[CF-metadata] new standard names for ECHAM5/CLM/ERA

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 23 Oct 2008 08:16:41 +0100

Dear Alison

You're right that an ice-shelf is ice that formed on land and flowed over the
sea as an extension of an ice-sheet or glacier.

I think that one question is whether we want the standard name itself to
indicate what sort of ice it is. That is, is the thickness of sea ice a
different geophysical quantity from the thickness of lake ice, ice-shelf
or iceberg ice. Is the heat-flux through these media the same geophysical
quantity, just in different fractions of the area of the gridbox? We've already
got different standard names for sea_ice_thickness and land_ice_thickness,
so we could distinguish the others too.

Alternatively, we could aggregate lake ice and sea ice on the one hand,
and ice-shelf and icebergs on the other, as you suggest, by making the
distinction according to whether it formed by freezing liquid water
from the sea or lake, or from snow. (Ice that formed from snow is
called "meteoric" in glaciology.) However, snow falls on sea-ice, and in some
circumstances becomes ice that contributes to the sea-ice thickness. Also,
sea-water freezes onto the bottom of ice-shelves, so part of the ice-shelf
and iceberg thickness is frozen sea-water. So this distinction not as clear
as it appears. Therefore I don't think "formed by freezing of water body"
is a satifactory category.

I suggest that either of these two approaches could work:

* Aggregate sea-ice, lake ice, ice-shelf and iceberg on the basis that they
are floating. Then we would have standard_names of floating_ice_thickness
and downward_heat_flux_in_floating_ice. In principle all the existing
sea_ice names could have corresponding floating_ice names.

* Distinguish all four of them and give them separate standard names, such
as lake_ice_thickness and ice_shelf_thickness (not yet requested).

I think that we probably need both approaches, according to circumstances.
For Heinke's request, I would suggest the floating_ice names, but since she
wants it only to apply to lake and sea ice, I would suggest introducing an
area_type of lake_ice_or_sea_ice, to be perfectly clear. That is actually
shorter than ice_covered_water_body anyway i.e.
  floating_ice_thickness where lake_ice_or_sea_ice
  downward_heat_flux_in_floating_ice where lake_ice_or_sea_ice
We could also introduce an area_type of floating_ice, which would include
ice-shelf and iceberg.

Best wishes

Jonathan
Received on Thu Oct 23 2008 - 01:16:41 BST