Sporadic Sea-level Oscillations along the Western Australian Coastline

Abstract

Sporadic sea-level oscillations were recorded on the Western Australian continental shelf. The largest oscillations with amplitudes up to 50 cm occur on the shelf between Perth and Geraldton. It is shown that magnification of the oscillation in this area is caused by resonance in a near-shore channel, formed by the shore and a submerged reef-chain parallel to the shore at an average distance of 5500 m offshore. The estimated resonance amplification factor is about 10. Predominant period of oscillations is about 30 min. Statistical analysis of the oscillations during the period between 1963 and 1978 indicated a significant correlation with solar activity. Seasonal variations in oscillation energy were found to have a significant peak during Southern Hemisphere winter months, when storms in the Indian and Southern Oceans are more frequent. This supports the hypothesis that the near-shore oscillations observed have the same 'excitation- from-the-ocean' resonance mechanism as that established by Miles and Munk for harbours.