POAC09-07 THE RESPONSE OF SEA ICE DYNAMICS MODELS TO WIND Ivana Kubat 1 , Mohamed Sayed 1 , Stuart B. Savage 2 , Tom Carrieres 3 1 NRC-Canadian Hydraulics Centre, Ottawa, Canada 2 McGill University, Montreal, Canada 3 Canadian Ice Service, Ottawa, Canada ABSTRACT This paper examines the response of ice dynamics models to wind forcing. The emphasis is on implicit models that employ the viscous plastic approach of Hibler (1979). Such implicit models are commonly used in operational forecasting because of their efficiency. A one dimensional problem is considered to test model performance. An explicit solution, which produces reliable response time to wind forcing, was obtained for that problem. Testing of an implicit model based on the method of Zhang and Hibler (1997) showed that the response to wind forcing can be inappropriately slow. Cases of relatively large thickness and area coverage can result in very slow response. Testing has revealed that the large values of the viscosity coefficients in such cases produce the unrealistic delayed response. A simple method was devised to overcome that problem. A modification to the relaxation method was found to produce the appropriate response to wind forcing under a wide range of conditions. INTRODUCTION The response of floating ice to changes in wind forcing is a significant issue for forecasting operations. Sea ice is often observed to respond over short time to rapid changes in wind. On the other hand, experience with operational forecasting has shown that numerical forecasting models are often slow to respond to changes in wind. The Canadian Ice Service (CIS) regularly run ice dynamics models to produce short-term forecasts. Several aspects of those models are under continuing development. This paper describes some of the developments underway to improve the response of the forecasting models to wind response. As in most operational forecasting models, developments at CIS are based on the viscous plastic formulation of Hibler (1979). Solution of the governing equations also follows the iterative implicit scheme of Hibler (1979), or the more recent one of Zhang-Hibler (1997). The developments at CIS addressed a number of modules, such as advection (Sayed and Carrieres, 1999; and Sayed et al. 2002) that can be adopted in the operational forecasts. The developments include a ridging model by Savage (2008), which is intended for small-scale forecasts. In most studies dealing with ice forecasts over complex geographies and environmental forcing, slow response to wind changes may be difficult to notice. A case of simple geometry and forcing POAC 09 Luleå, Sweden Proceedings of the 20th International Conference on Port and Ocean Engineering under Arctic Conditions June 9-12, 2009 Luleå, Sweden