Hello Sebastien,
I have to admit that coming from an observational background I do not fully understand the raft of mixed layer thickness Standard Names that I presume have their origins in model data. They've been around for a long while (dated 2006, but could predate that by a couple of years) so those who fully understood how they were to be used with the MLD definition criteria quantified may not be still reading the list on a regular basis.
It's quite clear from the name definitions that the MLD specifications are differences in temperature, sigma-theta and sigma-T and not absolute values. It's also quite clear that there are no Standard Names to describe such differences, which makes me think that you are possibly the first person to attempt to encode the criterion as a co-ordinate (though they could have done so with long names rather than Standard Names).
I have some concern about your proposals, particularly for temperature, because sea water surface temperature means many things in CF including skin temperature, subskin temperature and foundation temperature. It therefore might be better to have Standard Names like:
sea_water_temperature_difference_defining_mixed_layer
sea_water_sigma_theta_difference_defining_mixed_layer
sea_water_sigma_t_difference_defining_mixed_layer
This gets around the issue of what is meant by 'surface'. I also added 'sea_water' to the sigma names to be consistent with the existing names sea_water_sigma_theta and sea_water_sigma_t.
Are you going to have a go at producing definitions for these proposals?
Cheers, Roy.
Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to enquiries at bodc.ac.uk. Please also use this e-mail if your requirement is urgent.
________________________________
From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Sebastien Villaume <sebastien.villaume at ecmwf.int>
Sent: 05 April 2018 14:55
To: CF Metadata
Subject: Re: [CF-metadata] how to use ocean_mixed_layer_thickness_defined_by_*
Hi all,
It seems that my question did not attract much response. :(
Is it because no one knows how to use these standard names and properly encode the "quantity that differs from its surface value by a certain amount"?
Giving it more thoughts I feel that I need new standard names to describe this properly.
Would it make sense to describe it this way:
float swtd ;
swtd:standard_name = "sea_water_temperature_difference_wrt_sea_surface" ;
swtd:units = "degC" ;
swtd:axis = "Z" ;
swtd:positive = "down" ;
swtd:long_name = "temperature difference wrt its surface value"
float omlt(t, j, i) ;
omlt:standard_name = "ocean_mixed_layer_thickness_defined_by_temperature" ;
omlt:units = "m" ;
omlt:coordinates = "time swtd1 latitude longitude" ;
omlt:long_name = "ocean mixed layer defined by difference of temperature from surface"
and the scalar value swtd can be 0.5 degC, 1.0 degC, etc.
In this case, I need standard names working with temperature, sigma_theta and sigma_t:
sea_water_temperature_difference_wrt_sea_surface
sigma_theta_difference_wrt_sea_surface
sigma_t_difference_wrt_sea_surface
any quick suggestions are very welcome!
thanks
/S?bastien
----- Original Message -----
> From: "Sebastien Villaume" <sebastien.villaume at ecmwf.int>
> To: "CF Metadata" <cf-metadata at cgd.ucar.edu>
> Sent: Wednesday, 4 April, 2018 14:04:42
> Subject: [CF-metadata] how to use ocean_mixed_layer_thickness_defined_by_*
> Dear list,
>
> I have a question regarding the use of the standard names of the form
> ocean_mixed_layer_thickness_defined_by_*
>
> the definition from the official standard name table is:
>
> "The ocean mixed layer is the upper part of the ocean, regarded as being
> well-mixed. The base of the mixed layer defined by temperature, sigma or
> sigma_theta is the level at which the quantity indicated differs from its
> surface value by a certain amount."
>
> From what I understand, in the case of
> ocean_mixed_layer_thickness_defined_by_temperature, I should specify some
> quantity as a scalar (Z axis), but it is actually a temperature difference that
> I need to encode, not a plain temperature : temp_surf - temp_base_level =
> temp_delta_defining_mixed_layer_thickness
>
> if it was simply a temperature I would maybe use:
>
> float swpt ;
> swpt:standard_name = "sea_water_potential_temperature" ;
> swpt:units = "degC" ;
> swpt:axis = "Z" ;
> swpt:positive = "down" ;
>
> but what I really want to encode is a temperature difference. How can I specify
> that? Is "sea_water_potential_temperature" the correct standard name to use?
>
>
> same question for ocean_mixed_layer_thickness_defined_by_sigma_theta, how do I
> encode a "difference" in sigma_theta?
>
> thanks,
>
> ____________________________________
>
> Dr. S?bastien Villaume
>
> M.A.R.S. Analyst
> ECMWF Data Governance facilitator
>
> ECMWF
> Shinfield Park,
> Reading RG2 9AX, UK
> +44 (0)118 949 9301
> +44 (0)7825 521592
> sebastien.villaume at ecmwf.int
> ____________________________________
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