[CF-metadata] New standard names for NEMO ocean model output

From: Kevin Marsh <kevin.marsh>
Date: Tue, 13 Dec 2016 11:19:11 +0000 (GMT-00:00)

Hi Jonathan,
many thanks for your comments. I've been spoken to members of our NEMO team and their responses are below.

**********************
For
1. bottom_pressure_equivalent_height (m)
'Difference between the sea level height and the ocean steric height.'

and

3. ocean_steric_height (m)
'The steric measures the height by which a column of water with standard temperature T=0?C and salinity S=35.0 expands if its temperature and salinity are changed to the observed values.'

The idea behind these two variables is that local sea level variations can be divided into volume changes (or steric changes) and mass changes (visible in the eq bottom pressure height).
 
The steric height is estimated as the vertical integral of the density (relative to a reference density where T=0K and S=35psu). The bottom pressure is the mass of the water column at a given location.

The bottom pressure equivalent height is estimated indirectly as the difference between the steric height and the sea level. This is just a diagnostic variable we use to check the mass budget in our system.

(we'll gladly accept you suggestion, and if 'ocean_steric_height' is a thickness we'd be happy to change it to 'ocean_steric_thickness' as long as the definition is correctly stated)

so we suggest:

1. bottom_pressure_equivalent_height (m)
'Difference between the sea level height and the ocean steric height above sea level.'

3. ocean_steric_height_above_sea_level (m)
'The steric measures the height by which a column of water with standard temperature T=0?C and salinity S=35.0 expands if its temperature and salinity are changed to the observed values.'

**********************

2. Instead of "ocean_turbocline_depth (m)" we suggest:

ocean_turbocline_thickness (m)
'The turbocline thickness is similar to the mixed layer thickness but is estimated in models as the thickness at which the vertical eddy diffusivity coefficient (resulting from the vertical physics alone) falls below a given value defined locally.'

**********************
6. temperature_profile_anomaly_correction (K s-1)
This is a temperature difference in K weighted by a relaxation coefficient in s-1 (1/(relaxation timescale)). The relaxation timescale represents how strongly you want your model to be close to climatology.

we would be happy with your suggestion:

ratio_of_sea_water_potential_temperature_anomaly_to_relaxation_timescale (K s-1)

'This term is estimated as the deviation of the local sea water potential temperature from an ocean model wrt an observation-based climatology (eg World Ocean Database) weighted by a user-specified relaxation coefficient in s-1 (1/(relaxation timescale)). The relaxation coefficient depends on the timescale on which the correction is applied.'

**********************

Thanks,
Kevin

----- Original Message -----
From: "j m gregory" <j.m.gregory at reading.ac.uk>
To: cf-metadata at cgd.ucar.edu
Cc: "Kevin Marsh" <kevin.marsh at ecmwf.int>
Sent: Thursday, 24 November, 2016 17:09:18
Subject: Re: [CF-metadata] New standard names for NEMO ocean model output

Dear Kevin and Alison

> 1. bottom_pressure_equivalent_height (m)
> 'Difference between the sea level height and the ocean steric height.'

Is that really what it means? The ocean steric height is already a difference
from sea level by definition (see below). It sounds as though this ought to
mean the ocean bottom pressure converted into a thickness of water of some
standard density.

> 2. ocean_turbocline_depth (m)
> 'The turbocline depth is similar to the mixed layer depth but is estimated in models as the depth at which the vertical eddy diffusivity coefficient (resulting from the vertical physics alone) fall below a given value defined locally.

For consistent with the mixed layer names, this should perhaps be thickness,
rather than depth e.g. ocean_mixed_layer_thickness.

> 3. ocean_steric_height (m)
> 'The steric measures the height by which a column of water with standard temperature T=0?C and salinity S=35.0 expands if its temperature and salinity are changed to the observed values.'

I have found that definition in papers too. It's actually a thickness, as
Alison notes, but we could maybe call it ocean_steric_height_above_sea_level,
which would be consistent with some other std names.

> 6. temperature_profile_anomaly_correction (K s-1)
> 'Correction term estimated as the deviation the local sea water potential temperature from an ocean model wrt to an observation-based climatology (eg World Ocean Database) multiplied by an user-specified relaxation coefficient. The relaxation coefficient depends on the timescale on which the correction is applied.'

I think there are number of problems with this name. (a) It should be
sea_water_potential_temperature, not just temperature, (b) profile is
not really part of the definition of the quantity - it depends on depth,
but standard names do not usually indicate which coordinates are relevant,
(c) it's not obvious what an "anomaly correction" means. It might equally
well mean something in K, for instance, because all other "corrections" are
in fact quantities with the same units as the thing being corrected. I would
suggest calling this
  ratio_of_sea_water_potential_temperature_anomaly_to_relaxation_timescale
  
Best wishes

Jonathan
Received on Tue Dec 13 2016 - 04:19:11 GMT