Modelling of Labrador Sea pack ice, with an application to estimating geostrophic currents

Abstract

A model of the dynamics of sea ice originally developed by W.D. Hibler has been adapted for the Labrador Sea to assess its usefulness for simulating ice motion. Besides the standard comparison of model results to observations, it was also desired to study the effect of the internal stress term and the potential use of the model to estimate geostrophic currents. Two simulation periods, 8–15 and 20–23 February, 1977, were selected because ice drift data were available for these periods for certain locations in the Labrador Sea. Additional ice date were obtained from the ice maps produced by Ice Centre of Environment Canada. Winds were obtained from ship observations and weather maps. Initially the input geostrophic currents were derived from a climatological data set. The results of the simulations are presented in the form of maps of ice concentrations, thicknesses, and velocities and in the form of observed and simulated drift tracks. The maps of ice characteristics are generally uninformative in assessing the validity of the simulations except in a qualitative sense, but the drift tracks are more useful, and a comparison of the observed with simulated tracks gave good results for the 8–15 February period and poor results for the 20–23 February period. For both periods the simulation with and without the internal stress were quite similar except the ice velocities were somewhat lower for simulations without the internal stress term. The estimates of time-varying geostrophic currents required to fit the model results with observed drift tracks are consistent with what is known of currents in the Labrador Sea, though in some cases the magnitudes approach 1.5 m s −1. Estimated current magnitudes and spatial structures are comparable to those derived using a similar approach with iceberg drift data and models.