Dear Jonathan and Philip,
Thank you for your feedback.
Finally I think we don't need to insist on this story of average vs cell
methods, I made a confusion. The process is actually easier.
>From sea surface heights NetCDF products ('sea_surface_height_above_sea_level'
>in CF) we are computing the tendency of these heights for each grid point.
>Which can basically be translated in CF to
"tendency_of_sea_surface_height_above_sea_level". Am I Right?
Olivier.
-----Message d'origine-----
De : CF-metadata [mailto:[email protected]] De la part de
Cameron-smith, Philip
Envoyé : vendredi 6 juillet 2012 19:38
À : Jonathan Gregory; [email protected]
Objet : Re: [CF-metadata] Standard names for sea level change
Hi Olivier, et al.,
I note that we have several different types of sea_level defined in CF. I have
copied here the ones I found (there may be others). Does one of these meet your
needs?
global_average_sea_level_change
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_steric_sea_level_change
Global average steric sea level change is caused by changes in sea water
density due to changes in temperature (thermosteric) and salinity (halosteric).
Zero sea level change is an arbitrary level.
global_average_thermosteric_sea_level_change
Global average thermosteric sea level change is the part caused by change in
density due to change in temperature i.e. thermal expansion. Zero sea level
change is an arbitrary level.
ocean_rigid_lid_pressure_expressed_as_sea_surface_height_above_geoid
"Ocean rigid lid pressure" means the pressure at the surface of an ocean model
assuming that it is bounded above by a rigid lid.
sea_surface_height_above_geoid
alias: sea_surface_elevation
alias: sea_surface_elevation_anomaly
The geoid is a surface of constant geopotential with which mean sea level would
coincide if the ocean were at rest. (The volume enclosed between the geoid and
the sea floor equals the mean volume of water in the ocean.) In an ocean GCM
the geoid is the surface of zero depth, or the rigid lid if the model uses that
approximation. "Sea surface height" is a time-varying quantity. By definition
of the geoid, the global average of the time-mean sea surface height (i.e. mean
sea level) above the geoid must be zero. The standard name for the height of
the sea surface above mean sea level is sea_surface_height_above_sea_level. The
standard name for the height of the sea surface above the reference ellipsoid
is sea_surface_height_above_reference_ellipsoid.
sea_surface_height_above_sea_level
alias: sea_surface_height
sea_surface_height_above_reference_ellipsoid
"Sea surface height" is a time-varying quantity. A reference ellipsoid is a
mathematical figure that approximates the geoid. The geoid is a surface of
constant geopotential with which mean sea level would coincide if the ocean
were at rest. The ellipsoid is an approximation because the geoid is an
irregular shape. A number of reference ellipsoids are defined for use in the
field of geodesy. The standard name for the height of the sea surface above the
geoid is sea_surface_height_above_geoid. The standard name for the height of
the sea surface above mean sea level is sea_surface_height_above_sea_level.
Best wishes,
Philip
-----------------------------------------------------------------------
Dr Philip Cameron-Smith, [email protected], Lawrence Livermore National Lab.
-----------------------------------------------------------------------
> -----Original Message-----
> From: CF-metadata [mailto:[email protected]] On Behalf
> Of Jonathan Gregory
> Sent: Friday, July 06, 2012 8:01 AM
> To: [email protected]
> Subject: Re: [CF-metadata] Standard names for sea level change
>
> Dear Olivier
>
> > I appreciate the idea suggested by Philip, which is remove 'local' and
> > simply
> use "tendency_of_average_sea_level_change". I think it's a fine solution.
>
> I'm sorry to say I still have concerns with this:
>
> * Why is "average" needed? As Philip said, we usually convey that idea in the
> cell_methods, which can distinguish if necessary between a local point
> measurement e.g. "lat: lon: point" and an area-average "lat: lon: mean"
> or "area: mean". Or does "average" refer to the time-mean?
>
> * "Sea level change" is not well-defined. Could you say more precisely what
> this quantity is, if it is not change in ocean thickness (that was my guess)?
>
> Best wishes and thanks
>
> Jonathan
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