Tide level in time and frequency domains at Dili port: Characteristic feature of a Lorentz oscillator

Abstract

Tide level during one year in time-domain measured at Dili port (East Timor) is analyzed by the frequency spectrum with the Fast Fourier Transform (FFT), together with the autocorrelation function (AF). The frequency spectrum shows a characteristic feature of the Lorentz-type resonance (Lorentz oscillator) with the special peaks which are attributed to the major tide constituents related to the gravitational motions of the sun and the moon. The Lorentz-type resonance occurs in water fluid systems under the periodic change in gravitational potential, which is similar to the electronic polarization under an electric potential change. The 1/f characteristics found at high frequencies in the power spectrum (the so-called 1/f characteristics in frequency domain) can be originated only from the gravitational effect, while its origin is usually discussed in terms of meteorology such as atmospheric pressure.

Keywords

• tide level
• fast Fourier transform (FFT)
• autocorrelation function
• Lorentz oscillator
• 1/f fluctuation