Chapter 17 - Coastal Processes and Tides
17.6 Important Concepts
- 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.
- 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.
- Tides are important for navigation; they influence accurate geodetic measurements;
and they change the orbits and rotation of planets, moons, and stars in galaxies.
- 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.
- 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.
- 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.
- 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.
- The dissipation of tidal energy in the ocean transfers angular momentum
from moon to Earth, causing the day to become longer.
- 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.