[ncl-talk] Regrid ECMWF to an equal-area grid (EASE) for SOM

[Mattias Cape]

Hi David,

Thank you for putting in the time to go over my question. I tested your code with varying parameters to understand it and its output works great to reproject my datasets.

I appreciate your help!

Cheers,

Mattias

> On Jul 23, 2015, at 5:58 PM, David Brown <dbrown at ucar.edu> wrote:
> 
> Hi Mattias,
> I'm sorry no one has responded to your question yet. After a bit of
> research, I have learned that the EASE grids, as supported by (e.g.)
> NSIDC, use two different projections, a lambert equal-area grid for
> plots centered on the poles, and a cylindrical equal area grid for
> global data. Both of these projections are supported by NCL and
> therefore one way to generate a destination grid would be to use NCL's
> mapping routines in conjunction with the NCL function ndctodata.
> Another way to do this would be to use the proj4 tool. There is
> actually an interface to this tool in NCL and so you could do this in
> NCL also.
> 
> It seems that the output grid you use could be somewhat arbitrary as
> long as it is equal area and covers the area of your input data. So I
> have created an example using the ndctodata method with a Lambert
> EqualArea projection centered at lat 90 lon 280. It writes out a
> NetCDF file with the lat and lon points that I think could be used as
> a destination grid. This may not be exactly what you are looking for
> but hopefully it gives you a starting point to work from.
> -dave
> 
> 
> On Mon, Jul 20, 2015 at 6:05 AM, Mattias Cape <mcape at whoi.edu> wrote:
>> Hi,
>> 
>> I am working with ECMWF ERA-40 data (2.5 x 2.5º grid, example attached), using self organizing maps to look at patterns of variability in synoptic atmospheric circulation.  These datasets are typically regridded to an equal area grid (250 x 250 km for example) to allow for uniform spatial sampling prior to analysis (e.g. http://onlinelibrary.wiley.com/doi/10.1029/2006JD007460/abstract).
>> 
>> I’ve been having trouble defining the gridding parameters to accomplish this. There are several examples on the NCL website demonstrating how to use ESMF software, but I am unsure how to define the destination (EASE) grid. I am only working with a spatial subset of the ERA-40 dataset covering the region 85°N 80°W 40°N 0°E.
>> 
>> If anyone has any insight into how to accomplish this regridding, or at least how to define the destination grid, I would appreciate it.
>> 
>> Cheers,
>> 
>> Mattias
>> 
>> 
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