Because center finite differencing is based on data either side of the output gridpoint, you effectively lose all data at the topographic boundary when using the uv2dv_cfd function; that's why the apparent mask is different for the divergence plot. If you want to keep the mask the same, then you can set the 'boundOpt' argument in the function to 2 (see the function documentation).
http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2dv_cfd.shtml
Will
From: Cheung <zuibeidemei@126.com<mailto:zuibeidemei@126.com>>
Date: Tue, 10 May 2011 10:46:25 -0700
To: "ncl-talk@ucar.edu<mailto:ncl-talk@ucar.edu>" <ncl-talk@ucar.edu<mailto:ncl-talk@ucar.edu>>
Subject: Weird Problem
Dear All:
I first compute divergence by using uv2dv_cfd, and then I mask the grid under terrian, But The area which is masked is different from the area when u or v is individually masked. (see attached file) . why ?
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Received on Tue May 10 12:26:32 2011
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