velocity from psi

[Eduardo Agosta Scarel]

Hi you all!
I am traying to estimate the velocity field u,v using thestreamfunction psi, by doing
'define e=psi''define dex=cdiff(e,x)''define dey=cdiff(e,y)''define dx=cdiff(lon,x)*3.1416/180''define dy=cdiff(lat,y)*3.1416/180''define v=-dex/(6.37e6*cos(lat*3.1416/180)*dx)''define u=dey/(6.37e6*dy)''undefine e'
but it seems it doesn´t work (wind vector are too large). Any idea to help?Thanks in advance.Eduardo