[CF-metadata] Fwd: cf-conventions-dimensionless coordinates

[Jonathan Gregory]

Dear Brian

Maybe it is generally the case that sigma=0 is the surface and sigma=1 is the
bed in ice-sheet models.

In some cases there could be more than one formula for a given dimensionless
vertical coordinate, as there are different ways of using it. The various
formulae could have different selections of terms.

Best wishes

Jonathan