Drift Ice

Drift ice is sea ice not attached to the shore that moves under wind, current, and Coriolis forcing, the open-drift and close-pack counterpart to fast ice in the WMO Sea-Ice Nomenclature (WMO No. 259). Drift speed runs near 2% of the surface wind plus the current vector, with the ice tracking roughly 20 to 40 degrees to the right of the wind in the Northern Hemisphere. Concentration sets the navigation regime: open drift ice (4 to 6 tenths) lets a strengthened ship pass, while close and very close pack (7 to 10 tenths) drives ridging and besetting. Drift ice carries the floes that POLARIS scores by ice type and concentration.