Modeling five Great Lakes ice-circulation system using an unstructured-grid coupled model

An unstructured Finite Volume Coastal Ocean Model was modified by replacing the Euler forward scheme with the centered differencing scheme, and applied to all five Great Lakes simultaneously to simulate circulation and thermal structure from 1993 to 2008. Model results are compared to available observations of currents and temperature and previous modeling work. Maps of climatological circulation for all the five Great lakes were presented. Winter currents show a two-gyre type circulation Lakes Ontario and Erie and one large-scale cyclonic circulation in Lakes Michigan, Huron, and Superior. During the summer, a cyclonic circulation remains in Lakes Superior; a primarily cyclonic circulation dominates the upper and central Lake Huron; Lake Ontario turns to have a single cyclonic circulation, while circulation in the central basin of Lake Erie remains two-gyre type; Lake Michigan has a cyclonic gyre in the north and an anti-cyclonic one in the south. The temperature profile during the summer is well simulated when a surface wind-wave mixing scheme is included in the model. Main features of the seasonal evolution of water temperature, such as reverse stratification during the winter, the spring and autumn overturn, the thermal bar, and the stratification during summer are well reproduced. The lakes exhibit significant annual and interannual variations in current speed and temperature. The model successfully reproduced seasonal cycle of lake ice cover, the lake-wide mean surface temperature and lake circulation.