Dear Jonathan,
I'm OK with losing the 'principal'. I know what I mean by that, but there are some (many) who might not! 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 enquir...@bodc.ac.uk. Please also use this e-mail if your requirement is urgent. ________________________________ From: CF-metadata <cf-metadata-boun...@cgd.ucar.edu> on behalf of Jonathan Gregory <j.m.greg...@reading.ac.uk> Sent: 14 June 2017 16:58 To: cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] Standard names for mean sea level change Dear Roy and Alison > To clarify, what I was getting at with the rationalisation of syntax was > mixed use of 'average' and 'mean' for the same statistic and the fact that > the names are opposite ways around. For example, instead of > thermosteric_change_in_mean_sea_level and > global_average_thermosteric_sea_level_change why not have > average_thermosteric_sea_level_change and > global_average_thermosteric_sea_level_change (possibly with all averages > changed to means)? The use of "average" rather than "mean" (my choice, I admit) was made to avoid confusion with "mean sea level". However if we're introducing "mean" now anyway I wouldn't mind changing "average" to "mean", since "mean" is more common. However, there is some subtlety and potential for confusion still! global_mean_[thermosteric_]sea_level_change is not the [thermosteric] change in global mean sea level, because there is no such quantity as "global mean sea level" without "change". The "mean" here means a spatial average. Moreover, you don't necessarily calculate these global quantities as a global mean of local quantities, because they really refer to change in the volume of the world ocean, divided by world ocean surface area. If they were really spatial means, we could use cell_methods to describe them instead of distinct standard names. thermosteric_change_in_mean_sea_level is the thermosteric change in (local) mean sea level. The "mean" here means a temporal average. > Finally, thinking about it my concerns about these new names being abused > could be alleviated by the following definition: > > "Mean sea level" means the time mean of sea surface elevation at a given > location over an arbitrary period sufficient to eliminate the principal tidal > signal. Zero mean sea level change is an arbitrary level. That is fine with me, especially if it alleviates Roy's concerns. I would slightly prefer "tidal signals" instead of "principal tidal signal". Roy is quite right that climate models don't usually have tides anyway. For precision in the real world it is essential to specify a particular geopotential datum, since MSL is vague. Nonetheless "above MSL" is a commonly used phrase. Best wishes Jonathan _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata CF-metadata Info Page - mailman.cgd.ucar.edu Mailing Lists<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. ________________________________ 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. ________________________________
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