Dear Alison,
Thanks for adding the new standard name.
I think it is not necessary to explicitly exclude the ice shelves here.
In principle the mass of ice shelves can change, so there might by a
need for this standard name with respect to the ice shelves. For my data
set I would just add a comment to the meta data clarifying that the data
solely refer to the grounded part of land ice.
On this occasion, one could think about adding a second variable
referring to the time derivative of the change_in_land_ice_amount.
For example, in this way the pattern of the linear trend of the
change_in_land_ice_amount could be described. I propose the following:
tendency_of_change_in_land_ice_amount (canonical units: kg m-2 s-1) '
"Amount" means mass per unit area. Zero change in land ice amount is an
arbitrary level. "Land ice" means glaciers, ice-caps and ice-sheets
resting on bedrock and also includes ice-shelves. "tendency_of_X" means
derivative of X with respect to time. '
Best regards,
Andreas
On 03.03.2016 18:17, alison.pamm...@stfc.ac.uk wrote:
Dear Andreas,
Thank you for the explanation. I agree that for your data it would
not be straightforward to provide the time bounds of any ice mass
change.
So that leaves us with: change_in_land_ice_amount (canonical units:
kg m-2) ' "Amount" means mass per unit area. Zero change in land ice
amount is an arbitrary level. "Land ice" means glaciers, ice-caps and
ice-sheets resting on bedrock and also includes ice-shelves.'
This name is accepted and will be added to the standard name table.
As regards the definition of land ice, I think it was probably
proposed alongside some of the existing standard names that use it. I
am not an expert on ice, but certainly I don't think we should alter
the definition unless it is factually incorrect because it could
affect the interpretation of data that have already been written with
the existing names. If it were an issue for your data we could make
it clear that ice shelves are not included by using a standard name
like change_in_land_ice_amount_excluding_ice_shelves. Would that be
better? Both names can be added to the standard name table if they
are needed.
Best wishes, Alison
------ Alison Pamment
Tel: +44 1235 778065 Centre for Environmental Data Analysis
Email: alison.pamm...@stfc.ac.uk STFC Rutherford Appleton Laboratory
R25, 2.22 Harwell Campus, Didcot, OX11 0QX, U.K.
-----Original Message----- From: CF-metadata
[mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of Andreas
Groh Sent: 03 March 2016 08:53 To: cf-metadata@cgd.ucar.edu
Subject: Re: [CF-metadata] ice mass change standard name
Dear Alison and Jonathan
Thanks for considering my previous post as a proposal.
Unfortunately I missed to post an official proposal.
I am fine with your proposed definition. I would not call it
change_over_time_in_land_ice_amount, since the dataset usually
provides a time series of mass changes wrt an arbitrary zero level,
instead of a single value for the mass change over a certain
period. Of course, the mass change at every step of the time series
can be interpreted as the mass change over the period defined by
the difference between the actual time and the time at which the
mass change is zero by definition. But this period is not directly
accessible and needs to be derived from the time dimension (with
additional information on the time of zero mass change). Hence, I
would stick to the name change_in_land_ice_amount without referring
to the time. This is comparable to the definition of
global_average_sea_level_change.
Another point to be discussed is the definition of "land ice",
which says that it also include ice-shelves. Usually, if the change
in land ice is investigated one aims on that portion of ice
contributing to a change in global sea level. This is not the case
for the already floating ice-shelves. I am not aware of any
investigation focussing on the mass of ice-shelves, while their
thickness and velocity is subject to many studies. However, the
same definition of "land ice" seems do be used for all standard
names. This makes perfect sense and using a deviating definition
here would be confusing. Moreover, it should not be a problem for
the proposed standard name, since the spatial domain of the dataset
indicates whether ice-shelves are included or not.
To sum up, I think that your proposed definition describes the
dataset appropriately:
change_in_land_ice_amount (canonical units: kg m-2) ' "Amount"
means mass per unit area. Zero change in land ice amount is an
arbitrary level. "Land ice" means glaciers, ice-caps and ice-sheets
resting on bedrock and also includes ice-shelves.'
Best regards,
Andreas
On 02.03.2016 18:39, alison.pamm...@stfc.ac.uk wrote:
Dear Jonathan and Andreas,
I will regard this name as having been proposed! So I think at
the moment we have:
change_in_land_ice_amount (canonical units: kg m-2) ' "Amount"
means mass per unit area. Zero change in land ice amount is an
arbitrary level. "Land ice" means glaciers, ice-caps and
ice-sheets resting on bedrock and also includes ice-shelves.'
I note that many of our existing "change" names actually say
"change_over_time_in_X" defined as ' "change_over_time_in_X"
means change in a quantity X over a time-interval, which should
be defined by the bounds of the time coordinate.' I wonder if
that would be appropriate for your variable?
Best wishes, Alison
------ Alison Pamment Tel: +44 1235 778065 Centre for
Environmental Data Analysis Email: alison.pamm...@stfc.ac.uk STFC
Rutherford Appleton Laboratory R25, 2.22 Harwell Campus, Didcot,
OX11 0QX, U.K.
-----Original Message----- From: CF-metadata
[mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of
Jonathan Gregory Sent: 25 February 2016 10:13 To:
cf-metadata@cgd.ucar.edu Subject: Re: [CF-metadata] ice mass
change standard name
Dear Andreas
I think a variable of the form change_in_land_ice_amount [kg
m-2] would be appropriate, since my dataset describes the
amount of land ice with reference to an arbitrary level. The
description of the standard name
global_average_sea_level_change includes the sentence: "Zero
sea level change is an arbitrary level.". An equivalent
phrase ("Zero change in land ice amount is an arbitrary
level.") added to the description of a potential standard
name change_in_land_ice_amount would unambiguously describe
the dataset I am working on.
That makes sense to me.
How could such a new standard name be defined and added to
the
conventions?
If you propose the new standard name, its canonical unit, and
the definition to this list, anyone else might comment; once
there is agreement, or if there is no disagreement expressed,
Alison will schedule the new name to be added to the table.
Best wishes
Jonathan _______________________________________________
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-- ----------------------------------- Dr.-Ing. Andreas Groh
Institut für Planetare Geodäsie Geodätische Erdsystemforschung
Technische Universität Dresden D-01062 Dresden, Germany phone :
+49-351-463.33416 fax : +49-351-463.37063 email :
andreas.g...@tu-dresden.de web : tu-dresden.de/geo/ipg/gef
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--
-----------------------------------
Dr.-Ing. Andreas Groh
Institut für Planetare Geodäsie
Geodätische Erdsystemforschung
Technische Universität Dresden
D-01062 Dresden, Germany
phone : +49-351-463.33416
fax : +49-351-463.37063
email : andreas.g...@tu-dresden.de
web : tu-dresden.de/geo/ipg/gef
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