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:[email protected]] On Behalf Of > Jonathan Gregory > Sent: 24 April 2018 17:08 > To: [email protected] > 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:[email protected]] On Behalf > > Of Jonathan Gregory > > Sent: 24 April 2018 14:26 > > To: [email protected] > > 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" > > <[email protected]> ----- > > > > > Date: Tue, 24 Apr 2018 07:17:48 +0000 > > > From: "Saulter, Andrew" <[email protected]> > > > To: "[email protected]" <[email protected]> > > > 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:[email protected]] > > > Sent: 23 April 2018 17:57 > > > To: Saulter, Andrew <[email protected]> > > > Cc: CF Metadata List <[email protected]> > > > 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 > > > > <[email protected]> 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:[email protected]] On > > > > Behalf Of Saulter, Andrew > > > > Sent: 20 April 2018 17:04 > > > > To: [email protected] > > > > 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:[email protected]] On > > > > Behalf Of Jonathan Gregory > > > > Sent: 11 April 2018 18:37 > > > > To: [email protected] > > > > 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." > > > > <[email protected]> > > > > ----- > > > > > > > >> Date: Tue, 10 Apr 2018 13:14:16 +0000 > > > >> From: "Snaith, Helen M." <[email protected]> > > > >> To: "Saulter, Andrew" <[email protected]> > > > >> CC: "[email protected]" <[email protected]> > > > >> 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 > > > >> <[email protected]<mailto:[email protected]>> > > > >> 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 > > > >> [email protected]<mailto:[email protected] > > > >> ov > > > >> .u > > > >> k > > > >>> http://www.metoffice.gov.uk<http://www.metoffice.gov.uk/> > > > >> > > > >> > > > >> -- > > > >> This message has been scanned for viruses and dangerous content > > > >> by MailScanner<http://www.mailscanner.info/>, and is believed to > > > >> be clean. _______________________________________________ > > > >> CF-metadata mailing list > > > >> [email protected]<mailto:[email protected]> > > > >> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > >> > > > >> ________________________________ > > > >> This message (and any attachments) is for the recipient only. 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