plotting grid sub-regions

Hello,

I have been trying to figure out a way to plot a subset of my data (from
MM5, so with 2-d lat and lon data) that is bounded by four corner points
with four unique lat and lon values. I know how to use upper/lower lats
and left/right longs to plot a map bounded by lats and longs, but that
doesn't work as I'd like in the high latitudes of interest (south of 60 S).

Another way of thinking about this is that I have a nice rectangle in
the i,j-grid space with i and j values analogous to the
minLat/maxLat/minLon/maxLon values used for mpLimitMode="LatLon". Of
course those i,j values correspond to four unique pairs of lat/long
values in lat/lon space, thereby creating the problem I've been unable
to solve.

Specifically, I'd like to use something like these corners to subset (in
clockwise order):
60 S, 55 W
72 S, 20 W
84 S, 102 W
67 S, 93 W

My best result so far comes from using mpLimitMode="Corners" (LeftCorner
= -67,-93, RightCorner = -72,-20) and mpProjection="Stereographic" with
gsn_csm_contour_map. This seems really close to what I want but when I
compare it to the result from using gsn_csm_contour_map_polar (i.e., a
full south polar map in "polar sterographic") I see some differences in
scaling as I move towards the pole (i.e., areal distortion) that I'm not
comfortable with. Is it possible I'm just seeing irreconciliable
differences between the projections? If not, what am I missing to get
to where I want to be?

I have put a tar-file (ncl_test.tgz) with all the related files at
http://public.me.com/dbreusch. If the above text is unclear, hopefully
the plots included in this file will explain things better.

Thanks!
Dave

-- 
517 Deike Building
Earth & Environmental Systems Institute
Penn State University
University Park, PA 16802
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