Characteristics of Turbulent Cross and Alongshore Momentum Exchanges During a Thermal Bar Episode in lake Ontario

Time series flow data obtained during the thermal bar episode of 17 April to 24 May 1990 in Lake Ontario are analyzed to provide a kinematic description of the coastal flow and cross-margin exchange characteristics. A thermal bar is a shore-parallel front which separates descending waters at or near the fresh water temperature of maximum density (4°C) during Spring and Fall seasons. Thermal bars are important because of their influence mixing, cross-shore exchanges, and the variability of biotic factors in coastal zones. The analysis shows that cross-frontal exchange coefficients, K y , are nearly constant and consistently smaller than along-frontal counterparts, K x . Moreover, these exchange coefficients are several orders of magnitude smaller than typical coastal and oceanic values in the absence of the bar. The turbulent kinetic energy represents less than 6% of the total kinetic energy in the flow. These results suggest that small-scale horizontal fluctuations and cross-frontal turbulent momentum exchanges are severely inhibited in the spring during the thermal bar.