[CF-metadata] Question about cf conventions-dimensionless coordinates

[Jonathan Gregory]

Dear Brian

You are quite right. This is an omission; we do need a formula for the
working out the altitude coord from the land-ice sigma coord. Is it correct
that sigma is 0 at the bed and 1 and the surface? If so I reckon the formula is
  surface_altitude(n,k,j,i) = bedrock_altitude(n,j,i)
  + land_ice_thickness(n,j,i)*land_ice_sigma_coordinate(k)
where i,j are horizontal gridpoint indices, k level, n time. I'd propose
formula terms of bedrock_altitude, land_ice_thickness and
land_ice_sigma_coordinate. These are all standard names. In most of the
formulae we have used abbreviations to identify the terms, but why not
spell them out?

Best wishes

Jonathan