Freak Waves in the Black Sea Resulting from Nonlinear Processes: Field Measurements

According to instrumental measurements with the Spoondrifter Spotter buoy in the Black Sea, examples of abnormally high waves with light winds are given. Such waves are formed due to nonlinear processes with a possible increase in wave steepness because of growing winds and their interaction with a current. It is shown that in this case, a characteristic change in the wave spectrum occurs, which is accompanied by a discrete shift in the frequency of the spectrum peak to the low-frequency range. A case of a multi-cascade frequency downshifting of the spectrum peak (previously described in laboratory conditions) has been revealed. This case is considered as a characteristic one for interaction of waves with a current.