[CF-metadata] question about proper cell bounds for ocean_volume_transport_across_line

Jim Biard jbiard at cicsnc.org
Thu Jan 17 08:37:56 MST 2019


There is a netCDF/CF Simple Geometries project that Tim Whiteaker and 
others are working on. It might fill the bill.



On 1/17/19 8:39 AM, Jonathan Gregory wrote:
> Dear Matthias
>> Recap: I have a time series of ocean volume transport (given in
>> Sverdrup) across a line. The line has two end points, and the transport
>> is computed over a specific depth range. I would like to represent this
>> in a clever way in a netcdf file with CF conventions.
>> As far as variables go, I really only have two (happy to add more to
>> e.g. contain the cell boundaries), and their standard_names are:
>>     time
>>     ocean_volume_transport_across_line
>> I know how to include bounds for the time such that I can show over how
>> many days my data were averaged.
> Yes, including a cell_methods of "mean" for time.
>> I suppose I could figure out the depth range by including a single
>> scalar for depth, with associated bounds, and having a "coordinates"
>> attribute on my transport that points to the depth. Does this sound
>> correct?
> Yes, that would be right. The cell_methods for depth would be "sum".
>> How about the two section endpoints? And when I have those, how would
>> the user know which direction across that section is counted positive?
> So far, the tranport across line has been used only with "named" sections. The
> names of the sections haven't been standardised in CF, but there's a list of
> them for CMIP6, defined by endpoints, in Griffies et al. 2016, Table J1,
> doi:10.5194/gmd-9-3231-2016. The reason for using names is that the exact line
> depends on the model, so matching the names facilitates model comparison. I
> don't remember a discussion about how to specify them more quantitatively. I
> think it would be reasonable to attach scalar latitude and longitude (like the
> depth range) and use their bounds to specify the endpoints.
> The standard name table doesn't mention the sign convention. We should have
> defined that. Griffies et al. says it's positive for northwards and eastwards.
> But what if the normal to the section is north-west or south-east? Do you have
> any in those quandrants? We ought to generalise this.
> Best wishes
> Jonathan
>> Cheers, Matthias
>> On Tue, 2016-04-26 at 08:25 -0700, Matthias Lankhorst wrote:
>>> Dear CF,
>>> what is the proper way to define the shape and boundaries of an oceanic
>>> section, for which I want to report the volume transport across that
>>> section?
>>> The use case is an irregular-shaped section like OSNAP
>>> (http://www.o-snap.org/wp-content/uploads/2013/11/20160329_OSNAP_planeview.jpg), and the property to be reported is the seawater volume transport in a given depth range as a timeseries with this CF standard_name:
>>> ocean_volume_transport_across_line
>>> There needs to be some ancillary variable to say what the line
>>> coordinates are, and I am not sure how to squeeze that into
>>> "cell_bounds".
>>> In addition, how about the lower limit vertically if this is the
>>> seafloor? If the transports were to be everything below e.g. 1000 m,
>>> would it be appropriate to state vertical cell bounds as 1000 to 5000 m,
>>> even if the ocean is not 5000 m deep? I.e. is the user intelligent
>>> enough to realize that "5000" really means "5000 m or the seafloor,
>>> whichever is shallower"?
>>> Thanks, Matthias
>> -- 
>> _______________________________________
>>   Dr. Matthias Lankhorst
>>   Scripps Institution of Oceanography
>>   9500 Gilman Drive, Mail Code 0230
>>   La Jolla, CA 92093-0230
>>   USA
>>   Phone:  +1 858 822 5013
>>   Fax:    +1 858 534 9820
>>   E-Mail: mlankhorst at ucsd.edu
>>   http://pordlabs.ucsd.edu/mlankhorst/
>> _______________________________________________
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