Change Sea-ice cover (code 401) to Sea-ice concentration, name, definition and units

[jeffrkey]

Initial request

This request is to change the name, definition, and units of the variable Sea-ice cover (code 401). The current definition of "cover" is the fraction of an ocean area. That is the definition of sea-ice concentration as commonly used by the scientific community. Sea-ice cover, like snow cover, is typically a binary variable, where the area of interest (i.e. a satellite pixel or a model grid cell) is considered to be either snow covered or snow free. Snow fraction is analogous to sea-ice concentration in that it is the fraction of some area covered by snow. We therefore propose a name change and a small change to the definition. While the variable Sea-ice cover could be retained, it's definition should be modified.

Current name: Sea-ice cover Proposed name: Sea-ice concentration Current definition: Fraction of an ocean area where ice is present. Proposed definition: Fraction of an ocean area covered by sea ice. Current units, Measuring and Uncertainy: %, Horizontal: km, Stability: % (per decade) Current units, Measuring and Uncertainy: %, Horizontal: m, Stability: % (per decade)

Amendment details

The proposed update of the existing variable is as follows:

notation	name	definition
401	Sea-ice concentration	Fraction of an ocean area covered by sea ice.

All units required already exist and no further change is needed.

Requestor(s)

Group: Global Cryosphere Watch (GCW) POCs:

Jeff Key ([email protected]), University of Wisconsin Petra Heil, University of Tasmania and Australian Antarctic Division, [email protected] Rodica Nitu, WMO, [email protected]

Stakeholder(s)

National and international ice services, e.g., US National Ice Center, North American Ice Service, Norwegian Ice Service; scientific community for remote sensing validation, meteorological/climatological and modeling applications.

Applications or Systems

• [x] OSCAR/Surface
• [x] OSCAR/requirements
• [ ] Radar/DB
• [ ] OceanOPS
• [ ] WHOS
• [ ] WDQMS
• [ ] GBON Compliance Monitor
• [ ] Other

Expected impact of change

LOW

Collaborators

GCW Sea Ice Best Practices team; GCW Cryosphere and Polar Observations (CRYORA) team Belén Martín Míguez, Ocean Earth System Category (ESAC)

References

To be added

Comments

No response

Publication(s)

Manual on Codes (WMO-No. 306), Volume I.3, WMO Codes Registry - WMDR

To be added

Validation

There are countless publications on the validation of satellite-derived sea ice concentration.

[IARC2000]

Strongly endorsing the proposed change of variable name and definition to: Proposed name: Sea-ice concentration and Proposed definition: Fraction of an ocean area covered by sea ice.

Not in agreement with retaining the current variable name: "While the variable Sea-ice cover could be retained, it's definition should be modified." -> Sea-ice cover is qualitative while sea-ice concentration is quantitative.

[hansl2022]

I noticed that there is an element ‘Sea-ice concentration’ in BUFR table B, which is given in a code table (0 20 034), not in ‘%’. Shall we consider the consistency between different tables？

[hansl2022]

A definition from WMO-No. 8 <Guide to Instruments and Methods of Observation Volume IV>: The fraction of an ocean area where ice is detected. (For reference)

[amilan17]

Code table 1-01-03.csv ObservedVariableOcean Observed variable - measurand (ocean)

with path: Ocean/Cryosphere/Sea ice

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/Meeting.2025.06.12 notes: @jeffrkey please review comments above to help prepare this for FT2025-2

[jeffrkey]

Everything in the request text is acceptable.

[amilan17]

https://github.com/wmo-im/tt-wigosmd/wiki/Meeting.2025.07.01 notes:

the team discussed options for changing the definition and decided that it's ready to go as is.