[ncl-talk] EOF analysis with NARR data (LON, LAT values)

[Dave Allured - NOAA Affiliate]

Jothiganesh,

Yes you can directly read NARR data and compute EOF's without regridding.
The underlying EOF functions eofunc and eofunc_ts do not use any spatial
coordinates.  They operate purely on numeric arrays.

The first EOF example uses coordinate subscripting and the lonFlip
function.  If you remove both of these methods from the example, then you
can compute EOF's over the entire NARR grid.

However, to generate valid plots, you will need to retain the NARR
coordinate metadata, and modify the plot section to use one of the plotting
methods shown on the NARR examples page.

I recommend one of the projection methods in NARR example 4, because they
use the retained 2-D coordinate grids to directly align the data with the
underlying map.  After you get that working, you can switch back to Lambert
or some other projection of your choice.

--Dave


On Tue, Jun 16, 2015 at 6:39 PM, Jothi Ganesh Shanmuga Sundaram <
joshanmugasundaram at mix.wvu.edu> wrote:

> Hello,
>
> I use NARR gridded data (349x277 Lambert Conformal Conic grid) in netcdf
> format in NCL. I am able to plot graphics without any problem using the
> existing script in NCL website.
>
> I want to do EOF analysis with NARR data. When I tried to use the EOF
> script available from NCL website to analyze NARR data, it is not working.
> When I checked the data using ncl_file dump the lon, lat formats are very
> different. My question is
>
> 1) Whether I can do EOF analysis in NCL by directly reading NARR data? If
> so, I cannot define the LON LAT value, as NARR has a projected coordinates
> value?
>
> 2) Do I need to regrid the NARR curvilinear to rectlinear data before
> doing EOF? or Is there a way to convert the format of LON, LAT in grid
> without regridding inorder to do EOF analysis in NCL
>
> Thanks for your help.
>
> Regards
> Jothiganesh
>
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