[CF-metadata] additional standard name for ISMIP6

Jonathan Gregory j.m.gregory at reading.ac.uk
Wed Jan 25 10:27:34 MST 2017

Dear Alison

Thanks as always for your skillful and meticulous work and very useful
questions and remarks. Reading through this, I noticed a couple of things:

> > > 17. land_ice_mass_not_displacing_sea_water (kg)
> The name and units are agreed. I suggest the following as the definition:
> ' "Land ice not displacing sea water" means land ice that would not alter sea level if removed. It excludes ice shelves and grounded ice-sheets resting on bedrock that is below sea level. It includes glaciers, floating ice caps and ice-sheets resting on bedrock above sea level. The quantity with standard name land_ice_mass_not_displacing_sea_water is the total mass integrated over an area of land ice. The geographical extent of the ice over which the mass was calculated should be described by providing bounds on the horizontal coordinate variables.'
> Is the bit about glaciers and ice caps correct? I put it in because the definition of land_ice usually refers to them and I want to be as clear as possible about how this name differs from the others.

Glaciers is correct, but not "floating ice caps". You could say "ice caps".
Glaciologists use "ice cap" to mean a thing like a glacier or an ice sheet
but of intermediate size. (Journalists, confusingly, sometimes use "ice cap"
to refer to Arctic sea-ice.)

> > > 18. grounded_ice_sheet_area (m2)
> Okay, so the quantity you need is the actual area of the grounded ice sheet. Unfortunately, we can't just call it 'area' because the definition of the existing names refers to the area within a grid cell. I think we would have to call it an integral. You say that it is summed over the entire grid, so is this a truly global quantity? If so, we could perhaps call it global_integral_of_grounded_ice_sheet_area by analogy with the existing global_average_sea_level names. If you want to be able to calculate the quantity for individual ice sheets then we'd have to call it something like integral_of_grounded_ice_sheet_wrt_xy, where xy essentially means the horizontal coordinates. You could then supply bounds on the coordinate variables to show the geographical extent of the area integral. What do you think?

Are you sure we can't call it area? It seems to me it's fine to call it that
if the coordinates indicate it refers to the whole world (regarded as one
grid cell) or to some large region (containing an entire ice sheet).

> 21. floating_ice_sheet_area_fraction (1)
> ' "X_area_fraction" means the fraction of horizontal area occupied by X. A "floating ice sheet", sometimes called an "ice shelf", indicates where the ice sheet is flowing over sea water.'

Shouldn't that be floating_ice_shelf_area_fraction?

Best wishes


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