Re: [ferret_users] Why does ferret fail to support swapping integraland differential?

[FENG HE <fenghe@xxxxxxxx>]

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
> 
> 
>