Hello All, After some hunting, I found a copy of a letter from Frank Millero (1993 - "What is PSU") ( http://www.marbef.org/wiki/Salinity_sensors -- box on right) which is adamant that PSU is not a unit and the "Joint Panel on Oceanographic Tables and Standards" has made this clear in their definition of the international equation of state.
There is perhaps a parallel here with "Decibel", which is accepted by cf-python and rejected by Udunits. There has been discussion on unidata pages, the outcome of which, I think, is that Decibel is a reference to a methodolgy used to arrive at a non-dimensional number, not a unit of measure. The CF Standard Name list now has distinct standard names for salinities defined by different algorithms (e.g. sea_water_practical_salinity, sea_water_cox_salinity). One compromise might be to add some recognised standard methodological keywords and define a way of placing them in NetCDF files, regards, Martin ________________________________ From: Lowry, Roy K. [[email protected]] Sent: 18 July 2017 14:36 To: V. Balaji - NOAA Affiliate Cc: Juckes, Martin (STFC,RAL,RALSP); [email protected]; [email protected]; [email protected] Subject: Re: [CF-metadata] Is "psu" a valid cf unit? Dear Balaji, I think there are some crossed wires here. The dimensionless Practical Salinity and a Practical Salinity in PSU are exact numeric equivalents. The only difference is the name that's given to the unit of measure - that's why to make this crystal clear CF includes the scaling factor of 10^-3. So I don't think that this can affect storage precision. Cheers, Roy. Please note that I partially retired on 01/11/2015. I am now only working 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my day in the office. All vocabulary queries should be sent to [email protected]. Please also use this e-mail if your requirement is urgent. ________________________________ From: V. Balaji - NOAA Affiliate <[email protected]> Sent: 18 July 2017 14:12 To: Lowry, Roy K. Cc: [email protected]; [email protected]; [email protected]; [email protected] Subject: Re: [CF-metadata] Is "psu" a valid cf unit? The ocean modeling community is adamant that they will continue to use PSUs for salinity: it's this unit, rather than its SI or dimensionless equivalent, that gives the maximum digits of precision in a floating-point representation of salinity. It's a valid concern, and CF should perhaps reconsider, with a new discussion giving weight to the views of modelers as well as physical oceanographers. Thanks, Lowry, Roy K. writes: > Hello Martin, > > > This topic has been debated at length in CF. To cut a long story short, the > term 'Practical Salinity Unit' was coined when the 1978 Practical Salinity > scale was devised. However, the term fell out of favour with the physical > oceanographic community whose current recommended practice is that Practical > Salinity - a ratio - should be a dimensionless number. CF followed this > recommendation and so PSU is not a part of CF. > > > Have a dig around in the mailing list archive if you want to find out more. > > > Cheers, Roy. > > > Please note that I partially retired on 01/11/2015. I am now only working 7.5 > hours a week and can only guarantee e-mail response on Wednesdays, my day in > the office. All vocabulary queries should be sent to [email protected]. > Please also use this e-mail if your requirement is urgent. > > > ________________________________ > From: CF-metadata <[email protected]> on behalf of > [email protected] <[email protected]> > Sent: 18 July 2017 13:43 > To: [email protected]; [email protected]; > [email protected] > Subject: [CF-metadata] Is "psu" a valid cf unit? > > Hello David, all, > > Is "psu" a valus CF unit? It is not in Udunits, but it is added in cf-python > as a unit alias and also appears to be accpeted by the cf-checker. I can't > see any mention of it in the CF Convention document: the latter only lists > level, layer, and sigma_level permitted departures from Udunits, > > regards, > Martin > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata CF-metadata Info Page - University Corporation for ...<http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> mailman.cgd.ucar.edu This is an unmoderated list for discussions about interpretation, clarification, and proposals for extensions or change to the CF conventions. > CF-metadata Info Page - University Corporation for > ...<http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> CF-metadata Info Page - University Corporation for ...<http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata> mailman.cgd.ucar.edu This is an unmoderated list for discussions about interpretation, clarification, and proposals for extensions or change to the CF conventions. > mailman.cgd.ucar.edu > This is an unmoderated list for discussions about interpretation, > clarification, and proposals for extensions or change to the CF conventions. > > > > ________________________________ > 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. > ________________________________ > -- V. Balaji Office: +1-609-452-6516 Head, Modeling Systems Group, GFDL Mobile: +1-917-273-9824 Princeton University Email: [email protected] https://www.gfdl.noaa.gov/v-balaji-homepage v-balaji-homepage – Geophysical Fluid Dynamics Laboratory<https://www.gfdl.noaa.gov/v-balaji-homepage> www.gfdl.noaa.gov Bio Dr. V. Balaji is affiliated with Princeton University's Cooperative Institute on Climate Sciences. He has headed the Modeling Systems Group at NOAA's Geophysical ... ________________________________ 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 [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
