Breaking of ocean surface waves

Wind-generated waves are the most prominent feature of the ocean surface, and so are breaking waves manifested by the appearance of sporadic whitecaps. Such breaking represents one of the most interesting and most challenging problems for both fluid mechanics and physical oceanography. It is an intermittent random process, very fast by comparison with other processes in the wave system. Distribution of the wave breaking on the water surface is not continuous, but its role in maintaining the energy balance within the continuous wind-wave field is critical. Ocean wave breaking also plays the primary role in the air-sea exchange of momentum, mass and heat, and it is of significant importance for ocean remote sensing, coastal and maritime engineering, navigation and other practical applications. Understanding the wave breaking, predicting its occurrence, the breaking rates and breaking strength, and even ability to describe its onset has been hindered for decades by the strong non-linearity of the process, together with its irregular and ferocious nature. Recently, this knowledge has significantly advanced, and the review paper is an attempt to summarise the facts into a consistent, albeit still incomplete, picture of the phenomenon. In the paper, variety of definitions related to the wave breaking are discussed and formulated, and methods for breaking detection and measurements are examined. Most of attention is dedicated to the research of wave-breaking probability and severity. Experimental, observational, numerical, analytical and statistical approaches and their outcomes are reviewed. Present state of the wave-breaking research and knowledge is analysed and main outstanding problems are outlined.