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Tides Tide producing forces Semi-diurnal; diurnal tides Lunar and solar tides Resonance Shallow water waves Tidal ellipses Tidal residuals Tidal-stream.

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Presentation on theme: "Tides Tide producing forces Semi-diurnal; diurnal tides Lunar and solar tides Resonance Shallow water waves Tidal ellipses Tidal residuals Tidal-stream."— Presentation transcript:

1 Tides Tide producing forces Semi-diurnal; diurnal tides Lunar and solar tides Resonance Shallow water waves Tidal ellipses Tidal residuals Tidal-stream selective transport

2 England San Francisco Philippines Korea

3 Not this kind of “tidal wave”…

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7 Moon’s gravitational attraction

8 The point “Z” stays fixed, and the earth-moon system rotates about it

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10 Force imbalance in earth-moon system creates tidal bulges

11 By the time the Earth has completed one revolution (one day), the moon has moved slightly, so the Earth needs to rotate a bit more to catch up with the moon…

12 M 2 period (12.42 hours) Semi-diurnal period

13 Declination offsets bulge from the equator (Diurnal period)

14 Main Tidal constituents Origin Symbol period coefficient generation (hours) Semidiurnal tides Moon M semidiurnal principal lunar tide Sun S semidiurnal principal solar tide Moon N elliptical M2 tide Diurnal tides M&S K principal declination tide Moon O diurnal principal lunar tide Sun P diurnal principal solar tide

15 Sun and moon effects can be additive or not…

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17 Amphidromic point (point around which tides propagate and where tidal elevation at a minimum)

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19 Kelvin wave: propagates with the coast on its right in the northern hemisphere and its amplitude decays offshore

20 M 2 cotidal charts for the Atlantic Ocean Amplitude (cm) Phase (degrees)

21 Co-tidal Chart for M2 tide

22 M2 tidal

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24 Tidal Resonance: amplification of tidal signal (e.g., amplitude) that occurs in an embayment or on a shelf, when the “length” of the embayment or shelf is near one-quarter of the wavelength of the wave.

25 Variations in tidal form world wide

26 semidiurnal Mixed, SD dominant Mixed, D dominant diurnal

27 Bay of Fundy – tide gets huge (15 m) because of resonance High tide Low tide (  6 hours later)

28 Some engineering applications using tidal resonance and their effects

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33 Tidal currents (tidal ellipses) 60m 100m 200m

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35 Deep water waves: Wavelength short relative to water depth Shallow water waves: Wavelength long relative to water depth

36 Velocity felt all the way to the bottom Velocity decays before reaching the bottom

37 Tidal currents – can be very complicated (from near Australia) Current hodograph shows direction and speed of slow every hour (each point) over 15 days. Pattern doesn’t even repeat!

38 Biological applications… Tidal residuals Transport Retention Selective tidal-stream transport

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40 Tidal ellipses Residual (time-averaged) currents

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42 Another way of looking at residual currents... this time in the English Channel and North Sea

43 Plaice migration: as adults they migrate from the feeding areas to the spawning grounds and back. How do they do it?

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45 Simulated tracks with day- night (diel) vertical migration: not much net displacement

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47 Northward swimming Westward swimming


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