...
It is important to check the return value in IRET to ensure the call has been successful.
If INTOUT is called before INTUVP , the U and V fields will be generated and also interpolated during production. Otherwise, the U and V fields will have the same form as the vorticity and divergence fields; eg spectral vorticity and divergence fields generate spectral U and V.
...
The returned value is 0 if the call is successful.