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

Abstract

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, Ky, are nearly constant and consistently smaller than along-frontal counterparts, Kx. 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.