Dept. of Geosciences Colloquium: The description of the ocean wave problem from a moving reference frame and the investigation of low frequency waves on the Israeli Mediterranean shores

Abstract:

MEPLab aims to advance our knowledge on ocean waves and currents in the East Mediterranean region using a wholesome approach combining theory, modelling, technological advancements and measurements. The first part of the talk will be dedicated to present a fundamental theoretical aspect of wave-current interactions — its description form a moving reference frame. The second part of the talk will present the investigation of low frequency oscillations (periods of tens of minutes) in the vicinity and within Haifa Bay. To conclude, some of the laboratory’s measurement infrastructure will be presented
Different Marine technologies, such as free-floating wave buoys, drones and autonomous unmanned vehicles, take measurements while propagating in arbitrary directions and with different velocities relative to the fluid and waves. In will be presented how the surface gravity wave problem is generalized for an arbitrary inertial reference frame. The new formulation provides the foundation for accounting for moving measurement effects on the classical wave-current problem. Contrary to common assumption, it is shown that current and viewer velocities affect the mathematical representation of the problem in distinct ways. 

A new generalized form of dispersion will be derived. The form more clearly shows the dispersion symmetries for different viewers. Still water will be shown to be a degenerate case, exhibiting a loss of Galilean symmetries. For a viewer moving with current, still water symmetries are not recovered and only a subset of intrinsic frequencies are represented. The generalized boundary value problem also yields a more general expression for pressure. Importance of the results for interpreting wave and pressure measurements, and theoretical considerations, such as determination of resonance conditions, will be discussed. 

Sea level elevation observations ADCPs, tide gauges and wave staves indicate the existence of persistent low-frequency oscillations on the Israeli continental shelf. The dominant frequencies are shown to be consistent with a shelf resonance models. A shallow water numerical model of Haifa Cape to Achziv shelf edge shows that this constellation enables energy trapping and occurrence of resonating standing waves. It has been found that the resonance periods fit also the ones of a tsunami (and possibly metro-tsunami) event with capability for a deep-to-shallow signal increase of up to two orders of magnitude(!) indicating Haifa Bay and Naharia areas to be extremely vulnerable to such an event.

Event Organizers: Dr. Roy Barkan and Dr. Asaf Inbal