OBSERVATIONS AND NUMERICAL MODELING OF LAKE-ONTARIO BREEZES

Analysis of two years of land-based data shows that the Lake Ontario b reeze develops on 30% of the days during summer. It typically develops in mid-morning and persists until the late evening when it is replace d by a well developed land-breeze regime. Simulations of 4 cases with the Colorado State University mesoscale model show good agreement with observations and suggest that local lake breezes are strongly influen ced by adjacent water bodies (e.g. Lake Erie), the elongated shape of the lake, and the large-scale wind direction. With gradient flows acro ss the long axis of the lake, a broad band of along-lake flow develops during the afternoon (easterly winds during southerly gradient flows and westerly winds during northerly gradient flows). Furthermore, duri ng west-to-northwesterly gradient flow a nocturnal cyclonic eddy is pr edicted at the western end of the lake. These results imply that wind- field models applied in the vicinity of Lake Ontario should incorporat e the entire lake in their modelling domain.