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Articles

1979: Vol. LVI, No. 2

A Note on Extreme Tidal Levels

Submitted
August 7, 2015
Published
2015-07-10

Abstract

A method of predicting extreme peaks of predominant semi-diurnal tides on the basis of 'Highest Astronomical Tide’ (HAT) is investigated. Cartwright's (1974) views and comments hold in general, but some variations are observed between the extreme physical tides and HAT's. These variations are understandably due to nonlinearities in the response function of phase lags. The constituents of frictional origin tend to minimise the range of extreme physical tides. The order of these marginally reduced levels at various near-extremes can be easily reversed by nonlinearities of the response function. Although extreme peaks follow the moon's perigee these extremes occur when the longitude of the moon's node is near autumn equinox. It appears to be impossible to specify a simple rule for absolute determination of extreme tidal levels, but if a tolerance in accuracy of a few centimetres is allowed then the method as presented can work adequately.