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Overview of physical processes in large lakes: Internal waves : Effects of the Earth’s Rotation

For large lakes such as Lake Ontario the Coriolis force due to the Earth’s rotation is not negligible. In the northern hemisphere, surface waters are deflected to the right of the wind direction and the Coriolis force will cause water to move in a circle [9]. The Coriolis force is dependent on latitude and the speed of the current. The Coriolis force is maximum at poles and zero at the equator. During the stratified season internal waves are also affected by the Coriolis force [9].

One metric that estimates the effect of the Earth's rotations is the Rossby Radius, which determines the horizontal scale at which rotational effects become as important as buoyancy effects. The accepted basin dimensions at latitudes of the Great Lakes at which the geostrophic effects of the Earth’s rotation on long surface and internal waves come into effect is ~15 km. The Rossby Radius for the Great Lakes is estimated to be on the order of 3-5 km [1].

In the upwelling region there is a balance of forces between the wind stress, Coriolis force, and internal pressure gradient. When the wind subsides, the balance is broken. Where the bottom is flat the balance is established by generating two types of free internal waves: the Kelvin wave and the Poincaré wave [9]. In a large lake such Lake Ontario there is a significant influence on the internal wave field from the Coriolis force, as the the shortest dimension (width of the lake) is much larger than the Rossby Radius. Consequently, low frequency internal waves such as Kelvin or Poincare waves are formed [5, 7]. These waves are the main transport process in Lake Ontario below the thermocline.