Change Sea-ice motion (code 403) definition and units

[jeffrkey]

Initial request

This request is to change the definition and units of the variable Sea-ice motion (code 403). The current definition simply a repeat of the name, which therefore isn't a definition at all. The new definition should reflect the vector nature of velocity, as velocity implies (in science) speed and direction.

Current name: Sea-ice motion
Proposed name: Unchanged
Current definition: Sea-ice motion
Proposed definition: Horizontal displacement of sea ice over a defined time interval, specified as a two-element vector quantity: u and v. Related terms found in the literature are "Sea-ice velocity" and "Sea-ice drift".
Current units, Measuring and Uncertainy: km/day, Horizontal: km, Stability: km/day (per decade)
Current units, Measuring and Uncertainy: m/s, Horizontal: m, Stability: m/s (per decade)

Amendment details

The proposed update of the existing variable is as follows:

notation	name	definition
403	Sea-ice motion	Horizontal displacement of sea ice over a defined time interval, specified as a two-element vector quantity: u and v. Related terms found in the literature are "Sea-ice velocity" and "Sea-ice drift".

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

Requestor(s)

Group: Global Cryosphere Watch (GCW)
POCs:

Jeff Key (jeff.key@wisc.edu), University of Wisconsin
Petra Heil, University of Tasmania and Australian Antarctic Division, petra.heil@utas.edu.au
Rodica Nitu, WMO, rnitu@wmo.int

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

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

Expected impact of change

LOW

Collaborators

GCW Sea Ice Best Practices team and other GCW sea ice experts; 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

Relevant publications will be added

Validation

Yes, validation has been performed. Publications will be added that describe various validation studies.

[IARC2000]

Fully endorse this one. Thank you.

[TomLav]

Dear @jeffrkey ,

While I support giving a more explicit definition and units for sea-ice motion, I am wondering if the proposed definition is not too restrictive for the variety of measurement techniques that can be employed for sea-ice motion.

The proposed definition is :

Horizontal displacement of sea ice over a defined time interval, specified as a two-element vector quantity: u and v

with the Measuring and Uncertainy units: m/s

First we have the cases of sea-ice tethered position loggers (e.g. GPS tags attached to buoys). These do record lat/lon positions at given times. These trajectories of lat/lon/time can indeed be transformed to sea-ice motion velocity vectors, but the observation is generally stored as series of lat/lon/time. Would this type of observation need to be transformed to velocity vectors in order to be accepted as "sea-ice motion (code 403)"?

There are also the cases of fixed Upward Looking Sonars (ULS) that record sea-ice speed (m/s) (via Doppler), but not the direction. These only sense one component of the drift vector, not a two-element vector quantity. Are these accepted in "sea-ice motion (code 403)"? I guess ship-borne, coastal or even space-borne radar doppler-based estimates of sea-ice motion also fall in this category of single-component observations.

Finally, I wonder if the specification of u and v as names for the components implies zonal / meridional components (a widely used naming convention), or if other components would be accepted (e.g. x and y along grid axes, or even speed + direction, in which case the units of direction could not be m/s).

I apologize if the above has already been discussed and concluded upon in previous meetings (to which I might even have been invited to insert-face-palm-emoji). If this is the case we can hopefully record the decisions in the github issue for traceability.

[TomLav]

Questions to @hansl2022 : do you "own" this issue or should all sea-ice related requests be owned by the same person?

I would like to ask how we are supposed to move this (and other) issues forward. Do we have to build a consensus through discussion here? Is there a cut-off date at which the proposal must be concluded? In this particular case, I made a comment and asked questions but did propose an update to the proposed definition. Should I make such a proposal in a later issue?