Dear Martin
The reason for giving names to the transects and basins is because they are
numerically a bit imprecise - they will differ from model to model - but still
the Atlantic in one model should be regarded as comparable to the Atlantic in
another model, etc. I agree we do not have a way at present to record precisely
what it means in a given case. Since transects might be jagged lines and coasts
always are, a more general solution than endpoints would be a way to associate
a named line or outline (a geographical feature) with a list of coordinates
that trace it out, perhaps. Is there a use-case for this extra metadata? Has it
been requested in CMIP6?
Best wishes
Jonathan
----- Forwarded message from martin.juckes at stfc.ac.uk -----
> Date: Mon, 29 Jun 2015 12:31:37 +0000
> From: martin.juckes at stfc.ac.uk
> To: cf-metadata at cgd.ucar.edu
> Subject: [CF-metadata] Specifying latitude and longitude of transects and
> regions
>
> Hello All,
>
> There are some variables in the CMIP5 archive which lack explicit latitude and longitude information, such as mfo (standard name sea_water_transport_across_line) and msftzzzba (ocean_y_overturning_mass_streamfunction_due_to_bolus_advection). The first is a mass flux across a transect and the second is a zonally averaged stream function, averaged across an ocean basin.
>
> For transects, the mfo variable is encoded with an index dimension and a coordinate "passage" which labels transects by the name of the passage they cross (e.g. fram_strait). The information about precisely which part of the Fram Strait is used is in a document referred to from the MIP tables. It would be nice to have a means of encoding the end points of the transect in the CF metadata. I looked into using the "bounds" attribute, but that is defined to represent cell boundaries, so an extension to the convention is, I think, needed. It makes sense to follow the pattern used to represent cell boundaries. I propose defining a new attribute "transect" which, like the "bounds" attribute, can be attached to coordinate variables and takes the name of another variable as its value. The named variable should contain the end points of the transect.
>
> The same approach could be used for the streamfunction .. which is a mean across an east-west transect (this approach would lead to a specifcation of the east and west endpoints of each basin at each latitude -- but I'm not sure that it would be feasible to collect that much detail in the CMIP data files).
>
> Is there a cleaner way of encoding transect and basin coordinates?
>
> regards,
> Martin
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----- End forwarded message -----
Received on Mon Jun 29 2015 - 10:37:15 BST
