Wrong diagnostic for sea ice extent in common_ocean_post.txt
The diagnostic for sea ice extent ("sie") is not calculated according to the sea ice community's standards. The National Snow and Ice Data Center defines sea ice extent as
- SUM( grid_cell_area WHERE sea_ice_concentration > 0.15 ) (http://nsidc.org/cryosphere/seaice/data/terminology.html)
whereas the current diagnostic in ocean_diagnostics is
- SUM (grid_cell_area * sea_ice_concentration WHERE sea_ice_concentration > 0.15) (common_ocean_post.txt, line 804: variable ${d}Extend is read from the output of the program compiled from /cfu/software/cdftools2.1/cdficediags.f90; both 1) and 2) diagnostics are calculated, but ?Extend corresponds to the wrong one).
To do: ${d}Extend has to be changed into ${d}Exnsidc in common_ocean_post.txt
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Impacts
This can make a very large difference: on a random NetCDF I have about 2.3 million km² difference in the Southern Hemisphere, 0.6 million km² in the Northern Hemisphere. This is actually critical in summer.
Northern Hemisphere
NVolume (10^9 m3) 29254.219726848001
NArea (10^9 m2) 12637.677027328000
NExtend (10^9 m2) 12603.235500032000
NExnsidc (10^9 m2) 13283.136372736000
Southern Hemisphere
SVolume (10^9 m3) 3912.7739269120002
SArea (10^9 m2) 10679.136288768001
SExtend (10^9 m2) 10458.337640448000
SExnsidc (10^9 m2) 12769.259683840000