oceanic processes
relevant to climate and climate change.  CFCs may well provide the best
present diagnostic.  This paper is written honestly and
straightforwardly.  Most of the points raised in my comments above will
be easy to address.  The last comment above (Comment 9) is probably the
most important substantive concern, but this too should be easy to
address.  Because of its very nature, most of this paper is
descriptive, and one cannot expect it to propose a cure for the
problem.  It is sufficient to lay out the facts, and this paper
generally does this very well.  I recommend publication after
appropriate revision.

Referee 2:
- ---------

I include below my review of the paper by Dutay et al. submitted to 
Ocean Modeling.  Overall, I liked the paper and recommend that
it be accepted for publication subject to a satisfactory response
to my comments and questions below.  

Several of the figures kept crashing my printer.  I don't know if this
is a problem with my printer (although I've never had it occur before)
or the postscript files, but I thought I would let you know.

Review of "Evaluation of ocean model ventilation with CFC-11:
comparison of 13 global ocean models", by Dutay et al.

This paper sets the ambitious goal of comparing CFC distributions
in 13 global models to observations and each other, and also
attempting to interpret differences between models and data
in terms of the model formulations.  While there are naturally
some limitations with direct relationships to model design,
I think that overall the paper achieves its goal.  I have some
suggestions and questions for the author's consideration, but I
found no major flaws with the paper.  I recommend that it be accepted
for publication in Ocean Modeling, provided the following issues
are addressed.

The subject and verb are often not in agreement (e.g. in the
Abstract, "This analysis charactarize (sp)..." or "Large range
in the ... are largely...").  Such errors need to be corrected
throughout.  A spell check would also be a good idea.

Some mention of the model performance in the Atlantic should be
included in the Abstract, both NADW and STMW.

The integrated inventory and penetration depth figures are very
difficult to read.  It would be a help if the lines corresponding
to different models were done in different colors.

Page 3:  I do not get the connection between including river 
input and the evaluation of the thermohaline circulation.

Page 4:  It should be noted that, although the concentrations of
CFCs can be measured to high precision, the spatial and temporal
resolution of the data is very low.

Page 10:  Label Figure 4 as a, b, c.  Fig4b in the sentence
"In the observations, the geatest (sp) CFC-11..." should be
Fig. 4c.  To what extent is the shallow penetration depth
in the subpolar gyre due to treatment of the marginal sea and
strait exchange?

It is interesting that there is not always a correspondence
between depth of penetration and inventory, is this a
reflection of errors in the stratification?

What are the uncertainties in the data due to spatial coverage,
temporal and spatial variability in the ocean, and interpolation?
Can you provide error bars?

Page 11:  Three of the four models that have very low CFC uptake
in the subtropical gyre are forced with annual means.  Such 
forcing does not correctly reproduce the deep winter mixed
layers and subduction that is strongly seasonally aliased.  

Most of the models also seem to exaggerate the deep maximum at
~1200m (Fig. 5), although this does not show up in the summary
diagnostics (Fig. 6).  Where is this deep maximum in NADW coming
from?  Are the models convecting too deep elsewhere and it
is being advected into the eastern NA?  Is it related to the
poor treatment of overflows?
What is the treatment of the Med in each of the models?  

Page 12:  Mark the data in Fig. 7 in degrees W, as the models
and discussion use.  Does the DWBC velocity core correspond 
to the tracer core?

Page 13:  Shade the data figure as the model figures.  It would
be useful to know if the different tracer distributions along
the western boundary are due to mixing parameterizations or
advection.  Are the DWBC narrow (usual Munk layer width) or
wide in those that spread tracers into the interior?

Figure 12:  Shade the data as the model results.

Discussion:  Can you be more explicit about the cause of
the failure of the Subantarctic mode water ventilation
in models with horizontal mixing?
Is it due to the direction of mixing (isopycnal, pressure),
eddy tracer transports, or differences in the mean flow?

What is the diapycnal mixing parameterization in the NERSC
isopycnal model?  This is likely too small so that NADW
goes too deep and there is excessive CFC uptake around

What is the motivation/justification for the particular
parameterization of brine rejection used in the LLNL model?
If it is not model tuning, be more specific.

The GM type eddy parameterization will probably overestimate
mixing in the DWBC because it neglects the stabilizing 
influence of bottom topography.

Conclusion:  The circulation fields are never discussed, and
certainly not evaluated or compared, in this paper.  The
first sentence is misleading.

- -----------------------------------------------------------------------
Ocean Modelling; editor
Dr. Peter D. Killworth, James Rennell Division for Ocean Circulation
and Climate, Southampton Oceanography Centre, Empress Dock, Southampton
SO14 3ZH, England.
Tel: +44 (0)23-80596202
Fax: +44 (0)23-80596204
Email: P.Killworth@soc.soton.ac.uk
Web: http://www.soc.soton.ac.uk/JRD/PROC/people/pki/pki.html
Ocean Modelling Newsletter: http://www.elsevier.nl/locate/omodol/
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