When it’s passing the station, we can get a rough visual on how high the wave is. The next term that we use is wave height, and to determine this, we first must look at the wave when it passes our station. The example above highlights the crest to crest concept of wavelength. Wavelength is defined as the distance between two crests or between two troughs as seen in the image above. These currents circulate around the globe in a thousand-year cycle.When meteorologists are forecasting for ocean-going vessels, there are a few terms that we need to understand. This is the start of what scientists call the “global conveyor belt,” a system of connected deep and surface currents that moves water around the globe. This water also cools and sinks, keeping a deep current in motion. The denser water sinks, and as it does, more ocean water moves in to fill the space it once occupied. It is left behind in the ocean water that lies just under the ice, making that water extra salty and dense. The salt naturally present in seawater does not become part of the ice, however. In the North Atlantic Ocean, near Iceland, the water becomes so cold that sea ice starts to form. The water cools as it moves into higher northern latitudes, and the more it cools, the denser it becomes. It all starts with surface currents carrying warm water north from the equator. The process that creates deep currents is called thermohaline circulation-“thermo” referring to temperature and “haline” to saltiness. In contrast to wind-driven surface currents, deep-ocean currents are caused by differences in water density. Subtropical gyres are also responsible for concentrating plastic trash in certain areas of the ocean. These surface currents play an important role in moderating climate by transferring heat from the equator towards the poles. There are five main gyres: the North and South Pacific Subtropical Gyres, the North and South Atlantic Subtropical Gyres, and the Indian Ocean Subtropical Gyre. Large rotating currents that start near the equator are called subtropical gyres. The same thing happens below the equator, in the Southern Hemisphere, except that here the Coriolis effect bends surface currents to the left, producing a counter-clockwise loop. At about 30 degrees north latitude, a different set of winds, the westerlies, push the currents back to the east, producing a closed clockwise loop. The currents then bend to the right, heading north. As these currents flow westward, the Coriolis effect-a force that results from the rotation of the Earth-deflects them. The winds pull surface water with them, creating currents. In the Northern Hemisphere, for example, predictable winds called trade winds blow from east to west just above the equator. Other things, including the shape of the coastline and the seafloor, and most importantly the rotation of the Earth, influence the path of surface currents. The water starts flowing in the same direction as the wind.īut currents do not simply track the wind. Major surface ocean currents in the open ocean, however, are set in motion by the wind, which drags on the surface of the water as it blows. Tides contribute to coastal currents that travel short distances. They carry nutrients and food to organisms that live permanently attached in one place, and carry reproductive cells and ocean life to new places. Ocean currents are also critically important to sea life. Some currents flow for short distances others cross entire ocean basins and even circle the globe.īy moving heat from the equator toward the poles, ocean currents play an important role in controlling the climate. Some ocean currents flow at the surface others flow deep within water. Ocean currents flow like vast rivers, sweeping along predictable paths. Ocean water is constantly moving, and not only in the form of waves and tides.
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