Streamfunction/velocity potential: using fish with libbjt

[Arlindo da Silva]

On Wed, Apr 2, 2008 at 10:49 AM, See Hai Ooi <axl419 at yahoo.com> wrote:

> Dear Mr Arlindo,
>
>     Thank you very much.  After modifying slightly
> your latest script, it works beautifully.  Please see
> the attached document.
>
>     Your grads-1.9.0-rc1.win32_superpack.exe has
> already included the B.-J.'s functions.  I need not
> run the script under gradsdods.


You need "gradsdods" to get the latest GFS forecast from NOMAD, not to run
the extensions.


>  I notice that
> auxiliary fields replace your original enlarging and
> resetting x domain sections.  If possible, I would
> greatly appreciate it if you could kindly provide me a
> brief write-up on the derivation of auxiliary fields
> and the advection functions to understand them better.
>

I am not sure what you are referring to as "auxiliary fields"; "one" and
"cosphi" is what I meant, and these are simply convenience fields. The
actual vorticity/divergence is computed by functions madvu/madvv which are
fully documented here:

          http://opengrads.org/doc/udxt/libbjt/

These functions figure out what to do in the boundaries without the need for
you to enlarge the domain. Look under "ADVECTION FUNCTIONS". The new version
of fish() to be released soon will provide functions fish_psi(u,v) and
fish_chi(u,v) which calls these "advection functions" internally.

    Arlindo

--
Arlindo da Silva
dasilva at alum.mit.edu
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