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The explanation of tides in 11 steps

The explanation of tides in 11 steps. Marc Philippart Rijkswaterstaat. Generation of tides. main drivers are Moon and Sun explaining the tides in 11 steps. Step 1: gravity force of moon. No continents, just water (equilibrium tide) Only influenced by attraction of the moon. earth. moon.

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The explanation of tides in 11 steps

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  1. The explanationof tides in 11 steps Marc Philippart Rijkswaterstaat

  2. Generation of tides • main drivers are Moon and Sun • explaining the tides in 11 steps

  3. Step 1: gravity force of moon • No continents, just water (equilibrium tide) • Only influenced by attraction of the moon earth moon

  4. Step 2: centrifugal force • If this was the only force, the moon would crash on the earth • Also centrifugal force due to rotation around centre of gravity

  5. gravity centrifugal combination Step 3: combined forces

  6. t=o 13º 54 min. 23h56 Step 4: twice a day? • twice a day would mean every 12 hour • however, we see 12 hour and 25 minutes • where is this ‘error’ of 50 minutes a day ? • moon travels around earth in 27.32 days • after one full earth rotation • moon travels also 13 dgr t=24h50

  7. t=o 1º = 4 min. 23h56 Step 5: the sun • sun acts the same as moon • amplitude ca 25% of moon • rotation of earth: 23 h 56 minutes eg. at 12h, sun in South after 23h56 + 4 min, sun in South (by definition)t=24h00

  8. Step 6: the sun moon interaction • effect of tide by moon

  9. Step 6: the sun moon interaction • sun and moon work together: Spring Tide • during full moon and during new moon

  10. Step 6: the sun moon interaction • sun and moon work opposite: Neap Tide • firts quarter and last quarter of the moon

  11. rotation of earth rotation of earth 23,5º declination h2 h1 equator equator Step 7: diurnal inequality • inequality due to the declination of earth axis

  12. Step 7: diurnal inequality • spring tide neap tide cycle sensitive

  13. Step 8: variation in driving forces • distance moon to earth varies (ellipsoid, 27,55 day) • direction ellipsoid varies in 8,85 yr. • distance sun to earth varies • plane of moon varies 5 degrees around 23,5 (18,61 yr.) • plane of sun varies with the precession (25.765 yr.)

  14. Step 9: continents & coriolis • the equilibrium tide runs around the southern hemisphere • further it travels around the world with a delay • tides in the north sea are more than 2 days old • the coriolis force (due to rotation of the earth) influences the tides

  15. Step 9: continents & coriolis

  16. Step 10: non-lineair effects • due to bottom friction the tide will deform • allthough the driving forces consist of 2 forces, called M2 (moon) and S2 (sun), at our coast a set of nearly 200 components are needed to reconstruct the tide

  17. Step 11: wind effects • due to meteorological influences the actual tide differs • surge bij NW storm • negative surge by Easterly winds

  18. Forecast of tides • there are two ways of forecasting (predicting) • 1: harmonical analyse and composing • observed tide > decomposing > reconstruction • 2: modelling • calibrating model > meteo input > result

  19. observed harmonic analyse of tide predicted decomposition continuation of decomposition

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