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[ferret_users] regarding sigma coordinates on depth axis



Dear Ferreters,

I am facing a problem in converting the depth axis from sigma coordinates to the "meter" axis. The formula that is provided in the model output is shown below.

double lev(lev) ;
lev:long_name = "ocean sigma coordinate" ;
lev:positive = "up" ;
lev:axis = "Z" ;
lev:bounds = "lev_bnds" ;
lev:formula = "z(n,k,j,i) = eta(n,j,i) + sigma(k)*(depth(j,i)+eta(n,j,i))" ;    !!!!!    formula    !!!!!

the structure of the file is as follows

name     title                                                        I         J         K              L         M         N
 ETA      Sea Surface Height                              1:360     1:180     ...        1:6000    ...       ...
 DEPTH    Sea Floor Depth                                1:360     1:180     ...           ...       ...       ...
 THETAO   Sea Water Potential Temperature       1:360     1:180     1:40      1:6000    ...       ...


and here is my script to compute the use the formula provided and use it as a depth axis for my data.

use pictrl-remap.nc

let ppp=z[gz=thetao]

let qwe=depth[gt=thetao@asn]*eta

let sig=qwe*ppp[gx=thetao,gy=thetao,gz=thetao]             !!!!   formula used !!!!!!!

let dep=eta+sig

let depth1=dep[l=1@ave]

define axis/z/from_data/units="meters"/depth depth_axis=depth1[k=1:40]

let theta=thetao[gz=depth_axis@asn]



But I am getting an error for this as

**ERROR: improper grid or axis definition: data for DEFINE AXIS/FROM_VARIABLE is ambiguous

any help will be appreciated

cheers, saurabh

--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434

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