[MITgcm-support] phiHydLow

[Martin Losch]

Hi,

I extensively used the diagnostic of phyHydLow and there were never any 
problems with it in the MITgcm-code, the masking of the (non-zero) 
density values below the ocean floor is correct, no reasons to worry. 
We looked at this closely, because we wanted to compare to the pressure 
coordinate model, and found everything consistent.

But here is a small caveat, which does not really affect your 
discussion:
unless Jean-Michel has found a miraculous way to do it, I remember that 
there is no way to consistently diagnose the pressure or phiHyd 
(perturbation) at the bottom unless you use the (non-conservative) form 
of the discretization of the phiHyd computations (integr_GeoPot.EQ.1). 
If you don't use this discretization, phyHydLow will not be 100% 
consistent, but since this variable is not used for any dynamic 
computations it shouldn't matter.

Martin

On Aug 14, 2004, at 9:40 PM, Chris Hill wrote:

> In general you need to repect the masks and hfac values appropriately 
> for
> any vertical integral. For example depth averaged salinity or vertical 
> heat
> content or vertical average temperature etc.... would all come out 
> awry if
> you account for land incorrectly. This sounds like the same thing so I 
> think
> its not an issue in the prognostic model so much as in making sure 
> correct
> formula are implemented for analysis.
>
> Chris
>
>> -----Original Message-----
>> From: mitgcm-support-bounces at mitgcm.org
>> [mailto:mitgcm-support-bounces at mitgcm.org] On Behalf Of
>> Dimitris Menemenlis
>> Sent: Saturday, August 14, 2004 8:25 AM
>> To: mitgcm-support at mitgcm.org
>> Subject: [MITgcm-support] phiHydLow
>>
>> Does anyone have experience in using phiHydLow ?
>>
>> Dimitris
>>
>> ----------  Forwarded Message  ----------
>>
>> Subject: Re: [Fwd: Re: bottom pressure]
>> Date: Friday 13 August 2004 06:11 pm
>> From: Ichiro Fukumori <fukumori at jpl.nasa.gov>
>> To: Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
>> Cc: Benny Cheng <bcheng at jpl.nasa.gov>, christopher Hill <cnh at mit.edu>
>>
>> Dimitris,
>>
>> phiHydLow seems to have a bug for it to be ocean bottom pressure.
>> Benny was able to reproduce phiHydLow offline from TS and ETA
>> but we found that that calculation had a bug; density is
>> non-zero below ocean bottom and pressure calculation sums up
>> the contribution from these non-zero densities below
>> topography.  The problem is in how values below ocean bottom
>> are masked.  A similar bug may be present in MITGCM itself.
>>
>> -- Ichiro
>>
>>> From: Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
>>> Organization: JPL
>>> To: Benny Cheng <bcheng at jpl.nasa.gov>
>>> Subject: Re: bottom pressure
>>> Date: Fri, 6 Aug 2004 13:39:47 -0700
>>> User-Agent: KMail/1.6.2
>>> Cc: Ichiro Fukumori <fukumori at jpl.nasa.gov>,
>>> dimitri at pacific.jpl.nasa.gov
>>> References: <5.1.0.14.2.20040806101117.02854ec0 at pacific.jpl.nasa.gov>
>>>         <1091823500.12635.81.camel at lochness.jpl.nasa.gov>
>>> In-Reply-To: <1091823500.12635.81.camel at lochness.jpl.nasa.gov>
>>> MIME-Version: 1.0
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>>>
>>> On Friday 06 August 2004 01:18 pm, Benny Cheng wrote:
>>>> how do you enable bottom pressure output on the MITgcm ?
>>>
>>> Benny, you need to save the variable
>>>
>>> C     phiHydLow  :: Phi-Hydrostatic at r-lower boundary
>>> C                  (bottom in z-coordinates, top in p-coordinates)
>>>
>>> or
>>>
>>> C     phiHydLowtave:: Hydrostatic (ocean) pressure / (atmos)
>> geo- Potential
>>> C                     at the fixed boundary: (ocean) bottom pressure
>>> C                     (atmos) geo- Potential
>>>
>>> I had disabled the dump of phiHydLowtave in pkg/timeave
>> using CPP flag
>>> HRCUBE.  So you can either reenable it there for
>> time-averaged values,
>>> or you can dump instantaneous values of phiHydLow directly.
>>>
>>> D.
>>>
>>> --
>>> Dimitris Menemenlis <menemenlis at jpl.nasa.gov> Jet Propulsion Lab,
>>> California Institute of Technology MS 300-323, 4800 Oak Grove Dr,
>>> Pasadena CA 91109-8099
>>> tel: 818-354-1656;  fax: 818-393-6720
>>
>> ===============================================================
>> Ichiro Fukumori               | Jet Propulsion Laboratory
>> e-mail: fukumori at jpl.nasa.gov | Mail Stop 300-323
>> phone: +1 (818) 354-6965      | 4800 Oak Grove Drive
>> fax: +1 (818) 393-6720        | Pasadena, California 91109, U.S.A.
>> ===============================================================
>>
>>
>>
>> -------------------------------------------------------
>>
>> --
>> Dimitris Menemenlis <menemenlis at jpl.nasa.gov> Jet Propulsion
>> Lab, California Institute of Technology MS 300-323, 4800 Oak
>> Grove Dr, Pasadena CA 91109-8099
>> tel: 818-354-1656;  fax: 818-393-6720
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>
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