substract 2D data at specific depth

[Dongxiao Zhang <dzhang@xxxxxxxxxxxxxxxxxxxx>]

Hi Ferrets,

I am impressed by Steve's reply to Stefan's question about ...

> 3. How can I e.g. subtract a 2-d field from a 3-d field, e.g. if I
> wanted to subtract the temperature at level 1 (at each i,j) from the
> temperatures at every level (for the same i,j)? (There are useful
> applications for this e.g. to define a mixed layer depth.)

Steve wrote:

Ferret will subtract a 2D field from a 3D field as in

        LET temp_anomaly = temp - sst           ! temp is 3D, sst is 2D
  or
        LET temp_anomaly = temp - temp[z=0]     ! temp[Z=0] is a 2D field


My question is:

Is there any way to substract a 2D field from a 3D data only at a specific
depth level and leave the other levels not being changed?  This is useful,
for example, to get rid of the Ekman component in the upper layer of
velocity field. 

Thanks,

Dongxiao
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Dongxiao Zhang
Division of Meteorology and Physical Oceanography
Rosenstiel School of Marine and Atmospheric Science
4600 Rickenbacker Causeway
Miami, FL 33149
Phone  : (305)361-4806
Fax    : (305)361-4696
Office : MSC Room 309
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