Observations of Lateral Shear in the Nearshore Zone of a Great Lake

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  • 1 Lakes Research Division, Canada Centre for Inland Waters, Burlington, Ontario
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Abstract

Observations of currents across a nearshore zone from 2 to 6 km offshore indicate that unsteady longshore flow and complete reversals in flow are usually accompanied by large values of lateral shear. These values often approach and may exceed 10−4 sec−1, near the value of the Coriolis parameter at mid-latitude. At times when lateral shear is high, other turbulent properties such as variance at a point are also high. The variations of lateral shear are highly temporal and can be qualitatively related to the cycles of cyclone-anti-cyclone activity in the area. High shear values usually do not coincide with high winds, but are usually related to the inability of the nearshore currents to adjust to a slowly varying wind regime. Simple momentum arguments suggest that the time for adjustment decreases as water depth nearshore decreases.

Abstract

Observations of currents across a nearshore zone from 2 to 6 km offshore indicate that unsteady longshore flow and complete reversals in flow are usually accompanied by large values of lateral shear. These values often approach and may exceed 10−4 sec−1, near the value of the Coriolis parameter at mid-latitude. At times when lateral shear is high, other turbulent properties such as variance at a point are also high. The variations of lateral shear are highly temporal and can be qualitatively related to the cycles of cyclone-anti-cyclone activity in the area. High shear values usually do not coincide with high winds, but are usually related to the inability of the nearshore currents to adjust to a slowly varying wind regime. Simple momentum arguments suggest that the time for adjustment decreases as water depth nearshore decreases.

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