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Re: [ferret_users] Why does ferret fail to support swapping integraland differential?
Hi Ansley
Thank you for your reply.
Right now, I understand the curvature of earth gives the difficulty for
this problem.
I would like to know what is the right way to calculate the
streamfunction using Kessler's script
(http://ferret.pmel.noaa.gov/Ferret/Mail_Archives/fu_2002/msg00155.html)
Mathematically, the solution (Psi = Int{y0:y}u dy - Int{x_0:x}v(x,y_0)
dx) is perfect, but in Ferret, because it could not support swapping
integral and differential, I could not reproduce v using -d(Psi)/dx
Best regards
Feng He
Center for Climate Research
Atmospheric and Oceanic Sciences
University of Wisconsin - Madison
----- Original Message -----
From: Ansley Manke <Ansley.B.Manke@noaa.gov>
Date: Friday, March 17, 2006 10:02 am
Subject: Re: [ferret_users] Why does ferret fail to support swapping
integral and differential?
To: FENG HE <fenghe@wisc.edu>
Cc: oar.pmel.ferret_users@noaa.gov
> Hi Feng,
> Thank you for sending a clear example.
>
> This turns out to be because derivatives and integrals on fields in
> latitude and longitude are done in units of meters on the earth,
> rather
> than degrees latitude and longitude. The fact that degrees of
> longitude
> are not a constant length over the earth means that the
> computations are
> not linear. Try this case, where the numbers may be easier to
> interpret.
> yes? use coads_climatology
> yes? set reg/x=1:3/y=51:55/L=1
>
> yes? let uu_ddb = uu[x=@ddb]
> yes? let uu_ddb_iin = uu_ddb[y=@iin]
> yes? let uu_iin = uu[y=@iin]
> yes? let uu_iin_ddb = uu_iin[x=@ddb]
>
> ! Define a function with simple integer values
>
> yes? let uu = x[gx=uwnd] + y[gy=uwnd]
> yes? list uu
>
> ! Set the axes so they are NOT in units of degrees
> ! longitude and latitude.
>
> yes? set axis/units=" " coadsx
> yes? set axis/units=" " coadsy
>
> ! The results are as you would expect.
>
> yes? list uu_ddb
> yes? list uu_iin
> yes? list uu_ddb_iin
> yes? list uu_iin_ddb
>
>
>
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