Dear Alison I agree that an alias mechanism would be better than abolishing something we have introduced. Although it might sound inaccurate, "land ice" is a term that is used in the literature to mean ice sheets and glaciers, rather than all ice on land. It contrasts with sea ice, as has been remarked,
I think that ice_on_land could be confused with land_ice. In addition, ice_on_land could be confusing because snow *is* ice; there isn't a clear distinction between snow and non-snow ice, and ice_and_snow_on_land could mean the same as ice_on_land. Therefore I suggest that we made ice_on_land into an alias of ice_and_snow_on_land. Best wishes Jonathan ----- Forwarded message from Alison Pamment - UKRI STFC <[email protected]> ----- > Date: Wed, 17 Oct 2018 15:05:06 +0000 > From: Alison Pamment - UKRI STFC <[email protected]> > To: Karl Taylor <[email protected]>, Martin Juckes - UKRI STFC > <[email protected]>, "CF-metadata ([email protected])" > <[email protected]> > Subject: Re: [CF-metadata] ice_sheet/land_ice confusion > > Dear Karl et al., > > Thank you all for the comments in this discussion, which I have been watching > with interest. > > I think we can regard the three existing land ice area_types as nested: > ice_sheets = Grounded ice sheets + Floating ice shelves; > land_ice = ice_sheets + Glaciers + Ice caps; > ice_on_land = land_ice + River ice + Lake ice + Other ice on land, e.g frozen > flood water. > > In addition we have: > ice_and_snow_on_land = snow overlying ice_on_land + snow overlying bare > ground or vegetation > > As Martin says, ice_on_land and ice_and_snow_on_land were designed to work > with LS3MIP standard names. They include all frozen terrestrial water and are > therefore wider than the other two categories. I can't comment on whether or > not they are currently being used in the CMIP6 archive, but certainly that > was the intention. The reason was to enable the use of the surface_albedo > standard name along with specifying an area_type, instead of introducing lots > of separate albedo standard names for different surface types. This approach > received support in the mailing list discussions of LS3MIP names. We also > introduced some standard names: > change_over_time_in_amount_of_ice_and_snow_on_land and > change_over_time_in_amount_of_ice_and_snow_on_land. The definition of > "ice_and_snow_on_land" in these names follows that of the area_type. > > Martin has supported Karl's suggestion to modify the description of > ice_sheet. In addition, Martin and Jonathan have suggested adding Greenland > and Antarctica as examples rather than part of the basic definition so that > the area_type can also be used for paleoclimate models. That seems like a > good approach, hence I suggest: > 'An area type of "ice_sheet" indicates where ice sheets are present, for > example, in the present climate this would refer to the Greenland and > Antarctic ice sheets. 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).' > > Karl has asked whether ice_on_land includes snow. I think it doesn't, because > as already mentioned we have ice_and_snow_on_land as a separate area_type. > Therefore, I support Karl's suggestion to modify the description of > ice_on_land to make that point clear: > '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 (but excluding snow). This is > distinct from the area type 'land ice' which has a narrower definition. The > area_type ice_and_snow_on_land is defined similarly, but includes lying snow.' > > It would also make sense to add a corresponding cross-reference in the > description of ice_and_snow_on_land: > 'The area type "ice_and_snow_on_land" means ice in glaciers, ice caps, ice > sheets (grounded and floating shelves), river and lake ice, any other ice on > a land surface, such as frozen flood water, and snow lying on such ice or on > the land surface. The area_type ice_on_land is defined similarly, but > excludes lying snow.' > > I am cautious about Jonathan's suggestion to remove ice_on_land - it was > introduced specifically to cope with CMIP6, so might it not be needed in due > course? Also, I don't know that the Conventions have anything to say about > simply removing an area_type once it's gone into the table. I have been > managing the area_types vocabulary following a parallel procedure to standard > names. It would be nice if we could think of a better term, so as to cause > less confusion with land_ice. We could then turn ice_on_land into an alias, > just as we would with a standard name. > > I agree with Martin that Evan will probably need to request some new > area_types to work with his microwave data. Evan's suggestion of > land_without_snow_or_ice sounds like a good starting point. Similarly we can > discuss new area types for lakes with or without snow and/or ice. The key > thing with all of these, as with standard names, is to describe them clearly. > Where categories sound similar, or perhaps overlap, we need to be very clear > about what is included or excluded in each area_type. > > Best wishes, > Alison > > ------ > Alison Pamment Tel: +44 1235 778065 > NCAS/Centre for Environmental Data Archival Email: > [email protected] > STFC Rutherford Appleton Laboratory > R25, 2.22 > Harwell Oxford, Didcot, OX11 0QX, U.K. > > > -----Original Message----- > From: CF-metadata <[email protected]> On Behalf Of Martin > Juckes - UKRI STFC > Sent: 17 October 2018 12:44 > To: Taylor, Karl E. <[email protected]>; [email protected] > Subject: Re: [CF-metadata] ice_sheet/land_ice confusion > > Hello All, > > > I agree with Karl's suggestion that it is useful to mention Greenland and > Antarctica to clarify the intended meaning of "ice_sheet", and also with with > Jonathan point that there needs to be a caveat (perhaps "present era", rather > than "modern world" -- the latter is often used to describe a much shorter > timescale than we want here). > > > The CMIP approach to dividing the world is a little different from the > approach Evan : the term "land_ice" has been introduced long ago and includes > floating ice shelves. This could be described as a process driven approach: > "land_ice" includes ice formed on land which has moved out to sea and has > very different characteristics to "sea_ice", which is ice that has formed at > sea. > > > In CMIP6 "land" is interpreted as including floating ice shelves when it > refers to the surface. In CMIP5 the models did not include a physical > representation of floating ice shelves, so areas such as the Ross Sea would > generally be represented as grounded ice sheets, I believe. For CMIP6, we did > discuss restricting "land" to exclude floating ice shelves and introducing a > new area type for the broader meaning, but in the end opted for continuity > with CMIP5. "land" is also taken to include lakes -- the fact that we have a > small number of lakes and inland seas resolved in CMIP models is not yet > reflected in the area types. > > > Consequently, Evan's requirements will need some new area types which will > need to be named carefully to avoid confusion with existing ones. > > "ice_on_land" appears to have been introduced following a discussion of > LS3MIP variables, one of which was originally an albedo of ice and snow on > land but later got changed to an albedo of snow on land, hence this area type > is not used. > > regards, > Martin > ________________________________ > From: CF-metadata <[email protected]> on behalf of Taylor, > Karl E. <[email protected]> > Sent: 17 October 2018 05:38 > To: [email protected] > Subject: Re: [CF-metadata] ice_sheet/land_ice confusion > > 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 > _______________________________________________ > 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 ----- End forwarded message ----- _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
