Hi Alison,

Fine with me too.


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: 26 June 2017 13:39
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] Fw: Standard names for mean sea level change

Dear Alison

Thanks very much for this. I think that is all fine.

Best wishes

Jonathan

----- Forwarded message from alison.pamm...@stfc.ac.uk -----

> Date: Mon, 26 Jun 2017 10:32:33 +0000
> From: alison.pamm...@stfc.ac.uk
> To: r...@bodc.ac.uk, cf-metadata@cgd.ucar.edu
> 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: 
> alison.pamm...@stfc.ac.uk
> STFC Rutherford Appleton Laboratory
> R25, 2.22
> Harwell Campus, Didcot, OX11 0QX, U.K.
>
>
> From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
> Lowry, Roy K.
> Sent: 23 June 2017 18:21
> To: cf-metadata@cgd.ucar.edu
> 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 enquir...@bodc.ac.uk. 
> 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 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: 23 June 2017 13:09
> To: cf-metadata@cgd.ucar.edu
> 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 <j.m.greg...@reading.ac.uk> 
> -----
>
> > Date: Fri, 23 Jun 2017 12:11:32 +0100
> > From: Jonathan Gregory <j.m.greg...@reading.ac.uk>
> > To: cf-metadata@cgd.ucar.edu
> > 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." <r...@bodc.ac.uk> -----
> >
> > > Date: Fri, 23 Jun 2017 08:01:01 +0000
> > > From: "Lowry, Roy K." <r...@bodc.ac.uk>
> > > To: Jonathan Gregory <j.m.greg...@reading.ac.uk>, 
> > > "cf-metadata@cgd.ucar.edu"
> > >      <cf-metadata@cgd.ucar.edu>
> > > 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 
> > > 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: 22 June 2017 18:12
> > > To: cf-metadata@cgd.ucar.edu
> > > 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 alison.pamm...@stfc.ac.uk -----
> > >
> > > > Date: Thu, 22 Jun 2017 11:49:35 +0000
> > > > From: alison.pamm...@stfc.ac.uk
> > > > To: r...@bodc.ac.uk, j.m.greg...@reading.ac.uk, cf-metadata@cgd.ucar.edu
> > > > 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: 
> > > > alison.pamm...@stfc.ac.uk
> > > > STFC Rutherford Appleton Laboratory
> > > > R25, 2.22
> > > > Harwell Campus, Didcot, OX11 0QX, U.K.
> > > >
> > > >
> > > > From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf 
> > > > Of Lowry, Roy K.
> > > > Sent: 14 June 2017 17:40
> > > > To: Jonathan Gregory; cf-metadata@cgd.ucar.edu
> > > > 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 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
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