Dear Ian,
48 new standard names is a good score!
A few comments I have in my mind:
*(T.2), (T.3), (T.5) about 'PME', 'SSH' and 'SSS'
Maybe we are facing some particular points of CF: until when may we have to be intelligible in the standard_name attribute? [a question I often ask to myself, I guess the answer is "as possible as it is"..]
For example by 'SSH' you perhaps mean 'sea surface height', and there are 3 kinds of different sea surface heights in the CF standard name table. What kind of SSH would it match? Do you think it changes the meaning of (T3) not to mention 'affecting_SSH'? I'm asking this because I am not sure it is..But I way be wrong, please tell me.
*(T.6)
Why not 'surface_downward_salt_flux'?
*(T13)
Good to see it, we have some needs here too with thermocline variables.
*(T.15)
If we refer to what is available in atmosphere ('atmosphere_energy_content' etc.) I think your proposal is OK
*(U3)
I am interested in the idea of introducing such 'derivative' terms, good
*(U2,V2,W4)
You are talking about velocity due to eddies; is it the same situation than when velocity components are computed from geostrophic balance, with pressure gradient equal to Coriolis forces? (Because in that case there are standard names for geostrophic velocities)
Olivier Lauret
-----Message d'origine-----
De?: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] De la part de Ian Culverwell
Envoy??: vendredi 20 juin 2008 17:26
??: cf-metadata at cgd.ucar.edu
Objet?: [CF-metadata] Proposed CF standard names for the NEMO ocean model
Dear all,
Apologies in advance for the rather long email that follows.
We work on the NEMO ocean model, and would like to propose the following
CF standard names for its (standard) output fields, to help us to make
the whole thing CF-compliant. This would bring an increasingly popular
ocean model into the CF-community. So: your comments gratefully
appreciated!
Background:
-----------
NEMO works on an Arakawa C-grid, with staggering of T-points and W-
points in the vertical, on a general curvilinear coordinate grid.
Variables are still logically rectangular, ie var(i,j,k) where i, j and
k run over constant ranges. Components of vector fields are aligned with
the coordinate axes; these are not EW/NS in general. NEMO produces four
output files, each containing fields defined on the same grid: T, U, V,
W. We consider each file's variables in turn. Finally we propose
standard names for some general grid variables which are not currently
output from NEMO, but whose inclusion, perhaps in a sister "gridfile" to
each "fieldsfile", would make some analysis and visualisation tasks
easier.
Some of the proposed names differ from existing ones in rather trivial
ways, eg upward_x rather than downward_x. However, we deem this
preferable to changing the output fields so that they match existing CF
standard names (eg by multiplying by -1), as existing non-CF-compliant
post-processing applications will need to carry on working with the CF-
compliant fields.
48 proposed new CF standard names follow. We've saved the best till
last!
*******************************************************************************************
=============
T-grid fields
=============
(T.1) upward_water_flux_from_ocean_to_sea_ice
---------------------------------------------
The water flux out of the ocean to the sea ice which results from the
melting or freezing of sea ice.
(T.2) upward_water_flux_from_ocean_due_to_PME
---------------------------------------------
The evaporation out of the ocean minus the precipitation into it.
(T.3) upward_water_flux_out_of_ocean_affecting_SSH
--------------------------------------------------
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.
(T.4) water_flux_out_of_ocean_to_rivers
---------------------------------------
This is -1 times the quantity with the existing standard name of
water_flux_into_ocean_from_rivers.
(T.5) upward_water_flux_out_of_ocean_affecting_SSS
--------------------------------------------------
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.
(T.6) downward_salt_flux_into_ocean_across sea_surface
------------------------------------------------------
The sea surface salt flux deriving from a concentration/dilution water
flux (5 above).
(T.7) ocean_mixed_layer_thickness_defined_by_eddy_diffusion_coefficient
-----------------------------------------------------------------------
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).
(T.8) surface_heat_flux_due_to_relaxation
-----------------------------------------
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).
(T.9) surface_water_flux_due_to_relaxation
------------------------------------------
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).
(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).
(T.11) ocean_equivalent_rigid_lid_surface_height
------------------------------------------------
This is the ocean surface pressure derived using a rigid lid
approximation, expressed as an equivalent sea surface height.
(T.12)
ocean_mixed_layer_thickness_in_model_levels_defined_by_sigma_theta
-------------------------------------------------------------------------
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.
(T.13) thermocline_depth
------------------------
The depth of the maximum vertical gradient of sea water potential
temperature.
(T.14) isotherm_depth
---------------------
The depth (if it exists) at which the sea water potential temperature
equals some specified value, which would be specified as a scalar
coordinate.
(T.15) ocean_heat_content
-------------------------
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?
(T.16) surface_sea_ice_temperature
----------------------------------
Temperature of surface of sea ice.
(T.17) sea_ice_albedo
--------------------
Albedo of sea ice.
*****************************************************************************************
=============
U-grid fields
=============
(U.1) x_sea_water_velocity
--------------------------
The sea water velocity in the x-direction.
(U.2) x_sea_water_velocity_due_to_eddies
----------------------------------------
Eddy-induced velocities are a feature of some parameterisations of
lateral diffusion in the ocean.
(U.3) x_derivative_of_ocean_surface_pressure
--------------------------------------------
(d/dx) of the ocean surface pressure, keeping the other horizontal
coordinate (y, presumably) constant.
*****************************************************************************************
=============
V-grid fields
=============
(V.1) y_sea_water_velocity
--------------------------
The sea water velocity in the y-direction.
(V.2) y_sea_water_velocity_due_to_eddies
----------------------------------------
Eddy-induced velocities are a feature of some parameterisations of
lateral diffusion in the ocean.
(V.3) y_derivative_of_ocean_surface_pressure
--------------------------------------------
(d/dy) of the ocean surface pressure, keeping the other horizontal
coordinate (x, presumably) constant.
*****************************************************************************************
=============
W-grid fields
=============
(W.1) upward_sea_water_velocity_due_to_eddies
---------------------------------------------
Eddy-induced velocities are a feature of some parameterisations of
lateral diffusion in the ocean.
(W.2) upward_sea_water_diffusivity_due_to_eddies
------------------------------------------------
The effect of eddies on the vertical diffusivity of sea water.
(W.3) upward_sea_water_diffusivity_due_to_convection
----------------------------------------------------
The enhanced diffusivity that is sometimes used to model the effect of
convective mixing on tracers in the ocean.
(W.4) upward_sea_water_viscosity_due_to_eddies
----------------------------------------------
The effect of eddies on the vertical viscosity of sea water.
(W.5) upward_sea_water_viscosity_due_to_convection
--------------------------------------------------
The enhanced viscosity that is sometimes used to model the effect of
convective mixing on momenta in the ocean.
(W.6) upward_salt_diffusivity_due_to_eddies
-------------------------------------------
The effect of eddies on the vertical diffusion of salinity.
(W.7) upward_sea_water_diffusivity_due_to_lateral_mixing
-------------------------------------------------
The vertical component of the diffusivity of sea water due to lateral
mixing. (This could appear in formulations of lateral diffusivity in
which "lateral" does not mean "iso-level", eg isopycnal diffusivity.)
(W.8) upward_sea_water_diffusivity_due_to_lateral_mixing_due_to_eddies
---------------------------------------------------------------
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 "lateral" does not mean "iso-level", eg
isopycnal diffusivity.) Eddy-induced velocities are a feature of some
parameterisations of lateral diffusion in the ocean.
*****************************************************************************************
=================================
General grid-descriptor variables
=================================
Throughout the following, r(i,j,k) is the vector 3D position on the
earth of the (i,j,k) gridpoint.
(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.
(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.
(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.
(G.4) direction_of_x_grid_wrt_east
----------------------------------
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.
(G.5) direction_of_y_grid_wrt_east
----------------------------------
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.
(G.6) cell_area
---------------
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 =
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?
(G.7) ocean_thickness_in_model_levels
-------------------------------------
The depth of the ocean expressed in model levels. We allow non-integral
values to handle (increasingly popular) _partial cells_ in ocean models.
In such models, the lowest ocean gridcell (at any point) need only be
partially full of sea water. Thus, for example, if this field were 23.4
at some location, it would mean the water column at that point comprised
23 full model levels plus 40% occupancy of the lowest (24th) gridcell.
This field, together with the corresponding (2D) horizontal area and
(1D) full gridcell thickness (from depth_bounds or the vertical scale
factor), would be enough, for z-coordinate models, to generate the full
3D gridcell volume field at a fraction of the space needed to store it
directly (via the cell_measures: volume attribute).
One of us (DB) has previously proposed this idea (without eliciting a
huge response from the CF mailing list ...) with the further suggestion
that the possible cell_measures (currently restricted to "area" and
"volume") be extended to include "partial_cell_thickness", which would
point to this variable. Formalising its status as a cell measure would
allow post-processing software to take the necessary account of the
partial cells when calculating integrals, plotting cross-sections etc.
Comments welcome!
That's all. Thank you for reading through all this. We look forward to
hearing your thoughts.
Thanks in advance,
Ian & Dan.
--
Ian Culverwell B-2-81 Ocean and Sea Ice Modelling
Met Office FitzRoy Road Exeter Devon EX1 3PB United Kingdom
Tel: +44 (0)1392 884017 Fax: +44 (0)1392 885861
E-mail: ian.culverwell at metoffice.gov.uk http://www.metoffice.gov.uk
Met Office climate change predictions can now be viewed on Google Earth
http://www.metoffice.gov.uk/research/hadleycentre/google/
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Received on Thu Jun 26 2008 - 07:43:15 BST
