Dear Evan,
To an oceanographer, the term 'sigma-theta' is as well-known as
'temperature' and the Standard Names include 'sea_water' to
give context. Also, sigma-theta (and sigma-t) are used in existing
Standard Names.
Avoiding sigma-theta would need something very verbose like 'density
difference between sea water and pure water computed at
sample potential temperature', which is both ugly and invisible to an
oceanographer's data searches.
Cheers, Roy
------------------------------------------------------------------------
*From:* CF-metadata <[email protected]> on behalf of
Manning, Evan M (398B) <[email protected]>
*Sent:* 26 April 2018 15:25
*Subject:* Re: [CF-metadata] how to use
ocean_mixed_layer_thickness_defined_by_*
It’s outside of my area so I don’t have an alternative to offer, but
it is bad practice to use the names of Greek letters in standard
names. Though I’m sure the meaning in context is clear to members of
the community, these letters have different meanings in different
contexts.
-- Evan
On 4/26/18, 6:04 AM, "Alison Pamment - UKRI STFC"
<[email protected]> wrote:
Dear Sebastien,
Thank you for your proposals for three new standard names for
coordinate variables that will be used to describe ocean mixed layer
thickness according to various physical criteria. Thank you also to
Jonathan and Roy for their suggestions.
I agree with the need for these names. I agree also with
Jonathan's approach of keeping the definitions of the new names
general while referring to the coordinate variables in the definitions
of the existing mixed_layer_thickness names.
The new names would then be as follows:
sea_water_temperature_difference (K)
'Sea water temperature is the in situ temperature of the sea water.'
sea_water_sigma_theta_difference (kg m-3)
'Sigma-theta of sea water is the potential density (i.e. the
density when moved adiabatically to a reference pressure) of water
having the same temperature and salinity, minus 1000 kg m-3.'
sea_water_sigma_t_difference (kg m-3)
'Sigma-t of sea water is the density of water at atmospheric
pressure (i.e. the surface) having the same temperature and salinity,
minus 1000 kg m-3.'
These three names are accepted for publication and will be added
in the May update of the standard name table.
In addition the definitions of the mixed_layer_thickness names
would be amended as follows:
ocean_mixed_layer_thickness_defined_by_temperature (m)
'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. A coordinate
variable or scalar coordinate variable with standard name
sea_water_temperature_difference can be used to specify the
temperature criterion that determines the layer thickness.'
ocean_mixed_layer_thickness_defined_by_sigma_t (m)
'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. A coordinate
variable or scalar coordinate variable with standard name
sea_water_sigma_t_difference can be used to specify the sigma_t
criterion that determines the layer thickness.'
ocean_mixed_layer_thickness_defined_by_sigma_theta (m)
' 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. A
coordinate variable or scalar coordinate variable with standard name
sea_water_sigma_theta_difference can be used to specify the
sigma_theta criterion that determines the layer thickness.'
These changes are also accepted and will be published in the May
standard names update.
Best wishes,
Alison
-----Original Message-----
From: CF-metadata [mailto:[email protected]] On
Behalf Of Sebastien Villaume
Sent: 13 April 2018 16:07
Subject: Re: [CF-metadata] how to use
ocean_mixed_layer_thickness_defined_by_*
Dear list,
any more comments? can we move forward and agree on these new
standard names?
thanks
/Sébastien
----- Original Message -----
> From: "Jonathan Gregory" <[email protected]>
> Sent: Wednesday, 11 April, 2018 18:32:30
> Subject: [CF-metadata] how to use
> ocean_mixed_layer_thickness_defined_by_*
> Dear Sebastien
>
> I would favour your alternative
>> Alternatively, we could move the last sentence of each
description to
>> the respective "ocean_mixed_layer_thickness_defined_by_*" standard
>> names to make that specific usage more explicit. We then keep a
more
>> general description for the new "*_difference" standard names.
> for the reason you give, which appeals to me.
>
> Also, instead of "auxiliary coordinate" I would say "coordinate
> variable or scalar coordinate variable". A scalar coord var is
> formally like a size-one auxiliary coord var. However the threshold
> variable could in principle be multi-valued; then you'd have a
> dimension for it, and it wouldn't be an aux coord var.
>
> Best wishes
>
> Jonathan
>
>
> ----- Forwarded message from Sebastien Villaume
> <[email protected]>
> -----
>
>> Date: Tue, 10 Apr 2018 10:36:21 +0000 (GMT-00:00)
>> From: Sebastien Villaume <[email protected]>
>> Subject: Re: [CF-metadata] how touse
>> ocean_mixed_layer_thickness_defined_by_*
>>
>> Dear CF list,
>>
>> I took a bit longer to write down the proposed definitions of
these 3
>> standard names.
>>
>>
>> standard name: sea_water_temperature_difference
>> units: K
>> description:
>> Sea water temperature is the in situ temperature of the sea water.
>> The standard name "sea_water_temperature_difference" can be
used (as
>> an auxiliary
>> coordinate) together with the standard name
>> "ocean_mixed_layer_thickness_defined_by_temperature" to define its
>> temperature criterion.
>>
>>
>> standard name: sea_water_sigma_theta_difference
>> units: kg/m3
>> description:
>> Sigma-theta of sea water is the potential density (i.e. the
density
>> when moved adiabatically to a reference pressure) of water
having the
>> same temperature and salinity, minus 1000 kg m-3. The standard
name
>> "sea_water_sigma_theta_difference" can be used (as an auxiliary
>> coordinate) together with the standard name
>> "ocean_mixed_layer_thickness_defined_by_sigma_theta" to define its
>> sigma_theta criterion.
>>
>> standard name: sea_water_sigma_t_difference
>> units: kg/m3
>> description:
>> Sigma-t of sea water is the density of water at atmospheric
pressure
>> (i.e. the
>> surface) having the same temperature and salinity, minus 1000
kg m-3.
>> The standard name "sea_water_sigma_t_difference" can be used
(as an
>> auxiliary
>> coordinate) together with the standard name
>> "ocean_mixed_layer_thickness_defined_by_sigma_t" to define its
>> sigma_t criterion.
>>
>>
>> Alternatively, we could move the last sentence of each
description to
>> the respective "ocean_mixed_layer_thickness_defined_by_*" standard
>> names to make that specific usage more explicit. We then keep a
more
>> general description for the new "*_difference" standard names.
>>
>> /Sébastien
>>
>> ----- Original Message -----
>> > From: "Jonathan Gregory" <[email protected]>
>> > Sent: Friday, 6 April, 2018 14:24:18
>> > Subject: Re: [CF-metadata] how touse
>> > ocean_mixed_layer_thickness_defined_by_*
>>
>> > Dear Sebastien and Roy
>> >
>> > Thanks. I agree that it's a good idea to include sea_water_.
>> >
>> > Best wishes
>> >
>> > Jonathan
>> >
>> > On Thu, Apr 05, 2018 at 07:04:26PM +0000, Sebastien Villaume
wrote:
>> >> Date: Thu, 5 Apr 2018 19:04:26 +0000 (GMT-00:00)
>> >> From: Sebastien Villaume <[email protected]>
>> >> Subject: Re: [CF-metadata] how touse
>> >> ocean_mixed_layer_thickness_defined_by_*
>> >>
>> >> Dear Jonathan and Roy,
>> >>
>> >> thank you for your suggestions.
>> >>
>> >> I am happy to go with a set of general standard names if it is
>> >> fine with everyone. I find it actually useful to make the
standard
>> >> names reusable by not hard-coding one of the reference. It is
>> >> pretty clear from the mixed layer definition that it is a
difference with respect to the sea surface.
>> >>
>> >> I am also happy to prefix sigma_theta and sigma_t with
sea_water:
>> >>
>> >> sea_water_temperature_difference (K)
>> >> sea_water_sigma_theta_difference (kg/m3)
>> >> sea_water_sigma_t_difference (kg/m3)
>> >>
>> >> I will draft some definitions for tomorrow.
>> >>
>> >> thanks!
>> >>
>> >> /Sébastien
>> >>
>> >> ----- Original Message -----
>> >> > From: "Lowry, Roy K." <[email protected]>
>> >> > Sent: Thursday, 5 April, 2018 18:34:48
>> >> > Subject: Re: [CF-metadata] how
>> >> > touseocean_mixed_layer_thickness_defined_by_*
>> >>
>> >> > Dear Jonathan and Sebastien,
>> >> >
>> >> > I was initially thinking of not including '
>> >> > _defining_mixed_layer' in my suggestion and am certainly
happy
>> >> > with leaving it out. However, I still think sigma_t and
sigma_theta should be prefixed with 'sea_water'. This would give:
>> >> >
>> >> > sea_water_temperature_difference
>> >> > sea_water_sigma_theta_difference sea_water_sigma_t_difference
>> >> >
>> >> > Cheers, Roy.
>> >> >
>> >> > From: CF-metadata <[email protected]> on
behalf
>> >> > of Jonathan Gregory <[email protected]>
>> >> > Sent: 05 April 2018 18:28
>> >> > Subject: Re: [CF-metadata] how to use
>> >> > ocean_mixed_layer_thickness_defined_by_*
>> >> > Dear Sebastien
>> >> >
>> >> > It's interesting that this question hasn't been raised
before.
>> >> > Thanks for doing so now. I agree that new standard names
would
>> >> > be appropriate. There are already some standard names
containing
>> >> > "difference" in various ways. I would suggest that for your
>> >> > purpose the names don't have to be so specific. You could use
>> >> > sea_water_temperature_difference sigma_theta_difference
>> >> > sigma_t_difference because in the context of your use of
them it
>> >> > is obvious what difference you mean. That would make these
names
>> >> > perhaps useful for other purposes too. This is like the
rather
>> >> > generic name air_temperature_threshold which doesn't indicate
>> >> > what the threshold can be used for. I would also suggest that
>> >> > the definitions of the three kinds of mixed layer depth
should
>> >> > have a sentence added to say that the threshold should be
stored
>> >> > in a coordinate var, e.g. like the sentence for
number_of_days_with_air_temperature_above_threshold.
>> >> >
>> >> > Best wishes
>> >> >
>> >> > Jonathan
>> >> >
>> >> > ----- Forwarded message from Sebastien Villaume
>> >> > <[email protected]>
>> >> > -----
>> >> >
>> >> >> Date: Thu, 5 Apr 2018 13:55:50 +0000
>> >> >> From: Sebastien Villaume <[email protected]>
>> >> >> 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
>> >> >> /Sébastien
>> >> >>
>> >> >> ----- Original Message -----
>> >> >> > From: "Sebastien Villaume" <[email protected]>
>> >> >> > 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. Sébastien Villaume
