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 <[email protected]> ----- > >> Date: Tue, 9 Oct 2018 11:44:53 -0700 >> From: Karl Taylor <[email protected]> >> To: "Nowicki, Sophie (GSFC-6150)" <[email protected]>, >> "[email protected]" <[email protected]> >> CC: Jonathan Gregory <[email protected]> >> 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." <[email protected]> >>> To: "[email protected]" <[email protected]> >>> Subject: Re: [CF-metadata] ice_sheet / land_ice confusion >>> Message-ID: <[email protected]> >>> 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 ----- > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
