Dear all,
On 20th June 2008 we proposed a list of draft CF standard names for the
"standard" output from the NEMO ocean model. Most of these have been
revised following some lengthy discussions with Jonathan Gregory and
Olivier Lauret. For the record, we would therefore now like to place
the following revised list of proposals before you. Since these have
already been discussed in some detail, we're not exactly pleading for
further comments, but of course if any vital questions spring to mind,
please respond as usual to this email list. Thank you.
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.
Fortysomething proposed new CF standard names follow. Some of the
original suggestions were for quantities that already had standard
names, so they have been dropped from the list - although we have kept
the numbering of the original list. In addition, it became clear that
some existing standard names should probably be renamed, largely for
reasons of consistency. I don't know how this should be done - through
aliases? Anyway, these are listed first.
*******************************************************************************************
=======================================
New names of existing CF standard names
=======================================
(R.1) water_flux_into_sea_water (kg m2 s-1)
-------------------------------------------
This is a new name for water_flux_into_ocean. Its definition needs to be
extended to include relaxation, thus:
"Water" means water in all phases. The water flux into the ocean is the
freshwater entering the sea water as a result of precipitation,
evaporation, river inflow, sea ice effects and water flux relaxation and
correction (if applied). In accordance with common usage in geophysical
disciplines, "flux" implies per unit area, called "flux density" in
physics.
(R.2) water_flux_into_sea_water_from_rivers (kg m2 s-1)
--------------------------------------------------------
This is a new name for water_flux_into_ocean_from_rivers.
(R.3) water_volume_transport_into_sea_water_from_rivers (kg m2 s-1)
-------------------------------------------------------------------
This is a new name for water_volume_transport_into_ocean_from_rivers.
(R.4) wind_mixing_energy_flux_into_sea_water (W m-2)
----------------------------------------------------
This is a new name for wind_mixing_energy_flux_into_ocean.
(R.5) water_flux_into_sea_water_without_flux_correction (kg m-2 s-1)
--------------------------------------------------------------------
This is a new name for water_flux_into_ocean_without_flux_correction
(not yet an an official standard_name, but a proposal from Martina
Stockhause which has been agreed).
*******************************************************************************************
=============
T-grid fields
=============
(T.1) water_flux_out_of_sea_water_due_to_sea_ice_thermodynamics (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.
(T.3) water_flux_out_of_sea_ice_and_sea_water (kg m-2 s-1)
----------------------------------------------------------
The water flux leaving the ocean as a result of precipitation,
evaporation, river outflow and any water flux relaxation(s) and
correction(s) that may have been applied.
(T.4) minus_one_times_water_flux_into_sea_water_from_rivers (kg m-2 s-1)
------------------------------------------------------------------------
This is -1 times water_flux_into_sea_water_from_rivers (currently
water_flux_into_ocean_from_rivers - see R2 above).
(T.5) water_flux_out_of_sea_water (kg m-2 s-1)
----------------------------------------------
This is -1 times the quantity with the existing standard name of
water_flux_into_sea_water (currently water_flux_into_ocean - see R1
above). It includes the effects of precipitation, evaporation, river
outflow, sea-ice and any water flux relaxation(s) and correction(s) that
may have been applied.
(T.6) virtual_salt_flux_into_sea_water (kg m-2 s-1)
---------------------------------------------------
The salt flux that would have the same effect on the sea surface
salinity as the water_flux_out_of_sea_water. It includes the effects of
precipitation, evaporation, river outflow, sea-ice and any water flux
relaxation(s) and correction(s) that may have been applied.
(T.7) ocean_mixed_layer_thickness_defined_by_vertical_tracer_diffusivity
(m)
-------------------------------------------------------------------------------------
The depth at which the vertical tracer diffusivity differs from its sea
surface value by a
certain amount.
(T.8) heat_flux_into_sea_water_due_to_newtonian_relaxation (W m-2)
------------------------------------------------------------------
The heat flux into the sea-water as a result of Newtonian relaxation of
the sea surface temperature.
(T.9) water_flux_out_of_sea_water_due_to_newtonian_relaxation (kg m-2
s-1)
------------------------------------------------------------------------
The water flux into the sea-water as a result of Newtonian relaxation of
the sea surface salinity.
(T.10) virtual_salt_flux_into_sea_water_due_to_newtonian_relaxation (kg
m-2 s-1)
--------------------------------------------------------------------------------
The salt flux that would have the same effect on sea surface salinity as
water_flux_into_sea_water_due_to_newtonian_relaxation.
(T.11)
ocean_rigid_lid_pressure_expressed_as_sea_surface_height_above_geoid (m)
-------------------------------------------------------------------------------
This is the ocean surface pressure derived using a rigid lid
approximation, expressed as an equivalent sea surface height above the
geoid.
(T.12) model_level_number_at_base_of_ocean_mixed_defined_by_sigma_theta
(1)
---------------------------------------------------------------------------
This quantity (the "bowl index") is the base of that part of the upper
ocean which is considered well-mixed, as defined by a specified change
in the sea water potential density from its surface value, expressed in
model levels.
(T.13)
depth_at_maximum_upward_derivative_of_sea_water_potential_temperature
(m)
--------------------------------------------------------------------------------
This quantity (the "thermocline depth") is the depth of the maximum
vertical gradient of sea water potential temperature.
(T.14) depth_of_isosurface_of_sea_water_potential_temperature (m)
-----------------------------------------------------------------
This quantity (the "isotherm depth") is the depth (if it exists) at
which the sea water potential temperature equals some specified value.
(T.15)
integral_of_sea_water_potential_temperature_wrt_depth_expressed_as_heat_content
(J m-2)
--------------------------------------------------------------------------------------
The (assumed constant) specific heat capacity times density of sea water
multiplied by the integral, over a specified layer of the ocean, of the
sea water potential temperature wrt depth.
(T.17) sea_ice_albedo (1)
-------------------------
The albedo of sea ice.
*****************************************************************************************
=============
U-grid fields
=============
(U.2) bolus_sea_water_x_velocity (m s-1)
----------------------------------------
The "bolus" velocity in the x-coordinate direction, as used in some
parameterisations of lateral diffusion in the ocean.
(U.3) x_derivative_of_ocean_rigid_lid_pressure (N m-3)
------------------------------------------------------
(d/dx) of the ocean surface pressure, as derived by a rigid lid
approximation, keeping the other horizontal coordinate (y, presumably)
constant.
*****************************************************************************************
=============
V-grid fields
=============
(V.2) bolus_sea_water_y_velocity (m s-1)
----------------------------------------
The "bolus" velocity in the y-coordinate direction, as used in some
parameterisations of lateral diffusion in the ocean.
(V.3) y_derivative_of_ocean_rigid_lid_pressure (N m-3)
------------------------------------------------------
(d/dy) of the ocean surface pressure, as derived by a rigid lid
approximation, keeping the other horizontal coordinate (x, presumably)
constant.
*****************************************************************************************
=============
W-grid fields
=============
(W.2) ocean_vertical_heat_diffusivity (m2 s-1)
----------------------------------------------
The vertical component of the diffusivity of heat in the ocean.
(W.3) ocean_vertical_tracer_diffusivity_due_to_convection (m2 s-1)
------------------------------------------------------------------
The vertical component of the enhanced diffusivity of tracers that is
sometimes used to model the effect of convective mixing in the ocean.
(W.4) ocean_vertical_momentum_diffusivity (m2 s-1)
--------------------------------------------------
The vertical component of the diffusivity of momentum in the ocean.
(W.5) ocean_vertical_momentum_diffusivity_due_to_convection (m2 s-1)
--------------------------------------------------------------------
The vertical component of the enhanced diffusivity of momentum that is
sometimes used to model the effect of convective mixing in the ocean.
(W.6) ocean_vertical_salt_diffusivity (m2 s-1)
----------------------------------------------
The vertical component of the diffusivity of salt in the ocean.
(W.7) vertical_component_of_ocean_xy_tracer_diffusivity (m2 s-1)
----------------------------------------------------------------
The vertical component of the diffusivity of tracers in the ocean due to
lateral mixing. (This could appear in formulations of lateral
diffusivity in which ?lateral? does not mean ?iso-level?, eg isopycnal
diffusivity.)
*****************************************************************************************
=================================
General grid-descriptor variables
=================================
(G.1) magnitude_of_derivative_of_position_wrt_x_coordinate_index (m)
--------------------------------------------------------------------
This quantity (known in differential geometry as a "scale factor") is |
(dr/di)jk|, where
r(i,j,k) is the vector 3D position of the point with coordinate indices
(i,j,k). It is a measure of the gridblock spacing in the x-direction.
(G.2) magnitude_of_derivative_of_position_wrt_y_coordinate_index (m)
--------------------------------------------------------------------
This quantity (known in differential geometry as a "scale factor") is |
(dr/dj)ik|, where
r(i,j,k) is the vector 3D position of the point with coordinate indices
(i,j,k). It is a measure of the gridblock spacing in the y-direction.
(G.3) magnitude_of_derivative_of_position_wrt_model_level_number (m)
--------------------------------------------------------------------
This quantity (known in differential geometry as a "scale factor") is |
(dr/dk)ij|, where
r(i,j,k) is the vector 3D position of the point with coordinate indices
(i,j,k). It is a measure of the gridblock spacing in the z-direction.
(G.4) angle_of_rotation_from_east_to_x (degree)
-----------------------------------------------
This quantity is the angle, anticlockwise reckoned positive, between due
East and (dr/di)jk, where r(i,j,k) is the vector 3D position of the
point with coordinate indices (i,j,k). It could be used for rotating
vector fields between model space and latitude-longitude space.
(G.5) angle_of_rotation_from_east_to_y (degree)
-----------------------------------------------
This quantity is the angle, anticlockwise reckoned positive, between due
East and (dr/dj)ik, where r(i,j,k) is the vector 3D position of the
point with coordinate indices (i,j,k). It could be used for rotating
vector fields between model space and latitude-longitude space.
(G.6) cell_area (m2)
--------------------
The horizontal area of a gridcell.
(G.7) model_level_number_at_sea_floor (1)
-----------------------------------------
The depth of the ocean expressed in model levels. This could be non-
integral, to handle partial cells in ocean models. (So, 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.)
*****************************************************************************************
=============
Miscellaneous
=============
(M.1) derivative_of_X_wrt_Y ([X]/[Y])
-------------------------------------
In all the above definitions that include the term "derivative", we mean
the partial derivative. Since this includes the ordinary derivative as a
special case, we propose extending the standard name guidelines for this
as follows:
"derivative_of_X_wrt_Y | [X]/[Y] | dX/dY (keeping any other independent
variables constant, ie the partial derivative if appropriate).
(M.2) ocean_rigid_lid_pressure (N m-2)
--------------------------------------
Since some of the proposals depend on this, we may as well define it as
a standard name, thus:
The pressure at the surface of an ocean model assuming that it is
bounded above by a rigid lid.
*****************************************************************************************
That's all. Thanks for reading through all this. We look forward to
hearing any further thoughts you have on these proposals.
Regards,
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
Dan Bernie
HadGEM Physical Processes and Coupling Scientist
Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB
Tel: +44 (0)1392 884862 Fax: +44 (0)1392 885681
E-mail: dan.bernie 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/
Received on Wed Aug 13 2008 - 09:51:42 BST
