Re: [CF-metadata] proposed new standard name for storm surge residual

[Alison Pamment - UKRI STFC]

Dear Andy, Jonathan and Roy,

Apologies for the delay in reviewing this thread and thank you all for the 
considerable effort that clearly went into agreeing these names.

The discussion reached consensus in May, so all that remains is to accept the 
following three names for publication in the standard name table:

tidal_sea_surface_height_above_lowest_astronomical_tide (m)
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "Lowest astronomical tide" 
describes a local vertical reference based on the lowest water level that can 
be expected to occur under average meteorological conditions and under any 
combination of astronomical conditions. The tidal component of sea surface 
height describes the predicted variability of the sea surface due to astronomic 
forcing (chiefly lunar and solar cycles) and shallow water resonance of tidal 
components; for example as generated based on harmonic analysis, or resulting 
from the application of harmonic tidal series as boundary conditions to a 
numerical tidal model.

non_tidal_elevation_of_sea_surface_height (m)
"Sea surface height" is a time-varying quantity. "Non_tidal_elevation" 
describes the contribution to sea surface height variability made by processes 
other than astronomic forcing of the ocean and shallow water resonance of tidal 
components. These processes include storm surge (due to a combination of 
meteorological forcing of the ocean and interaction between the generated surge 
and tides), effects of surface ocean waves, and seasonal and climatic variation 
in ocean density and circulation. The contribution made by each process varies 
according to the averaging time of the variable as described by the "bounds" 
and "cell_methods" attributes.
 
tidal_sea_surface_height_above_mean_sea_level (m)
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "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. The tidal component of sea surface 
height describes the predicted variability of the sea surface due to astronomic 
forcing (chiefly lunar and solar cycles) and shallow water resonance of tidal 
components; for example as generated based on harmonic analysis, or resulting 
from the application of harmonic tidal series as boundary conditions to a 
numerical tidal model.

These names will be added in the next update, planned for 6th August.

Best wishes,
Alison


From: CF-metadata  on behalf of Jonathan 
Gregory 
Sent: 10 May 2018 16:32:30
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] Fwd: Re: proposed new standard name for storm surge 
residual 
 
Dear Andy

This looks good to me. Thanks for your persistence.

Best wishes

Jonathan

- Forwarded message from "Saulter, Andrew" 
 -

> Date: Thu, 10 May 2018 09:31:11 +0000
> From: "Saulter, Andrew" 
> To: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] proposed new standard name for storm surge
>    residual
> 
> Dear Jonathon,
> 
> Only did half a job with the LAT yesterday morning - sorry! The updated set 
> of names/descriptions is below:
> 
> tidal_sea_surface_height_above_lowest_astronomical_tide
> Units: m
> "Sea surface height" is a time-varying quantity. "Height_above_X" means the 
> vertical distance above the named surface X. "Lowest astronomical tide" 
> describes a local vertical reference based on the lowest water level that can 
> be expected to occur under average meteorological conditions and under any 
> combination of astronomical conditions. The tidal component of sea surface 
> height describes the predicted variability of the sea surface due to 
> astronomic forcing (chiefly lunar and solar cycles) and shallow water 
> resonance of tidal components; for example as generated based on harmonic 
> analysis, or resulting from the application of harmonic tidal series as 
> boundary conditions to a numerical tidal model.
> 
> non_tidal_elevation_of_sea_surface_height
> Units: m
> "Sea surface height" is a time-varying quantity. "Non_tidal_elevation" 
> describes the contribution to sea surface height variability made by 
> processes other than astronomic forcing of the ocean and shallow water 
> resonance of tidal components. These processes include storm surge (due to a 
> combination of meteorological forcing of the ocean and interaction between 
> the generated surge and tides), effects of surface ocean waves, and seasonal 
> and climatic variation in ocean density and circulation. The contribution 
> made by ea

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Dear Jonathon,

Only did half a job with the LAT yesterday morning - sorry! The updated set of 
names/descriptions is below:

tidal_sea_surface_height_above_lowest_astronomical_tide
Units: m
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "Lowest astronomical tide" 
describes a local vertical reference based on the lowest water level that can 
be expected to occur under average meteorological conditions and under any 
combination of astronomical conditions. The tidal component of sea surface 
height describes the predicted variability of the sea surface due to astronomic 
forcing (chiefly lunar and solar cycles) and shallow water resonance of tidal 
components; for example as generated based on harmonic analysis, or resulting 
from the application of harmonic tidal series as boundary conditions to a 
numerical tidal model.

non_tidal_elevation_of_sea_surface_height
Units: m
"Sea surface height" is a time-varying quantity. "Non_tidal_elevation" 
describes the contribution to sea surface height variability made by processes 
other than astronomic forcing of the ocean and shallow water resonance of tidal 
components. These processes include storm surge (due to a combination of 
meteorological forcing of the ocean and interaction between the generated surge 
and tides), effects of surface ocean waves, and seasonal and climatic variation 
in ocean density and circulation. The contribution made by each process varies 
according to the averaging time of the variable as described by the "bounds" 
and "cell_methods" attributes.

For completeness the unchanged new name from yesterday is:

tidal_sea_surface_height_above_mean_sea_level
Units: m
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "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. The tidal component of sea surface 
height describes the predicted variability of the sea surface due to astronomic 
forcing (chiefly lunar and solar cycles) and shallow water resonance of tidal 
components; for example as generated based on harmonic analysis, or resulting 
from the application of harmonic tidal series as boundary conditions to a 
numerical tidal model.

Many thanks
Andy


-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 09 May 2018 15:46
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

> tidal_sea_surface_height_above_lowest_astronomical_tide
> Units: m
> "Sea surface height" is a time-varying quantity. "Height_above_X" means the 
> vertical distance above the named surface X. "Chart datum" describes a local 
> vertical reference from which depths displayed on a nautical chart are 
> measured and which differs from mean sea level. For example, chart datum 
> based on "lowest astronomical tide" or "mean lower low water". The tidal 
> component of sea surface height describes the predicted variability of the 
> sea surface due to astronomic forcing (chiefly lunar and solar cycles) and 
> shallow water resonance of tidal components; for example as generated based 
> on harmonic analysis, or resulting from the application of harmonic tidal 
> series as boundary conditions to a numerical tidal model.

The definition above needs revision (simplification in fact) to remove "chart 
datum".

> non_tidal_elevation_of_sea_surface_height
> Units: m
> "Sea surface height" is a time-varying quantity. "Non_tidal_elevation" 
> describes the contribution to sea surface height variability made by 
> processes other than astronomic forcing of the ocean and shallow water 
> resonance of tidal components. These processes include storm surge (due to a 
> combination of meteorological forcing of the ocean and interaction between 
> the generated surge and tides), background ocean circulation, steric changes 
> in the water column and, at higher frequencies, effects of surface ocean 
> waves. The contribution made by these processes varies according to the 
> averaging time of the variable as described by the " bounds" and 
> "cell_methods" attributes.

I suggest, "These processes include storm surge (due to a combination of 
meteorological forcing of the ocean and interaction between the generated surge 
and tides), effects of surface ocean waves, and seasonal and climatic variation 
in ocean density and circulation."

Best wishes

Jonathan
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Re: [CF-metadata] proposed new standard name for storm surge residual

[Jonathan Gregory]

Dear Andy

> tidal_sea_surface_height_above_lowest_astronomical_tide
> Units: m
> "Sea surface height" is a time-varying quantity. "Height_above_X" means the 
> vertical distance above the named surface X. "Chart datum" describes a local 
> vertical reference from which depths displayed on a nautical chart are 
> measured and which differs from mean sea level. For example, chart datum 
> based on "lowest astronomical tide" or "mean lower low water". The tidal 
> component of sea surface height describes the predicted variability of the 
> sea surface due to astronomic forcing (chiefly lunar and solar cycles) and 
> shallow water resonance of tidal components; for example as generated based 
> on harmonic analysis, or resulting from the application of harmonic tidal 
> series as boundary conditions to a numerical tidal model.

The definition above needs revision (simplification in fact) to remove "chart
datum".

> non_tidal_elevation_of_sea_surface_height
> Units: m
> "Sea surface height" is a time-varying quantity. "Non_tidal_elevation" 
> describes the contribution to sea surface height variability made by 
> processes other than astronomic forcing of the ocean and shallow water 
> resonance of tidal components. These processes include storm surge (due to a 
> combination of meteorological forcing of the ocean and interaction between 
> the generated surge and tides), background ocean circulation, steric changes 
> in the water column and, at higher frequencies, effects of surface ocean 
> waves. The contribution made by these processes varies according to the 
> averaging time of the variable as described by the " bounds" and 
> "cell_methods" attributes.

I suggest, "These processes include storm surge (due to a combination of 
meteorological forcing of the ocean and interaction between the generated surge 
and tides), effects of surface ocean waves, and seasonal and climatic variation 
in ocean density and circulation."

Best wishes

Jonathan
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CF-metadata@cgd.ucar.edu
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Thanks Roy, Jonathon,

Going for the more specific LAT as a vertical datum is fine by me. So, based on 
that we have the below (Jonathon, I have also made an amendment to the 
non_tidal_elevation description to try and reflect the 'dynamic' contribution 
to the ocean a bit better):

tidal_sea_surface_height_above_mean_sea_level
Units: m
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "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. The tidal component of sea surface 
height describes the predicted variability of the sea surface due to astronomic 
forcing (chiefly lunar and solar cycles) and shallow water resonance of tidal 
components; for example as generated based on harmonic analysis, or resulting 
from the application of harmonic tidal series as boundary conditions to a 
numerical tidal model.

tidal_sea_surface_height_above_lowest_astronomical_tide
Units: m
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "Chart datum" describes a local 
vertical reference from which depths displayed on a nautical chart are measured 
and which differs from mean sea level. For example, chart datum based on 
"lowest astronomical tide" or "mean lower low water". The tidal component of 
sea surface height describes the predicted variability of the sea surface due 
to astronomic forcing (chiefly lunar and solar cycles) and shallow water 
resonance of tidal components; for example as generated based on harmonic 
analysis, or resulting from the application of harmonic tidal series as 
boundary conditions to a numerical tidal model.

non_tidal_elevation_of_sea_surface_height
Units: m
"Sea surface height" is a time-varying quantity. "Non_tidal_elevation" 
describes the contribution to sea surface height variability made by processes 
other than astronomic forcing of the ocean and shallow water resonance of tidal 
components. These processes include storm surge (due to a combination of 
meteorological forcing of the ocean and interaction between the generated surge 
and tides), background ocean circulation, steric changes in the water column 
and, at higher frequencies, effects of surface ocean waves. The contribution 
made by these processes varies according to the averaging time of the variable 
as described by the " bounds" and "cell_methods" attributes.

Cheers
Andy


From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of Lowry, 
Roy K.
Sent: 08 May 2018 16:04
To: Gregory, Jonathan ; cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual


Dear Andy,



I agree with Jonathan that specifically referencing LAT in the Standard Name 
would be better. In the UK sea level community there is a tendency to use the 
term 'chart datum' when what is really meant is 'Admiralty Chart Datum', which 
is defined as LAT.  Some other navies (e.g. Australia) use LAT as chart datum, 
but others do not. Therefore on a global scale 'chart datum' can have many 
meanings.



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<mailto:enquir...@bodc.ac.uk>. Please also use this e-mail 
if your requirement is urgent.


From: CF-metadata 
mailto:cf-metadata-boun...@cgd.ucar.edu>> on 
behalf of Jonathan Gregory 
mailto:j.m.greg...@reading.ac.uk>>
Sent: 08 May 2018 15:34
To: cf-metadata@cgd.ucar.edu<mailto:cf-metadata@cgd.ucar.edu>
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for this, and to Roy for support. I agree, I think we've pretty much
worked out what we mean now.

Instead of chart_datum I would prefer that we had standard names mentioning
the specific datums you want e.g. lowest_astronomical_tide, because it is more
informative and reduces the need for other information. Or is there a need to
be vague about it?

We have a mechanism, viz grid_mapping, to identify datums more precisely. If
we can't do that currently for MSL we could extend the convention.

As well as steric changes, I think non-tidal includes ocean dynamics (on all
timescales). I think your definitions look right.

Best wishes

Jonathan

- Forwarded message from "Saulter, Andrew" 
mailto:andrew.saul...@metoffice.gov.uk>> -

> Date: Tue, 8 May 2018 08:08:13 +0000
> From: "Saulter, Andrew" 
> mailto:andrew.saul...@metoffice.gov.uk>>
> To: "cf-metadata

Re: [CF-metadata] proposed new standard name for storm surge residual

[Lowry, Roy K.]

Dear Andy,


I agree with Jonathan that specifically referencing LAT in the Standard Name 
would be better. In the UK sea level community there is a tendency to use the 
term 'chart datum' when what is really meant is 'Admiralty Chart Datum', which 
is defined as LAT.  Some other navies (e.g. Australia) use LAT as chart datum, 
but others do not. Therefore on a global scale 'chart datum' can have many 
meanings.


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  on behalf of Jonathan 
Gregory 
Sent: 08 May 2018 15:34
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for this, and to Roy for support. I agree, I think we've pretty much
worked out what we mean now.

Instead of chart_datum I would prefer that we had standard names mentioning
the specific datums you want e.g. lowest_astronomical_tide, because it is more
informative and reduces the need for other information. Or is there a need to
be vague about it?

We have a mechanism, viz grid_mapping, to identify datums more precisely. If
we can't do that currently for MSL we could extend the convention.

As well as steric changes, I think non-tidal includes ocean dynamics (on all
timescales). I think your definitions look right.

Best wishes

Jonathan

- Forwarded message from "Saulter, Andrew" 
 -

> Date: Tue, 8 May 2018 08:08:13 +
> From: "Saulter, Andrew" 
> To: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] proposed new standard name for storm surge
>residual
>
> Dear Jonathon,
>
> Thanks for all the constructive inputs - this feels like we are getting 
> somewhere :-)
>
> I'd be very happy with "non_tidal_elevation_of_sea_surface_height"; elevation 
> references positive when SSH is increased but also acknowledges suppression 
> of SSH with high pressure/negative surge; non-tidal gives us the very useful 
> catchall that there are various processes at play.
>
> Regards the tidal SSH, you are absolutely right about assumptions. Normally 
> the tidal predictions we would be using (either directly or as boundary 
> inputs to a model) would be derived from a harmonic analysis of data covering 
> a given averaging period (varies, but anything from a month as a minimum that 
> captures a single spring-neap cycle, to 19-odd years to capture a full set of 
> sun-moon variations that cause the very largest tides). It is generally 
> assumed that the averaging will cancel out many of the other ocean effects - 
> any errors where this hasn't happened correctly will manifest themselves in 
> the non_tidal part (which is why I'm comfortable that this name makes more 
> sense than surge for observed values).
>
> Being the wild optimist that I am, I've taken the below and tried to flesh it 
> out a bit for the tide and non-tidal variables we would have in our use 
> cases. Please let me know what you reckon - the descriptions might still need 
> some work?
>
>  tidal_sea_surface_height_above_mean_sea_level
> Units: m
> "Sea surface height" is a time-varying quantity. "Height_above_X" means the 
> vertical distance above the named surface X. "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. The tidal component of sea surface 
> height describes the predicted variability of the sea surface due to 
> astronomic forcing (chiefly lunar and solar cycles) and shallow water 
> resonance of tidal components; for example as generated based on harmonic 
> analysis, or resulting from the application of harmonic tidal series as 
> boundary conditions to a numerical tidal model.
>
> tidal_sea_surface_height_above_chart_datum
> Units: m
> "Sea surface height" is a time-varying quantity. "Height_above_X" means the 
> vertical distance above the named surface X. "Chart datum" describes a local 
> vertical reference from which depths displayed on a nautical chart are 
> measured and which differs from mean sea level. For example, chart datum 
> based on "lowest astronomical tide" or "mean lower low water". The tidal 
> component of sea surface height describes the predicted variability of the 
> sea surface due to astronomic forcing (chiefly lunar and solar cycles) and 
> shallow water resonance of tidal components; for example as gener

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

t; > > > > > > components, or resulting from the application of such components 
> > > > > > > as boundary conditions to a numerical tidal model.

-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 04 May 2018 19:40
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for this. I have few comments to add because our thoughts are pretty 
much the same, I'm glad to say.

I am a bit uncomfortable with the phrase "SSH due to X" anyway, because SSH has 
no meaning except wrt a datum, not in an absolute sense. The phrase "due to X"
aptly describes contributions to something which could be zero in an absolute 
sense, so you can add up all the contributions to get the whole.

SSH is a fairly precise geophysical quantity (the level of the interface 
between air and water) - although not quite precise! - but as you say, the 
value it takes depends on the meaning period. CF describes meaning periods with 
time-bounds, so that's no problem.

"Residual" is maybe slightly jargon. We could spell it out more plainly.
I would suggest

sea_surface_height_above_X = tidal_sea_surface_height_above_X + 
non_tidal_elevation_of_sea_surface_height

Sometimes sea surface elevation is a synonym of sea surface height, but I hope 
that "elevation of SSH" obviously means making SSH higher - does it to you?
Alternatively, "increase in SSH" might be better. I assume that this term must 
include the seasonal non-tidal variation in SSH (due to the seasonal cycle in 
ocean dynamics, density and mass).

I still have a query about the tidal SSH above X. It must include assumptions 
for all the other effects - a particular surface pressure, surface winds, ocean 
currents, etc. What are they? Perhaps they are all assumed to be annual mean 
climatological values.

Best wishes

Jonathan


- Forwarded message from "Saulter, Andrew" 
 -

> Date: Fri, 4 May 2018 08:15:00 +
> From: "Saulter, Andrew" 
> To: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] proposed new standard name for storm surge
>   residual
> 
> Dear Jonathon,
> 
> Thought I was so close... :-)
> 
> But concerned that I am missing something, so I could do with some 
> clarification before suggesting another iteration. So please can you comment 
> on the below.
> 
> The thing that I am failing to understand is the relationship between 
> sea_surface_height and the components that should make it up. So here is what 
> I think I know:
> 
> 1. sea_surface_height should always be related to some vertical datum (MSL, 
> geoid, arbitrary reference) in order to be useful. 
> 
> 2. sea_surface_height is a time-varying quantity so must be made up of 
> a whole load of components (tide, steric effects, surge, ocean waves) 
> - and the parameter name/description is vague enough that how we 
> define this ends up in the eye of the beholder a bit; so a climate 
> scientist working with deep ocean data might choose a long temporal 
> averaging period that reduces sea surface height variations to 
> seasonal and longer effects only, whilst I'd be using a 15 minute 
> averaging period with my estimates so will need to include tide and 
> surge
> 
> 3. at some point the sum of these components must include an offset (Z) that 
> makes sea_surface_height relative to its vertical datum. This is where the 
> problem seems to lie in our discussion so far. For my users the answer is 
> simple - the referencing is included in the tide values and all other 
> components are relative. For the model tide and MSL case this becomes 
> simplified as Z=0 and the tide rises and falls around this point, but for 
> lowest astronomic tide as a datum then we either need to consider Z as some 
> finite value or understand that the tide component will nearly always be 
> positive ('cos you don't get much lower than lowest astronomic tide).
> 
> 4. If you go with idea that tide is referenced against a datum, which 
> I is really what I need to do in order to give my users a 
> straightforward dataset, then this implies that tide values should 
> link to a specific sea_surface_height_above_X (i.e. I can't link a 
> tide referenced against LAT with an SSH referenced against MSL)
> 
> Its these last two points where 'due_to' implying a relative quantity is 
> messing with my mind. From our conversations, I get than sense that 'due_to' 
> really implies that any component process we define should be transferable 
> universally between different sea_surface_height_above_Xs, and that this is 
> because there is another value that defines 

Re: [CF-metadata] proposed new standard name for storm surge residual

[Jonathan Gregory]

Dear Andy

Thanks for this. I have few comments to add because our thoughts are pretty
much the same, I'm glad to say.

I am a bit uncomfortable with the phrase "SSH due to X" anyway, because SSH has
no meaning except wrt a datum, not in an absolute sense. The phrase "due to X"
aptly describes contributions to something which could be zero in an absolute
sense, so you can add up all the contributions to get the whole.

SSH is a fairly precise geophysical quantity (the level of the interface
between air and water) - although not quite precise! - but as you say, the
value it takes depends on the meaning period. CF describes meaning periods
with time-bounds, so that's no problem.

"Residual" is maybe slightly jargon. We could spell it out more plainly.
I would suggest

sea_surface_height_above_X = tidal_sea_surface_height_above_X + 
non_tidal_elevation_of_sea_surface_height

Sometimes sea surface elevation is a synonym of sea surface height, but I hope
that "elevation of SSH" obviously means making SSH higher - does it to you?
Alternatively, "increase in SSH" might be better. I assume that this term must
include the seasonal non-tidal variation in SSH (due to the seasonal cycle in
ocean dynamics, density and mass).

I still have a query about the tidal SSH above X. It must include assumptions
for all the other effects - a particular surface pressure, surface winds, ocean
currents, etc. What are they? Perhaps they are all assumed to be annual mean
climatological values.

Best wishes

Jonathan


- Forwarded message from "Saulter, Andrew" 
 -

> Date: Fri, 4 May 2018 08:15:00 +
> From: "Saulter, Andrew" 
> To: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] proposed new standard name for storm surge
>   residual
> 
> Dear Jonathon,
> 
> Thought I was so close... :-)
> 
> But concerned that I am missing something, so I could do with some 
> clarification before suggesting another iteration. So please can you comment 
> on the below.
> 
> The thing that I am failing to understand is the relationship between 
> sea_surface_height and the components that should make it up. So here is what 
> I think I know:
> 
> 1. sea_surface_height should always be related to some vertical datum (MSL, 
> geoid, arbitrary reference) in order to be useful. 
> 
> 2. sea_surface_height is a time-varying quantity so must be made up of a 
> whole load of components (tide, steric effects, surge, ocean waves) - and the 
> parameter name/description is vague enough that how we define this ends up in 
> the eye of the beholder a bit; so a climate scientist working with deep ocean 
> data might choose a long temporal averaging period that reduces sea surface 
> height variations to seasonal and longer effects only, whilst I'd be using a 
> 15 minute averaging period with my estimates so will need to include tide and 
> surge
> 
> 3. at some point the sum of these components must include an offset (Z) that 
> makes sea_surface_height relative to its vertical datum. This is where the 
> problem seems to lie in our discussion so far. For my users the answer is 
> simple - the referencing is included in the tide values and all other 
> components are relative. For the model tide and MSL case this becomes 
> simplified as Z=0 and the tide rises and falls around this point, but for 
> lowest astronomic tide as a datum then we either need to consider Z as some 
> finite value or understand that the tide component will nearly always be 
> positive ('cos you don't get much lower than lowest astronomic tide).
> 
> 4. If you go with idea that tide is referenced against a datum, which I is 
> really what I need to do in order to give my users a straightforward dataset, 
> then this implies that tide values should link to a specific 
> sea_surface_height_above_X (i.e. I can't link a tide referenced against LAT 
> with an SSH referenced against MSL)
> 
> Its these last two points where 'due_to' implying a relative quantity is 
> messing with my mind. From our conversations, I get than sense that 'due_to' 
> really implies that any component process we define should be transferable 
> universally between different sea_surface_height_above_Xs, and that this is 
> because there is another value that defines what Z is. For this to work for 
> tide and surge,  this should actually mean that 'due_to' implies 'relative to 
> MSL for any processes occurring on a higher frequency than the MSL 
> definition'?
> 
> If that is the case, then 'due_to' will work fine for surge (which is a 
> transferable quantity) but not for tide in the context I want to use it in. 
> So do we actually need something like:
> 
&g

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

eference

Yes.

> Then, as I think we've all agreed, 'due_to_surge', 'due_to_tide' are simply 
> relative quantities.

Yes, I agree, such a definition is possible, where due_to_X means the 
difference between SSH with X and SSH without X.

> for my surge model, which is referenced to mean sea level and has a tide and 
> surge part that I can decompose, I could generate variables with standard 
> names:
> 
> 1. sea_surface_height_above_mean_sea_level - the total
> 
> 2.sea_surface_height_due_to_tide - the tide part
> 
> 3. sea_surface_height_due_to_surge - the surge part

And you also said
> a summation of these quantities should lead us to a 
> 'sea_surface_height_above_X', but on their own they are generic.
That's not true here, is it? (2) + (3) is not equal to 1. There must be another 
term (Z, say) in the sum, for SSH above MSL when there is no tide and no surge.

(1) SSH above MSL = (Z) SSH above MSL with no tide and no surge
  + (2) SSH elevation due to tide + (3) SSH elevation due to surge.

Or maybe what the model produces is Z + 2 i.e. SSH above MSL if there is no 
surge? We could call that 
sea_surface_height_above_mean_sea_level_assuming_no_surge

Or maybe Z=0? That is what I suggested initially about MSL, in effect.

Which term contains the seasonal cycle of SSH?

> the reference_datum should a) be stipulated and b) have a way of being mapped 
> to the reference_ellipsoid we would use for the coordinate system. A) would 
> need a new descriptive variable, e.g. 'reference_datum_name'. B) already has 
> a precedent in 'water_surface_reference_datum_altitude' but actually using 
> the existing 'height_above_reference_ellipsoid' might be more appropriate 
> (basically I'm not sure if a 
> 'reference_datum_height_above_reference_ellipsoid' is necessary)?

I'm not too keen on the generic reference_datum, and feel it would be better to 
add names for the specific datums you use, if they are geophysical surfaces.
If they are arbitrary benchmarks, I agree that some way to name them is needed.

> Hopefully I'm not talking total nonsense.

Of course not. Sorry this is so hard.

Best wishes

Jonathan

> -Original Message-
> From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf 
> Of Jonathan Gregory
> Sent: 02 May 2018 14:27
> To: cf-metadata@cgd.ucar.edu
> Subject: [CF-metadata] proposed new standard name for storm surge 
> residual
> 
> Dear Andy
> 
> Thanks for your email. This is surprisingly mind-bending. Although MSL could 
> mean time-means on various periods, I believe that when we refer to it as a 
> surface in CF standard names we mean a very long-term mean, to get rid of all 
> variations. Of course, that's still not well-defined, because on very long 
> timescales other things change like climate and ocean basin bathymetry.
> 
> I don't think this is the point at issue. What I'm struggling with is whether 
> the elevation of the sea surface due to tide has a datum (MSL, reference 
> ellipsoid, geoid, etc.) or not. If, like "due to surge", it has no datum, it 
> means the difference between SSH with tide and without tide. What does 
> "without tide" mean, then? It could mean "with permanent tide but no 
> time-varying tide", for instance. If you include a datum you get something 
> like "elevation of sea surface above reference elliposid due to tide", but 
> I'm not sure what the attribution to tide means in that case. What's the 
> difference between this quantity and 
> sea_surface_height_above_reference_ellipsoid, which is already a standard 
> name? The difference would seem to be the part "due to tide". But that 
> returns us to the question of what "without the tide" means.
> 
> Best wishes
> 
> Jonathan
> 
> 
> 
> - Forwarded message from "Saulter, Andrew" 
>  -
> 
> > Date: Wed, 25 Apr 2018 07:08:01 +
> > From: "Saulter, Andrew" 
> > To: "cf-metadata@cgd.ucar.edu" 
> > Subject: Re: [CF-metadata] proposed new standard name for storm surge
> > residual
> > 
> > Thanks Jonathon,
> > 
> > From the below:
> > 
> > We use the term "sea" - agreed. "due_to_surge" has no need for a datum 
> > reference - agreed.
> > 
> > MSL implies no tide and no surge. I'd disagree with this; sea level at high 
> > frequency will comprise contributions from lots of different components and 
> > mean sea level is therefore a quantity where we have chosen to average 
> > these effects out as best as possible but they haven't gone away - for 
> > example a m

Re: [CF-metadata] proposed new standard name for storm surge residual

[Lowry, Roy K.]

Hi again,


Having read a bit more I see that 'surge'  is commonly used to cover the total 
forcing due to wind and pressure so ignore my previous comment!


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  on behalf of Lowry, Roy K. 

Sent: 03 May 2018 09:47
To: Saulter, Andrew; cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual


Hi Andy,


A thought that struck me as I read through your e-mail is that surges aren't 
the only meteorological forcing. Whilst in a model the non-tide contributions 
can be easily differentiated in observational data they cannot.


Would 'sea_surface_height_due_to_meteorological_forcing'  be a better to make 
the Standard Name appropriate to observational data as well? Or do you wish to 
clearly identify the forcing? If so, would it be a good idea to clearly state 
in the definition that surge is a variation in sea surface elevation due to 
variations in atmospheric pressure?


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  on behalf of Saulter, 
Andrew 
Sent: 03 May 2018 09:28
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Apologies; there were issues with the way my email formatted the last message - 
I've sorted this out below...

-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Saulter, Andrew
Sent: 03 May 2018 09:24
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Dear Jonathon,

Possibly, I have been over-thinking this! I went back to square one and looked 
at the family of 'sea_surface_height' variables again and read the phrasing as 
carefully as I could.

>From these:

'sea_surface_height' is a time-varying quantity - so implies a generic 
summation of components; in practise we determine what these are depending on 
our use and (should) reflect the choices underlying this in our metadata

'height_above_X' means the vertical distance above the named surface X - there 
are a whole set of these for 'sea_surface_height' ('above_geoid', 
'above_geopotential_datum', 'above_mean_sea_level') that set the vertical 
reference

Then, as I think we've all agreed, 'due_to_surge', 'due_to_tide' are simply 
relative quantities. In other words, a summation of these quantities should 
lead us to a 'sea_surface_height_above_X', but on their own they are generic.

Putting that lot together, what this should mean is that for my surge model, 
which is referenced to mean sea level and has a tide and surge part that I can 
decompose, I could generate variables with standard names:

1. sea_surface_height_above_mean_sea_level - the total

2.sea_surface_height_due_to_tide - the tide part

3. sea_surface_height_due_to_surge - the surge part

All good so far. The other example that I'm concerned about is a situation 
where the tide I'm using has been referenced to a datum which isn't necessarily 
the mean sea level or reference ellipsoid, e.g. Chart Datum or Lowest 
Astronomic Tide. In this case, I think the total water level and decomposition 
should comprise:

1. sea_surface_height_above_reference_datum (as per the existing 'water_height' 
example) - the total

2. sea_surface_height_due_to_tide - the tide part

3. sea_surface_height_due_to_surge - the surge part

These all work when it is clear that my 'due_to' components sum up to my 
'sea_surface_height_above' parameter, since that is where any datum reference 
gets applied. So, in an example where I've decided that the water level I'm 
predicting will be just fine if all I am doing is feeding in a tide prediction 
referenced to chart datum, then the CF name I use is 
'sea_surface_height_above_reference_datum' and not 
'sea_surface_height_due_to_tide' as it’s the overall level and not actually the 
components that I'm interested in. This was the source of my confusion...

The one addition to the above is that the reference_datum should a) be 
stipulated and b) have a way of being mapped to the reference_ellipsoid we 
would use for the coordinate system. A) would need a new descriptive va

Re: [CF-metadata] proposed new standard name for storm surge residual

[Lowry, Roy K.]

Hi Andy,


A thought that struck me as I read through your e-mail is that surges aren't 
the only meteorological forcing. Whilst in a model the non-tide contributions 
can be easily differentiated in observational data they cannot.


Would 'sea_surface_height_due_to_meteorological_forcing'  be a better to make 
the Standard Name appropriate to observational data as well? Or do you wish to 
clearly identify the forcing? If so, would it be a good idea to clearly state 
in the definition that surge is a variation in sea surface elevation due to 
variations in atmospheric pressure?


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  on behalf of Saulter, 
Andrew 
Sent: 03 May 2018 09:28
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Apologies; there were issues with the way my email formatted the last message - 
I've sorted this out below...

-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Saulter, Andrew
Sent: 03 May 2018 09:24
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Dear Jonathon,

Possibly, I have been over-thinking this! I went back to square one and looked 
at the family of 'sea_surface_height' variables again and read the phrasing as 
carefully as I could.

>From these:

'sea_surface_height' is a time-varying quantity - so implies a generic 
summation of components; in practise we determine what these are depending on 
our use and (should) reflect the choices underlying this in our metadata

'height_above_X' means the vertical distance above the named surface X - there 
are a whole set of these for 'sea_surface_height' ('above_geoid', 
'above_geopotential_datum', 'above_mean_sea_level') that set the vertical 
reference

Then, as I think we've all agreed, 'due_to_surge', 'due_to_tide' are simply 
relative quantities. In other words, a summation of these quantities should 
lead us to a 'sea_surface_height_above_X', but on their own they are generic.

Putting that lot together, what this should mean is that for my surge model, 
which is referenced to mean sea level and has a tide and surge part that I can 
decompose, I could generate variables with standard names:

1. sea_surface_height_above_mean_sea_level - the total

2.sea_surface_height_due_to_tide - the tide part

3. sea_surface_height_due_to_surge - the surge part

All good so far. The other example that I'm concerned about is a situation 
where the tide I'm using has been referenced to a datum which isn't necessarily 
the mean sea level or reference ellipsoid, e.g. Chart Datum or Lowest 
Astronomic Tide. In this case, I think the total water level and decomposition 
should comprise:

1. sea_surface_height_above_reference_datum (as per the existing 'water_height' 
example) - the total

2. sea_surface_height_due_to_tide - the tide part

3. sea_surface_height_due_to_surge - the surge part

These all work when it is clear that my 'due_to' components sum up to my 
'sea_surface_height_above' parameter, since that is where any datum reference 
gets applied. So, in an example where I've decided that the water level I'm 
predicting will be just fine if all I am doing is feeding in a tide prediction 
referenced to chart datum, then the CF name I use is 
'sea_surface_height_above_reference_datum' and not 
'sea_surface_height_due_to_tide' as it’s the overall level and not actually the 
components that I'm interested in. This was the source of my confusion...

The one addition to the above is that the reference_datum should a) be 
stipulated and b) have a way of being mapped to the reference_ellipsoid we 
would use for the coordinate system. A) would need a new descriptive variable, 
e.g. 'reference_datum_name'. B) already has a precedent in 
'water_surface_reference_datum_altitude' but actually using the existing 
'height_above_reference_ellipsoid' might be more appropriate (basically I'm not 
sure if a 'reference_datum_height_above_reference_ellipsoid' is necessary)?

Hopefully I'm not talking total nonsense.
Andy


-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 02 May 2018 14:27
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for your email. This is surprisingly mind-b

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Apologies; there were issues with the way my email formatted the last message - 
I've sorted this out below...

-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Saulter, Andrew
Sent: 03 May 2018 09:24
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Dear Jonathon,

Possibly, I have been over-thinking this! I went back to square one and looked 
at the family of 'sea_surface_height' variables again and read the phrasing as 
carefully as I could.

From these:

'sea_surface_height' is a time-varying quantity - so implies a generic 
summation of components; in practise we determine what these are depending on 
our use and (should) reflect the choices underlying this in our metadata

'height_above_X' means the vertical distance above the named surface X - there 
are a whole set of these for 'sea_surface_height' ('above_geoid', 
'above_geopotential_datum', 'above_mean_sea_level') that set the vertical 
reference

Then, as I think we've all agreed, 'due_to_surge', 'due_to_tide' are simply 
relative quantities. In other words, a summation of these quantities should 
lead us to a 'sea_surface_height_above_X', but on their own they are generic.

Putting that lot together, what this should mean is that for my surge model, 
which is referenced to mean sea level and has a tide and surge part that I can 
decompose, I could generate variables with standard names:

1. sea_surface_height_above_mean_sea_level - the total 

2.sea_surface_height_due_to_tide - the tide part 

3. sea_surface_height_due_to_surge - the surge part

All good so far. The other example that I'm concerned about is a situation 
where the tide I'm using has been referenced to a datum which isn't necessarily 
the mean sea level or reference ellipsoid, e.g. Chart Datum or Lowest 
Astronomic Tide. In this case, I think the total water level and decomposition 
should comprise:

1. sea_surface_height_above_reference_datum (as per the existing 'water_height' 
example) - the total 

2. sea_surface_height_due_to_tide - the tide part 

3. sea_surface_height_due_to_surge - the surge part

These all work when it is clear that my 'due_to' components sum up to my 
'sea_surface_height_above' parameter, since that is where any datum reference 
gets applied. So, in an example where I've decided that the water level I'm 
predicting will be just fine if all I am doing is feeding in a tide prediction 
referenced to chart datum, then the CF name I use is 
'sea_surface_height_above_reference_datum' and not 
'sea_surface_height_due_to_tide' as it’s the overall level and not actually the 
components that I'm interested in. This was the source of my confusion...

The one addition to the above is that the reference_datum should a) be 
stipulated and b) have a way of being mapped to the reference_ellipsoid we 
would use for the coordinate system. A) would need a new descriptive variable, 
e.g. 'reference_datum_name'. B) already has a precedent in 
'water_surface_reference_datum_altitude' but actually using the existing 
'height_above_reference_ellipsoid' might be more appropriate (basically I'm not 
sure if a 'reference_datum_height_above_reference_ellipsoid' is necessary)?

Hopefully I'm not talking total nonsense.
Andy


-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 02 May 2018 14:27
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for your email. This is surprisingly mind-bending. Although MSL could 
mean time-means on various periods, I believe that when we refer to it as a 
surface in CF standard names we mean a very long-term mean, to get rid of all 
variations. Of course, that's still not well-defined, because on very long 
timescales other things change like climate and ocean basin bathymetry.

I don't think this is the point at issue. What I'm struggling with is whether 
the elevation of the sea surface due to tide has a datum (MSL, reference 
ellipsoid, geoid, etc.) or not. If, like "due to surge", it has no datum, it 
means the difference between SSH with tide and without tide. What does "without 
tide" mean, then? It could mean "with permanent tide but no time-varying tide", 
for instance. If you include a datum you get something like "elevation of sea 
surface above reference elliposid due to tide", but I'm not sure what the 
attribution to tide means in that case. What's the difference between this 
quantity and sea_surface_height_above_reference_ellipsoid, which is already a 
standard name? The difference

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Dear Jonathon,

Possibly, I have been over-thinking this! I went back to square one and looked 
at the family of 'sea_surface_height' variables again and read the phrasing as 
carefully as I could.

From these:

'sea_surface_height' is a time-varying quantity - so implies a generic 
summation of components; in practise we determine what these are depending on 
our use and (should) reflect the choices underlying this in our metadata

'height_above_X' means the vertical distance above the named surface X - there 
are a whole set of these for 'sea_surface_height' ('above_geoid', 
'above_geopotential_datum', 'above_mean_sea_level') that set the vertical 
reference

Then, as I think we've all agreed, 'due_to_surge', 'due_to_tide' are simply 
relative quantities. In other words, a summation of these quantities should 
lead us to a 'sea_surface_height_above_X', but on their own they are generic.

Putting that lot together, what this should mean is that for my surge model, 
which is referenced to mean sea level and has a tide and surge part that I can 
decompose, I could generate variables with standard names:
sea_surface_height_above_mean_sea_level - the total
sea_surface_height_due_to_tide - the tide part
sea_surface_height_due_to_surge - the surge part

All good so far. The other example that I'm concerned about is a situation 
where the tide I'm using has been referenced to a datum which isn't necessarily 
the mean sea level or reference ellipsoid, e.g. Chart Datum or Lowest 
Astronomic Tide. In this case, I think the total water level and decomposition 
should comprise:
sea_surface_height_above_reference_datum (as per the existing 'water_height' 
example) - the total
sea_surface_height_due_to_tide - the tide part
sea_surface_height_due_to_surge - the surge part

These all work when it is clear that my 'due_to' components sum up to my 
'sea_surface_height_above' parameter, since that is where any datum reference 
gets applied. So, in an example where I've decided that the water level I'm 
predicting will be just fine if all I am doing is feeding in a tide prediction 
referenced to chart datum, then the CF name I use is 
'sea_surface_height_above_reference_datum' and not 
'sea_surface_height_due_to_tide' as it’s the overall level and not actually the 
components that I'm interested in. This was the source of my confusion...

The one addition to the above is that the reference_datum should a) be 
stipulated and b) have a way of being mapped to the reference_ellipsoid we 
would use for the coordinate system. A) would need a new descriptive variable, 
e.g. 'reference_datum_name'. B) already has a precedent in 
'water_surface_reference_datum_altitude' but actually using the existing 
'height_above_reference_ellipsoid' might be more appropriate (basically I'm not 
sure if a 'reference_datum_height_above_reference_ellipsoid' is necessary)?

Hopefully I'm not talking total nonsense.
Andy


-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 02 May 2018 14:27
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for your email. This is surprisingly mind-bending. Although MSL could 
mean time-means on various periods, I believe that when we refer to it as a 
surface in CF standard names we mean a very long-term mean, to get rid of all 
variations. Of course, that's still not well-defined, because on very long 
timescales other things change like climate and ocean basin bathymetry.

I don't think this is the point at issue. What I'm struggling with is whether 
the elevation of the sea surface due to tide has a datum (MSL, reference 
ellipsoid, geoid, etc.) or not. If, like "due to surge", it has no datum, it 
means the difference between SSH with tide and without tide. What does "without 
tide" mean, then? It could mean "with permanent tide but no time-varying tide", 
for instance. If you include a datum you get something like "elevation of sea 
surface above reference elliposid due to tide", but I'm not sure what the 
attribution to tide means in that case. What's the difference between this 
quantity and sea_surface_height_above_reference_ellipsoid, which is already a 
standard name? The difference would seem to be the part "due to tide". But that 
returns us to the question of what "without the tide" means.

Best wishes

Jonathan



- Forwarded message from "Saulter, Andrew" 
 -

> Date: Wed, 25 Apr 2018 07:08:01 +
> From: "Saulter, Andrew" 
> To: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] propose

Re: [CF-metadata] proposed new standard name for storm surge residual

[Lowry, Roy K.]

Dear Jonathan,


I'll leave it to Andy to explain 'without tide' from a modelling perspective - 
I can guess what they do but could be wrong. In NOC we measure and report the 
sea surface elevation relative to a datum - Lowest Astronomical Tide - but we 
then subtract the elevation relative to that datum predicted by a numerical 
model based solely on astronomical considerations to generate and additional 
parameter. This difference - due to meteorological forcings - is referred to as 
either the 'sea level residual' or the 'sea level without tide'.


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  on behalf of Jonathan 
Gregory 
Sent: 02 May 2018 14:27
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

Thanks for your email. This is surprisingly mind-bending. Although MSL could
mean time-means on various periods, I believe that when we refer to it as a
surface in CF standard names we mean a very long-term mean, to get rid of all
variations. Of course, that's still not well-defined, because on very long
timescales other things change like climate and ocean basin bathymetry.

I don't think this is the point at issue. What I'm struggling with is whether
the elevation of the sea surface due to tide has a datum (MSL, reference
ellipsoid, geoid, etc.) or not. If, like "due to surge", it has no datum, it
means the difference between SSH with tide and without tide. What does "without
tide" mean, then? It could mean "with permanent tide but no time-varying tide",
for instance. If you include a datum you get something like "elevation of
sea surface above reference elliposid due to tide", but I'm not sure what the
attribution to tide means in that case. What's the difference between this
quantity and sea_surface_height_above_reference_ellipsoid, which is already a
standard name? The difference would seem to be the part "due to tide". But that
returns us to the question of what "without the tide" means.

Best wishes

Jonathan



- Forwarded message from "Saulter, Andrew" 
 -

> Date: Wed, 25 Apr 2018 07:08:01 +
> From: "Saulter, Andrew" 
> To: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] proposed new standard name for storm surge
>residual
>
> Thanks Jonathon,
>
> From the below:
>
> We use the term "sea" - agreed. "due_to_surge" has no need for a datum 
> reference - agreed.
>
> MSL implies no tide and no surge. I'd disagree with this; sea level at high 
> frequency will comprise contributions from lots of different components and 
> mean sea level is therefore a quantity where we have chosen to average these 
> effects out as best as possible but they haven't gone away - for example a 
> monthly mean sea level from a coastal tide gauge may still comprise some 
> tidal signal (for example an asymmetry where the equinoxes occur in different 
> months) and will certainly include variation due to a seasonal changes in the 
> surge contribution.
>
> So from my perspective, the only difference between tide and surge is that we 
> would expect tide to always reference some form of fixed datum (which is 
> preferably more flexible than just MSL) in order to allow us to construct a 
> sea level series that is vertically referenced, whereas  surge and other 
> contributions will be relative quantities.
>
> Cheers
> Andy
>
>
>
> -Original Message-
> From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
> Jonathan Gregory
> Sent: 24 April 2018 18:30
> To: cf-metadata@cgd.ucar.edu
> Subject: Re: [CF-metadata] proposed new standard name for storm surge residual
>
> Dear Andy
>
> > - I'm only going to do this for sea water levels, so from my point of
> > view using the term "sea" is fine; I'm just aware that what comes
> > below could be applied in other water bodies
>
> Yes. However, we make our job simpler (as a principle in CF) by doing only 
> what we need to for the current use-cases.
>
> > - "due_to_surge" will either a) be derived as a residual value
> > calculated after taking a measured sea level value (referenced to some
> > fixed datum) and subtracting a predicted tide height (referenced to
> > same datum), or b) be a quantity that we would expect to add to a
> > predicted tide height in order to cr

Re: [CF-metadata] proposed new standard name for storm surge residual

[Lowry, Roy K.]

Hello Andrew,


I've been watching this thread without responding. Your request in this e-mail 
makes a lot of sense to me.


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  on behalf of Saulter, 
Andrew 
Sent: 24 April 2018 08:17
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

John,

I see where you are with that, but my understanding from Jonathon Gregory's 
email earlier is that the 'due_to' part of the phrasing identifies a component 
process that contributes to an overall quantity. In the case below 
'due_to_storm_surge' is a contribution to 'sea_surface_elevation' and that 
quantity is what needs to be referenced to some datum. Or maybe I'm not getting 
it? Steep learning curve this...

Anyway, having thought about datum's now I have done some further searching and 
noted the following already exist as standard names:

water_surface_height_above_reference_datum - this denotes the quantity

water_surface_reference_datum_altitude - references the datum to the 
(grid_mapping) geoid

These look much more like what I was after, so the question is can the 
'due_to_storm_surge' and 'due_to_tide' be sensibly appended to 
'water_surface_height_above_reference_datum'??

Cheers
Andy


-Original Message-
From: John Graybeal [mailto:jbgrayb...@mindspring.com]
Sent: 23 April 2018 17:57
To: Saulter, Andrew 
Cc: CF Metadata List 
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual


I actually find this new name/definition internally inconsistent. An elevation 
that is ‘due to storm surge’ seems to be relative to the elevation without the 
storm surge, which makes the datum irrelevant. Unless the change due to the 
storm surge would be measured differently under different datums, but I can’t 
imagine that. (Taking the other way, if it’s an elevation relative to some 
normal datum, then “due to storm surge” is irrelevant.)

In any case, under the new definition, the description needs to include exactly 
how the datum is specified. The computers and people will need to know where to 
look for that information, and ideally it should be a unique identifier that 
the computers can recognize and understand.


john


> On Apr 23, 2018, at 01:43, Saulter, Andrew  
> wrote:
>
> Apologies, a little bit more to add to the below following up from
> Jonathon's first email,
>
> For both tide and surge I would actually prefer to go with Jonathon's 
> suggestion that the 'height_above_mean_sea_level' part of my suggestions is 
> replaced with 'elevation'. This is a much more compact and flexible way of 
> expressing things and means, particularly with tide that we can reference 
> this to whichever datum we like (for example Chart Datum, Ordnance Datum, 
> MSL) dependent on source elsewhere in the metadata. I think it is also 
> appropriate that we think of "sea_surface_elevation" as a quantity that can 
> be contributed to via processes with many different timescales, e.g. tides, 
> surges, individual ocean waves.
>
> This would take us to:
>
> Proposed standard name:
> sea_surface_elevation_due_to_storm_surge
> Units: m
> "Sea surface elevation" is a time-varying quantity denoting the height of the 
> sea surface relative to a given datum. The specification of a physical 
> process by the phrase “due_to_process” means that the quantity named is a 
> single term in a sum of terms which together compose the general quantity 
> named by omitting the phrase. Storm surge effects, due to meteorological 
> forcing of the ocean and interaction between the generated surge and tides, 
> are a significant contributor to the observed sea surface height.
>
> Proposed standard name:
> sea_surface_elevation_due_to_tide
> Units: m
> "Sea surface elevation" is a time-varying quantity denoting the height of the 
> sea surface relative to a given datum. The specification of a physical 
> process by the phrase “due_to_process” means that the quantity named is a 
> single term in a sum of terms which together compose the general quantity 
> named by omitting the phrase. Tides are a significant contributor to the 
> observed sea surface height; here “tide” denotes a generic variable 
> describing the time varying tidal signal, for example as generated based on a 
> summation of harmonically analysed components, or resulting from the 
> application of such components as boundary conditions to

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Thanks Jonathon,

From the below:

We use the term "sea" - agreed. "due_to_surge" has no need for a datum 
reference - agreed.

MSL implies no tide and no surge. I'd disagree with this; sea level at high 
frequency will comprise contributions from lots of different components and 
mean sea level is therefore a quantity where we have chosen to average these 
effects out as best as possible but they haven't gone away - for example a 
monthly mean sea level from a coastal tide gauge may still comprise some tidal 
signal (for example an asymmetry where the equinoxes occur in different months) 
and will certainly include variation due to a seasonal changes in the surge 
contribution.

So from my perspective, the only difference between tide and surge is that we 
would expect tide to always reference some form of fixed datum (which is 
preferably more flexible than just MSL) in order to allow us to construct a sea 
level series that is vertically referenced, whereas  surge and other 
contributions will be relative quantities.

Cheers
Andy



-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 24 April 2018 18:30
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Dear Andy

> - I'm only going to do this for sea water levels, so from my point of 
> view using the term "sea" is fine; I'm just aware that what comes 
> below could be applied in other water bodies

Yes. However, we make our job simpler (as a principle in CF) by doing only what 
we need to for the current use-cases.

> - "due_to_surge" will either a) be derived as a residual value 
> calculated after taking a measured sea level value (referenced to some 
> fixed datum) and subtracting a predicted tide height (referenced to 
> same datum), or b) be a quantity that we would expect to add to a 
> predicted tide height in order to create a total water level (again 
> referenced to some fixed datum)

In both cases the datum is not relevant to the elevation due to surge.

> - "due_to_tide" will be the tide values mentioned above which will have to be 
> referenced against a datum or common benchmark, e.g. chart datum, mean sea 
> level, Ordnance Datum Newlyn, in order to make sense. 

... whereas here the datum *is* required.

So these cases seem different after all, and may need different sorts of name - 
at least, that's my first reaction. It's because there isn't a situation of "no 
tide", but there is a situation of "no surge". On second thoughts, I'm not sure 
about this distinction. No tide, I suppose, means MSL. On the other hand, no 
surge isn't uniquely defined - something must be assumed about the MSLP and the 
wind when there *isn't* a surge. What is that?

> So far these are variables that give us what we might term 'still water 
> level', i.e. neglecting wave effects. However, thinking about future 
> requirements you could easily see an extension to higher frequency parameters 
> such as "due_to_wave_induced_setup" (minutes to hours), "due_to_run_up" 
> (seconds to minutes), "due_to_waves" (seconds) if you were looking at a 
> detailed approach to evaluating total water levels. All these would work like 
> surge, in that these aren't referenced to a datum themselves but will 
> contribute to some total water level value that does need to be.

Right. If we can work out how to deal with the surge, I agree the others will 
follow when they are needed.

Best wishes

Jonathan

> Instinctively when I plot summations of these types of variables in 
> time-series I would write 'sea_surface_elevation' on the y-axis (since the 
> water goes down as well as up) but that, definitely, is just me! Personally I 
> have no objection to "elevation_of_sea_surface" either - it seems clear what 
> it means and if we are all happy that "sea" can be generic for "water" I'd be 
> good with this.
> 
> Thanks
> Andy
> 
> 
> -Original Message-
> From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf 
> Of Jonathan Gregory
> Sent: 24 April 2018 17:08
> To: cf-metadata@cgd.ucar.edu
> Subject: [CF-metadata] Fwd: Re: Fwd: Re: proposed new standard name 
> for storm surge residual
> 
> Dear Andy
> 
> > "elevation_of_sea_surface_due_to_X" sounds most appropriate.
> OK.
> 
> Since we already have
>   water_surface_height_above_reference_datum
>   water_surface_reference_datum_altitude
> in the table, I agree that water_surface is OK to use. In general in standard 
> names we have made the word "sea" signify all bodies of water, as we've not 
> 

Re: [CF-metadata] proposed new standard name for storm surge residual

[Jonathan Gregory]

2018 14:26
> > To: cf-metadata@cgd.ucar.edu
> > Subject: [CF-metadata] Fwd: Re: proposed new standard name for storm 
> > surge residual
> > 
> > Dear Andrew and John
> > 
> > I hadn't noticed that sea_surface_elevation is already in use as an alias.
> > That's a pity, but maybe it would be confusing anyway, given John's comment.
> > 
> > I think that what Andrew needs is terms that say how much higher the sea 
> > surface is because of influence X relative to how high it would be in the 
> > absence of influence X. Such terms do not need any datum (like geoid or 
> > MSL). The difference in z is the same regardless of what datum would be 
> > used for z itself. I suggested before that change_in would be a possibility 
> > but it doesn't sound quite right, because we aren't comparing SSH before 
> > and after a storm surge for example, which is what I'd understand by 
> > "change in SSH due to storm surge". Other ideas:
> > 
> > elevation_of_sea_surface_due_to_X
> > increment_to_sea_surface_height_due_to_X
> > increase_of_sea_surface_height_due_to_X
> > 
> > What others occur to you?
> > 
> > Best wishes
> > 
> > Jonathan
> > 
> > 
> > - Forwarded message from "Saulter, Andrew" 
> >  -
> > 
> > > Date: Tue, 24 Apr 2018 07:17:48 +
> > > From: "Saulter, Andrew" 
> > > To: "cf-metadata@cgd.ucar.edu" 
> > > Subject: Re: [CF-metadata] proposed new standard name for storm surge
> > >   residual
> > > 
> > > John,
> > > 
> > > I see where you are with that, but my understanding from Jonathon 
> > > Gregory's email earlier is that the 'due_to' part of the phrasing 
> > > identifies a component process that contributes to an overall quantity. 
> > > In the case below 'due_to_storm_surge' is a contribution to 
> > > 'sea_surface_elevation' and that quantity is what needs to be referenced 
> > > to some datum. Or maybe I'm not getting it? Steep learning curve this...
> > > 
> > > Anyway, having thought about datum's now I have done some further 
> > > searching and noted the following already exist as standard names:
> > > 
> > > water_surface_height_above_reference_datum - this denotes the 
> > > quantity
> > > 
> > > water_surface_reference_datum_altitude - references the datum to the
> > > (grid_mapping) geoid
> > > 
> > > These look much more like what I was after, so the question is can the 
> > > 'due_to_storm_surge' and 'due_to_tide' be sensibly appended to 
> > > 'water_surface_height_above_reference_datum'??
> > > 
> > > Cheers
> > > Andy
> > > 
> > > 
> > > -Original Message-
> > > From: John Graybeal [mailto:jbgrayb...@mindspring.com]
> > > Sent: 23 April 2018 17:57
> > > To: Saulter, Andrew 
> > > Cc: CF Metadata List 
> > > Subject: Re: [CF-metadata] proposed new standard name for storm 
> > > surge residual
> > > 
> > > 
> > > I actually find this new name/definition internally inconsistent. An 
> > > elevation that is ‘due to storm surge’ seems to be relative to the 
> > > elevation without the storm surge, which makes the datum irrelevant.
> > > Unless the change due to the storm surge would be measured 
> > > differently under different datums, but I can’t imagine that. 
> > > (Taking the other way, if it’s an elevation relative to some normal 
> > > datum, then “due to storm surge” is irrelevant.)
> > > 
> > > In any case, under the new definition, the description needs to include 
> > > exactly how the datum is specified. The computers and people will need to 
> > > know where to look for that information, and ideally it should be a 
> > > unique identifier that the computers can recognize and understand.
> > > 
> > > 
> > > john
> > > 
> > > 
> > > > On Apr 23, 2018, at 01:43, Saulter, Andrew 
> > > >  wrote:
> > > > 
> > > > Apologies, a little bit more to add to the below following up from 
> > > > Jonathon's first email,
> > > > 
> > > > For both tide and surge I would actually prefer to go with Jonathon's 
> > > > suggestion that the 'height_above_mean_sea_level' part of my 
> > > > suggestions is replaced with 

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

John,

I see where you are with that, but my understanding from Jonathon Gregory's 
email earlier is that the 'due_to' part of the phrasing identifies a component 
process that contributes to an overall quantity. In the case below 
'due_to_storm_surge' is a contribution to 'sea_surface_elevation' and that 
quantity is what needs to be referenced to some datum. Or maybe I'm not getting 
it? Steep learning curve this...

Anyway, having thought about datum's now I have done some further searching and 
noted the following already exist as standard names:

water_surface_height_above_reference_datum - this denotes the quantity

water_surface_reference_datum_altitude - references the datum to the 
(grid_mapping) geoid

These look much more like what I was after, so the question is can the 
'due_to_storm_surge' and 'due_to_tide' be sensibly appended to 
'water_surface_height_above_reference_datum'??

Cheers
Andy


-Original Message-
From: John Graybeal [mailto:jbgrayb...@mindspring.com] 
Sent: 23 April 2018 17:57
To: Saulter, Andrew 
Cc: CF Metadata List 
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual


I actually find this new name/definition internally inconsistent. An elevation 
that is ‘due to storm surge’ seems to be relative to the elevation without the 
storm surge, which makes the datum irrelevant. Unless the change due to the 
storm surge would be measured differently under different datums, but I can’t 
imagine that. (Taking the other way, if it’s an elevation relative to some 
normal datum, then “due to storm surge” is irrelevant.)

In any case, under the new definition, the description needs to include exactly 
how the datum is specified. The computers and people will need to know where to 
look for that information, and ideally it should be a unique identifier that 
the computers can recognize and understand.


john


> On Apr 23, 2018, at 01:43, Saulter, Andrew  
> wrote:
> 
> Apologies, a little bit more to add to the below following up from 
> Jonathon's first email,
> 
> For both tide and surge I would actually prefer to go with Jonathon's 
> suggestion that the 'height_above_mean_sea_level' part of my suggestions is 
> replaced with 'elevation'. This is a much more compact and flexible way of 
> expressing things and means, particularly with tide that we can reference 
> this to whichever datum we like (for example Chart Datum, Ordnance Datum, 
> MSL) dependent on source elsewhere in the metadata. I think it is also 
> appropriate that we think of "sea_surface_elevation" as a quantity that can 
> be contributed to via processes with many different timescales, e.g. tides, 
> surges, individual ocean waves.
> 
> This would take us to:
> 
> Proposed standard name: 
> sea_surface_elevation_due_to_storm_surge
> Units: m
> "Sea surface elevation" is a time-varying quantity denoting the height of the 
> sea surface relative to a given datum. The specification of a physical 
> process by the phrase “due_to_process” means that the quantity named is a 
> single term in a sum of terms which together compose the general quantity 
> named by omitting the phrase. Storm surge effects, due to meteorological 
> forcing of the ocean and interaction between the generated surge and tides, 
> are a significant contributor to the observed sea surface height.
> 
> Proposed standard name: 
> sea_surface_elevation_due_to_tide
> Units: m
> "Sea surface elevation" is a time-varying quantity denoting the height of the 
> sea surface relative to a given datum. The specification of a physical 
> process by the phrase “due_to_process” means that the quantity named is a 
> single term in a sum of terms which together compose the general quantity 
> named by omitting the phrase. Tides are a significant contributor to the 
> observed sea surface height; here “tide” denotes a generic variable 
> describing the time varying tidal signal, for example as generated based on a 
> summation of harmonically analysed components, or resulting from the 
> application of such components as boundary conditions to a numerical tidal 
> model.
> 
> However, I have one concern in that "sea_surface_elevation" is presently 
> given as an alias for "sea_surface_height_above_geoid". My worry is that the 
> latter has implications for the vertical datum and that we might choose to 
> disconnect this from other aspects of the grid_mapping variable (e.g. where 
> my station positions are in WGS84, but the vertical reference is to chart 
> datum) in which case we are not strictly referencing against the geoid any 
> more. In addition, the term "sea_surface_height" has more usually been 
> associated

Re: [CF-metadata] proposed new standard name for storm surge residual

[John Graybeal]

I actually find this new name/definition internally inconsistent. An elevation 
that is ‘due to storm surge’ seems to be relative to the elevation without the 
storm surge, which makes the datum irrelevant. Unless the change due to the 
storm surge would be measured differently under different datums, but I can’t 
imagine that. (Taking the other way, if it’s an elevation relative to some 
normal datum, then “due to storm surge” is irrelevant.)

In any case, under the new definition, the description needs to include exactly 
how the datum is specified. The computers and people will need to know where to 
look for that information, and ideally it should be a unique identifier that 
the computers can recognize and understand.


john


> On Apr 23, 2018, at 01:43, Saulter, Andrew  
> wrote:
> 
> Apologies, a little bit more to add to the below following up from Jonathon's 
> first email,
> 
> For both tide and surge I would actually prefer to go with Jonathon's 
> suggestion that the 'height_above_mean_sea_level' part of my suggestions is 
> replaced with 'elevation'. This is a much more compact and flexible way of 
> expressing things and means, particularly with tide that we can reference 
> this to whichever datum we like (for example Chart Datum, Ordnance Datum, 
> MSL) dependent on source elsewhere in the metadata. I think it is also 
> appropriate that we think of "sea_surface_elevation" as a quantity that can 
> be contributed to via processes with many different timescales, e.g. tides, 
> surges, individual ocean waves.
> 
> This would take us to:
> 
> Proposed standard name: 
> sea_surface_elevation_due_to_storm_surge
> Units: m
> "Sea surface elevation" is a time-varying quantity denoting the height of the 
> sea surface relative to a given datum. The specification of a physical 
> process by the phrase “due_to_process” means that the quantity named is a 
> single term in a sum of terms which together compose the general quantity 
> named by omitting the phrase. Storm surge effects, due to meteorological 
> forcing of the ocean and interaction between the generated surge and tides, 
> are a significant contributor to the observed sea surface height.
> 
> Proposed standard name: 
> sea_surface_elevation_due_to_tide
> Units: m
> "Sea surface elevation" is a time-varying quantity denoting the height of the 
> sea surface relative to a given datum. The specification of a physical 
> process by the phrase “due_to_process” means that the quantity named is a 
> single term in a sum of terms which together compose the general quantity 
> named by omitting the phrase. Tides are a significant contributor to the 
> observed sea surface height; here “tide” denotes a generic variable 
> describing the time varying tidal signal, for example as generated based on a 
> summation of harmonically analysed components, or resulting from the 
> application of such components as boundary conditions to a numerical tidal 
> model.
> 
> However, I have one concern in that "sea_surface_elevation" is presently 
> given as an alias for "sea_surface_height_above_geoid". My worry is that the 
> latter has implications for the vertical datum and that we might choose to 
> disconnect this from other aspects of the grid_mapping variable (e.g. where 
> my station positions are in WGS84, but the vertical reference is to chart 
> datum) in which case we are not strictly referencing against the geoid any 
> more. In addition, the term "sea_surface_height" has more usually been 
> associated with altimeter and model products where high frequency signals are 
> generally excluded? 
> 
> So some consensus as to whether "sea_surface_elevation" is the phrasing to go 
> for would be very helpful...
> 
> Cheers
> Andy
> 
> -Original Message-
> From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
> Saulter, Andrew
> Sent: 20 April 2018 17:04
> To: cf-metadata@cgd.ucar.edu
> Subject: Re: [CF-metadata] proposed new standard name for storm surge residual
> 
> Jonathon, Helen,
> 
> Thanks for the feedback.
> 
> I'd looked at the existing 'sea_surface_height' terms but had the same worry 
> as Jonathon that the use of 'amplitude' restricted these to some 
> (unspecified) time integral. What I'm after is definitely a variable that 
> varies as a function of time. It's also unusual in the coastal forecasting 
> community to want to split the various contributions to tide up.
> 
> The 'due_to_air_pressure_and_wind' term captures the primary meteorological 
> processes that induce surge. However, these do not capture the effect of 
> tide-surge in

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Apologies, a little bit more to add to the below following up from Jonathon's 
first email,

For both tide and surge I would actually prefer to go with Jonathon's 
suggestion that the 'height_above_mean_sea_level' part of my suggestions is 
replaced with 'elevation'. This is a much more compact and flexible way of 
expressing things and means, particularly with tide that we can reference this 
to whichever datum we like (for example Chart Datum, Ordnance Datum, MSL) 
dependent on source elsewhere in the metadata. I think it is also appropriate 
that we think of "sea_surface_elevation" as a quantity that can be contributed 
to via processes with many different timescales, e.g. tides, surges, individual 
ocean waves.

This would take us to:

 Proposed standard name: 
 sea_surface_elevation_due_to_storm_surge
 Units: m
 "Sea surface elevation" is a time-varying quantity denoting the height of the 
sea surface relative to a given datum. The specification of a physical process 
by the phrase “due_to_process” means that the quantity named is a single term 
in a sum of terms which together compose the general quantity named by omitting 
the phrase. Storm surge effects, due to meteorological forcing of the ocean and 
interaction between the generated surge and tides, are a significant 
contributor to the observed sea surface height.
 
 Proposed standard name: 
 sea_surface_elevation_due_to_tide
 Units: m
"Sea surface elevation" is a time-varying quantity denoting the height of the 
sea surface relative to a given datum. The specification of a physical process 
by the phrase “due_to_process” means that the quantity named is a single term 
in a sum of terms which together compose the general quantity named by omitting 
the phrase. Tides are a significant contributor to the observed sea surface 
height; here “tide” denotes a generic variable describing the time varying 
tidal signal, for example as generated based on a summation of harmonically 
analysed components, or resulting from the application of such components as 
boundary conditions to a numerical tidal model.

However, I have one concern in that "sea_surface_elevation" is presently given 
as an alias for "sea_surface_height_above_geoid". My worry is that the latter 
has implications for the vertical datum and that we might choose to disconnect 
this from other aspects of the grid_mapping variable (e.g. where my station 
positions are in WGS84, but the vertical reference is to chart datum) in which 
case we are not strictly referencing against the geoid any more. In addition, 
the term "sea_surface_height" has more usually been associated with altimeter 
and model products where high frequency signals are generally excluded? 

So some consensus as to whether "sea_surface_elevation" is the phrasing to go 
for would be very helpful...

Cheers
Andy

-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Saulter, Andrew
Sent: 20 April 2018 17:04
To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] proposed new standard name for storm surge residual

Jonathon, Helen,

Thanks for the feedback.

I'd looked at the existing 'sea_surface_height' terms but had the same worry as 
Jonathon that the use of 'amplitude' restricted these to some (unspecified) 
time integral. What I'm after is definitely a variable that varies as a 
function of time. It's also unusual in the coastal forecasting community to 
want to split the various contributions to tide up.

The 'due_to_air_pressure_and_wind' term captures the primary meteorological 
processes that induce surge. However, these do not capture the effect of 
tide-surge interaction in shallower waters (for example the extra surge 
elevation enhances the speed at which the tide propagates so a 'surge residual' 
can include the propagation speed delta as well as the background 
super-elevation) nor other secondary variability that we often see in surge 
residuals, such as steric changes of the water column. So I feel that using a 
catchall term 'storm_surge', although less specific would have a lot less 
potential to mislead a user. The option exists, I assume, in the comments 
attribute for a variable to be more precise about its derivation/generating 
processes.

So overall, I couldn't find a goldilocks term for either surge or tide that 
would fit my users understanding of the variables - hence the new suggestions.

Have a good weekend
Andy



-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 11 April 2018 18:37
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Helen and Andy

I noticed the sea_surface_height_amplitude_due_to_X_tide names as well, and I 
wondered, what does 

Re: [CF-metadata] proposed new standard name for storm surge residual

[Saulter, Andrew]

Jonathon, Helen,

Thanks for the feedback.

I'd looked at the existing 'sea_surface_height' terms but had the same worry as 
Jonathon that the use of 'amplitude' restricted these to some (unspecified) 
time integral. What I'm after is definitely a variable that varies as a 
function of time. It's also unusual in the coastal forecasting community to 
want to split the various contributions to tide up.

The 'due_to_air_pressure_and_wind' term captures the primary meteorological 
processes that induce surge. However, these do not capture the effect of 
tide-surge interaction in shallower waters (for example the extra surge 
elevation enhances the speed at which the tide propagates so a 'surge residual' 
can include the propagation speed delta as well as the background 
super-elevation) nor other secondary variability that we often see in surge 
residuals, such as steric changes of the water column. So I feel that using a 
catchall term 'storm_surge', although less specific would have a lot less 
potential to mislead a user. The option exists, I assume, in the comments 
attribute for a variable to be more precise about its derivation/generating 
processes.

So overall, I couldn't find a goldilocks term for either surge or tide that 
would fit my users understanding of the variables - hence the new suggestions.

Have a good weekend
Andy



-Original Message-
From: CF-metadata [mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of 
Jonathan Gregory
Sent: 11 April 2018 18:37
To: cf-metadata@cgd.ucar.edu
Subject: [CF-metadata] proposed new standard name for storm surge residual

Dear Helen and Andy

I noticed the sea_surface_height_amplitude_due_to_X_tide names as well, and I 
wondered, what does "amplitude" mean here? The definitions of these names don't 
say, and I feel that we should be clear. I guessed it might mean the amplitude 
of SSH due to the tidal cycle, whereas I think Andy means the actual tidal 
height as a function of time. Are you able to clarify?

It's a good point about due_to_air_pressure[_and_wind], thanks. That may not 
obviously mean "storm surge", which maybe could be inserted in the definition.

Best wishes

Jonathan

- Forwarded message from "Snaith, Helen M."  -

> Date: Tue, 10 Apr 2018 13:14:16 +
> From: "Snaith, Helen M." 
> To: "Saulter, Andrew" 
> CC: "cf-metadata@cgd.ucar.edu" 
> Subject: Re: [CF-metadata] proposed new standard name for storm surge
>   residual
> x-mailer: Apple Mail (2.3445.6.18)
> 
> Hi Andy
> 
> Many of the sea_surface_height terms have been used in satellite altimetry 
> for some time.
> The tidal components have been split out into 
> sea_surface_height_amplitude_due_to_equilibrium_ocean_tide void(0)> 
> sea_surface_height_amplitude_due_to_geocentric_ocean_tide oid(0)> 
> sea_surface_height_amplitude_due_to_non_equilibrium_ocean_tide ipt:void(0)>
> 
> And the pole tide
> sea_surface_height_amplitude_due_to_pole_tide
> 
> In these terms, amplitude has been used to identify the ‘above mean 
> level’ and sea_surface_height is as alias of 
> sea_surface_heigth_above_mean_sea_level
> 
> 
> Also included are the terms
> sea_surface_height_correction_due_to_air_pressure_and_wind_at_high_fre
> quency 
> sea_surface_height_correction_due_to_air_pressure_at_low_frequency ascript:void(0)>
> 
> The former of which is related to surge I think - it is normally determined 
> from a tidal model and is the response of sea level to changes in air 
> pressure and wind.
> 
> Even if these are not the correct terms, as you are not determining a 
> 'correction’ but a value - they should be related to the surge components, so 
> do they give the ‘due to’ component you need?
> 
> Helen
> 
> 
> On 4 Apr 2018, at 17:13, Saulter, Andrew 
> mailto:andrew.saul...@metoffice.gov.uk>> 
> wrote:
> 
> Dear all,
> 
> First posting to this list, so please forgive me if I’m doing it 
> wrong…
> 
> I’d like to request an addition to the standard name list to include storm 
> surge residual and tide. These variables are generated for the purpose of 
> coastal flood prediction and will be available in future, netCDF based, 
> operational products from the Met Office.
> 
> Proposed standard name: 
> sea_surface_height_above_mean_sea_level_due_to_storm_surge
> Units: m
> "Sea surface height" is a time-varying quantity. "Height_above_X" means the 
> vertical distance above the named surface X. "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. The specification of a physical 
> process by the phras

Re: [CF-metadata] proposed new standard name for storm surge residual

[Snaith, Helen M.]

Hi Andy

Many of the sea_surface_height terms have been used in satellite altimetry for 
some time.
The tidal components have been split out into
sea_surface_height_amplitude_due_to_equilibrium_ocean_tide
sea_surface_height_amplitude_due_to_geocentric_ocean_tide
sea_surface_height_amplitude_due_to_non_equilibrium_ocean_tide

And the pole tide
sea_surface_height_amplitude_due_to_pole_tide

In these terms, amplitude has been used to identify the ‘above mean level’ and 
sea_surface_height is as alias of sea_surface_heigth_above_mean_sea_level


Also included are the terms
sea_surface_height_correction_due_to_air_pressure_and_wind_at_high_frequency
sea_surface_height_correction_due_to_air_pressure_at_low_frequency

The former of which is related to surge I think - it is normally determined 
from a tidal model and is the response of sea level to changes in air pressure 
and wind.

Even if these are not the correct terms, as you are not determining a 
'correction’ but a value - they should be related to the surge components, so 
do they give the ‘due to’ component you need?

Helen


On 4 Apr 2018, at 17:13, Saulter, Andrew 
mailto:andrew.saul...@metoffice.gov.uk>> wrote:

Dear all,

First posting to this list, so please forgive me if I’m doing it wrong…

I’d like to request an addition to the standard name list to include storm 
surge residual and tide. These variables are generated for the purpose of 
coastal flood prediction and will be available in future, netCDF based, 
operational products from the Met Office.

Proposed standard name: 
sea_surface_height_above_mean_sea_level_due_to_storm_surge
Units: m
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "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. The specification of a physical 
process by the phrase “due_to_process” means that the quantity named is a 
single term in a sum of terms which together compose the general quantity named 
by omitting the phrase. Storm surge effects, due to meteorological forcing of 
the ocean and interaction between the generated surge and tides, are a 
significant contributor to the observed sea surface height.

Proposed standard name: sea_surface_height_above_mean_sea_level_due_to_tide
Units: m
"Sea surface height" is a time-varying quantity. "Height_above_X" means the 
vertical distance above the named surface X. "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. The specification of a physical 
process by the phrase “due_to_process” means that the quantity named is a 
single term in a sum of terms which together compose the general quantity named 
by omitting the phrase. Tides are a significant contributor to the observed sea 
surface height; here “tide” denotes a generic variable describing the time 
varying tidal signal, for example as generated based on a summation of 
harmonically analysed components, or resulting from the application of such 
components as boundary conditions to a numerical tidal model.

Many thanks
Andy


Andy Saulter
Surge, Waves and Metocean Projects Manager
Met Office  FitzRoy Road  Exeter  Devon EX1 3PB
Tel: +44 (0)1392 884703  Fax: +44 (0)1392 885681
andrew.saul...@metoffice.gov.uk 
http://www.metoffice.gov.uk


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