#140: Clarifying the role of attributes on boundary variables.
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Reporter: davidhassell | Owner: cf-conventions@…
Type: enhancement | Status: new
Priority: medium | Milestone:
Component: cf-conventions | Version:
Resolution: | Keywords: boundary variable, attribute
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Comment (by davidhassell):
Hello Karl, Jonathan and all,
It'd be nice to wrap this up! How about this text, which says "feel
free to put formula_terms on bounds, but if they're not there then
infer them from the parent parametric coordinate"
If a parametric coordinate variable with a formula_terms attribute
(ref section 4.3.2) also has a bounds attribute, then that formula
must also be associated with the boundary variable, because the
same `standard_name` describes both variables. The association is
explicit if the boundary variable also has a `formula_terms`
attribute defining the same terms (as specified in Appendix D),
but a different variable must be named for any term which depends
on the vertical dimension, because the boundary variables have one
more dimension. If the association is implicit then the
`formula_terms` attribute is omitted from the boundary variable
and it is assumed that the `formula_terms` attribute from the
parametric coordinate variable applies, but for any term which
depends on the vertical dimension, the named variable is replaced
with its boundary variable. In this case, such named variables
must be auxiliary coordinate variables with associated boundary
variabes.
Explicit example:
{{{
float eta(eta) ;
eta:long_name = "eta at layer midpoints" ;
eta:positive = "down" ;
eta:standard_name = " atmosphere_hybrid_sigma_pressure_coordinate" ;
eta:formula_terms = "a: a b: b ps: ps p0:p0”;
eta:bounds="etabnds";
float etabnds(eta,2);
etabnds:formula_terms = " a: abnds b: bbnds ps: ps p0:p0" ;
float a(eta);
a:long_name = "’a’ coefficient for vertical coordinate (at full
levels)";
a:units = ‘Pa’
float b(eta);
b:long_name = "’b’ coefficient for vertical coordinate (at full
levels)";
b:units = ‘Pa Pa-1’
float abnds(eta,2);
abnds:long_name = "’a’ coefficient for vertical coordinate (at half-
levels)";
float bbnds(eta,2);
bbnds:long_name = "’b’ coefficient for vertical coordinate (at half-
levels)";
float ps(lat, lon);
ps.units = 'Pa';
float p0;
p0.units = 'Pa';
float T(eta,lat,lon);
T:standard_name="air_temperature";
T:units="K";
}}}
Implicit example:
{{{
float eta(eta) ;
eta:long_name = "eta at layer midpoints" ;
eta:positive = "down" ;
eta:standard_name = " atmosphere_hybrid_sigma_pressure_coordinate" ;
eta:formula_terms = "a: a b: b ps: ps p0:p0”;
eta:bounds="etabnds";
float etabnds(eta,2);
float a(eta);
a:long_name = "’a’ coefficient for vertical coordinate (at full
levels)";
a:units = ‘Pa’
a:bounds = "abnds";
float b(eta);
b:long_name = "’b’ coefficient for vertical coordinate (at full
levels)";
b:units = ‘Pa Pa-1’
b:bounds = "bbnds";
float abnds(eta,2);
float bbnds(eta,2);
float ps(lat, lon);
ps.units = 'Pa';
float p0;
p0.units = 'Pa';
float T(eta,lat,lon);
T:standard_name="air_temperature";
T:units="K";
T:coordinates="a b";
}}}
Note also that there is nothing stopping the two methods being
combined, which the checker would have to look out for. E.g.
{{{
float eta(eta) ;
eta:long_name = "eta at layer midpoints" ;
eta:positive = "down" ;
eta:standard_name = " atmosphere_hybrid_sigma_pressure_coordinate" ;
eta:formula_terms = "a: a b: b ps: ps p0:p0”;
eta:bounds="etabnds";
float etabnds(eta,2);
etabnds:formula_terms = " a: abnds b: bbnds ps: ps p0:p0" ;
float a(eta);
a:long_name = "’a’ coefficient for vertical coordinate (at full
levels)";
a:units = ‘Pa’
a.bounds = 'abnds';
float b(eta);
b:long_name = "’b’ coefficient for vertical coordinate (at full
levels)";
b:units = 'Pa Pa-1';
b.bounds = 'bbnds';
float abnds(eta,2);
float bbnds(eta,2);
float ps(lat, lon);
ps.units = 'Pa';
float p0;
p0.units = 'Pa';
float T(eta,lat,lon);
T:standard_name="air_temperature";
T:units="K";
T.coordinates = 'a b';
}}}
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Ticket URL: <https://cf-trac.llnl.gov/trac/ticket/140#comment:10>
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