[gembud] Copying/plotting GEMAPK grid files from Mercator to Polar stereographic projection

• To: gembud@xxxxxxxxxxxxxxxx
• Subject: [gembud] Copying/plotting GEMAPK grid files from Mercator to Polar stereographic projection
• From: Kwan-Yin Kong - NOAA Federal <kwan-yin.kong@xxxxxxxx>
• Date: Tue, 7 Nov 2023 14:20:36 -0500

Hello all,

I am wondering if anyone has had experience copying GEMPAK grid files that
are originally in Mercator projection to ones that are in polar
stereographic projection.  I found that the data that was copied into the
polar projection (using GDDIAG) had odd behaviors over the polar regions
and especially right around the poles.  I suppose the oddities are
mathematical related due to the singularity right at the poles.  I am
attaching a couple of images to illustrate what I am seeing.  The red plus
signs are grid point locations, and the contours are isobars.  Notice that
there are no issues around the North Pole with the original dataset in
Mercator projection (there is a gap in the isobars right along the Prime
Meridian though).  However, there are obvious issues with the isobars near
the North Pole in the polar stereographic projection (created using GDDIAG).

I appreciate your insights into this issue.

Thank you,
Kwan

Attachment: Mercator-isobars.GIF
Description: GIF image

Attachment: Polarster-isobars.GIF
Description: GIF image