Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Forcing mechanisms and water column response over the West Louisiana Inner Continental Shelf (WLICS) are investigated at various temporal and spatial scales. The major mechanisms that have an effect on shallow-water currents over the WLICS are winds, runoff from the Mississippi and Atchafalaya rivers, and circulation of the northwestern Gulf of Mexico. Summer wind stress values are low and currents generally meander over the inner shelf during this period. A shift in the direction of the regional wind stress in late June causes a reversal in the current direction over the west Louisiana shelf. Autumn currents are primarily westward in response to predominantly westward wind stress. Winter currents are primarily westward, but during frontal passages the current swings rapidly to the east. As winds become easterly, the currents return to their westward set. During the spring the flood on the Mississippi and Atchafalaya rivers introduces a large amount of fresh water into the coastal waters. The fresh water causes density gradients, which decouple near-bottom flow from surface winds and increase the intensity of the westward currents. During the autumn and winter regional-scale cyclonic flow, generated by a succession of cold-front passages, helps to maintain flow over the WLICS in a westward direction. Four periods of frontal passage in 1979 are studied in detail. Strong alongshelf wind stress is common during the January and March frontal periods. An investigation of water column dynamics reveals that the alongshelf wind stress accelerates the water column and generates a frictional boundary layer at the bottom. A strong high pressure system pushes a front across the WLICS from the north during February. Dynamically, low alongshelf wind stress accelerates the water column, but it is not strong enough to establish a frictional balance. An alongshelf pressure gradient also influences the water column dynamics. South-southeasterly winds and freshwater runoff dominate the April frontal period. The alongshelf wind stress accelerates the water column, but no frictional balance is established. A pressure gradient term due to the Atchafalaya flood contributes to the momentum balance.

Pages

126

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