Lecture 3

4 Pages

Environmental Science
Course Code
Tanzina Mohsin

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Lecture 3: More on Oceans: waves, tides, and issues Review Lecture 2 Temperature increase- salinity increases Sudden change in temperature causes very small changes in density Ocean salinity is one factor that affects density Increasing salinity, increases density Density of sea water is also function of temperature Increasing temperature, decreases density Highest salinity (high evaporation) zone along Tropics of Cancer and Capricorn Lowest salinity (high rain) near equator (0-5 degree north and south) Surface salinity in polar regions varies seasonally due to formation and melting of sea ice Whenever there is ice, the water below the ice increase in salinity Origin of Waves The most common generating force of water waves is the moving wind Waves are caused by wind If wind is stronger, waves will be stronger- will see more dominant waves Wind has a higher energy than motion Wind driven ocean circulation is by far more energetic, but is confined mostly to the upper 100m or so Compared to ocean currents, ocean waves can be considered intermediate scale motion When the wind blows across a body of water, waves are generated The height of waves is proportional to the distance over which the wind blows over the water, and the strength of the wind Wave height: the vertical distance between the top of one wave crest and the bottom of the next trough Wave length: distance between the 2 crest One wind speed knot = 1.5 km Calm: 0 knots, light air: 1-3 knots, gentle breeze: 7-10 knots, moderate breeze: 11-16 knots, fresh breeze: 17-21 knots, strong breeze: 22-27 knots, near gale: 28-33 knots, gale: 23-40 knots, strong gale: 41-47 knots, storm: 48-55 knots, violent storm: 56-63 knots, hurricane: 64+ knots Wave Motion Wave motion: as wave approaches the shore, the circular motion of the water particles is interrupted by sea floor. This cause the wave to fall over and break against the shore An object in the water moves only up and down, unless the wave is breaking o This circular motions, called eddies, generate smaller and smaller eddies, which lead to turbulent diffusion within a water mass Waves formation: o Height of wave associated with the size of loop o As you go down in depth, the energy of loop decreases o At the bottom, there is no loop, called wave base o Wave motion is wavelength divided by 2 o Loops, circular motion are called eddies o As the eddies gets smaller, it leads to turbulent diffusion within a water mass Exchanges of gases and other chemicals Breaking of Waves As wave approaches shoreline, it breaks, wavelength decreases www.notesolution.com
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