Dear Alison Thanks very much for this. I think that is all fine.
Best wishes Jonathan ----- Forwarded message from [email protected] ----- > Date: Mon, 26 Jun 2017 10:32:33 +0000 > From: [email protected] > To: [email protected], [email protected] > Subject: Re: [CF-metadata] Fw: Standard names for mean sea level change > > Dear Jonathan and Roy, > > Thank you for getting back to me again. Just to recap, we have agreed on the > following new definition for mean sea level: > ' "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.' > In the case of names for changes in mean_sea_level we would add the > additional sentence 'Zero mean sea level change is an arbitrary level.' > > With the inclusion of this definition I think we have now agreed the three > new names: > thermosteric_change_in_mean_sea_level (m) > halosteric_change_in_mean_sea_level (m) > steric_change_in_mean_sea_level (m). > These are accepted for publication in the standard name table and will be > added in today's update. (The new version of the table will be published on > the CF website tomorrow). > > The following eight aliases for existing names are also accepted and will be > included in today's update. > sea_floor_depth_below_sea_level -> sea_floor_depth_below_mean_sea_level > sea_surface_height_above_sea_level -> sea_surface_height_above_mean_sea_level > surface_geostrophic_eastward_sea_water_velocity_assuming_sea_level_for_geoid > -> > surface_geostrophic_eastward_sea_water_velocity_assuming_mean_sea_level_for_geoid > surface_geostrophic_northward_sea_water_velocity_assuming_sea_level_for_geoid > -> > surface_geostrophic_northward_sea_water_velocity_assuming_mean_sea_level_for_geoid > surface_geostrophic_sea_water_x_velocity_assuming_sea_level_for_geoid -> > surface_geostrophic_sea_water_x_velocity_assuming_mean_sea_level_for_geoid > surface_geostrophic_sea_water_y_velocity_assuming_sea_level_for_geoid -> > surface_geostrophic_sea_water_y_velocity_assuming_mean_sea_level_for_geoid > tendency_of_sea_surface_height_above_sea_level -> > tendency_of_sea_surface_height_above_mean_sea_level > air_pressure_at_sea_level -> air_pressure_at_mean_sea_level > The definitions will all be amended to include the new definition of mean sea > level. > > The six existing names for global average sea level change will remain as > follows: > global_average_sea_level_change > tendency_of_global_average_sea_level_change > phase_of_global_average_sea_level_change > amplitude_of_global_average_sea_level_change > global_average_steric_sea_level_change > global_average_thermosteric_sea_level_change. > We have now settled on the following definition of global average sea level > change: > 'Global average sea level change quantifies the change in volume of the world > ocean, and is not calculated necessarily by considering local changes in mean > sea level.' I agree that > is better than my original suggestion. We can put it at the end of the > definitions, rather than the beginning. To make it read a bit better > alongside the existing text I've tweaked it slightly (my changes are in > capitals): > global_average_sea_level_change > 'Global average sea level change is due to change in volume of the water in > the ocean, caused by mass and/or density change, or to change in the volume > of the ocean basins, caused by tectonics etc. It is sometimes called > "eustatic", which is a term that also has other definitions. It differs from > the change in the global average sea surface height relative to the centre of > the Earth by the global average vertical movement of the ocean floor. Zero > sea level change is an arbitrary level. BECAUSE global average sea level > change quantifies the change in volume of the world ocean, IT is not > calculated necessarily by considering local changes in mean sea level.' > > The other definitions would be amended similarly. Is this okay? > > 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. > > > From: CF-metadata [mailto:[email protected]] On Behalf Of > Lowry, Roy K. > Sent: 23 June 2017 18:21 > To: [email protected] > Subject: [CF-metadata] Fw: Standard names for mean sea level change > > > > 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: Lowry, Roy K. > Sent: 23 June 2017 18:19 > To: Jonathan Gregory > Subject: Re: [CF-metadata] Standard names for mean sea level change > > Thanks Jonathan, > > Think I can live with that. > > 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 Jonathan > Gregory <[email protected]> > Sent: 23 June 2017 13:09 > To: [email protected] > Subject: Re: [CF-metadata] Standard names for mean sea level change > > Or better > > Global average sea level change quantifies the change in volume of the world > ocean, and is not calculated necessarily by considering local changes in mean > sea level. > > J > > ----- Forwarded message from Jonathan Gregory <[email protected]> > ----- > > > Date: Fri, 23 Jun 2017 12:11:32 +0100 > > From: Jonathan Gregory <[email protected]> > > To: [email protected] > > Subject: Re: [CF-metadata] Standard names for mean sea level change > > User-Agent: Mutt/1.5.21 (2010-09-15) > > > > Dear Roy > > > > Not quite, because it could be "understood" as that - but it's not > > necessary. > > > > Global average sea level change quantifies the volume of the world ocean, > > and > > is not calculated necessarily by considering local changes in mean sea > > level. > > > > Best wishes > > > > Jonathan > > > > ----- Forwarded message from "Lowry, Roy K." <[email protected]> ----- > > > > > Date: Fri, 23 Jun 2017 08:01:01 +0000 > > > From: "Lowry, Roy K." <[email protected]> > > > To: Jonathan Gregory <[email protected]>, > > > "[email protected]" > > > <[email protected]> > > > Subject: Re: [CF-metadata] Standard names for mean sea level change > > > > > > Dear Jonathan, > > > > > > > > > Would the following changes (in bold) to the caveat make you more > > > comfortable? > > > > > > > > > Global average sea level change is a calculated parameter and should NOT > > > be understood as the global spatial mean of local changes in observed > > > mean sea level! > > > > > > > > > I have no strong feelings about the position of the caveat in the > > > definition. > > > > > > > > > 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 > > > Jonathan Gregory <[email protected]> > > > Sent: 22 June 2017 18:12 > > > To: [email protected] > > > Subject: Re: [CF-metadata] Standard names for mean sea level change > > > > > > Dear Alison > > > > > > I agree with all you say below, except that I think the WARNING is a bit > > > too > > > severe. :-) I would suggest putting it a bit later in the definition. > > > Because > > > global average sea level change refers to the volume of the global ocean, > > > it > > > does not *have* to be calculated as the mean of local sea level change. > > > For > > > example, for the part of GMSLR which is due to adding water to the ocean > > > from > > > glaciers and ice-sheets, etc. (I'm not proposing a standard name for this > > > just > > > now, though we might need one) you do not need to calculate the effect > > > that > > > would have on local sea level, and from that the global mean. In fact the > > > local > > > MSL change is rather hard to calculate, because it involves the > > > propagation of > > > salinity change within the ocean, changes in ocean circulation, and the > > > effect > > > of the mass redistribution upon the geoid and the solid Earth. But none > > > of that > > > makes a difference to the global mean - it's just a redistribution. For > > > the > > > global mean, you just divide the volume of water added by the surface > > > area of > > > the world ocean - easy! However, you *could* go through all the > > > complexity, and > > > then average it out again. It would not be incorrect to do so. > > > > > > Best wishes > > > > > > Jonathan > > > > > > ----- Forwarded message from [email protected] ----- > > > > > > > Date: Thu, 22 Jun 2017 11:49:35 +0000 > > > > From: [email protected] > > > > To: [email protected], [email protected], [email protected] > > > > Subject: RE: [CF-metadata] Standard names for mean sea level change > > > > > > > > Dear Jonathan and Roy, > > > > > > > > Many thanks for your replies to this thread. Apologies, Roy, for > > > > missing your previous explanation about mean sea level in the thread > > > > about standard names for trac ticket 143. It seems that both > > > > discussions are converging on the same view that we should explicitly > > > > say 'mean_sea_level' in standard names where that is really the > > > > intention, rather than confining it to the definition. Therefore, I > > > > think this change is agreed for both existing and new names. > > > > > > > > In this thread we seem to have reached agreement that the general > > > > definition of mean_sea_level should be: > > > > ' "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.' In the case of names for either local or global mean > > > > changes in mean_sea_level we would add the additional sentence 'Zero > > > > mean sea level change is an arbitrary level.' > > > > > > > > For Jonathan's three newly proposed names in this thread, I think this > > > > leaves us with: > > > > > > > > thermosteric_change_in_mean_sea_level (m) > > > > 'Thermosteric sea level change is the part caused by change in sea > > > > water density due to change in temperature i.e. thermal expansion. > > > > "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. Zero mean sea level change is an arbitrary level. The > > > > sum of the quantities with standard names > > > > thermosteric_change_in_mean_sea_level and > > > > halosteric_change_in_mean_sea_level has the standard name > > > > steric_change_in_mean_sea_level.' > > > > > > > > halosteric_change_in_mean_sea_level (m) > > > > 'Halosteric sea level change is the part caused by change in sea water > > > > density due to change in salinity. "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. Zero mean sea level change > > > > is an arbitrary level. The sum of the quantities with standard names > > > > thermosteric_change_in_mean_sea_level and > > > > halosteric_change_in_mean_sea_level has the standard name > > > > steric_change_in_mean_sea_level.' > > > > > > > > steric_change_in_mean_sea_level (m) > > > > 'Steric sea level change is caused by changes in sea water density due > > > > to changes in temperature (thermosteric) and salinity (halosteric). > > > > "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. Zero mean sea level change is an arbitrary level. The > > > > sum of the quantities with standard names > > > > thermosteric_change_in_mean_sea_level and > > > > halosteric_change_in_mean_sea_level has the standard name > > > > steric_change_in_mean_sea_level.' > > > > > > > > Okay? > > > > > > > > The change to using mean_sea_level, rather than simply sea_level means > > > > that the following aliases need to be created: > > > > > > > > sea_floor_depth_below_sea_level -> sea_floor_depth_below_mean_sea_level > > > > > > > > sea_surface_height_above_sea_level -> > > > > sea_surface_height_above_mean_sea_level > > > > > > > > surface_geostrophic_eastward_sea_water_velocity_assuming_sea_level_for_geoid > > > > -> > > > > surface_geostrophic_eastward_sea_water_velocity_assuming_mean_sea_level_for_geoid > > > > > > > > surface_geostrophic_northward_sea_water_velocity_assuming_sea_level_for_geoid > > > > -> > > > > surface_geostrophic_northward_sea_water_velocity_assuming_mean_sea_level_for_geoid > > > > > > > > surface_geostrophic_sea_water_x_velocity_assuming_sea_level_for_geoid > > > > -> > > > > surface_geostrophic_sea_water_x_velocity_assuming_mean_sea_level_for_geoid > > > > > > > > surface_geostrophic_sea_water_y_velocity_assuming_sea_level_for_geoid > > > > -> > > > > surface_geostrophic_sea_water_y_velocity_assuming_mean_sea_level_for_geoid > > > > > > > > tendency_of_sea_surface_height_above_sea_level -> > > > > tendency_of_sea_surface_height_above_mean_sea_level > > > > > > > > air_pressure_at_sea_level -> air_pressure_at_mean_sea_level > > > > > > > > For all of these names the definitions would be unchanged except we > > > > would replace 'sea_level means mean sea level, which is close to the > > > > geoid in sea areas' with '"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.' Okay? > > > > > > > > Roy was concerned about the syntax used in the existing names: > > > > global_average_steric_sea_level_change > > > > global_average_sea_level_change > > > > global_average_thermosteric_sea_level_change > > > > phase_of_global_average_sea_level_change > > > > tendency_of_global_average_sea_level_change > > > > amplitude_of_global_average_sea_level_change > > > > Jonathan has pointed out that 'average' here refers to a global (i.e > > > > spatial) average/mean which is distinct from the time mean used to > > > > calculate local mean_sea_level. I'm leaning towards keeping > > > > 'global_average' in the names themselves. I think the use of different > > > > terminology helps to underline Jonathan's point that > > > > global_average_thermosteric_sea_level_change is not simply the global > > > > mean of thermosteric_change_in_mean_sea_level, which is very important > > > > to interpreting these names correctly. Certainly I think the order of > > > > the syntax is correct for these quantities (the mean/average definitely > > > > belongs with the 'global'). However, I do think there is room to > > > > improve the defintions. In fact, I would go so far as to say 'N.B. > > > > Global average sea level change should NOT be understood as the global > > > > spatial mean of local changes in mean sea level!' should be the first > > > > sentence in all the definitions. > > > > > > > > Currently the definition of global_average_sea_level_change reads: > > > > 'Global average sea level change is due to change in volume of the > > > > water in the ocean, caused by mass and/or density change, or to change > > > > in the volume of the ocean basins, caused by tectonics etc. It is > > > > sometimes called "eustatic", which is a term that also has other > > > > definitions. It differs from the change in the global average sea > > > > surface height relative to the centre of the Earth by the global > > > > average vertical movement of the ocean floor. Zero sea level change is > > > > an arbitrary level.' > > > > > > > > With the addition of the health warning above, I think this text is a > > > > good basis for use in all the names. I suggest amended definitions as > > > > listed below, in which I have also tried to make the wording describing > > > > steric changes match as closely as possible that used in Jonathan's > > > > three new names. > > > > > > > > global_average_sea_level_change (m) > > > > 'N.B. Global average sea level change should NOT be understood as the > > > > global spatial mean of local changes in mean sea level! Global average > > > > sea level change is due to change in volume of the water in the ocean, > > > > caused by mass and/or density change, or to change in the volume of the > > > > ocean basins, caused by tectonics etc. It is sometimes called > > > > "eustatic", which is a term that also has other definitions. It differs > > > > from the change in the global average sea surface height relative to > > > > the centre of the Earth by the global average vertical movement of the > > > > ocean floor. Zero sea level change is an arbitrary level.' > > > > > > > > tendency_of_global_average_sea_level_change (m year-1) > > > > 'N.B. Global average sea level change should NOT be understood as the > > > > global spatial mean of local changes in mean sea level! Global average > > > > sea level change is due to change in volume of the water in the ocean, > > > > caused by mass and/or density change, or to change in the volume of the > > > > ocean basins, caused by tectonics etc. It is sometimes called > > > > "eustatic", which is a term that also has other definitions. It differs > > > > from the change in the global average sea surface height relative to > > > > the centre of the Earth by the global average vertical movement of the > > > > ocean floor. Zero sea level change is an arbitrary level. > > > > "tendency_of_X" means derivative of X with respect to time.' > > > > > > > > amplitude_of_global_average_sea_level_change > > > > 'N.B. Global average sea level change should NOT be understood as the > > > > global spatial mean of local changes in mean sea level! Global average > > > > sea level change is due to change in volume of the water in the ocean, > > > > caused by mass and/or density change, or to change in the volume of the > > > > ocean basins, caused by tectonics etc. It is sometimes called > > > > "eustatic", which is a term that also has other definitions. It differs > > > > from the change in the global average sea surface height relative to > > > > the centre of the Earth by the global average vertical movement of the > > > > ocean floor. Zero sea level change is an arbitrary level. Amplitude is > > > > the magnitude of a wave modelled by a sinusoidal function. A coordinate > > > > variable of harmonic_period should be used to specify the period of the > > > > sinusoidal wave.' > > > > > > > > phase_of_global_average_sea_level_change (degree) > > > > 'N.B. Global average sea level change should NOT be understood as the > > > > global spatial mean of local changes in mean sea level! Global average > > > > sea level change is due to change in volume of the water in the ocean, > > > > caused by mass and/or density change, or to change in the volume of the > > > > ocean basins, caused by tectonics etc. It is sometimes called > > > > "eustatic", which is a term that also has other definitions. It differs > > > > from the change in the global average sea surface height relative to > > > > the centre of the Earth by the global average vertical movement of the > > > > ocean floor. Zero sea level change is an arbitrary level. Phase is the > > > > initial angle of a wave modelled by a sinusoidal function. A coordinate > > > > variable of harmonic_period should be used to specify the period of the > > > > sinusoidal wave.' > > > > > > > > global_average_steric_sea_level_change (m) > > > > 'N.B. Global average sea level change should NOT be understood as the > > > > global spatial mean of local changes in mean sea level! Global average > > > > steric sea level change is caused by changes in sea water density due > > > > to changes in temperature (thermosteric) and salinity (halosteric). > > > > This changes the volume of water in the ocean. Zero sea level change is > > > > an arbitrary level.' > > > > > > > > global_average_thermosteric_sea_level_change (m) > > > > 'N.B. Global average sea level change should NOT be understood as the > > > > global spatial mean of local changes in mean sea level! Global average > > > > thermosteric sea level change is the part caused by change in sea water > > > > density due to change in temperature i.e. thermal expansion. This > > > > changes the volume of water in the ocean. Zero sea level change is an > > > > arbitrary level.' > > > > > > > > What do you think of these? > > > > > > > > I hope I've managed to cover all the points raised in this discussion :) > > > > > > > > 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. > > > > > > > > > > > > From: CF-metadata [mailto:[email protected]] On Behalf > > > > Of Lowry, Roy K. > > > > Sent: 14 June 2017 17:40 > > > > To: Jonathan Gregory; [email protected] > > > > Subject: Re: [CF-metadata] Standard names for mean sea level change > > > > > > > > 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 [email protected]. Please also use this e-mail if your > > > > requirement is urgent. > > > > > > > > ________________________________________ > > > > From: CF-metadata <[email protected]> on behalf of > > > > Jonathan Gregory <[email protected]> > > > > Sent: 14 June 2017 16:58 > > > > To: [email protected] > > > > 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 > > > > [email protected] > > > > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > > > > CF-metadata Info Page - mailman.cgd.ucar.edu Mailing Lists > > > > 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. > > > > ________________________________________ > > > > > > ----- End forwarded message ----- > > > _______________________________________________ > > > CF-metadata mailing list > > > [email protected] > > > 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. > > > ________________________________ > > > > ----- End forwarded message ----- > > _______________________________________________ > > 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 > ________________________________________ > 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 ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
