Hi Lauret,
I am not an oceanographer, so hopefully you can help me understand what you mean by 'local' in your std_name proposal.
We already have a lot of std_names for quantities that are intensive, eg temperature, that are defined at every point (in principle), but which are usually averaged over some domain. CF usually handles this by omitting the word 'local' and then specifying the region of which the averaging is done using cell_bounds and cell_methods. As a non-specialist, this appears to me to be the case with your quantity too.
There are a few exceptions to the rule. All the exceptions I know of relate to global values where it seemed problematic to describe such a common integral through cell bounds and methods (there were some long email discussions about this a couple of years ago.)
One of the existing exceptions is global_average_sea_level_change<javascript:void(0)>.
Is your desire to have a spatially distributed version of this variable (as it appears to me in your map)? If so, I think it is best to use tendency_of_average_sea_level_change (I have just deleted 'local').
Or, does 'local' have some special meaning that I am not aware of?
I also confess that it isn't clear to me what 'average' means for this variable. But it is already part of the existing variable above, so I assume it was discussed at some point.
Best wishes,
Philip
-----------------------------------------------------------------------
Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
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From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Lauret Olivier
Sent: Wednesday, July 04, 2012 5:46 AM
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] Standard names for sea level change
Dear Alison and Jonathan,
Thank you very much for your comments.
1. Actually perhaps ?tendency_of_local_average_sea_level_change (m/year)? could be turned to ?local_tendency_of_global_average_sea_level_change (m/year)?, which seems to better reflect what the quantity really is? To give you an idea we basically compute the sea level trends at each NetCDF grid point to get a map like this one:
[cid:image001.jpg at 01CD5AD8.D19681F0]
2. ?global_average_sea_level_change_(semi)annual_amplitude? and ?global_average_sea_level_change_(semi)annual_phase ? would be simplified and turned to ?global_average_sea_level_change_amplitude? and ?global_average_sea_level_change_phase?, I am fine with that. Are there any examples of using ?cell methods? with range with years? or ?range within half a year??
3. In literature the phase is usually defined by the initial angle of a wave modeled by a sinusoidal function. In our case, from a geophysical point of view, the phase mainly corresponds to a date where the maxima of sinusoidal function is reached, that is to say when the range of sea level evolution is maximum. [(d/dt) sinusoidal function =0 implies date=- phase/? if sinusoidal function=A cos(?t+phase)]
I guess we should keep a classical definition for phase, I mean non-specific to sea level changes, because probably there will be other CF users for such information?
Olivier.
-----Message d'origine-----
De : CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu]<mailto:[mailto:cf-metadata-bounces at cgd.ucar.edu]> De la part de alison.pamment at stfc.ac.uk<mailto:alison.pamment at stfc.ac.uk>
Envoy? : lundi 2 juillet 2012 14:29
? : cf-metadata at cgd.ucar.edu<mailto:cf-metadata at cgd.ucar.edu>
Objet : Re: [CF-metadata] Standard names for sea level change
Dear Olivier,
Thank you for your proposals. I have some comments/questions (please see below).
> tendency_of_global_average_sea_level_change (m/year)
> Global average sea level change is due to change in volume of the water in the ocean, caused by mass
> and/or density change, or to change in the volume of the ocean basins, caused by tectonics etc. It is
> sometimes called "eustatic", which is a term that also has other definitions. It differs from the change
> in the global average sea surface height relative to the centre of the Earth by the global average
> vertical movement of the ocean floor. Zero sea level change is an arbitrary level. "tendency_of_X" means
> derivative of X with respect to time.
This name looks fine and is clearly related to the existing name global_average_sea_level_change. The units of m/year are sensible. We have used time units of years for one or two other names such as age_of_sea_ice. We should add the standard text for 'tendency' to the definition, i.e., ' "tendency_of_X" means derivative of X with respect to time.'
> tendency_of_local_average_sea_level_change (m/year)
> Global average sea level change is due to change in volume of the water in the ocean, caused by mass
> and/or density change, or to change in the volume of the ocean basins, caused by tectonics etc. It is
> sometimes called "eustatic", which is a term that also has other definitions. It differs from the change
> in the global average sea surface height relative to the centre of the Earth by the global average
> vertical movement of the ocean floor. Zero sea level change is an arbitrary level. Local means the
> quantity is depicted locally. "tendency_of_X" means derivative of X with respect to time.
This name looks fine. The units are OK. Again we need to add text to the definition regarding 'tendency'. By 'local' I assume you mean any area that is less than global and this would need to be indicated by adding bounds on the horizontal coordinate variables, or perhaps by using a coordinate variable with a standard name of 'region' if the area is something like the North Atlantic. We should add some explanatory text to the definition. Is this OK?
> global_average_sea_level_change_annual_amplitude (m)
> Global average sea level change is due to change in volume of the water in the ocean, caused by mass
> and/or density change, or to change in the volume of the ocean basins, caused by tectonics etc. It is
> sometimes called "eustatic", which is a term that also has other definitions. It differs from the change
> in the global average sea surface height relative to the centre of the Earth by the global average
> vertical movement of the ocean floor. Zero sea level change is an arbitrary level.
> global_average_sea_level_change_semiannual_amplitude (m)
> Global average sea level change is due to change in volume of the water in the ocean, caused by mass
> and/or density change, or to change in the volume of the ocean basins, caused by tectonics etc. It is
> sometimes called "eustatic", which is a term that also has other definitions. It differs from the change
> in the global average sea surface height relative to the centre of the Earth by the global average
> vertical movement of the ocean floor. Zero sea level change is an arbitrary level.
I wonder, do we really need "annual" and "semiannual" in the names? Presumably the date to which the amplitude applies would need to be specified by a time coordinate variable or scalar variable with bounds to indicate the averaging period. Couldn't we then have a general name of global_average_sea_level_change_amplitude without the need to specify annual or semiannual separately?
> global_average_sea_level_change_annual_phase (degree)
> Global average sea level change is due to change in volume of the water in the ocean, caused by mass
> and/or density change, or to change in the volume of the ocean basins, caused by tectonics etc. It is
> sometimes called "eustatic", which is a term that also has other definitions. It differs from the change
> in the global average sea surface height relative to the centre of the Earth by the global average
> vertical movement of the ocean floor. Zero sea level change is an arbitrary level.
> global_average_sea_level_change_semiannual_phase (degree)
> Global average sea level change is due to change in volume of the water in the ocean, caused by mass
> and/or density change, or to change in the volume of the ocean basins, caused by tectonics etc. It is
> sometimes called "eustatic", which is a term that also has other definitions. It differs from the change
> in the global average sea surface height relative to the centre of the Earth by the global average
> vertical movement of the ocean floor. Zero sea level change is an arbitrary level.
I'm not sure I understand what the phase quantities are. Do they indicate a seasonal cycle in sea level change? What is the datum for measuring the phase (i.e., what would a phase of zero degrees mean)? Also, as for the amplitude names, I wonder if we need separate 'annual' and 'semiannual' names for the phases?
Best wishes,
Alison
> Thanks for your comments!
>
> Best wishes
>
> Olivier.
>
>
>
> Olivier Lauret
> Project Engineer
> Satellite Oceanography Division
>
> E-mail: olauret at cls.fr<mailto:olauret at cls.fr>
> Tel. +33 561 394 851; Fax +33 561 393 782
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Email: alison.pamment at stfc.ac.uk<mailto:alison.pamment at stfc.ac.uk>
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
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