Computing divergence and curl of vector fields; WRF NCL scripts?

From: Tom Kilpatrick <thomaski_at_nyahnyahspammersnyahnyah>
Date: Mon Mar 28 2011 - 03:33:39 MDT

(NOTE: I also sent this to

I have a question about computing the divergence and curl of 2D vector
fields (eg low-level winds) on the WRF lambert grid. After reading a bit of
Haltiner & Williams 1980 I am wondering if the following is correct. For
a horizontal vector field with components (A,B) in the x- and y-directions
on the lambert grid, then the divergence is given by

m^2 * [ d/dx(A/m) + d/dy(B/m) ]

and the curl is

m^2 * [ d/dx(B/m) - d/dy(A/m) ],

where m is the map factor. The above formulae could be used to compute the
divergence at the theta (mass) points and the curl at the '+' pts on the

th u th
v + v
th u th

One could then average the '+' pts to get the curl at the interior mass-pts.

If the above is correct it might be helpful if there were built-in NCL
functions to do this. My apologies if there already are, but I couldn't find
anything on the site, and searching through the ncl-talk archives, it looks
other users have similar questions. Note that uv2dv_cfd, uv2vr_cfd don't
work for the lambert grid.

Tom Kilpatrick

Thomas Kilpatrick, M.S.
Graduate assistant
Department of Oceanography
University of Hawaii
1000 Pope Rd
Honolulu, HI 96822

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Received on Mon Mar 28 03:33:45 2011

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