[Go-essp-tech] Incorrect use of missing value in some MRI ocean data -- correction

Tue Dec 6 04:41:53 MST 2011

Hello Jamie,

For the surface layer of the ocean and for variables at the actual 
interface between the ocean and the atmosphere, I think it is clear that 
sftof, if properly reported, can be used in all cases to determine which 
grid cells are ocean (or sea ice), and which are not.   For models 
reported on their native grids, the values of sftof will I think either 
be 0. or 100. (%); for models regridded to latxlon grids, the values 
will vary between 0. and 100.  This will need to be communicated to 
users, and I'm open to suggestions about that.

For the ocean layers below the surface, there are several options, but 
perhaps no general solution.  For many fields (e.g., theto, so, 
masscello, etc.), a value of 0. clearly will indicate that the value is 
missing (because a reasonably realistic ocean would never have a value 
of 0.), or perhaps it will be set to "missing", so a user could use any 
of these to infer the mask.  I'm not sure how volcello is being reported 
when a grid cell is on land or below the bottom of the ocean.  I would 
think it would also be either 0.0 or "missing", so it could also be 
used, but I'm not sure whether for some ocean grids, cells can appear 
and disappear (at the bottom of the ocean). If so, then this field can't 
be used in general because it isn't time-dependent.  I think we need to 
find out from the modeling groups whether volcello would work in all cases.

regards
Karl

On 12/6/11 1:23 AM, Kettleborough, Jamie wrote:
> Hello Martin, Karl,
> aren't there other things coming out of this:
> 1. who is responsible for spotting cases where land points are 
> represented by 0.0, and cases where they are represented by missing 
> value.  I think the implication is at the moment its the users.  (I 
> guess it could have been CMOR - though thats too late now - it could 
> be something in 'QC' [though I may have used not quite the right term 
> in saying 'QC']).
> 2. how are users to know the best ways of dealing with the cases?  ie 
> to use sftof?  (I guess the danger in giving advice in general on 
> these sort of things is the advise turns out to be wrong, or not quite 
> applicable in a particular context).
> Jamie
>
>     ------------------------------------------------------------------------
>     *From:* go-essp-tech-bounces at ucar.edu
>     [mailto:go-essp-tech-bounces at ucar.edu] *On Behalf Of *Karl Taylor
>     *Sent:* 05 December 2011 18:59
>     *To:* martin.juckes at stfc.ac.uk
>     *Cc:* cmip5-users at jiscmail.ac.uk; go-essp-tech at ucar.edu;
>     graham.parton at stfc.ac.uk
>     *Subject:* Re: [Go-essp-tech] Incorrect use of missing value in
>     some MRI ocean data -- correction
>
>     Hi Martin,
>
>     Right again.
>
>     thanks,
>     Karl
>
>     On 12/5/11 10:39 AM, martin.juckes at stfc.ac.uk wrote:
>>     Hello Karl,
>>
>>     Seiji (from MRI) suggested people use sea-area fraction"sftof": I think "areacello" (standard name "cell_area") refers to the actual grid cell, which may be be partially or completely land. "volcello" (standard name "ocean_volume") doesn't have a definition in the current standard name table -- but from the name I would expect to refer to the volume of ocean, so that should be OK for the height dependent fields,
>>
>>     cheers,
>>     Martin
>>
>>     ________________________________
>>     From: Karl Taylor [taylor13 at llnl.gov]
>>     Sent: 05 December 2011 18:21
>>     To: Juckes, Martin (STFC,RAL,RALSP)
>>     Cc:go-essp-tech at ucar.edu; Parton, Graham (STFC,RAL,RALSP);cmip5-users at jiscmail.ac.uk
>>     Subject: Re: [Go-essp-tech] Incorrect use of missing value in some MRI ocean data -- correction
>>
>>     Hi Martin,
>>
>>     You're quite right.  It states:
>>
>>     "2. Unless otherwise specified, the ocean and sea-ice output (including Oclim, Oyr, Omon, and OImon) represents a mean over only the sea portion of each grid cell (i.e., it is interpreted as "where ocean over ocean"), and a value of 0.0 should be reported where the sea fraction is 0."
>>
>>     I'm can't recall whether this specification was the result of some requirement, or if it was simply a mistake.  Thinking about it now, I think the recommendation should have been to set it to the "missing" value, not 0.0, since over land the values are undefined.
>>
>>     Given that some groups will follow the specified rule, and others will put in the missing value for land points, users would be advised to obtain the areacello variable (or volcello) which should be set to 0.0 where there is no ocean.
>>
>>     Any other ideas?
>>
>>     Best regards,
>>     Karl
>>
>>     On 12/5/11 9:45 AM,martin.juckes at stfc.ac.uk<mailto:martin.juckes at stfc.ac.uk>  wrote:
>>
>>     Hello Karl,
>>
>>     In the following:
>>     http://cmip-pcmdi.llnl.gov/cmip5/docs/standard_output.xls, sheet "general", column A, row 15 and 17.
>>
>>     It says "the value 0.0 should be reported where the sea fraction is 0",
>>
>>     regards,
>>     Martin
>>
>>     ________________________________
>>     From: Karl Taylor [taylor13 at llnl.gov<mailto:taylor13 at llnl.gov>]
>>     Sent: 05 December 2011 16:42
>>     To: Juckes, Martin (STFC,RAL,RALSP)
>>     Cc:go-essp-tech at ucar.edu<mailto:go-essp-tech at ucar.edu>; Parton, Graham (STFC,RAL,RALSP);cmip5-users at jiscmail.ac.uk<mailto:cmip5-users at jiscmail.ac.uk>
>>     Subject: Re: [Go-essp-tech] Incorrect use of missing value in some MRI ocean data -- correction
>>
>>     Dear Martin and all,
>>
>>     For 3-d ocean fields like thetao, I think the missing value (not 0.0) should invariably be assigned to all land grid cells and for grid cells below the bottom of the ocean.  I can't find where in the document pointed to below it says otherwise.  I would like to correct the document, so please tell me where it needs revision.
>>
>>     thanks,
>>     Karl
>>
>>     On 12/4/11 8:07 PM,martin.juckes at stfc.ac.uk<mailto:martin.juckes at stfc.ac.uk><mailto:martin.juckes at stfc.ac.uk><mailto:martin.juckes at stfc.ac.uk>  wrote:
>>
>>     I owe MRI an apology -- the use of zero instead of a missing value is in fact recommended in (http://cmip-pcmdi.llnl.gov/cmip5/docs/standard_output.xls),
>>
>>     regards,
>>     Martin
>>     ________________________________________
>>     From: Juckes, Martin (STFC,RAL,RALSP)
>>     Sent: 04 December 2011 08:45
>>     To:go-essp-tech at ucar.edu<mailto:go-essp-tech at ucar.edu><mailto:go-essp-tech at ucar.edu><mailto:go-essp-tech at ucar.edu>; Parton, Graham (STFC,RAL,SSTD);cmip5-users at jiscmail.ac.uk<mailto:cmip5-users at jiscmail.ac.uk><mailto:cmip5-users at jiscmail.ac.uk><mailto:cmip5-users at jiscmail.ac.uk>
>>     Cc: Pascoe, Stephen (STFC,RAL,RALSP)
>>     Subject: Incorrect use of missing value in some MRI ocean data.
>>
>>     Hello,
>>
>>     It has come to light that some MRI ocean data has land grid points set to zero rather than to the declared missing value. This is likely to confuse some applications reading and plotting the data -- I've notified Seiji Yukimoto at MRI,
>>
>>     sincerely,
>>     Martin
>>
>
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