David Small wrote:
> Hello everyone,
>
> I’m trying to calculate the gradient of the geostrophic wind from
> ECMWF Reanalysis on a reduced gaussian grid. To do so, I’m using the
> centered finite difference routine in NCL to avoid a problem near the
> equator when using the spherical harmonic routines.
I do not understand this staement. The spherical harmonics
have no problems at the equator. The geostrophic winds are
problematical at the equator but not the spherical harmonics.
> I have no problem when I calculate the meridional derivative, it
> compares well to that which I calculated from the 2.5 degree ECMWF on
> a fixed grid. The problem is with the longitudinal derivative which is
> giving me junk. Does anyone have any clue what the problem might be?
I do not see anything wrong ... What is the "junk"?
>
> As always, thank you very much for all your help.
>
> Dave Small
>
>
> dlon = 1.125*0.0174533 ; convert to radians
> dlat = dlon*6378388.0
>
> do nl=0,72
>
> dX = 6378388.*cos(0.0174533*lat(nl))*dlon ; constant at this latitude
> v_grad_lon(:,:,nl,:) = center_finite_diff(v(:,:,nl,:), dX , True,0)
> u_grad_lon(:,:,nl,:) = center_finite_diff(u(:,:,nl,:), dX , True,0)
>
> end do
>
> --
> David Small
> Graduate Research Assistant
> Department of Atmospheric and Oceanic Sciences
> McGill University
> Montreal, Quebec, Canada
>
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-- ====================================================== Dennis J. Shea tel: 303-497-1361 | P.O. Box 3000 fax: 303-497-1333 | Climate Analysis Section | Climate & Global Dynamics Div. | National Center for Atmospheric Research | Boulder, CO 80307 | USA email: shea 'at' ucar.edu | ====================================================== _______________________________________________ ncl-talk mailing list List instructions, subscriber options, unsubscribe: http://mailman.ucar.edu/mailman/listinfo/ncl-talkReceived on Mon May 18 2009 - 11:24:50 MDT
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