High temporal resolution in--situ measurements of pancake ice drift are presented, from a pair of buoys deployed on floes in the Antarctic marginal ice zone during the winter sea ice expansion, over nine days in which the region was impacted by four polar cyclones. Concomitant measurements of wave-in-ice activity from the buoys is used to infer that pancake ice conditions were maintained over at least the first seven days. Analysis of the data shows: (i)~unprecedentedly fast drift speeds in the Southern Ocean; (ii)~high correlation of drift velocities with the surface wind velocities, indicating absence of internal ice stresses $>$100,km in from the edge in 100% remotely sensed ice concentration; and (iii)~presence of a strong inertial signature with a 13,h period. A Langrangian free drift model is developed, including a term for geostrophic currents that reproduces the 13,h period signature in the ice motion. The calibrated model is shown to provide accurate predictions of the ice drift for up to 2,days, and the calibrated parameters provide estimates of wind and ocean drag for pancake floes under storm conditions.
تحميل البحث