Dear Yilmaz > 1) "s(k) is the dimensionless coordinate at vertical gridpoint (k)" > Does this variable refer to itself, i.e. whose "formula_terms" attribute > is being parsed? If this is the case, why do we still include this > element > in the "formula_terms" attribute?
Yes, it does refer to itself. The idea is that the formula identifies all the variables which are needed to compute the dimensional vertical coordinate. It happens that s is one of the terms in the formula, not all kinds of vertical coordinate include themselves as one of the terms. > > 2) do variables which correspond to "depth" and "eta" need to have the same > units? That is, can one of them be in meters and the other in centimeters? > If they can be different, then doesn't the variable which > corresponds to "depth_c" > also need to have a unit? Do we need to expect a unit for it? The standard does not make this clear, but I agree, they all need units, and generic software should do appropriate units conversion. > Because since it is > a scalar variable, it is not required to have one according to CF > conventions(?). I think that's a confusion of the two meanings of "dimensionless". One sense of "dimensionless" means a pure number, without units. Quantities like that, such as sea-ice area fraction, do not need units. That's a different meaning of "dimensionless" meaning zero-dimensional i.e. scalar. Scalar quantities with physical dimensions do need units. > 3) We know that a dimensional coordinate variable is either > monotonically increasing > or decreasing. Will it be the case for dimensionless ones after > the formula is applied? > That is, do these formulas and associated variable contents > guarantee that, when the P > formula is applied, we will obtain a vector of pressure or height > values, which are monotonically > increasing or decreasing? (I would expect so since they are levels > of depth or pressure) I don't think that is guaranteed, though I agree it would be physically sensible to arrange it. But it's not a requirement of CF. > 4) "level", "layer", and "sigma_level" are deprecated according to CF > conventions, however, still > allowed. So how would it be possible for a generic application to > interpret them? They should all be interpreted as dimensionless, equivalent to 1. > 5) And finally, under section "2.4 Dimensions" it says that > "dimensions other than those of space > and time may be included". If this is the case, is it still possible > for a generic application to work > without being able to interpret those additional dimensions? That is, > how a could a generic application > decide on which index value to pass for that dimension without recognizing it? I don't really understand that question. The dimensions correspond to the array subscripts. You can subscript an array without knowing the physical meaning of the dimensions, can't you. Non-spatiotemporal dimensions should be identified by standard name, although that is not a requirement of CF. Cheers Jonathan _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
