Trapped Low Frequency Waves on the Northern Israeli Continental Shelf

Time series of sea level measurements from different instruments deployed around the Haifa Bay area are analyzed. All observations indicate the existence of persistent low frequency oscillations with periods corresponding to approximately 1 hour and to approximately 30 minutes. These oscillations are persistent throughout most of the year and reached maximal wave heights of around 30 cm, a comparable value to tidal variations, making these oscillations an important factor in determining the average sea level elevation. The work identifies the phenomenon as resonant trapped waves, which are normal modes of the continental shelf extending from Haifa promontory to Achziv Canyon. Their temporal and spatial characteristics are learned through field measurement data analysis, wavelet analysis, numerical simulations, and exploration of an analytic solution. Finally, possible mechanisms for the generation of these waves are discussed. Such waves, which are commonly not surveyed, can be an important factor affecting coastal dynamics such as breaker line and coast line locations. Furthermore, the resonance behavior found has the capability of increasing the deep-to-shallow amplitudes in up to two orders of magnitude depending on incident angle. Noting that seismic or atmospheric events can agitate oscillation with similar wave periods, the intensification poses a hazard to Haifa Bay and coastal area.