Abstract

In the Strait of Gibraltar, tide waves have been investigated through the spectral analysis of tide records. These traces have been recorded from the third quarter of the year 1997 to the third quarter of the year 2004 by the stations located at the Strait of Gibraltar: Huelva, Ceuta and Malaga. All the data refer to the Tide Gauge Zero (TGZ). These data have been sampled with a ratio of one sample per hour (1 SPH). Spectral analysis has been applied to these data to obtain the tidal components as well as the spectral amplitudes of the harmonic components present in each tide record. The principal harmonic components of this digital record correspond to the tide waves. They are easily identified in the amplitude spectrum because they always appear with larger amplitudes than the other harmonic components. Thus, the tide waves are identified visually in the amplitude spectrum and their period is read directly from this spectrum. Spectral analysis has also been used to investigate the behaviour of these principal harmonic components (or tide waves), showing that the spectral amplitudes of the tide waves are not always constant. The spectral amplitudes of the tide waves M₂, S₂and N₂ have a temporal variation with a period of 1.28 years.

Key words: FFT, tide waves, Strait of Gibraltar.