[MITgcm-devel] Fwd: TEOS-10 and MITgcm

Thu Feb 21 04:11:51 EST 2013

Hi there,

for your interest: I had a short email contact with Trevor McDougall about the TEOS-10. Apparently, in order to complete "our" implementation, something needs to be done before applying the surface bulk formulae (also for sea-ice). Shouldn't be hard to do: there needs to be function/subroutine that converts theta (for TEOS-10 theta is interpreted as convservative temperature) to potential temperature. That routine can be part of model/src/seawater.F
Maybe the best to have a global field that is computed once per time step and used for all surface interaction?

Further I should think about other places were all of this matters, e.g. in the shelfice package.

Martin

Begin forwarded message:

> From: Stephen Griffies - NOAA Federal <stephen.griffies at noaa.gov>
> Subject: Re: TEOS-10 and MITgcm
> Date: February 21, 2013 5:04:24 AM GMT+01:00
> To: Trevor McDougall <trevor.mcdougall at unsw.edu.au>
> Cc: Martin Losch <Martin.Losch at awi.de>, "Paul.Barker at csiro.au" <Paul.Barker at csiro.au>, John Marshall <johncmarshall54 at gmail.com>
> 
> Martin,
> 
> Just to support Trevor's recommendation about converting CT to PT at surface (potential temp = insitu temp at surface).  A comparison to bulk formulae uncertainties is not quite relevant, since they are presumably random.  In contrast,  difference between CT and PT is systematic.  
> 
> Best,
>  Steve 
> 
> 
> 
> 
> On Wed, Feb 20, 2013 at 8:20 PM, Trevor McDougall <trevor.mcdougall at unsw.edu.au> wrote:
> Hello Martin,
> 
>     Thanks for this info.  I am pushing to get TEOS-10 into all ocean
> models, mainly by simply encouragement of the principals, such as you.  So
> it is great that you have already got the guts of TEOS-10 into MITgcm.
> 
>     A little team of me, Simon Marsland, Steve Griffies, Paul Barker, Russ
> Fiedler and I are inserting TEOS-10 into MOM, and we will test the
> importance of the change in salinity (by pursuing the two-salinity
> variable approach that is formally recommended in the TEOS-10 Manual) as
> well as the change in temperature.
> 
>     When we have done this we will have better definitive advice for you
> and MITgcm.  For example, I would hope that we will be able to tell you
> that yes indeed, having just one salinity variable, namely Absolute
> Salinity, is fine for say 150 years into the future.  So I wold say that
> what you have done for salinity is sensible.
> 
>     But I am sure that we will be telling you that at p = 0 (se surface)
> MITgcm should convert the temperature from the model prognostic
> temperature, Conservative Temperature, to potential temperature, so that
> this can be used for air-sea flux bulk formulae.  This would be the main
> thing I would advise to you right now.  If you do this, then I would be
> happy that this TEOS-10 implementation in MITgcm has enough of my
> "blessing" that it could be regarded as the default option of the MITgcm.
> The GSW code to do this is GSW_pt_from_CT(SA,CT).  Conceptually, it is
> easiest to think of the conversion from Conservative Temperature to
> potential temperature as occurring only in the air-sea interaction module
> of the model.
> 
>     Fabian Roquet of the University of Stockholm is planning to implement
> TEOS-10 into NEMO in the way you have, but with the conversion to
> potential temperature at the sea surface, as I suggest to you, above.
> 
>     As a summary of the expected changes under TEOS-10 compared with
> EOS-80, (1) the horizontal density gradient (thermal wind) is improved by
> 4% in the Southern Ocean and by 10% in the North Pacific (in both case,
> for deeper than 1000m).  (2) the SST will be improved by 0.25C in the
> equatorial Pacific (and up to 1C in some small locations that are very
> fresh).
> 
>     Trevor
> 
> 
> 
> Trevor J McDougall
> Scientia Professor of Ocean Physics
> School of Mathematics and Statistics
> University of New South Wales
> NSW 2052, Australia
> 
> email: Trevor.McDougall at unsw.edu.au
> tel: +61 2 9385 3498
> fax: +61 2 9385 7123
> mob: +61 407 518 183
> 
> 
> 
> 
> 
> 
> On 20/02/13 7:20 PM, "Martin Losch" <Martin.Losch at awi.de> wrote:
> 
> >Hi Trevor,
> >
> >I added TEOS-10 to the MITgcm as an alternative to the other EOS's that
> >we already have. I am not absolutely positive, but I think I started from
> >the FORTRAN version, at least that's what it says in the head of the
> >subroutine (o:, please have a look at
> ><http://mitgcm.org/viewvc/MITgcm/MITgcm/model/src/find_rho.F?revision=1.41
> >&view=markup> starting around line 720, if you are interested in the
> >details.
> >
> >I am afraid, that I did things as sloppily as usual, and implementing the
> >TEOS-10 was more of a fun exercise: I assume that once TEOS-10 is used
> >the temperature and salinity variables of the model (THETA and SALT) are
> >(interpreted as) conservative temperature and absolute salinity. Other
> >than that, nothing changes, i.e. there is no conversion from conservative
> >to potential temperature for the air-sea-interaction. The underlying
> >assumption is that, the uncertainties in the bulk formulae are larger
> >than any differences between the different hydrographic variables. Maybe
> >you will disagree and I'll have to go back and read the TEOS-10
> >publications more carefully. I have not yet done any serious tests on the
> >effects of the new EOS on the solutions of an ocean circulation
> >configuration, as I did not expect the effects to be large and
> >significant. Wrong again?
> >
> >Martin
> >
> >On Feb 19, 2013, at 1:21 AM, Trevor McDougall
> ><trevor.mcdougall at unsw.edu.au> wrote:
> >
> >> Hello Martin,
> >>
> >> I hear that you have put TEOS-10 into the MITgcm.
> >>
> >> Can you please tell me what you did with salinity?   I am assuming that
> >>you have only one salinity variable, namely Absolute Salinity.   And I
> >>assume that you treat Absolute Salinity as a conservative variable, yes?
> >>
> >> And I expect that your model temperature is Conservative Temperature,
> >>and that in the air-sea interaction calculation, you calculate potential
> >>temperature (from knowledge of Absolute Salinity and Conservative
> >>Temperature there).
> >>
> >> Have I guessed what you have done correctly?
> >>
> >> By the way, which version of the GSW code did you start from? The
> >>Matlab, the FORTRAN or the C version?
> >>
> >> I am in a small group that is implementing TEOS-10 into MOM (we are
> >>keeping two different salinity variables, Preformed Salinity, and
> >>another ratio term, F_delta), and any experience that you have found
> >>that you want to share would be much appreciated.
> >>
> >> Also I hear that Fabien Roqet is implementing TEOS-10 into NEMO,
> >>probably in the same manner that I am guessing you have done.
> >>
> >>    With very best wishes,
> >>
> >>       Trevor
> >>
> >>
> >>
> >> Trevor J McDougall
> >> Scientia Professor of Ocean Physics
> >> School of Mathematics and Statistics
> >> University of New South Wales
> >> NSW 2052, Australia
> >>
> >> email: Trevor.McDougall at unsw.edu.au
> >> tel: +61 2 9385 3498
> >> fax: +61 2 9385 7123
> >> mob: +61 407 518 183
> >>
> >
> 
> 
> 
> 
> -- 
> Dr. Stephen M. Griffies
> NOAA Geophysical Fluid Dynamics Lab
> 201 Forrestal Road
> Princeton, NJ 08542 
> USA  
> 

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