Hi Mark,
Yes, in CMIP5 we asked for a single monthly-mean variable (mfo)
involving a "transect" be reported. This was the
sea water transport through (or associated with) the following straits,
openings, channels, passages, etc.: barents_opening, bering_strait,
canadian_archipelago, denmark_strait, drake_passage, english_channel,
pacific_equatorial_undercurrent, faroe_scotland_channel,
florida_bahamas_strait, fram_strait, iceland_faroe_channel,
indonesian_throughflow, mozambique_channel, taiwan_luzon_straits, and
windward_passage. For definitions see the following WGOMD document:
http://www.clivar.org/sites/default/files/documents/137_WGOMD_ModelOutput.pdf
Section 4.4 of that document explains how "transects" are defined
(approximately). The point of reporting this variable was that modelers
were supposed to be given some leeway in defining exactly what transect
should be used to compare their model with observations. Given the
large uncertainty in observations and the approximate nature of model
topology, I don't think anyone using the data will be particularly
interested in exactly how the transects were defined. I'm not saying
that the data would be completely useless (after all you would need this
information to redo the calculation of sea water transport), but we
decided that for a single variable it wasn't worth complicating CMOR
further to record the details. The approximate end-points are given in
the WGOMD document.
Perhaps Martin knows of someone who wants this information saved for
CMIP6 and why. [I don't recall if he gave examples.]
best regards,
Karl
)
On 7/17/15 8:21 AM, Hedley, Mark wrote:
> Hello Karl
>
> I thought that Martin had presented a use case from CMIP5 which was expected to be repeated in CMIP6
>
> Thus, I thought it likely that specifying data variables related to transects and regions would be done quite widely in CMIP6
>
> You seem to think this is not the case, please may you elaborate a little on why for us?
>
> thank you
> mark
>
> ________________________________________
> From: CF-metadata [cf-metadata-bounces at cgd.ucar.edu] on behalf of Karl Taylor [taylor13 at llnl.gov]
> Sent: 08 July 2015 01:26
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] Specifying latitude and longitude of transects and regions
>
> Hi Martin, Mark, and all,
>
> I can see that theoretically one might want to define a transect, but do
> we have any compelling use case to do this at the moment? I don't think
> CMIP6 is such a case.
>
> cheers,
> Karl
>
> On 7/1/15 6:33 AM, Hedley, Mark wrote:
>> Hello Martin,
>>
>>> If the two end points can be specified with bounds within the existing convention, it might be simpler to use that. Can you explain to me how this is done? The only reference to bounds which I could find in the convention was in connection with cell boundaries.
>> I don't think it can be done. I agree with your analysis, the only reference to bounds is with regard to cell boundaries. It think it is sensible to keep it this way and provide a separate mechanism for your transect use case. I think overloading the current bounds mechanism is likely to lead to problems.
>>
>>> The flow direction does need to be defined .. I suppose that would involve a clarification of the standard_name ocean_volume_transport_across_line. As you say, this should not be too complicated once we have a definition of the line to refer to.
>> It would be good to consider if this could be defined for the transect, so that standard_name descriptions can remain unchanged. I'll think on this some more.
>>
>>> The approach I was thinking of could easily accommodate multiple points on a line, though I don't have a use for it at present. e.g.
>> excellent.
>>
>> I'll follow up on this soon
>> mark
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