Hi Antonio, > I wonder how to calculate the vertical gradient of zonal wind > (du/dz) from my data which has isobaric level. I guess you can use this relation du/dz = (du/dp)(dp/dz) = (du/dp) / (dz/dp) . Since you are working with isobaric coordinates, you should have the variable z(x,y,p) . Regards, Ryo