On predicting iceberg drift

Abstract

A model to predict the drift of an iceberg has been developed and tested for operational use by the International Ice Patrol. Differential equations which balance the iceberg acceleration with the water drag, the air drag, the Coriolis acceleration, and a sea surface slope term are solved by a fourth order Runge-Kutta technique. The water drag is summed over up to four layers of the iceberg by using a constant geostrophic current plus a time dependent Ekman current which is averaged over each layer. The air drag is determined from prognosis wind data supplied by the U. S. Naval Fleet Numerical Weather Central. The iceberg areal and mass characteristics used in the model are average values that allow seven different sizes or types of icebergs to be considered. Testing of the model using observed drifts of icebergs indicates that the model error remains relatively constant for drift periods of up to three weeks duration. At present the primary limitation in accuracy is belived to be not in the physics of the model itself, but in the accuracy of the operational inputs supplied to the model, most notably the current and wind information. © 1980.