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-boun...@cgd.ucar.edu] On Behalf Of Saulter, Andrew Sent: 20 April 2018 17:04 To: cf-metadata@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-boun...@cgd.ucar.edu] On Behalf Of Jonathan Gregory Sent: 11 April 2018 18:37 To: cf-metadata@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.sna...@bodc.ac.uk> ----- > Date: Tue, 10 Apr 2018 13:14:16 +0000 > From: "Snaith, Helen M." <h.sna...@bodc.ac.uk> > To: "Saulter, Andrew" <andrew.saul...@metoffice.gov.uk> > CC: "cf-metadata@cgd.ucar.edu" <cf-metadata@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<javascr > 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_high_fre > quency<javascript:void(0)> > sea_surface_height_correction_due_to_air_pressure_at_low_frequency<jav > 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.saul...@metoffice.gov.uk<mailto:andrew.saul...@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.saul...@metoffice.gov.uk<mailto:andrew.saul...@metoffice.gov.uk > > 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 > CF-metadata@cgd.ucar.edu<mailto:CF-metadata@cgd.ucar.edu> > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > ________________________________ > This message (and any attachments) is for the recipient only. NERC is subject > to the Freedom of Information Act 2000 and the contents of this email and any > reply you make may be disclosed by NERC unless it is exempt from release > under the Act. Any material supplied to NERC may be stored in an electronic > records management system. > ________________________________ > _______________________________________________ > CF-metadata mailing list > CF-metadata@cgd.ucar.edu > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
