Using gradsnc to read the CCSM3 POP (ocean) data

[Eric DeWeaver]

Hi Ching-Yee,

I think the trouble is that the ocean model uses a grid in which the pole
is displaced to Greenland.  I had the same problem with the CCSM3 sea ice
data.  With the sea ice data, output from ncdump -h includes

        float TLON(nlat, nlon) ;
                TLON:long_name = "T grid center longitude" ;
                TLON:units = "degrees_east" ;
        float TLAT(nlat, nlon) ;
                TLAT:long_name = "T grid center latitude" ;
                TLAT:units = "degrees_north" ;
        float ULON(nlat, nlon) ;
                ULON:long_name = "U grid center longitude" ;
                ULON:units = "degrees_east" ;
        float ULAT(nlat, nlon) ;
                ULAT:long_name = "U grid center latitude" ;
                ULAT:units = "degrees_north" ;
                ULAT:comment = "Latitude of NE corner of T grid cell" ;

So instead of having a "discernable x-coordinate" there are arrays which
give the latitude and longitude of the (i,j)th grid cell.  To make things
even more complicated, it's a B-grid, so there are different latitudes
and longitudes for the temperature and the velocity.

I couldn't find a way to plot this in grads.  I did it in matlab, and
I'll be happy to send you the script.  One other suggestion: PCMDI has
ocean and sea ice data for the IPCC AR4 model simulations which has been
regridded to a standard lat/lon grid.  I know they have some data from
CCSM3, maybe they have the stuff you want.  Their webpage is

  http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php

Also, they might have a code that converts from the ocean model grid
to a lat/lon grid.  Either that or somebody at NCAR has a code that
does it (maybe an ncl code?).  You could contact the NCAR ocean
model working group, they have a community liason who might know
(see http://www.ccsm.ucar.edu/working_groups/Ocean/).

Best Wishes,

Eric


On Thu, 9 Feb 2006, Ching-Yee wrote:

> Dear grads users,
> I would like to use gradsnc to read the CCSM3 ocean model (POP) output data
> (in netCDF format), but when I use sdfopen the data, it said that "SDF file
> has no discernable X coordinate."
> I know there are CCSM3 POP output data that are placed at PCMDI/IPCC website
> which are also in netCDF format, but accessible via gradsnc (sdfopen).
>
> Does anyone have any suggestions on how to use gradsnc to read the data?
>
> Thank you in advance.
>
> Ching-Yee
>