Calculation of vertical gradient

["Satheesh C. Shenoi" <shenoi@xxxxxxxxxxxxxxxx>]

Dear Ferret Gurus,

Since I did't receive any reply for the past few days, I am repeating the
same. Ferret Gurus may please help.

I want to calculate the density gradient at the bottom of the mixed layer
using the Levitus climatology. I calculated the mixed layer height 'h' 
as follows:

let dens = rho_un(salt,temp,z)
let mix_layer_dens = dens[k=1]+0.2
let zero_at_mix_layer_dens = dens - mix_layer_dens
let h = zero_at_mix_layer_dens[z=@loc:0]

Now how do I calculate the vertical gradient of 'dens' at depth 'h', or
just below it (below the mixed layer)? I want to estimate the
stratification just below the mixed layer.

Using the transform WEQ, I could calculate density at depth h, but it does
not seem to work for the gradient (I tried @ddf).

Hope someone can help me!

Thanks in advance.
satheesh

Satheesh C. Shenoi                     Ph.:   (91)(832) 226253-56 ext4224/4400
Physical Oceanography Division,        Fax:   (91)(832) 223340/221360
National Institute of Oceanography,    email: shenoi@darya.nio.org
					      shenoi@csnio.ren.nic.in
Dona Paula, Goa 403 004, India.	       Ph.:   (91)(832) 233453 (home)