[CF-metadata] Proposed CF standard names for the NEMO ocean model

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 7 Aug 2008 10:51:08 +0100

Dear Ian and Dan

Thanks for your email. I believe we agree on the following (omitting the
descriptions for the sake of the overview).

Rename:

water_flux_into_ocean
water_flux_into_ocean_from_rivers
water_volume_transport_into_ocean_from_rivers
wind_mixing_energy_flux_into_ocean
water_flux_into_ocean_without_flux_correction (proposal agreed with Martina)

by replacing "ocean" with "sea_water".

Include Newtonian relaxation in the definitions of water_flux_into_sea_water,
water_flux_out_of_sea_water (T5), water_flux_out_of_sea_ice_and_sea_water
(T3), virtual_salt_flux_into_sea_water (T6).

New names:

T1 water_flux_out_of_sea_water_due_to_sea_ice_thermodynamics (kg m-2 s-1)
T3 water_flux_out_of_sea_ice_and_sea_water (kg m-2 s-1)
T4 minus_one_times_water_flux_into_sea_water_from_rivers (kg m-2 s-1)
T5 water_flux_out_of_sea_water (kg m-2 s-1)
T7 ocean_mixed_layer_thickness_defined_by_vertical_tracer_diffusivity (m)
T8 heat_flux_into_sea_water_due_to_newtonian_relaxation (W m-2)
T9 water_flux_out_of_sea_water_due_to_newtonian_relaxation (kg m-2 s-1)
T12 model_level_number_at_base_of_ocean_mixed_layer_defined_by_sigma_theta (1)
T13 depth_at_maximum_upward_derivative_of_sea_water_potential_temperature (m)
T15 ocean_integral_of_sea_water_potential_temperature_wrt_depth_expressed_as_heat_content (J m-2)
T17 sea_ice_albedo (1)
U2 bolus_sea_water_x_velocity (m s-1)
U3 x_derivative_of_ocean_rigid_lid_pressure (N m-3)
V2 bolus_sea_water_y_velocity (m s-1)
V3 y_derivative_of_ocean_rigid_lid_pressure (N m-3)
W2 vertical_sea_water_temperature_diffusivity (m2 s-1)
W4 vertical_sea_water_momentum_diffusivity (m2 s-1)
W5 vertical_sea_water_momentum_diffusivity_due_to_convection (m2 s-1)
W6 vertical_sea_water_salinity_diffusivity (m2 s-1)
G4 angle_of_rotation_from_east_to_x (degree)
G5 angle_of_rotation_from_east_to_y (degree)
G6 cell_area (m2)
G7 model_level_number_at_sea_floor (1)

Others are either agreed to be equivalent to existing names, or discussed
below (T6, T10, T11, W3, W7, G1-3).

T3: This quantity includes rivers, flux adjustment and relaxation. Without
these i.e. only the fluxes at the surface of the sea ice and sea water, the
name would be surface_upward_water_flux, since "surface" means "bottom of
atmosphere" in effect. We also agreed that T2 is surface_upward_water_flux,
over the open ocean i.e. it is P-E where there is no sea-ice. These would be
distinguished by cell_methods. T2 is "where ice_free_sea", but if sea-ice is
included there is no need for "where" because it applies to the whole
gridbox. You can also have "where sea_ice", which would mean the
precipitation, evaporation and sublimation from the sea-ice surface.

T4: I agree with you that, though inelegant, this is preferable to using
the scale_factor. That's intended for packing, not for defining the sign of
the quantity.

T6: In your email you explain this as just being -T5*SSS (I think I am right
to put in minus, since T5 is upward, and your original proposal for T6 is
downward). This is related to the salinity flux, which is
-T5*SSS/density. That being so, your word "virtual", which has the virtue of
being often used, may be best to indicate it's not really a physical salt
flux. So for consistency with T5 I would now propose
virtual_salt_flux_into_sea_water (kg m-2 s-1).

T8, T9. I agree with your insertion of "newtonian".

T10. Following T6, I would now suggest
virtual_salt_flux_into_sea_water_due_to_newtonian_relaxation (kg m-2 s-1).

T11. Things should have the same standard name if they are intended to be
compared. They need different standard names if you want to distinguish them.
So the choice depends on the application, to some extent. I think that
sea_surface_height_above_geoid is OK for the quantity derived from the rigid
lid, as used in CMIP3, but if you want to show where it comes from, my
modified suggestion of yours would be
ocean_rigid_lid_pressure_expressed_as_sea_surface_height_above_geoid. We don't
currently have a standard name of ocean_rigid_lid_pressure but it might
plausibly be proposed. We have other uses of "expressed as". What would you
prefer?

T13. We haven't put "depth" in other "ocean depth" names so I've omitted
it from your proposal.

T14. We have a standard name of plain "depth" meaning distance below the
surface, which is what you want, I think. It's fine to give it a coordinate of
sea_water_potential_temperature. If there is another quantity with that
standard name, they just have to have different variable names. Good solution!
There is a symmetry about having both sea_water_potential_temperature with a
coordinate of depth, and vice-versa. My only reservation is that the standard
name of the data variable doesn't indicate it's in the ocean, but I think
that's OK. The coord variable implies this, and anyway "depth" is really
independent of medium.

T15. "ocean" seems a bit unnecessary and it's only there to indicate the
integral is through the whole depth of the ocean, as contrasted with a layer.
We make this distinction in many standard names, however, and I'd like to get
rid of it, but that should be a separate proposal.

U3. A slight simplification of your latest version; I hope that's OK. N m-3
and Pa m-1 are both fine, being equivalent!

W3. Is this also temperature rather than tracer?

W4. You are right, we have not made this distinction; we have not used the
word "viscosity" at all so far because of the potential ambiguity.

W7. As alternative to introducing the term "lateral" we could perhaps call
this xy, to mean the coordinate plane. In other contexts we use the word
"horizontal" to mean this (as it usually is) but a vertical component of
something horizontal would certainly be a mysterious concept! Why do you
prefer "part" to "component"? I think
vertical_component_of_sea_water_tracer_xy_diffusivity would be intelligible.

G1-G3. I like your suggestion of "coordinate index". That gives us
  magnitude_of_derivative_of_distance_wrt_x_coordinate_index (m)
  magnitude_of_derivative_of_distance_wrt_y_coordinate_index (m)
  magnitude_of_derivative_of_distance_wrt_model_level_number (m)
but I wonder whether we might be better off with x_distance, y_distance
and depth? Although this is repetition, "distance" is rather a vague word
and that might clarify the picture. Since they are magnitudes it doesn't
matter whether it is depth or height, and depth seems more intuitive for
an ocean model. What do you think?

G4. The sign convention anticlockwise=positive should be stated in the
definition, as you say.

G6. I did prefer "area" earlier but you have changed my mind.

G7. Yes, you are right in thinking that the proposed change of the CF
cell_measures attribute, as described in our original email would need a trac
ticket raised, with a sponsor etc? This applies likewise to G1-G3, which
could also be cell_measures.

Best wishes

Jonathan
Received on Thu Aug 07 2008 - 03:51:08 BST