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RE: [ferret_users] Calculating relative vorticity

Hi Ryo,

Thanks very much indeed!

Just one query, your formula for calculating relative vorticity in ferret in
fine provided we ASSUME zeta = du/dx - dv/dy. BUT I think the actual formula
for calculating relative vorticity is zeta = dv/dx - du/dy. This may lead to
slight modification to the code. Please verify.


-----Original Message-----
From: owner-ferret_users@xxxxxxxx [mailto:owner-ferret_users@xxxxxxxx] On
Behalf Of Ryo Furue
Sent: Thursday, 26 June 2008 8:05 AM
To: ferret_users@xxxxxxxx
Subject: Re: [ferret_users] Calculating relative vorticity

Hi Billy,

Thanks for your highest praise!

| Amazingly, I think Ryo is wrong about the sphere/cosine business. If  
| (u,v) is given on a lat/lon grid, then Ferret will do this  
| automatically.

But, I don't think Ferret distinguishes vectors from scalars
when it takes derivatives.  Derivatives of vectors are different
from those of scalars.  Look at my formula again:

    d(u cos(phi))/dy

u[y=@DDC] would give you du/dy, which isn't what we want, right?
Or would Ferret somehow figure out that u is an x-component of
a vector and multiply the cosine factor before taking
the derivative?


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