Dear Andy
> - I'm only going to do this for sea water levels, so from my point of view using the term "sea" is fine; I'm just aware that what comes below could be applied in other water bodies
Yes. However, we make our job simpler (as a principle in CF) by doing only what
we need to for the current use-cases.
> - "due_to_surge" will either a) be derived as a residual value calculated after taking a measured sea level value (referenced to some fixed datum) and subtracting a predicted tide height (referenced to same datum), or b) be a quantity that we would expect to add to a predicted tide height in order to create a total water level (again referenced to some fixed datum)
In both cases the datum is not relevant to the elevation due to surge.
> - "due_to_tide" will be the tide values mentioned above which will have to be referenced against a datum or common benchmark, e.g. chart datum, mean sea level, Ordnance Datum Newlyn, in order to make sense.
... whereas here the datum *is* required.
So these cases seem different after all, and may need different sorts of name -
at least, that's my first reaction. It's because there isn't a situation of
"no tide", but there is a situation of "no surge". On second thoughts, I'm not
sure about this distinction. No tide, I suppose, means MSL. On the other hand,
no surge isn't uniquely defined - something must be assumed about the MSLP and
the wind when there *isn't* a surge. What is that?
> So far these are variables that give us what we might term 'still water level', i.e. neglecting wave effects. However, thinking about future requirements you could easily see an extension to higher frequency parameters such as "due_to_wave_induced_setup" (minutes to hours), "due_to_run_up" (seconds to minutes), "due_to_waves" (seconds) if you were looking at a detailed approach to evaluating total water levels. All these would work like surge, in that these aren't referenced to a datum themselves but will contribute to some total water level value that does need to be.
Right. If we can work out how to deal with the surge, I agree the others will
follow when they are needed.
Best wishes
Jonathan
> Instinctively when I plot summations of these types of variables in time-series I would write 'sea_surface_elevation' on the y-axis (since the water goes down as well as up) but that, definitely, is just me! Personally I have no objection to "elevation_of_sea_surface" either - it seems clear what it means and if we are all happy that "sea" can be generic for "water" I'd be good with this.
>
> Thanks
> Andy
>
>
> -----Original Message-----
> From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory
> Sent: 24 April 2018 17:08
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Fwd: Re: Fwd: Re: proposed new standard name for storm surge residual
>
> Dear Andy
>
> > "elevation_of_sea_surface_due_to_X" sounds most appropriate.
> OK.
>
> Since we already have
> water_surface_height_above_reference_datum
> water_surface_reference_datum_altitude
> in the table, I agree that water_surface is OK to use. In general in standard names we have made the word "sea" signify all bodies of water, as we've not been able to find another neat and clear word for them. However, we've already departed from that rule in this case. Do you need to use these names for lakes?
> If your use is just sea, I would rather stick to sea names, since we've got a lot more of those.
>
> I would say that the reference_datum names should be avoided if your datum is something that can be geophysically defined, such as mean_sea_level or the geoid. We have names mentioning those levels, which are more specific and useful. I think the reference_datum names are for arbitrary levels, indicated by some physical benchmark.
>
> I feel that
> elevation_of_water|sea_surface
> would be better than
> water|sea_surface_elevation
> because to me the former sounds like "making the water surface higher", which is what we mean, while the latter means "how high the water surface is". That is rather subtle and language-dependent, so I'm a bit nervous about it. It also might just be me! How does it sound to you?
>
> Best wishes
>
> Jonathan
>
> >
> > -----Original Message-----
> > From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf
> > Of Jonathan Gregory
> > Sent: 24 April 2018 14:26
> > To: cf-metadata at cgd.ucar.edu
> > Subject: [CF-metadata] Fwd: Re: proposed new standard name for storm
> > surge residual
> >
> > Dear Andrew and John
> >
> > I hadn't noticed that sea_surface_elevation is already in use as an alias.
> > That's a pity, but maybe it would be confusing anyway, given John's comment.
> >
> > I think that what Andrew needs is terms that say how much higher the sea surface is because of influence X relative to how high it would be in the absence of influence X. Such terms do not need any datum (like geoid or MSL). The difference in z is the same regardless of what datum would be used for z itself. I suggested before that change_in would be a possibility but it doesn't sound quite right, because we aren't comparing SSH before and after a storm surge for example, which is what I'd understand by "change in SSH due to storm surge". Other ideas:
> >
> > elevation_of_sea_surface_due_to_X
> > increment_to_sea_surface_height_due_to_X
> > increase_of_sea_surface_height_due_to_X
> >
> > What others occur to you?
> >
> > Best wishes
> >
> > Jonathan
> >
> >
> > ----- Forwarded message from "Saulter, Andrew"
> > <andrew.saulter at metoffice.gov.uk> -----
> >
> > > Date: Tue, 24 Apr 2018 07:17:48 +0000
> > > From: "Saulter, Andrew" <andrew.saulter at metoffice.gov.uk>
> > > To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> > > Subject: Re: [CF-metadata] proposed new standard name for storm surge
> > > residual
> > >
> > > John,
> > >
> > > I see where you are with that, but my understanding from Jonathon Gregory's email earlier is that the 'due_to' part of the phrasing identifies a component process that contributes to an overall quantity. In the case below 'due_to_storm_surge' is a contribution to 'sea_surface_elevation' and that quantity is what needs to be referenced to some datum. Or maybe I'm not getting it? Steep learning curve this...
> > >
> > > Anyway, having thought about datum's now I have done some further searching and noted the following already exist as standard names:
> > >
> > > water_surface_height_above_reference_datum - this denotes the
> > > quantity
> > >
> > > water_surface_reference_datum_altitude - references the datum to the
> > > (grid_mapping) geoid
> > >
> > > These look much more like what I was after, so the question is can the 'due_to_storm_surge' and 'due_to_tide' be sensibly appended to 'water_surface_height_above_reference_datum'??
> > >
> > > Cheers
> > > Andy
> > >
> > >
> > > -----Original Message-----
> > > From: John Graybeal [mailto:jbgraybeal at mindspring.com]
> > > Sent: 23 April 2018 17:57
> > > To: Saulter, Andrew <andrew.saulter at metoffice.gov.uk>
> > > Cc: CF Metadata List <cf-metadata at cgd.ucar.edu>
> > > Subject: Re: [CF-metadata] proposed new standard name for storm
> > > surge residual
> > >
> > >
> > > I actually find this new name/definition internally inconsistent. An
> > > elevation that is ?due to storm surge? seems to be relative to the
> > > elevation without the storm surge, which makes the datum irrelevant.
> > > Unless the change due to the storm surge would be measured
> > > differently under different datums, but I can?t imagine that.
> > > (Taking the other way, if it?s an elevation relative to some normal
> > > datum, then ?due to storm surge? is irrelevant.)
> > >
> > > In any case, under the new definition, the description needs to include exactly how the datum is specified. The computers and people will need to know where to look for that information, and ideally it should be a unique identifier that the computers can recognize and understand.
> > >
> > >
> > > john
> > >
> > >
> > > > On Apr 23, 2018, at 01:43, Saulter, Andrew <andrew.saulter at metoffice.gov.uk> wrote:
> > > >
> > > > Apologies, a little bit more to add to the below following up from
> > > > Jonathon's first email,
> > > >
> > > > For both tide and surge I would actually prefer to go with Jonathon's suggestion that the 'height_above_mean_sea_level' part of my suggestions is replaced with 'elevation'. This is a much more compact and flexible way of expressing things and means, particularly with tide that we can reference this to whichever datum we like (for example Chart Datum, Ordnance Datum, MSL) dependent on source elsewhere in the metadata. I think it is also appropriate that we think of "sea_surface_elevation" as a quantity that can be contributed to via processes with many different timescales, e.g. tides, surges, individual ocean waves.
> > > >
> > > > This would take us to:
> > > >
> > > > Proposed standard name:
> > > > sea_surface_elevation_due_to_storm_surge
> > > > Units: m
> > > > "Sea surface elevation" is a time-varying quantity denoting the height of the sea surface relative to a given datum. The specification of a physical process by the phrase ?due_to_process? means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. Storm surge effects, due to meteorological forcing of the ocean and interaction between the generated surge and tides, are a significant contributor to the observed sea surface height.
> > > >
> > > > Proposed standard name:
> > > > sea_surface_elevation_due_to_tide
> > > > Units: m
> > > > "Sea surface elevation" is a time-varying quantity denoting the height of the sea surface relative to a given datum. The specification of a physical process by the phrase ?due_to_process? means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. Tides are a significant contributor to the observed sea surface height; here ?tide? denotes a generic variable describing the time varying tidal signal, for example as generated based on a summation of harmonically analysed components, or resulting from the application of such components as boundary conditions to a numerical tidal model.
> > > >
> > > > However, I have one concern in that "sea_surface_elevation" is presently given as an alias for "sea_surface_height_above_geoid". My worry is that the latter has implications for the vertical datum and that we might choose to disconnect this from other aspects of the grid_mapping variable (e.g. where my station positions are in WGS84, but the vertical reference is to chart datum) in which case we are not strictly referencing against the geoid any more. In addition, the term "sea_surface_height" has more usually been associated with altimeter and model products where high frequency signals are generally excluded?
> > > >
> > > > So some consensus as to whether "sea_surface_elevation" is the phrasing to go for would be very helpful...
> > > >
> > > > Cheers
> > > > Andy
> > > >
> > > > -----Original Message-----
> > > > From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On
> > > > Behalf Of Saulter, Andrew
> > > > Sent: 20 April 2018 17:04
> > > > To: cf-metadata at cgd.ucar.edu
> > > > Subject: Re: [CF-metadata] proposed new standard name for storm
> > > > surge residual
> > > >
> > > > Jonathon, Helen,
> > > >
> > > > Thanks for the feedback.
> > > >
> > > > I'd looked at the existing 'sea_surface_height' terms but had the same worry as Jonathon that the use of 'amplitude' restricted these to some (unspecified) time integral. What I'm after is definitely a variable that varies as a function of time. It's also unusual in the coastal forecasting community to want to split the various contributions to tide up.
> > > >
> > > > The 'due_to_air_pressure_and_wind' term captures the primary meteorological processes that induce surge. However, these do not capture the effect of tide-surge interaction in shallower waters (for example the extra surge elevation enhances the speed at which the tide propagates so a 'surge residual' can include the propagation speed delta as well as the background super-elevation) nor other secondary variability that we often see in surge residuals, such as steric changes of the water column. So I feel that using a catchall term 'storm_surge', although less specific would have a lot less potential to mislead a user. The option exists, I assume, in the comments attribute for a variable to be more precise about its derivation/generating processes.
> > > >
> > > > So overall, I couldn't find a goldilocks term for either surge or tide that would fit my users understanding of the variables - hence the new suggestions.
> > > >
> > > > Have a good weekend
> > > > Andy
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On
> > > > Behalf Of Jonathan Gregory
> > > > Sent: 11 April 2018 18:37
> > > > To: cf-metadata at cgd.ucar.edu
> > > > Subject: [CF-metadata] proposed new standard name for storm surge
> > > > residual
> > > >
> > > > Dear Helen and Andy
> > > >
> > > > I noticed the sea_surface_height_amplitude_due_to_X_tide names as well, and I wondered, what does "amplitude" mean here? The definitions of these names don't say, and I feel that we should be clear. I guessed it might mean the amplitude of SSH due to the tidal cycle, whereas I think Andy means the actual tidal height as a function of time. Are you able to clarify?
> > > >
> > > > It's a good point about due_to_air_pressure[_and_wind], thanks. That may not obviously mean "storm surge", which maybe could be inserted in the definition.
> > > >
> > > > Best wishes
> > > >
> > > > Jonathan
> > > >
> > > > ----- Forwarded message from "Snaith, Helen M."
> > > > <h.snaith at bodc.ac.uk>
> > > > -----
> > > >
> > > >> Date: Tue, 10 Apr 2018 13:14:16 +0000
> > > >> From: "Snaith, Helen M." <h.snaith at bodc.ac.uk>
> > > >> To: "Saulter, Andrew" <andrew.saulter at metoffice.gov.uk>
> > > >> CC: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> > > >> Subject: Re: [CF-metadata] proposed new standard name for storm surge
> > > >> residual
> > > >> x-mailer: Apple Mail (2.3445.6.18)
> > > >>
> > > >> Hi Andy
> > > >>
> > > >> Many of the sea_surface_height terms have been used in satellite altimetry for some time.
> > > >> The tidal components have been split out into
> > > >> sea_surface_height_amplitude_due_to_equilibrium_ocean_tide<javascript:
> > > >> void(0)>
> > > >> sea_surface_height_amplitude_due_to_geocentric_ocean_tide<javascript:
> > > >> v
> > > >> oid(0)>
> > > >> sea_surface_height_amplitude_due_to_non_equilibrium_ocean_tide<ja
> > > >> va
> > > >> sc
> > > >> r
> > > >> ipt:void(0)>
> > > >>
> > > >> And the pole tide
> > > >> sea_surface_height_amplitude_due_to_pole_tide<javascript:void(0)>
> > > >>
> > > >> In these terms, amplitude has been used to identify the ?above
> > > >> mean level? and sea_surface_height is as alias of
> > > >> sea_surface_heigth_above_mean_sea_level
> > > >>
> > > >>
> > > >> Also included are the terms
> > > >> sea_surface_height_correction_due_to_air_pressure_and_wind_at_hig
> > > >> h_
> > > >> fr
> > > >> e
> > > >> quency<javascript:void(0)>
> > > >> sea_surface_height_correction_due_to_air_pressure_at_low_frequenc
> > > >> y<
> > > >> ja
> > > >> v
> > > >> ascript:void(0)>
> > > >>
> > > >> The former of which is related to surge I think - it is normally determined from a tidal model and is the response of sea level to changes in air pressure and wind.
> > > >>
> > > >> Even if these are not the correct terms, as you are not determining a 'correction? but a value - they should be related to the surge components, so do they give the ?due to? component you need?
> > > >>
> > > >> Helen
> > > >>
> > > >>
> > > >> On 4 Apr 2018, at 17:13, Saulter, Andrew <andrew.saulter at metoffice.gov.uk<mailto:andrew.saulter at metoffice.gov.uk>> wrote:
> > > >>
> > > >> Dear all,
> > > >>
> > > >> First posting to this list, so please forgive me if I?m doing it
> > > >> wrong?
> > > >>
> > > >> I?d like to request an addition to the standard name list to include storm surge residual and tide. These variables are generated for the purpose of coastal flood prediction and will be available in future, netCDF based, operational products from the Met Office.
> > > >>
> > > >> Proposed standard name:
> > > >> sea_surface_height_above_mean_sea_level_due_to_storm_surge
> > > >> Units: m
> > > >> "Sea surface height" is a time-varying quantity. "Height_above_X" means the vertical distance above the named surface X. "Mean sea level" means the time mean of sea surface elevation at a given location over an arbitrary period sufficient to eliminate the tidal signals. The specification of a physical process by the phrase ?due_to_process? means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. Storm surge effects, due to meteorological forcing of the ocean and interaction between the generated surge and tides, are a significant contributor to the observed sea surface height.
> > > >>
> > > >> Proposed standard name:
> > > >> sea_surface_height_above_mean_sea_level_due_to_tide
> > > >> Units: m
> > > >> "Sea surface height" is a time-varying quantity. "Height_above_X" means the vertical distance above the named surface X. "Mean sea level" means the time mean of sea surface elevation at a given location over an arbitrary period sufficient to eliminate the tidal signals. The specification of a physical process by the phrase ?due_to_process? means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. Tides are a significant contributor to the observed sea surface height; here ?tide? denotes a generic variable describing the time varying tidal signal, for example as generated based on a summation of harmonically analysed components, or resulting from the application of such components as boundary conditions to a numerical tidal model.
> > > >>
> > > >> Many thanks
> > > >> Andy
> > > >>
> > > >>
> > > >> Andy Saulter
> > > >> Surge, Waves and Metocean Projects Manager Met Office FitzRoy
> > > >> Road Exeter Devon EX1 3PB
> > > >> Tel: +44 (0)1392 884703 Fax: +44 (0)1392 885681
> > > >> andrew.saulter at metoffice.gov.uk<mailto:andrew.saulter at metoffice.g
> > > >> ov
> > > >> .u
> > > >> k
> > > >>> http://www.metoffice.gov.uk<http://www.metoffice.gov.uk/>
> > > >>
> > > >>
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