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derivatives on an uneven grid
Hi Ferret users,
I'm trying to calculate vertical derivatives on an uneven grid (the ncep
reanalysis pressure grid) that has a vertical axis:
yes? list/i=1/j=1/l=1 z[g=uwnd]
VARIABLE : Z
axis LEVEL
DATA SET : mean daily NMC reanalysis (2000)
FILENAME : uwnd.2000.nc
SUBSET : 17 points (HEIGHT (millibar))
10 / 1: 10.
20 / 2: 20.
30 / 3: 30.
50 / 4: 50.
70 / 5: 70.
100 / 6: 100.
150 / 7: 150.
200 / 8: 200.
250 / 9: 250.
300 / 10: 300.
400 / 11: 400.
500 / 12: 500.
600 / 13: 600.
700 / 14: 700.
850 / 15: 850.
925 / 16: 925.
1000 / 17: 1000.
If I use a standard centered-finite difference scheme I get the wrong
answer as the grid points aren't equally spaced. Has anyone
encountered/solved this problem before?
One way to deal with this is to assume a variable theta has the form:
theta=Ap**2 + Bp + C where p is pressure and A, B, and C are coefficients.
THen the vert. deriv dtheta/dp=2Ap + B. You can invert the 3x3 matrix to
get the coefficients and determine the deriv. I'm not sure how to do this
in ferrret w/out writing an external function which I'm trying to avoid.
Does anyone have a similar/better way to do this?
Thanks,
Brent
--
Brent A. McDaniel
Dept of Earth and Atmospheric Sciences
Georgia Institute of Technology
Atlanta, Ga. USA
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