[CF-metadata] CMIP6 Sea Ice MIP: General variables

From: Jonathan Gregory <j.m.gregory>
Date: Thu, 21 Jul 2016 14:27:33 +0100

Dear Dirk

> >> 5. sea_ice_melt_pond_thickness [m]
> >> the volume of water in meltponds divided by meltpond covered area
> >
> > OK, with a similar cell_methods issue: I think by default this would be
> > a local thickness, but it could be described as an area-mean.
>
> Our definition was simply based on the usual way of representing
> melt-pond water in model simulations. However, as this is meant to be a
> local thickness, we'd be happy to change the definition to simplyread
> "Local thickness of melt ponds"

Perhaps to be clear we could say something like "Thickness of melt pond.
The cell_methods indicates whether it is a local thickness, an area-mean
thickness or some other statistic."

> >> 6. thickness_of_sea_ice_melt_pond_refrozen_ice [m]
> >> the volume of refrozen ice in meltponds divided by meltpond covered area
> >
> > Is this ice floating on top of the meltpond?
>
> Yes, it is. Do you believe that the definition should be changed?

I wasn't clear what the quantity is. We already have a standard name of
floating_ice_thickness, of which this is a special case. So we could use the
existing name and distinguish this case in cell_methods with
"area: mean where sea_ice_melt_pond". Would that be acceptable?

> >> 22. sea_ice_specific_x_force_due_to_sea_surface_tilt [N m-2]
> >> 23. sea_ice_specific_y_force_due_to_sea_surface_tilt [N m-2]
> >> 24. sea_ice_specific_x_force_due_to_coriolis_term [N m-2]
> >> 25. sea_ice_spcecific_y_force_due_to_coriolis_term [N m-2]
> >> 26. sea_ice_specific_x_force_due_to_internal_forces [N m-2]
> >> 27. sea_ice_specific_y_force_due_to_internal_forces [N m-2]
> >
> > In other N m-2 = Pa names, we use "stress" rather than "specific force" but
> > I suppose this is different because they are not fluxes of momentum, but
> > divergences of momentum i.e. force per unit mass. Is "specific force" a
> > usual term for this? Could we say "coriolis_effect" rather than "term",
> > which sounds more algorithmic than geophysical?
>
> In trying to follow CF_conventions, we adopted "specific" to point out
> that these forces are calculated per unit area. We'd be very happy to
> drop "specific":
>
> 26+27 could then simply be referred to as "sea_ice_internal_stress_x"
> and "sea_ice_internal_stress_y".
>
> For 22-25, it would be non-standard in the sea-ice community to call
> those "stress", as both coriolis and surface tilt act as body forces.
> Standard terminology would be to simply refer to them as
> "coriolis_force_on_sea_ice" and "sea_surface_tilt_force", but this is
> probably not consistent with CF-conventions as units are force per area.
> Do you have any other suggestion of how we could call these "forces per
> sea-ice area"?

Thanks for explaining. We do already have some standard names with the longer
phrase per_unit_area in them, so maybe that would be the best pattern to
follow:
  sea_ice_[xy]_force_per_unit_area_due_to_X
where X is sea_surface_tilt, coriolis_effect or internal_stress. Would
that be correct and make sense?

Best wishes

Jonathan
Received on Thu Jul 21 2016 - 07:27:33 BST