Tides Tides Tidal Characteristics Tidal Characteristics ◆ single waves - stretch across entire single waves - stretch across entire ocean basins. ocean basins. ◆ shallow-water shallow-water waves waves – wavelengths greatly exceed the depth of wavelengths greatly exceed the depth of the ocean. the ocean. ◆ complex interactions of complex interactions of moon and moon and sun sun Origin of the Tides Origin of the Tides ◆ Unlike wind-driven surface waves Unlike wind-driven surface waves and unlike tsunamis, tides are and unlike tsunamis, tides are caused by two principal factors: caused by two principal factors: – Gravitational attraction Gravitational attraction – Centrifugal force Centrifugal force Gravitational Attraction Gravitational Attraction ◆ All masses are drawn to each other. All masses are drawn to each other. ◆ The The moon moon because of its closeness because of its closeness to the Earth to the Earth exerts a greater exerts a greater gravitational effect on the Earth than gravitational effect on the Earth than the Sun the Sun , despite the fact that the Sun , despite the fact that the Sun is much more massive than the is much more massive than the Moon. Moon. Gravitational Effect of Moon Gravitational Effect of Moon Animation 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 Centrifugal Force Centrifugal Force ◆ Earth and Moon revolving around Earth and Moon revolving around one another. one another. ◆ unequal masses unequal masses of Earth and Moon of Earth and Moon – center of rotation lies beneath the center of rotation lies beneath the Earth’s surface. Earth’s surface. ◆ second tidal bulge second tidal bulge – ocean shifts ocean shifts away away from center of from center of rotation rotation Centrifugal Forces: Center of Rotation Centrifugal Forces: Center of Rotation 2 Bulges from Gravitational Attraction 2 Bulges from Gravitational Attraction & Centrifugal Force & Centrifugal Force Animation Animation [...]... characteristics of both progressive and standing waves Standing Waves x Sea, swell, and surf are progressive waves x Standing waves (seiches)… – Oscillate back and forth about a node, i.e., a fixed point Node = Fixed Point Antinode = maximum displacement Dynamic Model of theTides Dynamic Model of theTides Earth rotates from W to E Tidal bulge to W Pressure Gradient Coriolis cut-away cut-away Pressure Gradient... Diurnal: have one high tide and one low tide daily (high lat) x Semidiurnal: have two high tides and two low tides daily (low lat) x Mixed: there are two high tides and two low tides daily, but of unequal shape (mid lat) Classification by Monthly Record x Spring tide: phase when tidal range is maximal x Neap tide: phase when tidal range is minimal x There are 2 spring and 2 neap tides each month Spring... 2 neap tides each month Spring & Neap Tides x Spring tides occur when the Earth, Sun, and Moon are aligned – New Moon and Full Moon phases – Constructive interference x Neap tides occur when the Sun and Moon are aligned at right angles to one another – Quarter Moon phases – Destructive interference Sun/Moon/Earth - Spring & Neap Can you read a tide table? Marine Biorhythms x Cyclical behaviors associated... Coriolis Dynamic Model x equilibrium model of the tides is good, BUT – not totally detailed and accurate – oceans are separated by continents – oceans not infinitely deep Animation 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 . progressive and standing waves progressive and standing waves . . Standing Standing Waves Waves ◆ Sea, swell, and surf are progressive Sea, swell, and surf are progressive waves. waves. ◆ Standing. interactions of moon and moon and sun sun Origin of the Tides Origin of the Tides ◆ Unlike wind-driven surface waves Unlike wind-driven surface waves and unlike tsunamis, tides are and unlike tsunamis,. Characteristics Tidal Characteristics ◆ single waves - stretch across entire single waves - stretch across entire ocean basins. ocean basins. ◆ shallow-water shallow-water waves waves – wavelengths greatly