Copyright © by The International Society of Offshore and Polar Engineers Variations in Air-ice Drag Coefficient Due to Ice Surface Roughness

Wind profiles collected by satellite-tracked ice beacons and ice surface roughness data by a helicopter-borne laser altimeter are used to study variation in the air-ice drag coefficient due to surface roughness of the pack ice in Canada’s Gulf of the St. Lawrence. The results show that the air-ice drag coefficient referenced to 10 m (C10) varied by an order of magnitude from 05 × 10−3 over smooth ice with above-freezing air temperatures to 54×10−3 over rough ice with below-freezing air temperatures. This range includes the value of 28×10−3 used by ice-ocean modelers to forecast ice drift along the Canadian east coast. Laser data showed that the root-mean-square (rms) elevation was 007 m for the smooth ice and 029 m for the rough ice. Linearly relating the roughness to the drag coefficient appears promising, but more data are required. With remotely sensed imagery increasing its capability to the classification of ice types and ice roughness conditions, variable drag coefficients based on imagery may become available for ice-ocean models