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Articles

1992: Vol. LXIX, No. 1

On Anomalous Tides in Australian Waters

Submitted
July 30, 2015
Published
2015-05-19

Abstract

The Coral Sea has been identified as the location of an anomaly in the semidiurnal tidal band with an apparently sharp local resonance in the vicinity of the frequency of L2. It is here shown that such a simple resonance does not exist but that the anomaly has a gravitational origin which may indicate a more complex mechanism. Long spans of tidal observations from Cairns, Townsville and nearby ports are analysed in an attempt to estimate the frequency response of the gravitational tide across the semi-diurnal spectral band. The identification of the response function is assisted by the treatment of perturbing energy from non-gravitational sources, in particular those associated with shallow water non-linear interaction. At both stations two terms emerge which are seen to be greatly amplified, one with an argument number (2-10000) is very close to N2 in the frequency spectrum while the other (210000) is near to L2. Together they form a conjugate pair of tidal lines about M2 and they are separated from their more conventional neighbours by only one cycle in 8.85 years, the period of the lunar perigee. The anomaly is discussed, and the suggestion is made that the amplification of these terms, (2±10000), may be due to their spatial distribution which is different from those of the principal tides, so exciting specific forcing functions in the response of the oceanic scale system.