using fish_chi extension for daily velocity potential

[Arlindo da Silva]

On Tue, Feb 3, 2009 at 2:19 PM, Ousmane Ndiaye <ousmane at iri.columbia.edu>wrote:

> Hi,
> I am using the function fish_chi to find the velocity potential from the
> horizontal wind components. The function works great but unfortunately the
> velocity potential that is defined is on the grid in longitude from 0 to 360
> and is not periodic. This is an issue because I would like to display the
> data over the African continent only, i.e. from longitude 30W to 60E and
> latitude from 30S to 30N. I have tried to solve this problem by making the
> input data to the fish_chi function be periodic,
> i.e. longitude from 0 to 720. When I do this I get the error message:
>
> Error from fish: rc = 1000
> Operation Error:  Error from fish function
> Operation Error:  Error from fish_chi function
>  Error ocurred at column 1
> DEFINE error:  Invalid expression.
>
> Any suggestions on how I can overcome this issue would be greatly
> appreciated. Or anyone who has the Re-analysis daily velocity potential
> available that he want to share with.


Try this:

open model
set lon -180 180
set lev 200
chi = fish_chi(ua,va)
set lon -30 60
set lat -50 60
d chi

You should get the attached plot. The trick is to set the domain to
[180W,180E] before calling the function.

    Arlindo




>
> Ousmane
>



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