[ferret_users] post processing (interpolating) MOM4 (CM2.1) output with CURV_TO_RECT

[Malte Stuecker <stuecker@xxxxxxxxxxxxxxxx>]

Dear mailing list,

I am currently postprocessing MOM4 (CM2.1) output following this example:

http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/appendix-a-external-functions/CURV-TO-RECT

Having the following variable on the curvilinear grid:

 name     title                             I         J         K         L

 CELL_AREA

          cell area                        1:360     1:200     ...       ...

 COSROT   COSROT,SINROT points east        1:360     1:200     ...       ...

 GEOLAT   latitude                         1:360     1:200     ...       ...

 GEOLON   longitude                        1:360     1:200     ...       ...

 SINROT   -SINROT,COSROT points north      1:360     1:200     ...       ...

 CN       ice concentration                1:360     1:200     1:5       1:900

I followed the instructions in the provided example as:

yes? let lonin = geolon[d=1]

yes? let latin = geolat[d=1]

yes? define axis/x=0:359:1/modulo/units=degrees xax

yes? define axis/y=50:90:1/units=degrees yax

yes? let lonlatout = y[gy=yax] + x[gx=xax]

yes? let map = curv_to_rect_map(lonin,latin,lonlatout,10)

yes? save/clobber/file=curv_map_NH_1deg.nc map

yes? cancel var/all

use curv_map_NH_1deg.nc

    2> ./curv_map_NH_1deg.nc  (default)

 name     title                             I         J         K         L

 MAP      CURV_TO_RECT_MAP(LONIN,LATIN,LO  1:360     1:41      1:4       1:3

However the generated map matrix has zero values everywhere. I assume this is not correct? I get the same result when using a smaller radius (e.g. 3 degrees) in the interpolation function:

yes? let map = curv_to_rect_map(lonin,latin,lonlatout,3)

I am wondering what I am doing wrong here.

Thank you very much in advance!