Non-linear effects in the tide of the Bay of Fundy

Abstract

The inspection of 33 years of observations on the water level at St John, New Brunswick reveals that some of the semidiurnal components of the tide have abnormal amplitudes while others exhibit slow periodicities which cannot be attributed to their second order nodal modulation: this is caused by frictional effects. The modulation of M 2 at St John is slightly reduced from its full oceanic range while it, in turn, controls some of the damping of S 2. Quadratic friction creates new semidiurnal components which may interfere with or alter some of the components of the incoming tide. Third order effects are also noticeable in the semidiurnal band. The diurnal components although small, are unperturbed because only convective interaction with the semidiurnal currents could affect them, necessitating stronger diurnal currents than those which actually exist in the Bay of Fundy. Finally it is possible to predict with some success the relative magnitude and phase of the high frequency components present in the records of St John by scaling the field of currents and by using a simple but efficient approximation to the quadratic friction term.