[CF-metadata] proposed standard names

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 12 Apr 2004 21:28:58 +0100

Additions and changes to the standard name table

I propose the changes listed at the end of this posting to be made at the end
of this month (April) if no-one raises any concerns with them. Most of them
follow from earlier discussions. Here are some further explanations:

* Radial velocity of scatterers

The proposed name is the result of a lengthy discussion, convened by Ag
Stephens, among radar experts about the best terminology. The issue was
thoroughly debated!

* Sea floor/level height/depth quantities

Looking at various references, I find terminology in this area inconsistent, so
I think we need to be more explicit. The difficulties arise because of two
possible reference surfaces, namely (a) mean sea level (b) the geoid, reference
ellipsoid or datum. These may differ by O(1) m because the ocean is in motion,
so its mean surface isn't a gravitational equipotential. This distinction is
important for some quantities. Hence I propose pairs of quantities, above/below
"sea level", which means "mean sea level" in standard names, and "datum",
meaning a fixed surface that approximates an equipotential. For ocean models
with a rigid lid, "datum" will mean the lid. Hence sea_floor_depth_below_datum
is the model's usual bathymetry field.

We may need to introduce a scheme to name the datum, as different analyses or
countries use different ones, when this is relevant. That's been raised in the
past. Further distinction may be needed in future between the datum or
reference ellipsoid on the one hand, these being fixed geometrical
constructions, and the geoid on the other, since it is really a geopotential
and has bumps at many scales, and is altered if the mass of the ocean changes
e.g. because of changes in land ice, or when other masses change e.g. land ice,
because of their gravitational attraction.
 
The new quantity sea_level_altitude is the surface altitude of the sea i.e. it
is equivalent to surface_altitude_where_sea, which isn't in the table. In
standard names generally, "altitude" means above the datum/geoid, while
"height" means above the surface.

* Vertical velocities in terms of pressure and sigma

Those who voted were tied (2-all - not many voted!) on the best choice.
Allocating myself an extra 0.1 votes, I therefore propose we call them
Lagrangian tendencies. I like this because I think it's more future-proof, as
we may well need names for other such quantities (derivatives with the motion)
that we wouldn't call vertical velocities. I agree that this terminology may
not be so familiar, but I hope the new standard name search facility will help.
If we arrange that the help text for these quantities also describes them as
equivalent to vertical velocity, searching on the help text should find them.

* x- and y-velocities

Moving the x- and y- will accommodate longer phrases than "sea water" in front
for future standard names.

Cheers

Jonathan


Add radial_velocity_of_scatterers_away_from_instrument (m s-1)
Add sea_surface_height_above_sea_level (m)
Make sea_surface_height an alias of this
Add sea_surface_height_above_datum (m)
Make sea_surface_elevation an alias of this
Add sea_level_altitude (m)
Add sea_floor_depth_below_sea_level (m)
Make sea_floor_depth an alias of this
Add sea_floor_depth_below_datum (m)
Add lagrangian_tendency_of_air_pressure (Pa s-1)
Make vertical_air_velocity_expressed_as_tendency_of_pressure an alias of this
Add lagrangian_tendency_of_atmosphere_sigma_coordinate
Make vertical_air_velocity_expressed_as_tendency_of_sigma an alias of this
Add sea_water_x_velocity (m s-1)
Make x_sea_water_velocity an alias of this
Add sea_water_y_velocity (m s-1)
Make y_sea_water_velocity an alias of this
Received on Mon Apr 12 2004 - 14:28:58 BST