Motions driven by buoyancy forces and atmospheric stresses in the Avalon Channel, Newfoundland, Canada

• Main Author: Anderson, Carl, 1943-
• Format: Thesis
• Language: English
• Published: McGill University 1986
• Subjects: Sea level > Newfoundland and Labrador > Avalon Channel; Ocean-atmosphere interaction; Ocean currents > North Atlantic Ocean; Oceanography > Newfoundland and Labrador > Avalon Channel; Newfoundland; Canada; North Atlantic
• Online Access: http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72098

Currents and sea level fluctuations in the Avalon Channel, driven over a broad range of time scales by buoyancy forces, atmospheric pressure, and wind stress, are described and compared with dynamical theory. Seasonal fluctuations in adjusted coastal sea level at St. John's are shown to be consistent with steric height and bottom pressure variations 3 km offshore in a depth of 180 m. Low frequency fluctuations (periods of 7-50 d) in observed Avalon Channel currents and water properties suggest the presence of a baroclinically-unstable, buoyancy-driven coastal current. A kinematic analysis of the current fluctuations reveals an eddy structure resembling that predicted for baroclinically-unstable waves on a longshore current with the density stratification and vertical shear observed in the fall. Cross-spectral analysis of St. John's sea level and meteorological records, and Avalon Channel steric height estimates, shows that sea level responds isostatically to atmospheric pressure forcing at periods longer than 2 days, and to seasonal changes in steric height. Adjusted sea level responds 180 degrees out-of-phase to forcing by longshore wind stress at periods longer than 2 days. Longshore current responds in-phase to longshore wind stress forcing, with surface intensification of the response close to shore. Frequency response functions are derived from the shallow water equations of motion for the response of sea level and current to atmospheric pressure and wind stress forcing in homogeneous and two-layer, uniform-depth coastal ocean models, and in a homogeneous, step-shelf model. Linear bottom friction is assumed in the homogeneous ocean models. The phases of the observed sea level and current responses to wind stress suggest that the response is due to the existence of continental shelf waves originating at the northern edge of the Grand Banks, about 150 km away from the study site. The near-shore surface intensification of the current and sea level responses are consistent with the predictions of the two-layer uniform-depth model.