Chapter 17 - Coastal Processes and Tides

17.6 Important Concepts

1. Waves propagating into shallow water are refracted by features of the seafloor, and they eventually break on the beach. Breaking waves drive near-shore currents including long-shore currents, rip currents, and edge waves.



2. Storm surges are driven by strong winds in storms close to shore. The amplitude of the surge is a function of wind speed, the slope of the seafloor, and the propagation of the storm.



3. Tides are important for navigation; they influence accurate geodetic measurements; and they change the orbits and rotation of planets, moons, and stars in galaxies.



4. Tides are produced by a combination of time-varying gravitational potential of the moon and sun and the centrifugal forces generated as Earth rotates about the common center of mass of the Earth-moon-sun system.



5. Tides have six fundamental frequencies. The tide is the superposition of hundreds of tidal constituents, each having a frequency that is the sum and difference of five fundamental frequencies.



6. Shallow water tides are predicted using tide measurements made in ports and other locations along the coast. Tidal records of just a few months duration can be used to predict tides many years into the future.



7. Tides in deep water are calculated from altimetric measurements, especially Topex/Poseidon measurements. As a result, deep water tides are known almost everywhere with an accuracy approaching ± 2cm.



8. The dissipation of tidal energy in the ocean transfers angular momentum from moon to Earth, causing the day to become longer.



9. Tidal dissipation mixes water masses, and it is a major driver of the deep, meridional overturning circulation. Tides, abyssal circulation, and climate are closely linked.

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