using fish_chi extension for daily velocity potential

[Ousmane Ndiaye]

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.
Ousmane