[CF-metadata] Vertical Coordinate Systems

From: Schmidli Juerg <schmidli>
Date: Wed, 23 Jul 2003 15:00:35 +0200

Dear Jonathan

> atmosphere_sleve_coordinate: This looks OK. Presumably you are using it
> yourself and therefore need it to be added? Can you describe what the two
> surfaces zsurf1 and zsurf2 mean in physical terms? If we add this, I would
> prefer that we call it something more explicit such as the title you have
> given it ("smooth level"), because "sleve" is cryptic.

The sleve coordinate is similar to the hybrid height coordinate. The
difference
is that the topography zsurf(i,j,n) is split into a large-scale part
zsurf1(i,j,n)
and a small-scale part zsurf2(i,j,n). The clue of the sleve coordinate
is that
the small-scale part of the topography can be made to decay much faster
with height,
resulting in smoother computational levels in the upper troposphere and
stratosphere.

I would prefere the acronym sleve. The acronym is introduced in the
publication by
Schaer et al. 2002 which describes the new vertical coordinate and it is
widely
used by the community. However, atmosphere_smooth_level_coordinate would
also be
ok.

> naming and ordering: Where do you think we have been inconsistent about the
> names? I don't think the order matters. The terms in the formula_terms can
> be put in any order. To specify a particular order would be less convenient
> for the data-writer and probably not useful as it would very likely not always
> be followed.

ordering: I absolutely agree that the order should not play a role. My
suggestion
is only, to use a consistent ordering of the terms for the description
in Appendix C.
That is that the first term in the formula be related to ptop/ztop, and
the second
term to psurf/zsurf, if applicable. (see examples below)

naming:
The pressure/height at the model top is referred to as
ptop, for the
p0, for the atmosphere_hybrid_sigma_pressure_coordinate,
ztop, for the atmosphere_hybrid_height_coordinate,

The pressure/height of the surface is referred to as
ps, for atmosphere_sigma_coordinate and
atmosphere_hybrid_sigma_pressure_coordinate,
zsurface, for atmosphere_hybrid_height_coordinate,

My suggestion would be to use the same abbreviations for the
corresponding terms, thus

for atmosphere_sigma_coordinate:
p(n,k,j,i) = (1-sigma)*ptop + sigma*psurf(n,j,i)
formula_terms = "sigma:var1 ptop:var2 psurf:var3"

for atmoshpere_hybrid_sigma_pressure_coordinate:
p(n,k,j,i) = a(k)*ptop + b(k)*psurf(n,j,i)
formula_terms = "a:var1 b:var2 ptop:var3 psurf:var4"

for atmoshpere_hybrid_height_coordinate:
z(n,k,j,i) = a(k)*ztop + b(k)*zsurf(n,j,i)
formula_terms = "a:var1 b:var2 ztop:var3 zsurf:var4"

for atmosphere_sleve_coordinate:
z(n,k,j,i) = a(k)*ztop + b1(k)*zsurf1(n,j,i) + b2(k)*zsurf2(n,j,i)
formula_terms = "a:var1 b1:var2 b2:var3 ztop:var4 zsurf1:var5
zsurf2:var6"


Juerg
Received on Wed Jul 23 2003 - 07:00:35 BST