Dear Alison and Nan Many thanks for doing this, Alison, and apologies that I didn't have time for it sooner myself. I think this is all fine except for the phrase defining geopotential datum, which appears in several of them. I would say
The "geopotential datum" is any estimated surface of constant geopotential used as a datum i.e. a reference level; for the geoid as a datum, specific standard names are available. The geoid is a geopotential (equipotential) surface, namely the one which encloses (between itself and the solid Earth below) a volume equal to the volume of the ocean, often informally described as the surface the ocean would have if it were at rest. The ellipsoid isn't a geopotential surface. We intro- duced the term "geopotential datum" in https://cf-trac.llnl.gov/trac/ticket/118 Nan commented Re: The term 'height_above_sea_level', defined as "Height_above_X" means the vertical distance above the named surface X. "sea_level" means *mean* sea level, which is close to the geoid in sea areas.' Someone recording observed met data on a buoy, looking for the best term for the sensor heights, might easily choose this instead of 'height', but the height in that case is above actual sea level; varying over time. If this variable is meant to be 'height above mean sea level', that should be its name. There are about a dozen standard names using sea_level to mean mean_sea_level consistently, and we don't currently use the phrase mean_sea_level at all. If people agree, we could rename the existing standard names as Nan suggests for this new one. Best wishes Jonathan ----- Forwarded message from [email protected] ----- > Date: Thu, 18 May 2017 11:37:54 +0000 > From: [email protected] > To: [email protected] > Subject: [CF-metadata] Standard names for CF trac ticket #143 > > Dear Jonathan, All, > > CF trac ticket #143 (https://cf-trac.llnl.gov/trac/ticket/143) has been > agreed and will be included in CF 1.7. A number of new standard names are > needed to support the implementation of this ticket. They are names for > constants used in the formula_terms attribute of parameterized vertical > coordinates. > > The following names are proposed. > > air_pressure_at_top_of_atmosphere_model (Pa) > ' "Top of atmosphere model" means the upper boundary of the top layer of an > atmosphere model.' > > altitude_at_top_of_atmosphere_model (m) > 'Altitude is the (geometric) height above the geoid, which is the reference > geopotential surface. The geoid is similar to mean sea level. "Top of > atmosphere model" means the upper boundary of the top layer of an atmosphere > model.' > > reference_air_pressure_for_atmosphere_vertical_coordinate (Pa) > 'For models using a dimensionless vertical coordinate, for example, sigma, > hybrid sigma-pressure or eta, the values of the vertical coordinate at the > model levels are calculated relative to a reference level. "Reference air > pressure" is the air pressure at the model reference level. It is a > model-dependent constant." > > height_above_geopotential_datum_at_top_of_atmosphere_model (m) > ' "Height_above_X" means the vertical distance above the named surface X. The > "geopotential datum" is the geopotential reference level (level of zero > geopotential) where this is not a specifically named level such as the geoid > or a reference ellipsoid. "Top of atmosphere model" means the upper boundary > of the top layer of an atmosphere model.' > > height_above_geopotential_datum (m) > '"Height_above_X" means the vertical distance above the named surface X. The > "geopotential datum" is the geopotential reference level (level of zero > geopotential) where this is not a specifically named level such as the geoid > or a reference ellipsoid.' > > surface_height_above_geopotential_datum (m) > ' "Height_above_X" means the vertical distance above the named surface X. The > surface called "surface" means the lower boundary of the atmosphere. The > "geopotential datum" is the geopotential reference level (level of zero > geopotential) where this is not a specifically named level such as the geoid > or a reference ellipsoid.' > > sea_surface_height_above_geopotential_datum (m) > ' "Height_above_X" means the vertical distance above the named surface X. The > "geopotential datum" is the geopotential reference level (level of zero > geopotential) where this is not a specifically named level such as the geoid > or a reference ellipsoid. "Sea surface height" is a time-varying quantity.' > > sea_floor_depth_below_geopotential_datum (m) > ' "Depth_below_X" means the vertical distance below the named surface X. The > "geopotential datum" is the geopotential reference level (level of zero > geopotential) where this is not a specifically named level such as the geoid > or a reference ellipsoid.' > > sea_floor_depth_below_reference_ellipsoid (m) > ' "Depth_below_X" means the vertical distance below the named surface X. A > reference ellipsoid is a regular mathematical figure that approximates the > irregular shape of the geoid. A number of reference ellipsoids are defined > for use in the field of geodesy.' > > height_above_sea_level (m) > ' "Height_above_X" means the vertical distance above the named surface X. > "sea_level" means mean sea level, which is close to the geoid in sea areas.' > > I have based the definitions on my own reading of ticket #143 and on existing > names. I'd welcome comments to improve them. > > Best wishes, > Alison > > ------ > Alison Pamment Tel: +44 > 1235 778065 > Centre for Environmental Data Analysis Email: > [email protected] > STFC Rutherford Appleton Laboratory > R25, 2.22 > Harwell Campus, Didcot, OX11 0QX, U.K. > > > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
