[CF-metadata] Proposed CF standard names for the NEMO ocean model
Dear Ian and Dan
Thanks for taking the time to compile this list. I agree with you that it
would be good for NEMO netCDF output to be described by standard names. Are
all these names actually required for output fields that NEMO produces? We
don't usually define names until they are needed, to avoid having to foresee
too much of the future. Standard names need to have "canonical units"
i.e. indicating the physical dimension. I have added what I suppose these to
be in the list below but please correct me and fill in. I have made detailed
comments on most of the proposed names but many are minor.
Best wishes
Jonathan
> (T.1) upward_water_flux_from_ocean_to_sea_ice kg m-2 s-1
> ---------------------------------------------
> The water flux out of the ocean to the sea ice which results from the
> melting or freezing of sea ice.
This and following names point out a problem with the existing name
water_flux_into_ocean, which includes the flux due to sea-ice processes. Its
definition explicitly says it's the flux into the sea-water. But the sea-ice
is really, or at least arguably, part of the ocean, so this is unclear or
inconsistent. You use "ocean" here in the same same sense of the liquid. I
think we should clear up this confusion by renaming
water_flux_into_ocean
water_flux_into_ocean_from_rivers
water_volume_transport_into_ocean_from_rivers
wind_mixing_energy_flux_into_ocean
and Martina's proposed name
water_flux_into_ocean_without_flux_correction
by replacing "ocean" with "sea_water". Then I would suggest your name could be
water_flux_out_of_sea_water_due_to_sea_ice_thermodynamics
There is no need for "upward" if you have "out of" (or "from") and the
due_to phrase is used in other names.
> (T.2) upward_water_flux_from_ocean_due_to_PME kg m-2 s-1
> ---------------------------------------------
> The evaporation out of the ocean minus the precipitation into it.
I think this is the same as the existing name surface_upward_water_flux (over
the ocean) isn't it?
> (T.3) upward_water_flux_out_of_ocean_affecting_SSH kg m-2 s-1
> --------------------------------------------------
> The volumetric freshwater leaving the sea water as a result of
> precipitation, evaporation, river outflow and any water flux correction
> (s) that may have been applied.
This flux is the one which alters the mass of the ocean (=water+ice). It is
the same as -water_flux_into_sea_water except that it does not include the
sea-ice processes. Is that right? If so, I suggest
water_flux_out_of_sea_ice_and_sea_water
In your description you say "volumetric", though. Is that really what you
mean i.e. is it m s-1 rather than kg m-2 s-1? Is it liquid water equivalent
if so?
> (T.4) water_flux_out_of_ocean_to_rivers kg m-2 s-1
> ---------------------------------------
> This is -1 times the quantity with the existing standard name of
> water_flux_into_ocean_from_rivers.
That is logical but strikingly unphysical :-) and therefore it may be better
to spell it out as
minus_one_times_water_flux_into_sea_water_from_rivers
> (T.5) upward_water_flux_out_of_ocean_affecting_SSS kg m-2 s-1
> --------------------------------------------------
> The water flux out of the ocean affecting SSS is the
> "concentration/dilution" freshwater leaving the sea water as a result of
> precipitation, evaporation, river outflow, sea ice effects and any water
> flux correction(s) that may have been applied.
If I understand correctly, this is the same as -water_flux_into_sea_water
(currently -water_flux_into_ocean), isn't it? If so I would call it
water_flux_out_of_sea_water
which contrasts with T3.
> (T.6) downward_salt_flux_into_ocean_across sea_surface
> ------------------------------------------------------
> The sea surface salt flux deriving from a concentration/dilution water
> flux (5 above).
Is it really a salt flux (kg m-2 s-1) or it is a salinity flux (PSU m s-1)?
If it is a salt flux, it isn't a physical one, I guess, so we should make that
explicit by including some such word as "equivalent". Then I would try to make
it correspond somehow to T5.
> (T.7) ocean_mixed_layer_thickness_defined_by_eddy_diffusion_coefficient m
> -----------------------------------------------------------------------
> The base of the mixed layer defined by eddy diffusion coefficient is the
> level at which this diffusivity differs from its surface value by a
> certain amount (specified by a scalar coordinate).
As in Martina's and other existing names, this should be diffusivity rather
than diffusion_coefficient. Is it tracer_diffusivity or momentum_diffusivity?
What is meant by "eddy" here? - is "eddy" necessary?
> (T.8) surface_heat_flux_due_to_relaxation W m-2
> -----------------------------------------
> The heat flux applied at the sea surface in order to restore the sea
> surface temperature to some specified reference value (specified by a
> scalar coordinate).
This needs "downward" after "surface" to specify the sign. "surface" means
the bottom of the atmos, but this is presumably applied to sea_water (not
the sea_ice surface). In that case, it might be better to treat it like the
water fluxes and call it
heat_flux_into_sea_water_due_to_relaxation
> (T.9) surface_water_flux_due_to_relaxation kg m-2 s-1
> ------------------------------------------
> The surface water flux applied at the sea surface in order to restore
> the sea surface salinity to some specified reference value (specified by
> a scalar coordinate).
Following T8 this would be
water_flux_into_sea_water_due_to_relaxation
and that would be consistent with the other water_flux names, which is nice.
Do you think we should include "relaxation" in the definition of the general
water_flux_into_sea_water as well as flux correction? Or could we say that
"relaxation" is actually a kind of flux correction?
> (T.10) surface_salt_flux_due_to_relaxation
> ------------------------------------------
> The surface salt flux applied at the sea surface in order to restore the
> sea surface salinity to some specified reference value (specified by a
> scalar coordinate).
Similar comment to T6: is it really a salt flux? Is it equivalent to T9?
> (T.11) ocean_equivalent_rigid_lid_surface_height m
> ------------------------------------------------
> This is the ocean surface pressure derived using a rigid lid
> approximation, expressed as an equivalent sea surface height.
In data for CMIP3, we called this
sea_surface_height_above_geoid
just as if it had been obtained from a free surface. Do you need to specify
explicitly it was inferred from the rigid-lid pressure?
> (T.12)
> ocean_mixed_layer_thickness_in_model_levels_defined_by_sigma_theta 1
> -------------------------------------------------------------------------
> This quantity (the "bowl index") is the base level of that part of the
> upper ocean which is considered well-mixed, expressed in terms of model
> levels.
I think this is analogous to existing names of the form
model_level_number_at_SPECIAL_LEVEL so I would suggest
model_level_number_at_base_of_ocean_mixed_layer_defined_by_sigma_theta
> (T.13) thermocline_depth m
> ------------------------
> The depth of the maximum vertical gradient of sea water potential
> temperature.
This would benefit from ocean_ in front. But is this really *the* definition
of the thermocline depth? I suspect "thermocline depth" can be understood in
various ways. If so, something more explicit might help.
> (T.14) isotherm_depth m
> ---------------------
> The depth (if it exists) at which the sea water potential temperature
> equals some specified value, which would be specified as a scalar
> coordinate.
This also needs ocean_ in front.
> (T.15) ocean_heat_content J
> -------------------------
> The (assumed constant) specific heat capacity times density of sea water
> multiplied by the integral from z1 to z2 of sea water potential
> temperature wrt depth. Following CF rules, the data variable needs to
> have an axis for depth specifying [z1, z2] as bounds. How is this done
> in practice? And is "ocean_heat_content" a sufficiently unambiguous
> name? How, for instance, would we distinguish between this quantity and
> the equivalent heat content calculated using the in situ density and
> heat capacity?
The depth range is specified by giving the variable a scalar coordinate
variable of depth, or a dimension of depth with size one and a coordinate
variable, and then in either case attaching a bounds variable to the
coordinate variable. Your concerns about ambiguity worry me as well. We
already have a standard name of
ocean_integral_of_sea_water_temperature_wrt_depth
so perhaps it would be safer to be explicit about the heat content thus:
ocean_integral_of_sea_water_potential_temperature_wrt_depth_expressed_as_heat
What do you think?
> (T.16) surface_sea_ice_temperature K
> ----------------------------------
> Temperature of surface of sea ice.
This doesn't need a new name; it should just be surface_temperature for the
sea-ice portion of the box, which is specified using "where" in cell_methods
(according to the ticket which I hope will soon be agreed).
> (T.17) sea_ice_albedo 1
> --------------------
> Albedo of sea ice.
OK. I think this one does need its own name because it's a material property.
> (U.1) x_sea_water_velocity m s-1
> --------------------------
> The sea water velocity in the x-direction.
We already have sea_water_x_velocity
> (U.2) x_sea_water_velocity_due_to_eddies m s-1
> ----------------------------------------
> Eddy-induced velocities are a feature of some parameterisations of
> lateral diffusion in the ocean.
Is that the same as bolus transport (GM)? We have names for bolus velocity
components already, and the analogous one would be
bolus_sea_water_x_velocity
> (U.3) x_derivative_of_ocean_surface_pressure Pa m-1
> --------------------------------------------
> (d/dx) of the ocean surface pressure, keeping the other horizontal
> coordinate (y, presumably) constant.
x_derivative is fine, and I think we should note it in the standard name
guidelines. What is ocean_surface_pressure (air, rigid-lid, something else)?
V1-3 as U1-3
> (W.1) upward_sea_water_velocity_due_to_eddies m s-1
> ---------------------------------------------
> Eddy-induced velocities are a feature of some parameterisations of
> lateral diffusion in the ocean. =
See U2. Is this bolus_upward_sea_water_velocity, which exists already?
> (W.2) upward_sea_water_diffusivity_due_to_eddies m2 s-1
> ------------------------------------------------
> The effect of eddies on the vertical diffusivity of sea water.
diffusivity doesn't have a direction, does it, so upward->vertical. Is this
heat_diffusivity or tracer_diffusivity? What are eddies?
> (W.3) upward_sea_water_diffusivity_due_to_convection m2 s-1
> ----------------------------------------------------
> The enhanced diffusivity that is sometimes used to model the effect of
> convective mixing on tracers in the ocean.
Like W2 re upward and tracer.
> (W.4) upward_sea_water_viscosity_due_to_eddies m2 s-1
> ----------------------------------------------
> The effect of eddies on the vertical viscosity of sea water.
Like W2 re upward and eddies. viscosity->momentum_diffusivity, as in existing
names (if indeed it is m2 s-1) since viscosity has other dimensions.
> (W.5) upward_sea_water_viscosity_due_to_convection m2 s-1
> --------------------------------------------------
> The enhanced viscosity that is sometimes used to model the effect of
> convective mixing on momenta in the ocean.
Like W2 re upward. Like W4 re viscosity.
> (W.6) upward_salt_diffusivity_due_to_eddies m2 s-1
> -------------------------------------------
> The effect of eddies on the vertical diffusion of salinity.
Like W2 re upward and eddies.
> (W.7) upward_sea_water_diffusivity_due_to_lateral_mixing m2 s-1
> -------------------------------------------------
> The vertical component of the diffusivity of sea water due to lateral
> mixing. (This could appear in formulations of lateral diffusivity in
> which =B4lateral=A1 does not mean =B4iso-level=A1, eg isopycnal diffusivity
>
> (W.8) upward_sea_water_diffusivity_due_to_lateral_mixing_due_to_eddies m2 s-1
> ---------------------------------------------------------------
> The vertical component of the diffusivity of sea water due to the eddy-
> induced component of lateral mixing.(This could appear in formulations
> of lateral diffusivity in which =B4lateral=A1 does not mean =B4iso-level=A1=
> , eg
> isopycnal diffusivity.) Eddy-induced velocities are a feature of some
> parameterisations of lateral diffusion in the ocean.
Does NEMO output components of diffusivity? Components of flux seem more
physical to me.
> (G.1) magnitude_of_derivative_of_distance_wrt_x_coordinate
> ----------------------------------------------------------
> Known in differential geometry as a scale factor, this quantity is |
> (dr/di)jk|. It is a measure of the gridblock spacing in the x-
> direction.
What is x_coordinate? Is it an index? I think we should record a new standard
name guideline for "magnitude" of a scalar, meaning "absolute value of".
> (G.2) magnitude_of_derivative_of_distance_wrt_y_coordinate
> ----------------------------------------------------------
> Known in differential geometry as a scale factor, this quantity is |
> (dr/dj)ik|. It is a measure of the gridblock spacing in the y-
> direction.
As G1.
> (G.3) magnitude_of_derivative_of_distance_wrt_z_coordinate
> ----------------------------------------------------------
> Known in differential geometry as a scale factor, this quantity is |
> (dr/dk)ij|. It is a measure of the gridblock spacing in the z-
> direction.
As G1. If z_coordinate is an index, is it the same as model_level_number?
> (G.4) direction_of_x_grid_wrt_east degree
> ----------------------------------
> This quantity is the angle between due East and (dr/di)jk. It could be
> used for rotating vector fields between model space and latitude-
> longitude space.
"direction" has a restricted meaning in standard names. To avoid that and to
be explicit about the sign, could we call this
angle_of_rotation_from_east_to_x
if that is correct?
> (G.5) direction_of_y_grid_wrt_east degree
> ----------------------------------
> This quantity is the angle between due East and (dr/dj)ik. It could be
> used for rotating vector fields between model space and latitude-
> longitude space.
Like G4.
> (G.6) cell_area m2
> ---------------
> The horizontal area of a gridcell. See Sec 7.2 of CF documentation.
> Since this can be associated with a variable by means of cell_measure =3D
> area: attribute, it doesn't need a standard name, being considered part
> of the variable's metadata. However, we don't think there's any harm in
> proposing such a standard name. Comments?
I think it's OK.
> (G.7) ocean_thickness_in_model_levels 1
> -------------------------------------
> The depth of the ocean expressed in model levels.
I would call this model_level_number_at_sea_floor. The definition could note
that it does not have to be integer.
Received on Wed Jul 16 2008 - 11:43:15 BST
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