The Energy Source for the Coastal-Trapped Waves in the Australian Coastal Experiment Region

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  • 1 Division of Oceanography, CSIRO Marine Laboratories, Hobart, Tasmania 7001, Australia
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Abstract

The sea level on the southern Australian coast is examined for the source of the coastal-trapped wave energy observed during the Australian Coastal Experiment. Sea level, adjusted for atmospheric pressure, and atmospheric pressure are observed to propagate eastward at about 10 m s−1. At the lowest frequency examined (24-day period), some energy travels south along the west coast of Tasmania, but does not reach the east coast of mainland Australia, while some energy travels through Bass Strait to reach the east coast of mainland Australia. At the most energetic frequency (8-day period), adjusted sea levels are coherent over the 3700 km of coastline from southern Australia to the east coast, and much of the wind-forced coastal-trapped wave energy appears to travel through Bass Strait to the mainland east coast. We have not identified a mechanism for energy transfer through Bass Strait, and we do not know what fraction of the coastal-trapped wave energy incident on western Bass Strait actually reaches the east coast. It is suggested that at low frequencies the long wavelength waves are not affected by relatively small gaps in the coastline, but that at higher frequencies the wavelength is smaller and breaks in the coastline become more important. The first and second coastal-trapped wave modes observed at Cape Howe during the Australian Coastal Experiment are most coherent with the sea level at Lakes Entrance at the eastern edge of Bass Strait. It is suggested that these coastal-trapped wave modes are generated when the east-west flow through Bass Strait has to adjust to the narrow shelf of the east Australian coast and that the second mode is preferentially generated because its length scale (k−1) more closely approximates the north-south extent of this east–west flow.

Abstract

The sea level on the southern Australian coast is examined for the source of the coastal-trapped wave energy observed during the Australian Coastal Experiment. Sea level, adjusted for atmospheric pressure, and atmospheric pressure are observed to propagate eastward at about 10 m s−1. At the lowest frequency examined (24-day period), some energy travels south along the west coast of Tasmania, but does not reach the east coast of mainland Australia, while some energy travels through Bass Strait to reach the east coast of mainland Australia. At the most energetic frequency (8-day period), adjusted sea levels are coherent over the 3700 km of coastline from southern Australia to the east coast, and much of the wind-forced coastal-trapped wave energy appears to travel through Bass Strait to the mainland east coast. We have not identified a mechanism for energy transfer through Bass Strait, and we do not know what fraction of the coastal-trapped wave energy incident on western Bass Strait actually reaches the east coast. It is suggested that at low frequencies the long wavelength waves are not affected by relatively small gaps in the coastline, but that at higher frequencies the wavelength is smaller and breaks in the coastline become more important. The first and second coastal-trapped wave modes observed at Cape Howe during the Australian Coastal Experiment are most coherent with the sea level at Lakes Entrance at the eastern edge of Bass Strait. It is suggested that these coastal-trapped wave modes are generated when the east-west flow through Bass Strait has to adjust to the narrow shelf of the east Australian coast and that the second mode is preferentially generated because its length scale (k−1) more closely approximates the north-south extent of this east–west flow.

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