Re: GCM output on i,j grid instead of lat,lon

Mira,

It looks like the BNU model might have its data on a curvilinear grid.

That is, the grid is defined by 2D lat/lon arrays, rather than by
1D lat/lon arrays (rectilinear). For curvlinear variables, you won't
have the lat/lon arrays attached as coordinate arrays. You will
have to read them in separately.

Sometimes there's an additional attribute called "coordinates" attached
to your variable that tells you what the name of the lat/lon variables are
on the file.

For example:

      float TEMP ( time, z_t, nlat, nlon )
         long_name : Potential Temperature
         units : degC
         coordinates : TLONG TLAT z_t time <-------
         cell_methods : time: mean
         _FillValue : 9.96921e+36
         missing_value : 9.96921e+36

The above information tells me to look for TLONG and TLAT variables on the file.

Does the "sicBNU_6070_rcp45" variable have any other attribute
information other than what you included below? If so, look for
an attribute called "coordinates", which then might give you
the name of the lat/lon variables on the file to use.

If this doesn't help, then can you provide us with a sample file?

http://www.ncl.ucar.edu/report_bug.shtml#HowToFTP

Thanks,

--Mary

On Jun 1, 2013, at 10:34 AM, Mira Berdahl wrote:

> Hi everyone,
>
> I am experiencing a problem when plotting sea ice extent as a spaghetti
> plot from one of the CMIP5 output models. It seems that the BNU model is
> on an i,j grid whereas all other models (that I have used at least) are on
> a lat,lon grid.
>
> So when I printVarSummary for the BNU variable I am trying to plot I get:
> Variable: sicBNU_6070_rcp45
> Type: float
> Total Size: 144000 bytes
> 36000 values
> Number of Dimensions: 2
> Dimensions and sizes: [j | 100] x [i | 360]
> Coordinates:
> j: [101..200]
> i: [1..360]
> Number Of Attributes: 11
> standard_name : sea_ice_area_fraction
> long_name : Sea Ice Area Fraction
> comment : fraction of grid cell covered by sea ice.
>
>
>
>
> Whereas for the other models I get something like:
>
> Variable: sicMIROC_CHEM_6070_rcp45
> Type: float
> Total Size: 98304 bytes
> 24576 values
> Number of Dimensions: 2
> Dimensions and sizes: [lat | 96] x [lon | 256]
> Coordinates:
> lat: [0.2790889739990234..89.14443969726562]
> lon: [0.703125..359.296875]
> Number Of Attributes: 11
> standard_name : sea_ice_area_fraction
> long_name : Sea Ice Area Fraction
> comment : fraction of grid cell covered by sea ice.
>
>
> When I try to make the spaghetti plot, it runs but gives a very wrong
> looking result for the BNU model. The other models look good. I should
> mention that the BNU output does indeed have lat and lon but as separate
> variables. When I use ncview to look at the BNU data it looks fine, but I
> am assuming NCL is having problems since its dimensions are not lat,lon.
> Is that right? Does anyone see a good way to work around this?
>
> Thanks in advance for any help or suggestions!
> MB
>
>
>
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Received on Mon Jun 3 10:33:09 2013