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Land Surface Mask - Not applying properly

Added by Sarah O'Keefe over 6 years ago

Hi! I have a simple problem that has stumped me. I am trying to apply a Land Surface Mask to a Sea Ice file (see attached). I previously had filled in missing vals in the sea ice file and interpolated it to match the mask grid.

But when I apply the mask - (cdo mul) things go wonky. Can someone help me figure out what is wrong and how to fix it??

Thx.

Download all files
lsm_n96_invert.nc (112 KB) lsm_n96_invert.nc Mask
HadISST_all_sic_HadGEM_test_fm_remp.nc (12.7 MB) HadISST_all_sic_HadGEM_test_fm_remp.nc Sea Ice

Replies (2)

RE: Land Surface Mask - Not applying properly - Added by Uwe Schulzweida over 6 years ago

Multiplication with a mask is often not a good idea because the rules are possibly not very intuitive.
The result of 0 multiplied with missing_value is 0. See https://code.mpimet.mpg.de/projects/cdo/embedded/index.html#x1-310001.7 for the rules how missing values are handled.
My advise is to use the division when working with masks.

Cheers,
Uwe

RE: Land Surface Mask - Not applying properly - Added by Karin Meier-Fleischer over 6 years ago

Hi Sarah,

your mask file contains the value 1 or missing value which causes the problem. To mask your data file do

cdo -f nc ifthen lsm_n96_invert.nc HadISST_all_sic_HadGEM_test_fm_remp.nc outfile.nc

-Karin

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