2Tidal Characteristics single waves - stretch across entire ocean basins.shallow-water waveswavelengths greatly exceed the depth of the ocean.complex interactions of moon and sun
3Origin of the TidesUnlike wind-driven surface waves and unlike tsunamis, tides are caused by two principal factors:Gravitational attractionCentrifugal force
4Gravitational Attraction All masses are drawn to each other.The moon because of its closeness to the Earth exerts a greater gravitational effect on the Earth than the Sun, despite the fact that the Sun is much more massive than the Moon.
6Animation courtesy of NASA Goddard Space Flight Center: The Moon's gravity tugs at the Earth, causing ocean water to slosh back and forth in predictable waves called tides. We can visibly observe some of that energy dissipate at the beach, with waves rolling across coastal shallows and shoals. Most of the energy dissipates due to friction between the water and the shallow floor beneath it
7Centrifugal Force Earth and Moon revolving around one another. unequal masses of Earth and Mooncenter of rotation lies beneath the Earth’s surface.second tidal bulgeocean shifts away from center of rotationAWAY from centercan be observed in action on a passenger riding in a car. If the car swerves around a corner, the passenger's body pushes against the outer edge of the car
12True Tidal Waves (not tsunamis!) The motion of water around the basin is a rotary wave.The crest is at one side of the basin.The trough is at the other side of the basin.Tides have characteristics of both progressive and standing waves.
13Standing Waves Sea, swell, and surf are progressive waves. Standing waves (seiches)…Oscillate back and forth about a node, i.e., a fixed point.
14Node = Fixed Point Antinode = maximum displacement Form when winds blow in one direction which causes water to pile up at one end of a basin.
16Dynamic Model of theTides Earth rotates fromW to ETidal bulge to WPressure GradientCorioliscut-awayPressure GradientCoriolisPressure GradientCorioliscut-away
17Dynamic Model equilibrium model of the tides is good, BUT... not totally detailed and accurateoceans are separated by continentsoceans not infinitely deep
18Animation courtesy of NASA Goddard Space Flight Center: Using 6 years of data from TOPEX/Poseidon satellite altimeter, they derived a 16-day set of predictive data, showing a synthetic view of how the tides move around the world's oceans.
19Key Features of Tides High tide : Wave crest Low tide : Wave trough Tidal range : Wave heightTidal periods depending on location:12 hours, 25 minutes24 hours, 30 minutes
21Tidal Periods Moon moves forward in it’s orbit each day. why not exactly 24 hours or 12 hours?Moon moves forward in it’s orbit each day.Takes 50 additional minutes for a spot on the Earth’s surface to regain it’s position relative to the Moon.
22Classification by Daily Record Diurnal: have one high tide and one low tide daily (high lat).Semidiurnal: have two high tides and two low tides daily (low lat).Mixed: there are two high tides and two low tides daily, but of unequal shape (mid lat).
23Classification by Monthly Record Spring tide: phase when tidal range is maximal.Neap tide: phase when tidal range is minimal.There are 2 spring and 2 neap tides each month
24Spring & Neap TidesSpring tides occur when the Earth, Sun, and Moon are aligned.New Moon and Full Moon phasesConstructive interferenceNeap tides occur when the Sun and Moon are aligned at right angles to one another.Quarter Moon phasesDestructive interference