[ncl-talk] using gc_inout over the Central Arctic

[Rick Brownrigg]

Hi Rym,

I don't definitively know a solution, but I wonder if you might be able to
get what you need by either i) rotating/translating your data somewhere off
pole to do the in/out calculation, then rotating back,  or ii) performing
the calculation in a map projection, and again, deprojecting the results
back ?

Rick

On Thu, Dec 1, 2016 at 7:10 AM, Rym Msadek <msadek at cerfacs.fr> wrote:

> Hi,
>
> I am trying to use the gc_inout function to define a polygon over the
> Arctic region and use that as a mask to average an oceanic field like
> potential temperature.
> I have an issue when the longitudes and latitudes of the polygon cover a
> region that crosses the North pole. gcinout gives me a contour that is not
> closed and I can’t figure out how to overcome this issue.
>
> Here are the lon lat that define my polygon, over the Eurasian basin of
> the Arctic.
> ---------
> latC=(/81,81.5,82,82.7,82.4,81.6,80,78.8,77,78,79,81,82,
> 84,88,88.5,89,86,85,85,84,83,82,82,81/)
> lonC=(/27,36,48,60,77,94,107,114,121,134,140,141,145,149,
> 132,149,-79,-55,-43,-22,-20,-17,-9,5,27/)
>
> in_obs=gc_inout(nav_lono,nav_lato,lonC,latC)
>
> mask_eurasia = where(in_obs.eq.True,1,0)
> plot= gsn_csm_contour_map_polar(wks,mask_eurasia,res)
> --------
> I’m attaching the resulting plot that I get.
> Note that I have used this same gc_inout function to define other polygons
> in the Arctic and it works fine when the region was not over the central
> Arctic.
>
> Any help would be appreciated.
>
> Thanks,
>
> Rym
>
> ------
> Rym Msadek
> CNRS-CERFACS
> 42 Avenue Gaspard Coriolis
> 31057 Toulouse
> Tel: 05 61 19 31 92
>
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