More than half of the world's fish catch is taken from these upwelling areas, which comprise less than 0.1 percent of the total ocean surface. Occasionally, atmospheric circulations change and terminate the upwelling for a period of time, causing havoc to local fishing interests and leading to periods of uncharacteristic weather over large areas. Along the anchovy-rich fishing grounds that are off the coast of Peru this cessation of upswelling is part of the El Nino disturbance. For a complete classification of major warm and cold ocean currents, click here . With a fetch of about 200 mi and the same conditions, waves of 15 ft. are likely to occur.
Water waves form when the wind exerts a shearing stress on the sea surface.
Because of variations in the wind speed, referred to as turbulent fluctuations, pressure differences develop on the ocean that cause some areas of water to be higher than others. As the wind continues to blow, the differences in pressure between the trough and crest of the waves cause them to grow. The development of waves by this mechanism takes time, which explains the dependency of wave size on the fetch, as well as on the length of time the wind blows. After the wind speed decreases, waves subside, as their energy of motion is dissipated quickly along shorelines or lost slowly by internal friction. Waves that spread beyond their region of formation are referred to as swells.