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:
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] De la part de alison.pamment at stfc.ac.uk
Envoy? : lundi 2 juillet 2012 14:29
? : 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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