Using gradsnc to read the CCSM3 POP (ocean) data

[Ching-Yee]

Thank you all for your reply.

I know that POP data are in different grid and needed to be interpolated,
which I've done by using ncl pop_remap.ncl script (suggested by the CCSM3
user guide). It seems that the output data from the pop_remap.ncl have the
same grid that's readable by gradsnc (for example the output from CAM3),
however, I still got the same response from gradsnc when using sdfopen.
Maybe I still don't understand ncl and /or netCDF files enough.( It might
not be appropriate to ask details about my ncl script.)

James, do you use pop_remap.ncl to do the interpolation?

Eric, I'd like to know how to use matlab to read the data. Can you please
send me your matlab script?

Thank you all very much.

Ching-Yee


-----Original Message-----
From: Eric DeWeaver [mailto:deweaver at aos.wisc.edu]
Sent: Thursday, February 09, 2006 11:15 AM
To: Ching-Yee
Cc: GRADSUSR at LIST.CINECA.IT
Subject: Re: Using gradsnc to read the CCSM3 POP (ocean) data


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
>