TIDES Chapter 10

Study Plan Tides are the longest of all Ocean Waves Tides are the longest of all Ocean Waves Tides are forced waves formed by gravity and Inertia Tides are forced waves formed by gravity and Inertia The Dynamic Theory of Tides adds fluid motion dynamics to the Equilibrium Theory The Dynamic Theory of Tides adds fluid motion dynamics to the Equilibrium Theory

Study Plan Most tides can be predicted accurately Most tides can be predicted accurately Tidal Patterns can affect Marine Organisms Tidal Patterns can affect Marine Organisms Power can be extracted from tidal motion Power can be extracted from tidal motion

Tides are the longest of all Ocean Waves Tides: periodic, short-term changes in the ocean surface’s height at a particular place, caused by a combination of the gravitational force of the moon and sun and the motion of Earth Tides: periodic, short-term changes in the ocean surface’s height at a particular place, caused by a combination of the gravitational force of the moon and sun and the motion of Earth

Equilibrium Theory Isaac Newton described the gravitational attraction between the Earth, Moon, and Sun, but did not factor in the DEPTH of the ocean and CONTINENTS Isaac Newton described the gravitational attraction between the Earth, Moon, and Sun, but did not factor in the DEPTH of the ocean and CONTINENTS

Dynamic Theory Pierre-Simon Laplace described tides and taking into account the speed of the long wavelength tide wave in shallow water, the presence of continents, and the sloshing back and forth of water in ocean basins. Pierre-Simon Laplace described tides and taking into account the speed of the long wavelength tide wave in shallow water, the presence of continents, and the sloshing back and forth of water in ocean basins.

Tides are forced waves formed by gravity and Inertia

Tide-producing forces Gravity and Gravity and motions among Earth, Moon, and Sun

Centripetal force “tethers” Moon to Earth Centripetal force “tethers” Moon to Earth –Directed away from barycenter

Resultant tidal forces Gravitational force, Earth and Moon Gravitational force, Earth and Moon Centripetal force, Earth and Moon Centripetal force, Earth and Moon Resultant force moves ocean water horizontally Resultant force moves ocean water horizontally Fig Fig. 10-6

Tidal bulges Two equal and opposite tidal bulges Two equal and opposite tidal bulges Earth rotates beneath tidal bulges Earth rotates beneath tidal bulges Two high tides Two high tides Two low tides Two low tides Per day Per day

Complications to simplest equilibrium theory Oceans do not cover entire Earth Oceans do not cover entire Earth Oceans do not have uniform depth Oceans do not have uniform depth Friction between ocean and seafloor Friction between ocean and seafloor Continents Continents Moon not always in same place with respect to Earth Moon not always in same place with respect to Earth Lunar day longer than solar day Lunar day longer than solar day

Lunar day Moon revolves around Earth Moon revolves around Earth Earth has to “catch up” with Moon to reach same position Earth has to “catch up” with Moon to reach same position

Time between successive high tides shifts day after day Time between successive high tides shifts day after day Moon rises later each successive night Moon rises later each successive night

The Sun also Generates Tractive Forces Tide-producing force of Sun less than half of Moon’s Tide-producing force of Sun less than half of Moon’s Sun much farther away Sun much farther away

Month tidal cycle Spring tides Spring tides –New Moon, Full Moon –Earth, Moon, Sun syzygy –Higher than usual high tides

Neap tide Neap tide –First Quarter, Last Quarter –Earth, Moon, Sun quadrature –Lower than usual high tide

Declination of Sun and Moon Orientation of Sun, Moon to Earth’s equator Orientation of Sun, Moon to Earth’s equator –Sun 23.5 o N and S, yearly cycle –Moon 28.5 o N and S, monthly cycle Unequal tides Unequal tides –Successive tides different tidal range

Unequal tidal range Fig

Elliptical orbits Perigee Perigee –Lunar tidal force greater –Higher high tides Apogee Apogee –Lunar tidal force lesser –Lower high tides Fig

Astronomical Tides Tides generated from inertia and the sun’s and moon’s gravitational attraction Tides generated from inertia and the sun’s and moon’s gravitational attraction

Meteorological Tide Tides generated with an influence from the weather Tides generated with an influence from the weather

The Dynamic Theory of Tides adds fluid motion dynamics to the Equilibrium Theory Continents in the way Continents in the way Ocean depth Ocean depth Weather Weather

Dynamic theory of tides Tide shallow-water wave Tide shallow-water wave –Speed varies with depth –Lags behind Earth’s rotation Rotary flow in open ocean basins Rotary flow in open ocean basins –Amphidromic point –Cotidal lines

Rotary flow Crest (high tide) rotates Crest (high tide) rotates Counterclockwise in Northern Hemisphere Counterclockwise in Northern Hemisphere Clockwise in Southern Hemisphere Clockwise in Southern Hemisphere

Tidal patterns Diurnal Diurnal –One high, one low tide per lunar day –Period of tidal cycle 24 hours 50 minutes Semidiurnal Semidiurnal –Two high, two low tides per lunar day –Period 12 hours 25 minutes –Equal range

Mixed Mixed –Two high, two low tides per lunar day –Unequal range Most tides are mixed Most tides are mixed

Bay of Fundy Largest tidal range (spring tide max 17 m) Largest tidal range (spring tide max 17 m) Shape of basin Shape of basin Oscillation period close to tidal period Oscillation period close to tidal period Shoals and narrows to north Shoals and narrows to north Basin oriented toward right (Coriolis moves water toward right) Basin oriented toward right (Coriolis moves water toward right) Fig

Gulf of CA Large tidal range (spring tide max 7 m) Large tidal range (spring tide max 7 m)

Tidal bores Wave created by tide rushes upstream Wave created by tide rushes upstream Large tidal range Large tidal range Low-lying coastal river Low-lying coastal river Max 8 m high Max 8 m high

Most tides can be predicted accurately Up to 3 cm (1.2 inches) tidal height Up to 3 cm (1.2 inches) tidal height

Tidal Patterns can affect Marine Organisms

Power can be extracted from tidal motion