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The Local and Nonlocal Response of Conception Bay to Wind Forcing

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  • 1 Department of Physics, Memorial University of Newfoundland, St. John's, Newfoundland, Canada
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Abstract

In this paper the response of Conception Bay to wind forcing is discussed. Current meter and thermistor chain observations are analysed and compared with output from a reduced-gravity numerical model. The model incorporates realistic coastal geometry and is driven by wind stress calculated from observed winds.

Moorings were deployed in the bay during 1989 and 1990. In 1990 the moorings were placed within the coastal waveguide around the head of the bay and show that southwesterly winds generate an upwelling event on the western side that moves around the head of the bay and is suggestive of Kelvin wave propagation. Data analysis shows that the thermocline response is strongly coherent between each mooring at periods of 2–10 days, and winds measured at a nearby station are found to be strongly coherent with the observed temperature fluctuations.

Two versions of the reduced-gravity model are applied—one models Conception Bay alone and ignores “upstream” influences and another includes neighboring Trinity Bay, located to the northwest and “upstream” in the sense of Kelvin wave propagation. The local model does reasonably well at reproducing the observed movement of the thermocline but underestimates its amplitude. The nonlocal model, which includes the neighboring bay, does much better at simulating the observation including the amplitude of the response, and also the upper-layer currents. The comparisons clearly show the importance of nonlocal effects.

Abstract

In this paper the response of Conception Bay to wind forcing is discussed. Current meter and thermistor chain observations are analysed and compared with output from a reduced-gravity numerical model. The model incorporates realistic coastal geometry and is driven by wind stress calculated from observed winds.

Moorings were deployed in the bay during 1989 and 1990. In 1990 the moorings were placed within the coastal waveguide around the head of the bay and show that southwesterly winds generate an upwelling event on the western side that moves around the head of the bay and is suggestive of Kelvin wave propagation. Data analysis shows that the thermocline response is strongly coherent between each mooring at periods of 2–10 days, and winds measured at a nearby station are found to be strongly coherent with the observed temperature fluctuations.

Two versions of the reduced-gravity model are applied—one models Conception Bay alone and ignores “upstream” influences and another includes neighboring Trinity Bay, located to the northwest and “upstream” in the sense of Kelvin wave propagation. The local model does reasonably well at reproducing the observed movement of the thermocline but underestimates its amplitude. The nonlocal model, which includes the neighboring bay, does much better at simulating the observation including the amplitude of the response, and also the upper-layer currents. The comparisons clearly show the importance of nonlocal effects.

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