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[CF-metadata] Standard names for sea level change

From: Bert Jagers <bert.jagers>
Date: Fri, 06 Jul 2012 09:17:01 +0200

Hi Lauret,

Indeed, looking at the map you showed I think that this looks like any
quantity that varies per cell of a computational grid.
In my interpretation the "average" goes with the word "global"; the
global_average_sea_level_change is the global_average of the
sea_level_change which could be extended to something like
region_average_sea_level_change, but shouldn't be extended to a local
point-by-point name.

Hence, I think that it's more consistent to drop both words "local" and
"average", so I would suggest: tendency_of_sea_level_change

Having said that, I would like to raise the issue of meaning and
supporting meta data. What do you actually want to store in this quantity?
The quantity (global_average_)sea_level_change is an integral quantity:
it is the total change in sea_level over a certain period. To correctly
describe this quantity one needs to add a start and end time of the
considered period. By adding tendency_of_ you add a time element, which
would need another meta data time element and I'm not sure how that
would work out. Is tendency_of_global_average_sea_level_change the
tendency of global_average_sea_level_change predictions for a specific
period as technology improves, or is it the tendency of that quantity if
you extend the considered simulation period? Your map title indicates
"Regional MSL trends from Oct-1992 to Feb-2012 (mm/year)" which I could
also interpret as just the mean rate of change of the "mean sea level";
couldn't this be stored as the tendency_of_sea_surface_height (would be
a new name) with cell methods indicating that it's a mean over a certain
period? Or, would that mix long and short term concepts too much?

Best regards,

Bert
--------

On 06/07/2012 03:29, Cameron-smith, Philip wrote:
>
> 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.
>
> -----------------------------------------------------------------------
>
> *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:
>
> MSL_Map_MERGED_Global_IB_RWT_NoGIA_Adjust.gif
>
> 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.
>
> --
>
> Scanned by iCritical.
>
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