Hi all,
In CMIP5? only one of the three terms under discussion here was used:
"land_ice" (in the standard_name "land_ice_area_fraction"), which was
described as "fraction of grid cell occupied by "permanent" ice (i.e.,
glaciers)."? This was a "fixed" (time-independent) field.
As far as I can tell, "ice_on_land" isn't needed by CMIP6 (and it wasn't
needed or used in CMIP5).? I don't know (or have forgotten) what led it
to be introduced as a valid surface type.
best regards,
Karl
On 10/14/18 7:30 AM, Jonathan Gregory wrote:
> Reposting this, which didn't get to the list.
>
> Dear Karl, Sophie, Alison
>
> If we define ice_sheet to mean those of Greenland and Antarctica, it won't be
> applicable for palaeoclimate, so I think it's too restrictive. Although it's
> a continuum, there is a distinction between "ice sheet" and "glacier"
> that refers to size, with "ice-cap" being in the middle (and not used in IPCC
> to make things simpler). Ice sheets are big enough to bury the bedrock
> topography, so that the surface shape is determined by mass balance and
> dynamics. Glaciers are smaller, and confined within bedrock topography,
> which strongly influences their shape.
>
> If we want to mention Greenland and Antarctica explicitly, it would be a
> good idea to say "for example, in the modern world".
>
> No doubt it was discussed and I have forgotten, but being confronted with it
> now, I feel rather uncomfortable about there being distinct area_types of
> land_ice and ice_on_land. These types are not self-describing, in that the
> difference in wording does not convey anything about the difference in meaning.
>
> When and why was ice_on_land introduced?
>
> Best wishes
>
> Jonathan
>
> ----- Forwarded message from Karl Taylor <taylor13 at llnl.gov> -----
>
>> Date: Tue, 9 Oct 2018 11:44:53 -0700
>> From: Karl Taylor <taylor13 at llnl.gov>
>> To: "Nowicki, Sophie (GSFC-6150)" <sophie.nowicki at nasa.gov>,
>> "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
>> CC: Jonathan Gregory <j.m.gregory at reading.ac.uk>
>> Subject: Re: ice_sheet/land_ice confusion
>> User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0)
>> Gecko/20100101 Thunderbird/52.9.1
>>
>> Thanks, Sophie, for your quick response.? Given your clarification,
>> perhaps we might replace the description of ice_sheet, which
>> currently reads:
>>
>> > ice_sheet: An area type of "ice sheet" indicates where ice sheets are
>> > present. It includes both grounded ice sheets resting over bedrock and
>> > ice shelves flowing over the ocean, but excludes ice-caps and glaciers
>> > (in contrast to land_ice, which includes all components).
>>
>> with this description:
>>
>> ice_sheet: An area type of "ice_sheet" indicates where the Greenland
>> and Antarctic ice sheets are present.? It includes both the grounded
>> portion of those ice sheets (i.e., the portion resting on bedrock
>> either above or below sea level) and the portion that is floating as
>> ice shelves.? It excludes all other ice on land (in contrast to
>> land_ice, which includes, for example, small mountain glaciers and
>> in contrast to ice_on_land, which is comprehensively inclusive of
>> all types of ice on land).
>>
>> Also I think it should be clarified whether "snow" is considered to
>> be "ice_on_land".? If not, I think the descriptive phrase "any other
>> ice on a land surface" should be modified to read "any other ice on
>> a land surface (except snow)".
>>
>> Best regards,
>> Karl
>>
>>
>>
>> On 10/9/18 11:03 AM, Nowicki, Sophie (GSFC-6150) wrote:
>>> Hi Karl,
>>>
>>> I am responding to your question about ice_sheet/land_ice (CF-metadata Digest, Message 2, Vol 186, Issue11), and deleted the other topics from the thread.
>>>
>>> ?ice_sheet would be the Greenland and Antarctic ice sheets. It contains both the grounded_ice_sheet (part of the ice sheet flowing over bedrock, and you are technically right that an ice sheet is a combination of many many glaciers) and floating_ice_shelf (the part that only flows on water).
>>>
>>> land_ice is much bigger as it includes the polar ice sheets, glaciers in non-polar regions (glaciers are considered small body of ice: for example in the Alps, or the US), and the small ice caps. The ice caps are also a large combinations of glaciers, but too small to be considered an ice sheets. For example the Svartissen Ice Cap in northern Norway.
>>>
>>> For ISMIP6, we are interested in ice_sheet, but some climate models may also include glaciers and ice caps (which ISMIP6 does not care about). Hence the use of both ice_sheet and land_ice in the ISMIP6 protocol (and I cant recall if land_ice was already present in CMIP5, but I think that it was).
>>>
>>> I don?t know the origin of ice_on_land.
>>>
>>> Jonathan: please help me make my answers less confusing...
>>>
>>> I hope that this helps,
>>>
>>> Sophie
>>> Message: 2
>>> Date: Tue, 9 Oct 2018 17:19:36 +0000
>>> From: "Taylor, Karl E." <taylor13 at llnl.gov>
>>> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
>>> Subject: Re: [CF-metadata] ice_sheet / land_ice confusion
>>> Message-ID: <ec366da6-0f45-0c3a-0ebe-d7b20f7cfb55 at llnl.gov>
>>> Content-Type: text/plain; charset="utf-8"
>>> HI all,
>>> Can anyone provide any guidance on the difference between ice_sheet and
>>> land_ice (see below)?? It has a bearing on metadata to be stored with
>>> CMIP6 model output.
>>> thanks and best regards,
>>> Karl
>>> On 10/4/18 10:29 AM, Taylor, Karl E. wrote:
>>> > Hi all,
>>> >
>>> > I think there might be a mistake in the descriptions of "ice_sheet"
>>> > and/or "land_ice" in the "area type" table at
>>> > http://cfconventions.org/Data/area-type-table/current/build/area-type-table.html
>>> > .
>>> >
>>> > I find there the following definitions:
>>> >
>>> > ice_sheet: An area type of "ice sheet" indicates where ice sheets are
>>> > present. It includes both grounded ice sheets resting over bedrock and
>>> > ice shelves flowing over the ocean, but excludes ice-caps and glaciers
>>> > (in contrast to land_ice, which includes all components).
>>> >
>>> > land_ice: "Land ice" means glaciers, ice-caps, grounded ice sheets
>>> > resting on bedrock and floating ice-shelves.
>>> >
>>> > ice_on_land: The area type "ice_on_land" means ice in glaciers, ice
>>> > caps, grounded ice sheets (grounded and floating shelves), river and
>>> > lake ice, and any other ice on a land surface, such as frozen flood
>>> > water. This is distinct from the area type 'land ice' which has a
>>> > narrower definition.
>>> >
>>> > Are "ice-caps" and "glaciers" really excluded from "ice_sheet".? I would
>>> > have thought that "ice-cap" would be an ice_sheet located over a pole
>>> > (or something to that effect).? And i thought ice_sheets were just big
>>> > glaciers.
>>> >
>>> > ice_on_land is pretty clearly any frozen water, except sea ice,
>>> > icebergs, and ice particles in clouds, that is exposed to the atmosphere.
>>> >
>>> > So, I guess I'm trying to understand the difference between ice_sheet
>>> > and land_ice, and why do we need both of these?
>>> >
>>> > thanks and best regards,
>>> > Karl
>>> End of CF-metadata Digest, Vol 186, Issue 11
>>> ********************************************
>>>
> ----- End forwarded message -----
>
> ----- End forwarded message -----
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Received on Tue Oct 16 2018 - 22:38:59 BST
