Streamfunction/velocity potential: using fish with libbjt

[See Hai Ooi]

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.  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 still hope that someone would contribute
streamfunction/velocity potential function in limited
and irregular domain in the near future.  As you could
have recalled in my previous email to you,  I used the
manipulative way to convert the MM5 limited and
irregular domain into a global and regular domain
using your original script.  I hope that someone would
tell me that my method is totally unacceptable.  In
the meantime, I also hope that someone would tell me
how to relabel the global lat/lon into the limited
lat/lon as in MM5.

    Once again, thank you and best regards.

Sincerely,

Ooi See Hai
(Malaysia)


--- Arlindo da Silva <dasilva at ALUM.MIT.EDU> wrote:

> See et al,
>
>     One of the main issues with the fish() extension
is that it requires globally defined
vorticity/divergence fields and the GrADS intrinsic
functions (hcurl, hdivg) tend to place undefined
values at the boundaries. I just realized that B.-J.
Tsuang's function collection includes a set of
"advection functions" which can be used as a
replacement for hcurl/hdivg.

> B.-J.'s functions are documented here:
>
>    http://opengrads.org/doc/udxt/libbjt/
>
> (This extension library includes over 30 very useful
new functions besides the advection ones used here).
>
>  The attached example script, which should be run
under gradsdods, demonstrates how you can use B.-J.'s
functions to compute psi, chi as well as the
rotational and divergent wind.  Please notice the
restrictions:
>
>     - global and uniform grid; use re() if grid is
not uniform
>     - first and last latitudinal grid points cannot
be at the poles
>
>  Of course, you must have GrADS v1.9.0-rc1 and the
OpenGrADS extensions installed; these extensions do
not yet work with GrADS v2. More information here:
>
>
>
http://opengrads.org/wiki/index.php?title=User_Defined_Extensions
>
>  Good Luck,
>
>      Arlindo
>
> --
> Arlindo da Silva
> dasilva at alum.mit.edu

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